Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1998-12-04
2001-08-14
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S191000, C427S195000, C427S208400, C427S208600, C427S307000, C427S322000, C427S327000, C427S598000
Reexamination Certificate
active
06274205
ABSTRACT:
The invention relates to a process for the at least partial, direct coating of an extensible backing material with a pressure-sensitive adhesive composition, the backing material being guided by a transporting apparatus against a coating apparatus in such a way that the latter applies the pressure-sensitive adhesive composition to the backing material.
The use of extensible materials as backings having elastic or plastically formable properties is known in both industry and medicine. They are used in a wide variety of areas—inter alia, as base materials in the production of plasters and adhesive dressings.
The term “plastically or elastically deformable” is intended to denote the extensibility of a material. In accordance with this a material is extensible if under a load of 10 N/cm it exhibits an increase in length of at least 20%.
It is also known that the extensible backing materials can be coated with various adhesive systems. In general, coating can be performed over the whole area or else partially. With medical, self-adhesively treated backing materials it is found in this case that, given appropriately porous backing materials, the result is a highly air-permeable and water-vapour-permeable film which in general can also be detached fairly easily again after it has been bonded to the skin of the patient.
Half-tone printing is widespread as a process for producing such partially coated backing materials—especially screen, gravure or flexographic printing. It is also known that the self-adhesive treatment can also be applied to more than one side, in the case, for example, of use as fixings.
The adhesive compositions which can be used are, in principle, solvent-based or dispersion-based systems, or else 100% systems. When processing the 100% systems it is an advantage that there is no need to remove the solvents or dispersion auxiliaries. This increases the productivity and at the same time reduces the expenditure on machinery and the energy costs.
Elastic or plastically formable backing materials can generally be coated directly or indirectly. In the case of indirect coating, a preferably rigid or fairly nonelastic auxiliary support is coated first of all and then the adhesive composition is transferred in a laminating process to the elastic or plastically formable backing. For indirect coating it has been found advantageous that in this case the backing material can be laminated essentially without deformation and prior loading, so leading to the extensive retention of shape and of textile technological features such as basis weight, maximum tensile strength, extension under maximum tension, and hysteresis extension.
The disadvantage of indirect coating lies in the relatively poor anchorage of the adhesive composition to the elastic or plastically deformable backing. Here it is found that, especially in the case of temperature-sensitive backing materials, thermal lamination is impossible or largely unsuccessful. In the case of thick, porous backing materials, lamination may be accompanied by the adhesive film being pressed completely into the backing, with the consequence of a drastic deterioration in both the bonding properties and the elasticity.
Direct coating, although it permits a much improved anchorage of the adhesive composition, entails greater stress on the backing both thermally and mechanically. Especially in the case of partial application of adhesive composition to an at least partially elastically or plastically formable backing material it is found that this material, although the backing is placed unstressed and without deformation into the coating unit, is stressed in some cases to such an extent that there is an irreparable change in its properties. This is a consequence of the fact that the adhesive system adheres to the coating system with a system-dependent force.
In order to separate the self-adhesively treated backing from this coating unit, it is necessary to exert a force on the backing, as a result of which the latter experiences an impairment of its properties, especially its elasticity and basis weight.
The object of the invention was to develop a direct coating process which makes it possible to coat an extensible backing material at least partially with a pressure-sensitive adhesive composition without altering the properties of the backing.
This object is achieved by a process as described in more detail in Claim
1
. The subclaims represent advantageous embodiments.
Accordingly, in the process of the invention for the at least partial, direct coating of an extensible backing material with a pressure-sensitive adhesive composition, the backing material is guided by a transporting apparatus against a coating apparatus in such a way that the latter applies the pressure-sensitive adhesive composition to the backing material, with the coating apparatus being abhesively treated, so that coating is not accompanied by any change in the properties of the backing.
In one advantageous embodiment of the process, the backing material is coated over its whole area.
The abhesive (anti-adhesive) treatment consists preferably of silicones or fluorine compounds, or plasma-coated release systems.
Also preferably, the abhesive is applied with a weight per unit area of from 0.01 to 350 g/m
2
, more preferably 0.1 to 10 g/m
2
.
In a particularly preferred embodiment the transporting apparatus consists of a pressure roller and the coating apparatus of a rotating, seamless, drum-shaped, perforated and abhesively treated cylindrical screen which is fed via a nozzle with the pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition being applied by way of a nozzle lip through the cylindrical screen and onto the backing material that is conveyed past it.
The pressure roller can consist preferably of metal, ceramic or plastic. It can be generally plastic, elastic or rigid in configuration.
Furthermore, there can be adhesion devices or holding devices present on the transporting apparatus.
The holding apparatuses consist in particular of needles which project from the transporting apparatus and engage in the backing material, and which have a length greater than 10 &mgr;m, preferably between 30 and 5000 &mgr;m and, with particular preference, between 35 and 1000 &mgr;m.
Moreover, the needles can at least in part be mobile on the surface of the transporting apparatus.
A combination that has been found to be very advantageous is that of thermal screen printing with needles in the counterpressure roller. Depending on the target application it is possible to equip the counterpressure roller such that the roughness and/or the needles are present uniformly, randomly distributed or in a defined geometric pattern on the roller surface. The geometric form and extent of the adhesion elements are also adapted to the backing. The configuration of needle orientation has also been found advantageous.
For specific uses, the angle of needle orientation can be between 10° and 170° to the tangent to the surface of the roller in the coating direction and perpendicular to the coating direction. In addition, the angle of needle orientation can, for specific uses, be between 10° and 170° to the web direction.
The needles can, moreover, be designed at least in part to be mobile, so that their orientation and/or size may change during one revolution of the counterpressure roller as a result, for example, of exposure to a magnetic field or of eccentric constructions.
In addition, the surface of the counterpressure roller and/or of the adhesion elements can be pretreated both physically and chemically. By way of example, mention may be made here of siliconization and of Teflonization. A static or else antistatic treatment may give rise to applications-related advantages.
Techniques for applying such release coverings are adequately described in the technical literature, with examples being dipping, brushing, spraying and printing. The release coverings can be cured both physically and chemically. Chemically curing systems have been found advantageous for the proc
Himmelsbach Peter
Jauchen Peter
Keite-Telgenbüscher Klaus
Lehder Matthias
Beiersdorf AG
Norris & McLaughlin & Marcus
Pianalto Bernard
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