Method of forming container with high-crystallinity sidewall and low-crystallinity base
View Patent ↗A method of making a polyester container having an enhanced level of crystallinity in the sidewall while maintaining a low level of crystallinity in a thickened base portion. The container is particularly useful as a refillable container which can withstand higher caustic wash temperatures and exhibits reduced flavor carryover, or as a hot-fill container. According to the method, a sidewall-forming section of a preform is initially expanded, heated to contract and crystallize the same, and than reexpanded; a base-forming portion of the preform is shielded from the heat treatment and is expanded either before or after the heat treatment step.
1. A method of making a container having a sidewall and base, the method including:
a first expansion step in which a substantially amorphous polyester preform is at least partially expanded into an intermediate article, the preform including a base-forming section which is not expanded during the first expansion step,
a heating step in which the intermediate article is at least partially heated to contract and crystallize the intermediate article, the base-forming section remaining substantially unchanged in crystallinity during the heating step, and
a second expansion step in which the contracted intermediate article is re-expanded to form the container, the base-forming section being expanded without significant crystallinity change during the second expansion step.
2. The method of claim 1 , wherein the preform includes a sidewall-forming section which is at least partially expanded in the first expansion step, and wherein the base-forming section has a wall-thickness substantially greater than that of the sidewall-forming section.
3. The method of claim 1 , wherein the base-forming section is substantially thicker than other sections of the preform so as to resist heating and crystallization during the heating step.
4. The method of claim 1 , wherein the base-forming section is shielded during the heating step.
5. The method of claim 1 , wherein the base-forming section is cooled during the heating step.
6. The method of claim 1 , wherein a contracting centering rod is positioned within the contracting intermediate article to control contraction of the article.
7. The method of claim 1 , wherein an internal pressure within the intermediate article is provided to control contraction of the article.
8. The method of claim 1 , wherein the resulting container has a relatively thin sidewall panel portion of high orientation and high crystallinity, and a thickened base portion of low orientation and low crystallinity.
9. The method of claim 1 , wherein the resulting container has a sidewall panel portion with an average crystallinity of at least 25%, and a base portion with an average crystallinity of no greater than 10%.
10. The method of claim 1 , wherein the resulting container is a freestanding pressurizable container.
11. The method of claim 1 , wherein the resulting container is a multilayer carbonated beverage container including one or more layers of biaxially-oriented polyester polymer.
12. The method of claim 1 , wherein the resulting container is a refillable freestanding pressurizable container including a polyalkylene homopolymer or copolymer.