Heel construction method for injection molded article of footwear

Abstract

A method of constructing an article of footwear having a molded integrated vamp and sole is described. The method comprises molding the integrated vamp and sole with an external cavity formed in an exterior surface of a heel portion of the integrated vamp and sole. A plug is formed for close fit in the cavity. The plug has inner and outer surfaces and a contour side wall. In one embodiment of assembly, a heat reactive glue is applied to a bottom surface of the cavity and the inner surface of the plug, and at least a portion of the heel portion, having the cavity, and the plug are heated whereby to soften the glue to effect a bond between the bottom surface of the cavity and the inner surface of the plug when the plug is placed in the cavity with the inner surface of the plug facing the bottom surface of the cavity. Pressure is applied across the heel portion and the plug to bond the plug in the cavity. In another embodiment of assembly, the plug is glued in the cavity during assembly by applying a glue which is not heat reactive.

I claim: 
     
         1 . A method of constructing an article of footwear having a molded integrated vamp and sole, said method comprising the steps of:
 i) molding said integrated vamp and sole with an external cavity formed in an exterior surface of a heel portion of said integrated vamp and sole,   ii) forming a plug for close fit in said cavity, said plug having an inner and outer surface and a contour side wall,   iii) gluing said plug in said cavity with said inner surface of said plug facing said bottom surface of said cavity to bond said plug in said cavity.   
     
     
         2 . A method as claimed in  claim 1  wherein said step (iii) comprises the further steps of:
 (a) applying a heat reactive glue to a bottom surface of said cavity and said inner surface of said plug, and 
 (b) heating at least a portion of said heel portion having said cavity and said plug whereby to soften said glue to effect a bond between said bottom surface of said cavity and said inner surface of said plug. 
 
     
     
         3 . A method as claimed in  claim 2  wherein after step (iii) there is provided the further step of applying pressure across said heel portion and said plug to effect a secure bond between said plug and said cavity. 
     
     
         4 . A method as claimed in  claim 1  wherein said step (i) further comprises forming spaced-apart cavities in a rigid smooth heel inner surface of said heel portion to reduce the mass of injected material in said heel portion while retaining said rigid smooth inner flat surface. 
     
     
         5 . A method as claimed in  claim 2  wherein said step (ii) further comprises forming cavities in said inner surface of said plug in a surface area of less than 50% to reduce the mass of injected material in said plug while retaining sufficient inner surface area to assure said bond between said plug and said cavity. 
     
     
         6 . A method as claimed in  claim 3  wherein said step (ii) further comprises forming a through bore in said heel portion between said bottom surface of said cavity and a rigid inner flat surface of said heel portion to reduce the weight of injected material in said heel portion and to permit evacuation of compressed air when said plug is inserted in said cavity and press-fitted therein. 
     
     
         7 . A method as claimed in  claim 3  wherein said step (b) comprises providing a heating chamber having an open-top end with a support screen thereacross for the passage of heat therethrough, placing said integrated vamp and sole and plug on said support screen to soften said heat reactive glue for a predetermined time period, and removing said integrated vamp and sole and said plug therefrom to effect said bonding of said plug in said cavity. 
     
     
         8 . A method as claimed in  claim 7  wherein said heating chamber is provided with temperature controllable heating elements, said heating elements having temperature control means which are adjusted for said heating chamber to generate heat at a temperature of about 100° F. 
     
     
         9 . A method as claimed in  claim 1  wherein said step (ii) comprises forming said plug with a contrasting color material. 
     
     
         10 . A method as claimed in  claim 1  wherein said step (ii) comprises forming said plug with said outer surface thereof having a traction design or logo molded therein. 
     
     
         11 . A method as claimed in  claim 1  wherein said plug is formed with said contour side wall tapering outwardly from said inner surface thereof to said outer surface wherein said plug is bonded in friction-fit within said cavity. 
     
     
         12 . A method as claimed in  claim 1  wherein said step (iii) further comprises applying glue to said contour side wall of said plug and peripheral side walls of said cavity. 
     
     
         13 . A method as claimed in  claim 1  wherein after said step (iii) there is further provided the steps of securing an upper to said integrated vamp and sole, and positioning a single insole over an inner surface of said integrated vamp and sole and extending over said rigid smooth inner surface of said heel portion. 
     
     
         14 . A method as claimed in  claim 2  wherein said steps (i), (ii) and (a) are carried out at a molding plant and said step (b) is carried out at a remote assembly plant to ensure quality control in the assembly of said article of footwear. 
     
     
         15 . A method as claimed in  claim 13  wherein said upper is secured to said integrated vamp and sole prior to effecting said steps (b) and (iii) and wherein said single insole inserted thereafter. 
     
     
         16 . A method as claimed in  claim 5  wherein said step of forming cavities in said rigid smooth heel inner surface of said heel portion comprises forming cavities in less than 50% of said rigid smooth inner surface. 
     
     
         17 . A method as claimed in  claim 4  wherein step (i) comprises molding said integrated vamp and sole in a dye having at least two parts, said cavities in said heel portion having reduced the mass of injected material therein preventing said rigid smooth inner surface from deforming when said dye parts are separated after molding whereby to maintain said smooth heel inner surface free of deformation to eliminate the need to have a further insole over said heel inner surface. 
     
     
         18 . An article of footwear constructed in accordance with  claim 1  and containing an upper secured to said integrated vamp and sole, and a single insole disposed over said heel inner surface. 
     
     
         19 . A waterproof article of footwear constructed in accordance with  claim 1  and containing an upper secured to said integrated vamp and sole, and a single insole disposed over said heel inner surface.