Stiffeners for use in footwear

Abstract

The present invention relates to a process and composition for stiffening materials for use in the manufacturing of footwear using a combination of stiffeners and adhesives.

Description

[0001] This application is a divisional of U.S. patent application Ser. No. 11 / 159,688, filed Jun. 23, 2005, which claims priority on U.S. Provisional Patent Appl. No. 60 / 584,519, filed Jul. 1, 2004 and U.S. Provisional Patent Appl. No. 60 / 640,947, filed Dec. 30, 2004.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates to stiffeners, such as the stiffeners used in the manufacture of shoes to retain the shape of heel and toe portions of the footwear. [0004] 2. Description of the Related Art [0005] There are a number of different types of stiffeners used in the shoe industry. U.S. Pat. Nos. 3,523,103; 3,590,411; 3,647,616; 3,891,785; 3,973,285; 4,814,037; 6,391,380 and 6,475,619 disclose methods and materials for improving the stiffness and adhesive qualities of materials for use in the footwear industry (all of which are incorporated by referenced). The stiffening plastic resins are selected from styrene butadiene, polystyrene, polyvinylacetate, ...

AI Technical Summary

Benefits of technology

[0011] Polycaprolactone has good water, oil, solvent and chlorine resistance. It has a low melting-point (58-60° C.) and low viscosity, and it is easy to process. Additional low melting point plastic adhesive resins, such as plastic resins with a melting point below 85° C. can also be employed in the present invention. An additional low melting point plastic adhesive resin is ethylene methyl acrylate copolymer, sold commercially as 2260 EMAC by Eastman Chemicals. 2260 EMAC has a melting point of 76° C.

[0014] One process involves co-extruding with either a coextrusion block or a manifold die using polymers of PETG copolyester with adhesives such as polycaprolactone, to form a polymer sheet stiffener that has both stiffening properties and adhesive properties in one step. The uniqueness of the process and the material is that it allows for two materials of significantly different melting points and viscosity to form a sheet material in one step. These sheets can then be heat activated to form a bond with the shoe components when heated and molded and at the same time produce a stiff material depending on the ratio of the ingredients and their weight. The formulation produces a stiff material with high resiliency and toughness. The two unique characteristics of this product and process are the fact that they can coextrude and form an acceptable sheet from two highly different melt index and melting point materials. Additionally it is more cost effective to perform in one step what usually takes two steps and at the same time it is possible to use a smaller amount of the adhesive resin since it all sits on the two outer surfaces of the sheet. It is also possible to use regrind in place of virgin polymer.

[0015] A second process involves mixing polymer blends of copolyester with adhesives, such as a polycaprolactone to form a dry mixture in a continuous mixer or an extruder. This results in a polymer sheet stiffener that has both stiffening properties and adhesive properties in a single step. The unique process and the material allows for two materials of significantly different melting points to form a homogeneous mix. These sheets can then be heat activated to form a bond with the shoe components when heated and molded and at the same time produce a stiff material depending on the ratio of the ingredients and their weight. The formulation produces a stiff material with high resiliency and toughness.

Problems solved by technology

The saturated stiffeners can be made stiff but usually the stiffer grades do not have high resiliency.

The powder coated stiffeners usually involve a need for cryogrinding to be able to create a fine powder from a low melting point adhesive which results in added costs as well as a need for a critical particle size distribution.

This adds additional cost and additional weight.