EVA-PP Midsole Composition for Resilience and Shrinkage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional plastic compositions for midsoles, such as those made from ethylene vinyl acetate (EVA), face challenges in achieving high resilience and low shrinkage rates, leading to increased manufacturing costs due to the need for different foaming ratios and molds to produce midsoles with varying properties.
Innovation Solution
A plastic composition comprising an ethylene-vinyl acetate copolymer, two ethylene-α-olefin copolymers with specific hardness ranges, and polypropylene, which is formulated to achieve a resilience of at least 55% and a shrinkage rate of no more than 1.5%, allowing for the production of midsoles with consistent properties using the same foaming ratio and mold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional plastic compositions including EVA are used to produce midsoles, then midsoles can achieve good resilience (not less than 55%) and appropriate softness, but the shrinkage rate is undesirably greater than 1.5%, leading to poor dimensional accuracy
Solution Approach 1:
The patent uses a composite plastic composition consisting of multiple components: EVA (30-70 wt%), polypropylene (10-40 wt%), and a copolymer (10-40 wt%). This multi-component composite system combines the high resilience of EVA with the dimensional stability of polypropylene and the complementary properties of the copolymer, achieving both ≥55% resilience and ≤1.5% shrinkage rate simultaneously
Solution Approach 2:
The patent optimizes specific parameters of each component: EVA with vinyl acetate content of 24-29% and melt flow index of 0.9-9 g/10 min; copolymer with hardness of 55-60 Shore A and specific melt flow index range. By precisely controlling these parameters, the composition achieves the dual target of high resilience and low shrinkage rate
2Adaptability or versatility
If different plastic compositions and foaming ratios are selected to produce midsoles with varying properties, then midsoles can meet different performance requirements, but the cost of manufacturing increases due to the need for different forming molds
Solution Approach 1:
The patent creates a universal plastic composition formulation that can produce midsoles with different resilience and shrinkage properties by adjusting the weight ratios of components, while using the same forming mold and foaming ratio. The composition's multi-component design allows flexible property adjustment without requiring different molds, making the manufacturing system universally applicable
Solution Approach 2:
The patent enables performance variability through parameter changes in the composition formulation rather than through different molds. By adjusting the weight percentages of EVA, polypropylene, and copolymer, midsoles with varying resilience and shrinkage rates can be produced using identical molding equipment, decoupling product differentiation from equipment complexity
Data Source
AI summary
A plastic composition includes a polymer component. The polymer component includes an ethylene-vinyl (EVA) copolymer, a first ethylene-α-olefin copolymer having a hardness ranging from 55 Shore A to 60 Shore A measured according to ASTM D2240, a second ethylene-α-olefin copolymer having a hardness ranging from 85 Shore A to 90 Shore A measured according to ASTM D2240, and polypropylene (PP). The plastic product made from the composition has a loss factor ratio of tan δ(−20° C.) to tan δ(40° C.) at a frequency of 10 Hz, which ranges from 2.5 to 3.8. A midsole and a method of producing the midsole are also disclosed.