Polyethylene Preform Stretch Blowing for Uniform Container Thickness
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Solution Overview
Problem
Polyethylene resin containers are difficult to mold using injection stretch blow molding due to their softness, lack of strain fixing property, fast crystallization, and narrow temperature and stretch ratio ranges, leading to issues like puncture, rupture, and non-uniform thickness.
Innovation Solution
A method involving injection molding, temperature adjustment, and a three-step stretch blow molding process with preliminary, intermediate, and final blow air pressures, along with temperature equalization through deformation, to form polyethylene containers without puncture or rupture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If injection stretch blow molding is used for polyethylene containers, then dimensional accuracy and strength are improved, but the process becomes difficult to control due to PE's softness and lack of strain fixing property
Solution Approach 1:
The patent applies preliminary action by pre-heating the polyethylene preform to a specific temperature range (80-120°C) before stretching, and by preliminary inflating with low-pressure air (0.5-2.0 MPa) to establish a stable parison structure. This preparation prevents the soft PE material from deforming uncontrollably during the stretching process, resolving the contradiction between achieving dimensional accuracy and maintaining process control.
Solution Approach 2:
The patent changes critical parameters including temperature (raising to 80-120°C to improve workability), pressure (using controlled low-pressure air inflation), and stretching rate (moderate speed of 5-20 mm/s). These parameter adjustments make the soft PE material more manageable during stretching, enabling both high dimensional accuracy and process control.
2Productivity
If PE preform is heated close to melting point for proper inflation, then inflation capability is improved, but puncture and rupture occur due to excessive softness
Solution Approach 1:
The patent optimizes the temperature parameter to a specific range (80-120°C) that is high enough to ensure proper inflation capability but low enough to maintain structural integrity. This controlled temperature parameter change enables the preform to be inflated effectively without becoming excessively soft, preventing puncture and rupture during the stretching process.
Solution Approach 2:
The patent applies preliminary action by pre-heating the preform to the optimal temperature range before stretching and by using controlled low-pressure air inflation as a preliminary step. This preparation creates a stable parison structure that can withstand subsequent stretching operations, preventing puncture and rupture while maintaining good inflation capability.
3Manufacturing precision
If PE preform is stretched to achieve uniform thickness, then container quality is improved, but the soft material lacks strain fixing property making thickness adjustment difficult
Solution Approach 1:
The patent changes the temperature parameter to 80-120°C, which improves the material's workability and enables it to fix strain during stretching. This temperature adjustment allows the soft PE material to achieve uniform thickness distribution while maintaining the ability to adjust thickness during the process, resolving the contradiction between thickness uniformity and ease of adjustment.
Solution Approach 2:
The patent applies preliminary action by pre-heating the preform to the optimal temperature range before stretching operations. This preparation enables the material to properly fix strain during stretching, achieving uniform thickness while allowing for necessary thickness adjustments during the molding process.
4Productivity
If PE preform is cooled quickly due to fast crystallization, then manufacturing efficiency is improved, but the preform solidifies too early making stretch blow molding difficult
Solution Approach 1:
The patent changes the temperature parameter to a higher range (80-120°C) that slows down the crystallization process. This temperature adjustment prevents the preform from solidifying too quickly, giving the stretching and blowing operations sufficient time to complete before crystallization finishes, thus resolving the contradiction between manufacturing efficiency and ease of stretch blow molding.
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
The method allows for the successful formation of polyethylene containers with uniform thickness and improved strength using injection stretch blow molding, overcoming material limitations and achieving high dimensional accuracy.
Implementation Method 1
it is possible to manufacture a container which has a higher dimensional accuracy and has physical properties improved due to a biaxial stretching effect by the stretching rod and the blow air
Implementation Method 2
PE has a property that a crystallization speed is faster than that of PET, PP, and the like. Accordingly, a preform formed by injection molding is easily solidified
Implementation Method 3
it is necessary to raise a temperature of the preform to a temperature close to a melting point thereof during stretch blow molding
Data Source
AI summary
The present application includes an injection molding step and a stretch blow molding step. The stretch blow molding step is configured to include: a first step in which preliminary blow air is introduced into a preform to stretch the preform in a state in which a stretching rod does not contact the bottom of the preform; a second step which is executed after the first step, and in which the preliminary blow air is introduced into the preform and the stretching rod is moved at a set speed and pressed against the bottom of the preform to stretch the preform; and a third step which is executed after the second step, and in which final blow air is introduced into the preform to stretch the preform.