Air-permeable substrate material with a self-adhesive coating, process for its production and its use

Carrier material having a self-adhesive finish and a hotmelt self-adhesive composition applied to the entire area of at least one side, characterized in that the thermoplastic adhesive composition is foamed and the product has an air permeability of at least 3 cm.sup.3 /cm.sup.2 /s for an amount applied of at least 20 g/m.sup.2.

The invention relates to air-permeable carrier materials with a
 self-adhesive finish which are coated over the entire area of at least one
 side with a hotmelt self-adhesive composition, to a process for their
 preparation and to their use.
 Hotmelt self-adhesive compositions based on natural and synthetic rubbers
 and on other synthetic polymers are known and are increasingly being
 employed. Their essential advantage is that, unlike the compositions which
 are applied from solution or as an aqueous dispersion, there is no need
 for the laborious and in some cases environmentally polluting methods of
 removing the solvents or the water.
 It has already been proposed to employ self-adhesive compositions of this
 kind, especially those based on acrylates, for medical properties, in
 which case air-permeable woven fabrics or nonwovens are also mentioned as
 carrier material (U.S. Pat. No. 4,762,888, U.S. Pat. No. 4,879,178, EP-B
 436 159 and EP-B 578 151). A disadvantage of these products coated over
 their entire area, however, is their inadequate permeability to air and
 water vapour. Moreover, an improvement in the adhesion properties can
 usually only be achieved by a higher amount of composition being applied.
 In addition, it is known to apply such self-adhesive compositions not only
 over the entire area but also in a dot pattern, for example by screen
 printing (DE-C 42 37 252), in which case the dots of adhesive can also be
 distributed with varying sizes and/or varying distribution (EP-B 353 972),
 or by intaglio printing, in lines which join one another in the
 longitudinal and transverse direction (DE-C 43 08 649).
 The advantage of the patterned application is that, given an appropriately
 porous carrier material, the adhesive materials are permeable to air and
 water vapour and in general are readily redetachable.
 A disadvantage of these products, however, is that if the area covered by
 the adhesive film, which per se is impermeable, is too large there is a
 corresponding reduction in the permeability to air and water vapour, and
 the consumption of adhesive composition rises, and if the area covered by
 the adhesive film is too low the adhesion properties suffer, i.e. the
 product becomes detached too readily from the substrate.
 In accordance with WO 95/01408, specific elasto-meric hotmelt adhesive
 foams based on block copolymer are employed as laminating adhesive in the
 production of nappies, although the only critical factor is their elastic
 properties.
 The object of the invention, therefore, was to avoid the abovementioned
 disadvantages and to develop a product and process which features--given
 an appropriately porous carrier material--very good permeability to air
 and water vapour and also generally good adhesion properties coupled with
 low consumption of adhesive composition.
 This object is achieved by an air-permeable carrier material having a
 self-adhesive finish and a hotmelt adhesive composition applied to the
 entire area of at least one side, which material is characterized in that
 the thermoplastic adhesive composition is foamed and the product has an
 air permeability of at least 3 cm.sup.3 /cm.sup.2 /s, preferably 30-160
 g/m.sup.2, for an amount applied of at least 20 g/m.sup.2.
 Products which have proved particularly suitable are those having an air
 permeability of 3-150 cm.sup.3 /cm.sup.2 /s, preferably 15-125 cm.sup.3
 /cm.sup.2 /s and, in particular, 25-100 cm.sup.3 /cm.sup.2 /s.
 At the same time, the water-vapour permeability should be at least 100
 g/m.sup.2 /24 h, preferably 100-5000 g/m.sup.2 /24 h and, in particular,
 500-3000 g/m.sup.2 /24 h.
 Depending on the carrier material and its sensitivity to temperature, the
 self-adhesive layer can be applied directly or first applied to an
 auxiliary carrier and then transferred to the ultimate carrier. Subsequent
 calendering of the coated product and/or pretreatment of the carrier, such
 as corona irradiation, for better anchorage of the adhesive layer, may
 also be advantageous.
 The adhesive compositions are preferably foamed using inert gases such as
 nitrogen, carbon dioxide, noble gases, hydrocarbons or air, or mixtures
 thereof. In some cases, foaming by thermal decomposition of gas-evolving
 substances such as azo, carbonate and hydrazide compounds has also been
 found to be appropriate.
 The degree of foaming, i.e. the proportion of gas, should be at least about
 10% by volume and can range up to about 80%. In practice, values of
 30-70%, preferably 50% proportion of gas have become well established.
 Operation at relatively high temperatures of about 100.degree. C. and at a
 comparatively high internal pressure produces very open-pored adhesive
 foam layers which are of particularly good permeability to air and water
 vapour.
 Self-adhesive compositions which can be employed are the known
 thermoplastic hotmelt adhesive compositions based on natural and synthetic
 rubbers and on other synthetic polymers such as acrylates, methacrylates,
 polyurethanes, polyolefins, polyvinyl derivatives, polyesters or silicones
 with appropriate additives such as adhesion resins, plasticizers,
 stabilizers and other auxiliaries where necessary. Their softening point
 should be higher than 80.degree. C., since the application temperature is
 generally at least 90.degree. C., preferably between 120 and 150.degree.
 C. or 180-220.degree. C. in the case of silicones. If desired,
 post-crosslinking by UV or electron-beam irradiation may be appropriate.
 Self-adhesive compositions which have proven particularly suitable are
 those based on A-B-A block copolymers which consist of hard and soft
 segments. A is preferably a polymer block based on styrene and B is
 preferably a polymer block based on ethylene, propylene, butylene,
 butadiene, isoprene or mixtures thereof such as ethylene/butylene. In
 addition, such hotmelt adhesive compositions generally comprise one or
 more aliphatic or aromatic hydrocarbon resins as adhesion resins, one or
 more medium- or long-chain fatty acids or esters thereof and also
 stabilizers and, if desired, other auxiliaries. The ranges of amounts of
 constituents are usually between 15-70% block copolymers, 20-70% adhesion
 resins, 10-50% plasticizers and small amounts of stabilizers and other
 auxiliaries.
 Carrier materials which can be employed are virtually all carriers which
 are air-permeable and porous per se and are customarily used for
 industrial or medical purposes, i.e. woven or knitted fabrics, elastic or
 inelastic materials, plastics films, papers, nonwovens, foam materials or
 laminates thereof.
 The carrier materials having a self-adhesive finish which are coated in
 accordance with the invention with a foamed hotmelt self-adhesive
 composition are notable for a range of advantages. As a result of the
 foaming of the adhesive composition and the consequentially open pores in
 the composition, the products coated with the adhesive composition are of
 good permeability to water vapour and air when an inherently porous
 carrier is used. The amount of adhesive composition required is
 considerably reduced without adversely affecting the adhesion properties.
 The adhesive compositions have a surprisingly high tack, since per gram of
 composition more volume and thus adhesive surface area is available for
 the wetting of the substrate on which bonding is to take place, and the
 plasticity of the adhesive compositions is increased as a result of the
 foam structure. In addition, anchorage on the carrier material is thereby
 improved. Furthermore, the foamed adhesive coating gives the products a
 soft and smooth feel.
 As a result of the foaming, moreover, the viscosity of the adhesive
 compositions is generally lowered. This saves on melting energy, and it is
 also possible to carry out direct coating of thermally unstable carrier
 materials.
 The subjective product advantages of tack and smoothness can be quantified
 readily using a dynamo-mechanical frequency measurement. In this case, use
 is made of a rheometer controlled by shear stress.
 The results of this measurement method give information on the physical
 properties of a material through taking into account the viscoelastic
 component. In this case, at a predetermined constant temperature, the
 pressure-sensitive hotmelt adhesive is set in oscillation between two
 plane-parallel plates with variable frequencies and low deformation
 (region of linear viscoelasticity). By way of a pickup control unit, with
 computer assistance, the quotient (Q=tan .delta.) between the loss modulus
 (G", viscous component) and the storage modulus (G', elastic component) is
 determined. A high frequency is chosen for the subjective sensing of the
 tack and a low frequency for the smoothness, and the corresponding
 quotients are determined from the degree of foaming. The higher the
 corresponding numerical value of the quotient, the better the subjective
 property.
 It was possible in accordance with the invention to improve the tack and
 smoothness, as shown in the table.

Smoothness Tack
 low high frequency/
 Designation frequency/RT RT
 Pressure-sensitive tan .delta. = 0.35 .+-. tan .delta. = 0.45 .+-.
 hotmelt adhesive A 0.05 0.05
 (unfoamed)
 Pressure-sensitive tan .delta. = 0.46 .+-. tan .delta. = 0.65 .+-.
 hotmelt adhesive A 0.05 0.05
 foam vol. (N.sub.2) = 50%
 Pressure-sensitive tan .delta. = 0.35 .+-. tan .delta. = 0.45 4
 hotmelt adhesive A 0.05 0.05
 (unfoamed)
 Pressure-sensitive tan .delta. = 0.58 .+-. tan .delta. = 0.88 .+-.
 hotmelt adhesive A 0.05 0.05
 foam vol. (N.sub.2) = 70%
 Pressure-sensitive tan .delta. = 0.05 .+-. tan .delta. = 0.84 .+-.
 hotmelt adhesive B 0.03 0.05
 (unfoamed)
 Pressure-sensitive tan .delta. = 0.27 .+-. tan .delta. = 1.15 .+-.
 hotmelt adhesive B 0.05 0.05
 foam vol. (N.sub.2) = 50%
 Pressure-sensitive tan .delta. = 0.06 .+-. tan .delta. = 0.93 .+-.
 hotmelt adhesive C 0.03 0.05
 (unfoamed)
 Pressure-sensitive tan .delta. = 0.31 .+-. tan .delta. = 1.25 .+-.
 hotmelt adhesive C 0.05 0.05
 foam vol. (N.sub.2) = 50%
 Various pressure-sensitive hotmelt adhesives were chosen, i.e. A based on
 acrylate and B and C on block copolymers, and the results indicate a
 marked increase in the tan .delta. values as a result of foaming, i.e. a
 measurably better smoothness and tack.
 The advantages demonstrated make the novel carrier materials particularly
 suitable for medical purposes. Plasters or bandages, or dressings
 additionally provided with a wound pad, for example, produced there-from
 are particularly good in their skin compatibility given an appropriately
 selected air-permeable carrier material and a hypoallergenic adhesive
 composition, since they are of pronounced permeability to air and water
 vapour over the entire surface and are soft and smooth. They have a
 cushioned effect and, as a result, couple good properties when being worn
 with good adhesion.
 The product advantages as a result of the foaming of the adhesive
 compositions, such as high adhesive strength and good permeability to air
 and water vapour, can be derived from the following measurements.
 1. Plaster bandages with foamed hotmelt adhesive compositions stick more
 strongly on the skin than plaster bandages with unfoamed adhesive
 compositions, with identical amounts of composition applied. Since the
 adhesive force on the skin varies from one skin type to another, the
 unfoamed adhesive composition was given an index of 100 and the foamed
 plaster bandage was related thereto. This gave the following results:
 Index=adhesive force on the skin (foamed)/adhesive force on the skin
 (unfoamed)
 TABLE 1
 Increase in adhesive force on skin
 Amount Woven fabric Woven fabric
 applied (inelast.) (elast.) Nonwoven
 40 g/m.sup.2 105-110%
 60 g/m.sup.2 120-130%
 80 g/m.sup.2 110-125% 110-120%
 120 g/m.sup.2 120-170%
 2. Plaster bandages with foamed hotmelt adhesive compositions are more
 air-permeable than plaster bandages with unfoamed adhesive compositions,
 for the same amount of composition applied. The air permeability of
 plaster bandages with unfoamed adhesive compositions was &lt;1 cm.sup.3
 /cm.sup.2 /sec in the case of the samples tested. The air permeabilities
 relate to a degree of foaming of 50% in the end product.
 TABLE 2
 Air permeability as a function of amount applied
 Woven
 Woven fabric Woven
 fabric (elast.) fabric
 Amount (in- un- (elast.)
 applied elast.) stretched stretched Nonwoven
 40 g/m.sup.2 6-19 cm.sup.3 /
 cm.sup.2 /sec
 60 g/m.sup.2 90-100
 cm.sup.3 /cm.sup.2 /
 sec
 80 g/m.sup.2 3-8 cm.sup.3 / 20-35 90-110
 cm.sup.2 /sec cm.sup.3 /cm.sup.2 / cm.sup.3 /cm.sup.2 /
 sec sec
 120 g/m.sup.2 0-5-3
 cm.sup.3 /cm.sup.2 /
 sec
 3. The air permeability is dependent on the degree of foaming. The results
 were found for an amount applied of 80 g/m.sup.2.
 TABLE 3
 Dependency of air permeability on the degree of
 foaming
 Degree of foaming inelast. woven fabric
 30% 2-5 cm.sup.3 /cm.sup.2 /sec
 50% 3-8 cm.sup.3 /cm.sup.2 /sec
 70% 7-25 cm.sup.3 /cm.sup.2 /sec
 4. In addition, the permeability for water vapour is particularly important
 for the skin. Similar plaster bandages with unfoamed adhesive compositions
 are not permeable to water vapour. The samples shown were conditioned
 beforehand at 23.5.degree. C. Exemplary testing parameters are the
 temperature 37.degree. C., the saturation vapour pressure 6.274 kPa and
 the relative atmospheric humidity 30%.
 TABLE 4
 Water vapour permeability rate as a function of
 amount applied
 Woven fabric
 Woven fabric (elast.)
 Amount (inelast.) unstretched Nonwoven
 applied in g/m.sup.2 /24 h in g/m.sup.2 /24 h in g/m.sup.2 /24 h
 40 g/m.sup.2 1020
 60 g/m.sup.2 2740
 80 g/m.sup.2 520 2510
 120 g/m.sup.2 138
 5. The dependency of water-vapour permeability on the degree of foaming is
 shown below. For this purpose, an amount applied of 80 g/m.sup.2 was
 chosen. The parameters described in section 4 remained constant.
 TABLE 5
 Water-vapour permeability rate as a function of
 the degree of foaming
 inelast. woven fabric
 Degree of foaming in g/m.sup.2 /24 h
 30% 240
 50% 520
 70% 990
 Cohesive adhesion coatings i.e. anti-slip coatings which stick only to
 themselves or have a virtually non-adhering character, can also be
 produced in accordance with the invention.
 The advantageous properties of the novel adhesive coatings, such as low
 consumption of adhesive, high tack and good smoothness on both irregular
 and even surfaces, as a result of the elasticity and plasticity of the
 foamed adhesive compositions, can also be utilized in a purely industrial
 field. The resulting self-adhesive tapes and other products given a
 self-adhesive finish in this way are versatile in their possibilities for
 employment.
 A particularly suitable process for producing the carrier materials given a
 self-adhesive finish in accordance with the invention operate in
 accordance with the foam-mix system. In this case, the thermoplastic
 pressure-sensitive adhesive is reacted under high pressure at about 120
 degrees Celsius with dry gases, for example nitrogen, air or carbon
 dioxide in various proportions by volume (about 10-80%), in a stator/rotor
 system. While the gas feed pressure is &gt;100 bar, the mixing pressures of
 gas/thermoplastic in the system are 40-100 bar, preferably 40-70 bar. The
 pressure-sensitive adhesive foam produced in this way passes via a line to
 the nozzle applicator system of a melt coating unit.

The invention is illustrated in more detail by means of examples.
 EXAMPLE 1
 For the functional tape dressings which are customary in orthopaedics,
 relatively rigid, inelastic woven fabrics are employed. Tape dressings are
 used for immobilizing the apparatus of motion and as support dressings
 for, inter alia, prophylaxis, first aid, therapy and restoration. For this
 purpose, rigid carrier materials with a maximum tensile force of about 60
 N/cm and a maximum tensile-force elongation of less than 20% are coated on
 one side with an adhesive composition.
 In accordance with the invention, a foamed hotmelt adhesive composition
 based on a block copolymer was used. To this end, rigid woven fabrics were
 coated with about 40, 80 and 120 g/m.sup.2. All samples stick to the skin
 and are air-permeable. The greater the amount of adhesive composition
 applied, the stronger the bonding of the bandage to the skin. The air
 permeability decreases as the amount of composition applied goes up. The
 bandage finished with 40 g/M.sup.2 of adhesive composition showed the best
 permeability to water vapour. The degree of foaming was about 50%.
 It was thereby possible to show that the permeability to air and water
 vapour depend functionally on the amount of composition applied.
 Furthermore, rigid woven fabrics were produced with different degrees of
 foaming. In this case, the functional relationship of the permeability to
 air and water vapour as a function of the degree of foaming is evident.
 The higher the proportion of gas in the applied adhesive composition, the
 greater the permeability. Products with a degree of foaming of 70% had the
 highest permeability in the experimental series (Tab. 3 and Tab. 5).
 Samples with the same adhesive composition which, however, is unfoamed
 exhibit markedly lower permeabilities if any.
 EXAMPLE 2
 To date, elastic bandages have generally been coated indirectly. In this
 context, the adhesive composition is spread onto silicone-coated release
 paper and the solvent is removed in a drying tunnel. The elastic carrier
 material, a woven or knitted material, is then laminated on. However, a
 bandage produced in this way is not always of sufficient air-permeability.
 A bandage produced in accordance with the invention was coated by the
 hotmelt coating process with a nitrogen-foamed adhesive composition based
 on a block copolymer, with an amount applied of about 80 g/m.sup.2. The
 block copolymer is a styrene-ethylene-butylene-styrene block copolymer to
 which paraffinic hydrocarbons have been added. The ratio was one part of
 polymer to one part of paraffinic hydrocarbon. 10% of polystyrene resin
 (e.g. Amoco 18240) were added to the mixture produced. The adhesive also
 contained one per cent of anti-ageing agent (n-octadecyl
 .beta.-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate, trade name IRGANOX
 1076) and further hydro-carbon resins and fatty acid esters, which are
 present only in small amounts in the overall adhesive. The adhesive is
 obtainable commercially (from Fuller). The adhesive composition was foamed
 with nitrogen in a ratio of 1:2 at 120.degree. C. by the method described
 above. The resulting proportion of gas in the end product was then 50%.
 The air permeability of the bandage was 20-35 cm.sup.3 /cm.sup.2 /s in the
 unstretched state and about 100 cm.sup.3 /cm.sup.2 /s in the stretched
 state. The water-vapour permeability was greater than 500 g/m.sup.2 /24 h.
 As a result of the foamed, partially open-pored adhesive composition, the
 bandage is permeable to air and water vapour even in a multilayer
 dressing. It is employed for compression, support and release bandages,
 the high immediate and long-term adhesive force being advantageous.
 Furthermore, as a result of the elasticity of the adhesive, the adhesive
 composition based on the block copolymer supports the compressive action
 of the bandage. The modelling properties and user perception were improved
 by the foaming of the adhesive composition.