Abstract:
A shell for a boot or other footwear includes a first section of molded of a first thermoplastic material and a second section molded of a second thermoplastic material and integrally bonded with the first section. The first and second thermoplastic materials preferably have different material properties, such as color, hardness, or density, to enhance the aesthetic and/or functional design of the footwear. Methods of making molded multi-material shells and footwear including such shells are also disclosed.

Description:
TECHNICAL FIELD  
       [0001]     This application relates to footwear and, more particularly, to molded thermoplastic shells for footwear and methods of molding such shells.  
       BACKGROUND OF THE INVENTION  
       [0002]     Waterproof winter boots and other kinds of footwear sometimes include a semi-rigid molded plastic shell in the configuration of a slipper, to which an outsole may be molded, glued, or stitched. An insole and/or foot bed may be inserted inside the shell to provide cushioning. Finally, a flexible fabric or leather upper including lacing eyelets is typically stitched or glued along the rim of the shell to complete the boot or other article of footwear.  
         [0003]     U.S. patent application Ser. No. 10/889,586 of Laska et al., filed Jul. 12, 2004, which is incorporated herein by reference, describes a molded shell for footwear and a method of molding the shell around a skirt of the upper to provide a strong molded connection between the shell and the upper.  
         [0004]     The present inventor has recognized a need for improvements in footwear and molded shells, in particular, for providing an enhanced aesthetic appearance or improved flexibility characteristics for enhanced comfort.  
       SUMMARY  
       [0005]     In accordance with embodiments disclosed herein, a shell for a boot or other footwear includes a first molded thermoplastic section and a second molded thermoplastic section integrally bonded with the first section. The first section may be pre-formed by molding a first thermoplastic resin in a first mold or by other means, then inserted into a second mold in which the second section is formed by over-molding a second thermoplastic resin into integral chemical and/or mechanical engagement with at least a portion of a perimeter of the first section to form a unitary structure. In alternate embodiments, the first and second sections are formed simultaneously or sequentially in a single mold, during one or more mold cycles. An outsole and an upper are preferably attached to the shell after it has been molded.  
         [0006]     The physical properties of the first thermoplastic material, such as color, hardness, elasticity, and others, may differ from the physical properties of the second thermoplastic material, thereby forming a shell having regions of different colors, hardnesses, elasticity, or other properties. In one embodiment a generally U-shaped collar of a first material of a first color extends from the medial ankle region forward, over the instep, and rearward to the lateral ankle region. A second section of the shell, including the toe box, lower sidewalls, heel region and underfoot portion, is formed of thermoplastic material of a second color. The material of the second section may provide enhanced insulation capabilities and an aesthetically pleasing color contrast from the first portion.  
         [0007]     The multiple material shell concept can also be extended for shells of three or more different molded materials.  
         [0008]     Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a front-top-lateral side perspective view of a boot including a shell according to a preferred embodiment, wherein the stippling indicates color;  
         [0010]      FIG. 2  is a rear-lateral side perspective view of the boot of  FIG. 1  with regions broken out to show detail;  
         [0011]      FIG. 3  is an exploded assembly view of the boot of  FIG. 1  with the upper omitted and showing detail of an insole, the shell, and an outsole of the boot;  
         [0012]      FIGS. 4-7  are a pictogram showing steps for molding the shell of  FIG. 3 , including inserting a preformed plastic collar section of the shell into the mold ( FIGS. 4-5 ), closing the mold around the collar and a core of the mold ( FIGS. 5-6 ), and, after injecting a material to form a second section of the shell, opening the mold and removing the shell ( FIG. 7 );  
         [0013]      FIG. 8  is a cross section view of the mold of  FIGS. 4-7  showing cross sectional detail of the molded shell;  
         [0014]      FIG. 9  is a cross section view of the mold and shell of  FIG. 8  taken along lines  9 - 9  of  FIG. 8 ;  
         [0015]     FIG. 10  is a cross section view of the mold and shell of  FIG. 8  taken along lines  10 - 10  of  FIG. 8 ; and  
         [0016]      FIG. 11  is a cross section view of the mold and shell of  FIG. 8  taken along lines  11 - 11  of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]     Throughout the specification, reference to “one embodiment,” “an embodiment,” or “some embodiments” means that a particular described feature, structure, or characteristic is included in at least one embodiment. Thus appearances of the phrases “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout this specification are not necessarily all referring to the same embodiment.  
         [0018]     Furthermore, the described features, structures, characteristics, and methods may be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize that the various embodiments can be practiced without one or more of the specific details or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or not described in detail to avoid obscuring aspects of the embodiments.  
         [0019]     With reference to  FIGS. 1-3 , a boot  10  according to a preferred embodiment includes a shell  20  to which an upper  24  of boot  10  is attached via a flange  28  ( FIG. 2 ) of a shell  20 . Upper  24  may be made in any suitable manner and is preferably assembled primarily of soft fabric, leather, or synthetic material components. Upper  24  may be attached to shell by adhesives, stitching, taping, molding, heat bonding, or any other means. A sole  30 , including a cushioning midsole  32  and an wear-resistant outsole  34 , is attached to shell  20  opposite upper  12  by any suitable method. However, it may be preferably to glue or mold the sole  30  to shell  20 , to preserve a waterproof aspect of the shell that might otherwise be compromised by a stitched attachment. Prior to its attachment to upper  24  and sole  30 , shell  20  is formed by a molding process, a preferred embodiment of which is described below with reference to  FIGS. 4-7 . An insole  46  ( FIG. 3 ) may be inserted into shell  20 , after it is made, to provide cushioning and arch support.  
         [0020]     With reference to  FIGS. 2 and 3 , shell  20  comprises a first molded thermoplastic section  40  and a second molded thermoplastic section  42 . The first section  40  is preferably preformed as a U-shaped collar (open at the heel) in a preliminary injection molding operation. The second section  42  is then preferably overmolded onto first section  40  in a second injection molding operation, i.e., an over-molding operation described below with reference to  FIGS. 4-7 . The first and second sections  40 ,  42  are preferably formed of two different thermoplastic materials that are selected to be chemically compatible so as to form a chemical bond at their interface  48 . A chemical bond helps to strengthen the semi-rigid shell  20  and to form a unitary waterproof structure that is resistant to separation, tearing, or leaking at the interface  48 . Compatibility of the materials of the first and second sections  40 ,  42  may also result in a mechanical bond at the interface  48 , due to re-melting of the material of first section  40  during the over-molding of second section  42  and attendant mixing of the two materials at the interface. Without forgoing the desired chemical compatibility, the first and second materials may comprise two different formulations and colors of thermoplastic material.  
         [0021]     Shells  20  according to the present disclosure may have two or more regions of different colors, hardnesses, elasticity, surface finish, strength, insulating capability, and other physical properties. The particular combinations of properties and colors are virtually unlimited, and subject only to the availability of chemically compatible materials having the desired properties.  
         [0022]     The physical properties of the first thermoplastic material of first section  40 , preferably differ from the physical properties of the second thermoplastic material of the second section  42  in a manner that results in improved footwear performance characteristics. For example, first section  40  may be formed of a material having a light color and low hardness for fashion and enhanced flexibility across the instep, while the second section  42  may be formed of a darker material having a higher hardness to provide scuff resistance and hide dirt and scuffs lower on the boot  10 , where the shell  20  is more likely to contact soil, rocks, and other objects. The contrasting dark and light bands of shell  10  can be achieved without expensive painting or gluing operations.  
         [0023]     In one embodiment, the first section  40  is formed of a first material comprising a medium hardness thermoplastic elastomer, such as a thermoplastic polyurethane (TPU) having a durometer of approximately  80  Shore A. One suitable high-density TPU material for first section  40  is sold under the name ELASTOLLAN® S80 by BASF Corporation. The second section  42  may be formed of a second material comprising a harder TPU having a durometer of approximately 85 Shore A. A suitable hard TPU material is sold under the name AVALON® 85AB by Huntsman Chemical Company (formerly ICI Plastics). The coloring of the materials may preferably be due to colorants mixed with the resin, which will not bleed or separate.  
         [0024]     The first section  40  may be pre-formed by molding a first thermoplastic resin in a first mold or by other means, then inserted into a second mold. With reference to  FIG. 4 , first section  40  may comprise a preformed collar  50  that is inserted on a mold core  54  or into a cavity of a mold  60  ( FIG. 5 ) for forming second section  42 . Collar  50  may take any suitable shape. In the embodiment shown, collar  50  extends from the medial ankle region forward, over the instep, and rearward to the lateral ankle region. In other embodiments, the first section comprises panels or components of other shapes and configurations. In some embodiments, the first section  40  comprises two or more pieces that are both inserted into mold  60  at the same time for over-molding the second section  42  thereto. Skilled persons will appreciate that the thicknesses, positions, and widths of various regions of the sections of different materials can be customized to achieve desired design and performance attributes, such as flexibility, lateral stability, comfort, weight, and others.  
         [0025]     After first section  40  has been inserted into mold  60  or onto core  54 , the mold  60  may be closed as depicted in  FIG. 5 . Mold  60  may preferably include a dam  64  comprising a small sharp rib extending within the cavity of the mold and positioned to come into contact with or press against a lower perimeter region of collar  50  adjacent where interface  48  will be formed when second section  42  is molded. Dam  64  helps to achieve a crisp transition between the first and second materials by preventing the second material of second section  42  from flowing around first section  40  during the molding step. Dam  64  may preferably extend along the entire lower perimeter of first section  40 , as depicted by the broken line numbered  64  in of  FIG. 8 .  
         [0026]     As shown in  FIG. 6 , when mold  60  is closed, a cavity  70  is formed around first section  40 . The cavity includes a toe box region  72 , lower sidewalls  74 , a heel region  76  and underfoot region  78 , which, when filled with the thermoplastic material, as depicted in  FIGS. 7 and 8 , will form corresponding regions of the second section of the shell  20 .  
         [0027]     A part line  80  of the mold runs along a portion of the lower perimeter of first section  40  to correspond with dam  64  for at least a portion of the length of shell  20 .  FIGS. 8-11  show the placement of part line  80  and dam  64  in greater detail. Strategic placement of part line  80  can help minimize mold flash and result in an aesthetically pleasing shell  20 , devoid of part lines along the top of the shell.  
         [0028]     In an alternative embodiment, the molding process is repeated one or more times to add third or further shell sections, so that shell may comprise three or more sections of different molded materials. In still other embodiments, the first and second sections are formed simultaneously or sequentially in a single mold, during one or more mold cycles. In yet other embodiments the first and second sections are formed by a co-molding process.  
         [0029]     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.