Hot-melt pressure sensitive adhesive for adhesive strips

The present invention relates to a pressure-sensitive hot-melt adhesive composition characterized in that it includes PA1 a) at least one ethylene-vinyl acetate, ethylene-methyl acrylate or ethylene-butyl acrylate copolymer PA1 b) a solid tackifying resin PA1 c) a liquid tackifying resin PA1 d) an antioxidant PA1 e) and optionally a diluent. The invention also relates to the use of the pressure-sensitive hot-melt adhesive composition for the preparation of labels and adhesive tapes and more particularly of the tapes intended to come into contact with the skin.

FIELD OF THE INVENTION
 The invention relates to a pressure-sensitive hot-melt adhesive composition
 and to its use for the manufacture of labels and adhesive tapes and more
 particularly of tapes intended to come into contact with the skin.
 BACKGROUND OF THE INVENTION
 Adhesives in suspension or in solution in organic solvents are
 conventionally employed in the manufacture of adhesive tapes. When these
 adhesives are used it is necessary to carry out a stage of evaporation of
 the solvent, and this has the result of, on the one hand, limiting the
 production rate and, on the other hand, producing effluents of toxic
 character, the removal of which is found to be costly and tricky.
 In order to avoid the use of solvents it has been proposed to employ
 pressure-sensitive hot-melt adhesives.
 In WO 93/23488 an adhesive is proposed permitting the adhesive bonding of
 materials of low surface energy, for example a polyethylene film and a
 nonwoven fabric. This adhesive includes 75-98% of a diblock copolymer A-B,
 in which A consists predominantly of polystyrene or its derivatives and B
 is poly-1,3-butadiene, and a mixture consisting of a solid tackifying
 resin and of a liquid or oily tackifying resin
 In U.S. Pat. No. 5,290,842, a composition is described for the adhesive
 pasting of labels, which has good cohesion at ambient temperature. This
 composition includes a first elastomer, for example polybutadiene, and a
 second elastomer which has a glass transition temperature that is higher
 than that of the first elastomer, for example polyisoprene, and a
 tackifying agent which is miscible with the second elastomer.
 Patent EP 0104005-A describes an adhesive composition for the adhesive
 bonding of female protections to garments. This composition includes a
 viscoelastic polymer of A-B-A type in which B denotes a polyolefin, for
 example an ethylene-butylene copolymer, and A denotes a polystyrene, and a
 tackifying resin.
 Finally, in WO 93/10734, a positioning adhesive is proposed for female
 protections on silk, cotton and synthetic fibres. This adhesive includes
 6-25% of a copolymer of formula (A-B).sub.n -Y, in which Y is a polyvalent
 coupling agent, A is a vinyl monomer substituted by an aromatic radical
 and B is polybutadiene, 30-70% of a compatible tackifying resin and 10-40%
 of a plasticizing oil.
 The pressure-sensitive thermoplastic adhesives which have just been
 mentioned, while making it possible to avoid the use of solvent, are not,
 however, completely satisfactory. Thus, the adhesive tapes which are
 coated therewith exhibit, after being pulled off, a tendency to transfer
 the adhesive onto the support In addition, the adhesive tapes in contact
 with the skin exhibit poor resistance to perspiration.

DESCRIPTION OF THE INVENTION
 The present invention proposes a new pressure-sensitive hot-melt adhesive
 composition exhibiting high cohesion and good resistance to moisture, this
 composition being characterized in that it includes
 a) at least one ethylene-vinyl acetate, ethylene-methyl acrylate or
 ethylene-butyl acrylate copolymer
 b) a solid tackifying resin
 c) a liquid tackifying resin
 d) an antioxidant
 e) and optionally a diluent.
 The term "solid tackifying resin" here denotes tackifying resins exhibiting
 a ring-and-ball softening point higher than 60.degree. C.
 The term "liquid tackifying resin" here denotes a tackifying resin
 exhibiting a ring-and-ball softening point lower than 60.degree. C.
 Another subject of the present invention is the use of the said
 pressure-sensitive hot-melt adhesive composition for the manufacture of
 labels and adhesive tapes and more particularly of adhesive tapes intended
 to be adhesively bonded to the skin, such as, for example, bandages and
 dressings.
 The copolymer according to the invention is generally chosen from
 copolymers exhibiting a vinyl acetate or methyl or butyl acrylate content
 of between 15 and 65% and preferably 30 and 50% by weight.
 Copolymers exhibiting a melt index of between 1 and 1000 and preferably 2
 and 500 are preferably employed.
 Such copolymers can be obtained conventionally by high-pressure radical
 polymerization from ethylene and from vinyl acetate or methyl or butyl
 acrylate (see, for example, U.S. Pat. No. 5,298,582).
 The solid tackifying resin according to the invention is generally chosen
 from natural or modified, for example dimerized, hydrogenated or
 polymerized, rosin esters, such as pentaerythritol, diethylene glycol and
 glycerol esters, polyterpene resins, for example "-pinene dipentene,
 copolymers of terpenes and of aromatic monomers such as styrene,
 vinyltoluene and "-methylstyrene, terpenephenolic resins, for example
 Dertophene T marketed by DRT, hydrocarbon resins of aliphatic and/or
 aromatic nature which are unhydrogenated or partially or completely
 hydrogenated, and mixtures of these compounds.
 Hydrocarbon resins are preferably employed, and especially when the
 adhesive is intended to come into contact with the skin.
 Such solid resins exhibiting a ring-and-ball softening point of between 60
 and 140.degree. C. and preferably 80 and 120.degree. C. are advantageously
 employed.
 The liquid tackifying resin acording to the invention is generally chosen
 from natural or modified, for example dimerized, hydrogenated or
 polymerized, rosin esters, for example glycerol and di- and triethylene
 glycol esters, polyterpene resins, for example "-pinene dipentene,
 copolymers of terpenes and of aromatic monomers such as styrene,
 vinyltoluene and"-methylstyrene, terpenephenolic resins, hydrocarbon
 resins of aliphatic and/or aromatic nature which are unhydrogenated or
 partially or completely hydrogenated and mixtures of these compounds.
 Polyterpene resins and hydrocarbon resins are preferably employed, and
 especially when the adhesive is intended to come into contact with the
 skin.
 Such liquid resins exhibiting a ring-and-ball softening point lower than
 40.degree. C. are preferably employed.
 The antioxidant is generally chosen from the compounds of the sterically
 hindered phenol type, such as Irganox, marketed by Ciba Geigy, amines,
 phosphites and mixtures of these compounds.
 The diluent according to the invention may be chosen from any type of
 diluent which is compatible with the copolymer employed. Polybutene,
 phthalates such as dioctyl phthalate (DOP), diisononyl phthalate (DINP) or
 diisodecyl phthalate (DIDP) and naphthenic or paraffinic oils are
 preferably employed.
 The pressure-sensitive hot-melt adhesive composition according to the
 invention is obtained by fixing the various abovementioned constituents at
 a temperature which is generally between 120 and 150.degree. C.
 The pressure-sensitive hot-melt adhesive composition according to the
 invention generally includes from 30 to 50% by weight and preferably 30 to
 40% of copolymer, from 10 to 40% and preferably 15 to 35% of solid
 tackifying agent, from 10 to 40% and preferably 15 to 35% of liquid
 tackifying resin, from 0.1 to 2% of antioxidant and from 0 to 20% of
 diluent.
 When the composition is intended to be in contact with the skin the use of
 diluent is preferably avoided.
 The pressure-sensitive hot-melt adhesive composition in accordance with the
 invention may be employed for the preparation of labels and adhesive tapes
 of any type. Purely by way of illustration it is possible to mention the
 coating, for example by means of a book nozzle, of substrates such as
 films based on polyethylene, polypropylene and polyvinyl chloride.
 As a result of its properties of resistance to perspiration, the
 composition in accordance with the invention is particularly recommended
 for the preparation of adhesive tapes for cutaneous use such as adhesive
 dressings and strappings. In addition, such tapes exhibit a greater
 adhesiveness at the temperature of use close to 37.degree. C. than at
 ambient temperature, and this allows easy repositioning of the tape on the
 skin in the event of incorrect application.
 EXAMPLES
 The examples which follow enable the invention to be illustrated.
 In the examples the shear strength under stress (holding power) is measured
 according to PSTC standard 7.
 The 180.degree. peel is measured according to PSTC standard 1.
 The T peel test is measured according to the method which consists in
 folding back onto itself the substrate coated with the adhesive to be
 tested, applying a moderate manual pressure to the said folded-back
 substrate and unbonding the portions thus adhesively bonded. The test is
 satisfactory when the substrate retains the appearance and adhesive
 properties of the substrate before bonding.
 EXAMPLE 1
 A pressure-sensitive hot-melt adhesive composition is produced by mixing
 the following compounds (in % by weight):

EVA 4055 32.0
 (ethylene-vinyl acetate copolymer;
 vinyl acetate: 40%; melt index:
 55; Bayer)
 Liquid petroleum resin (ECR 2520; 38.8
 Exxon)
 Solid petroleum resin (ECR 368 LC; 29.0
 Exxon)
 Antioxidant (IRGANOX 1010; 0.2
 Ciba Geigy)
 The composition thus obtained is applied onto a polyvinyl chloride film at
 a rate of 40 g/m.sup.2 to form a dressing.
 The coated substrate has a holding power equal to 50 mm and a 180.degree.
 peel of 18 N/25 mm at 23.degree. C. and 36 N/25 mm at 40.degree. C.
 The T peel test is satisfactory.
 After application of the dressing to the skin it is found that the rupture
 on the skin is adhesive without transfer of adhesive onto the skin.
 EXAMPLE 2
 The conditions of Example 1 are followed in the presence of the following
 compounds (in % by weight):

EVA 4055 30.0
 (ethylene-vinyl acetate copolymer;
 vinyl acetate: 40%; melt index: 55;
 Bayer)
 Liquid petroleum resin (ECR 2520; 36.8
 Exxon)
 Solid petroleum resin (Escorez 5320; 33.0
 Exxon)
 Antioxidant (Irganox 1010; 0.2
 Ciba Geigy)
 The coated substrate (dressing) exhibits a holding power equal to 80 mm and
 a 180.degree. peel of 19 N/25 mm at 23.degree. C.
 The T peel test is satisfactory.
 After application of the coated substrate onto the skin it is found that
 the rupture on the skin is adhesive without transfer of the adhesive onto
 the skin.
 EXAMPLE 3
 The conditions of Example 1 are followed in the presence of the following
 compounds (in a by weight):

Lotryl 28MA175 32.0
 (ethylene-methyl acrylate copolymer;
 methyl acrylate: 28%; melt index: 175;
 Elf Atochem S.A.)
 Liquid petroleum resin (ECR 2520; 29.0
 Exxon)
 Solid petroleum resin (ECR 385; 38.8
 Exxon)
 Antioxidant (IRGANOX; Ciba Geigy) 0.2
 The coated substrate (dressing) exhibits a holding power of 7 mm and a
 180.degree. peel of 25 N/25 mm at 23.degree. C.
 The T peel test is satisfactory.
 After application of the coated substrate onto the skin it is found that
 the rapture on the skin is adhesive, without transfer of adhesive onto the
 skin.
 EXAMPLE 4
 A self-adhesive hot-melt composition is prepared by mixing together the
 following compounds (in % by weight):

Lotryl 28MA175 30.0
 (ethylene/methyl acrylate copolymer;
 28% methyl acrylate; melt index: 175;
 Elf Atochem S.A.)
 Lotryl 35BA320 15.0
 (ethylene/butyl acrylate copolymer;
 35% butyl acrylate; melt index: 320;
 Elf Atochem S.A.)
 Liquid petroleum resin (ECR 2520; 25.0
 Exxon)
 Solid petroleum resin (ECR 6372; 29.8
 Exxon)
 Antioxidant (Irganox 1010; 0.2
 Ciba-Geigy)
 The composition thus obtained has a Brookfield viscosity at 160.degree. C.
 equal to 6000 mPa s and a ring-and-ball softening point equal to
 66.degree. C.
 This composition is applied to a film of polyvinyl chloride at a rate of 40
 g/m.sup.2 to form a dressing.
 The T peel test is correct.
 Although the invention has been described in conjunction with specific
 embodiments, it is evident that many alternatives and variations will be
 apparent to those skilled in the art in light of the foregoing
 description. Accordingly, the invention is intended to embrace all of the
 alternatives and variations that fall within the spirit and scope of the
 appended claims. The above references are hereby incorporated by
 reference.
 After applying the dressing to the skin, it is observed that the rupture on
 the skin is adhesive without transfer of adhesive onto the skin.