Low-Density EVA Sole Structure to Prevent Heel Wrinkling
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Solution Overview
Problem
Low-density EVA footwear soles with a hardness of less than 40 Shore A tend to wrinkle, particularly in the heel area, due to high stress and load during walking, leading to permanent aesthetic damage.
Innovation Solution
A low-density EVA sole with a hardness of 25-35 Shore A, featuring a thicker heel, variable central part thickness, lightening apertures, and embossed surfaces with protrusions to prevent wrinkling, while maintaining softness and comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If low-density EVA is used to make a sole with density less than 0.4 g/cm³ and hardness less than 40 Shore A to achieve lighter weight and softer comfort, then the sole becomes more comfortable and lighter, but the sole develops permanent wrinkles in the heel area due to high stress and load during walking
Solution Approach 1:
The patent applies local quality by differentiating the heel area from the rest of the sole. The heel is provided with embossed surfaces that create a textured pattern, making this specific area resistant to wrinkle formation while maintaining the overall softness and low density of the sole. This localized treatment addresses the wrinkle problem in the high-stress heel area without compromising the comfort properties of the entire sole.
Solution Approach 2:
The embossed surfaces are pre-formed on the heel area before the sole is put into service. This preliminary structuring of the heel surface creates a pattern that prevents wrinkle formation from the outset, rather than attempting to correct wrinkles after they form. The embossed pattern is created during manufacturing to proactively prevent the harmful effect of wrinkling.
2Strength
If the heel area is made thicker to withstand higher stress and load during walking, then the mechanical resistance of the heel is improved, but the overall weight and volume of the sole increases
Solution Approach 1:
The patent utilizes the porous structure of low-density EVA foam material throughout the sole, including the heel area. This porous structure provides adequate mechanical resistance while maintaining low weight and density. The embossed surfaces on the heel further enhance its load-bearing capacity through geometric reinforcement without adding significant mass, as the embossing creates surface texture rather than substantial material addition.
Solution Approach 2:
The patent effectively uses the composite structure of crosslinked EVA polymer foam, combining the material's inherent cushioning properties with the structural reinforcement of embossed surfaces on the heel. This composite approach allows the heel to withstand higher stresses while the rest of the sole remains lightweight and soft, achieving a balance between mechanical resistance and weight.
3Strength
If medium-density EVA with hardness of approximately 50 Shore A is used to achieve a good compromise between mechanical resistance, comfort, and lightness, then the sole has adequate mechanical strength, but the sole is not soft enough and not comfortable enough according to modern footwear market requirements
Solution Approach 1:
The patent applies different effective properties to different areas of the sole. The heel area receives embossed surfaces that provide enhanced mechanical resistance and wrinkle resistance, while the rest of the sole maintains the soft, low-density EVA structure for maximum comfort. This local differentiation allows the sole to be softer overall (hardness less than 40 Shore A) while still providing adequate mechanical resistance where needed.
Solution Approach 2:
The patent changes the hardness parameter from the conventional 50 Shore A to less than 40 Shore A, and density to less than 0.4 g/cm³, to achieve softer and more comfortable soles. The embossed surfaces on the heel compensate for the reduced material hardness by providing structural reinforcement through geometric design, allowing the use of softer material without sacrificing mechanical resistance in critical areas.
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 solution effectively prevents wrinkling in the heel area by using embossed surfaces and structural design, ensuring the sole remains aesthetically appealing and comfortable.
Implementation Method 1
The sole (1) is made of low-density EVA by means of molding in a mold for footwear soles wherein the EVA polymer crosslinks
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Sole (1) molded from low-density ethylene vinyl acetate (EVA) in such a way that said sole (1) has a density of less than 0.4 g/cm3 and a hardness of less than 40 Shore A, wherein said sole (1) comprises a heel (2), a central part (3) at a plantar arch and a front part (4), and said heel (2) has an external lateral surface (20) and an embossing (9) made in said external lateral surface (20) of the heel; said embossing (9) having protrusions (90) that protrude from said external lateral surface (20) of the heel.