Polypropylene Skin Molding Cycle Reduction
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Solution Overview
Problem
The production of skin-covered foamed molded articles using polypropylene-based resins faces challenges with prolonged molding cycle times due to the need for sufficient cooling of the skin to ensure punchability for heating medium supply pins, which can lead to excessive stretching and leakage issues, especially with complex shapes or thin skins.
Innovation Solution
A polypropylene-based resin composition with specific properties, including a tensile elongation at break of 300 to 1,000% and a half-crystallization time of 5 to 50 seconds, is used to form the skin, allowing for improved punchability and efficient insertion of heating medium supply pins without excessive stretching, along with the addition of crystallization promoters like aromatic phosphoric ester metal salt compounds and sorbitol compounds to adjust these properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the skin is cooled sufficiently to ensure punchability for pin insertion, then the pins can be inserted without excessive stretching, but the molding cycle time is prolonged
Solution Approach 1:
The patent changes the material parameters of the skin by using a polypropylene-based resin composition with specific properties: tensile elongation at break of 300-1000% and half-crystallization time of 5-50 seconds. This allows the skin to maintain punchability at higher temperatures, eliminating the need for prolonged cooling while ensuring successful pin insertion without excessive stretching.
Solution Approach 2:
The patent performs preliminary action by selecting and preparing the polypropylene-based resin composition with specific crystallization properties before the molding process. The resin is pre-formulated to achieve the desired balance between punchability and cooling time, allowing the skin to be ready for pin insertion at optimal temperature without requiring extended cooling periods.
2Productivity
If the skin is not cooled sufficiently, then the molding cycle time is shortened, but the resin around the pins is excessively stretched making pin insertion impossible or causing leakage
Solution Approach 1:
The patent modifies the material parameters by using a polypropylene-based resin composition with tensile elongation at break of 300-1000% and half-crystallization time of 5-50 seconds. This enables the skin to tolerate higher temperatures during pin insertion without excessive stretching, allowing shorter cooling periods and faster cycle times while maintaining reliable pin insertion and preventing leakage.
3Loss of time
If pins are inserted through the skin at higher temperatures, then the molding cycle time is reduced, but steam leakage occurs through the stretched skin around the outlet ports
Solution Approach 1:
The patent changes the thermal and mechanical parameters of the skin material by using a polypropylene-based resin composition with specific half-crystallization time (5-50 seconds) and tensile elongation (300-1000%). This allows the skin to be inserted with pins at higher temperatures without excessive stretching that would cause leakage, enabling reduced cooling time while maintaining steam-tight seals.
Solution Approach 2:
The patent employs a composite material approach by using a polypropylene-based resin composition with specific crystallization properties and elongation characteristics. This composite material structure provides both the thermal resistance needed to prevent steam leakage and the mechanical flexibility to accommodate pin insertion at higher temperatures without stretching.
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 enables the production of skin-covered foamed molded articles with high fusion-bonding strength between expanded beads and the skin, while significantly shortening the molding cycle time by allowing steam pin insertion at higher temperatures and preventing steam leakage, resulting in a more efficient and practical manufacturing process.
Implementation Method 1
supplying a heating medium into the hollow interior space through heating medium supply pins to heat the expanded beads filled in the hollow interior space so that the expanded beads are fuse-bonded to each other
Implementation Method 2
the polypropylene-based resin composition has a half-crystallization time at 130°C of 5 to 50 seconds
Data Source
AI summary
A method for producing a skin-covered foamed molded article, including blow-molding a parison of a polypropylene-based resin composition into a skin defining a hollow space, placing thermoplastic resin expanded beads in the hollow space, and heating the expanded beads placed in the hollow space to fuse-bond the expanded beads together, wherein the polypropylene-based resin composition has a tensile elongation at break at 80°C of 300 to 1,000% and a half-crystallization time at 130°C of 5 to 50 seconds.