Nitrile Rubber Low-Temperature Sealing via Silane-Modified Crosslinking
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Solution Overview
Problem
Cross-linked nitrile rubber compositions used in sealing applications lack sufficient sealing properties at low temperatures, despite exhibiting high tensile strength and elongation at break, limiting their suitability for low-temperature environments.
Innovation Solution
A cross-linked rubber composition is developed by incorporating a surface-treated silicate with an amino group-containing silane coupling agent and a polyamine-based cross-linking agent in a carboxyl group-containing highly saturated nitrile rubber, enhancing the sealing properties at low temperatures while maintaining tensile strength and elongation at break.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional cross-linked nitrile rubber composition is used, then tensile strength and elongation at break are improved, but sealing property at low temperature deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters by introducing a silane-modified nitrile rubber component and adjusting the crosslinking agent ratios. Specifically, it uses a nitrile rubber with 15-45 mass% acrylonitrile units and incorporates silane-modified components to alter the molecular structure, enabling the rubber to maintain both high tensile strength and improved low-temperature sealing properties through modified chemical parameters
Solution Approach 2:
The patent creates a composite rubber system by combining conventional nitrile rubber with silane-modified nitrile rubber components. The composite composition includes multiple polymer phases with different properties: the base nitrile rubber provides tensile strength while the silane-modified component contributes to low-temperature flexibility and sealing performance, resolving the contradiction between strength and low-temperature reliability
2Duration of action of moving object
If cross-linking density is increased to improve tensile strength, then elongation at break is improved, but compression stress relaxation time decreases
Solution Approach 1:
The patent introduces silane-modified components as intermediary elements between the crosslinked network and the rubber matrix. These modifiers act as buffers that slow down stress relaxation while maintaining the crosslinked structure's strength. The silane groups create intermediate bonding states that extend the compression stress relaxation time without sacrificing tensile strength
Solution Approach 2:
The patent optimizes the crosslinking parameters by controlling the type and amount of crosslinking agents used. It employs specific ratios of polyamine crosslinking agents and adjusts the crosslinking density to achieve a balance where sufficient tensile strength is maintained while the compression stress relaxation time is extended to at least 300 hours at 150°C
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 resulting cross-linked rubber exhibits improved sealing performance at low temperatures, with a compression stress relaxation time of 300 hours or more, and a TR70 temperature of -19°C or lower, making it suitable for various sealing applications in low-temperature environments.
Implementation Method 1
a surface treated silicate (b) prepared by surface treating a silicate with an amino group-containing silane coupling agent
Implementation Method 2
cross-linking a nitrile rubber composition comprising: a carboxyl group-containing highly saturated nitrile rubber (a)... and a polyamine-based cross-linking agent (c)
Implementation Method 3
when the cross-linked rubber is subjected to a compression stress relaxation test in which the cross-linked rubber is maintained at 150°C in a state of being compressed by 25%
Data Source
AI summary
The present invention provides a cross-linked rubber prepared by cross-linking a nitrile rubber composition, the nitrile rubber composition comprising: a carboxyl group-containing highly saturated nitrile rubber (a) containing 5 to 60 wt% of an α,β-ethylenically unsaturated nitrile monomer unit, and an α,β-ethylenically unsaturated monocarboxylic acid ester monomer unit, and having an iodine value of 120 or less; a surface treated silicate (b); and a polyamine-based cross-linking agent (c), wherein a content of the polyamine-based cross-linking agent (c) is 0.1 to 20 parts by weight with respect to 100 parts by weight of the carboxyl group-containing highly saturated nitrile rubber (a), wherein when the cross-linked rubber is subjected to a compression stress relaxation test in which the cross-linked rubber is maintained at 150°C in a state of being compressed by 25%, the time until which the compression stress comes to be 50% of the initial compression stress at the start of the compression stress relaxation test, the compression stress after 30 minutes from the start of the compression stress relaxation test, is 300 hours or more.