WO2000014284A9

WO2000014284A9 - Antimicrobial footwear and process of manufacture

Info

Publication number: WO2000014284A9
Application number: PCT/US1999/020190
Authority: WO
Inventors: John E Barry; Jeffrey A Trogolo; Lise-Helene Heroux
Original assignee: Healthshield Technologies L L
Priority date: 1998-09-04
Filing date: 1999-09-02
Publication date: 2000-09-08
Also published as: AU6025399A; WO2000014284A1

Abstract

Leather footwear is provided having an inorganic antimicrobial material to attack bacteria and prevent odor. The inorganic material contains an antibiotic metal in particle form, such as antimicrobial zeolite, that is embedded in the leather at least on the surface of the footwear that encases the foot. In a method of manufacturing the leather footwear a solution of antimicrobial solids is prepared and applied to the leather either by soaking the leather in the solution or by topically applying it to one or both surfaces of the leather. The solution of antimicrobial solids can be mixed with a solution for treatment, such as stain resistant coatings, moisture retaining compounds designed to prevent the leather from drying, and water repellent coatings, etc. The leather is dried to embed particles of the antimicrobial into the leather and the footwear is made from the leather with the embedded antimicrobial particles.

Description

ANTIMICROBIAL FOOTWEAR AND PROCESS OF MANUFACTURE

Field of the Invention

This invention relates to footwear having antimicrobial properties

to combat fungus and foot odor and the process of making such footwear.

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 1 2, 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 1 2 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 4,91 1 ,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, 1 80,585; 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 4,91 1 ,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-Al₂θ₃-YSiθ₂-ZH₂O. 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 = 1 1 .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 1 50 m²/g (anhydrous zeolite as standard) and the

SiO₂/AI₂O₃ mol ratio in the zeolite composition is preferably less than 14,

more preferably less than 1 1 . 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 co/i,

Pseudomonas aeruginosa,

Staphylococcus aureυs,

Streptococcus faecal is,

Aspergillus niger, Aureobasiduim pul/ulans,

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.

Claims

WE CLAIM:

1 . Leather footwear incorporating an inorganic antimicrobial

agent.

2. Leather footwear as in claim 1 in which said agent comprises

particles embedded in the leather.

3. Leather footwear as in claim 1 wherein said agent is an

antibiotic metal containing composition that imparts substantial antimicrobial

action.

4. Leather footwear as in claim 3 wherein said antibiotic metal

consists of one or more of the metals selected from the group consisting of

silver, copper, zinc, and gold.

5. Leather footwear as in claim 1 wherein said antibiotic

particles comprise antibiotic zeolite prepared by replacing all or part of the ion-

exchangeable ions in zeolite with an antibiotic metal ion.

6. Leather footwear as in claim 5 wherein said antibiotic metal

ion consists of one or more of the metals selected from the group consisting

of silver, copper, zinc, and gold.

7. Leather footwear as in claim 1 wherein said inorganic

antimicrobial agent is on both surfaces of the footwear.

8. Leather footwear as in claim 1 wherein said inorganic

antimicrobial agent is on only the footwear interior surface.

9. A process of producing leather footwear comprising:

preparing a solution of antimicrobial solids;

applying said solution of antimicrobial solids to the leather;

drying the leather to embed particles of the antimicrobial into the

leather; and

thereafter forming the footwear from the leather with the

embedded antimicrobial particles.

1 0. A process as in claim 9 wherein said solution of

antimicrobial solids is mixed with a solution for treatment of the leather.

1 1 . A process as in claim 1 0 wherein between 0.01 and

20.0% solids antimicrobial solution is added to between 0.01 and 20.0%

solids standard leather treatment solution to result in an antimicrobial

concentration of between 0.01 and 1 0.0% of the solids remaining in the

leather.

1 2. A process as in claim 10 wherein the leather is soaked in a

bath of the mixture of said solution of antimicrobial solids and leather

treatment solution.

1 3. A process as in claim 9 wherein said solution of

antimicrobial solids is topically applied to the leather.

1 4. A process as in claim 1 3 wherein said solution of

antimicrobial solids is topically applied to only one surface of the leather.

1 5. A process as in claim 1 3 wherein said solution of

antimicrobial solids is mixed with a solution for treatment of the leather for

topical application to the leather.

1 6. A process as in claim 1 5 wherein between 0.01 and

20.0% solids antimicrobial solution is added to between 0.01 and 20.0%

solids standard leather treatment solution to result in an antimicrobial

concentration of between 0.01 and 1 0.0% of the solids remaining in the

leather.

1 7. A process as in claim 9 wherein a solution of a material for

treating the leather and the antimicrobial solution are applied separately.

1 8. Leather footwear incorporating an inorganic antimicrobial

agent containing silver cations as an active ingredient.

1 9. Leather footwear as in claim 1 8 in which said agent

comprises particles embedded in the leather.

20. Leather footwear as in claim 1 8 wherein said antimicrobial

agent comprises particles comprising antimicrobial zeolite prepared by

replacing all or part of the ion-exchangeable ions in zeolite with silver cations.

21 . Leather footwear as in claim 1 8 wherein said inorganic

antimicrobial agent is on both surfaces of the footwear.

22. Leather footwear as in claim 1 8 wherein said inorganic

antimicrobial agent is on only the footwear interior surface.

23. A process of producing leather footwear comprising:

preparing a dispersion of antimicrobial inorganic particles

containing silver cations as an active ingredient;

applying said dispersion of said antimicrobial inorganic particles

to the leather;

drying the leather to embed said antimicrobial inorganic particles

in the leather; and thereafter forming the footwear from the leather with the

embedded antimicrobial inorganic particles, whereby said leather has

antimicrobial properties.

24. A process as in claim 23 wherein said dispersion of

antimicrobial particles is mixed with a fluid for treatment of the leather.

25. A process as in claim 24 wherein a dispersion comprising

between 0.01 and 20.0% antimicrobial solids is added to a leather treatment

comprising between 0.01 and 20.0% solids to result in an antimicrobial

concentration of between 0.01 and 1 0.0% of the solids embedded in the

leather after drying.

26. A process as in claim 24 wherein the leather is soaked in a

bath of the mixture of said dispersion of antimicrobial solids and leather

treatment fluid.

27. A process as in claim 23 wherein said dispersion of

antimicrobial solids is applied to the leather.

28. A process as in claim 27 wherein said dispersion of

antimicrobial solids is applied to only one surface of the leather.

29. A process as in claim 27 wherein said dispersion of

antimicrobial solids is mixed with a solution for treatment of the leather for

topical application to the leather.

30. A process as in claim 29 wherein a dispersion comprising

between 0.01 and 20.0% antimicrobial solids is added to a leather treatment

comprising between 0.01 and 20.0% solids to result in an antimicrobial

concentration of between 0.01 and 10.0% of the solids embedded in the

leather after drying.

31 . A process as in claim 23 wherein a solution of a material

for treating the leather and the antimicrobial dispersion are applied separately.

32. The method of claim 23 wherein said dispersion comprises

a substance selected from the group consisting of a waterproofing compound,

a stain resistant coating, polyurethane, a silicone compound, and a moisture

retaining compound.

33. The method of claim 23 wherein said inorganic particles

are ceramic.

34. The method of claim 24 wherein said ceramic particles are

selected from the group consisting of zeolites, hydroxy apatite and zirconium phosphate.