"Auto-adhesive"as used herein is intended to mean an adhesive that bonds to itself or to a substrate and unwinds from itself and from the substrate without much effort.

BACKGROUND OF THE INVENTION The adhesive compositions of this invention are designed for cohesive elastic conforming bandages. Such bandages adhere to themselves, but not to skin, hair or clothes. Auto-adhesive bandages are used for dressing retention and are easy to apply especially on difficult parts of the body. They are also used for fixation of padding material, cannulae and tubes, and for light compression and support bandages, and for application to the skin to protect wounds from contamination thereby reducing the danger of infection and guarding against further injury.

Natural rubber latex provides adhesive compositions with excellent auto-adhesion and non-residue properties, but the problem of allergic reaction to proteins in these natural rubber latex persists.

It is known in the prior art to reduce the protein content of natural rubber latex. Several methods to remove these proteins are utilised including, for example, leaching, however the most efficient method is by enzyme treatment as it removes both water soluble and combined proteins. Prior art examples of protein removal include complexing the proteins of natural rubber latex with e. g. ion exchange resins and thereafter separating the resulting protein-resin complex from the latex (as described

in US Pat. No. 5, 563, 241), or by incubating the latex with a proteolytic enzyme in the presence of a combination of surfactants and then washing with water to remove both the protein combined with rubber molecules and the water-soluble proteins (as described by Shinichi Nakade"Progress in Prevention : Developments Achieved in Low-Allergen NR Products"paper presented at"Latex Protein Allergy"Conference, Amsterdam, Netherlands. 19 February 1996).

Other prior art methods of reducing the allergic affect of proteins in natural rubber latex, such as that exemplified by U. S. Pat no. 5776484, rely on forming a barrier layer to prevent or minimise contact between the skin and the latex or by bonding the protein in natural rubber latex to a material, such as a copolymer, and thereby lessening the ability of the protein to be transported to the skin.

Although it is known to use low protein natural rubber latex in rubber products such as gloves to reduce the allergic affect of proteins, the use of such latex in auto-adhesives has heretofore not been considered viable due to the belief that they would impart poor auto-adhesion properties to such adhesives.

The drive and motivation as described in the prior art has been towards the continued use of protein-containing natural rubber latex in adhesive compositions combined with a means of preventing or minimising the transfer of proteins from the adhesive composition to the skin by utilising physical barriers or restraints. This ensures the adhesive continues to obtain the benefits of auto-adhesion and elasticity known to be provided by protein-containing natural rubber latex.

It is to the prior-art problem of providing adhesives containing natural rubber latex whilst retaining the desired properties of auto adhesion and peel strength that the present invention is specifically directed.

SUMMARY OF THE INVENTION

It has now been discovered that auto-adhesive dressings made from specific blends of a low protein natural rubber latex and one or more polymers possess good adhesion and non-residue properties.

According to the present invention, adhesives are made of specific blends of low protein natural rubber latex in combination with at least one polymer. Proportions of these components may vary according to the requirements of the specific end products but in order to achieve the desired results of the present invention, at least 90 percent by weight of the low protein natural rubber latex and at least 1 percent by weight of the polymer are necessary in the adhesive. The low protein natural rubber latex is preferably present from 90 to 99 percent by weight, more preferably from 90 to 97 percent by weight, and the polymer is preferably present from 1 to 10 percent by weight, more preferably from 3 to 10 percent by weight.

The adhesives of this invention are useful to prepare medical adhesive articles such as surgical bandages, athletic tapes, wound dressings and the like. These adhesives may be coated onto any backing suitable for medical uses including occlusive (substantially non-breathable) and non-occlusive backings (breathable). Occlusive backings are also known as low porosity backings. Non limiting examples of occlusive backings include films, foams and laminates thereof. Non limiting examples of non- occlusive backings include woven substrates, non woven substrates or melt blown webs, foams and thermally embossed non woven substrates.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides adhesive compositions comprising low-protein natural rubber latex and at least one polymer. More particularly, the low-protein natural rubber latex content of the adhesive is at least 90 percent by weight, preferably from 90 to 99 percent by weight, more preferably from 90 to 97 percent by weight and the polymer is present in at least 1 percent by weight, preferably from 1 to 10 percent by weight, more preferably from 3 to 10 percent by weight.

The term"natural rubber latex"as used in this invention is the naturally occurring form of rubber, i. e., cis-1, 4-polyisoprene. Amongst its natural sources is included the sap of the Havea brasiliensis rubber tree. Natural rubber latex also comprises 1-2% proteins and it is known that some individuals are allergic to these proteins.

It is known to remove proteins from natural rubber latex, for example through incubation with a proteolytic enzyme in the presence of surfactants followed by washing with water. This results in the removal of rubber proteins and water-soluble proteins. The colloidal properties of the deproteinised natural rubber latex are maintained by addition of appropriate surfactants. However, once the proteins have been removed the intrinsic properties of natural rubber latex are modified. Such modification effectively reduces auto-adhesion and elasticity.

Deproteinised natural rubber latex is known and used to lessen the allergic effects of e. g. surgical gloves and similar rubber products. However, it has not heretofore been known that such latex could be used in combination with polymers of this invention to provide adhesives having desirable properties.

The adhesive composition of this invention comprises deproteinised natural rubber latex and at least one polymer. The adhesive is applied to a bandage to provide good auto-adhesion, low or no residue skin adhesion after peeling, good viscosity during production and good peel coating weight. This invention provides the first adhesive product comprising deproteinised natural rubber latex having the above properties.

For the purpose of this invention,"polymer"refers to a homopolymer, a copolymer or an adhesive polymer as well as any mixtures or blends of one or more homopolymers, and/or one or more copolymers, and/or one or more adhesive polymers.

"Copolymer"refers to a polymeric material produced by the polymerisation of two or more dissimilar monomers, either with or without another functional group grafted thereto, as well as to a homopolymer with a functional group grafted thereto. Thus, the term"copolymer" includes, without limitation, random copolymers, block copolymers, sequential copolymers, and graft copolymers. Typical monomers include, but are not limited to, hydroxyl substituted

C1 to C12 esters of acrylic and methacrylic acids, vinyl esters (vinyl acetate and vinyl propionate), vinyl ethers, fumarates, maleates, styrene, acrylonitrile.

"Adhesive polymer"refers to a polymer that is inherently adhesive, or has been rendered adhesive by combining additives and/or modifiers with the polymer.

Examples of suitable additives and/or modifiers include, without limitation, tackifiers, plasticisers, stabilisers, cross-linking agents, and combinations thereof.

Typical polymers include, without limitation, for example, polyolefins, non-elastomeric polyesters, non-elastomeric polyamides, cellulosic derived polymers, vinyl acetates, acrylates, vinyl chlorides and polyvinyl alcohols. Examples of trade name polymers suitable for use in the present invention include without limitation : Vinamul 62118 : a dextrine stabilised vinyl acetate-dibutyl maleate copolymer available from Vinamul ; Vinamul 6152 : a vinyl acetate-dibutyl maleate available from Vinamul ; Airflex 920 : a carboxylated Vinyl Acetate-Ethylene copolymer available from Air Product ; Duroset 78-6964 E250 : a ethylene/vinyl acetate copolymer available from National Starch and Chemical Company ; Vinnapas LL8647 : a mixture of copolymers of vinyl-acetate, acrylic acid ester and ethylene available from Wacker ; Luphen D200A : a polyurethane elastomer available from BASF ; Aquastick 1120 : a chloroprene and methacrylic acid copolymer available from DuPont Dow Elastomers ; Synthomer VL10533 : a carboxylated butadiene methyl methacrylate copolymer latex from available from Synthomer ; Revacryl 239 : a styrene/acrylic ester copolymer dispersion available from Harlow Chemical Company.

Other ingredients may be employed as desired and may include, for example, stabilisers, tackifiers, antioxidants, fibrous fillers, non-fibrous fillers, humectants, colorants, and deodorants or fragrances.

A typical stabiliser that may be utilised in the mix to form the compositions of the present invention includes, for example the trade name product, Nopco S. This is a highly sulphated fatty acid used in rubber industry to stabilise lattices during compounding, storage and application and is available from Henkel. Other stabilisers may include Dapro DF 900 from KRAHN CHEMIE GmbH and Byk-033 from BYK-CHEMIE GmbH.

Typical antioxidants and/or metal transition ion scavengers that may be utilised in the mix to form the compositions of the present invention includes, for example hindered phenols, amines, and sulfur and phosphorous hydroxide decomposers. A list of common antioxidants is given in McCutcheon's Functional Materials (1991), pp 13-18.

A suitable antioxidant is available under the trade name product, Dispersion 2074M from Vita Liquid Polymers, this is an aqueous dispersion of Zinc Dibutyl Dithiocarbamate.

The preparation according to the invention may also include a humectant. Suitable humectants include glycerin, sorbitol, polyethylene glycol, propylene glycol, and other polyhydric alcohols.

A suitable humectant is available under the trade name Polyethylene glycol 200 from ICI Surfactant-this is also called polyoxyethylene glycol Defoaming agents may be used in the mix. The most common defoamers are given in McCutcheon's Functional Materials (1991), pgs. 89-112. Typical defoamers include aluminium stearate, amyl alcohol, caprillic alcohol, capryl alcohol, castor oil, corn oil, decyl alcohol, diethylene glycol monolaurate, glyceryl monostearate, mineral oil, pine oil, polyalkyl glycol, silicone oils, stearic acid, sulfonic acid salts, tributyl citrate and, tributyl phosphate. A suitable defoamer is available from Henkel under the trade name product Dehydran 1620. This is a blend of modified fatty alcools and a polysiloxane The above additives and other components such as the cure activators, pH control agents, and silicone oils employed in the latex formulations of the present invention may be present in the range of from 2 percent by weight to 9 percent by weight of the latex.

The adhesive compositions of the invention may be prepared by mixing the latex and polymer, and any other desired ingredients, e. g. tackifiers, antioxidants, fillers etc. in any convenient way (e. g. in a Sigma mixer). The mixing can be carried out in a liquid

medium which is a solvent for some or all of the ingredients, or which is an aqueous medium. Each of the ingredients can be added to the mixture as a solid, or as a molten liquid, or as a solution, mulsion or dispersion, as appropriate. The resulting liquid mixture, i. e. solution, emulsion or dispersion in a liquid carrier, can be applied, if desired after further dilution, to the backing in conventional fashion, e. g. by spraying, painting, dipping or rolling.

EXAMPLES The following adhesive composition was prepared in accordance with the present invention. Ingredient Percentage by wt. KDP150 93. 25% Dehydran 1620 0. 30% Nopco S 0. 20% Dispersion 2074M 0. 80% Potassium hydroxide 0. 10% Revacryl 239 3. 00% PEG 200 1. 00% Water 1. 35% 1. KDP 150 is an highly deproteinised Natural Rubber Latex available from Kao Corporation under this trade name.

2. Revacryl 239 is a hard styrene/acrylic ester copolymer available from Harlow Chemical Company under this trade name.

3. Dehydran 1620 is a blend of modified fatty alcools and a polysiloxane available from Henkel under this trade name.

4. Nopco S. is a highly sutphated fatty and is available from Henkel under this trade name.

5. Dispersion 2074M is an aqueous dispersion of Zinc Dibutyl Dithiocarbamate available from Vita Liquid Polymers under this trade name.

This adhesive composition had a density of 0. 95 ; a solids content of 59 to 62% ; a pH of 9. 5 to 10. 5 ; and a viscosity in the range 80 to 130 cps.

The following Examples are based on the above formulation but with differing amounts (by. Weight) of KDP 150 and/or Revacryl 239, or by replacing KDP 150 with LATZ Latex at the stated level (LATZ Latex is a low-ammonia protein-containing natural rubber latex available from Lewis and Peat under this trade name), or by replacing Revacryl 239 with another suitable polymer at the stated level.

Tpeel (ASTM D1876-61T) refers to the force required to separate the adhesive to adhesive bond using paper strips that are 1 inch wide, 12 inches long and 3011m coated with the adhesive. The specimens are bonded over 9 inches. They are tested on an Instron tensometer 5 min after bonding. The paper strips are peeled apart and the force to do so recorded. Higher Tpeel force means higher transfer from one side of the paper strip to the other. Adhesives having Tpeel values between 2 and 4 N/25mm indicate acceptable tack levels and auto-adhesive properties.

The term"transfer"means auto-adhesion is higher than the adhesion between the adhesive and the paper.

Adhesion to skin was measured as follows : tape samples 1 inch wide by 3 inches long were placed on the skin of a human subject using a predetermined constant pressure. The tape was removed and a subjective evaluation of adhesion and residual tack was made and rated as :

0 no adhesion to skin.

1 to 2 good adhesion ; no tack.

3 good adhesion ; tack. Example Percent Percent by Viscosity Solids pH Tpeel Tpeel Adhesion by wt wt. 2/20/23 Coating force/wth to Skin Latex Polymer after 2w Weight N/25mm 1 93.251 3.002 144 59. 7 9. 7 7.5 2.52 1 2 94. 25' 2. 00 133 60. 6 10. 2 8 3.23 1 3 95.251 1.002 107 61 9.9 7.5 2.61 1 4 91.751 4.502 152 61.5 10.1 9.5 2.10 1 5 90.251 6.002 222 60 9.8 7.5 2.83 1 6 93. 25' 3. 00 94 61. 8 9. 9 8 3. 20 1 7 93. 25' 3. 00" 99 58. 8 10. 3 8 3. 19 1 8 93. 25' 3. 00 240 54. 7 9. 9 7.5 3.52 2 9 93.251 3.006 155 59. 5 9. 8 6.5 2.99 1.5 10 93.251 3.007 252 59.6 9.9 6 3.66 1.5 11 93. 25' 3. 00 73 56. 5 10. 1 7. 5 3. 38 1 12 93. 25' 3. 00 104 59. 5 10.1 8 3.33 1 13 93. 25' 3. 00"'98 60 10. 2 6 2. 72 1. 5 14 90.0511 4.502 144 61.2 9.7 8.5 4.67 3 15 86.251 10.002 212 50.7 9.5 7 0.59 0 16 76.251 20.002 585 59.2 9.4 11.5 5. 70 3 17 70.001 26.252 632 58.6 9.4 7.5 5. 59 3

'= KDP 150 Duroset 78-6964 2= Revacryl 239 8= Luphen D200A 3= Vinamul 62118 9=Vinamul 6152 4 = Aquastick 1120'° = Synthomer VL10533 5= Vinnapas LL8647 11= LATZ Latex 6= Airflex 920 Examples 1 to 13 were formulated according to the teachings of the present invention.

All of these formulations show Tpeel values between 2 and 4 N/25mm and have good skin adhesion with no residual tack.

In comparative Example 14, KDP 150 (highly deproteinised natural rubber latex) was substituted by a protein-containing natural rubber latex. This formulation has a high Tpeel force and shows residual tack on skin.

Comparative Example 15 contains polymer and highly derproteinised latex according to the invention, but the latex is present at level less than the claimed amount. This formulation has very low Tpeel force and shows no adhesion on skin.

Comparative Example 16 contains latex and polymer according to this invention, but both are present at levels outside their claimed amounts. This formulation shows very high Tpeel force and shows residual tack on skin.

From the above Examples it is clearly seen that the key amount of low-protein natural rubber latex is 90 to 97 percent by weight and the key amount by weight of polymer is 1 to 6 percent by weight.