Variable-density footwear soles via single-step injection molding
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Solution Overview
Problem
Traditional polyurethane injection methods for manufacturing shoe midsoles require multiple molds and increased production time and cost, limiting the use of materials with varying densities, which can result in heavier and less comfortable footwear.
Innovation Solution
A method for creating a dual-density sole by directly molding a low-density polyurethane compound onto a strobel board and then injecting a higher-density polyurethane compound around it, using a single injection process based on a foot pressure map to optimize cushioning and reduce weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional polyurethane injection methods are used to manufacture midsoles, then manufacturing process is standardized, but production time and cost increase due to multiple molds and curing steps
Solution Approach 1:
The patent combines multiple injection steps into a single continuous process where a first polyurethane composition is injected and cured, then a second polyurethane composition is injected over it without removing the first mold. This merging of steps eliminates the need for multiple molds and separate curing cycles, thereby reducing production time while maintaining manufacturing standardization.
Solution Approach 2:
The first polyurethane composition is injected and cured as a preliminary layer before the second composition is added. This preliminary action creates a stable base that allows the second injection to proceed without requiring mold removal or additional preparation steps, thus streamlining the overall production process.
2Strength
If higher density polyurethane materials are used to improve midsole physical properties, then abrasion resistance and tensile strength increase, but footwear weight increases
Solution Approach 1:
The patent applies different density polyurethane compositions to different regions of the midsole. The first composition (higher density) provides structural support and durability in areas requiring strength, while the second composition (lower density) provides cushioning and comfort in areas where weight reduction is prioritized. This local differentiation optimizes the strength-to-weight ratio of the overall footwear.
Solution Approach 2:
The patent creates a composite midsole structure by layering two different polyurethane compositions with varying densities. This composite approach allows the footwear to benefit from both the high strength and abrasion resistance of denser materials and the lightweight properties of less dense materials, achieving an optimal balance between durability and weight.
3Ease of operation
If multiple materials with different densities are used in midsole, then cushioning and comfort improve, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the manufacturing of multiple density layers into a single injection process. By keeping the first mold in place and directly injecting the second composition over the cured first layer, the process eliminates the complexity of coordinating multiple molds, alignment procedures, and separate curing cycles, thereby reducing manufacturing complexity while maintaining multi-density cushioning benefits.
4Weight of moving object
If low density polyurethane compounds are used, then footwear weight decreases and comfort improves, but physical properties such as durability decrease
Solution Approach 1:
The patent assigns the low-density polyurethane composition to specific regions of the midsole where cushioning and comfort are prioritized, while the higher-density composition is placed in regions requiring durability and structural support. This spatial differentiation allows the footwear to be lightweight and comfortable without sacrificing durability in critical areas.
Solution Approach 2:
The patent creates a composite midsole where low-density and high-density polyurethane layers work together. The low-density layer provides weight reduction and comfort, while the high-density layer provides durability and structural integrity. This composite structure allows the footwear to simultaneously achieve light weight and high reliability.
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
This approach allows for a lightweight, comfortable, and durable sole with reduced production time and cost, while maintaining the necessary protection and structure, by using materials that would otherwise be unsuitable due to weak physical properties.
Implementation Method 1
the first composition is injected into a mold and cured to form a first layer
Implementation Method 2
a second composition is injected over the first layer without removing the mold from the first layer
Data Source
AI summary
Variable-density soles for articles of footwear and methods for constructing said soles are provided herein. In one embodiment, a variable-density sole for a footwear article comprises a first layer comprising a first density coupled to a bottom surface of an upper of the article of footwear; and a second layer comprising a second density greater than the density of the first layer, wherein the first layer is physically coupled to the second layer forming an interface between the layers. In this way, comfort of the article of footwear may be increased while decreasing the weight of the article of footwear. Further, forming the variable-density sole includes directly molding the first layer to a strobel board, stitching the strobel board to an upper, and injecting the second layer to the upper with the strobel board and the first layer. In this way, the production of a footwear article is simplified.