EMULSION POLYMERS

Abstract: Emulsion adhesive polymers which comprise residues of acrylic monomers containing 80 to 98.5% by weight of residues of alkyl esters of acrylic or methacrylic acid in which the alkyl group contains from 3 to 12 carbon atoms, from 0.1 to 20% by weight of residues of monoesters of methacrylic acid and 0.1 to 5% by weight of residues of a compound of the formula (I). in which R, is a C₁₀ - C₁₄ alkyl radical and M is hydrogen, ammonia or an alkali metal, are described. Preferred emul­ sion adhesives are pressure sensitive adhesives which are suitable for application to the skin and may be used in surgical or medical dressings. A process for preparing the emulsion adhesive polymers is also described.

Description: EMULSION POLYMERS The present invention relates to emulsion polymer adhesives and more particularly to emulsion polyacrylate adhesives which are suitable for application to the skin, and to methods of manufacturing the same. It is known in the art to form polymers by emulsion polymerisation. Such processes are preferred because they avoid the use of solvents which may be environmentally undesirable. The emulsion polymerisation process employs a surfactant to form a stable emulsion of monomers and other ingredients and to prevent coagulation of the polymer emulsion after it has formed. Conventionally a nonpolymerisable surfactant is used. However, the residual surfactant in the polymer can be extracted by water and so renders the polymer sensitive to water. To avoid this problem the use of polymerisable surfactants has been proposed. For example, British Patent No. 1,430,136 discloses emulsion polymerised polymers as industrial adhesives suitable for use on masking tapes and lists copolymerisable surfactants suitable for this purpose. British Patent No. 1,220,476 discloses inter alia copolymerisable surfactants having the general formula: EMI2.1 in which m is an integer from 2 to 4, n is an integer 1 or 2, R is a C1 -C22 alkyl radical and Y is -S(02)OM where X is hydrogen, ammonia or an alkali metal. Such.surfactants may be employed in emulsion polymerisation reactions with other vinylic compounds to prepare emulsion polymers which are useful as coatings on substrates such as textiles or plastics to provide antistatic properties or as dye assistants. I have now found that by employing copolymerisable surfactants selected from the above group and having the formula: EMI2.2 in which Riis a C10 to C14 alkyl radical and M is hydrogen, ammonia or an alkali metal, in emulsion polymerisation reactions with one or more copolymerisable acrylic monomers then emulsion polymers are obtained which have adhesive properties and are suitable for application to the skin. Accordingly the present invention provides an emulsion adhesive polymer comprising residues of one or more acrylic monomers and residues of a compound of the formula (I) EMI3.1 in which RXis a C10 - C14 alkyl radical and M is hydrogen, ammonia or an alkali metal. Compounds of formula. (I) will form stable emulsions with acrylic monomers and will prevent coagulation of any such emulsions during an emulsion polymerisation process. The residues of compound (I) form part of the polymer formed by the process. The polymer produced by the emulsion polymerisation reaction will be an adhesive polymer, that is an acrylic adhesive polymer. Adhesive polymers of this type may be pressure sensitive adhesive polymers. Such pressure sensitive adhesives may be used on skin, for example in surgical or medical dressings. in order to maintain good adhesion to skin it is especially desirable that such adhesives are not water sensitive (in that water does not significantly affect their adhesive properties). Neither of the aforementioned British Patents disclose pressure sensitive adhesives for use on skin, for example in surgical or medical dressings. Aptly compounds of formula (I) will be in the form of an ammonia or alkali metal salt and more suitably will be in the form of the sodium or potassium salt. In a preferred form the compound of formula (I) will be in the form of the sodium salt. Suitably the alkyl radical will contain from 10 to 14 carbon atoms and more suitably will contain from 11 to 13 carbon atoms and preferably will be an alkyl radical which contains 12 carbon atoms. In the preparation of preferred adhesive polymers, therefore, in the compound of formula (I) Rlis an alkyl radical containing 12 carbon atoms and M is sodium, that is the preferred compound is sodium mono-lauryl itaconoxypropane . sulphonate. The emulsion adhesive polymer of Che invention may suitably contain 0.1 to 5% by weight and preferably 0.1 to 1% by weight of residues of a compound of formula (I) or a salt thereof. In apt polymers of the invention the acrylic polymer component consists mainly of acrylic residues for which the monomer is an alkyl ester of acrylic or methacrylic acid, in which the residue contains 2 to 20 carbon atoms. Favoured pressure sensitive adhesive forming alkyl acrylate monomers are alkyl esters of acrylic acid in which the alkyl group contains 3 to 12 carbon atoms and preferably 4 to 9 carbon atoms. Alkyl acrylates of this type include n-butyl acrylate, 2-ethylhexyl acrylate and other octyl acrylates. Favourable monomers include n-butyl acrylate and 2-ethylhexyl acrylate. Aptly these acrylic residues will be derived from a mixture of two monomer species in roughly equal proportions and the acrylic residues may form from 95 to 99.9% by weight of the polymer. However, the adhesive polymers of the invention may advantageously contain residues of other acrylic monomers as hereinafter described. In these instances the acrylic residues may form 80 to 98.5% by weight of the polymer and preferably will form from 88 to 94X by weight of the polymer. The pressure sensitive adhesive polymers of the present invention may advantageously contain residues of other acrylic monomers. Suitable monomers include acrylic esters comprising monoesters such as optionally hydroxylated or alkoxylated alkyl esters of acrylic or methacrylic acid. Preferred other acrylic monomers are monoesters of methacrylic acid selected from the group consisting of lower alkyl, hydroxylated or alkoxylated alkyl esters, for example methyl methacrylate, n-butyl methacrylate, hydroxyethyl methacrylate and methoxyethyl methacrylate. Preferred monomers include hydroxyethyl methacrylate, methyl methacrylate and n-butyl methacrylate. Also suitable but not preferred are esters such as glycidyl methacrylate. Such residues may form 0.1 to 20% by weight of the polymerr and more suitably up to 12% by weight and preferably from 5 to 12% by weight of the polymer. The most apt proportion of such residues will depend to some extent on the particular monomer species, the monomer species of the major components, the emulsion polymerisation conditions and the desired physical properties of the pressure sensitive adhesives. Thus hydroxyethyl methacrylate residues may be present from 0.3 to 5% by weight of the polymer and lower alkyl methacrylate residues may be present as 1 to 15% by weight of the polymer. In one aspect therefore the present invention provides an emulsion adhesive polymer comprising residues of acrylic monomers from 80 to 98.5% by weight of residues of an alkyl ester of acrylic or methacrylic acid in which the alkyl group contains from 3 to 12 carbon atoms, 0.1 to 20% by weight of residues of a monoester of methacrylic acid and 0.1 to 5% by weight of residues of a compound of formula (C). A suitable pressure sensitive adhesive polymer comprises 36 to 50% by weight of n-butyl acrylate residues, 39 to 59% by weight of 2-ethyl hexyl acrylate residues, 1 to 15 by weight of lower alkyl methacrylate residues, 0.3 to 5% by weight of hydroxyethyl methacrylate residues and 0.1 to 5% by weight of residues of a compound of formula (I). Lower alkyl when used herein means an alkyl radical containing from 1 to 6 carbon atoms. A favoured pressure sensitive adhesive polymer comprises 39 to 45% by weight of n-butyl acrylate residues, 47 to 49.5% by weight of 2-ethyl hexyl acrylate residues, 5 to 10% by weight of lower alkyl methacrylate residues, 0.8 to 3% by weight of hydroxyethyl methacrylate residues and 0.1 to 1% by weight of residues of a compound of formula (I). A preferred pressure sensitive adhesive polymer comprises 44.5% by weight of n-butyl acrylate residues, 49.5% by weight of 2-ethyl hexyl acrylate residues, 5% by weight of n-butyl acrylate residues, 1% by weight of hydroxyethyl methacrylate residues and 0.2% by weight of sodium mono-lauryl itaconoxypropane sulphate. The pressure sensitive adhesives of the invention can be used for adhesive surgical and medical dressings and therefore adhesive surgical and medical dressings employing an adhesive of this invention are an important aspect of this invention. The adhesive of the invention may therefore be coated onto any of the well known backing materials which find use in the medical or surgical fields. Thus the backing may be, for example, a conventional non-woven fabric, woven fabric knit, paper or synthetic film backing. Favoured backings include porous polyvinyl chloride film,polyurethane film, integral nets and the like. Suitable backing materials for moisture vapour permeable adhesive dressings are disclosed in British Patent No. 1280631 and in European Application 50935 and backings which permit passage of tissue or wound exudate there through include non-woven fabrics, woven fabrics, knits, nets and apertured films. The backing material may be of any desr-ed shape to provide adhesive coated sheet materials as adhesive tapes, strips, wound dressings, surgical drapes or the like. The emulsion pressure-sensitive adhesive polymer may be applied to the backing by conventional methods, for example by coating an aqueous dispersion of the emulsion which has been suitably thickened onto a silicone-coated release paper, drying the adhesive and transfer coating onto the appropriate backing material. The compound of formula (I) may be formed by the processes described in British Patent No. 1220476 which is incorporated herein by cross-reference. The preferred copolymerisable surfactant, sodium mono-lauryl itaconoxypropane sulphonate may be prepared in a similar manner to that described in Example 1 of British Patent No. 1220476. The adhesive polymers of the invention can be prepared by a process which comprises polymerising as an emulsion one or more acrylic monomers and a compound of formula (I) as herein before described in the presence of a free radical catalyst. The emulsion may conveniently be made by initially forming an aqueous solution containing the surfactant and a heavy metal chelating agent. If present one of the minor monomers may be added to this solution, for example hydroxyethyl methacrylate may be in this solution. The remaining monomers may be premixed and added to the aqueous solution gradually over a period of from 15 minutes to 1 hour while the aqueous mixture is being stirred at highshear. The resulting emulsion may be left to deaerate. The resulting monomer emulsion typically has a solids content in the range of 15 to 70% by weight and preferably 50 to 60; by weight The resulting monomer emulsion may then be added to an aqueous solution of free radical catalyst, for example ammonium persulphate, and polymerisation effected by heating, typically at 800 to 950C, under an inert atmosphere such as nitrogen or carbon dioxide. Advantageously, the monomer emulsion may be added to the catalyst solution over a period of time during the polymerisation reaction. The resultant polymer emulsion may be cooled and stored until required. The polyacrylate adhesive emulsions of the invention prior to use may be thickened using a conventional poly acrylate thickener, for example Primal ASE 60 (Trade Mark) neutralised with ammonium hydroxide. The adhesive can be coated onto a suitable substrate by a direct or transfer coating process using conventional coating techniques. EXAMPIJE 1 Preparation of Emulsion.Polyacrylate Adhesive Water (65g) was placed in an open-topped beaker. The head of a Silverson mixer with a high shear head was introduced into the water and the water mixed during the addition of sodium tripolyphosphate (0.02g), sodium mono-lauryl itaconoxy propane sulphonate (0.17g) and hydroxy ethyl methacrylate (0.85g). A separate mixture of 2-ethyl hexyl acrylate (42g), n-butyl acrylate (38g) and n-butyl methacrylate (4.25g) was prepared. This second mixture was added over 20 minutes to the stirred contents of the beaker. When the addition was complete the mixture was stored for a further 15 minutes and then the mixer switched off.:. The mixture was allowed to deareate for 30 minutes. Water (60g) was placed in a reaction flask fitted with a stirrer and having means of heating the contents of the flask. The water was heated to 820C in the stirring and then ammonium persuiphate (0.000442g) was added. The monomer emulsion prepared above was added to the flask over 3 hours whilst stirring and maintaining the temperature at 85 to 90or. The resultant polymer emulsion was cooled to 40 C before being transferred to a storage jar. EXAMPLE 2 Preparation of Emulsion Polyacrylate Adhesive An emulsion polymer was prepared in a similar manner to that described in Example 1 except that 4.25g of methyl methacrylate were used in place of the n-butyl methacrylate. EXAMPLE 3 Preparation of Emulsion Polyacrylate Adhesives An emulsion polymer was prepared in a similar manner to that described in Example 1 except that 8.5g of n-butyl methacrylate and 33.75g of n-butyl acrylate were used in place of the quantities given in Example 1. EXAMPLE 4 Preparation of Surgical Adhesive Tape The polyacrylate adhesive emulsion prepared as described in Example 1 was thickened by the addition of a thickening agent Primal.ASE 60 (trade mark, available from Rohm and Haas) neutralised with ammonium hydroxide and an antioxidant Nonox WSL (trade mark) was also added (0.6% by weight based on the weight of emulsion). This mixture was coated onto a silicone coated release paper (Steralese, trade mark, available from Sterling Coated Papers Limited) by means of a blade over flat bed coater and dried in an air circulating oven at a temperature of 1100 + 50C to give a dried pressure sensitive adhesive coating with a weight per unit area of 40g/m2. The adhesive coating was transferred to either a polyester film or to an integral net backing (see Example 2 of British Patent No. 1531715) and cut into 2.5cm wide surgical tapes. The resulting surgical tape adhered well to human skin under dry and wet conditions and onto sweaty skin.

Claims: CLAIMS 1. An emulsion adhesive polymer comprising residues of acrylic monomers containing 80 to 98.5% by weight of residues of alkyl esters of acrylic or methacrylic acid in which the alkyl group contains from 3 to 12 carbon atoms, from 0.1 to 20% by weight of residues of monoesters of methacrylic acid and 0.1 to 5% by weight of residues of a compound of the formula (I), EMI14.1 in which Rl is a C1O - C1¯ alkyl radical and M is hydrogen, ammonia or an alkali metal. 2, An emulsion adhesive polymer according to claim 1 in which the compound of formula (I) is a sodium or potassium salt and R1 is an alkyl radical which contains from 11 to 13 carbon atoms. 3. An emulsion adhesive polymer according to claim 2 in which the compound of the formula (I) is sodium mono-lauryl itaconoxypropane sulphonate. 4. An emulsion adhesive polymer according to claim 1 in which the polymer contains from 88 to 94S by weight of residues of a mixture of n-butyl acrylate and 2-ethyl hexyl acrylate monomer. 5. An emulsion adhesive polymer according to claim 1 in which the polymer contains from 0.3 to 5% by weight of residues of hydroxyethyl methacrylate monomer. 6. An emulsion adhesive polymer according to claim 1 in which the polymer contains from 1 to 15% by weight of residues of a lower alkyl methacrylate monomer. 7. An emulsion adhesive polymer according to claim 1 which is a pressure sensitive adhesive polymer which comprises 36 to 50% by weight of n-butyl acrylate residues, 39 to 59% by weight of 2-ethyl hexyl acrylate residues, 1 to 15% by weight of lower alkyl methacrylate residues, 0.3 to 5% by weight of hydroxyethyl methacrylate residues and 0.1 to 5% by weight of residues of a salt of mono-lauryl itaconoxy propane sulphonic acid. 8. An emulsion adhesive polymer according to claim 7 in which the pressure sensitive adhesive polymer comprises 39 to 459 by weight of n-butyl acrylate residues, 47 to 49.5% by weight of 2-ethyl hexyl acrylate residues, 5 to 10% by weight of lower alkyl methacrylate residues, 0.8 to 3S by weight of hydroxyethyl methacrylate residues and 0.1 to 10% by weight of sodium mono-lauryl itaconoxy propane sulphonate. 9. A process for the preparation of an emulsion adhesive polymer which process comprises polymerising as an emulsion acrylic monomers containing 80 to 98.5S by weight of alkyl esters of acrylic or methacrylic and in which the alkyl group contains from 3 to 12 carbon atoms, from 0.1 to 20S by weight of monoesters of methacrylic acid selected from the group consisting of lower alkyl, hydroxylated or alkoxylated alkyl esters and 0.1 to 5% of residues or a compound of the formula (I), EMI16.1 in which R, is a C1 - C,, alkyl radical and M is hydrogen, ammonia or an alkali metal, in the presence of a free radical catalyst and a metal ion chelating agent. 10. A process according to claim 9 in which the metal ion chelating agent is sodium polyphosphate. 11. An adhesive surgical or medical dressing comprising an emulsion adhesive polymer according to claim 1.

Inventors: HOWES, JOHN GORDON BERNARD
Applicants: SMITH & NEPHEW PLC
Application year: 1986
Main classification: C08F220
IPC codes: A61L15, C08F220, C09J133