Resin Molded Body Coating Structure to Hide Parting Lines
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Solution Overview
Problem
Existing in-mold coating methods for forming outer layers on resin-based molded bodies result in visible parting lines, poor appearance, increased manufacturing processes, and costs due to separate skin molding and complex shapes, especially when the molded body has convex and concave surfaces.
Innovation Solution
A molded body design where the inner layer covers the convex surface and the outer layer extends to cover the parting line, with the parting line positioned to be hidden by an attachment target member, and the inner and outer layers are folded to conceal the line, reducing the need for additional coating processes and materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If in-mold coating is used to form an outer layer on the molded body, then the appearance quality should be improved, but visible parting lines appear on the surface causing poor appearance
Solution Approach 1:
The invention divides the mold into multiple cavities, with at least one cavity forming a molded body and another cavity forming a coating material application surface. This segmentation allows the coating material to be applied in a separate region that does not create visible parting lines on the final product surface, thereby resolving the contradiction between achieving surface quality and avoiding parting line visibility.
Solution Approach 2:
The invention introduces a coating material as an intermediary substance that is applied to the molded body surface through a dedicated coating cavity rather than through the main molding cavity. This intermediary approach allows the coating to be applied without creating visible parting lines, as the coating material is transferred from a separate application surface rather than from the mold parting line area.
2Manufacturing precision
If separate molds are used for skin molding and base material molding, then the appearance quality can be improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The invention merges the base material molding function and the coating material application function into a single mold structure with multiple cavities. The mold includes both a cavity for forming the molded body and another cavity for forming the coating material application surface, thereby combining what would traditionally require separate molds into one integrated system. This reduces device complexity while maintaining the ability to produce high-quality coated surfaces.
Solution Approach 2:
The mold structure is designed to perform multiple functions: it can form the base molded body in one cavity and simultaneously or sequentially form the coating material application surface in another cavity. This multi-functional design eliminates the need for separate dedicated molds for each function, reducing overall device complexity and manufacturing cost while maintaining surface quality.
3Manufacturing precision
If coating material is applied to both upper and lower dies, then the outer layer coverage is complete, but the manufacturing process and cost increase
Solution Approach 1:
The invention applies coating material selectively to specific regions rather than uniformly to all surfaces. The mold includes a dedicated coating material application cavity that applies coating material only where needed on the molded body surface, rather than applying coating material to both upper and lower dies universally. This localized approach maintains complete coating coverage where required while reducing unnecessary coating application, thereby improving manufacturing efficiency and reducing costs.
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
Prevents deterioration of appearance due to parting lines, simplifies manufacturing processes, and reduces costs by minimizing visible parting lines and eliminating the need for burr treatment, while accommodating complex shapes.
Implementation Method 1
a molded body made of a resin material and a method for molding the molded body... formed by injection molding the resin material into a mold
Implementation Method 2
in-mold coating is also known, in which an outer resin material that becomes the skin is applied to the inner surface of the mold, and then inner resin material is injected into the cavity for transfer
Data Source
AI summary
A molded body includes: a plate-like base material which is formed of a resin material and in which one surface in the thickness direction serves as a convex surface and the other surface serves as a concave surface; an inner layer which is formed of urethane and covers at least the convex surface of the base material; and an outer layer which is formed of a coating material and covers at least the coating region of the convex surface of the inner layer. The molded body is attached to an attachment target member with the convex surface facing outward. On a left end part of the base material, an undercut part is formed by injection molding in an inner layer that covers the left end part, and the outer layer covers up to the undercut part.