Expandable Rubber Composition for Low Bond Line Read-Through
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Solution Overview
Problem
Existing thermally expandable rubber compositions used for bonding substrates in automotive applications suffer from issues such as incorrect porous foam structure, inadequate bead expansion, and increased bond line read-through (BLRT) due to differences in thermal expansion coefficients between substrates and adhesives, particularly with thinner sheet metals.
Innovation Solution
A rubber composition comprising specific types and ratios of solid rubber, processing oil, vulcanization system, and blowing agents, including 4,4'-oxybis(benzenesulfonyl hydrazide), p-toluenesulfonyl hydrazide, and azodicarbonic acid diamide, to achieve optimal volume expansion and reduced BLRT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thermally expandable rubber composition is used for bonding substrates, then volume expansion increases to improve flexibility, but bond line read-through (BLRT) increases causing visible distortion
Solution Approach 1:
The patent applies porous materials by incorporating a blowing agent that creates a controlled porous foam structure within the rubber composition. This porous structure reduces the effective thermal expansion coefficient by introducing air pockets that compress during thermal expansion, thereby minimizing bond line read-through while maintaining volume expansion for flexibility.
Solution Approach 2:
The patent uses composite materials by combining rubber base polymer with blowing agent, filler, and curing system to create a multi-phase thermally expandable composition. The composite structure allows simultaneous achievement of volume expansion (for flexibility) and controlled BLRT (through porous foam architecture) that single-phase materials cannot provide.
2Weight of moving object
If thinner sheet metals are used for light weighting, then weight reduction is achieved, but bond line read-through occurs more frequently due to decreased bending stiffness
Solution Approach 1:
The porous foam structure created by the blowing agent acts as a buffer that compensates for the reduced stiffness of thin sheet metals. The compressible air pockets absorb thermal expansion stresses, preventing visible distortion at the bond line even when bonding to lightweight thin-gauge metals.
Solution Approach 2:
The patent changes the thermal expansion parameter of the adhesive by incorporating the blowing agent, transforming it from a rigid high-expansion material to a compliant low-effective-expansion material. This parameter change allows successful bonding to thin sheet metals without BLRT.
3Shape
If incorrect porous foam structure occurs, then expansion behavior is compromised, but manufacturing complexity increases
Solution Approach 1:
The blowing agent system is designed to self-regulate foam structure formation during the curing process. The chemical decomposition of the blowing agent automatically generates gas bubbles that create the desired porous structure without requiring external control mechanisms, mold complexities, or additional processing steps.
Solution Approach 2:
The patent utilizes phase transitions of the blowing agent (from solid/liquid to gas upon heating) to automatically create the porous foam structure. This phase change occurs naturally during the standard curing process, forming the desired expansion behavior without adding manufacturing complexity.
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 composition provides a correct porous foam structure, right expanded bead, and significantly reduces BLRT, enhancing sound dampening and vibration reduction in automotive applications.
Implementation Method 1
e) 0.25 to 0.55 wt-%, based on the total weight of the rubber composition, of 4,4'-oxybis(benzenesulfonyl hydrazide) BA1; f) 0.25 to 0.55 wt-%, based on the total weight of the rubber composition, of p-toluenesulfonyl hydrazide BA2; g) 0.1 to 0.5 wt-%, based on the total weight of the rubber composition, of azodicarbonic acid diamide BA3.
Implementation Method 2
A suitable rubber composition to connect these parts/substrates for vibration reduction is able to expand its volume when heat is applied in order to increase its flexibility
Data Source
AI summary
Disclosed is a thermally expandable rubber composition, comprising at least one solid rubber, at least one processing oil, at least one vulcanization system, at least one filler G, 0.25 and 0.55 wt-% of 4,4'- oxybis(benzenesulfonyl hydrazide), 0.25 and 0.55 wt-% of p- toluenesulfonylhydrazide and 0.1 and 0.5 wt-% of azodicarbonic acid diamide. The thermally expandable rubber composition provides good foam structure and reduced bond line read through.