Blow Mold Temperature Control for Polyester Resin Containers
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Solution Overview
Problem
Thin-walled polyester-based resin containers used for aseptic filling lack sufficient heat resistance and rigidity, leading to demolding defects and buckling deformation during hot-water rinsing, as high mold temperatures cause the unstretched portions to soften and adhere to the mold, while lowering mold temperatures compromise the grounding part's ability to stand after rinsing.
Innovation Solution
A blow mold with a temperature control mechanism for separate bottom-part center and periphery molds, where the center mold is cooled and the periphery mold is heated to selectively heat-set the periphery, maintaining the bottom-part center at low crystallinity and the periphery at moderate crystallinity, preventing demolding defects and enhancing heat resistance for aseptic filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the mold temperature is raised to prevent buckling deformation of thin-walled containers, then heat resistance is improved, but demolding defects occur due to adhesion of unstretched portions to the mold
Solution Approach 1:
The patent applies different temperature conditions to different regions of the mold: the stretched portions are maintained at higher temperatures to prevent buckling, while the unstretched portions (such as the bottom plate and ground-contacting part) are cooled to prevent adhesion during demolding. This local differentiation of thermal conditions resolves the contradiction between preventing deformation and avoiding demolding defects.
Solution Approach 2:
The mold is divided into multiple temperature control zones, with separate temperature control for stretched portions and unstretched portions. This segmentation allows independent optimization of temperature conditions for each region, enabling simultaneous prevention of buckling in stretched areas and adhesion in unstretched areas.
2Manufacturing precision
If the mold temperature is lowered to prevent adhesion of unstretched portions, then demolding defects are prevented, but heat resistance deteriorates causing buckling deformation
Solution Approach 1:
Different regions of the container are assigned different thermal properties: stretched portions are given higher crystallinity and heat resistance through higher mold temperatures, while unstretched portions are given lower crystallinity and lower heat resistance through lower mold temperatures, matching their respective functional requirements.
Solution Approach 2:
The patent changes the crystallinity parameter differentially across the container structure by controlling mold temperature locally. Stretched portions are crystallized at higher temperatures to achieve high crystallinity (30-80%) for heat resistance, while unstretched portions are kept at lower crystallinity (0-20%) through lower temperatures, preventing adhesion while maintaining appropriate heat resistance for each region.
3Quantity of substance
If the container wall thickness is reduced to achieve lightweight and cost reduction, then material usage is decreased, but rigidity and heat resistance are compromised
Solution Approach 1:
The container is formed as a composite structure with regions of different crystallinity: high-crystallinity stretched portions provide strength and rigidity, while low-crystallinity unstretched portions provide flexibility and ease of demolding. This composite crystalline structure allows thin-walled design while maintaining overall rigidity through the reinforced stretched regions.
Solution Approach 2:
By changing the crystallinity parameter through differential temperature control during molding, the patent achieves high rigidity in stretched portions (30-80% crystallinity) even with reduced wall thickness, while maintaining manufacturability through low crystallinity in unstretched portions.
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 solution prevents demolding defects and provides moderate heat resistance to hot-water treatment, ensuring the container's structural integrity and preventing shrinkage of the grounding part during rinsing, thus maintaining the container's shape and functionality.
Implementation Method 1
a heating element is wound around a peripheral surface of the bottom-part periphery mold, and while cooling the bottom-part center mold, the bottom-part periphery mold is heated
Implementation Method 2
the bottom-part periphery including the periphery part is selectively heat-set to increase the degree of crystallinity
Implementation Method 3
the bottom-part center mold and the bottom-part periphery mold formed as a separate body are combined with each other through a heat insulation material, and the resulting combined molds are bonded to a support inside which a temperature control medium passage through which a temperature control medium at a low temperature is circulated is formed
Implementation Method 4
the bottom-part center mold and the bottom-part periphery mold formed as a separate body are combined with each other through a heat insulation material
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
When a pre-form P undergoes biaxial stretch blow molding using a blow mold 1 provided with a bottom-part mold 3 having a bottom-part center mold 31 for shaping a bottom-part center including a bottom plate part C51, and a bottom-part periphery mold 32 for shaping a bottom-part periphery including a periphery part C52, while cooling the bottom-part center mold 31, the bottom-part periphery mold 32 is heated to selectively heat-set the bottom-part periphery including the periphery part C52. The operation provides heat resistance to hot-water treatment in a rinsing step when filling with a content liquid by means of aseptic filling, while preventing a demolding defect from occurring upon opening the mold following molding.