PET with stress cracking resistance, preform and container made therewith and method

Abstract

A preform comprising an open-ended mouth forming portion, an intermediate body forming portion, and a closed base forming portion comprising a stress cracking resistant polyester composition comprising poly(ethylene terephthalate) based resin and an impact modifier. The preform is blow molded to form a corresponding container. Polyester compositions and methods are also disclosed. The impact modifier improves the stress cracking resistance of low IV PET such that the containers perform similar to those made of high IV PET.

Description

TECHNICAL FIELD [0001] This application relates to poly(ethylene terephthalate)—based compositions and more particularly to stress cracking resistance of articles such as containers made with poly(ethylene terephthalate)—based compositions. BACKGROUND OF THE INVENTION [0002] 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 like due to their excellent combination of mechanical and gas barrier properties. Unfortunately, a phenomenon known as environmental stress cracking (ESC) has been a persistent annoyance in PET containers used for carbonated beverages since the advent of the one-piece container design. The ultimate failure caused by ESC is a rupture in the base of the container resulting in the loss of the container's contents and subsequent contamination o...

AI Technical Summary

Benefits of technology

[0016] Without wishing to be bound by theory, the impact modifier is believed to improve the relaxation phenomenon of the poly(ethylene terephthalate) based resin such that a lower molecular weight (i.e. lower intrinsic viscosity) poly(ethylene terephthalate) based resin behaves as a higher molecular weight resin and resists stress cracking. In preferred embodiments the poly(ethylene terephthalate) based resin has an IV of from about 0.65 to about 0.90 dL / g, more preferably from about 0.65 to about 0.86 dL / g, even more preferably from about 0.65 to about 0.80 dL / g and still even more preferably from about 0.68 to about 0.76 dL / g. Thus, as a result of this invention, less expensive, lower IV poly(ethylene terephthalate) based resin when combined with the impact modifier can be used to make such preforms and containers. Further the same preform and container can be used for a variety of applications including CSD and bottled water containers.

Problems solved by technology

Unfortunately, a phenomenon known as environmental stress cracking (ESC) has been a persistent annoyance in PET containers used for carbonated beverages since the advent of the one-piece container design.

The ultimate failure caused by ESC is a rupture in the base of the container resulting in the loss of the container's contents and subsequent contamination of the surroundings.

Clean-up is laborious.

Product and liability losses can be expensive.

Usually 10 to 20 stress crack failure containers per million is considered excessive.

Direct causes for failures are often difficult to determine.

Crazes can then develop into cracks and failure may occur in forms of a rupture or leakage.

ESC can be also caused by excessive stress seen in the carbonation of beverages.

However, over pressurization creates added stress to the container and thus a higher possibility for rupture.

The physical aging that containers experience before filling may be a primary factor responsible for the increased rate of failures often observed during the hot summer months.

However, base design can not protect containers from contact with stress-inducing chemical agents.

This method, however, has the same problem inherent with all the methods above: the nature of the material is not changed.

This method, however, can not solve problems associated with other chemicals such as cleansers, contaminants from water, and the like that can cause stress cracking.

This method, however, requires additional steps in the container making process and thus adds more cost to the container.

The method is not applicable in all container making or filling sites either due to space limitations.

However, higher IV PET requires longer solid state polymerization (SSP) time, and higher injection molding temperature due to higher melt viscosity.

Unfortunately, this means higher IV PET is more expensive to make than lower IV PET.

Application of such lower IV PETs in one-piece-CSD containers has been limited solely because of its bad performance in stress cracking resistance.

Some facilities do not have enough capability to have so many inventories.

Although impact modifiers are generally known for the above applications, there has been no attempt of using the same family of chemicals to improve the stress cracking resistance of PET containers for carbonated beverage application, especially those made with lower IV PET.

Although much effort has been made to understand and solve the stress cracking problem, the root causes of the stress cracking are still unknown.

Stress cracking can have costly ramifications in terms of clean-up or liability.

As can be seen, no one method currently available solves the stress cracking problems of PET containers used for CSDs.

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