Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1998-12-09
2002-08-20
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S345000, C428S3550AC, C428S474400, C427S208000, C156S244110
Reexamination Certificate
active
06436530
ABSTRACT:
The invention relates to an adhesive tape which has been given a pressure-sensitive adhesive coating, having an elastomeric backing layer, a single- or double-sided energy-elastic interlayer and a pressure-sensitive adhesive layer on one or both sides.
The use of interlayers between the actual backing layer and the pressure-sensitive adhesive coating is known. One of the purposes of these interlayers is to prevent or lessen the migration of constituents from the backing layer into the pressure-sensitive adhesive. Migration of this kind may lead to structural alterations in the pressure-sensitive adhesive layer and/or to deposits on the surface of the pressure-sensitive adhesive, and hence to a reduction in the adhesion. A further function of the interlayers is to smooth out uneven backing surfaces.
In the case of the bonded adhesive tape, interlayers—especially if they are energy-elastically deformable—may have the function of absorbing stress peaks greater than the average force acting on the bond area and of distributing such peak stresses over the area of the bond in order thereby to counter fracture of the bond.
For example, it is known for this application to use thin layers of polymers which are in an energy-elastic state thermodynamically owing to their high glass transition temperature and/or their partial crystallinity. Polyamides in particular meet the requirements that are placed on an interlayer.
A disadvantage of the interlayers consisting of polyamides, however, is that, while they often fulfil the barrier, smoothing and force-absorbing function, at the same time their adhesion to the underlying backing is inadequate. At relatively high stress levels, especially in the case of stresses in which peel forces become active, there is a possibility that the adhesive tape might suffer delamination, instances of which may lead to complete failure of the bond.
The object of the invention, therefore, was to provide an adhesive tape which, with an elastomeric backing layer, has an energy-elastic interlayer anchored securely on the backing layer.
To achieve this object the invention proposes an adhesive tape which has been given a single- or double-sided pressure-sensitive adhesive treatment and has an elastomeric backing layer, the polymeric framework of the backing layer consisting essentially of natural rubber or of a mixture of natural rubber with at least one styrene-butadiene rubber.
The styrene-butadiene rubber of the backing layer can be a random copolymer having a styrene content of about 23% by weight. The natural rubber or mixture of natural rubber with styrene-butadiene rubber that is used for the backing layer is crosslinkable by means of electron beams.
In accordance with the invention the backing layer comprises an electron beam-crosslinkable, polyfunctional crosslinker, preferably oligoacrylate or oligovinyl ether, which is partially soluble in the polymeric framework and whose physical forces of interaction with the polymeric framework are so low that it tends towards diffusion to the surface of the backing layer where, together with its fraction which is not dissolved in the polymeric framework, it forms a thin film which contacts the entire area of the polyamide interlayer.
In that case the electron beam-crosslinkable polyfunctional crosslinker is at least partially soluble in the polyamide and is therefore able to diffuse into it. Irradiation with electrons crosslinks the pure framework of the backing, the framework of the backing together with the crosslinker, the pure crosslinker dispersed in the backing, the crosslinker present like a film on the surface of the backing, and those fractions of the crosslinker that have diffused into the polyamide interlayer, this crosslinking possibly taking place with attachment to the polyamide, so that an indissoluble, predominantly covalent attachment of the interlayer to the backing is achieved.
It is advantageous if the combined product composed of backing, crosslinker film and polyamide is irradiated with electrons before the latter has diffused to that side of the polyamide which is opposite the rubber backing.
The combined product can be irradiated, for example, with an electron accelerator of the scanner type at a radiation dose of from 10 to 200 kGy, preferably from 50 to 100 kGy and, with particular preference, 80 kGy. The required acceleration voltage depends on the thickness of the combined product that is to be crosslinked. To achieve sufficient homogeneity of crosslinking, the combined product can be irradiated from both sides.
The crosslinked combined product composed of backing, crosslinker film and polyamide interlayer preferably carries, on the interlayer, a polyacrylate-based pressure-sensitive adhesive, which may or may not be crosslinked.
The pressure-sensitive adhesive can be crosslinked separately on an auxiliary support or in combination with interlayer and backing by means of a chemical reaction, via an inherent mechanism and/or physically by irradiation with electrons in the course of the crosslinking of the backing with the interlayer.
The crosslinker which is supplied to the backing, diffuses onto its surface as a soluble fraction and is deposited there, inter alia, as an insoluble fraction, and which, following partial diffusion into the adjacent polyamide interlayer, brings about anchorage of the interlayer to the backing following its crosslinking with electron beams, is a polyfunctional—especially di-, tri- or tetrafunctional—oligoacrylate or an oligovinyl ether having terminal, electron beam-crosslinkable vinyl groups. The base compound carrying the vinyl groups may, for example, be an ethoxylated or non-ethoxylated polyol, an oligoether, or an oligourethane having terminal OH groups.
In accordance with the invention the crosslinker can be admixed alone or in a blend with one or more other crosslinkers of the same or different functionality to the backing formulation.
For example, a bifunctional urethane acrylate having an average molecular weight of 5000 or a tetrafunctional oligoether acrylate having an average molecular weight of 1000 or a tetrafunctional oligoether acrylate, such as ethoxylated trimethylolpropane triacrylate, can be employed per se. It is also possible, however, to blend the bifunctional urethane acrylate or the tetrafunctional oligoether acrylate in equal or unequal parts with the trifunctional ethoxylated trimethylolpropane triacrylate.
Preferably, the crosslinker or the mixture of different crosslinkers is added to the backing formulation in an amount of from 5 to 20% by weight, especially 7% by weight.
To increase the durability of the backing it can be admixed with customary anti-ageing agents, which, depending on the particular application, may originate from the class of the discolouring or non-discolouring anti-ageing agents, in particular in the range from 0 to 10 phr, and also with known light stabilizers or ozone protectants. Blending with plasticizers is also possible.
In order establish specifically the desired properties of the backing it is possible if desired to use fillers. For instance, the natural rubber or the mixture of natural rubber and styrene-butadiene rubber can be admixed with reinforcing, semi-reinforcing or non-reinforcing carbon blacks, in particular at from 0 to 50 phr, with zinc oxide, in particular at from 0 to 50 phr, and/or with other fillers, such as silica, silicates or chalk. Fillers other than those mentioned can also be used. It is possible in addition to add resins from the class of the phenolic resins and/or hydrocarbon resins, in the range, in particular, of from 0 to 50 phr. Depending on the intended application of the adhesive tape, all of these additives referred to can be employed either alone or in any desired combination with one another to produce the backing, in order to obtain optimum tailoring to the utility. Through the use of these additives it is also readily possible to provide the black coloration of the backing which is generally required by the industry.
The backing layer has a thickness of from 400 to 3
Karmann Werner
Kluge-Paletta Worner
Szonn Bodo
Norris & McLaughlin & Marcus
tesa AG
Zirker Daniel
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