Multilayer Resin Preform Molding for Thick-Bottom Containers
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Solution Overview
Problem
Existing hot parison type blow molding methods for resin containers face challenges such as wrinkle formation, temperature unevenness, and prolonged molding cycles when molding thick preforms, particularly for cosmetic containers, leading to impaired quality and increased manufacturing costs.
Innovation Solution
A two-step injection molding process is employed, first forming an intermediate molded body and then adding a second layer to create a multilayered preform, followed by blow molding to achieve a thick bottom and thin body structure, utilizing a specialized blow-molding apparatus with temperature adjustment to optimize heat distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a thick preform is injection-molded using conventional hot parison type blow molding, then the container achieves a luxurious heavy feeling appearance, but the injection/cooling time becomes excessively long
Solution Approach 1:
The preform manufacturing process is divided into two separate injection molding steps: first forming a thin-walled intermediate molded body, then forming a thick-walled preform by injecting additional resin. This segmentation allows each step to be optimized independently, avoiding the need for excessively long cooling times required for conventional single-step thick preform molding.
Solution Approach 2:
The intermediate molded body is formed in advance as a preliminary structure that serves as the base for the final thick preform. This preliminary action enables the subsequent resin injection to occur on an already-formed substrate, reducing the overall molding cycle time while achieving the desired thick bottom portion.
2Productivity
If injection speed is increased to reduce injection time, then productivity improves, but wrinkles are generated at the bottom portion of the preform
Solution Approach 1:
The injection process is segmented into two stages with different speed requirements. The first stage forms the intermediate molded body with controlled injection speed to prevent wrinkles. The second stage injects additional resin onto the intermediate body, allowing higher injection speeds without causing surface defects, thus improving overall productivity while maintaining quality.
3Productivity
If the preform is cooled insufficiently to maintain molding speed, then productivity is maintained, but whitening due to crystallization occurs
Solution Approach 1:
The molding process is segmented such that the intermediate molded body is formed with sufficient cooling to prevent crystallization. The subsequent resin injection and blow molding steps are designed to occur rapidly, maintaining productivity while the already-cooled intermediate structure prevents whitening issues during the faster second stage.
4Shape
If a thick preform is used to achieve the desired container appearance, then aesthetic quality improves, but temperature unevenness increases causing wavy inner wall surfaces
Solution Approach 1:
The preform structure is segmented into two resin layers with different thermal properties. The intermediate molded body provides a thermally stable base with uniform temperature distribution. The additional resin layer is injected and molded rapidly, minimizing temperature gradients. This segmented structure achieves the desired thick bottom appearance while reducing overall temperature unevenness that causes wavy inner surfaces.
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 method reduces the injection/cooling time, minimizes defects like wrinkles and crystallization, and shortens the molding cycle while enhancing the aesthetic and luxurious feel of the resin containers, offering improved quality and reduced manufacturing costs.
Implementation Method 1
a first injection-molding step of injection-molding a bottomed cylindrical resin intermediate molded body
Implementation Method 2
injection-molding a resin material on an outer side of the intermediate molded body to manufacture a multilayered preform
Implementation Method 3
a blow-molding step of blow-molding the preform to manufacture a resin container having a thick portion
Implementation Method 4
blow-molding the preform to manufacture a resin container having a thick portion
Implementation Method 5
utilizing a specialized blow-molding apparatus with temperature adjustment to optimize heat distribution
Data Source
AI summary
A method for manufacturing a resin container includes: a first injection-molding step of injection-molding a bottomed cylindrical resin intermediate molded body; a second injection-molding step of injection-molding a resin material on an outer side of the intermediate molded body to manufacture a multilayered preform having a resin layer laminated on an outer peripheral side of the intermediate molded body; and a blow-molding step of blow-molding the preform to manufacture a resin container having a thick portion.