Millable Silicone Rubber Sponge Open Cell Formation
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Solution Overview
Problem
Existing methods for producing silicone rubber sponges with open cells often result in impaired rubber elasticity and increased hardness due to residual resin components, making it difficult to achieve a thick sponge with a low compression set and uniform fine-cell structure.
Innovation Solution
A method involving a heat-curable silicone rubber composition with unexpanded thermally expandable microcapsules and a solid high-temperature decomposition-type organic foaming agent is used, allowing for the formation of open cells without additional heating steps, thereby maintaining the inherent properties of silicone rubber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermally expandable microcapsules are used as foaming agent, then sponge cell size can be controlled, but resin components remain in the rubber causing increased hardness and impaired elasticity
Solution Approach 1:
The patent extracts and removes the harmful resin components from the rubber matrix through extraction solvents. The solvent penetrates the cured rubber and dissolves the resin components from thermally expandable microcapsules, which are then removed by washing, eliminating the cause of increased hardness and impaired elasticity while preserving the sponge structure.
Solution Approach 2:
The patent discards the harmful resin components through solvent extraction and washing processes. The extraction solvent selectively removes resin components from the rubber matrix, allowing the harmful substances to be discarded while recovering the elastic properties of the silicone rubber sponge.
2Object-generated harmful factors
If multiple heating steps are used for curing and open cell formation, then open cells can be formed, but properties of silicone rubber sponge deteriorate
Solution Approach 1:
The patent merges the curing process and open cell formation into a single integrated process. The organic peroxide crosslinking agent decomposes at elevated temperatures to generate gas bubbles that form open cells simultaneously with the crosslinking reaction, eliminating the need for separate heating steps and preventing deterioration of silicone rubber properties.
Solution Approach 2:
The patent incorporates the open cell formation capability into the curing process itself. The crosslinking agent is selected to decompose and generate gas bubbles during the curing temperature range, so that open cells are formed preliminarily during the necessary heating step for crosslinking, without requiring additional heating that would deteriorate the sponge properties.
3Quantity of substance
If large amount of thermally expandable microcapsules is employed to reduce specific gravity, then sponge density decreases, but compression set increases making thick sponge production difficult
Solution Approach 1:
The patent changes the parameters of the crosslinking system by using organic peroxide crosslinking agents with specific decomposition temperatures matched to the microcapsule expansion temperatures. This allows optimal control of the foaming process and rubber matrix formation, achieving low density with acceptable compression set by precisely controlling the timing and conditions of cell formation during curing.
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 method enables the production of silicone rubber sponges with adjustable density, excellent surface smoothness, and a uniform fine-cell structure, while maintaining the heat resistance and elasticity of the silicone rubber.
Implementation Method 1
the thermally expandable microcapsules expand as the solvent inside the thermally expandable microcapsules vaporizes when heated
Implementation Method 2
an organic peroxide crosslinking agent... the crosslinking reaction proceeds with generation of gas bubbles, thereby transforming the closed cells into open cells
Implementation Method 3
crosslinking reaction... an organic peroxide crosslinking agent... the crosslinking reaction proceeds with generation of gas bubbles
Data Source
Figure 1
AI summary
Provided are a millable silicone rubber composition; a millable silicone rubber sponge; and a method for producing this sponge. The method is a method for producing a millable silicone rubber sponge with an open cell ratio of not lower than 20%, comprising: performing a heat treatment on a silicone rubber composition at 200°C or higher, the silicone rubber composition containing: (A) an organopolysiloxane having at least two alkenyl groups in one molecule and a polymerization degree of not lower than 3,000, the organopolysiloxane being represented by the following average composition formula (I) R1aSiO4-a/2 (I) wherein R1 represents an identical or different monovalent hydrocarbon group, and a represents a positive number of 1.95 to 2.04; (B) a reinforcing silica; (C) thermally expandable microcapsules exhibiting an expansion starting temperature of 90 to 150°C, and contracting from a maximum expansion volume by 20% or more when heated at 200°C for 5 min; (D) a curing agent which is an organic peroxide; and (E) an open cell-forming agent which is a solid high temperature decomposition-type organic foaming agent having a decomposition starting temperature of not lower than 180°C, and starting to decompose after the component (A) is cured.