US3496654A - Footwear having improved block copolymer foxing adhesion - Google Patents

Description

United States Patent Int. Cl. A43b 1/14 US. Cl. 36-9 5 Claims ABSTRACT OF THE DISCLOSURE Footwear assemblies are provided comprising a textile upper, a polymer soling and a block copolymer foxing wherein the foxing adhesion to the upper under wet conditions is substantially improved by pretreatment of the uppers with polychloroprene.

This invention relates to improvements in the wet peel strength of foxing to footwear having textile uppers. More particularly it relates to footwear uppers bearing a coating which promotes adhesion of foxing, the latter comprising block copolymers.

Numerous types of footwear are designed to perform their function under a variety of physical conditions. While it is a reasonably easy task to design a shoe assembly which will perform satisfactorily under dry conditions, the so-called wet peel strength of polymeric foxing often leaves much to be desired. This is probably due in substantial part to the lack of true adhesion of the foxing material, which is usually non-polar or substantially so, to the textile, which is often polar in character, as in the case of cellulosic fibers and the like. Textile top shoes, in particular, are subjected to a number of situations which unless adequately met, result in disintegration of the assembly. Thus, under rainy conditions, and especially at the area of flexing, the foxing strip around the base of the upper may tend to separate from the textile upper. Also, when washed in the presence of hot water and detergents, foxing separation may be a severe problem. More specifically the problem of wet peel strength is especially apparent in such footwear as canvas topped shoes. In such articles it is not only important to maintain a high degree of flexibility, improve abrasion resistance and dry peel strength but also and perhaps more importantly to maintain a high level of peel strength when the textiles are subjected to moisture or wet conditions.

It is the usual practice in the shoe trade to laminate two layers of canvas together with a polymeric combining paste and then to bond (or decorate) the canvas laminate to a thermoplastic or elastomeric sole portion of the shoe with a strip applied either simultaneously or subsequently which is known as a foxing strip. This foxing is the strip of material which covers the upper part of the sole edge and the lower part of the canvas upper edge *where the upper and lower sole meet. In many instances in the past, the combining paste has been made out of vulcanized material such as vulcanized SBR or with thermoplastic compositions such as polyvinyl chloride and the like. These are highly intractable materials once they have been thermoformed, especially so in the case of the vulcanized elastomers. Moreover, it has been found by experience that these combining paste compositions lack the ability of physically promoting adherence of block polymer foxing especially under wet conditions.

Canvas top shoes and the like must be marketed under highly competitive conditions. Consequently any economies which may be effected in the manufacture of the articles improve the competitive position thereof. The necessity for vulcanizing prior art compositions used as foxing or other footwear components reduces this competitive position and consequently it would be highly desirable to avoid vulcanizing and at the same time to provide improved wet peel strength for foxing compounds.

It is an object of the present invention to improve the physical properties of footwear assemblies. It is a particular object of the invention to provide improved footwear as materials to result in superior wet peel strength.

Now, in accordance with the present invention, improved footwear assemblies are provided comprising a textile footwear upper bearing a coating of a polychloroprene thereon at least in the area contacted by the foxing, said foxing consisting essentially of a block polymer having the general configuration:

wherein each A is a polymer block of a monovinyl arene and B is a polymer block of a conjugated diene, each block A having an average molecular weight between about 8,000 and 45,000 and B block having an average molecular weight between about 25,000 and 150,000.'It has been found that surprisingly improved wet peel strengths of foxing to the textile upper are obtained.

While the assembly in its broadest aspects thus contemplates the formation of a high wet peel strength single textile upper bearing a foxing strip comprising a block copolymer. A more particular aspect of the invention contemplates the situation in which two textile layers are combined by means of a intervening combining composition. More particularly, the compositions performing the function of combining compounds may comprise not only the block copolymer referred to above, but compositions in which the block copolymer is modified with one or more ingredients including especially polystyrene, tackifying resins, hydrocarbon extending oils and or mineral particulate fillers, all as more particularly described hereinafter. Other combining compounds may comprise vulcanized SBR, polychloroprene or polyvinyl chloride.

The most important application of the present invention at this time, is in the manufacture of sport shoes generally referred to as tennis shoes or the like. The problem of foxing adhesion referred to hereinafter is substantially eliminated or largely minimized by the use of the present invention. As the data given hereinafter will show, the application of polychloroprene to at least the area of the textile upper contacted by the foxing and thereafter manufacturing shoes such as by injection molding of a block copolymer foxing and a soling onto this upper results in surprisingly improved wet peel strength of the resulting article.

The textile involved in the articles of the present invention may be either woven or non-woven as the case may be and if two or more layers of textile are present they be either similar or dissimilar. The textile upper may be impregnated with a superficial amount of block polymer, if so desired, for the purpose of improving abrasion resistance and reducing Water permeability as long as the essential presence of a polychloroprene is applied to the upper at least in the area later contacted by foxing (and preferably also in the combining compound), in conjunction with foxing which comprises essentially the subject class of block copolymers. The term combining compound is used in the shoe trade for the composition which is utilized for laminating one layer of textile to at least a second layer, resulting in a composite textile especially designed for the preparation of textile shoe uppers.

The block copolymers to be used in foxing, and optionally in soling and combining compounds have the general configuration about the same ranges. Two preferred species of such' block copolymers include those having the block configuration polystyrene poly-butadiene-polystyrene and polystyrene-polyisoprene-polystyrene as Well as their hydro; genated counterparts; The hydrogenated counterpart of the second of the above defined block copolymers is of special interest, not only because of its high stability but because of the elastomeric nature ofthe hydrogenated mid-section which resembles that of an ethylene-propylene rubber while the end blocks either remain as polyvinyl arene blocks or; if hydrogenated, become saturated blocks made up of polyvinylcyclohexane units. Thus, the fully hydrogenated preferred species has a block configuration which corresponds closely to polyvinylcyclohexaneethylenepropylene copolymer-polyvinylcyclohexane.

These particuiar block'copoly-mers have the unique feature of attaining the stress-strain properties of an elastomer Without having been subjected to curing or vulcanization. Thus, they are sharply differentiated from other rubbers such at natural rubber, polybutadiene, SBR and the like which require vulcanization in order to attain satisfactory stress-strain properties.

The block copolymers of this invention may be the major polymeric material utilized in the foxing but they may, if preferred be modified by the::presence of other components such as gplasticizers or other polymeric coating materials. Plasticizers such as rubber :extending mineral oils may be employed and polymers such as polystyrene, polyethylene, polypropylene and the like may be incorporated with the block copolymers.

' The compositions which are contemplated for the present purpose especially where canvas top sport shoes are concerned include particularly ;at least foxing compounds which arezcombinations of 100 parts by weight of the subject block copolymers with 15-100 parts by weight of polystyrene. Normally, still further modifications-of such compositions are possible and are utilized for improving the flexibility and reducing the modulus of the compositions if desired as well as for reducing the overall cost. 1 r 1% In the articles contemplated herein and especially in the case of canvas shoe uppers, the combining compound utilized for joining two layers of textile together may be the same or different from the composition utilized for the polychloroprene coating on at least one of the textile layers, namely, adjacent to the foxing strip around the bottom edge of a shoe upper joining the shoe upper with the shoe soling or at least masking said joint.

Gne aspect of the present invention involves-the modification of the above foxing composition with polymer extender oils both for the purpose of reducing the cost of the compositions and more particularly for imparting better processing and physical properties thereto. This' is especially important as the average molecular weight of the block copolymer increases. In some instances, due to the high molecular weights processing becomes extremely difficult at ordinary processing temperature short of decomposition temperatures in the absence of extender'oils. It is preferred that the extender oils be those utilized for extending other polymers and particularly rubbers and that these have no more than about 50% aromatis and greater than about 45% ;of saturates, usually naphthenic types of hydrocarbons.

The extender oils should be utilized in amounts between about 2 and about 300 parts (preferably 5-130 parts) by weight per parts by weight of the block copolymer.

Another important component is a particulate solid, including fillers, mineral extenders, and pigments. These include various carbon blacks, titanium dioxide, calcium carbonate, clays, as well as mineral pigments such as the earth colors, including the iron oxides and the like. Fillers are normally utilized in as large amounts as pos sible while still maintaining desired physical properties; usually this will be an amount between about 25 and 400 parts by Weight per 100 parts by weight of the block copolymer. The compositions of this invention as referred to hereinabove come into play in the incorporation of these particulate solids in that the presence of polystyrene unaccountably and substantially raises the retention of the particulate solids which otherwise may :be loosely held if at all by the block copolymers.

As is usual for elastomer compounds, protection against oxidativedegradation is provided by including in'the composition one or a mixture of several antioxidants in the amount of approximately 1 part by weight per 100 parts by weight of the "block copolymer.

The incorporation of these materials together may take place on the usual polymer processing mills and internal mixers or in an extrusion type of apparatus or may be composited by frneans of other masterbatching processes, particularly a solution masterbatch. In this process a solution of the block copolymer is formed in a solvent which is either a non-solvent or only a partial solvent for polystyrene. Specifically, such a solvent will comprise 21-85% by volume of an open-chain hydrocarbon having from 4-8 carbon atoms per molecule and 79-15% by volume of a cyclic hydrocarbon having from 5-8 carbon atoms per molecule. The polymer solution (cement) so formed is then combined with 5-200 parts by weight of polystyrene and 25-400 'parts by'weight of the finely divided particulate solids per 100 parts by weight of the block copolymer. The mixture is then subjected to coagulating procedure so as to isolate the solid materials from the solvents. This is best effected by forcing the mixture into a vessel containing steam and hot water under such conditions that the solvent is flashed oif and the composition becomes suspended in a bath of water in'the form of crum'bs These are then separated from the water by screening or decantation and subjected to grinding if necessary to effect relatively uniform particle size after which the particles are subjected to drying procedures as in moving belt drier, expander drier or' the like. The use of this particular type of solvent accentuates the effectiveness of the polystyrene'in retaining the finely divided particulate solids. Apparently, the polystyrene exists under these conditions as a gummy highly swollen material which aids in the incorporation of the particulate solids within the body of the block copolymer.

Again referring to sport shoe uppers, the term will include those textiles Well known in the art for this purpose. While they often are cotton canvas exclusively, they may becombinations of cotton with synthetic materials or regenerated cellulose such as rayon, or may comprise at least in part textiles such as nylon and the like. The present invention moreover contemplates the additional presence of interseles, toe stiffeners, heel stiifeners and cloth interlays.

One of the essential features of the present invention comprises the impregnation or coating or both of at least a portion of the textile upper of the present shoe assemblies with a polychloroprene. The area which must be treated with polychloroprene according to the present invention is that area of the textile upper'which is later contacted with the block copolymer foxing strip.

The' polychloroprenes utilized for this purpose have molecular weights in the order of between about 20,000 and 1,000,000 and to predominate in species "having molecular weights between about 50,000 and 250,000.

They may be utilized either in an unvulcanized condition or they may be compounded with vulcanizers and accelerators resulting in a vulcanized polychloroprene area. In the latter case heat for vulcanization is supplied by the injection molding process itself; that is, the polychloroprene coating vulcanizes when it is contacted by the hot block polymer foxing compound. Furthermore, it has been found advantageous if the polychloroprene is to be vulcanized to include at least a portion of the vulcanizing agent in the block copolymer foxing compound, thus ca-using a certain amount of chemical interlinking between the foxing strip and the area of textile treated with polychloroprene. The particularly unexpected feature of the present invention is to find that the treatment of the textile with polychloroprene increases the adhesion of the block copolymer foxing strip even under wet conditions and in spite of the fact that these two polymers are so dissimilar chemically.

The vulcanizing agents utilized for the vulcanization of polychloroprene are well known in the art and include especially zinc oxide and preferably mixtures of zinc oxide with magnesium oxide, although litharge or red lead may be utilized in place or in addition to these materials. Accelerators may be utilized to promote vulcanizing if desired. Advantages of zinc oxide and other non-sulfur-donating vulcanizing agents in this system are that they do not vulcanize the block copolymers herein described. Vulcanization of the block copolymers is not only unnecessary but may be deleterious to physical properties.

The polychloroprene may be modified by the presence of pigments, plasticizers and tackifying resins such as the phenol formaldehyde or coumarone-indene resins. The polychloroprene treatment of the area to be later contacted with the foxing strip should be present in an amount based on the area being so treated of between about 0.002 and 0.02 gram per square centimeter. The polychloroprene may be applied to the textile as a solution, as an aerosol or as an emulsion. -It is preferred to include at least a substantial amount of a chlorinated hydrocarbon solvent in the composition utilized for this purpose since it has been found to promote the adhesion of the foxing strip to the textile due to some, as yet undetermined, modification of physical form of the polychloroprene.

The present invention is enhanced by the utilization of polychloroprene in the combining compounds as well as in the superficial treatment of the area of the upper to be contacted with the foxing strip.

Especially for use in the preparation of canvas uppers for sport shoes, it is particularly contemplated to utilize a combining composition which is used in the form of either a latex or a cement and in such consistency that the combining composition when deposited on one surface of the canvas essentally remains on that surface and does not cause any appreciable amount of strikethrough. This is primarily for appearance purposes, since the outer surface of the canvas or the canvas laminate should appear to be unmodified canvas. The consistency specifically employed for this purpose will depend upon the equipment and working conditions encountered in such application and will be easily adjusted by experts in the art. If solvent compositions are utilized, e.g., cements, then readily volatilized hydrocarbon solvents such as cyclohexane or toluene are especially contemplated to apply the combining paste on one surface of a first textile layer such as by means of a blading application, then applying a second layer on the top side of the combining paste, passing the laminate so formed between heated rolls or at least over a heated surface to compress the laminate and volatilize any solvent or water which may be present therein to result in a laminate of the two textile, e.g., canvas layers. For the purpose of forming shoe uppers, these layers are then cut by any desired means and the edges stitched to prevent raveling In the instance where molded shoe soles are then to be attached to these uppers, the latter are fitted onto suitable forms in an injection molding shoe making machine which is provided with proper spaces and inlets for the injection of the block copolymer utilized in the sole composition, space also being provided in the same machine for the simultaneous formation of a foxing strip around the area of joining the lower part of the canvas upper to the edge of the shoe sole. The treatment of the lower area of the textile upper may take place before or after fitting the uppers on the machine forms. but before application of the foxing strip. The conditions are then adjusted such that the shoe soling and foxing composition is injected in a sufficiently thermoplastic condition to allow flow throughout the cavity provided in the machine for the shoe sole and foxing to form in the proper shape. Under these circumstances, sport shoes are prepared having superior wearing property and also superior resistance to foxing separation.

The degree of wetting which shoes are subjected to will vary. For example, this may be due to rainy weather, to washing the shoes for the purpose of removing soil or dirt. Perspiration or body oils may also create a condition similar to other types of moisture and the like which cause the general condition encountered in Wet peel.

The wet peel strength is usually determined by an Instron tester at 180 to angle pulled at 0.2 inch per minute at 23 C.

The following examples illustrate the results obtained by the use of the present invention.

EXAMPLE I Comparative tests were performed on shoe assemblies with and without a polychloroprene treatment. Canvas sheeting was laminated with a cured SBR combining paste to form a canvas laminate which was cut into the form of tennis shoe uppers. The area which was to be contacted with the foxing strip was treated with a solution comprising 60/40 methyl ethyl ketone/normal hexane containing 8% by weight of a polychloroprene having a relatively high viscosity, a fast crystallization rate and light color. The polychloroprene used was of the type which does not contain sulfur linkages or a thiuram disulfide, as do some commercial grades. Impregnation was 0.0075 g./cm.

The solution also contained suspended 0.75 phr. of accelerator, namely, 2-mercaptoimidazoline and 4 phr. of magnesium oxide. After evaporation of the solvent the treated canvas uppers were fixed on a shoe molding machine form and a compound designed for both soling and foxing injected into the mold. The injection molding conditions consisted of a polymer melt temperature of about 400 F., injection pressure of 250 p.s.i. (gauge), pressure within the mold of p.s.i. (gauge). Injection time was about 3 seconds and the formed shoe assembly was held in the mold for approximately one additional minute to allow the thermoplastic rubber compound to become firm through cooling. The compound used for this latter purpose comprised parts by weight of a block copolymer, parts by weight of a naphthenic mineral rubber extending oil, 30 parts by weight of crystal polystyrene, 85 parts by weight of an inorganic filler, namely, clay and titanium dioxide mixture, and 1 part by weight of antioxidant. The formulation also contained 25 parts by weight of the zinc oxide which acted as a curing agent for the polychloroprene.

In order to test the effectiveness of the polychloroprene treatment, a parallel test shoe assembly was prepared utilizing all of the same conditions and components with the exception of the polychloroprene treatment and the zinc oxide component of the soling and foxing compound. The resulting shoes were tested in the Instron tester under both wet and dry conditions. The shoe assembly having the polychloroprene treatment had a dry peel strength of 13.5 pounds per linear inch and a wet peel strength even higher, namely, 15.0 p.l.i. Contrasted to this, the shoe assembly in which the polychloroprene treatment was omitted had a dry peel strength of 14.7 p.l.i. while its wet peel strength was only 9.0 p.l.i.

The block copolymer used in both shoe assemblies had the structure polystyrene-polybutadiene-polystrene, the block molecular weights being 23,000-41,000-23,000.

EXAMPLE 11 Tests were performed to determine the effect of varying the type of solvent by which the polychloroprene was applied to the canvas uppers insofar as wet peel strength of the block copolymer foxing was concerned. At the same time further comparative tests were made to determine the effect of polychloroprene treatment of the canvas versus no treatment since there was a change in the foxing formulation from that described in Example I. For the present tests, the same canvas laminate was utilized cut into the shape of tennis shoe uppers. Comparative samples were treated with polychloroprene, one by means of a chloroform solution and the other by means of a methyl ethyl ketone/hexane solution. The block copolymer compound described more fully hereinafter was utilized for injection molding of a soling and foxing onto these treated uppers. The wet peel strength of the foxing was found to be 27 pounds per linear inch for the shoe assembly treated with polychloroprene in chloroform solution and compared with 15 pounds per linear inch for the shoe assembly in which the canvas was treated with polychloroprene in methyl ethyl ketone/hexane solution. The comparable shoe assembly was prepared in which the foxing and soling was molded onto the canvas uppers in the absence of any prior treatment with polychloroprene. The wet peel strength in this instance was only 6 p.l.i.

The block copolymer formulation utilized for soling and foxing was as follows:

Parts by weight Block copolymer 100 Naphthenic mineral rubber extending oil 110 Crystal grade polystyrene 60 Mineral filler 90 Zinc oxide, when used 25 Antioxidant 1 EXAMPLE Ill Tests were performed to determine the wet and dry peel strengths of shoe assemblies with and without a polychloroprene treatment as in Example I except that the polychloroprene solution contained 5 phr. of suspended zinc oxide in addition to 0.75 phr. Z-mercaptoimidazoline and 4 phr. of magnesium oxide, and the foxing compound used contained no zinc oxide. In this case a wet peel strength of 14.2 p.l.i. was obtained for the shoe' assembly having the polychloroprene treatment, compared to 7.4 p.l.i. for the untreated shoes. Dry peel strengths were 13.0 p.l.i. for the treated foxing and 10.7 p.l.i. for the untreated foxing.

8 EXAMPLE IV Comparative tests were conducted to determine the wet and dry peel strengths of shoe assemblies with and without a polychloroprene treatment as in Example I except that the curing agents were omitted from the polychloroprene solution and no zinc oxide was in the foxing compound. In this experiment the concentration of polychloroprene in the solution was 12% by weight. Wet peel strengths were 20.5 p.l.i. for the treated shoe assemblies and 6.6 p.l.i. for the untreated shoes. Dry peel strengths were 18.1 p.l.i. for the treated foxing and 10.5 p.l.i. without treatment.

EXAMPLE V Tests were performed to determine the wet and dry peel strengths of shoe assemblies with and without polychloroprene treatment after laundering and drying the fabricated shoes in a household automatic washer and dryer through two separate cycles. The polychloroprene treatment and foxing compounds were essentially the same as those in Example I. The wet and dry peel strengths of polychloroprene-treated shoe assemblies were 16.4 and 15.3 p.l.i., respectively, while those of non-treated shoes were 5.7 and 4.9 p.l.i., respectively, after two complete cycles of washing and drying.

I claim as my invention:

1: In a footwear assembly comprising a textile upper, a polymeric soling and a foxing, the improvement comprising a coating of a chloroprene polymer at least on the area of the upper which is contacted with the foxing, said foxing comprising a block copolymer having the general configuration wherein each A is a polymer block of a monovinyl arene and B is a polymer block of a conjugated diene.

2. A shoe assembly according to claim 1 wherein the textile bears between about 0.002 and about 0.02 gram per square centimeter of polychloroprene in the area of the textile upper contacted by the foxing.

3. A shoe assembly according to claim 1 wherein the textile upper comprises a canvas laminate combined with a combining composition comprising polychloroprene.

4. A shoe assembly according to claim 1 wherein the foxing composition contains a curing agent for polychloroprene.

5. A process of preparing the shoe assembly of claim 1 wherein the polychloroprene is applied to the textile in a chlorinated hydrocarbon solution.

References Cited UNITED STATES PATENTS 3,145,487 8/1964 Cronin 36l4 X 3,217,345 11/1965 Snitzer 36-14 X 3,293,494 12/1966 Fischer 364 3,373,150 3/1968 Pears et al 26092.8

PATRICK D. LAWSON, Primary Examiner