Resin Container Preform Cooling to Prevent Bottom Whitening
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The hot parison blow molding method faces challenges in preventing whitening due to slow cooling and increased shear heat generation in the central region of the bottom portion of the preform, especially when high stretching ratios and shortened cooling times are used.
Innovation Solution
The method involves injection molding a preform with a thicker bottom portion relative to the body portion (0.7 to 0.85 times) and using a coolant to introduce compressed air for localized cooling, reducing shear heat generation and suppressing whitening during high-speed molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cooling time in injection molding is shortened to increase productivity, then the molding cycle speed is improved, but the bottom portion of the preform cannot be sufficiently cooled leading to whitening
Solution Approach 1:
The patent applies local quality by making the bottom portion thickness different from the body portion thickness. Specifically, the bottom portion is designed with a thickness ratio of 0.5 to 0.7 times that of the body portion, creating localized thermal characteristics that enable sufficient cooling of the bottom portion even during high-speed molding cycles.
Solution Approach 2:
The patent changes the geometric parameter of the preform by controlling the thickness ratio between the bottom portion and body portion. This parameter change (thickness ratio of 0.5 to 0.7) fundamentally alters the cooling characteristics, allowing the bottom portion to cool sufficiently while maintaining high productivity.
2Temperature
If the thickness of the bottom portion is reduced to about a half of the body portion thickness to increase injection cooling efficiency, then the cooling efficiency is improved, but the flow resistance of molten resin increases and shear heat generation increases
Solution Approach 1:
The patent optimizes the thickness ratio parameter of the bottom portion to fall within 0.5 to 0.7 times that of the body portion. This parameter optimization balances two competing effects: sufficient cooling efficiency while controlling shear heat generation during injection molding.
Solution Approach 2:
The patent creates local quality differences in the preform structure by making the bottom portion thinner than the body portion. This localized thickness variation (0.5 to 0.7 times ratio) specifically targets the cooling requirement of the bottom portion while the body portion maintains its structural integrity and flow characteristics.
3Manufacturing precision
If the preform is blow-molded at high stretching ratio to improve container quality, then the physical properties and appearance are improved, but the central region of the bottom portion is more prone to whitening
Solution Approach 1:
The patent applies preliminary action by pre-cooling the bottom portion of the preform during injection molding before the blow molding process. The localized thickness design (0.5 to 0.7 times ratio) enables the bottom portion to reach sufficient cooling in advance, creating a temperature gradient that prevents whitening during subsequent high-stretching blow molding.
Solution Approach 2:
The patent changes the geometric parameter of the preform by controlling the bottom portion thickness to be 0.5 to 0.7 times that of the body portion. This parameter change creates different thermal characteristics in the bottom portion, enabling it to cool sufficiently before blow molding and preventing whitening during high-stretching processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in high-quality, transparent containers with reduced shear heat and minimal whitening, maintaining high residual heat for efficient blow molding without sink marks or breakage.
Implementation Method 1
a coolant is introduced into the preform to cool the bottom portion of the preform
Data Source
AI summary
A method for manufacturing a resin container includes: injection molding a preform made of a resin and having a body portion and a bottom portion; adjusting a temperature of the preform manufactured in the injection molding; and a blow molding step of blow-molding the preform having the adjusted temperature to manufacture a resin container. In the injection molding, the preform is injection-molded using an injection mold in which a thickness of the bottom portion is 0.7 to 0.85 relative to a thickness of the body portion. Further, in the adjusting the temperature, a coolant is introduced into the preform to cool the bottom portion of the preform.