Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1998-10-14
2002-05-07
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550AC, C428S3550AC, C428S346000, C442S150000, C427S208200, C427S208400
Reexamination Certificate
active
06383630
ABSTRACT:
The invention relates to carrier materials which have been treated to make them self-adhesive and which are coated over not 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 other synthetic polymers are known and are increasingly being employed. Their essential advantage is that, unlike compositions which are applied from solution or as an aqueous dispersion, there is no need for the laborious and in some cases environmentally polluting techniques of removing the solvents or the water.
It is also known to apply such self-adhesive compositions not only over the entire area but also in the form of a pattern of dots, for example by screen printing (DE-C 42 37 252), in which case the dots of adhesive can also differ in their size and/or distribution (EP-B 353 972), or by intaglio printing, in lines which interconnect in the longitudinal and transverse directions (DE-C 43 08 649).
The advantage of the patterned application is that the adhesive materials, given an appropriately porous carrier material, 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 small, the adhesion properties suffer, i.e. the product is detached too readily from the substrate.
The object of the invention, therefore, was to avoid these disadvantages and to develop a product and process featuring—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 a carrier material which has been given a self-adhesive finish and has a hotmelt adhesive composition applied not over the entire area of at least one side, which material is characterized in that the adhesive composition is foamed.
This foamed self-adhesive layer applied not over the entire area can be patterned, preferably in dome form by means of screen printing, or else can be applied in a different pattern, such as lattices, stripes, zigzag lines and, for example, also by intaglio printing. Furthermore, it can, for example, also be sprayed on, giving a more or less irregular application pattern.
The self-adhesive composition can be distributed uniformly on the carrier material; however, it can also be applied with varying thickness or density as appropriate for the function of the product.
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 final carrier. In addition, subsequent calendering of the coated product and/or pretreatment of the carrier, such as corona treatment, for better anchoring of the adhesive layer may be advantageous.
The percentage of the area coated with foamed self-adhesive composition should be at least 20% and can range up to about 95%, for specific products preferably 40-60%. and from 70 to 95%. The weight per unit area of the applied adhesive composition should be at least 15 g/m
2
in order to give sufficient adhesion levels, preferably 30-160 g/m
2
depending on the carrier employed.
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 may also prove suitable.
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%. Values which have been found favourable in practice for the proportion of gas are 30-70%, preferably 50%. Operation at relatively high temperatures of around 100° C. and at a comparatively high internal pressure produces open-pored adhesive foam layers which are of particularly good permeability to air and water vapour. The dot pattern of the coating supports the air permeability values within broad limits.
If no particular worth is attached to this property, it is also possible, by altering the parameters, to produce and use closed-pored foam structures.
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, postcrosslinking 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, hotmelt adhesive compositions of this kind 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 for the amounts of the constituents are generally 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 commonly used for industrial or medical purposes, i.e. woven or knitted materials, elastic or inelastic materials, plastics films or metal foils, papers, nonwovens, foam materials or laminates thereof.
The carrier materials which have been given a self-adhesive treatment and which, in accordance with the invention, are partially coated 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 consequent pores in the composition, when the carrier used is porous per se the regions coated with adhesive composition are also of good permeability to water vapour and air. The amount of adhesive composition required is considerably reduced with no adverse effect on the adhesive properties. The adhesive compositions are of surprisingly high tack, since per gram of composition there is more volume and thus adhesive surface area for the wetting of the substrate on which bonding is to take place, and the plasticity of the adhesive compositions is increased as as 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.
The subjective advantages of the product, tack and smoothness, can readily be quantified using a dynamomechanical frequency measurement. In this case, use is made of a rheometer controlled by shearing stress.
The results of this measurement method give information on the physical properties of a substance by taking into account the viscoelastic component. In this instance, at a preset constant temperature, the hotmelt pressure-sensitive adhesive is set in oscillation between two plane-parallel plates with variable frequencies and low deformation (region of linear viscoelasticity). Via a pickup control unit, with computer assistance, the quotient (Q=tan &dgr;) between the loss modulus (G″, viscous component) and the storage modulus (G′,
Himmelsbach Peter
Jauchen Peter
Beiersdorf AG
Norris & McLaughlin & Marcus
Zirker Daniel
LandOfFree
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