PET copolymer composition with enhanced mechanical properties and stretch ratio, articles made therewith, and methods

Abstract

A container is made from a preform comprising a PET Copolymer comprising a diol component having repeat units from ethylene glycol and a non-ethylene glycol diol component and a diacid component having repeat units from terephthalic acid and a non-terephthalic acid diacid component. The total amount of non-ethylene glycol diol component and non-terephthalic acid diacid component is present in the poly(ethylene terephthalate) copolymer in an amount from about 0.2 mole percent to less than 2.2 mole percent. The container is useful in packaging beverages and corresponding methods are disclosed.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application claims priority Under 35 U.S.C. §119 to U.S. provisional patent application Ser. No. 60 / 423,221 filed on Nov. 1, 2002.FIELD OF THE INVENTION [0002] This invention relates to preforms and their containers made with poly(ethylene terephthalate)-based resin compositions that possess low levels diol and acid modification, such as naphthalenedicarboxylic acid and diethylene glycol. More particularly, this invention relates to low stretch ratio preforms and their containers, which exhibit enhanced mechanical properties relative to containers made using conventional poly(ethylene terephthalate)-based resin compositions. BACKGROUND OF THE INVENTION [0003] Poly(ethylene terephthalate)-based resins, which are commonly referred to in the industry simply as “PET” even though they may and often do contain minor amounts of additional components, have widely been used to make containers for carbonated soft drink, juice, water and the l...

AI Technical Summary

Benefits of technology

[0010] In preferred embodiments, the preforms are designed to have a stretch ratio in the range from about 8 to about 12, enabling the preforms to have a reduced wall thickness. Thus the cycle time for manufacture of the preforms is reduced. Because the material utilization is higher, less material needs to be used and the cost of goods is lowered, while the containers produced exhibit improved thermal stability and sidewall rigidity characteristics.

[0018] The cycle time for making the container is reduced as compared to a second cycle time for making a second container comprising a poly(ethylene terephthalate) resin having comonomer modification greater than about 2.2 mole percent of a combination of a non-ethylene glycol diol component and a non-terephthalic acid diacid component.

[0019] Thus, embodiments of this invention provide two sets of improvements. In one set, the PET Copolymer is used with a conventional preform design to produce a container with enhanced mechanical properties, higher crystallinity and improved shelf life. In the other set, the PET Copolymer is used with a redesigned preform that has a stretch ratio of from about 8 to about 12, a reduced preform wall thickness, and reduced cycle time to produce a container of similar or improved quality compared to a container produced using conventional PET resin and a conventional preform design.

Problems solved by technology

Source reduction saves resources and energy; however, with PET additional source reduction is difficult to achieve, because of the physical performance requirements necessary for the major applications for this polymer.

For large sized containers, the amount of material utilization is already high, and further increases offer limited opportunity for source reduction.

However, there is a significant cost associated with increasing the preform stretch ratio.

Increasing the preform stretch ratio necessarily means increasing the wall thickness of the preform, which adversely impacts injection molding and blow molding cycle times. This consequently consumes more energy and increases the capital and operating cost for making PET containers.

This approach inherently sacrifices the mechanical integrity of the container, since sidewall rigidity relates to the second power of the thickness.

Although in principle the sidewall rigidity of a container could be maintained by increasing the modulus of the polymer, in practice this is difficult to achieve.

While an increase in the molecular weight of the PET or crystallinity level of the containers can increase the modulus of PET, these approaches have inherent limits.

An even minor increase in molecular weight also increases the melt viscosity of the PET, which can lead to significantly greater polymer degradation during the melt processing that produces the preforms.

Other means to achieve much higher crystallinity of containers, such as through nucleation agents or hyper-stretching, have not been successful.

However, the amount of additives required is high (1-5% by weight), and the additives claimed are relatively expensive compared to the cost of PET.

In addition, because these additives were not part of the polymer chains, they are potentially extractable, which is detrimental to their use in food contact applications.

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