Background of the Invention It is well known that conventional leather footwear presents a problem relative to health and esthetics. Typically, leather is used to make footwear and leather has the disadvantage of being able to harbor fungus and promote the growth of bacteria. This gives rise to problems of diseases, such as athletes foot, and also the promotion of foot odor. While various types of powders and sprays are used to attempt to combat these problems, they are relatively ineffective since they do not have a lasting effect and require an extra step in application. Thus, it would be highly desirable to be able to produce footwear that inherently is free of these problems. That is, the leather footwear should have"built in"antimicrobial properties.

Attempts have previously been made to impart antimicrobial properties to leather. For example, in U. S. Patent 5,586,483 a conveyor type

belt is shown that can be made of leather. The belt has a topical application of an organic antimicrobial agent which is intended to kill bacteria on the belt and prevent contamination of products placed on the belt. This patent has no application to footwear. Also, organic antimicrobial agents have problems and disadvantages, such as, not being long lasting, producing bacteria resistant to antibiotics, releasing toxic vapors and possibly irritating the skin. In U. S.

Patent 3,991,238 leather is treated with an epoxide, a fatty amine, and other constituents to have an antimicrobial finish. U. S. Patent 4,035,146 treats fabrics, including leather, by bonding with an amine, guanido, or quaternary ammonium containing compound. In U. S. Patent 5,709,870 an antimicrobial metal compound containing silver is used in porous articles, paper, leather and porous material. None of these patents are directed to footwear.

Brief Description of the Invention The present invention relates to leather footwear having antimicrobial properties provided by an inorganic antimicrobial agent. In accordance with the invention, the leather is treated with the agent in an amount sufficient to produce the desired antimicrobial action to combat the fungus and bacteria normally found in footwear, typical of which are S. aureus, E. coli, streptococcal strains and C. albicans. Preferred inorganic antimicrobial agents useful for leather footwear include, for example, zeolites containing an ion-exchanged metal selected from the group consisting of Ag, Cu and Zn.

The inorganic antimicrobial agent can be applied to the leather during the time of its treatment in bulk in a solution at the same time finishing materials such as stain resistant coatings, moisture retaining compounds designed to prevent the leather from drying, and water repellent coatings, etc. are applied An alternative is to topically apply the inorganic antimicrobial agent to one or both surfaces of the leather by dipping, spraying or roll coating either after the leather finishing materials have been applied or applied together with such materials.

The inorganic antimicrobial agents of the invention have a number of advantages. Since they are a part of the leather, they are permanent and do not have to be applied a number of times. They are relatively thermally stable, which is necessary in the hot environment of the footwear, and maintain their efficacy over a relatively long period of time.

Also, they have relatively few problems relating to skin sensitivity and do not have the problem of creating resistant strains of bacteria. In addition, the inorganic agents are not volatile and do not degrade into unwanted byproducts.

Objects of the invention It is therefore an object of the invention to provide footwear with antimicrobial properties and a process for making such footwear.

Another object is to provide leather footwear having an inorganic antimicrobial agent to combat fungus and bacteria.

An additional object is to provide leather footwear and a process of manufacture in which the leather is processed in bulk and has an antimicrobial agent applied as part of a material used during the leather finishing treatment or which agent is topically applied to the leather.

Brief Description of the Drawings Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which: Fig. 1 is an elevational view of a typical piece of footwear.

Detailed Description of the Invention Fig. 1 shows a typical piece of footwear 10, here shown as a shoe without laces. The footwear 10 has an upper piece 12, which is of leather, and a sole 14 of any suitable material such as leather or a plastic type material. The footwear 10 is made in a conventional manner with the sole being attached to the upper 12 by stitching. Normally, the outer surface of the upper 12 is processed to have a smoother surface finish than the inner surface of the upper.

The antimicrobial property of the leather footwear can be obtained using various processes. In a first process there is bulk treatment of the leather in a solution containing the inorganic antimicrobial agent. The solution of the antimicrobial is combined with a solution of a composition

used for any conventional finishing treatment of the leather. These include, for example, waterproofing, stain resistant coatings, the application of polyurethane, silicone and moisture retaining compounds (humectants) designed to prevent the leather from drying out. The humectant material is often used because the moisture it absorbs enhances the high-end release and antimicrobial activity of the inorganic antimicrobial agent.

In the process of treating leather in bulk, the inorganic antimicrobial agent in solution form is added to (mixed with) the leather finishing treatment solution in a concentration of from about 100 p. p. m. to about 10.0%. The leather is saturated with the solution in a tank or drum and preferably agitated for a period, such as between 1 and 24 hours. The time is selected to saturate the leather as fully as possible. The wet bulk leather is removed from the tank or drum and is dried in the usual manner, such as air drying at room temperature, drying in the sunlight or under a slightly heated atmosphere or by using standard vacuum drying techniques.

Upon being dried, particles of the inorganic antibiotic remain embedded in the leather. The leather so treated with the inorganic antimicrobial agent is thereafter used to make the shoe in the normal manner.

In a preferred embodiment of the invention, the inorganic antimicrobial solution is prepared by mixing dry antimicrobial powder or pre- dispersed powder in a slurry. The liquid portion of the solution or slurry is water or a solvent that wets the solid inorganic. For example, a 20.0% solids antimicrobial slurry is added to a 10.0% solids standard leather treatment

solution to result in an antimicrobial concentration of 5.0% of the solids remaining in the leather after bulk treatment. Particles of the agent remain embedded in the leather after drying and are present in the footwear interior where the antimicrobial action takes place to kill the bacteria.

As to the inorganic antimicrobial agent, a number of metal ions, which are inorganic materials, have been shown to possess antibiotic activity, including silver, copper, zinc, mercury, tin, lead, bismuth, cadmium, chromium and thallium ions. These antibiotic metal ions are believed to exert their effects by disrupting respiration and electron transport systems upon absorption into bacterial or fungal cells. Antimicrobial metal ions of silver, gold, copper and zinc, in particular, are considered safe even for in vivo use.

Antimicrobial silver ions are particularly useful for in vivo use due to the fact that they are not substantially absorbed into the body. That is, if such materials are used for the antimicrobial leather footwear, they should pose no hazard.

Antibiotic zeolites are preferred. These have been prepared by replacing all or part of the ion-exchangeable ions in zeolite with ammonium ions and antibiotic metal ions, as described in U. S. Patent Nos. 4,938,958 and 4,911,898. Such zeolites have been incorporated in antibiotic resins (as shown in U. S. Patent Nos. 4,938,955 and 4,906,464) and polymer articles (U. S. Patent No. 4,775,585). Polymers including the antibiotic zeolites have been used to make refrigerators, dish washers, rice cookers, plastic film, chopping boards, vacuum bottles, plastic pails, and garbage containers. Other

materials in which antibiotic zeolites have been incorporated include flooring, wall paper, cloth, paint, napkins, plastic automobile parts, catheters, bicycles, pens, toys, sand, and concrete. Examples of such uses are described in US Patents 5,714,445; 5,697,203; 5,562,872; 5,180,585; 5,714,430; and 5,102,401. These applications involve slow release of antibiotic silver from the zeolite particles which is suitable for the leather footwear application.

In another embodiment of the invention, the inorganic antibiotic metal containing composition is an antibiotic metal salt. Such salts include silver acetate, silver benzoate, silver carbonate, silver ionate, silver iodide, silver lactate, silver laureate, silver nitrate, silver oxide, silver palpitate, silver protein, and silver sulfadiazine. Silver nitrate is preferred. These salts are particularly quick acting, as no release from ceramic particles is necessary to impart antimicrobial function.

Antibiotic ceramic particles useful with the present invention include zeolites, hydroxy apatite, zirconium phosphates or other ion-exchange ceramics. Zeolites are preferred, and are described in the preferred embodiments described. Hydroxy apatite particles containing antimicrobial metals are described, e. g., in U. S. Patent No. 5,009,898. Zirconium phosphates containing antimicrobial metals are described, e. g., in U. S. Patent Nos. 5,296,238; 5,441,717; and 5,405,644.

Antibiotic zeolites are well-known and can be prepared for use in the present invention using known methods. These include the antibiotic zeolites disclosed, for example, in U. S. Patent Nos. 4,938,958 and

4,911,898.

Either natural zeolites or synthetic zeolites can be used to make the antibiotic zeolites used in the present invention."Zeolite"is an aluminosilicate having a three dimensional skeletal structure that is represented by the formula: XM2/nO-A1203-YSi02-ZH20. M represents an ion-exchangeable ion, generally a monovalent or divalent metal ion, n represents the atomic valency of the (metal) ion, X and Y represent coefficients of metal oxide and silica respectively, and Z represents the number of water of crystallization. Examples of such zeolites include A-type zeolites, X-type zeolites, Y-type zeolites, T-type zeolites, high-silica zeolites, sodalite, mordenite, analcite, clinoptilolite, chabazite and erionite. The present invention is not restricted to use of these specific zeolites.

The ion-exchange capacities of these zeolites are as follows : A-type zeolite = 7 meq/g; X-type zeolite = 6.4 meq/g; Y-type zeolite = 5 meq/g; T-type zeolite = 3.4 meq/g; sodalite = 11. 5 meq/g; mordenite = 2. 6 meq/g; analcite = 5 meq/g; clinoptilolite = 2.6 meq/g; chabazite = 5 meq/g; and erionite = 3.8 meq/g. These ion-exchange capacities are sufficient for the zeolites to undergo ion-exchange with ammonium and antibiotic metal ions.

The specific surface area of preferred zeolite particles is preferably at least 150 m2/g (anhydrous zeolite as standard) and the SiO2/A1203 mol ratio in the zeolite composition is preferably less than 14, more preferably less than 11.

The antibiotic metal ions used in the antibiotic zeolites should be retained on the zeolite particles through an ion-exchange reaction. Antibiotic metal ions which are adsorbed or attached without an ion-exchange reaction exhibit a decreased bacteriocidal effect and their antibiotic effect is not long- lasting.

In the ion-exchange process, the antibiotic metal ions tend to be converted into their oxides, hydroxides, basic salts etc. either in the micro pores or on the surfaces of the zeolite and also tend to deposit there, particularly when the concentration of metal ions in the vicinity of the zeolite surface is high. Such deposition tends to adversely affect the bactericidal properties of ion-exchanged zeolite.

In an embodiment of the antibiotic zeolites, a relatively low degree of ion exchange is employed to obtain superior bactericidal properties.

It is believed to be required that at least a portion of the zeolite particles retain metal ions having bactericidal properties at ion-exchangeable sites of the zeolite in an amount less than the ion-exchange saturation capacity of the zeolite. In one embodiment, the zeolite employed in the present invention retains antimicrobial metal ions in an amount up to 41 % of the theoretical ion-exchange capacity of the zeolite. Such ion-exchanged zeolite with a relatively low degree of ion-exchange may be prepared by performing ion-exchange using a metal ion solution having a low concentration as compared with solutions conventionally used for ion exchange.

Inorganic antimicrobial materials suitable and preferred for use in

the solution or slurry for application to the leather for the footwear include an ion-exchanged zeolite, this being a ceramic with ion exchange sites having a portion of the sites substituted by at least one kind of an ion exchangeable metal selected from the group consisting of Ag, Cu and Zn. A typical particle size for the agent is between 0.8 and 10 microns. Other inorganic antimicrobial agents, i. e., compounds containing silver, copper, lead, gold, tin, zinc and mercury. can be used. These materials are known to be able to kill many of the types of bacteria that are found in footwear.

In another embodiment of the invention, an inorganic antibiotic solution is topically applied to the surface of the leather by dipping, spraying, roll coating, or some other suitable process. This has an advantage in that only one surface of the leather has to be treated, the surface that would be closest to the foot in the shoe, resulting in a saving of material.

In this process the inorganic antimicrobial solution is applied onto the leather. While application is described as being accomplished by spraying, any of the other application processes previously described can be used. At the same time as the antimicrobial solution is applied, any of the conventional leather finishing treatment solutions also can be applied. That is, there can be a mixture of the antimicrobial agent solution and a finishing material solution.

The mixture can be applied to one or both surfaces of the leather. Usually, the surface of the leather which is to be next to the foot is relatively rough as compared to the exposed surface. This has an advantage in that the rougher surface more readily retains the antimicrobial material.

The sprayed surface, or surfaces, of the leather is permitted to dry in air or under somewhat heated conditions and the solids of the mixture remain on the leather after the water or other carrier evaporates.

In a typical application of this process, the concentration of the antimicrobial material in the mixture is to result in an antimicrobial concentration of between. 01 % and 50%, by weight, of the solids remaining from the total mixture. Here also, the antimicrobial treated leather is processed into the footwear in the normal manner. The action of the inorganic antimicrobial agent is as previously described.

Is also possible to apply the antimicrobial solution to the leather, one or both surfaces, after it has undergone treatment with the finishing solution or solutions.

The antibiotic properties of the antibiotic zeolite particles used may be assayed while in aqueous formulations using conventional assay techniques, including for example determining the minimum growth inhibitory concentration (MIC) with respect to a variety of bacteria, eumycetes and yeast. In such a test, the bacteria listed below may be employed: Bacillus cereus var mycoides, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus faecalis, Aspergillus niger,

Aureobasiduim pullulans, Chaetomium globosum, Gliocladium virens, Penicillum funiculosum, Candida albicans, and Saccharomyces cerevisiae.

The assay for determining MIC can be carried out by smearing a solution containing bacteria for inoculation onto a plate culture medium to which a test sample of the encapsulated antibiotic zeolite particles is added in a particular concentration, followed by incubation and culturing of the plate.

The MIC is defined as a minimum concentration thereof required for inhibiting the growth of each bacteria.

Safety and biocompatibility tests were conducted on the antibiotic zeolites employed in the invention. ISO 10993-1 procedures were employed. The following results were obtained:

Cytotoxicity: Non-Toxic Acute Systemic Toxicity: Non-Toxic Intracutaneous Toxicity: Passed Skin Irritation Test: Non-Irritant Chronic Toxicity: No Observable Effect In-vitro Hemolysis : Non-Hemolytic 30-day Muscle Implant Test: Passed 60-day Muscle Implant Test: Passed 90-day Muscle Implant Test: Passed Ames Mutagenicity Test: Passed Pyrogenicity: Non-Pyrogenic Thus, the antibiotic zeolites are exceptionally suitable under relevant toxicity and biocompatibility standards for use in the leather footwear for the intended purposes.

In use, the antimicrobial action for the footwear is substantially permanent relative to the useful life of the footwear. That is, the antimicrobial effect of the agent that remains on the interior surface of the leather adjacent the foot has continued efficacy at all times. Further, since the foot warms the environment within the shoe, the action of the inorganic antimicrobial agent is more effective.

Specific features of the invention are shown in one or more of the drawings for convenience only, as each feature may be combined with other features in accordance with the invention. Alternative embodiments will be recognized by those skilled in the art and are intended to be included within the scope of the claims.