PET Preform Variable Wall Thickness for Stress Cracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional injection technology for PET preforms faces challenges in reducing wall thickness while maintaining structural strength, especially in small-sized containers, due to limitations in the BWT/WT ratio, leading to excessive stress, crystallinity, and difficulties in filling and cooling, which hinder the production of lightweight containers with complex shapes.
Innovation Solution
The use of injection compression molding technology allows for a preform design with a variable BWT/WT ratio between 0.20 and 0.55, enabling a gradual transition in wall thickness and reducing material waste around the injection point, resulting in a lighter preform with improved mechanical properties and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the BWT/WT ratio is reduced below 0.7 to make lighter preforms, then the weight of the preform is reduced, but excessive stress develops around the injection point leading to crystallinity and filling defects
Solution Approach 1:
The patent applies local quality by varying the wall thickness distribution in different zones of the preform. Specifically, it creates a first zone with a first wall thickness and a second zone with a second wall thickness that is different from the first, optimizing the BWT/WT ratio locally around the injection point to reduce stress concentration while maintaining overall preform lightness
Solution Approach 2:
The patent changes the geometric parameters of the preform, specifically the wall thickness distribution and the BWT/WT ratio, to optimize performance. By adjusting these parameters and creating distinct zones with different thicknesses, the patent achieves lighter preforms without excessive stress around the injection point
2Weight of moving object
If the wall thickness is reduced below 2 mm to make lighter containers, then the preform weight is reduced, but frictional forces increase opposing the sliding of PET within the injection mold cavity
Solution Approach 1:
The patent applies local quality by creating zones with different wall thicknesses, including a first zone with a first wall thickness and a second zone with a second wall thickness. This localized variation in thickness distribution reduces overall weight while maintaining adequate thickness in critical areas to reduce frictional forces during injection molding
3Quantity of substance
If the BWT/WT ratio is maintained at 0.7-0.95 to ensure proper filling, then the preform can be filled completely, but the amount of PET material is increased preventing further weight reduction
Solution Approach 1:
The patent applies local quality by creating distinct zones with different wall thicknesses. The first zone has a first wall thickness and the second zone has a second wall thickness, allowing optimization of material distribution. This enables complete mold filling with appropriate BWT/WT ratio in critical areas while reducing overall PET material consumption through thinner walls in non-critical areas
Solution Approach 2:
The patent changes the geometric parameters of the preform, specifically the wall thickness distribution and BWT/WT ratio in different zones. By optimizing these parameters locally rather than uniformly, the patent achieves complete filling while reducing overall material quantity and preform weight
Data Source
AI summary
The invention relates to a new PET preform design that enables a more precise distribution of material in the bottle bottom and avoids the waste of material around the injection point. The thickness BWTmin of the wall at the center of the gate or tip (3) (injection point) is reduced to a minimum in order to avoid the waste of material around the injection point when the preform is blown. This is particular important for carbonated soft drink application since the reduced amount of amorphous material at the center of the gate (3) helps to reduce the risk of stress cracking on the bottle base. Furthermore a step (4) having thickness WTmax in the body wall thickness, in the region of the periphery of the base with WTmax>WT, allows enough material to be available for the proper blowing of the bottle bottom making the bottle more stable.