ADHESIVE COMPOSITIONS

Abstract: A medical adhesive product is provided having a conformable backing layer and on one surface thereof a layer of an adhesive comprising an acrylate polymer containing residues of an alkyl acrylate or methacrylate in which the alkyl portion contains from 12 to 20 carbon atoms. The adhesive has no significant tack at 25 DEG C and sufficient tack at skin temperature to adhere to the skin and the product may have a moisture transmission rate of at least 350 gm m<-2> 24 hrs<-1> at 37 DEG C and at a relative humidity difference of from 100 to 10 %.

Description: ADHESIVE COMPOSITIONS The present invention relates to adhesive which are capable of adhering to oily skin and adhesive dressings which comprise such adhesives. Favoured adhesives of this invention have low tack at below skin temperature and higher tack at skin temperatures. Traditionally, the adhesives used on adhesive dressings have been made of a natural or synthetic rubber and a tackifying resin or liquid which renders the rubber pressure sensitive adhesive. In recent years, however, synthetic polymers, such as acrylic polymers, have become available which are inherently pressure sensitive adhesive and which therefore do not require a tackifying additive. Acrylic pressure sensitive adhesives are now widely used on adhesive dressings. The conventional acrylic pressure sensitive adhesives used on adhesive dressings have been found to adhere well to relative clean dry skin. Such acrylic presssure sensitive adhesives, however, which typically comprise a copolymer which contains residues of alkyl acrylates or methacrylate in which the alkyl groups have an average of less than 10 carbon atoms, have relatively poor or no adhesion to skin contaminated with an oily substance such as paraffin. There are, however, many situations for example during the treatment of a wound such as an ulcer or burn with a paraffin tulle gras or during the application of an oiled skin graft to a donor site when the skin surrounding a wound may be become contaminated with an oily substance. It would therefore be advantageous to have adhesive dressings which are capable of adhering to oily skin as well as to clean dry skin. Acrylic adhesives which have no or low tack at below skin temperature and higher tack at skin temperature have improved handling and performance characteristics. A significant advantage for such adhesives would be for them to have a relatively high moisture vapour transmission rate (HVTR) when used at thicknesses normally employed on adhesive dressings. A skin temperature activated adhesive had now been found which has a usefully high HVTR. Heat activated adhesive compositions have been proposed which are substantially non-tacky at room temperature eg. about 20 β C and which become tacky at elevated temperatures. In US Patent No. 4880683, there is disclosed an acrylic polymer based composition for use as a electric current conductor which is substantially non-tacky at 20°C and in which the acrylic polymer has Tg or weight-averaged Tg of from -10°C to 80°C. In order to activate the adhesive the composition has to be heated to temperatures at least as high as 50°C above the Tg point. The present invention now provides adhesive compositions and dressing formed therefrom which can be applied to oily skin and dressings in which the adhesive becomes tacky at skin temperatures. The present invention accordingly provides a medical adhesive product having a conformable backing layer and on one surface thereof a layer of an adhesive comprising an acrylate polymer containing residues of an alkyl acrylate or methacrylate in which the alkyl portion contains from 12 to 20 carbon atoms. In an embodiment of the invention there is provided a medical adhesive product which comprises a substrate coated on one surface with an adhesive wherein such adhesive has no significant take at 25°C and sufficient tack at skin temperature to adhere to the skin and wherein such product has a moisture vapour transmission rate of at least 350 g m -2 24 hours-1 at 37°C at 100-10% relative humidity difference. Skin temperature is normally in the range 28°C-35°C and the adhesive products of this invention will exhibit sufficient tack to adhere to the skin at skin temperatures whilst exhibiting no significant tack at ambient temperature (i.e. 25°C or less). As used herein "no significant tack" means that the adhesive in products of the invention wil have little or no tendancy to stick to themselves at ambient temperature. However when applied to the skin the tack will be sufficient to adhere to the skin within thirty seconds of being applied. Another embodiment of the present invention provides an adhesive product comprising a backing layer and on at least a portion of one surface thereof a layer of adhesive which adhesive comprises a copolymer which contains at least 80% by weight of (A) alkyl acrylate or methacrylate residues in which the alkyl group has 12 to 20 carbon atoms and (B) alkyl acrylate or methacrylate residues in which the alkyl group has less than 12 and more than 3 carbon atoms and the alkyl groups in the (A) and (B) residues have an average of 13 to 17 carbon atoms. The substrate or backing layer of the invention can be any of the substrates used on conventional adhesive dressings. The substrate of the invention will suitably comprise a woven or knitted material, a non-woven material, a foam or a continuous or non-continuous filmic materials. More suitably the substrate will comprise a continuous filmic material with a relatively high moisture vapour permeability. The adhesive dressing will normally comprise a layer of pressure sensitive adhesive composition of the invention on at least one side of a backing layer. The backing layer and adhesive layers, however, can form part of a composite adhesive dressing such as the adhesive dressings described in European Patent Application No. 0107915 and 0147119 the disclosure of which is herein incorporated by reference. The adhesive layer of the adhesive dressing can 2 suitably have a weight per unit area of 20 to 80g/m , more suitably have a weight per unit area of 20 to 2 45g/m and can preferably have a weight per unit area 2 of 25 to 35g/m . The adhesive layer can be a continuous or discontinuous layer for example a porous layer such as a microporous layer or pattern spread layer. Suitable continuous and apertured flexible films include those disclosed in hereinbefore mentioned European Patent Application Nos. 0107915 and 0147119. The continuous films for use as a substrate in the invention can suitably have a thickness of at least lOμm, more suitably of at least 20 / /m preferably of at least 25μm. The continuous films for use as a substrate in the invention can suitably have a thickness not exceeding 250/m, aptly less than 50,vm, suitably not exceeding 160/m, more suitably less than 40 / /m and preferably not exceeding 35 / /m, for example 30 m. Continuous flexible films for the backing layer include both moisture vapour permeable and relatively moisture vapour impermeable films. Preferred are continuous moisture vapour permeable films and in particular those films which have a moisture vapour 2 transmission rate (MVTR) of at least 500g/m /24 hours at 37°C at 100% to 10% relative humidity difference when in contact with moisture vapour (hereinafter referred to GSM), more suitably at least 1000GSM. Preferably such backing films have an MVTR of at least 2000GSM, more preferably at least 3000GSM. Such moisture vapour permeable continuous films can advantageously render the adhesive dressing of the invention permeable to moisture vapour but impermeable to liquid and bacteria. Aptly the MVTR of the dressing will be at least 500GSM and more aptly at least 550GSM. Apt moisture vapour permeable continuous films include polyether polyester thermoplastic copolymers (for example HYTREL manufactured by the Shell Chemical Company); polyether polyamides (for example PEBAX manufactured by ATO Chem) and polyurethanes (for example ESTANE manufactured by Goodrich Chemicals). Aptly such films will comprise polyalkylene oxide blocks such as a polyethyleneoxide or polypropyleneoxide blocks. Favoured moisture vapour permeable continuous films comprise polyurethane. Suitable polyurethanes include hydrophilic water absorbing polyurethanes such as those disclosed in European Patent Application Nos. 0107915 and 0147119, linear polyether and linear polyester polyurethanes such as those known as Estane (available from Goodrich Chemicals) and blends of polyurethane with an incompatible polymer such as those disclosed in European Patent Application No. 0046071. An apt film for use in the invention is a 25 m V - 8 - thick film of a polyether-polyurethane known as Estane 4714F which film has moisture vapour transmission rate of approximately 1800 GSM. The moisture vapour transmission rate (MVTR) of both the backing films and dressings may be measured by the Payne Cup method. This method uses a cup 1.5cm deep which has a flanged top. The inner diameter of 2 the flange provides an area of 10cm of material through which moisture vapour may pass. In this method 10ml of distilled water is added to the cup and a sample of the material under test, large enough to completely cover the flange, is clamped over the cup. When the test material has an adhesive surface it is clamped with the adhesive surface facing into the cup. The complete assembly is then weighed and placed in a fan assisted electric oven where the temperature and relative humidity are maintained at 37 β C and 10% respectively. The relative humidity within the oven is maintained at 10% by placing 1 Kg of anhydrous 3-8 mesh calcium chloride on the floor of the oven. After a suitable period of time, for example 17 hours, the cup is removed from the oven and allowed to cool for 20 minutes to reach room temperature. After reweighing the mass of water lost by vapour transmission is calculated. The moisture vapour permeability is -2 -1 expressed in unit of gm m 24hr at 37°C, 100% to 10% relative humidity difference, that is it is the mass of water transmitted through a square meter of material in a 24 hour period when maintained at 37°C and there are differences of relative humidity at the two surfaces of the material of 100% inside the cup and 10% outside. This is the moisture vapour transmission rate when the film or dressing is in contact with moisture vapour. The moisture vapour transmission rate when the adhesive is in contact with water may be measured using the same apparatus. When the cup is place in the oven the cup is inverted so that liquid water (and not moisture vapour) is in contact with the test material. Favoured relatively moisture vapour impermeable continuous films for use in the invention include films of 1,2-polybutadiene such as those known as RB 810, RB 820 and RB 830 available from Japan Synthetic Rubber Company and films of styrene-butadiene block copolymers including styrene-butadiene-styrene block copolymers such as those known as Kraton or Cariflex available from Shell Chemicals. An apt continuous film of 1,2 polybutadiene for use in the invention is a 150 / -/m thick film of RB 830. An apt continuous film of styrene-butadiene-styrene copolymer is a 30 m thick film of Kraton 1101. Suitable apertured films for use in the invention include films containing perforations or slits and plastic nets. Favoured apertured films containing perforations or slits include those disclosed in European Patent Application No. 0107915 and 0147119. Apt apertured films containing slits which comprise 1,2 polybutadiene or styrene-butadiene styrene-copolymer are disclosed in Examples 2 and 7 of European Patent Application No. 0147119. Favoured plastics net for use in the invention are high density polyethylene-polystyrene blend nets disclosed in British Patent No. 1531715. An apt net of 2 this type which has a weight per unit area of 42g/m is known as net 909 X510S available from Smith & Nephew Plastics Limited. The pressure sensitive adhesive may comprise a copolymer which contains at least 80% by weight of (A) alkyl acrylate or methacrylate residues in which the alkyl group has 12 to 20 carbon atoms and (B) alkyl acrylate or methacrylate residues in which the alkyl group has less than 12 and more than 3 carbon atoms and - li ¬ the alkyl groups in the (A) and (B) residues have an average of 13 to 17 carbon atoms. The adhesive copolymer of the invention thus contain residues of alkyl acrylate or methacrylate in which the alkyl groups have a higher average number of carbon atoms than that of conventional acrylic adhesives which it is believed renders the adhesive compositions of the invention more tolerant to oily substances such as paraffin and therefore also capable of adhering to oily skin. The adhesive compositions of the invention also exhibit good adhesion to clean dry skin. A preferred group of these copolymers also have the desirable property of being of higher tack at skin temperature and of lower tack at lower temperatures. The residues (A) can suitably be residues of an alkyl acrylate or methacrylate which has a straight or branched chain alkyl group containing 16 to 20 carbon atoms or a mixture of two or more of such alkyl acrylate or methacrylates. (A) can favourably be residues of a straight or branched chain alkyl group containing 16 to 18 carbon atoms such as cetyl methyacrylate or preferably stearyl methacrylate or mixtures thereof. The residues (B) can be residues of an alkyl acrylate or methacrylate which has a straight or branched chain alkyl group containing suitably 4 to 11 carbon atoms, favourably 6 to 10 carbon atoms and preferably 8 carbon atoms of which 2-ethyl hexyl acrylate is the most preferred. Certain favoured copolymers of the adhesive composition of the invention thus comprise residues of stearyl methacrylate and 2-ethyl hexyl acrylateε. The proportion of (A) residues in the copolymer will advantageously be sufficient to render the adhesive composition adherent to oily skin. Providing that the average number of carbon atoms in the alkyl groups of the (A) and (B) residues is 13 to 17 it is believed that the (A) residues can suitably be at least 30% by weight of the copolymer, can favourably be at least 45% by weight and can preferably be at least 50% by weight of the copolymer. The ratio of (A) to (B) residues in the copolymer can be adapted to provide the adhesive composition with adequate pressure sensitive adhesive properties. Such ratios, however, will depend on the chosen (A) and (B) residues. The ratio of residues of stearyl methacrylate to residues of 2-ethyl hexyl acrylate in favoured adhesive copolymers which are tacky over a wide temperature range can suitably be 1:1 to 6:1 and can preferably be 1:1 to 4:1. The copolymer of the adhesive composition of the invention will comprise at least 80% by weight of (A) and (B) residues, desirably at least 85% by weight and preferably at least 90% by weight of (A) and (B) residues. The copolymer, however, can optionally comprise constituents which modify the physical properties of the adhesive. For example the copolymer may contain residues of monomers which modify the adhesive properties, such as the cohesive strength of the adhesive composition and/or to crosslink the copolymer. Suitable monomers for modifying the cohesive strength of the adhesive composition include acrylic acid, methacrylic acid, acrylamide, ethyl acrylate and methyl methacrylate. Favoured monomers are acrylic acid, acrylamide and methyl methacrylate. Copolymers of the adhesive composition of the invention can suitably comprise upto 10% by weight of acrylic acid residues and can preferably comprise 2% to 8% for example 6% by weight of acrylic acid residues. Copolymers of the adhesive composition of the invention can suitably comprise upto 10% by weight of acrylamide residues and can preferably comprise 2% to 85 by for example 2% or 6% by weight of acrylamide residues. Copolymers of the adhesive composition of the invention can suitably comprise upto 20% by weight of methyl methacylate residues and can preferably comprise 10% to 15% by weight of methyl methacrylate residues. An apt copolymer for use in the adhesive composition of the invention comprises residues of stearyl methacrylate (47% by weight), 2-ethyl hexyl acrylate (47% by weight) and acrylic acid (6% by weight) . The adhesive will suitably comprise 50-96% of residues (X), 1-40% of residues (Y) and 1-10% of residues (Z) wherein (X), is an alkyl acrylate or methacrylate wherein the alkyl portion contains 12-20 carbon atoms (Y) is a hydrophilic acrylate or . methacrylate ester and (Z) is a polar acrylate or methacrylate residue. Such adhesives form an important aspect of this invention. The polar acrylate or methacrylate residues may be the acid or an amide thereof or the like. Most suitably Z is acrylic acid or methacrylic acid. Preferably Z is acrylic acid. Generally the total number of different monomers residues X and Y is not more than 4, more suitably not more than 3 and preferably not more than 2. This helps maintain sufficient regularity in the polymer for waxy properties (that is low tack) to be achieved at ambient temperature (eg. at 20°C). The adhesives employed may be any which has little or no tack at temperture below skin temperature but which have higher tack at skin temperature and which are significantly permeable to water vapour (by which is meant that a 25// layer of the adhesive will have a MVTR of at least 400 gm -2 24 hrs -1 at 37°C at 100-10% relative humidity difference). The residues (X) are more aptly present in excess of 60%. It is desirable that the alkyl components in X contain 12 to 20 carbon atoms, for example cetyl, lauryl, stearyl or the like residues. The residues (X) can be suitably residues of an alkyl acrylate or methacrylate or combinations thereof whch have a straight or branched chain. Suitably the alkyl group contains 16 to 20 carbon atoms. The residues (X) can favourably be residues of a straight chain alkyl group containing 16-18 carbon atoms such as cetyl methacrylate. The residues (X) preferably contain straight chain alkyl groups of 18 carbon atoms for example stearyl methacrylate. The residues (Y) can be residues of a hydrophilic acrylate or methacrylte ester. The residues (Y) will suitably be an alkyl acrylate or methacrylate substituted by one or more hydrophilic groups such as ether groups, amide group, hydroxyl groups, dialkyl amine groups and the like. Aptly the residues (Y) will contain one or more alkoxy groups, for example ether groups. Aptly the residues (Y) will contain an alkoxy group containing 1-4 carbon atoms. Aptly the alkoxy group will be carried by an alkyl group of 1-6 carbon atoms. Apt alkoxy groups include methoxy, ethoxy, n-propoxy and n-butoxy groups. Apt alkyl groups substituted by such alkyoxy groups include ethyl, n-propyl, n-butyl, isobutyl, sec-butyl and the like. Other apt residues (Y) will contain a number of -(CH-CH-O)- residues, for example capped polyethylenoxide acrylates or methacrylates such as their monomethyl ethers such as the monomethyl ether of PEG 1000 acrylate. Particularly apt adhesives will contain 1 - 40% of residues (Y). Certain favoured adhesives will contain 20 - 32% of residues (Y). Certain preferred adhesives will contain 26-30% of residues (Y), for example 28%. Certain preferred adhesives employed in this invention will comprise 60-70% of residues (X) and 4 - 10% of residues (Z). In such compositions residue Z is preferably the residue of acrylic acid. In such compositions the residues (X) are aptly residues of 2 or 3 different monomers and are most aptly residues of 2 different monomers, for example a stearyl acrylate or methacrylate and a lauryl acrylte or methacrylate. One favoured adhesive of ths invention comprises Stearyl Methacrylate (66%) Butoxyethyl Acrylate (28%) Acrylic Acid (6%). A further favoured adhesive of this invention comprises Stearyl Methacrylate (66%) Ethyoxyethyl Methacrylate (28%) Acrylic Acid. A particularly preferred adhesive formulation employed in this invention comprises the residues of stearyl methacrylate (66%), 3 methoxylbutylacrylate (28%) and acrylic acid (6%). The relative proportions of residues (X), (Y) and (Z) will determine the temperature activated properties of the pressure sensitive adhesive. The adhesive compositions of the invention can optionally comprise in addition to the copolymer for example fillers or medicaments such as topically effective medicaments which includes chlorhexidine and its salts, cetrimide and silver sulphadiazine. The medical adhesive product of the invention will normally comprise a layer of the skin temperature activated pressure sensitive adhesive on at least one side of substrate. The adhesive layer can be applied to the substrate by an convenient method for example by direct or transfer coating. The adhesive layer will suitably have a weight _2 per unit area of at least lOgm , more suitably at _2 least 20gm-2 and preferably at least 25gm . The pressure sensitive adhesive layer will suitably have a _2 weight per unit area not exceeding 50 gm , more _2 suitably not exceeding 40 gm and preferably not exceeding 35 gm -2, for example 30gm-2 The adhesive layer should suitably have low or no tack at a temperature of less than 20°C, more suitably it should have low or no tack at a temperature of less than 22°C and preferably it should have low or no tack at a temperature of less than 25°C. More preferably it should have low or no tack at a temperature of less than 28°C. At temperatures above 29°C the adhesive layer should preferably have higher tack thereby assuming the properties of a pressure sensitive adhesive at skin temperature which is normally in the range 29-35°C. The copolymers employed for the adhesives used in the invention can be formed by any suitable acrylate monomer polymerisation process including solvent, emulsion and bulk polymerisation process. The copolymers, however, can conveniently be formed by polymerising in a suitable solvent such as ethyl acetate, a mixture of the appropriate alkyl acrylate or methacrylate monomers and optionally other monomers in the presence of a free radical catalyst such as bis (4-tertiary butyl cyclohexyl) peroxy-dicarbonate (BCHPC) available from Laporte Industries. In the solvent polymerisation process the monomer in liquid form and a solution of the catalyst are preferably slowly added to the solvent, heated is reflux, in a suitable container over a period of 4 to 10 hours. further amounts of solvent can be added during this period to maintain the polymerisation mixture in a viscous state but non gelled state. The resultant solution of the copolymer can then be diluted if necessary with a further solvent such as SBP2 petroleum spirit to obtain a solution of the adhesive composition suitable for coating onto a backing layer. Solid monomers such stearyl methacrylate can be rendered liquid by heating for example to approximately 25°C before being added to the polymerisation mixture. The stearyl methacrylate monomer, however, can conveniently be part of a liquid mixture of monomers. An apt mixture of this type is known as stearyl methacrylate 17.4 available from Rohm GmbH. Stearyl methacrylate 17.4 is a mixture of stearyl methacrylate (50% by wt); cetyl methacrylate (24% by wt), myristyl methacrylate (8.3% by wt) and other alkyl methacrylates (17.7% by wt) in which the averge number of carbon atoms in the alkyl groups is 16. Adhesive sheets for forming the adhesive dressings of the invention can be prepared by coating the adhesive composition onto a suitable backing layer using a convention coating technique and then if necessary drying the coated adhesive layer. The adhesive composition, can be coated for example from solution directly onto the backing layer or preferably can be first coated onto a release sheet such as release coated paper or film and then transferred, when dried to the backing layer by laminating the layers under pressure and if necessary heat. The adhesive coated backing layer can then be converted into adhesive dressings of the invention in a conventional mannner. In one particularly desirable aspect this invention provides an adhesive which is tacky at skin temperature but which is less tacky and preferably non-tacky at lower temperatures. This results in adhesive products employing the adhesive being easier to handle than prior products employing adhesives which are always tacky. Aptly the adhesives and dressings of the present invention had little or no tack at room temperature eg. about 20°C, but will readily adhere to skin at skin temperature. This property is particularly useful for large area products such as surgical incise drapes which can be notoriously difficult to apply because of difficulties of the adhesive face accidently touching itself and causing the drape to stick together in a way which is difficult and sometimes impossible to reverse. The adhesive dressings of the invention can advantageously be used in the form of wound dressings and may be moved and positioned at an appropriate location on the body before they warm to body temperature and become tacky. Whereupon, the application of slight pressure will cause the dressing to finally adhere to the body. One class of copolymer utilised in the present invention comprise 60 - 96% of residues (X), 0 - 30% of residues (Y) and 0 - 10% of residues (Z) wherein (X) is an alkyl acrylate or methacrylate wherein the alkyl portion contains 12 - 20 carbon atoms, (Y) is an alkyl acrylate or methyacrylate wherein the alkyl portion contains 1 to 11 carbon atoms, (Z) is polar acrylate or methacrylate residue; and wherein the average number of carbon atoms present in (X) and (Y) is at least 12. The polar acrylate or methacrylate residues may be the acid or an amide thereof or the like. Most suitably Z is acrylic acid or methacrylate acid. Preferably Z is acrylic acid. Generally the number of different monomers residues X and Y is not more than 4, more suitably not more than 3 and preferably not more than 2. This helps maintain sufficient regularity in the polymer for waxy properties (that is low tack) to be achieved at ambient temperature (eg. at about 20°C). The residues (X) are more aptly present in excess of 65%. Favourably the residues (X) are unbranched. It is desirably that the alkyl components in X contain 14 to 18 carbon atoms, for example cetyl, lauryl, stearyl or the like residues. The comments hereinbefore regarding component (A) may be consulted. The residues (Y) are as hereinbefore referred to in consideration of residues (B). Particularly apt polymers will contain 0 - 15% of residues (Y). Certain favoured polymers will contain 0 - 10% of residues (Y) . Certain preferred polymers will contain 0% of residues (Y). Thus certain preferred polymers of this invention will comprise 90 - 96% of residues (X) and 4 - 10% of residues (Z). In such compositions residue Z is preferably the residue of acrylic acid. In such compositions the residues (X) are aptly residues of 2 or 3 different monomers and are most aptly residues of 2 different monomers, for example a stearyl acrylate or methacrylate and a lauryl acrylate or methacrylate. A particularly preferred polymer of this invention comprises the residues of stearyl methacrylate (47%), lauryl methacrylate (47%) and acrylic acid (60%). The adhesive dressings of the invention can be wound dressing which include first aid dressings, dressing strips, burns dressings, ulcer dressings, dressing for graft donor sites and dressings for treating medical and surgical wounds including exuding wounds. The adhesive dressings of the present invention may also be employed as surgical incise drapes and also for use in ostomy application for attaching medical devices to intact skin. For use as a surgical drape the area of the product of the invention can be any suitable size for application to the body. For use as a surgical drape such areas could be for example, 84cm x 56cm, 45cm x 55cm, 45cm x 28cm, 30cm x 28cm or 15cm x 20cm. A surgical drape as previously described can be applied to the skin by any suitable method. Particularly favoured forms of presentation are those described in European Patent Specification Nos. 161865 and 341045 which are herein incorporate by reference. For use as a surgical drape the product of the invention can be applied without wrinkles, folds and channels being formed. The heat insulation provided by surgeons gloves allow the drapes or dressings coated with the waxy polymer to be handled easily allowing unhurried and methodical attachment by means of a gentle smoothing action. Contact with the skin for a few seconds allows the polymer to melt and assume the properties of the pressure sensitive adhesive which adheres to the skin in the normal way. This property of the device of the invention offers particular advantages for large surgical drapes which are notoriously difficult to handle. It also offers economical advantages in that it reduces waste caused by application failure. For use as a surgical dressing the area of the product could be, for example, 15cm x 10cm, 10cm x 10cm. For use as a catheter retention dressing the area of the product of the invention could be, for example, 5cm x 7cm. Such dressings can be applied to the skin by any suitable method. Particularly favoured forms of presentation are those described for surgical drapes. In a further embodiment the product of the invention can be a first-aid dressing of any suitable size or form for such dressings. For example, as a strip, as a fingertip dressing, as an anchor dressing or as an eye occlusion patch. Sizes of such products could be for example 3.8cm x 2.2cm, 7.5cm x 3.7cm or 7.5cm x 5cm. In a further embodiment the product of the invention can be a medical tape in the form of a roll of varying width and length for example from 1.25cm x 10cm to 30cm x 10cm. In a further embodiment the product of the invention can be a product for ostomy care in the form of an adhesive face place attached to which would be a gasket and the ostomy pouch. In a further embodiment the product of the invention can be a product for incontinence care in the form of an adhesive face plate to which the incontinence such as a urine collection sheath could then be attached. The resultant product can be provided on a bacteria proof pouch and sterilised by a convenient method such as gamma irradiation or ethylene oxide. In a further embodiment of the invention, the adhesive composition described hereinbefore can be used as a coating on a medical adhesive product. Such medical adhesive product would comprise a substrate composite comprising a substrate of that described hereinbefore coated with a pressure sensitive adhesive on one face of the substrate and a coating on the pressure sensitive adhesive of an adhesive as described hereinbefore. Suitable pressure sensitive adhesives for use in this embodiment of the invention include any of those normally employed in medical adhesive products. Examples of suitable pressure sensitive adhesives include vinyl ether and acrylic adhesives. More suitably the pressure sensitive adhesive should comprise an acrylic copolymer emulsion such as described in European Patent Application No. 194881 which is herein incorporated by reference. Most suitably the pressure sensitive adhesive will comprise an acrylic ester copolymer as described in European Patent No. 35399 which is herein incorporated by reference. The pressure sensitive adhesive layer in this embodiment of the invention will suitably have a weight _2 per unit area of at least 10 gm , more suitably at least 20 gm -2 and preferably at least 22 gm-2. The pressure sensitive adhesive layer in this embodiment of the invention will suitably have a weight per unit area _2 of not exceeding 50 gm , more suitably not exceeding 35 gm -2 and preferably not exceeding 30 gm-2, for _2 example 25 gm The coating will suitably have a weight per unit area of at least 1 gm -2, more suitably at least 3 gm-2 _2 and preferably at least 4 gm . The coating will suitably have a weight per unit area not exceeding 20 gm -2, more suitably not exceeding 10 gm-2 and _2 preferably not exceeding 8 gm , for example 5, 6 or 7 _2 gm . The thickness and continuity of the coating for the pressure sensitive adhesive layer should be sufficient to block the pressure sensitive adhesive layer at below skin temperature whilst simultaneously being of sufficient thickness to exhibit its pressure sensitive adhesive properties within a few seconds of being applied to the skin. The adhesive dressings of the invention, which comprise an adhesive composition which is capable of adhering to oils skin can advantageously be used in situations where the skin surrounding the wound is likely to be contaminated with an oily substance such as paraffin. Such situations can occur for example when a wound area such as a burn or ulcer is treated with a paraffin tulle gras, paraffin based ointment or an oiled donor skin graft before the adhesive dressing is applied over the wound. The invention will now be illustrated by reference to the following examples. Example 1 A mixture of stearyl methacrylate (46.4g) 2-ethyhexyl acrylate (46.4g) and acrylic acid (7.2g) monomers and a solution of catalyst BCHPC (0.2g) in ethyl acetate (lOOg) was slowly added by means of dropper funnels to ethyl acetate (50g) heated under reflux (80°C) in a resin flask over a period of approximately 6 hours. Further ethyl acetate (50g) was added to the mixture during the polymerisation to maintain the mixture in a viscous by ungelled state. The resultant solution contained 33% by weight of the copolymer. The alkyl groups of the residues in the copolymer had an average of 13 carbon atoms. Example 2 A solution (25% by weight) of an adhesive copolymer of the invention was made in the same manner as example 1 using the following ingredients: Stearyl methacrylate 17.4 82.3g 2-ethyl hexyl acrylate 11.7g Acrylic acid 6g BCHPC catalyst 0.2g Ethyl acetate 200g Petroleum Spirit (SBP2) lOOg The petroleum spirit was used to dilute the solution of copolymer after the polymerisation process had been completed. The alkyl groups of the monomer residues in the copolymer had an average of 15 carbon atoms. Example 3 A solution of (28.5% by wt) of an adhesive copolymer of the invention was made in the same manner as Example 2 using the following ingredients: Stearyl methacrylate 17.4 47g 2-ethyl hexyl acrylate 47g Acylamide 6g Ethyl acetate 200g Petroleum Spirit (SBP2) 50g In this example the monomer mixture was added to the flask as a warmed (50°C) solution in ethyl acetate (50g). The alkyl groups of the monomer residues in the copolymer had an average of 13 carbon atoms. Example 4 A solution (25% by wt) of an adhesive copolymer of the invention was made in the same manner as Example 3 using the following ingredients: Stearyl methacrylate 17.4 86g 2-ethyl hexyl acrylate 12g Acylamide 2g Ethyl acetate 200g Petroleum Spirit (SBP2) lOOg In this example all the monomer solution was added to the flask at the start of the polymerisation reaction. The petroleum spirit was added to the polymerisation mixture before the reaction was complete to prevent gelation. The alkyl groups of the monomer residues in the copolymer had an average of 15 carbon atoms. Adhesive dressings The adhesive copolymer solutions of Examples 1 to 4 were individually coated onto plastics net (reference net 909 X510S - Smith & Nephew Plastics Limited) to form adhesive dressing strips of the invention. In the coating process the adhesive copolymer solution was first coated on a release paper, dried in an oven to 2 give a coating weight of 30g/m and then transferred to the plastics net by laminating the coated paper to the plastics net. The coated net was then cut into adhesive dressing strips (75mm long, 25mm wide). Performance Test The adhesive dressing strips so formed an similar comparison adhesive dressing strips comprising the plastics net coated with a convention acylic pressure 2 sensitive adhesive (30g/m ) were adhered to dry clean and oily skin (skin contaminated with paraffin) on the back of volunteers hands and the adhesion of these dressing strips to such skin subjectively assessed. The conventional acrylic pressure sensitive adhesive used in the comparison adhesive dressing strips was a copolymer of 2-ethyl hexyl acrylate (47% by wt) butyl acrylate (47% by wt) and acrylic acid (6% by wt) prepared according to Example 2 of European Patent Application No. 81300847.1 published as No. 0035399. The results showed that adhesive dressing strips of Examples 1 to 4 which are coated with a pressure sensitive adhesive composition of the invention exhibited fairly good to good adhesion to both clean and dry skin and to oily skin whereas the comparison adhesive strip which is coated with a conventional acrylic pressure sensitive adhesive composition exhibited good adhesion to clean dry skin but only poor or no adhesion to oily skin. Example 5 A polymer was prepared by the method of Example 1 employing a stearyl methacrylate (65.8g), 2-ethylhexyl ac-rylate (28.2g) and acrylic acid (6g). The resulting adhesive was applied to a polyurethane film (30gsm of Estane 1417) at a weight per unit area of 30gsm. The adhesive was pressure sensitive at 27°C but not at 20% which enabled dressings (10 x 10cm and 20 x 40 cm) made from the coated film to be applied easily to the skin. Examples 6 - 11 The following adhesives were prepared by the method of Example 1: Each of the adhesive may be used to provide dressings as described in Example 5. The adhesive of Example 6 was particularly good exhibiting no significant tack at about 20°C but showing good pressure sensitive adhesive properties at 30°C. Surgical drapes made as described in Example 5 employing the polymer of Example 6 was able to be applied without wrinkling, folds or channel being formed. The heat insulation provided by surgeon's gloves allow the drapes coated with the waxy polymer be handled easily allowing unhurried and methodical attachment by means of a gentle smoothing action. Contact with the skin for a few seconds allowed melting of the polymer which then assumes pressure sensitive adhesive properties which adhere to the skin in the normal way. Example 12 A mixture of stearyl methacrylate (65.8g) 3 methoxybutylacrylate (28.2g) and acrylic acid (6g) monomers and a solution of catalyst BCHPC (0.2g) in ethyl acetate (lOOg) was slowly added by means of dropper funnels to ethyl acetate (50g) heated under reflux (80°C) in a resin flask over a period of approximately 6 hours. Further ethyl acetate (50g) was added to the mixture during the polymerisation to maintain the mixture in a viscous by ungelled state. The resultant solution contained 24% by weight of the copolymer. The adhesive prepared according to Example 1 was _2 applied at a weight per unit area of 30 gm to a _2 polyurethane film (30 gm Estane 5714F). The adhesive was found to be non-tacky at 20°C but tacky at 28°C. The MVTR of the completed product is approximately 600 gm -2 24 hrs-1 Example 13 The adhesive prepared according to Example 12 was _2 applied at a weight per unit area of 7 gm to a _2 polyurethane film (30 gm of Estane 5714F) which had previously been coated on one surface with an acrylate ester copolymer pressure sensitive adhesive (PSA ) at a _2 weight per unit area 30 gm . The coating of the adhesive was applied to the layer of the film which contained the coating of the acrylate ester copolymer PSA. The adhesive coating was found to be pressure sensitive at 28°C which enabled dressings (10cm x 10cm) or drapes (20cm x 40cm) made from the coated film to be applied easily to the skin without wrinking or folding. The MVTR of the completed product was found to be 677 gm "2 24 hrs "1 . The heat insulation provided by surgeons' gloves allow the drapes to be coated with the waxy polymer to be handled easily allowing unhurried and methodical attachment by means of a gentle smoothing action. Contact with the skin for a few seconds allowed melting of the polymer which then assumes pressure sensitive adhesive properties which adhere to the skin the normal way. Example 14 and 15 Examples 12 and 13 were repeated but the adhesive was prepared by substituting ethyl acetate for acetone in the same proportions. The reflux temperature was 60°C and was carried out for approximately 12 hours.

Claims: CLAIMS 1. A medical adhesive product having a conformable backing layer and on one surface thereof a layer of an adhesive comprising an acrylate polymer containing residues of an alkyl acrylate or methacrylate in which the alkyl portion contains from 12 to 20 carbon atoms. 2. A product as claimed in claim 1 in which the adhesive is tacky at skin temperature but less tacky a temperatures lower than skin temperature. 3. A medical adhesive product which comprises a substrate coated on one surface with an adhesive wherein such adhesive has no significant tack at 25°C and sufficient tack at skin temperature to adhere to the skin and wherein such product has a moisture transmission rate of at least 350gm m —2 24hrε—1 at 37° and at a relative humidity difference of from 100 to 10%. 4. An adhesive product comprising a backing layer having on at least a portion of one surface thereof a layer of adhesive which adhesive comprises a copolymer which contains at least 80% by weight of residues derived from (A) an alkyl acrylate or methacrylate in which the alkyl group has 12 to 20 carbon atoms and (B an alkyl acrylate or methacrylate in which the alkyl group has less than 12 and more than 3 carbon atoms and wherein the average number of carbon atoms in the alkyl groups of the (A) and (B) residues is from 13 to 17 carbon atoms. 5. A product as claimed in any of claims 1 to 4 in which the adhesive comprises 50-96% of residues (X), 1-40% of residues (Y) and 1-10% of residues (Z) wherein (X) is an alkyl acrylate or methacrylate in which the alkyl portion contains 12-20 carbon atoms, (Y) is a hydrophilic acrylate or methacrylate ester and (2) is a polar acrylate or methacrylate residue. 6. A product as claimed in any one of claims 1 or 5 in the form of a wound dressing, surgical incise drape or an ostomy product. 7. A product as claimed in any one of claims 1 to 6 in which the backing layer is a moisture vapour transmitting continuous film. 8. A product as claimed in any one of claims 1 to 6 in which the backing layer is on an apertured film. 9. A product as claimed in any one of claims 1 to 8 in which the adhesive is a discontinuous layer. 10. A product as claimed in claim 9 in which the adhesive layer is a porous, microporous or pattern spread layer. 11. A product as claimed in any one of claims 1 to 10 having a moisture transmission rate of at least 550 gm m 2 24hr-1 at 37°C and at a relative humidity of from 1( to 100°C when in contact with moisture vapour. 12. A product as claimed in any one of claims 1 to 11 wherein the adhesive is moisture vapour transmitting. 13. A product as claimed in claim 12 wherein the adhesive has a moisture vapour transmission rate of at least 500 gm m -2 24hr-l at 37°C and at a relative humidity difference of from 100 to 10%. 14. A product as claimed in any one of claims 1 to 13 wh rein the adhesive has substantially no tack at temperatures of less than 28°C. 15. A product as claimed in any one of claims 1 to 14 in which the adhesive comprises a copolymer derived from residues of stearyl methacrylate and 2-ethyl hexyl acrylate. 16. A dressing as claimed in claim 15 in which the ratio of residues of stearyl methacrylate to those of 2-ethyl hexyl acrylates is from 1 to 6:1. 17. A product as claimed in any one of claims 1 to 16 wherein said copolymer comprises residues derived from acrylic acid, methacrylic acid, acrylamide, ethyl acrylate or methyl methacrylate. 18. A product as claimed in any one of claims 5 to 17 in which the (Y) residues contain an alkoxy group having 1 to 4 carbon atoms. 19. A product as claimed in claim 18 wherein the (Y) residues comprise a alkoxy substituted alkyl group in which the alkyl group contain 1 to 6 carbon atoms. 20. A product as claimed in any one claims 1 to 19 comprising about 66% stearyl methacrylate, about 28% 3-methoxylbutyl acrylate and about 6% acrylic acid. 21. A product as claimed in any one of claims 1 to 20 in which the adhesive comprises 60 to 90% of residues of an alkyl acrylate or methacrylate wherein the alkyl portion contains 12 to 20 carbon atoms, 0-30% by weight of residues of an alkyl acrylate or methacrylate wherein the alkyl proportion contains from 1 to 11 carbon atoms and upto 10% of residues of a polar acrylate or methacrylate wherein the average number of carbon atoms in the alkyl groups of the C., ,., alkyl acrylates or methacrylates and C 12 _ 20 alkyl acrylates or methacrylates is at least 12. 22. A product as claimed in any one of claims 1 to 21 wherein the adhesive further comprises a topically effective medicament.

Inventors: PECK ROGER FRANCIS, PECK, ROGER, FRANCIS
Applicants: SMITH & NEPHEW, SMITH & NEPHEW PLC
Application year: 1991
Main classification: C09J133
IPC codes: A61L15, A61L24, A61L26, C09J7, C09J133