Method of preparing modified polyester bottle resins

Abstract

The present invention is a method of preparing a high molecular weight copolyester bottle resin that has excellent melt processing characteristics. The method includes the steps of reacting a diacid or diester component and a diol component to form modified polyethylene terephthalate, wherein diol component is present in excess of stoichiometric proportions. Together, the diacid or diester component and the diol component must include at least 7 percent comonomer. The remainder of the diacid component is terephthalic acid or dimethyl terephthalate and the remainder of the diol component is ethylene glycol. The modified polyethylene terephthalate is copolymerized in the melt phase to an intrinsic viscosity of between about 0.25 dl / g and 0.40 dl / g to thereby form a copolyester prepolymer. Thereafter the copolyester prepolymer is polymerized in the solid phase to form a high molecular weight bottle resin that has an intrinsic viscosity of at least about 0.70 dl / g, and a solid phase density of less than 1.413 g / cc.

Description

[0001] This application is a divisional application of copending U.S. application Ser. No. 09 / 456,253, filed Dec. 7, 1999, which is hereby incorporated herein by reference.[0002] The present invention relates to polyester bottle resins and methods of preparing polyester bottle resins. In particular, the invention relates to methods of polymerizing modified polyesters in the solid phase to yield bottle resins.[0003] Polyester resins, polyethylene terephthalate (PET) and its copolyesters, are widely used to produce rigid packaging, such as two-liter soft drink containers. Polyester packages produced by stretch blow molding possess high strength and shatter resistance, and have excellent gas barrier and organoleptic properties as well. Consequently, such plastics have virtually replaced glass in packaging numerous consumer products (e.g., such as carbonated soft drinks, fruit juices, and peanut butter).[0004] In conventional techniques of making bottle resin, polyethylene terephthalate...

AI Technical Summary

Benefits of technology

[0014] Accordingly, it is an object of this invention to provide a cost-effective method of making a modified polyester bottle resin that has excellent properties with respect to melt extrusion, injection molding, and other kinds of melt processing.

[0015] In one aspect, the invention is a method of polymerizing copolyester prepolymer to yield high molecular weight copolyester possessing excellent melt processing properties. In contrast to most conventional processes, the present method relies more on solid state polymerization (SSP) and less upon melt polymerization to increase molecular weight. In contrast to other solid state processes, the present method yields a copolyester bottle resin that can be manufactured into essentially haze-free bottle preforms at significantly lower temperatures.

[0016] In another aspect, the invention is a low molecular weight copolyester prepolymer composition that is useful for producing higher molecular weight copolyester bottle resin having improved melt-processing characteristics. Preferably, the copolyester prepolymer composition is a modified polyethylene terephthalate prepolymer having an intrinsic viscosity between about 0.25 dl / g and 0.40 dl / g, and more preferably between about 0.30 dl / g and 0.36 dl / g. In yet another aspect, the invention is a high molecular weight copolyester bottle resin made from the low molecular weight copolyester prepolymer. This copolyester bottle resin has excellent melt processing characteristics. Preferably, the copolyester bottle resin is modified polyethylene terephthalate having an intrinsic viscosity of at least 0.70 dl / g.

Problems solved by technology

Melt phase polymerization, however, is relatively expensive as compared to solid state polymerization (SSP).

Polymer melt theory suggests that this combination causes high haze point temperatures.

This complicates the conventional processing of resins produced according to the DuPont teachings.

The '420 patent also results in prepolymer having relatively large crystallite sizes.

These patent disclosures, however, fail to teach the present method for preparing copolyester bottle resins that have excellent melt processing characteristics, specifically a low haze point temperature.

These Goodyear patents, however, fail to appreciate that solid state polymerizing prepolymer having a relatively large average crystallite size will result in resins that possesses unacceptably high melt temperatures.

These methods, however, yield polyester compositions that possess unacceptably high haze points.

Processing such polyester compositions through preform molding equipment at conventional temperature settings results in hazy bottles.

This requires more cooling time, which slows process throughput as compared to conventional processes.

Moreover, higher preform molding temperatures lead to high levels of polyethylene terephthalate decomposition products, such as acetaldehyde and color bodies.

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