Expanded plastics are also known as foamed plastics or cellular plastics. Expanded plastics can be flexible, semi flexible, semi rigid or rigid. They can also be thermoplastic or thermosetting and can exist as open-celled or closed-celled materials. The Polyurethanes are among the most recent additions to the many commercially important classes of polymers. Urethanes can be considered esters of the unstable carbamics acid or amide esters of carbonic acid. The present book covers processes of expanded plastics, polyurethane, polyamides with other related information required by an entrepreneur. This book is very useful for technocrats, researchers, entrepreneurs and professionals.
Polyesters
PRODUCING EXPANDED AND CURED POLYESTER RESIN
Highlights of the Technological Achievement: Polyester resin is expanded and cured using monosubstituted sulfonyl hydrazide blowing agent, organic peroxide curative and certain metal promoters.
Background: It has been found that polyester resins (PER) can be expanded and cured simultaneously when employing monosubstituted sulfonyl hydrazides (MRSH), a primary organic metal salt promoter, with or without a secondary organic metal salt promoter, a surfactant and an organic peroxide or hydroperoxide at low concentrations of peroxide and promoters.
Process Conditions: This process provides low density foams prepared from liquid ethylenically unsaturated polyester resins by blending various ingredients as outlined on the listing below.
| Ingredient | General | Preferred | Most Preferred |
| Polyester resin, parts | 100 | 100 | 100 |
| MRSH blowing agent, mm | 2.7-32 | 5.4-27 | 11-22 |
| Primary promoter, parts | 0.001-2 | 0.001-1.5 | 0.01-1 |
| Secondary promoter, parts | 0-0.4 | 0-0.25 | 0.01-0.2 |
| Surface active agent, parts | 0-2 | 0.5-1 .5 | 0.75-1.25 |
| Filler, parts | 0-250 | 0-150 | 0-100 |
| Organic peroxide (or hydro-peroxide) curative, [per 100 parts of (a) plus (f)] | 0.2-2.5 | 0.5-2 | 1-2 |
The following guidelines may be useful for the practitioner: if no (d) is present, then the amount of (c) is preferably at least 0.025 part. Also, if no (d) is present and the level of (c) is at least 0.01 part, then the concentration of (b) should preferably be at least 11 mm, and that of (g) greater than two parts. It should also be noted that if (b) is present at a 5.5 mm or higher level, and (g) is present at one part or more, the concentration of (c) should preferably be at least about 0.5 part in the absence of (d).
Using the proper concentrations of components, foamed polyester structures may be obtained exhibiting most preferably at least 30% or more of density reduction when compared to the nonfoamed polyester resin.
The liquid unsaturated polyester resins in the composition comprise a linear or only slightly branched polyester resin and an ethylenically unsaturated monomeric compound.
Examples of saturated polybasic acid include: isophthalic acid, orthophthalic acid, terephthalic acid, adipic acid, succinic acid and azelaic acid.
Flexible resins employ greater amounts of adipates or azeleates, while more rigid resins use phthalates, with a variety of different glycols. This process is useful for making rigid and semirigid polyester foams suitable as structural-type foams. Such resins have a formulation, for example, of about 3 to 5 mols of glycol, 1.5 to 3.0 mols of adipic acid, and 0 to 1.5 mols of phthalic anhydride, with from 1.0 to 2.5 mols of styrene or vinyl toluene.
The chemical blowing agents suitable for preparing the foamed and cured polyester are monosubstituted sulfonyl hydrazide having the structural formula RSO2NHNH2, wherein R is a hydrocarbyl radical selected from C1-2 alkyl, C5-6 cycloalkyl, C7-10 aralkyl, phenyl, naphthyl, also phenyl substituted with halogen, C1-2 alkyl, or C1-12 alkoxy.
FOAMED UNSATURATED POLYESTER RESINS WITH GEL COAT
Highlights of the Technological Achievement: A process for the production of foamed products from an unsaturated polyester resin composition, the composition comprising polyester resin, unsaturated monomer, a promotor, initiator, physical blowing agent, and compatible surfactant whereby a known gel time "T" results, foaming the composition by exposing it to microwave radiation prior to 1 T, thereafter permitting the foam structure to exotherm to obtain a fully cured product.
Background: Microwave energy has been suggested for the curing of foam materials in the past. One example of this is Jacobs, U.S. Patent 3,216,849.
While unsaturated polyester resin is mentioned, a thorough consideration of this patent will show that the system disclosed is only applicable to the polyurethane foam which is specifically described.
The Jacobs process is distinctly different from this process. With the polyester system, quick energy addition is necessary to volatilize the foaming agent and to control the rate of gelling. Stated another way, Jacobs reaction causes the foaming and the microwave source is an ancillary finishing step, while in this process the microwave energy causes the foaming and the material has no cellular structure prior to such exposure.
Process Conditions: The time of exposure to the microwave energy is sufficient to volatilize the foaming agent and to accelerate crosslinking of the resin to or close to the gel condition. Preferably the initial exposure is made between 0.2 and 0.7 T.
The process also resides in products produced according to this method. Unfilled products can be made having a density of usually 8 to 15 pcf while filled products usually have a density of 10 to 50 pcf.
In a further aspect for the production of foam products from an unsaturated polyester resin composition, the composition comprising a polyester resin, styrene, promoter, and surfactant and having upon subsequent addition of an initiator a gel time of "T," the process comprising adding initiator and a physical blowing agent to the composition, exposing the composition to microwave radiation at a time greater than 0.2 T (preferably between 0.2 and 0.7 T) and less than 1 T whereby foaming takes place prior to gellation, thereafter permitting the foam structure to exotherm to obtain a fully cured product.
From the above, it can be seen that the basic concept of the process can be simply stated. The microwave energy, when applied at the proper time in the reaction process, supplies uniform and intense heat to the resin system, thus allowing vaporization of the dissolved physical foaming agent. At constant microwave energy input, application of the energy too early in the process will lead to gross bubble formation and/or cell collapse prior to gellation. Application too late in the process will lead to premature gellation and an unworkable foam. Similarly, at a fixed point in the reaction process, exposure for too short a time will lead to low foaming levels and long gellation times outside the microwave unit, yielding bubble coalescence and cell collapse. If the exposure time is too long, excess foaming and gellation occur inside the microwave unit, yielding overheating, styrene vaporization and catastrophic cell wall rupture.
Figure 1: These curves show the effect of waiting time before exposure to microwave energy on final foam density as measured volumetrically in all tests. 20 sec/half power microwave exposure 50 ml material at 75°F. Arrows indicate point where resin gelled at microwave exit.
CROSSLINKED POLYESTER
Highlights of the Technological Achievement: Vesiculated fibrils of crosslinked polyester resin of length 50mm-5 cm diameter 1 mm-2 mm and aspect ratio of 10-50 are prepared by pouring into water with stirring a selected solution in unsaturated monomer of a carboxylated unsaturated polyester resin of acid value 10-90 mg KOH per g, the water containing both a base having a pKb value of 8 maximum and a dispersion stabilizer, and initiating polymerization.
Background: It has been found that one particular group of polyester resins can be used to prepare fibrillar particles of crosslinked resin in which the individual fibril has a vesiculated structure. The term "fibril", means fibrous particles which have diameters of the order of 1 mm to 2 mm and aspect ratios, that is, the ratios of the lengths of the fibrils to their diameters, from 10 to 50. The fibers may be circular or elliptical in cross-section; in the latter case, the "diameter" is considered to be the major axis of the ellipse. The fibril length is typically within the range of 0.5 to 5.0 mm, although by suitable manufacturing techniques this can be extended to about 5 cm.
By a vesiculated structure, is meant that the core of the fibril comprises a plurality of discrete cells or vesicles of liquid or vapor and formed within the body of the fibril. The vesicles vary somewhat in shape, but are usually either spheroidal or elongated, in the manner of a prolate spheroid. An important and distinctive feature is, however, that the internal cells are discrete, isolated entities as distinct from open-ended axial ducts. They are, therefore, not directly accessible to liquids in which the fibrils might be immersed. The vesicle volume of a typical fibril has been shown by mercury porosimetry to be of the order of 45% of the total fibril volume, although fibrils of appreciably lower vesicle volume may be made.
The fibril composition is that of unsaturated polyester resin crosslinked by reaction with ethylenically unsaturated monomer. It is essential that the polyester resin also comprises free carboxyl groups. The preferred concentration of carboxyl groups varies somewhat with the overall composition of the resin, but in general the acid values of useful resins lie within the range of 10 to 90 mg KOH per gram of resin.
It has been discovered that the carboxylated polyester resins which will yield fibrillar particles are distinguished by their performance in the following buoyancy test.
Test - The test is carried out at ambient temperature on a solution of unsaturated polyester resin in ethylenically unsaturated monomer at the ratio of resin to monomer selected to give the desired overall crosslinked resin composition, the ratio being such that the proportion of unsaturated polyester resin in the solution is at least 40% by weight. This solution is hereinafter known as "the test solution."
A droplet of test solution is transferred gently from a probe to the surface of water adjusted to a pH of at least 10 with ammonia. The size of the droplet is not critical, a convenient diameter being 2 to 3 mm. If the test solution is unsatisfactory for fibril manufacture, the droplet will proceed with little if any delay, to drop through the water to the bottom of the container in which it is held. A droplet of test solution suitable for fibril manufacture, will, in direct and obvious contrast, remain suspended on or adjacent to the surface for an appreciable time.
Process Conditions: It has been found preferably to use monomer at least 50% by weight of which is styrene. Poly-functional monomer, for example, ethylene glycol dimethacrylate, is normally used at weight concentrations of less than 10% of the total unsaturated monomer, when a polymer with high crosslinking density is required.
For the satisfactory commercial formation of vesiculated fibrils, the polyester resin must constitute at least 40% by weight of the polyester solution in monomer.
The selected polyester is first dissolved in the ethyleni-
cally unsaturated monomer required for the crosslinking
reaction.
The polyester solution is then poured into water, in the presence of a base, with continuous mechanical stirring. Discrete fibril precursor particles having the general shape and size of the required fibrils are so-formed.
Example: An unsaturated polyester resin was prepared from the following materials:
| Parts |
| Propyleneglycol | 27.11 |
| Fumaric acid | 20.44 |
| Phthalic anhydride | 13.04 |
| Adipic acid | 12.86 |
| Xylene | 3.70 |
The reaction was carried out at 210ºC using the xylene as entraining solvent to strip out water of reaction. The batch was cooled and thinned with 22.81 parts of styrene containing 0.017 parts of hydroquinone, to give a solution of unsaturated polyester resin in ethylenically unsaturated monomer, with the following properties.
| Acid value (calculated on solid resin) | 34.8 mgm KOH/g |
| Gardner-Holdt viscosity | Y- |
| Nonvolatile content | 68.7% by wt |
A drop of the solution when tested by the buoyancy test described here in above floated at the surface of the water.
A mixture of 6.29 parts of the above solution and 0.11 parts of ethanolamine was poured slowly, with continuous mechanical stirring, into 17.24 parts of water containing 2.26 parts of 0.880 ammonium hydroxide, 2.3 parts of a 7.5% solution by weight in water of poly (vinyl alcohol) and 2.3 parts of a 1.5% solution by weight of hydroxyethylcellulose in water. The grade of poly(vinyl alcohol) used was a partially hydrolyzed (approximately 88%) poly (vinyl acetate) which as a 4% by wt solution in water had a viscosity of 40 cp at 20°C. The hydroxyethylcellulose was a high viscosity grade, which had a viscosity of 1800 cp at 20ºC when tested as a 1% by wt solution in water.
Discrete fibrillar suspended particles of polyester resin solution were formed in the water.
The suspension was diluted with 70 parts of water, and the following materials added slowly and sequentially to it to initiate curing of the particles by a cross-linking reaction between the polyester resin and styrene monomer:
| Parts |
| Cumene hydroperoxide | 0.090 |
| Diethylene triamine (as a 10% wt soln. in water) | 0.044 |
| Ferrous sulfate (as a 10% wt soln. in water) | 0.001 |
The cured product was a fluffy suspension of fibrils, the individual fibrils having a diameter of the order of 50 mm and length of 1 to 3 mm. Transverse fractures of the fibrils examined by scanning electron microscope confirmed the presence of a vesiculated structure. The crosslinked nature of the fibrils was shown by their insolubility in warm acetone.
Polyurethanes
FLAME RETARDANCE
Low Molecular Weight Polyurethane Modifier Compounds Yielding Flame Retardance
Highlights of the Technological Achievement: Foamed polymers such as polyurethanes useful, for instance, as cushioning, insulation, and in reaction injection molding to produce thin section moldings can be produced without substantial reduction in physical properties by the incorporation of 2 to 75% by weight based upon the weight of polymer of at least one non-reactive, liquid polyurethane modifier compound processing aid or flame-retardant additive.
Background: Flexible polyurethane foams have been rendered permanently flame-retardant by the incorporation of halogenated glycols such as tribromoneopentyl glycol or dibromoneopentyl glycol in combination with phosphoric anhydride which has been reacted with an alkylene oxide or haloalkylene oxides.
Process Conditions: There are disclosed foamed polymers such as polyurethane compositions comprising the reaction product (a) of at least one polyhydric alcohol with at least one organic polyisocyanate in admixture with (b) a low molecular weight non-reactive modifier compound which is the reaction product of at least one polyisocyanate with at least one monohydric alcohol or at least one mono-functional isocyanate with a stoichiometric amount of at least one monohydric alcohol or at least one monofunctional isocyanate with a stoichiometric amount of at least one polyhydric alcohol or at least one isocyanate-terminated prepolymer with a stoichiometric amount of at least one monohydric alcohol. The disclosed modifier compounds are useful as processing aids or flame-retardant additives for polyurethane foams. Microcellular, rigid, high-resilience, and flexible foam poly-urethanes can be prepared. The foamed polyurethanes can be rendered flame retardant, if desired, by use of a halogenated monohydric or polyhydric alcohol in the preparation of the modifier compound.
The Modifier Compound: The preparation of the low-molecular weight modifier compounds is more particularly described by reference to the following equations:
where in R is monovalent or polyvalent and R' is monovalent each individually selected from aliphatic, alicyclic, aromatic, aralkyl, and alkaryl radicals having up to 18 carbon atoms in the aliphatic portion of the radical and 6 to 12 carbon atoms in the aromatic portion of the radical, Z is equal to z and is the number of mols of alcohol or isocyanate compound utilized, and z is an integer corresponding to the valence of R and is equal to the number of functional groups on the alcohol or isocyanate compound. The modifier compounds have a molecular weight of preferably 150 to 900.
Flame-Retardant Polyurethane Foam Prepared by Incorporating a Graft Polymer Having a Particle Size Greater than 0.5 Micron
Highlights of the Technological Acheivement: In the preparation of conventional or high resiliency flexible polyurethane flame retarded foams by reacting organic polyisocyanates with polyols containing vinylic polymers and employing flame-retardant compounds, less flame-retardant compound is required to pass the California Bulletin No. 117 flame test when the particle size of the vinylic polymers is greater than 0.5 micron.
Background: The preparation of flexible polyurethane flame-retardant foam compositions are generally well known as evidenced by the following prior art. U.S. Patent 4,022,718 teaches the preparation of high resilience cold-cured polyurethane foams incorporating 2,3-dibromo-1,4-butanediol as a chain extender and flame-retardant component.
Process Conditions: This process applies to both high-resiliency, flexible polyurethane foam compositions and conventional flexible polyurethane foam compositions which are prepared by the reaction of an organic compound having at least two active hydrogen atoms and having a vinylic polymer content with an organic polyisocyanate in the presence of an effective amount of a flame-retardant compound. The amount of flame-retardant compound required may be significantly decreased if the graft polymer dispersions have a vinyl particle size greater than 0.5 micron.
Among the flame retardant compounds which may be employed are Antiglaze 19, Antiblaze 78, Thermolin 101, FE 55, Firemaster LVT23P, Bromochlor 50, Wiltrof HF, Citex BC26, Fyrol PCF, Fyrol FR2, Fyrol EFF, BCL 462, Phosflex 500, Brominex 161, Firemaster 901, FR 212, FR 1138, Phosgard 2XC20, BC48, Phosgard C-22R, Brominex 214P, Brominex 257, and Fyrol 99.
Low Fire Hazard Rigid Polyurethane Insulation Foam
Highlights of the Technological Achievement: A low fire hazard rigid polyurethane insulation foam having high compressive strength and low friability is disclosed. Rigid foam products of this process have a Class I flame hazard rating according to the ASTM E-84 Steiner tunnel test. The polyurethane foam contains a halogenated base polyol and a modifying amount of a 2,5-bis-hydroxymethyl)furan component.
Background: The fire retardant, or, "low fire hazard" properties of furan ring-containing materials is well known due to the self-extinguishing property of the char which forms when furan-containing materials are burned. The disclosure in U.S. Patent 4,029,61 1 shows a rigid cellular foam having carbodiimide and isocyanurate linkages prepared by catalytically condensing an organic polyisocyanate in the presence of a carbodiimide-promoting catalyst, a trimerization catalyst, and a polyfurfuryl alcohol polymer. The resulting isocyanurate foam has improved flame retardancy. The polyfurfuryl alcohol polymer employed includes the condensation products of furfuryl alcohol with formaldehyde, furfural, urea or mixtures, thereof, produced by reaction in the presence of an acid catalyst providing a pH of preferably 1.5 to 3, at a temperature of 25° to 120°C.
Process Conditions: A preferred hydroxyl composition for use in manufacture of rigid urethane insulating foams, in accordance with this process, comprises 12 to 24% 2,5-bis-(hydroxymethyl) furan component, 76 to 88% halogenated polyol base polyhydroxyl component, as well as 25 to 40 phr (parts per hundred polyol components) blowing agent, 0.8 to 1 .0 catalyst, 1 .5 to 2 surfactant, and 2 to 7 phr of an acid scavenger, such as, for example, an epoxy compound. (Ciba-Geigy CY 179 is eminently satisfactory as an acid scavenger. The latter acid scavenger is 3,4 epoxycyclohexylmethyl-3,4 epoxycyclohexane carboxylate.) This composition is stable for shipment, and can be used as the polyhydroxyl stream in a so-called "one-shot" method, in conjunction with a second, isocyanate stream, to produce rigid insulating foams in accordance with this process.
An example of a commercially available mixture of this type is the material known as FA-REZ B-260 (The Quaker Oats Company). This commercially available product is reported to have a viscosity of about 1 0,000 cp, has a hydroxyl content of 16 to 18%, a water content of 0.5 to 1 .0% furfuryl alcohol content of up to 3% and is reportedly 85% polyhydroxymethyl functionality.
Generally speaking, the polyhydroxymethyl furan mixtures useful in accordance with this process preferably have a viscosity in the range of 6,000 to 12,000 cp at 25°C, contains 35 to 45%, inclusive, monomeric bis-hydroxymethyl furan, less than 3% furfuryl alcohol monomer, less than 1.2% water and have an acid number of less than or equal to 3.5.
Such a hydroxymethyl furan diol mixture which is useful as an ingredient in accordance with this process, can be produced in a number of ways. For example, it can be produced by low acidic (i.e., pH above 4) polymerization of 2,5-bis-(hydroxymethyl) furan, as well as by the hydroxymethylation of furfuryl alcohol with formaldehyde using a weak acid such as, for example, acetic acid, propionic acid, or formic acid, under conditions which provide a pH above 4. Generally speaking, such products can be produced by hydroxymethylation of a furan ring-containing compound selected from the group furan and furfuryl alcohol, wherein the furan compound is contacted with formaldehyde in the presence of a catalytical amount of a weak acid catalyst having a pKa value at 25°C between 3.0 and 5.0 inclusive, under conditions which provide a reaction mixture having a room temperature acidity pH greater than or equal
to 4.0, the contacting taking place between 50° and 160°C
inclusive.
Intumescent Flexible Polyurethane Foam
Highlights of the Technological Achievement: Flexible, resilient, polyurethane foam having improved flame retardancy and intumescent properties is prepared from a reaction mixture comprising a polyester polyol, an organic polyisocyanate, a blowing agent, a surfactant, a catalyst, a melamine derivative wherein one or more hydrogens have been replaced by a methylol and/or lower alkoxymethyl group, a flame retardant, and hydrated alumina.
Background: Flexible resilient polyurethane foams are made by the reaction of polyols and organic polyisocyanates in the presence of one or more blowing agents, one or more surfactants, and one or more catalysts. The foams find a variety of uses, such as carpet underlay, textile innerlining, mattresses, pillows, furniture padding, cushions, automobile crash pads, and insulation.
Process Conditions: The melamine derivatives used in the practice of this process are those compounds having the formula below.
In the preceding formula. A, B, D, E, F and G are hydrogen, hydroxymethyl-(methylol) or ROCH2-, wherein R is an alkyl radical containing from 1 to 4 carbon atoms, such as methyl, ethyl or t-butyl. At least one of A, B, D, E, F and G is hydroxymethyl or ROCH2-. Examples of compounds falling within the scope of the formula are tris-(hydroxymethyl) melamine, tris-(hydroxymethyl)-tris-(methoxymethyl) melamine, hexa-(methoxymethyl) melamine, hexa-(hydroxymethyl)-melamine and tetra-(n-butoxymethyl) melamine.
In general, the amount of compound or compounds of the formula used will be from about 10 to 30 parts by weight per 100 parts by weight of the polyester polyol present in the mixture to be foamed, but greater or lesser amounts can be used without departing from the scope of the process.
The preferred amount is from 15 to 25 parts by weight, per 100 parts by weight of the polyester polyol. The melamine derivatives can be used either as solutions or dispersions in water or other solvents, or as essentially 100% active materials without solvent. It is preferred to use the latter form, in the absence of water, to provide greater latitude in formulating a reaction mixture. When water is used as a blowing agent, it is preferred to add it separately rather than as a solvent for the melamine compound.
A particularly preferred melamine derivative is hexamethy-oxymethylmelamine, which is readily obtainable in a form free, or substantially free, from water. Although it is preferred to use a single melamine derivative, for simplicity in formulating, it may sometimes be desirable to use two or more, and such combinations are included in the scope of the process.
Suitable flame retardants are those conventionally used in the art of making flexible polyurethane foams, and include tri-esters of phosphoric acid, halogenated tri-esters of phosphoric acid, halogenated hydrocarbons, and the like.
The polyester polyol reactants useful in the process include any conventionally used in the preparation of flexible and semiflexible urethane polymer foams. The poly-hydric polyester reactant has a molecular weight of optimally between 500 and 5,000. The hydroxyl number of the compound is correspondingly in the range of 15 to 300. The preferred average hydroxyl functionality for the polyester resins is from 2.2 to 2.8.
Reduced Tendency to Form Embers When Burned
Highlights of the Technological Achievement: Flexible polyurethane foam having reduced tendency to form burning embers when it is ignited and burned is provided by incorporating into the reaction mixture before foaming a ketone or benzalde-hyde.
In a preferred embodiment, flexible polyurethane foam of increased flame retardance is provided by also incorporating a flame retardant into the reaction mixture before foaming.
Background: It is known in the art to add various flame-retardant chemicals to polyurethane foam-forming reaction mixtures, in particular to add halogenated esters of phosphorus. This has resulted in some improvement in the flammability properties, the extent of burning after ignition being reduced and the foams may even be made self-extinguishing to some degree; but while combustion does occur the foam melts and drips flaming embers which may ignite other flammable materials in the vicinity and thus cause the fire to spread. In order to overcome this problem, other additives have been added to polyurethane foam-forming reaction mixtures to render the finished foams intumescent, or to produce a char, once they have been ignitied. Such foams are less prone to the development of flaming, dripping, embers during combustion, and may produce a char which acts as a thermal insulation and thus aids in preventing the spread of a fire.
Process Conditions: This process provides flexible, resilient, polyurethane foam with reduced tendency to form burning, dripping, embers during combustion. These foams are substantially equal in non-drip properties to those provided by the disclosure of U.S. Patent 4,139,501, and are obtained at lower cost. This improvement is provided by adding to a conventional polyurethane foam-forming reaction mixture at least one drip inhibitor such as benzaldehyde or a ketone. The drip inhibitors are generally less costly per weight and generally effective in lesser amounts as compared with the melamine derivatives used in the method of U.S. Patent 4,139,501. The foam-forming reaction mixture also contains a halogenated phosphate ester as a flame retardant.
The products of this process, rather than being stiff and rigid, retain substantially the flexibility, resilience, cell structure, permeability, and hand of conventional flexible polyurethane foams which do not contain the drip inhibitors employed in this process. As a consequence, the foams of this process can be used in most or all of the applications where conventional flexible foams have here to fore been used.
Product: Of the following examples, one of which is a comparative example according to the prior art and others of which are according to this process, those made according to this process are illustrative thereof but not limitative thereof. In these examples, all amounts shown are parts by weight.
The foams were evaluated by a modification of the procedure of UL 94, Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances, published by Underwriters Laboratories Inc. The modification of UL 94 was in the measurement of flame time. The standard test calls for starting to count flame time 60 seconds after ignition, whereas in the procedure used herein flame time was counted from the start of ignition.
The following are the identities of the various ingredients used in the examples. TDI stands for tolylene diisocyanate (also called toluene diisocyanate). The numbers which follow TDI indicate the ratio of the 2,4 and 2,6 isomers (e.g., TDI 65/35 is a 65/35 mixture of tolylene 2,4-diisocyanate and tolylene 2,6-diisocya-nate). A-390 (Witco) is a surfactant comprised of a mixture of modified fatty acid esters plus a silicone; NEM is N-ethylmorpho-line (Jefferson Chemical, Than-cat NEM); DM-16D is n-hexadecyldimethylamine (Lonza, Baircat B-16); NCM is N-cocomorpholine (Lonza, Baircat NCM); C-2 is stannous octoate (M&T Chemicals, Fomrez C-2); Kaydol (Witco) is a white mineral oil; 73D is a dispersion of black pigments in an organic vehicle (black paste); and FR-2 is tris (1,3-dichloropropyl)
phosphate (Stauffer Chemical, Fyrol FR-2).
Examples (parts by weight)
| Ingredients | 1 | 2 | 3 | 4 |
| Polyester prepared from diethylene glycol, adipic acid, and trimethylol- ethane; OH No. 56 | 100.0 | 100.0 | 100.0 | 100.0 |
| TDI 65/35 | 50.1 | 50.1 | 50.1 | 50.1 |
| Black dispersion 73D | 7.45 | 7.45 | 7.45 | 7.45 |
| A-390 | 2.0 | 2.0 | 2.0 | 2.0 |
| Water | 3.7 | 3.7 | 3.7 | 3.7 |
| NCM 0.8 | 0.8 | 0.8 | 0.8 |
| Kaydol | 0.2 | 0.2 | 0.2 | 0.2 |
| NEM | 0.5 | 0.5 | 0.5 | 0.5 |
| DM-16D | 0.3 | 0.3 | 0.3 | 0.3 |
| C-2 | 1.5 | 1.5 | 1.5 | 1.5 |
| FR-2 | 20.0 | 20.0 | 20.0 | 20.0 |
| Methyl isobutyl ketone | - | 5.0 | - | - |
| Cyclohexanone | - | - | 5.0 | - |
| Benzaldehyde | - | - | - | 5.0 |
The index of these examples was 111. Example 1 is a comparator, made according to the prior art and not containing a drip inhibitor, and Examples 2 through 4 are according to this process. Each of the examples yielded a flexible, resilient, foam having a uniform cell structure. The flammability characteristics of the foams were evaluated by a modified UL94 procedure, and the results are shown below.
Examples
| 1 | 2 | 3 | 4 |
| Average time of burn, seconds | 58.7 | 71.9 | 60.5 | 56.3 |
| Average extent of burn, inches | 1.95 | 2.85 | 2.15 | 2.03 |
| Drip formation | Yes | No | No | No |
| Char formation | No | No | No | No |
During combustion, dripping embers formed from the product of Example 1 and no char formed. Although the products of Examples 2 through 4 also did not form a char during combustion, they were free from dripping, burning, embers.
Flame Retardant Flexible Polyurethane Foam Containing Finely Divided Inorganic Salt
Highlights of the Technological Achievement: Flexible polyurethane foams which are the product of reaction under foam producing conditions of a combination of: (a) an aromatic polyisocyanate; (b) a polyether polyol with the optional use of a minor amount of a crosslinking polyol; (c) antimony oxide; (d) a polyhalogenated aromatic compound; and (e) a hydrated inorganic salt.
The foams of the process meet very stringent tests for fire retardance required of seat cushioning, mattresses, and like materials in aircraft, institutions such as hospitals, convalescent homes, and the like.
Background: Fire retardant flexible and semi-flexible polyurethane foams which are characterized by good physical properties and good fire resistance are well known in the art; see U.S. Patent 3,909,464 and the art cited therein. The patent discloses the very efficacious combination of antimony oxide, a polyhalogenated aromatic compound and alumina trihydrate. The latter is not actually a hydrate but is rather a true hydroxide.
It has been found that certain hydrated inorganic salts can be employed in place of alumina trihydrate in the fire retardant combination disclosed in U.S. Patent 3,909,464 without there being a problem with excessive or unwanted blowing action in the formation of fire retardant polyurethane foams. In fact, the flexible foams in accordance with this process have physical properties equal, and, in some cases superior, to those of the cited art.
Process Conditions: This process comprises flame retardant flexible polyurethane foams prepared under foam producing conditions from an aromatic polyisocyanate, a polyether polyol having an equivalent weight from 500 to 2,500 and a functionality from 2.0 to 4.0, antimony oxide and a polyhalogenated aromatic compound wherein the improvement comprises employing in the foam forming reaction mixture the following ingredients in parts by weight based on 100 parts of the polyether polyol:
(a) from 4 to 30 parts of antimony oxide;
(b) from 4 to 40 parts of a polyhalogenated aromatic compound; and
(c) from 30 to 60 parts of a finely divided hydrated inorganic salt wherein a mol of the salt compaints at least 5 mols of water of hydration, and employing a ratio of isocyanate equivalents to total the foam-forming reaction mixture within a range of 0.90: 1 .0 to 1.0: 1.0.
Fiber Production
COMPOSITIONS
A variety of polyester compositions have been developed in an attempt to improve fiber properties - particularly dyeability. Litigation has been instituted by Du Pont against Eastman Chemical Products charging infringement of U.S. Patent 3,018,272 issued to Du Pont. That patent involves introduction of sulfonate groups into a polyester polymer chain to give a fiber which can be dyed with basic dyes.
Celanese
A composition developed by R.W. Stockman and D.E. Sargent; U.S. Patent 3,507,835; April 21, 1970; assigned to Celanese Corporation is a composition having improved dyeability properties comprising a synthetic linear thermoplastic polymer and at least 0.5 weight percent of a sulfonated pyrrole.
Du Pont
A process developed by R.E. Taylor; U.S. Patent 3,446,766; May 27, 1969; assigned to E.I, du Pont de Nemours and Co. produces reinforcing yarns and cords of polyester having low free carboxyl group contents which give superior performance in pneumatic tires and other reinforced rubber articles where heat degradation is a problem. A copper salt of an organic carboxylic acid and a molar excess of alkali metal iodide are mixed with fully polymerized, molten polyester to reduce the free carboxyl groups prior to melt spinning. If desired, the metal iodide may be present during formation of the polyester.
Eastman Kodak
A composition developed by H.W. Coover, Jr., and F.B. Jayner; U.S. Patent 3,492,368; January 27, 1970; assigned to Eastman Kodak Company relates to modifications of linear polyesters to provide compositions readily spinnable into fibers and yarns susceptible of permanent dyeing to deep shades by a wide variety of dyes including premetallized and acid wool dyes as well as conventional disperse and other conventional polyester dyes.
Those high molecular weight, fiber-forming polyesters which have met with commercial success in the form of synthetic fibers such as Docron or Kodel polyester fibers are relatively insoluble, hydrophobic materials. Since they are not readily permeable to water, they cannot be dyed satisfactorily by the ordinary inexpensive dyeing procedures. Since they lack reactive groups such as those that abound in cellulosic and protein fibers, they can be dyed satisfactorily only by a limited class of disperse dyes.
Usually it is necessary in obtaining even only light and medium shades to employ high temperature dyeing procedures which are operated at temperatures above 100°C. or with the use of carriers or the use of both high temperature and carriers. Since many dyestuffs decompose at temperatures above 100°C. (e.g., some blues will redden), careful selection of dyestuffs must be made for high-temperature dyeing of polyester yarns and fibers. This markedly limits the utility of these materials in the textile field, because they cannot be dyed readily on conventional commercial dyeing equipment. In addition, carrier dyeing involves considerable extra cost, since (1) the carriers are themselves expensive, (2) the dyed yarns have a pronounced tendency to retain the odor of the carrier and require very thorough washing to eliminate it and (3) residual carrier left in the fiber seriously impairs the light fastness of the dyed material.
The hydrophobic nature of linear polyesters is also manifested in their low moisture regain. The low moisture regain of these materials is conducive to the development of static during processing operations, such as picking, carding, winding and weaving. Although static troubles may be substantially eliminated during processing operations by the application of lubricants and hydrophilic sizing materials, garments produced from linear polyester yarns tend to develop static charges during wear which attract dirt, dust, lint and other materials, thereby causing the fabrics to become rapidly soiled. Furthermore, unmodified polyester fibers, when dyed with the conventional disperse or polyester dyes, have poor resistance to dry cleaning solvents such as trichloroethylene, experience having shown that dry cleaning solvents of this type often extract the dyestuffs from the fibers causing a reduction in shade or producing a mattled effect. As will be more fully set forth hereinafter, this process is directed to overcoming these difficulties and to providing polyester fibers and yarns which can be readily and satisfactorily dyed with a wide variety of dyes including premetallized and acid wool dyes as well as conventional disperse dyes.
This process is based on the discovery that certain polymeric blends of fiber-forming linear polyesters with certain condensation copolyamides or homopolyamides can be melt spun or formed into high strength fibers, filaments, and yarns having excellent offinity for premetallized and acid wool dyes as well as disperse dyes and other polyster dyes. The dyed materials obtained thereby exhibit excellent light and gas fastness, and are resistent to the action of prechloroethylene or other dry cleaning solvents.
More specifically the products of this process consist essentially of a chemically heterogenous blend of (A) a linear condensation polyester having an inherent viscosity of at least about 0 .4 and a melting point in the range of about 150° to about 350°C. and (B) a linear condensation polyamide wherein the carbon amide groups are separated by at least two carbon atoms and are an integral part of the main polymer chain, said polyamide having an inherent viscosity of at least about 0.6 and having a melt viscosity substantially equal to or less than that of said polyester.
Societe Rhodiaceta
A process developed by
Y. Vaginay; U.S. Patent 3,576,773; April 27, 1971; assigned to Societe Rhodioceto, France involves extruding, in the fused state a branched polyethylene terephthalate containing y/n-2 to z/n-2 equivalent percent of n valent chain units where n is 3 or 4, y is 0.2 and Z is 2 having a specific viscosity of 0.47 to 0 .72 and a melt viscosity of 600 to 2,500 poises and orienting the yarns thus obtained by stretching.
The polymers used to prepare these products are branched polyethylene terephthalates and may be prepared by incorporating a branching agent, having three or four groups capable of forming stable bonds, such as ester, ether or amide bonds with the acid or alcohol groups, into the monomer mixture.
The preferred branching agents are polyols such as trimethylolpropane, trimethylolethone, pentaerythritol or glycerine; polyacids such as trimesic acid, trimellitic acid or anhydride or pyromellitic acid or anhydride; polyphenols such as phloroglucinal or hydroxyhydroquinone; amino acids and acid-alcohols such as hydroxyisophthalic acid or aminophthalic acid; 2,2-bis(4-epoxypropoxyphenyl)propane or diethanolamine.
Depending on the method of polyester synthesis employed 0.2 to 2 mols percent of the trifunctional branching agent relative to the terephthalic acid, or the terephthalic acid derivative, are used. Amounts of the order of 0.1 to 1 mol percent are preferred. The polyesters which may be used in the process are essentially derived from terephthalic acid, ethylene glycol and a branching agent. They can, however, contain a proportion, up to 10 mol percent, of another glycol containing an aliphatic, cycloaliphotic or aromatic group or heteroatoms such as propanediol, butanediol, hexanediol, decanediol, dimethylpropanediol, cyclohexa-nedimethanol, cyclobutanedimethanol, xylylene glycol, polyoxyethylene glycol of molecular weight less than 6,000, polytetrahydrofuran, another diacid such as adipic, sebacic, dodecanedioic, isophthalic or hexahydro or terephthalic acid, or dimeric acids derived from linoleic acid.
These polymers are preferably prepared in the presence of the usual transesterification and polycondensation catalysts and may contain agents to improve their color or heat stability such as phosphorus derivatives e.g., phosphorous acid, phosphoric acid, phenylphosphonic acid or triphenylphosphite. They can also be matted, for example by adding a suspension of titanium oxide.
Fabrics woven from yarns of polyester fibers derived from terephthalic acid and ethylene glycol have exceptional strength, abrasion resistance and pleat retention. However, the development of the use of polyester fibers in loosely woven or knitted fabrics is restricted to a large extent by the problem of pilling. In fact, in these types of fabric the individual fibers tend to migrate towards the surface and to form fibrous globules or pills which cannot become detached because of the high abrasion resistance and tensile
strength of the polyester, i.e., the rubbing forces are much lower than the force required to tear the polyester fibers holding the pill.
As it is very difficult to prevent migration of the fibers attempts have been made to lower the mechanical properties of the polyester fibers and to adapt their tensile strength to the rubbing forces applied during normal wear. During wear, the abrasion progressively lowers the tensile strength until it corresponds to the rubbing forces and pill drops off.
It has been attempted to lower the mechanical properties of the polyester fibers using polymers of lower molecular weight. Unfortunately the reduction in the molecular weight of the polyester is accompanied by a reduction in the viscosity in the fused state and in industry it is very difficult to spin a polyester having a viscosity in the fused state at 285°C. of less than 600 poises without the fibers sticking together. It is, therefore, difficult to obtain a fiber suitable for normal commercial use.
Although many attempts have been made to lower the tensile strength by treating the yarn or the woven fabric they have always come up against practically insoluble problems of reproducibility. This provides oriented polyethylene terephthalate fibers which are easily accessible industrially and yarns of fibers which do not give rise to pilling. It provides a polyester-based fiber having an elongation at break of greater than 15% and a tensile strength of 18 to 36 g./tex which comprises a branched polyethylene terephthalate having a specific viscosity of 0.47 to 0.72 and melt viscosity of 600 to 2,500 poises at 285°C. The fibers of this composition may be used in the manufacture of woven or knitted fabrics which substantially do not form pills.
SPINNING
Du Pont
A process developed by D.G. Bennie and T.R. Jones, Jr.; U.S. Patent 3,372,218; March 5, 1968; assigned to E.I, du Pont de Nemours and Company relates to an improvement in melt-spinning artificial fibers. More specifically, it relates to a process for treating the outer face of a spinneret used in the preparation of artificial fibers by the melt-spinning process and to the treated spinneret produced thereby.
The general procedure of forming thermoplastic resins into shapes by forcing them under heat and pressure through an opening generally referred to as an extrusion die is well-known. This procedure of extruding includes a forming of a thermoplastic resin through a specially designed extrusion die known as a spinneret, which is usually referred to as "melt-spinning."
In conventional melt-spinning processes, the spinneret is suspended so as to permit the hot, extruded liquid to fall downward, the extruded streams being cooled and solidified into the filament form during this descent. Among the problems encountered in this process have been flicking, bending, and dripping. Flicking is an obvious and repeated deviation of the liquid stream in the face of the spinneret from the normal path of descent. This phenomenon may occur at regular or irregular intervals. At times, an oscillating effect is observed. When the liquid stream is permanently deflected from its normal path of descent, it is said to have undergone bending. Where the liquid stream has flicked or bent to such an extent that it touches and wets the spinneret face, fouling occurs, the continuous liquid stream is broken, and the liquid thereafter drips from the orifice. This is known as dripping. It has been the practice to wipe the outer face of such spinnerets with a brass rod on a scheduled basis to avoid these problems in so far as is practical.
Several methods have been suggested for treating the face of the spinneret in order to reduce the flicking, bending, or dripping tendencies. This coating was found to be effective for a short period of time but eventually degraded, at the high temperature necessary for melt-spinning of polyesters, and the spinneret then required an even greater amount of wiping until removed from service. An alternate procedure suggested by U.S. Patent 2,403,476, consisting of manufacturing the entire extrusion die from a block of tetrafluoroethylene polymer, has not been found practical for melt-spinning because of inability to machine the small orifices to critical dimensions, particularly non-round orifices.
In accordance with this process, the outer face of a spinneret is coated with a film of an unusually high molecular weight fluorocarbon polymer, by applying a dispersion of the polymer and fusing the coating at considerably higher temperatures, than will be encountered in the melt-spinning process. A film of fluorocarbon polymer having a molecular weight of about 25,000 to 35,000 is particularly effective for overcoming the difficulties mentioned. As a result, the number of spinning discontinuities have been reduced by as much as 70% of the number of discontinuities which result when using one of the techniques of the prior art. In addition, there is no longer any need to wipe spinnerets routinely to remove accumulated deposits. The following is a specific example of the application of the present technique to the improved melt-spinning of polyester fibers.
Example 1: The spinneret is washed with a detergent in water and then dried, inspected, and repaired if necessary. The cleaned spinneret is coated with about 20 mg. of fluorocarbon polymer having a number average molecular weight of about 30,000. The coating is applied by spraying with the described 25% dispersion reduced to half strength with perchloroethylene solvent, using a De Vilbiss spray gun (Model MBC-510-30E) with pressure cup under 25 pounds per square inch (1.8 kg. per sq. cm.) air pressure. The spray adjustments on the gun are set to give a fine mist about the same size as the spinneret diameter. The coated spinneret is placed in a Lindberg Electric Cyclone furnace and held at 370°C. ± 10°C. for 30 minutes. The coated spinneret is then cooled and assembled in conventional melt-spinning assembly. Molten polyethylene terephthalate is then fed to the spinneret assembly at a temperature of 290°C. and under pressure of about 2,500 psi. The extruded melt is spun at a rate of at least 1,500 yards per minute into a 4.35-denier per filament, 600-filament yarn, which provides a'typical 1 ,5-denier per filament yarn after drawing. In a test continuing over a 9-day period using 16 spinning positions, the number of drips per pound of yarn spun is 0 .019.
The following table compares the above run with a run using a lower molecular weight fluorocarbon coating (2), with a run using a silicone coating (3), and with a run using no coating at all on the spinneret (4).
| Example No. | Coating on Spinneret | Molecular Weight | Drips per pound of Spun Yarn |
| 1 | Fluorocarbon | 30,000 | 0.019 |
| 2 | Fluorocarbon | 3,700 | 0.176 |
| 3 | Silicone | - | 0.038 |
| 4 | None | - | 0.18 |
A process developed by N.C. Pierce; U.S. Patent 3,437,725; April 8, 1969; assigned to E.I, du Pont de Nemours and Company relates to the melt-spinning of synthetic polymers and particularly to a method of spinning polymers having higher melt viscosities without polymer degradation and with reduced orientation of the polymer in the spun yarn. It is especially useful in the formation of filaments which have a final denier of less than 50 after they have been drawn.
In melt-spinning of yarns, synthetic linear polymer is melted, forced through the filter of a spinneret pack, then through spinneret capillaries, and quenched to form filaments which are converged into a bundle. The filament bundle is processed to provide the desired physical properties and finally the yarn product is packaged for shipment. Most melt-spinnable polymers are temperature sensitive and degrade rapidly at elevated temperatures. The lower the spinning temperature the higher the pressure required to force the molten polymer through the spinneret. Non-uniform flow, and melt fracture, will occur if the spinning temperature is too low consequently, a compromise is always made between a high spinning temperature for a minimum of polymer degradation.
Another approach to reducing spinning pressures is to increase the size of the capillary. If the same filament size (denier) is desired, this approach requires an increase in the attenuation or stretching of the molten material leaving the spinneret and, ideally, before it solidifies. Unfortunately, this stretching can seldom be done under sufficiently ideal conditions to avoid a spun orientation which adversely affects the final yarn properties. Further, when a heavy filament is spun, the inner portion is not quenched properly due to the insulating properties of the outer portion. This causes non-uniformities across the fiber as well as along the fiber. Frequently, it is necessary to use hot-gas annealing directly below the spinneret to counteract these adverse effects and obtain a more uniform yarn. However, this is costly, both in initial cost and operating costs.
Yet another approach has been tried in which the molten polymer is kept at a relatively low temperature until it is heated as it passes through a heated spinneret which is maintained at a temperature much higher than the melt. In practice, this has not worked because polymer in contact with the top face of the spinneret stagnates, becomes too hot and degrades. The search for better and better yarns goes on continuously. It is now known that improved physical properties, e.g., higher tensile strength, can be provided by polymers with higher melt viscosities, either from high molecular weight polymers or from polymers with stiff chain structures. However, this further complicates the compromise among high spinning temperatures, high spinning pressures, and capillary size. In some instances, it has been impossible to make commercial quality yarns from high viscosity polymers. The process makes possible the spinning of such polymers. For other polymers, it reduces the spun orientation and enables improved properties to be produced in the drawn yarn products.
This process is an improvement over the above processes, and spinneret packs, of the type wherein molten synthetic, linear polymer is supplied to a filterholder at sufficient pressure for the subsequent extrusion into filaments, the polymer is passed through the filter medium in the filter and is extruded through spinning capillaries in a spinneret plate. In accordance with this process, the spinning plate is separated from the filterholder by an insulating medium and spinning capillaries are formed by hollow inserts in the spinnerat plate which provided passages through the insulating medium from the filterholder. The spinning process included (a) passing the molten polymer through the filterholder at initial temperatures within a temperature range below that at which significant polymer degradation will occur, (b) passing the polymer into a plurality of passages each of which leads to a different spinning capillary in the spinneret plate and has an entrance temperature within the initial temperature range, (c) heating the spinneret plate to increase the temperature along the passages from said temperature at the entrance to a temperature at least 60° higher at the spinning capillary, and (d) extruding the polymer from the spinning capillary after a maximum of 4 seconds of travel through the heated passages.
Figure 1 is a sectional view and a detail showing the preferred spinning pack assembly featured in the process. As shown in the figure, lid 10, filterholder 12 and spinneret assembly 14 comprise the main elements of the spinneret pack assembly. Lid 10 is attached to filterholder 12 by a number of bolts 16, while the spinneret assembly 14 is similarly attached to the filterholder by a number of bolts 18. The entire pack assembly is mounted into the spinning machine by bolts 20. Inlet port 22 connects the top face of lid 10 to a plurality of distribution channels 24 which exit on the lower face of lid 10. Sands or screens, or a combination of the two, are placed in cavity 26 in filterholder 12. Distribution channels 28 connect cavity 26 with the downstream face of filterholder 12. Gasket 30, placed between filterholder 12 and spinneret assembly 14, is of sufficient thickness to form distribution space 32.
As shown in the detail in the lower part of the figure, the spinneret assembly 14 includes top plate 34, heating plate 36, and lower plate 38. An electric resistance heating element 40, spirally wound, is embedded in lower plate 38. Spacer 42 provides an air space between top plate 34 and heating plate 36, which acts as a thermal barrier between these two plates. The assembly is bolted together by bolts 44. Hollow inserts 46, one for each filament to be spun, are placed in top plate 34 and extend to the bottom face of lower plate 38. The relatively long tubular passageway 48 of the insert connects the top face of plate 34 to the final capillary 50.
In operation, molten polymer is supplied under pressure by a metering pump (not shown) to inlet port 22 and is distributed equally to the top of cavity 26 by distribution channels 24. After being filtered and sheared by passing through the sand, screens, etc., it is distributed to distribution space 32 by distribution channels 28. Temperature conditions maintained up to this point are such that the temperature of the molten polymer in the distribution space 32 is essentially the same as the temperature of the adjacent metal.
The molten polymer at this temperature is then forced into the top-plate ends of the inserts for spinning through capillaries 50, where the polymer exists in filament shape. Electrical heater 40 supplies heat to maintain the lower plate 38, heating plate 36, and the lower portions of insert 46 at a temperature at least 60°C. higher than the temperature of the supplied molten polymer. Because of the insulation effects of the air space between the plates, very little of this heat reaches top' plate 34, which remains essentially at the same temperature as the molten polymer. Due to the resulting temperature difference, the poor heat transfer characteristics of the polymer, and the extremely short time (a maximum of 4 seconds) that the polymer stays in contact with the high temperature portions of insert 46, a steep temperature gradient is given to the polymer flowing through each insert 46.
Figure 2. illustrates temperature profiles for polymer flowing through a portion of an insert 46. Initially, the temperature profile across the polymer in insert 46 is essentially constant as shown by Ta (corresponding to point a in the detail of the spinning pack); while at point b, the beginning of a temperature gradient is shown by curve Tb. Just before the polymer enters capillary 50, that is, at point c, there is a steep temperature gradient as illustrated by curve Tc. With a higher temperature on the walls of the entrance hole, the outer layer of polymer has a lower apparent viscosity. Consequently, the pressure required to force the polymer from the entrance hole 48 into capillary 50 and through capillary 50 is considerably reduced even though the temperature of the bulk of the polymer'flowing through capillary 50 has not been increased enough to have an appreciable effect on the polymer.
Figure 3. shows the bulge and temperature profiles for prior art spinning (in the upper view) and for the process (in the lower view). The upper view shows the "carrot" or bulge below a spinneret capillary of sufficient size to spin a high viscosity polymer with a reasonable pressure drop. Line 60 indicates the temperature profile across the polymer just below the capillary. Notice that the temperature of the center portion is slightly higher than that of the outer portion. Line 62 indicates the temperature profile at a short distance from the capillary. Since the exterior of the polymer is being cooled by a quenching medium, the center portion now has a considerably higher temperature than the exterior. It has been found, and is well known in the art, that this temperature profile causes nonuniformities in a filament.
The lower view shows a relatively smaller capillary which can be used with the same polymer when spinning with a heated capillary spinneret according to the process. It illustrates the reduced "carrot" or bulge that results because of less shearing action and less pressure required to force the polymer through the capillary. Furthermore, in order to get the same filament size or denier, less spin stretch is required under these conditions. Line 64 indicates the temperature profile just below the capillary exit. Note that the outer portions of this filament are hotter than the inner portions. A short distance below, line 66 illustrates the profile after some cooling has taken place. Notice that, by this time, the temperature gradient across the filament is very small . This leads to improved product uniformity.
FIGURE 1 : SECTIONAL DIAGRAM OF POLYESTER SPINNING PACK ASSEMBLY
The heated capillary which generates the steep temperature gradient reduces the shear stress at the wall of the capillary without excessive thermal degradation of the polymer. Further, since smaller capillaries can be used without excessive pressure drops, lower spin- stretch ratios can be used to spin low birefringent yarns. In alternate designs, each insert could have a plurality of long entrance holes and capillaries. This is particularly advantageous when the capillaries are arranged in a straight row. Further, it may be helpful to use heat shields or barriers in the air space between the top plate and the lower plate. The following examples are cited to illustrate the operation of the process. The first two examples illustrate the spinning of high molecular weight polymers which cannot be spun with conventional spinnerets. The second two examples illustrate the reduction in spun filament orientation, and improvement in drawn yarn properties; they also demonstrate good spinning without the requirement of hot gas annealing.
FIGURE 2: TEMPERATURE PROFILES FOR POLYMER IN A SPINNERET
Example 1: A series of small batches were polymerized to high molecular weight polymer with the object of preparing fibers with as high a molecular weight as possible (consistent with good processing performance) to achieve superior fiber tensile properties. Inherent viscosities of the various polymer batches for each melt spinning experiment are listed in Table 1. Inherent viscosity ( hinh) is defined as:
where C is the concentration of polymer in the solvent, in g./100 ml. (nominally 0.32 g./100 ml.). The solvent is trifluoroacetic acid/methylene chloride (25/75 vol./vol.). q is the drop time of polymer solution through the capillary viscometer at 25°C. in seconds. q0 is the drop time of solvent through the capillary viscometer at 25°C. in seconds.
Polymer viscosities which could be melt processed by conventional melt spinning techniques had an upper limit of molecular weight of about hinh £ 0.85. Melt fracture occurred at higher molecular weights, preventing continuous spinning. In the examples of Table 1 with conventional spinnerets, a high spinning block temperature of 320° to 325°C. was used, which alleviated melt fracture to some degree but was not sufficient to eliminate the problem. Higher block temperatures degraded the polymer melt. When using the heated capillary spinneret of this method, no melt fracture problems were encountered at a significantly higher molecular weight level. Spun yarn extensibility at high molecular weights and the resulting physical properties were good for the heated capillary spinneret. No direct comparison with conventional yarn could be made because melt fracture prevented yarn processing at these higher molecular weight levels.
Example 2: Poly(bicyclohexyl-4,4'-dimethylene-4,4'-bibenzoate)polymer was produced as disclosed in British Patent 979,401. Its molecular weight was increased by solid phase polymerization. The polymer was heated and spun through a conventional spinneret, and through a heated capillary spinneret of this process. Drawable, smooth yarn is produced with small heated capillaries. With conventional capillaries, large enough to avoid melt fracture, the yarn was essentially undrawable and no low denier-per-filament yarn having good tensile properties could be made. When the test with the heated capillary spinneret was repeated with the capillary temperature reduced to the range of 360° to 375°C., slight melt fracture was observed.
Flex life is defined as the number of flex cycles to failure of the median of single filament samples as tested on a Masland Flex Tester at 70°F. and 62 1/2% RH . Filaments, under a load of approximately 0.33 gpd are flexed over a 0.001 (0.025 mm.) diameter tungsten wire, oscillating through a 180° arc at 150 to 154 cycles/minute.
Example 3: Conventional polyethylene terephthalate polymer melt was spun through a conventional spinneret, and a heated capillary spinneret, to ultimately form a staple product. With the conventional spinneret, the filaments were spun into 360 °C. inert gas in an annealing zone 6 inches long (15 cm.), followed by a delay baffle 16 inches long (41 cm.), a 6 inc (15 cm.) open space, and then to a radial quench unit. The spun yarn was wound up at 1 ,030 ypm (940 meters per min.), at 38 pounds per hour (17 kg. per hour) throughput. Several undrawn yarn bobbins were then combined and drawn on a staple draw machine at 4. OX draw ratio.
With the heated capillary spinneret, a small amount of inert gas (1 to 2 cubic feet per minute) was used to blanket the spinneret face, but no heat was supplied to the gas stream. The yarn was spun through a delay baffle 18 inches long (46 on a 6 inch (15 cm.) open space to the radial quench unit, and wound up at 1 ,030 ypm (940 meters per min.), at 29 pounds per hour (13 kg. per hour) throughput. Two tests were run, with different molecular weight polymers. The products were drawn in identical manner.
Comparison among the test items shows that the yarn from the heated capillary spinneret is much more uniform in diameter and orientation, and could be drawn to a high draw ratio and to superior physical properties without evidence of non-uniformity (e.g. , broken filaments). This was accomplished with the heated capillary spinneret without hot gas annealing.
Using the same heated capillary spinneret as used in Example 3, with the same type of annealing and quenching system for the control, and a small amount of unheated inert gas when operating with a heated capillary spinneret, polyethylene terephthalate industrial yarn was produced.
Three pairs of tests were run, varying the polymer RV and the draw ratio. These data clearly demonstrate that the heated capillary spinneret produces spun yarn with improved properties without hot gas annealing and that a smaller capillary can be used.
A process developed by J.M. Carpenter III and O.K. Smith; U.S. Patent 3,480,706; November 25, 1969; assigned to E.I. du Pont de Nemours and Company provides better filament continuity and a longer spinneret pack life, the improvement including the step of pumping the polymer at a high pressure in excess of 1,000 pounds per square inch gauge through a low pressure drop filter having a pressure drop of 200 to 800 psi to filter the polymer, the filtering being done prior to meter pumping the polymer through the spinneret pack for melt-spinning.
When molten polymer is filtered, agglomerated additives, solid polymer gel and the like are removed and the resultant filtered material is thus rendered more suitable for the production of shaped structures. The production of shaped structures, such as filaments, requires removal of particulate matter that would otherwise clog the exceedingly small spinning orifice. Further, any source of non-homogeneity should be removed so as to reduce accompanying variation in the properties of the filaments. In producing multifilament yarns it is particularly important that the filaments comprising the yarn be as uniform as possible. If, for instance, the yarn contains filaments that vary appreciably in denier or contain segments or markedly different viscosity, subsequent drawing of the yarn will cause objectionable filament breakage.
Figure 4. shows a polyester melt-spinning assembly incorporating such filter devices. Turning now to the drawing, molten polymer in polymer finisher or screw melter 1 is passed to screw pump 3 which forwards the polymer towards booster pump 7 and shear-filter devices 21 and 21' (transfer-line filters) located in transfer-line 5. Booster pump 7, run by motor 9, forwards the polymer through a downstream section of transfer-line 5 to either of shear-filter devices 21 or 21'. When valves 15 and 23 are open and valves 15' and 23' are closed, the polymer will pass through auxiliary line 13 and be filtered in device 21. When it is desired to replace device 21, valves 15 and 23_are closed and valves 15' and 23' are opened to pass the polymer through auxiliary line 13' and device 21'. Flanges 17 and 19, provided for the purpose, are broken, and new device 21 inserted and the flanges resealed. Flanges 17' and 19' are provided for changing device 21' in like manner.
FIGURE 4: SPINNING ASSEMBLY INCLUDING PUMPS, FILTERS AND SPINNERETS
On leaving device 21, the polymer passes to the downstream junction of auxiliary lines 13 and 13' where they unite to continue as transfer-line 5. On passing through transfer-line 5, the polymer travels through header 27 which serves to distribute the polymer to individual conduits such as at 29 and 31 which serve as the supply source of molten polymer for spinning. In spinning, the polymer passes through meter pump 33 in a precise amount and is filtered as it passes through filter 35 and is extruded as small precise streams from a multiplicity of orifices in spinneret 37 and is then quenched in chamber 42 to form the filaments. The filter agent and the spinneret are usually combined and the assembly referred to as a pack. The filaments are converged at guide 39 to form yarn 41. Excess polymer may be diverted as shown by the dotted lines at 4, if desired, to duplicate facilities to those described above.
Figure 5. is a sectional view of the filter used in the process. The assembly comprises an outer shell 53 having inlet 54 and outlet 55. A pipe having plurality of holes 56 which are positioned radially around the circumference and along the length extending into the interior of the pipe. The pipe is mounted concentrically within the interior of the shell. The end of the pipe adjacent the inlet is closed and the other end passes through the shell outlet and forming a fluidtight seal therewith. The pipe is wrapped with layers of various screens 57 to provide the desired filtration. The polymer passes through the screens and into the interior of the pipe and then out of the assembly through the shell outlet.
The following is a detailed example of the conduct of the process in the spinning of polyester fibers. Polyethylene tere-phthalate is polymerized to a relative viscosity of 26 in a polymer finisher, and the molten polymer, which is maintained at a temperature of 285°C., is pumped by means of a screw pump to the inlet of a one-stream gear-type booster pump. The booster pump has a capacity of 16.5 cc per revolution and is capable of delivering 9 to 100 pounds (4 to 68 kg.) of the polymer per hour. The inlet pressure of the booster pump is about 500 psi (35.3 kg./cm.2) gauge and the outlet pressure ranges from about 2,600 to 2,700 psi during test period.
FIGURE 5: SECTIONAL DETAIL OF POLYMER FILTER
The booster pump forces the molten polymer through a transfer-line filter of the type illustrated. The filter comprises a shell having an inlet and an outlet and a pipe of 3.5 cm. outside diameter for collecting the filtered polymer. The pipe has 8 rows of holes spaced 45° apart aligned along the longitudinal length of the pipe. The longitudinal distance between the holes is about 5 cm., and there are 4 holes per row. The pipe has one end closed and is concentrically mounted within the shell with the closed end being adjacent to the shell inlet and the other end passing through the shell outlet and forming a fluidtight seal therewith. For the filtering medium the pipe is first wrapped with 4 layers of 50 mesh screen (0.023 cm. wires), when 15 layers of 325 mesh screen (0.00355 cm. wires), then 4 layers of 50 mesh screen. The outside diameter of the wrapped pipe is now about 4.5 cm.
The polymer passes into the shell through the inlet and fills the annular space between the shell and the centrally mounted wrapped pipe. The booster pump forces the polymer through the screen wrappings and through the holes of the pipe. The filtered polymer next passes through the pipe and out of the shell through the outlet (via the pipe). The filter area is 580 cm.2 and each hour 11.5 kg. of polymer pass through the filter.
The molten polymer is passed to a header serving eight spinning packs. One of these units contains a pack having a filter consisting of 25 new screens having on effective filtration diameter of 5.08 cm. (19.7 cm.2). The polymer throughput rate through the test pack is 2.88 lb./hr. (1.31 kg.hr.) or 0.145 lb./hr. per cm.2 of effective filter surface. The transfer-line filtration rate per cm. 2 of filtration area is 0.0436 Ib./hr. per cm.2. The ratio of the pack filter rate per unit area to that of the transfer-line filter rate per unit area is 3.33:1. The seven top screens are 20 mesh, the next 16 screens are 200 mesh and the last 3 screens are 325 mesh. The pack also contains a spinneret with 34 orifices having a diameter of 0.038 cm. The system was evaluated for one week. The pressure at the transfer-line filter outlet remained relatively constant at about 2,000 pounds per square inch (141 kg./sq. cm.) gauge. The pressure at the filter inlet increased from 2,430 pounds per square inch (171 .3 kg./sq. cm.) gauge to 2,525 pounds per square inch (178 kg./sq. cm.) gauge over the 7-day test period.
The pressure drop across the pack filter initially was about 875 psi (61.7 kg./cm.2). During the first two days following its installation, the pack pressure increased from 1,830 to 1,890 pounds per square inch (129 to 133.2 kg./sq. cm.) gauge and remained unchanged for the remaining 5 days. When the same test was repeated except that no filter was used in the transfer-line, the pressure increased in a regular fashion from 1,820 to 2,030 pounds per square inch (128.3 to 143.1 kg. per sq. cm.) gauge over the 7-day period. In addition to producing more uniform polymer and filaments of the polymer, the process provides an extended and more uniform pack life.
FIGURE 6: APPARATUS FOR MONITORING POLYMER VISCOSITY IN A SPINNING UNIT
A process developed by T.R. Jones, Jr.; U.S. Patent 3,524,221; August 18, 1970; assigned to E.I. du Pont de Nemours and Company involves controlling filament uniformity by measuring the melt-viscosity of the polymer being extruded by measuring the pressure and temperature of the polymer after filtering and just prior to extrusion through the spinneret capillaries, comparing the viscosity with the viscosity desired, and then making the appropriate change in the reactor conditions to change the viscosity toward the desired viscosity.
Figure 6. is a schematic representation of a melt-spinning apparatus fitted with pressure transducer, thermocouple, recording means, and regulator means for correcting the conditions within the polymer finisher for bringing the viscosity back toward midrange together with a detail of a transducer-thermocouple installation in the spinneret plate. As shown in the main view in the figure, molten polymer from a source now shown is supplied to metering gear pump 1 which forces the polymer at a constant rate through conduit 2 into the sand cavity 3 of a melt-spinning head. The polymer traverses the top screen 4, sand filter 5, bottom screen 6 and then moves through channels 7 in the bottom of the sand holder to the space 8 immediately above the spinneret. The polymer is then forced through the spinneret capillaries 9 to form extruded filaments 10 which are quenched, passed over rotating roller 11 and then wound up in package 12.
The pressure of the polymer in space 8 is measured by means of pressure transducer 13, converter into on electrical signal in bulb 14 and indicated and recorded by recorder 15. The temperature of the spinneret is measured by thermocouple 16, with the temperature being indicated and recorded on recorder 17. In normal operation the temperature of the unit is maintained at the desired level by electrical or fluid heating means with the assistance of suitable insulation. The polymer finisher 20 is illustrated as having an associated viscosity regulator 21 which, in the case of condensation polymers, regulates the vacuum with the finisher, thereby effectively controlling polymer viscosity. Integrator and controller 22 determines the actual viscosity as based on the temperature and pressure above the spinneret, compares this with the desired viscosity, and transmits the appropriate signal to regulator 21.
The detail at the base of the figure shows schematically a spinneret plate 19 with a pressure transducer 13 fitted into the face of the spinneret and extending through the spinneret so that the pressure-sensing diaphragm is exposed at the top of the spinneret. Channel 18 is drilled into the body of the spinneret to provide a place for inserting a thermocouple for accurate measurement of the spinneret temperature. The pressure of the molten polymer above the spinneret may be measured with any suitable device of sufficient sensitivity which is stable at the temperature of operation. A suitable device is the Dynisco melt pressure transducer Model PT-422, available from the Dynisco Division of American Brake Shoe. This device uses a bonded strain gauge measuring element for converting pressure indications to electrical signals.
Amplifying and recording devices suitable for use in the process are well known in the art, and a wide choice of suitable instruments is available commercially. A constant rate of flow of polymer through the spinning apparatus may be maintained by any suitable positive displacement pump. Metering gear pumps are preferred.
Once the pressure above the spinneret and temperature of the polymer are known the melt viscosity may be calculated or taken from a previously prepared table based on the constant flow rate and cross-sectional area of the capillaries in the spinneret. The mathematical relationships are amplified by Mc Cabe and Smith in Unit Operations of Chemical Engineering. As before disclosed the process lends itself readily to automatic regulation of the polymer viscosity by controlling the reaction conditions within the polymer finisher.
Integrated Polyester Production Processes
DU PONT
A process developed by J.C. Busot; U.S. Patent 3,487,049; December 30, 1969; assigned to E.I., du Pont de Nemours and Company is a continuous process for producing fiber-forming linear polyester from dimelhyl terephthalate and ethylene glycol. Ester interchange to produce monomer and polymerization of the monomer are carried out continuously in a series of reaction vessels. The addition of a small amount of finely divided terephthalic acid at an intermediate point is shown to increase the degree of polymerization and improve the color under the same conditions, or to increase the rate at which fiber-forming molecular weight is obtained, in comparison with operation of the process without addition of the terephthalic acid.
The manufacturing process starts with the dimethyl ester of terephthalic acid, first carrying out an ester-exchange reaction with glycol at atmospheric pressure to produce the bis-glycol terephthalate, and then heating the bis-glycol terephthalate under reduced pressure to split out excess glycol and form the highly polymeric terephthalate polyester. The reactions are usually carried out continuously in several successive stages in a series of interconnected vessels. The vessels usually include an "exchanger" in which the initial exchange reaction is carried out, a "prepolymerizer" in which low molecular weight polymer is formed at an intermediate temperature and pressure, and a "finisher" where the final stages of polymerization are carried out at high temperature and low pressure. The presence of one or more catalysts is required to provide reaction rates high enough for commercial operation.
An increase in polymerization rate is highly desirable as it allows the use of smaller vessels for a given rate of polymer production, thereby decreasing the amount of capital investment required. Alternatively, an increase in polymerization rate may allow the use of higher pressures in the finisher, and thereby reduce the requirements of the vacuum producing system, or may allow the use of lower temperatures in the finisher with a consequent reduction in side reactions and color formation. Attempts to increase the polymerization rate by raising the catalyst concentration have not been entirely successful. For example, increasing the concentration of antimony oxide, a preferred polymerization catalyst, does not produce a corresponding increase in reaction rate. Furthermore, higher concentration of antimony oxide result in a "graying" of the polymer, presumably from the formulation of metallic antimony in divided form.
This process offers a method of increasing the degree of polymerization in the preparation of polyesters and at the same time providing a polymer having greatly improved color. The process allows higher rates of throughput for equipment of a given size, or for the use of smaller equipment for a given throughput. Other conditions being equal, the process allows for the production of a higher polymer viscosity or for the use of a lower temperature or for the use of a higher pressure in the finisher.
In accordance with this process, it has been found that, in the production of glycol terephthalate polyesters by a poly- esterification reaction carried out at elevated temperatures under reduced pressure, the degree of polymerization obtained is increased by injecting into the low molecular weight prepolymer, undergoing polymerization, a glycol slurry of finely divided terephthalic acid in amounts sufficient to provide from 0.01 to 4 percent by weight of terephthalic acid based upon the weight of polymer produced. Amounts of terephthalic acid smaller than about 0.1 percent by weight do not give an appreciable effect, while amounts greater than about 4 percent limit the degree of polymerization in conventional commercial procedures.
By the term "low molecular weight prepolymer" is meant a polymerizing mixture which has passed the monomeric stage but has not yet reached the desired final molecular weight. Preferably the glycol slurry of terephthalic acid is added to the prepolymer having an intrinsic viscosity in the range 0.1 to 0.5, which corresponds approximately to a 2 to 20 relative viscosity range. Figure 1. is a schematic illustration of the continuous polymerization system used in this process.
FIGURE 1: FLOW DIAGRAM OF INTEGRATED POLYMER SYNTHESIS AND SPINNING PROCESS FOR POLYESTER FIBERS
Referring now to the drawing, dimethyl terephthalate, ethylene glycol, and catalyst are supplied to ester interchange column 1 where the exchange reaction is carried out and methanol removed from the top of the column as vapor. Liquid product comprising primarily bis-b-hydroxyethylterephthalate containing a small amount of low polymer and glycol is continuously removed from column 1 through transfer line 2 and injected into the second stage vessel 3 which operates under moderately reduced pressure and elevated temperature to remove excess glycol. Liquid product from vessel 3 is transferred through conduit 4 to prepolymerizer 5 where the pressure is reduced further and the temperature raised sufficiently to give a low molecular weight product having an intrinsic viscosity of about 0.2 to 0.3. This "prepolymer" product is transferred continuously through transfer line 6 to the finish polymerizer vessel 7 where the polymerization is completed and the final product transferred to the spinning machine through conduit 8 for melt-spinning into yarn.
When operated in accordance with this process, terephthalic acid powder and glycol are supplied to mixer 9 for the preparation of a slurry. This slurry is then metered by means of valve 10 either through conduit 11 to prepolymerizer vessel 5 or through conduit 12 to prepolymer transfer line 6, the latter being preferred. It has been found that best results are obtained if the amount of terephthalic acid added to the polymerization system is adjusted to suit the degree of polymerization of the prepolymer at the point of addition. Preferably the amount of added terephthalic acid falls below an upper limit defined by
Z1 = e(1.93 - 0.151RV)
and above a lower limit defined by
Z2 = e - (0.380 + 0.151RV)
where Z is the weight percent, based on polymer, of terephthalic acid added and RV is the relative viscosity of the low molecular weight prepolymer to which the terephthalic acid is added. The concentration of the glycol slurry used in the process may vary over a wide range, but it will be recognized that in a practical commercial process a more concentrated slurry is desirable to prevent overloading the vacuum system with excess glycol. Preferably the slurry is a mixture of terephthalic acid and glycol in a mol ratio within the range 1:1 to 6:1.
This process is found to provide as much as a 50% increase in reaction rate as measured by increased throughput in continuous polymerization systems. The advantages are obtained not only for the production of medium molecular weight polyesters conventionally found in textile grade yarns, i.e., those having an intrinsic viscoisty of about 0.6, but more importantly the advantages are also obtained in the production of very high molecular weight polyesters useful as tire yarns, i.e., those with an intrinsic viscosity of about 0.8 to 0.95. Even when the glycol-terephthalic acid slurry is added in very small amounts which give only a minor increase in degree of polymerization, a marked improvement in polymer color is obtained. The following is a specific example of the conduct of this process.
A continuous polymerization system is used for the production of polyethylene terephthalate of fiber-forming molecular weight. Dimethyl terephthalate and ethylene glycol are supplied continuously to an ester exchanger which is operated in the manner described by Vodonik in U.S . Patent 2,829, 153, issued April 1 , 1958. Sufficient dimethyl terephthalate is supplied to produce approximately 95 lbs. (43.1 kg.) of polymer per hour. Catalysts introduced along with the glycol include 125 parts per million of manganese added as manganous acetate, 50 parts per million of sodium added as sodium acetate, and 510 parts per million of antimony added as antimony oxide. The product of the exchanger is primarily "monomer," i.e., bis-glycol terephthalate with a minor amount of low polymer.
The molten monomer is transferred continuously to a second vessel kept at 240°C. and a pressure of 70 mm. of mercury. A large amount of excess glycol is vaporised and removed in this vessel. The molten material is then transferred to a pre-polymerizing vessel operated at a temperature of about 272°C. and 30 mm. mercury pressure, where low molecular weight polymer is produced. The product of the prepolymerizer, which has a relative viscosity of about 4.5 (a degree of polymerization of about 10), is passed on to a finisher where the temperature is raised to 277°C. and the pressure is reduced to 1.85 mm. of mercury. The final polymerization reaction is carried out in the finisher and the product removed is ready for spinning into yarn.
When the continuous polymerization system described above is operated with a glycol slurry of terephthalic acid (4 to 1 mole ratio), continuously added to the prepolymerizer product at
the rate of 2.84 lbs. (1 .29 kg.) per hour (about 1 .20% based on polymer), the final polymer produced has a relative viscosity of 35.2. When no terephthalic acid slurry is added to the prepolymer, the final polymer viscosity is 27 RV. Thus, the addition of terephthalic acid slurry is found to provide a 30% increase in polymer viscosity under the conditions described.
FIBER INDUSTRIES
A process developed by T.C. Higgens; U.S, Patent 3,506,622; April 14, 1970; assigned to Fiber Industries, Inc. is a continuous process for the production of polyethylene terephthalate in which constant equilibrium conditions are maintained in the polymerization stages. Prior to the extrusion stage, excess polymer is removed and treated with ethylene glycol to produce the polymer precursor which is then added to the polymerization reaction at the point of corresponding intrinsic viscosity. The process obviates the necessity for the addition of solid scrap polymer in the final polymerization.
In the commercial production of polymethylene terephthalate polymers, it is highly desirable and feasible to produce large amounts of polymer using a continuous polymerization process. Various methods for the production of polymethylene terephthalate polymers on a continuous basis are known in the art, but these known processes have various disadvantages which can present extensive control problems and provide an undesirable non-uniform quality product. Attempts have been made to maintain a uniform polymer quality in continuous polymerization processes by controlling the level of the molten polymer in the final polymerization reactor by the continuous addition of solid scrap polymer to the monomeric material.
The amount being added being of necessity equal to the increased or decreased demand of the extrusion equipment from the polymer exit. Although it is possible to maintain a satisfactory control of the polymer quality utilizing the addition of solid scrap polymer, obvious disadvantages are present. Of the significant disadvantages of the known continuous polymerization processes, the quality of the scrap polymer to be added must be carefully selected to avoid the addition of undesirable foreign contaminants; the handling problems of the solid scrap polymer are significantly increased and a separate reaction stage is required to convert the solid highly polymeric waste into a liquid low polymer suitable for feeding into the system.
The major disadvantage, however, is in the fact that as the rate of demand for high polymer increases or decreases at the extrusion apparatus; the maintenance of a constant level in the reactor obviously gives rise to variations in residence time which can appreciably affect the degree of polymerization and polymer quality. Further, detection of level changes in the highly viscous polymer in the reactor is difficult instrumentally and the lag or delay between the detection of level changes and adjustment of the quantity of solid scrap being fed upsets the equilibrium conditions in the reactor.
It is the over-all object of this process to provide improvements in the continuous polymerization processes for the production of polymethylene terephthalate polymers wherein variations in supply of polymer to the extruder as required can readily be made while maintaining a uniform quality of polymer throughout the entire reaction process. It is a further object to provide an economic and convenient method for controlling the liquid polymer level throughout the reactor stages to provide a uniform quality polymer with a minimum amount of effort in the continuous production of polymethylene terephthalate polymers.
The objects of this process can be readily obtained in a continuous polymerization process for the production of polymethylene terephthalate polymer which polymerizes bis(hydroxyalkyl) terephthalate by polymerizing at a rate in excess of the maximum requirements and taking off as a side stream the excess polymer produced prior to the extrusion operation in molten state and adding sufficient amounts of the corresponding alkylene glycol containing 2 to 10 carbon atoms used to prepare said bis(hydroxyalkyl) terephthalate to said excess molten polymer to produce the precursor of said polymer. The precursor of the pol-er having an intrinsic viscosity lower than the final polymer can then be returned to the continuous polymerization reaction at the point wherein the intrinsic viscosity of the precursor corresponds essentially to the intrinsic viscosity of the material fed to the high polymer reactor, thus maintaining a constant level of the polymerization mass and at the same time constant throughput and residence time in the reactor. This method provides a unique manner of maintaining invariant conditions within the reactor irrespective of changes in demand for extrusion purposes, eliminates the need for level detection and the considerable upset in equilibrium associated with such methods of control. By virtue of this process modification, therefore the level and throughput of material in the reactor and hence, the residence time are held constant irrespective of extrusion requirements with obvious advantages.
A disadvantage of a continuous polymerization reaction is obvious, however, in that the production of the polymer product must be minutely regulated to the specific needs of the film casting or filament spinning operation. If interruptions occur in the extrusion operation, over production or under production of the polymer can seriously upset the equilibrium of the polymerization reaction. In waiting for the return to equilibrium, valuable periods of time can be lost in the production phase. If reduced extrusion demand suddenly occurs, the reduced throughput in the final polymerizing apparatus, if maintained at constant level of reactions as is taught in the prior art, tends to an increase in residence and reaction time, which can provide a number of undesirable results which include, among others, an appreciably higher molecular weight polymer than desired, producing a non-uniformity of the polymer product.
Additionally, a reduction of the polymer demand can also introduce contaminants in the polymer by increasing the level of the reactant due to relay or lag of the control detecting devices, and the polymer can splash on the upper walls of the reactor and detrimentally degrade. These and other disadvantages can occur. On the other hand, if under production occurs, the polymer to the subsequent metering pumps may be starved and the flow of the liquid polymer to the casting or spinning operation will tend to come in surges instead of in the form of a uniform feed. Such an interruption in the flow of the polymer to the extrusion operation necessitates eventual shutdown of the extrusion operation. In addition, the reduced residence time will cause a lower molecular weight polymer than desired.
A significant feature of this development is to provide a process wherein the deliberate over-production of the polymer which is sent to the extrusion operation can be advantageously utilized. Under these conditions, the excess molten polymethylene terephthalate polymer is removed prior to the extrusion operation. To the excess molten polymer is added sufficient amounts of the corresponding alkylene glycol utilized to prepare the monomeric bis(hydroxyalkyl) terephthalate under reaction conditions which will provide a precursor of the high molecular weight polymethylene terephthalate polymer; such as, monomeric bis(hydroxyalkyl) terephthalate, prepolymer or combinations thereof. The precursor thus produced is returned to the polymeri-zation reaction at the point where the reaction material corresponds essentially to the precursor in composition, in intrinsic viscosity, among other properties.
When the precursor is returned to the polymerization reaction, the supply of the monomeric bis(hydroxyalkyl) terephthalate is diminished or cut off in amounts to correspond to the amount of precursor added. Under these conditions, the level and flow rate and residence time of polymerizing material in the reactor is maintained substantially constant providing at all times a polymer of the desired uniform composition to the extrusion operation and irrespective of the change in demand. One feature which is indeed surprising relates to the absence of detrimental degradation, e.g. the production of contaminants, of the high molecular weight polymer in its reaction with the added alkylene glycol to produce the precursor which in turn can be further polymerized to obtain the desired high molecular weight polymer product. Figure 2 is a flow diagram showing the essential features of this process.
For the production of bis(2-hydroxyethyl) terephthalate from terephthalic acid and ethylene glycol, a direct esterification reactor 10 containing a terephthalic acid inlet line 11 and an ethylene glycol inlet line 12 is maintained at temperatures in the range from about 200° to about 275°C. The amounts of ethylene glycol and terephthalic acid added to the reactor can range from about 1.0/1.0 to about 3.0/1.0 molar ratios of glycol to terephthalic acid, respectively. The esterification reaction conditions are continually maintained, to produce the initial monomeric bis(2- hydroxyethyl) terephthalate products; such as, half esters, esters, dimers and the like. During the esterification reaction, the volatiles which form, such as water, are removed through exit line 13. Monomeric bis(2-hydroxyethyl) terephthalate product produced in reactor 10 is then passed through line 14 into the prepolymerizer 15 wherein the initial polymerization reaction occurs at temperatures in the range from about 250°C. to about 285°C. and at pressures in the range from about 5 to about 60 millimeters mercury.
During the prepolymerization reaction, the ethylene glycol removed can be recycled through lines 16 and 25, back to the source of the original ethylene glycol for further use without an additional purification step in the esterification. The prepolymer formed having an intrinsic viscosity in the range from about 0.1 to about 0.4 is then passed through line 17 into the final polymerizer 18 which is maintained under similar conditions as the prepolymer reaction but generally lower pressures in the range from about 0.5 to about 10 millimeters of mercury. As the prepolymer is passed through the final polymerizer, a more complete polymerization occurs, i.e. the intrinsic viscosity of the product increases from about 0.4 to about 1.1, or higher, progressively as it passes through the final polymerizer. The product of the final polymerizer is withdrawn when the desired intrinsic viscosity of the polymer is obtained or conditions can be adjusted to obtain the desired product out of the exit line 21 which can be passed on to an extrusion operation, such as spinning into fiber or filament production.
Assuming a sudden reduced demand of polymer rate to the extrusion apparatus, the excess amount of polymer produced can be withdrawn from line 2l through line 22. Line 22 is heated not only to maintain the excess polymer in a molten state but also to provide sufficient heat for the reaction of the added ethylene glycol to form the precursor described hereinafter. It is not desirable to maintain the excess polymer in its molten state over extended periods of time since contamination degradation can occur.
The excess molten polymer in this process can be treated in several ways for further use. The ethylene glycol which is produced in the final polymerizer can be added via lines 19 and 20 to the excess polymer in heated line 22 to produce the polymer precursor, i.e. prepolymer, monomer, or mixtures thereof. If sufficient ethylene glycol is recovered from the final polymerizer to produce the presursor equivalent in composition to the prepolymer in vessel 15 or line 17, the precursor can then be returned via line 22 through line 24 to vessel 15 and returned to the final polymerizer through line 17 for further polymerization. If the amount of ethylene glycol from the final polymerizer in line 20 is not sufficient, additional ethylene glycol can be supplied to line 20 or line 22.
A method of determining composition of the precursor in line 22 can be made by a measurement of intrinsic or melt viscosity of the precursor. It should be noted at this point, however, that if the precursor is added back to the final polymerizer, the amounts of prepolymer or monomeric material prepared prior to the final polymer should be diminished by adjusting the flow of materials fed via lines 11 and 22 and also 12, if desired, in amounts corresponding stoichiometrically to the amounts of the precursor added to the final polymerizer. Under these conditions, the desired process parameters in the final polymerizer will be maintained thereby assuring a uniform polymer product and avoiding production of undesirable contaminants. Additionally, if the precursor produced in line 22 is equivalent in composition to the monomeric material produced in the esterification reaction and supplied through line 14, the precursor produced in line 22 can be added through line 24 to the prepolymerizer, if desired, with the appropriate change of reactants via lines 11 and 22 mentioned above.
The highly perferred procedure is to transfer the excess molten polymer in line 22 to the esterification reactor 10 and ad-justing the supply of terephthalic acid and glycol. Under these conditions, control of the operating process pa
