FIELD OF THE INVENTION
- BACKGROUND OF THE INVENTION
The present invention relates to the field of footwear, and more particularly to injection-molded polyurethane footwear.
Currently, polyurethane molded footwear is produced as a light-weight abrasion-resistant alternative to rubber, thermoplastic rubber or polyvinyl chloride (PVC) footwear. However, a concern with existing polyurethane molded footwear is that polyurethane does not adjust well to cold environments. At colder temperatures, the polyurethane outsole material becomes hard and frozen and as a result becomes a slip and fall hazard, as the outsole material no longer adequately grips on walking surfaces.
Therefore, there is a need for footwear which combines polyurethane and rubber such that the final footwear product incorporates the light-weight properties of polyurethane with the cold-resistant properties of rubber. However, previous attempts to bond polyurethane and rubber using conventional footwear molding or gluing techniques have not been successful, with the different layers tending to separate under normal usage. Additionally, there is a need for a method of manufacturing such footwear in a cost-effective manner.
- SUMMARY OF THE INVENTION
It is an object of this invention to partially or completely fulfill one or more of the above-mentioned needs and shortcomings.
In accordance with one aspect of the present invention there is disclosed an article of footwear having a rubber outsole, a polyurethane midsole bonded to the rubber outsole by a polyurethane (PU) adhesive and by injection molding of the midsole, and a polyurethane upper bonded to the polyurethane midsole by the injection molding of the midsole.
In accordance with another aspect of the present invention there is disclosed a method of manufacturing an article of footwear comprising the steps of: a) applying a layer of primer to a selected portion of a rubber outsole and allowing said layer of primer to dry; b) applying a first layer of PU adhesive over the primed portion of the outsole and allowing said first layer of PU adhesive to dry; c) applying a second layer of PU adhesive over the dried first layer of PU adhesive and allowing said second layer of PU adhesive to dry; d) forming, separately, a polyurethane upper by injection molding; e) setting the outsole and the upper in a mold; and, f) forming, via injection molding, a polyurethane midsole between said polyurethane upper and said rubber outsole, with the injection molding serving to bond the polyurethane upper to the polyurethane midsole and to activate the polyurethane adhesive to bond the polyurethane midsole to the polyurethane upper, thereby forming the article of footwear.
The method can further include an additional step of inserting an insole into the footwear after the step of forming the midsole. The method can still further include a step of inserting one or both of a reinforced toe plate and a reinforced sole plate into the mold with the outsole and upper, such that the toe plate and the sole plate, when present, are integrated into the upper and midsole, respectively
Preferably, a polyurethane shaft is integrally formed with the polyurethane upper as part of said step of forming the polyurethane upper, such that the article of footwear is a boot.
BRIEF DESCRIPTION OF THE DRAWINGS
Other and further advantages and features of the invention will be apparent to those skilled in the art from the following detailed description thereof, taken in conjunction with the accompanying drawings.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which like numbers refer to like elements, wherein:
FIG. 1 is perspective view of an article of footwear, namely a boot, assembled according to the present invention;
FIG. 2 is a right side elevational view of the boot of FIG. 1;
FIG. 3 is a left side cross-section view of the boot of FIG. 1 along line 3-3 of FIG. 6;
FIG. 3A is a left side cross-section view equivalent to FIG. 3, with the toe cap removed;
FIG. 4 is a cross-sectional view along line 4-4 of FIG. 2;
FIG. 5 is a cross-sectional view along line 5-5 of FIG. 2;
FIG. 6 is a bottom plan view of the boot of FIG. 1;
FIG. 7 is a cross-sectional view along line 7-7 of FIG. 2; and,
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT AND METHOD
FIG. 8 is a flow chart of the process steps in manufacturing the boot of FIG. 1.
The inventive method presented herein comprises method of manufacturing an article of footwear 100 having three components as shown in FIG. 1: a) a light weight, abrasion resistant, polyurethane upper portion 400; b) a polyurethane midsole 300, which is preferably injected in a less dense format than the upper 400, to provide better insulation against cold weather conditions and fatigue resistance for the wearer, due to its relatively lighter weight; and, c) a rubber outsole 200, providing the wearer with superior grip and slip resistance in cold weather conditions without compromising weight, comfort, and performance of the article of footwear 100.
The article of footwear 100 as shown in FIG. 1 has all three components: i.e., rubber outsole 200, polyurethane midsole 300 and polyurethane upper 400. Where the article of footwear 100 is a boot, as is shown, a fourth element, being a polyurethane shaft 500. optionally extends integrally from the polyurethane upper 400 to surround the user's ankle and calf, depending on the height of the boot. The process, as described herein, is for manufacturing a boot as shown; however, the process can be applied to any other type of injection-molded footwear (e.g. shoes, clogs, covers, etc.).
As shown in FIGS. 3 and 3A, the article of footwear 100 can optionally include a toe plate 410 incorporated into the polyurethane upper 400 and/or a sole plate 310 incorporated into the polyurethane midsole 300. The toe plate 410 and sole plate 310, preferably constructed from steel, plastic, or composite materials, can provide piercing, impact and crush protection according to known standards, such as ANSI and CSA, or can merely provide a greater degree of shape and structural integrity to the article of footwear 100.
A presently preferred embodiment of the inventive process comprises the following process steps, as depicted in the flowchart of FIG. 8:
Starting with a rubber outsole 200, the whole or part of the inside portion of the rubber outsole 200 is huffed and blown clean of any stray or excess rubber chips or other detritus, to produce a clean, buffed surface (step 810).
A chemical primer for use with chlorine-based polyurethane adhesives is applied (step 820) to the buffed surface, the buffed surface being the whole of or part of the inside portion of the rubber outsole 200 as discussed above. Application is preferably by brushing; however, other methods as known in the art, such as spraying, can be used. The rubber outsole 200 is then preferably passed through a heating tunnel or chamber at about 50° C. to 55° C. for approximately 2 to 3 minutes to dry the primer.
A chlorine-based polyurethane adhesive is then applied (step 830) to the primed area of the rubber outsole 200 by brushing or other methods of application as are known in the art. The outsole then makes a second pass through the heating tunnel or chamber at about 50° C.-55° C. for approximately 3 to 5 minutes to dry the adhesive.
A second layer of the polyurethane adhesive is applied in the same manner (step 840) and the rubber outsole 200 then makes a third pass through the heating tunnel or chamber at about 50° C.-55° C. for approximately 1 to 2 minutes to dry the second adhesive layer. The resulting rubber outsole 200, with its two layers of adhesive, is then ready for use in the injection molding process.
In separate prior process, the polyurethane upper 400 and polyurethane shaft 500 (where required) of the article of footwear 100 are formed by injection molding with polyurethane foam, resulting in a fully formed polyurethane upper 400 and polyurethane shaft 500 for use in the claimed process of this invention.
The rubber outsole 200, with its double layer of adhesive, is then fixed inside a mold (not shown) along with the pre-formed polyurethane upper 400 and polyurethane shaft 500 (step 850). A second injection molding of polyurethane occurs (step 860) to form the polyurethane midsole 300 between the polyurethane upper 400 and the outsole 200 already positioned within the mold. While the injection of polyurethane material in this manner would, in and of itself, provide some degree of bonding of the rubber outsole 200 to the polyurethane upper 400, it would not, by itself, be sufficiently strong bonding to constitute a commercially acceptable product. Rather, and most importantly, the heat from the molten polyurethane material being injected serves to activate the polyurethane adhesive (at about 70 degrees Celsius) previously applied to the rubber outsole 200. thereby significantly strengthening the bond formed between the rubber outsole 200 and the polyurethane midsole 300. In this manner, the rubber outsole 200 is not separable from the polyurethane midsole 300 under normal conditions of use. The article of footwear 100 thus formed is commercially acceptable.
Preferably, the midsole 300 is formed from a foamed polyurethane having a density higher than the polyurethane used in forming the shaft 400, in order to provide more support for the foot of the user. Conversely, the foamed polyurethane used in forming the shaft 400 can have a lower density (i.e., more foaming agent used) so as to improve the insulative qualities of the shaft 400, whilst reducing the overall weight of the article of footwear 100. For example, the polyurethane midsole 300 is preferably formed from a foamed polyurethane having a Shore C hardness range of about 56 to 60 (using ASTM D2240), whereas the polyurethane used in the polyurethane shaft 400 preferably has a Shore C hardness range of about 51 to 55 (using ASTM D2240).
After the injection molding is completed, the assembled article of footwear 100 is removed from the mold and finished (step 870) by cleaning, labeling, and other steps as known in the art to be prepared for subsequent packaging and shipping for distribution.
The finished article of footwear 100 is thus comprised of a rubber outsole 200 bonded to a polyurethane midsole 300 and a polyurethane upper 400, which is itself optionally bonded to, or integrally formed with, a polyurethane shall 500, completing the article of footwear 100 as a boot. The resulting article of footwear 100 combines the cold-weather performance and traction characteristics of rubber on the outsole 200, with the light weight, abrasion resistance and insulative properties of polyurethane in the rest of the article of footwear 100.
A removable insole 420, of felt, foamed plastics material or the like, as is known in the art, and shown in cross-section in FIG. 4, can be optionally inserted into the article of footwear 100 to provide additional support and/or comfort for the user's foot, if desired.
Additionally, as an optional sub-step of the injection molding process, steel, plastic, or composite material sole and/or toe plates 310 and 410, as shown in FIGS. 3 and 3A, and as are known in the art, can also be inserted into the mold, thereby becoming integrated into the polyurethane midsole 300 and polyurethane upper 400 to provide protection from impact for the wearer as discussed above.
While the article of footwear and the method described above have been presented in the context of injection-molded cold-weather boots, the method is equally applicable to any type of injection-molded footwear.
This concludes the description of a presently preferred apparatus and method according to the invention. The foregoing description has been presented for the purpose of illustration and is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is intended the scope of the invention be limited not by this description but by the claims that follow.