Water-Soluble Core Resin for Smooth Injection-Molded Inner Surfaces
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Solution Overview
Problem
Existing water-soluble resins for cores in injection molding can cause roughening and chipping of the inner surface of outer molded bodies, particularly when made of metal powder for sintering, due to volume changes and heat during the molding process.
Innovation Solution
A polyvinyl alcohol-based resin for cores with an easy stripping agent content between 0.1 wt % and 1.2 wt %, along with a plasticizer up to 6.0 wt %, enhances easy stripping properties and maintains the shape during dissolution, using glycerin fatty acid esters and specific polymerization degrees to prevent surface roughening and chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a water-soluble resin is used for core in injection molding, then the core can be dissolved in water after molding, but the outer molded body may be affected by volume change of the resin causing roughening and chipping of the inner surface
Solution Approach 1:
The patent applies parameter changes by controlling the polymerization degree of polyvinyl alcohol within 800 or less and regulating the plasticizer content at 6.0 wt% or less. These parameter adjustments ensure the resin dissolves completely without excessive volume expansion, preventing inner surface roughening and chipping while maintaining dissolution capability
Solution Approach 2:
The patent uses a composite material system combining polyvinyl alcohol-based resin with specific plasticizers (ethylene glycol, glycerin, diglycerin, or trimethylolpropane) and easy stripping agents (glycerin fatty acid esters). This composite formulation achieves both complete water solubility and minimal volume change during dissolution, resolving the contradiction between ease of operation and manufacturing precision
2Strength
If the polymerization degree of polyvinyl alcohol is high, then the resin strength is improved, but the resin may change volume when dissolving in water causing shape distortion
Solution Approach 1:
The patent applies parameter changes by setting the polymerization degree of polyvinyl alcohol to 800 or less. This parameter optimization balances resin strength with dissolution behavior, ensuring the resin maintains sufficient strength during molding while dissolving completely without excessive volume expansion that would cause shape distortion
3Ease of manufacture
If more plasticizer is added to improve moldability, then the moldability of the outer molded body is enhanced, but the resin for core may not maintain its shape during molding
Solution Approach 1:
The patent applies parameter changes by controlling the plasticizer content at 6.0 wt% or less. This parameter regulation optimizes the balance between moldability enhancement and shape stability, ensuring the core maintains its shape during the molding process while still achieving good moldability of the outer molded body
4Ease of operation
If the easy stripping agent content is increased to enhance stripping properties, then the stripping ease is improved, but the inner surface may become roughened
Solution Approach 1:
The patent applies parameter changes by optimizing the easy stripping agent content within the range of more than 0.1 wt% and less than 1.2 wt%. This parameter optimization ensures sufficient stripping ease while preventing inner surface roughening, as excessive amounts would cause surface deterioration
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 resin ensures a smooth inner surface of the molded body with reduced chipping, allowing for high-quality sintered products by maintaining shape integrity and improving moldability.
Implementation Method 1
when the outer molded body is a molded body made of a metal powder for sintering, a part of the outer molded body may be broken or chipped due to a volume change of the water-soluble resin
Implementation Method 2
the resin for core preferably includes a plasticizer in a proportion of 6.0 wt % or less
Implementation Method 3
the resin for core including an easy stripping agent that enhances easy stripping properties when the resin for core dissolves
Data Source
AI summary
Provided is a resin for core used for injection molding, with which an inner surface of an outer molded body is less likely to be roughened, and an inner surface of a finally obtained molded body is smooth and less likely to have chipping. The resin for core includes a polyvinyl alcohol-based resin, used for an application in which a core is dissolved in water after an outer molded body is molded in an injection molding process, and includes an easy stripping agent that enhances easy stripping properties when the resin for core dissolves in a proportion of more than 0.1 wt % and less than 1.2 wt %.