Modified polyesters

Details Modified polyesters Modified polyesters

1999-07-20

2001-01-30

Boykin, Terressa M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S271000

Reexamination Certificate

active

06180750

ABSTRACT:

This invention relates to the use of methyl methacrylate/styrene copolymers as melt rheology modifiers for partially crystalline, partially aromatic polyesters. The invention also relates to modified polyesters and moldings produced from them.
STATE OF THE ART
Because of their extraordinarily good solvent resistance and their good processability in principle with low shrinkage, partially crystalline, partially aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, for example, are widely used, especially in the packaging industry, for example for food packages, in automobile manufacture, or in the textile industry, for example in fiber production. Many moldings, for example beverage bottles, fuel tanks, vacuum systems, etc., are manufactured from these materials by injection molding or extrusion blow-molding.
U.S. Pat. No. 4,179,479 describes plastic blends that can consist of at least 40 wt. % polyurethane and at most 60 wt. % polybutylene terephthalate and can contain 0.5-10 wt. % polyacrylate polymers with a molecular weight (number average) of 500,000 to 1,500,000 as processing aids. The polyacrylate can be a terpolymer of methyl methacrylate, n-butyl acrylate, and styrene, among others. No information is given on the proportions of monomeric components.
EP 0 328 273 B1 describes melt rheology modifiers for thermoplastic resins consisting of polymers with an average molecular weight of 1,500,000 to 10,000,000 of (meth)acrylic monomers with groups that can be alkyl, substituted alkyl, cycloalkyl, aryl, aralkyl, or alkaryl.
Example 58A describes the modification of polybutylene terephthalate with 10 wt. % of a polymer of 74% methyl methacrylate, 24% butyl methacrylate, and 2% methacrylic acid, with a molecular weight of 4.9×10
6
. The extrusion sag time in sec (a measure of melt viscosity) is increased by the added modifier from 5.2 to 10.5 compared to unmodified polybutylene terephthalate.
U.S. Pat. No. 5,352,500 claims blow-molded articles of a thermoplastic resin containing about 1-25 wt. % of a methacrylate polymer that consists of 70 wt. % (meth)acrylic monomers with groups that can be alkyl, substituted alkyl, cycloalkyl, aryl, aralkyl, or alkaryl. In Examples 2-4, the modification of a blend of polybutylene terephthalate and polycarbonate (43/57) is shown with an impact strength modifier based on polymethyl methacrylate/styrene with core-shell structure. The modification leads to an increase of extrusion sag time in sec (a measure of melt viscosity).
DE-OS 23 64 318 describes the modification of poly(1,4-butylene terephthalate) or its copolyesters with a smaller amount of an aliphatic or aromatic dicarboxylic acid or of an aliphatic polyol containing 1-80 wt. % of a reinforcing filler in the form of reinforcing metals, ceramic materials, silicates, quartz, glass, and carbon, by the addition of interpolymers or copolymers that contain styrene compounds. For example, the addition of an interpolymer of polypropylene and rubber-modified styrene to fiberglass-reinforced polybutylene terephthalate brings about improved hot dimensional stability and improved impact strength of the plastic. Among a number of suitable copolymers, those of methyl methacrylate and styrene are also mentioned. The effect of increasing the melt viscosity is not reported and also not obvious, since many of the mentioned additives in contrary manner lead to a lower melt viscosity.
Problem and Solution
A fundamental problem when processing partially crystalline, partially aromatic types of polyesters, for example polyethylene terephthalate or polybutylene terephthalate, consists of the fact that the viscosity declines very rapidly after surpassing the melting temperature. This can lead to production defects, especially the formation of holes, during extrusion blow-molding, or the breakage of strands during extrusion or fiber-spinning.
It was considered to be the objective to modify partially crystalline, partially aromatic polyesters so that the melt viscosity is clearly increased, but the other characteristics of these polyesters, especially the partially crystalline nature of the plastic, are not impaired or only insignificantly impaired.
The problem was solved by the use of a copolymer of
a) 60-98 wt. % methyl methacrylate and
b) 2-40 wt. % styrene and optionally
c) 0-20 wt. % maleic anhydride
as modifier to increase the melt viscosity of partially crystalline, partially aromatic polyesters, with the exception of poly(1,4-butylene terephthalate) or its copolyesters with a smaller amount of an aliphatic or aromatic dicarboxylic acid or of an aliphatic polyol containing 1-80 wt. % of a reinforcing filler in the form of reinforcing metals, ceramic materials, silicates, quartz, glass, and carbon.
The use pursuant to the invention of the copolymer as modifier (melt rheology modifier) makes possible improved processability of the partially crystalline, partially aromatic polyester, especially of polyethylene terephthalate and polybutylene terephthalate (with the exception of polybutylene terephthalate containing reinforcing fillers as claimed in DE-OS 23 64 318), because their melt viscosity increases substantially. At the same time, the other positive characteristics of the polyesters, especially partial crystallinity, are retained.
This is surprising, since although pure polymethyl methacrylate, for example with a solution viscosity in chloroform of about 50 ml/g according to ISO 1628-6, has a distinctly higher melt viscosity &eegr;
s
, about 800 Pas at 230° C./5 MPa, than that of polymethyl methacrylate/styrene copolymers, the desired effect is obtained only by the use of the copolymers pursuant to the invention. It is assumed that this is attributable to the ratios of the polymer melts in the blend.
A modified partially crystalline, partially aromatic polyester, also claimed, is obtained by the use pursuant to the invention of the copolymers as modifiers to increase melt viscosity. This is suitable for producing moldings, especially moldings produced by blow-molding.
Implementation of the Invention
Partially crystalline, partially aromatic polyesters in the context of this invention means products of condensation of terephthalic acid with aliphatic diol components such as ethylene glycol or 1,4-butanediol or with mixtures of diols. Examples of these are polyethylene terephthalate and polybutylene terephthalate.
The invention is particularly suitable for polyethylene terephthalate and polybutylene terephthalate. Polybutylene terephthalate is especially preferred.
Polybutylene terephthalate in the context of the invention means polymers that consist essentially of butylene terephthalate units. These are polymers containing at least about 95, preferably at least 98 wt. % butylene terephthalate or more. Polybutylene terephthalates can optionally also contain small fractions of other diol components, for example ethylene glycol. Mixtures with small amounts, e.g. 5-20%, of compatible polymers such as polycarbonate and/or acrylonitrile/butadiene/styrene copolymers (ABS) can also be present.
Polyethylene terephthalate in the context of the invention means polymers that consist essentially of ethylene terephthalate units. These are polymers containing at least about 95, preferably at least 98 wt. % ethylene terephthalate or more. Polyethylene terephthalates can optionally also contain small fractions of other diol components, for example butanediol. They can also contain inorganic fillers such as talc or glass fibers. Mixtures with small amounts, e.g. 5-20%, of compatible polymers such as polycarbonate and/or acrylonitrile/butadiene/styrene copolymers (ABS) can also be present.
The Modifiers for Increasing the Melt Viscosity of Partially Crystalline, Partially Aromatic Polyesters
The copolymers consist of a) 60-98 wt. % methyl methacrylate and b) 2-40 wt. % styrene and optionally c) 0-20 wt. % maleic anhydride and can be prepared by known methods from the monomers a.), b.), and c.) by radical, anionic, or group transfer polymerization. The polymerization can be carried o

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