MX2008010295A - Polyester solid phase polymerization catalyst for low acetaldehyde generating resins - Google Patents

Abstract

This invention discloses a process for producing a polyester resin having a low acetaldehyde generation rate comprised of the steps of polycondensing the polyester resin in the presence of tin and antimony;wherein the tin is present within the range of 50 to 110 ppm of the polyester resin and the antimony is present from 105 ppm to 265 ppm of the polyester resin, and solid phase polymerizing the polyester resin for sufficient time so as to increase the intrinsic viscosity of the polyester resin by at least 0.15 dl/g.

Description

SOLID PHASE POLYMERIZATION POLYMERIZATION CATALYST FOR RESINS WITH LOW GENERATION OF ACETALDEHYDE PRIORITY AND CROSS REFERENCES This patent application claims the benefit of the priority of the United States provisional patent application serial No. 60 / 772,192 filed on February 10, 2006. The teachings of this provisional patent application are hereby incorporated by reference in their entirety. .

FIELD OF THE INVENTION This invention relates to the field of manufacturing polyester resins using a solid phase polymerization process to more rapidly polypeptide the polyester resin but still produce a polyester resin with a low rate of acetaldehyde generation.

TECHNICAL BACKGROUND Polyester resins used in packaging have unique requirements. They are usually manufactured by making a polymer of low molecular weight to medium in liquid phase, pelletizing the polymer and then subjecting said pellets to a solid phase polymerization to further increase the molecular weight. It is well known in the art that some catalysts (for example titanium) work very well in the liquid, or melt polymerization step, but do not catalyze the reaction in the solid phase step. The choice of catalyst is also important because it is also known that different catalysts will affect the amount of acetaldehyde generated when the polyester resin is remelted and molded by injection into a preform or cast into a sheet. Minimization of acetaldehyde is a particular goal for packaging used to retain water. Acetaldehyde is absorbed from the packaging in the water, negatively affecting the taste of the water. There is therefore a need for a catalyst or catalyst system that will provide acceptable solid phase polymerization rates but still form a reduced amount of acetaldehyde. It has been found that the combination of tin and antimony provide such a catalyst system. The use of antimony and tin catalyst combinations is well known in the ancient polyester art. JP 54-135896, published on October 22, 1979 discloses the use of antimony, tin, cobalt and an alkali metal during the melt polycondensation catalyst to produce a good color resin for films. JP 54-135896 does not disclose anything about the catalyst capacity to function as a solid phase polymerization catalyst or the function of the catalyst to reduce the amount of acetaldehyde generated during the subsequent melt processing. JP 52-123489, published on October 17, 1977 discloses the use of antimony and tin during the fusion polycondensation catalyst to produce a good color resin for films. JP 52-123489 does not disclose anything about the catalyst capacity to function as a solid phase polymerization catalyst or the catalyst function to reduce the amount of acetaldehyde generated during the subsequent melt processing. JP 53-052595, published May 13, 1978 discloses the use of antimony and tin during the fusion polycondensation catalyst to produce a good color resin for films. JP 53-052595 does not disclose anything about the catalyst capacity to function as a solid phase polymerization catalyst or the catalyst function to reduce the amount of acetaldehyde generated during the subsequent melt processing. GB 1236949, published June 23, 1971, describes the use of antimony and tin as a catalyst for the polycondensation of polyester melt for use in fibers. GB 1236949 does not disclose anything about the ability of the catalyst to function as a solid phase polymerization catalyst or the function of the catalyst to reduce the amount of acetaldehyde generated during the subsequent melt processing.

U.S. Patent No. 5,714,570 describes the use of antimony, tin, in combination with titanium as a fusion polycondensation catalyst. U.S. Patent No. 5,714,570 does not disclose anything about the ability of the catalyst to function as a solid phase polymerization catalyst or the function of the catalyst in reducing the amount of acetaldehyde generated during the subsequent melt processing.

BRIEF DESCRIPTION OF THE INVENTION This invention discloses a process for producing a polyester resin having a low generation rate of acetaldehyde comprising polycondensing the polyester resin in the presence of tin and antimony; wherein the tin is present within the range of 50 to 110 ppm of the polyester resin and the antimony is present from 105 ppm to 265 ppm of the polyester resin, and to polymerize the polyester resin in solid phase during a sufficient time to increase the intrinsic viscosity of the polyester resin by at least 0.15 dl / g. Further, a catalyst composition for producing a polyester resin with low generation of acetaldehyde using a solid state process is described, wherein said catalyst composition comprises tin and antimony; wherein the tin is present within the range of 50 to 10 ppm of the polyester resin and the antimony is present from 105 ppm to 265 ppm of the polyester resin. It is further disclosed that the catalyst also comprises a molar equivalent amount of cobalt and phosphorus, wherein the cobalt is present in less than 15 ppm of the polyester resin.

DETAILED DESCRIPTION OF THE INVENTION This invention is based on the discovery that the antimony-tin combination can be used in the solid phase polymerization process, but at the same time exhibits a lower catalytic activity to the formation of acetaldehyde when the polyester resin is subsequently processed. This allows to take advantage of the fast fusion polymerization of the combination of antimony and tin, while at the same time the low generation rate of acetaldehyde is obtained. Although virtually any non-elemental antimony compound will work, the preferred antimony compounds used as a catalyst for preparing polyester include antimony oxides, such as antimony trioxide, antimony tetraoxide or antimony pentoxide, antimony halides, such as antimony trichloride or trifluoride. antimony, antimony carboxylates, such as antimony triacetate, antimony tristeate, antimony tribenzoate, antimony tri-2-ethylhexanoate or antimony trioctoate, an antimony compound combined with ether, such as antimony trimetoxide, antimony ethylene glyoxide, triisopropoxide antimony, antimony tri-n-butoxide and antimony triphenic, antimony hydroxide and antimony sulfide. Of these compounds, antimony trioxide and antimony triacetate are particularly preferred. As with antimony, vitually any non-elemental tin compound will work. Preferred organotin catalysts for use in the present invention all include at least one carbon-to-tin direct bond and an oxygen-to-tin direct bond. They can be described by the general formula: Rm Sn (OX) wherein R can be the same or different when more than one R is present, R is an alkyl of 1 to about 20 carbon atoms, or an aryl, alloyl or cycloalkyl from 6 to about 14 carbon atoms, and R can be saturated or unsaturated, substituted or unsubstituted; and m can be equal to 1 or 2, provided that when m = 1, (OX) represents 01 5, (O) OH or (OR ') 3; and When m = 2, (OX) represents O or (OR ') 2; wherein R 'may be the same or different when more than one R' is present and R 'is hydrogen, an alkyl of 1 to about 20 carbon atoms, or the residue of a monofunctional or multifunctional alcohol, carboxylic acid or ester; provided that when R 'is the residue of a multifunctional alcohol, carboxylic acid or ester, including one having two or more hydroxyl groups, two or more carboxylic acid groups or one of each, then the organotin compound may contain two or more portions of organotin in the same molecule bound together through the residue of the multifunctional anion, such that in each instance in which a multifunctional anion is attached to two or more tin atoms, the organotin catalyst can be a dimer , a trimer or a higher molecular weight polymer; and further, when (OX) represents (OR ') 2 or (OR') 3, one or two of the groups (OR '), respectively, can be replaced by an anion attached to the tin through an atom other than of oxygen, such as sulfur, phosphorus or nitrogen, or a monovalent ion, such as halide, directly attached to tin. The triorganotin content of the catalysts of the present invention should preferably be less than about 5%. The triorganotin compounds (ie m = 3 in the above formula) do not fall within the scope of the above formula, but are frequently undesirable byproducts in the manufacture of organotin compounds. Since triorganotin compounds are generally considered toxic, their content in the catalysts must be reduced to the minino. Heavy metals are also unwanted impurities and therefore the heavy metal content of the catalyst is preferably less than about 200 parts per million (ppm).

The organotin catalysts of the present invention may comprise one or more organotin compounds according to the above formula. However, each component organotin compound should preferably have a purity of less than about 90%. Examples of the organotin catalysts of this invention exemplified by the general formula Rm Sn (OX) include those in the following Table I: TABLE I Sample Tin Compounds Preferred organotin catalysts include, without restriction, hydroxybutyltin oxide (also known as butyl tatanoic acid), monobutyltin tris (2-ethylhexoate), and dibutyltin oxide. Other non-organotins, such as tin oxide, are also included. The amount of tin present may be on the scale from about 30 to 120 parts per million of the polyester resin, with 35 to 1 10 and 50 to 100 parts by weight. million of the polyester resin being more adequate amounts of tin. The amounts of antimony present may range from about 95 to 300 parts per million of the polyester resin, with 105 to 285 and 105 to 265 parts per million of the polyester resin being more suitable. Polyesters suitable for this invention are those polyesters that are capable of being polymerized in solid phase. The polyester polymers and copolymers can be prepared by melt phase polymerization involving the reaction of a diol with a dicarboxylic acid, or its corresponding diester. Several copolymers resulting from the use of multiple diols and diacids can also be used. Polymers that contain repeating units of only one chemical composition are homopolymers. Polymers with two or more chemically different repeating units in the same macromolecule are called copolymers.

For clarity, a polymer of terephthalate, and isophthalate and naphthalate with ethylene glycol, diethylene glycol and cyclohexadimethanol contains six different monomers and is considered a copolymer. The diversity of the repeated units depends on the number of different types of monomers present in the initial polymerization reaction. In the case of polyesters, copolymers include reacting one or more diols with one or more diacids, and sometimes they are terpolymers. Additionally, randomization of the monomers is not necessary. A copolymer or terpolymer also refers to a polymer with different monomers that are in block or random distribution. Suitable dicarboxylic acids include those comprising from about 6 to about 40 carbon atoms. Specific bicarboxylic acids include, without restriction, terephthalic acid, isophthalic acid, naphthalene 2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid, 1,2-acid. phenylenedioxydiacetic acid, 1,4-phenylenedioxydiacetic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid and the like. Specific esters include, without restriction, italic esters and naphthalic diesters. Also included are monomers that create polyester ionomers such as metal sulfonates. Included here are the sulfonated isophthalate salts of lithium, sulfur and phosphorus.

These acids or esters can react with an aliphatic diol having from about 2 to about 10 carbon atoms, a cycloaliphatic diol having from about 7 to about 14 carbon atoms, an aromatic diol having from about 6 carbon atoms. to about 15 carbon atoms or a glycol ether having from 4 to 10 carbon atoms. Suitable diols include, without restriction, 1,4-butenediol, trimethylene glycol, 1,6-hexanediol, 1,4-cyclohexanediamethanol, diethylene glycol, resorcinol, and hydroquinone. Polyfunctional comonomers can also be used, typically in amounts from from about 0.1 to about 3 mole percent. Suitable comonomers include, without restriction, trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride (PMDA) and pentaerythritol. Polyacids forming polyesters or polyols can also be used. A preferred polyester is polyethylene terephthalate (PET homopolymer) formed from the approximate 1: 1 stoichiometric reaction of terephthalic acid, or its ester, with ethylene glycol. Another preferred polyester is polyethylene naphthalate (PEN homopolymer) formed from the stoichiometric reaction of about 1: 1 to 1: 1.6 of naphthalene dicarboxylic acid, or its ester, with ethylene glycol. Even another preferred polyester is polybutylene terephthalate (PBT). PET copolymers, PEN copolymers and PBT copolymers are also preferred. Specific co and terpolymers of interest are PET in combinations of isophthalic acid or its diester, 2,6-naphthalic acid or its diester, and / or cyclohexanedimethanol. Another preferred polyester is polytrimethylene terephthalate (PTT). It can be prepared, for example, by reacting 1, 3-propanediol with at least one aromatic diacid or alkyl ester thereof. Preferred diacids and alkylesters include terephthalic acid (TPA) or dimethyl terephthalate (D T). Accordingly, the PTT preferably comprises at least about 80 mol% of either TPA or DMT. Other diols which can be copolymerized in said polyester include, for example, ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol and 1,4-butanediol. Aromatic and aliphatic acids that can be used simultaneously to make a copolymer include, for example, isophthalic acid and sebacic acid. The melt manufacturing step of the polyester usually takes place in two steps, the first step is the reaction of the raw materials to form low molecular weight oligomers. This step is typically called the esterification step. In the esterification process, it is known as the transesterification step. The low molecular weight oligomers are then subjected to a polycondensation step. It has been discovered that it is preferred to add the catalyst composition of this invention after the esterification step, immediately prior to the polycondensation step to avoid needing an additional polycondensation catalyst. After completion of the melt phase polymerization, the liquid polymer is cooled and then converted into pellets or fragments. The polyester fragments are crystallized and then polymerized in solid phase (SSP) to increase the molecular weight, as measured by the intrinsic viscosity, necessary for the manufacture of the bottle. The crystallization and polymerization can be carried out in a rotary dryer reaction in a batch-type system. Alternatively, crystallization and polymerization can be achieved in a continuous solid phase process whereby the polymer flows from one container to another after its predetermined heat treatment in each container. Crystallization conditions for polyester preferably include a temperature of from about 100 ° C to about 150 ° C. The solid base polymerization conditions preferably include a temperature of from about 200 ° C to about 235 ° C, and more preferably from about 215 ° C to about 235 ° C and include passing a nitrogen sweep or apply a vacuum to remove the products from the increase in molecular weight. The solid phase polymerization can be carried out for a period sufficient to raise the molecular weight to the desired level, which will depend on the application and initial intrinsic viscosity. For a typical bottle application, the preferred molecular weight corresponds to an intrinsic viscosity from about 0.68 to about 0.88 deciliters / grams, as determined by the methods described in the methods section. The time required to reach this molecular weight can be on the scale of around 8 to about 45 hours. Typical increases in I.V. are at least 0.1 dl / g, with increments of 0.2 to 0.4 dl / g more typical.

Experiments WORK EXAMPLE 1 7607 g terephthalic acid, 235 g gaseous acid, 0.01 g g SB138 dye, 0.0023 g SV50 dye, were loaded into a container containing a "bead" of approximately X g low molecular weight oligomers of the same final composition. The loaded containers and heel were mixed at atmospheric pressure for 10 minutes and 267 ° C. After 10 minutes, 3106 g of ethylene glycol, sufficient sodium acetate H3PO4 to achieve 0.001 ppt Na, and 0.013 ppt of phosphorus based on the total amount of the polymer were added. The contents were then stirred at 275-278 ° C, 3,378 bar until 1500 ml of water evolved (3 hours 1 1 minutes). Approximately 1/3 of the container contents were then transferred to a second container for polycondensation. The remaining contents in the first container form the "heel" for the next batch to be loaded. The contents of the second vessel were then polycondensated after adding 0.012 ppt based on the final cobalt polymer, such as cobalt acetate and mixed for 3 minutes, 0.30 ppt based on the final antimony polymer as antimony oxide and mixing for 3 minutes and 0.080 ppt based on the final polymer of monobutyltin tris (2-ethylhexoate), 0.907 g FeP (iron phosphide) and 150 g of ethylene glycol. The polycondensation was carried out by mixing the vessel at 272 ° C and reducing the pressure from 720 torr (95,992 Pa) to 1 torr (133 Pa) over a period of 1 hour. After reaching 1.0 torr (133 Pa), the pressure was reduced to .1 torr (33.3 Pa) and then the polymer was polycondensed until a pre-set torque was reached in a constant stirrer rpm. In this example, it was 26 minutes. It is this final step that is the polycondensation reported in table I. The final polymer was then discharged into a strand and formed into pellets. The polymer properties were 0.457 dl / g intrinsic viscosity, 52 meq carboxyl 247 ° C melting point, L * = 53.06, a * = -0.91, and b * = -2.67. The fused polycondensed polymer was then also polymerized in solid phase in a rotary vacuum solid state reactor. Various batches of the fused resin were combined in a large rotary vacuum vessel and exposed to a crystallization step followed by the actual polymerization step. The crystallization was achieved by lowering the pressure to 0.1 torr and setting the temperature of hot oil at 120 ° C for 3 hours. After the resin crystallized, the oil temperature was increased to 230 ° C and the polymer stirred in the rotating vessel until I.V. final was achieved. Samples were taken every two hours and analyzed for I.V. The solid state polymerization rate can be determined by a change in I.V. per unit time. In this particular example, the material was prematurely cooled to 0.719 dl / g and both were reheated to 0.745 dl / g of I.V. final. The solid phase polymerization rate for the uninterrupted cycle ending at 0.719 dl / g from 0.452 dl / g took place over 12 hours or 0.02225 dl / hr. The generation rate of acetaldehyde was determined by taking the finished polymer, injecting it into preforms at the same temperature, but in different cycle times. The preforms were then analyzed for acetaldehyde that had been formed during the injection cycle. From this information the generation rate of acetaldehyde can be determined. One skilled in the art will also recognize that the temperature could be varied and kinetics determined equally. The acetaldehyde generation rate of this polymer was 1.8 ppm / minute.

COMPARATIVE EXAMPLES Several comparative examples were run varying the levels of antimony and tin. Your data together with the work example are presented in table II RESULTS.

TABLE 2 Results In the following set of experiments, illustrated in table III, the results were validated in a larger piece of continuous polyester manufacturing line. These show very similar AAGRs (AA generation rates with an increased polycondensation production of 7.5% for the claimed catalyst combination.) Although 7.5% improvement may seem small, large plants operating at 15 tons per hour means that the plant is able to produce 1.25 tons per hour more, or approximately 8800 tons more per year.

TABLE Test results continue Methods The intrinsic viscosity of intermediate molecular weight and low crystalline polyethylene terephthalate and related polymers that are soluble in 60/40 phenol / tetrachloroethane can be determined by dissolving 0.1 gm of ground polymer or peda in 25 ml of 60/40 phenol / tetrachloroethane solution and determining the viscosity of the solution at 30 ° C +/- 0.05 relative to the solvent at the same temperature using a Ubbelohde 1 B viscometer. The intrinsic viscosity is calculated using the Billmeyer equation based on the relative viscosity. The intrinsic viscosity of high molecular weight or high crystalline polyethylene terephthalate and related polymers that are not soluble in phenol / tetrachloroethane was determined by dissolving 0.1 gm of polymer or ground pellet in 25 ml of 50/50 trifluoroacetic acid / dichloromethane and determining the viscosity of the solution at 30 ° C +/- 0.05 relative to the solvent at the same temperature using an Ubbelohde type OC viscometer. The intrinsic viscosity is calculated using the Billmeyer equation and converted using a linear regression to obtain results that are consistent with those obtained using 60/40 phenol / tertracloroethane solvent. The linear regression is I.V. in 60/40 phenol / tetrachloroethane = 0.8229 x IV in 50/50 trifluoroacetic acid / dichloromethane + 0.0124 ..

Claims (2)

NOVELTY OF THE INVENTION CLAIMS

1 .- A process for producing a polyester resin having a low generation rate of acetaldehyde comprising the steps of polycondensing the polyester resin in the presence of tin and antimony; wherein the tin is present within the range of 30 to 1 10 ppm of the polyester resin and the antimony is present from 95 ppm to 300 ppm of the polyester resin, and to polymerize the polyester resin in a solid phase for a sufficient time to increase the intrinsic viscosity of the polyester resin by at least 0.15 dl / g.

2. A catalyst composition for producing a polyester resin with low generation of acetaldehyde using a solid state process, wherein said catalyst composition comprises tin and antimony; wherein the tin is present within the range of 30 to 1 10 ppm of the polyester resin and the antimony is present from 95 ppm to 300 ppm of the polyester resin; and wherein the catalyst also comprises a molar equivalent amount of cobalt and phosphorus, wherein the cobalt is present at less than 15 ppm of the polyester resin.