Air-permeable substrate material with a self-adhesive...

Details Air-permeable substrate material with a self-adhesive... Air-permeable substrate material with a self-adhesive...

1998-10-15

2001-01-30

Zirker, Daniel (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Coated or impregnated woven, knit, or nonwoven fabric which...

Coating or impregnation intended to function as an adhesive...

C442S151000, C428S317300, C428S317500, C428S317700, C428S3550BL

Reexamination Certificate

active

06180544

ABSTRACT:

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
3
/cm
2
/s, preferably 30-160 g/m
2
, for an amount applied of at least 20 g/m
2
.
Products which have proved particularly suitable are those having an air permeability of 3-150 cm
3
/cm
2
/s, preferably 15-125 cm
3
/cm
2
/s and, in particular, 25-100 cm
3
/cm
2
/s.
At the same time, the water-vapour permeability should be at least 100 g/m
2
/24 h, preferably 100-5000 g/m
2
/24 h and, in particular, 500-3000 g/m
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° 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° C., since the application temperature is generally at least 90° C., preferably between 120 and 150° C. or 180-220° 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 pre

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