EPDM Sponge Weather Strip Composition for Compression Set and Discoloration
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Solution Overview
Problem
The existing EPDM rubber compositions used in vehicle weather strips face challenges with compression set and heat resistance, leading to reduced sealing performance and discoloration over time, especially under repetitive loads and varying temperatures.
Innovation Solution
An EPDM rubber composition is developed with a pattern viscosity of 90 or more, incorporating 5-ethylidene-2-norbornene at 9 wt% or more, 0.5 to 1.0 parts by weight of free sulfur, and 0.5 to 1.5 parts by weight of 1,6-bis(N,N-dibenzylthiocarbamoyldithio)-hexane (BDBzTH), which enhances compression set and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional EPDM rubber composition is used in weather strip sponge section, then the material provides basic sealing function, but compression set increases over time leading to reduced sealing performance
Solution Approach 1:
The patent changes the chemical composition parameters of EPDM rubber by specifying ENB content of 9 wt% or more and pattern viscosity of 90 or more, while using specific vulcanizing agents (free sulfur 0.5-1.0 parts and BDBzTH 0.5-1.5 parts) to optimize the crosslinking structure. These parameter changes result in improved compression set resistance while maintaining sealing performance.
Solution Approach 2:
The patent creates a composite vulcanizing system combining free sulfur and BDBzTH in specific ratios, which works synergistically to form an optimized crosslinked network structure in the EPDM rubber. This composite approach enhances the material's resistance to compression set compared to conventional single-agent vulcanization.
2Reliability
If conventional EPDM rubber composition is used, then the material provides adequate flexibility, but heat resistance is insufficient causing discoloration over time
Solution Approach 1:
The patent specifies precise compositional parameters including ENB content (9 wt% or more), pattern viscosity (90 or more), and vulcanizing agent ratios (free sulfur 0.5-1.0 parts, BDBzTH 0.5-1.5 parts). These parameter optimizations enhance the rubber's thermal stability and resistance to discoloration while maintaining flexibility.
Solution Approach 2:
BDBzTH acts as an intermediary vulcanizing agent that mediates the crosslinking process to create a more thermally stable network structure. This intermediary approach allows for controlled vulcanization that improves heat resistance and prevents discoloration without compromising the base rubber's flexibility.
3Strength
If high crosslinking density is achieved through conventional vulcanization, then compression set resistance improves, but heat resistance and color stability deteriorate
Solution Approach 1:
The patent employs a composite vulcanizing system with free sulfur (0.5-1.0 parts) and BDBzTH (0.5-1.5 parts) that creates a balanced crosslinked network. This composite approach achieves adequate compression set resistance (12% or less) while simultaneously improving heat resistance and preventing discoloration, avoiding the trade-off present in conventional high-crosslinking formulations.
Solution Approach 2:
By optimizing the vulcanizing agent ratio and EPDM composition parameters (ENB ≥9 wt%, pattern viscosity ≥90), the patent achieves a balanced crosslinking density that provides compression set resistance without excessive crosslinking. This balanced approach maintains heat resistance and color stability while achieving the required mechanical performance.
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 achieves a compression set of 12% or less and improved heat resistance, maintaining sealing performance and preventing discoloration, making it suitable for sponge sections in vehicle weather strips.
Implementation Method 1
from 0.5 to 1.0 part by weight of free sulfur; and from 0.5 to 1.5 parts by weight of 1,6-bis(N,N-dibenzylthiocarbamoyldithio)-hexane (BDBzTH)
Data Source
Figure 1
AI summary
An ethylene-propylene-diene monomer (EPDM) rubber composition for a sponge in a weather strip is provided. In the EPDM rubber composition free sulfur and 1,6-bis(N,N-dibenzylthiocarbamoyldithio)-hexane (BDBzTH) are included in a EPDM rubber having a pattern viscosity (ML1+8 at 125°C) value of 90 or more and a content of 5-ethylidene-2-norbornene (ENB) of 9 wt% or more. The EPDM rubber composition can improve compression set and provides a solution to the persistent discoloration problem of the EPDM rubber. Provided herein are EPDM compositions that are useful as a material of a sponge section in a weather strip of a passenger car.