Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2002-04-22
2004-03-02
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C528S275000, C528S281000, C528S487000, C528S503000, C528S298000, C528S301000, C528S302000, C528S307000, C528S308000, C528S308600, C524S745000
Reexamination Certificate
active
06699545
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the use of zinc p-toluenesulfonate as a catalyst in preparing polyester polymers and, more particularly, to a method for increasing the polymerization rate of such polyester polymers in the solid state by the addition of zinc p-toluenesulfonate to the polymer melt.
Some processes for the manufacture of bottle-grade poly(ethylene terephthalate), PET, presently employ antimony(III) oxide (~250-280 ppm Sb) as a polymerization catalyst. Typically, these processes require 24 hours or more under solid state polymerization conditions for the polymer to achieve the requisite high intrinsic viscosity (IV) of ca. 0.82 in the solid state polymerization reactor so that the resultant poly(ethylene terephthalate) is suitable for use in blow molded bottles. In addition, there are environmental and public health concerns about the degree of metal loading and the use of heavy metal, including antimony, based catalysts in the manufacture of food-grade polymeric packaging materials.
Metal salts of sulfonic acids are known in the art as effective catalysts for polycondensation in polyester manufacture. For example, European Patent Application 745 629 describes the preparation of saturated polyesters using a catalytic system comprising at least one derivative selected from those of antimony and germanium; at least one derivative selected from those of the metals of groups I-Va, I-VIIb, VIII and lanthanides; and, optionally, a sulfonic acid having the general formula
RSO
3
H
wherein R represents an organic alkyl radical, linear or branched, saturated cyclic or aromatic containing up to 20 carbon atoms. Examples of sulfonic acids which can be used include p-toluenesulfonic acid. Metals such as antimony or germanium are still required for effectiveness. Also, the solid state polymerization process per se is not addressed.
U.S. Pat. No. 5,644,019 describes a high activity catalyst system for preparing poly(ethylene terephthalate) (PET) which comprises a derivative from among antimony and germanium; a titanium derivative; and one from among a group of compounds that includes sulfonic acids, such as p-toluenesulfonic acid, and their salts. Again, antimony or germanium must be present, and solid state polymerization is not addressed.
The objects of the present invention are to provide an improved process for preparing high molecular weight polyester polymers that requires less solid state polymerization time to achieve goal IV; a process that allows the use of lower levels (as weight percent or ppm) of metal catalyst; and a process that allows the use of a more environmentally benign metal catalyst than antimony or germanium.
SUMMARY OF THE INVENTION
The present invention is a method for increasing the rate of polymerization in the solid state of a low molecular weight polyester prepolymer, said method comprising the steps:
(a) introducing an effective amount of zinc p-toluenesulfonate catalyst into a polyester prepolymer melt that is essentially free of antimony or germanium;
(b) forming molten droplets of the prepolymer melt;
(c) collecting and crystallizing said droplets; such that the pellets produced are solid state polymerizable at enhanced rates.
A second aspect of the present invention is an improved process for solid-state polymerization of a low molecular weight polyester polymer having a glass transition temperature (T
g
) greater than about 25° C., wherein said prepolymer is essentially free of antimony and germanium, said prepolymer comprising pellets of the type that are produced by metering a polyester polymer melt through a plurality of outlets in a rotatable container to form molten droplets and collecting the molten droplets as they are formed onto a moving solid surface that is maintained within a predetermined temperature range within a crystallization zone such that the pellets are maintained in contact with the surface within the crystallization zone for a predetermined period of time, said method comprising introducing into the polyester polymer melt a catalytic amount of zinc p-toluenesulfonate.
DETAILED DESCRIPTION OF THE INVENTION
The present invention resides in the discovery that the rate of polymerizing low molecular weight polyester polymers to desired higher levels of molecular weight in the solid state can be substantially increased by incorporating into the polymer melt from which the low molecular weight polymer is prepared, and which contains essentially no antimony or germanium, a catalytic amount of zinc p-toluenesulfonate.
Zinc p-toluenesulfonate (TSAZ) offers a unique combination of properties as a catalyst for the production of polyesters. It allows a lessening of the total amount of metal present in the final polymer. The metal is benign environmentally. It alleviates health and environmental concerns that arise from the use of antimony in food-contact products, since antimony is no longer needed. By increasing rates in the solid state polymerization process, it simultaneously improves process economics and minimizes side reactions and degradation. This is particularly important in the specific case of poly(ethylene terephthalate), where minimizing side reactions that produce diethylene glycol (DEG) and color-forming species is particularly desired.
The level of zinc p-toluenesulfonate (measured as zinc) for optimum results and reduced catalyst loading is in the range of from 50 ppm up to 150 ppm, but preferably 75 ppm up to 100 ppm. Higher or lower loadings can be used depending on the results desired in terms of solid state reaction rate. 75 to 100 ppm for zinc p-toluenesulfonate according to the invention compares to a typical loading of antimony catalyst of about 250 ppm, as antimony.
Polyesters
The process of the present invention is generally applicable for use regarding any dihydroxy ester of any dicarboxylic acid, or low molecular weight oligomer thereof. Diol addition, for ends balancing, would be dependent on the oligomer being processed. In the present invention, solid state polymerization rates are particularly enhanced when the hydroxyl/carboxyl (OH/COOH) ends ratio of the prepolymer that is to be solid state polymerized is greater than one.
Suitable diacid or diester components for the polyesters to which this invention pertains normally include alkyl dicarboxylic acids having 4 to 36 carbon atoms, diesters of alkyl dicarboxylic acids having 6 to 38 carbon atoms, aryl dicarboxylic acids which contain from 8 to 20 carbon atoms, diesters of aryl dicarboxylic acids which contain from 10 to 22 carbon atoms, alkyl substituted aryl dicarboxylic acids which contain from 9 to 22 carbon atoms, and diesters of alkyl substituted aryl dicarboxylic acids which contain from 11 to 22 carbon atoms. Typical alkyl dicarboxylic acids contain from 4 to 12 carbon atoms. Some representative examples of alkyl dicarboxylic acids include glutaric acid, adipic acid, pimelic acid and the like. Diesters of alkyl dicarboxylic acids will typically contain from 6 to 12 carbon atoms. A representative example of a diester of an alkyl dicarboxylic acid is azelaic acid. Aryl dicarboxylic acids will contain from 8 to 16 carbon atoms. Some representative examples of aryl dicarboxylic acids are terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and orthophthalic acid. Diesters of aryl dicarboxylic acids contain from 10 to 18 carbon atoms. Some representative examples of diesters of aryl dicarboxylic acids include diethyl terephthalate, diethyl isophthalate, diethyl orthophthalate, dimethyl naphthalate, diethyl naphthalate and the like. Alkyl substituted aryl dicarboxylic acids will contain from 9 to 16 carbon atoms and diesters of alkyl substituted aryl dicarboxylic acids will contain from 11 to 15 carbon atoms.
The diol component for polyesters used in practicing the invention includes glycols containing from 2 to 12 carbons atoms, glycol ethers containing from 4 to 12 carbon atoms and polyether glycols having the structural formula HO(AO)
n
H, wherein A is an alkylene group containing from 2 to 6 carbon a
Acquah Samuel A.
Krukiel Charles E.
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