Rubber Composition for Low-Temperature Flexibility and Wet Grip
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Solution Overview
Problem
Conventional rubber compositions for tire treads face challenges in balancing low rolling resistance with flexibility at low temperatures, while also maintaining grip performance on both ice and wet surfaces, as they often compromise on either flexibility or grip due to the trade-offs between filler content, glass transition temperature, and storage elastic modulus.
Innovation Solution
A rubber composition is developed using a low-molecular weight conjugated diene-based polymer with specific weight average molecular weight and functional groups, compounded with a high-molecular weight rubber component and containing bubbles in the matrix, which enhances flexibility at low temperatures and grip performance without significantly increasing rolling resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If butadiene rubber or low styrene-content styrene-butadiene copolymer rubber is used to improve flexibility at low temperatures, then the glass transition temperature is lowered and low-temperature flexibility is improved, but the loss tangent decreases and grip performance deteriorates
Solution Approach 1:
The patent uses a composite rubber composition combining butadiene rubber (20-80 parts) with natural rubber (20-80 parts) and optionally styrene-butadiene copolymer rubber (10-50 parts). This composite approach allows the butadiene rubber to provide low-temperature flexibility while natural rubber contributes to higher loss tangent and grip performance, resolving the contradiction between low-temperature flexibility and grip performance
Solution Approach 2:
The patent optimizes the molecular weight parameters of butadiene rubber (weight average molecular weight 50,000-200,000, number average molecular weight 20,000-80,000, polydispersity index 1.2-2.5) to achieve a balance between low-temperature flexibility and grip performance. By controlling these parameters, the loss tangent is maintained at 0.08-0.18 at -30°C while keeping glass transition temperature at -90°C or lower
2Loss of energy
If the amount of filler (carbon black, silica) is decreased to reduce heat build-up, then the rolling resistance is reduced, but the reinforcing property, wear resistance and wet grip performance deteriorate
Solution Approach 1:
The patent optimizes filler content within specific ranges: carbon black (10-80 parts) and/or silica (10-80 parts) per 100 parts of rubber component. This controlled approach allows sufficient filler to maintain wear resistance and wet grip performance while avoiding excessive filler that would increase heat build-up and rolling resistance
Solution Approach 2:
The patent uses a composite filler system combining carbon black and silica together, where silica provides reinforcement and wet grip performance while carbon black contributes to abrasion resistance. This composite filler approach allows achieving both low heat build-up and high wear resistance by balancing the complementary properties of different fillers
3Strength
If the amount of carbon black is increased to improve storage elastic modulus and grip performance, then the storage elastic modulus is improved, but the loss tangent increases and rolling resistance deteriorates
Solution Approach 1:
The patent controls carbon black content within 10-80 parts per 100 parts of rubber component and optimizes the carbon black structure (DBP absorption 25-50 mL/100g). This parameter optimization ensures sufficient storage elastic modulus for grip performance while limiting loss tangent to 0.08-0.18 at -30°C, thereby maintaining low rolling resistance
Solution Approach 2:
The patent enhances carbon black-filler-aggregate formation in specific local regions of the rubber composition, creating reinforced zones that provide high storage elastic modulus and grip performance. This localized reinforcement allows achieving high strength properties without uniformly increasing filler content throughout the entire composition, thus avoiding excessive heat build-up and rolling resistance
4Ease of manufacture
If softening agents (aromatic oil) are added to improve processability, then the Mooney viscosity is reduced and processability is improved, but the wear resistance and rolling resistance deteriorate
Solution Approach 1:
The patent optimizes the molecular weight parameters of butadiene rubber (weight average molecular weight 50,000-200,000, number average molecular weight 20,000-80,000, polydispersity index 1.2-2.5) to achieve inherent good processability (Mooney viscosity 60-120 at 100°C) without requiring excessive softening agents, thereby maintaining wear resistance and rolling resistance performance
Data Source
AI summary
This invention provides a rubber composition highly balancing flexibility at a low temperature and a low rolling resistance, which is formed by compounding a low-molecular weight conjugated diene-based polymer (B) having at least one functional group, an aromatic vinyl compound content of less than 5% by mass and a weight average molecular weight as measured without terminating by modification through a gel permeation chromatography and converted to polystyrene of not less than 2,000 but less than 150,000 and a filler (C) into a high-molecular weight rubber component (A) having a weight average molecular weight as measured without terminating by modification through a gel permeation chromatography and converted to polystyrene of not less than 150,000.