Multilayer adhesive tape

Details Multilayer adhesive tape Multilayer adhesive tape

1998-04-21

2001-12-18

Ahmad, Nasser (Department: 1772)

Stock material or miscellaneous articles

Layer or component removable to expose adhesive

C428S041300, C428S041500, C428S041700, C428S353000, C428S354000

Reexamination Certificate

active

06331336

ABSTRACT:

The invention relates to a self-adhesively coated adhesive tape having an elastomeric backing layer and an interlayer between backing layer and adhesive coating, and to processes for producing such an adhesive tape.
The use of interlayers between the actual backing layer and the adhesive coating is known. One of the purposes of these interlayers is to prevent or lessen the migration of constituents with which the backing layer may have been blended from the backing layer into the adhesive. Migration of this kind may lead to structural alterations in the adhesive layer and/or to deposits on the surface of the adhesive and hence to a reduction in the bonding strength. A further function of the interlayers is to smooth out uneven backing surfaces to that the adhesive layer which is to be laminated to it, and which is capable of more or less rubber-elastic deformation, is presented with an optimum bond surface at the time of lamination.
When the adhesive tape has been stuck on, 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.
Finally, interlayers are used as a primer between backing and adhesive if these two latter components adhere poorly to one another owing to their greatly differing polarities.
The use of thin polyamide layers, for example, is known for this purpose.
A disadvantage of the conventional interlayers is often that they fulfill the barrier, the smoothing and the force-absorbing function but are at the same time of inadequate adhesion to the underlying backing. At relatively high stress levels there is then a possibility that the adhesive tape might suffer delamination, instances of which may lead to complete failure of the adhesive bond.
The object of the invention, therefore, was to provide an adhesive tape which, with an elastomeric backing layer, has an interlayer anchored securely on the backing layer.
To achieve this object the invention proposes an adhesive tape which is equipped with a self-adhesive coating on one or both sides and has an elastomeric backing layer wherein the elastomer consists essentiallly of a styrene-butadiene copolymer.
Applied to one or both sides of the backing layer is a self-adhesive composition, with an interlayer of polyphenylene ether between backing layer and self-adhesive composition.
In a preferred embodiment the polyphenylene ether is poly(oxy-2,6-dimethyl-p-phenylene), it being possible for the latter to have been flexibilized by blending advantageously with minor amounts of polystyrene, polyamide or a styrene-acrylonitrile copolymer. For the same purpose it is also possible to mix the polyphenylene ether with a block copolymer based on SEBS.
The interlayer here can be prepared by extrusion with or without an auxiliary backing, and in a thickness of from 5 &mgr;m to 40 &mgr;m, in particular 8 &mgr;m.
Alternatively, the interlayer can be prepared from solution on an auxiliary backing.
Where an auxiliary backing is used, the interlayer can be peeled off again from this backing without restriction.
The styrene content in the overall composition of the backing layer is preferably at least 12% by weight.
Advantageously, the styrene-butadiene copolymer of the backing layer can be a random copolymer, prepared from solution or by emulsion polymerization, with a styrene fraction of at least 23% by weight.
The styrene-butadiene copolymer used for the backing layer can be crosslinkable physically—for example, by crosslinking using electron beams—or chemically.
To increase the durability of the adhesive tape it can be filled with customary anti-ageing agents, which depending on the particular application may originate from the class of the discoloring of non-discoloring anti-ageing agents, especially in the range from 0 to 10 phr, and also with known light stabilizers or ozone protectants. Also possible is blending with vulcanizing agents (such as, for example, peroxides or sulphur, sulphur donors or accelerators) and/or the addition of fatty acid, especially in the range from 0 to 10 phr, and the use of plasticizers.
In order to establish specifically the desired properties of the backing it is possible if desired to use additional fillers. For instance, the styrene-butadiene copolymer 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 additionally possible to add resins from the class of the phenolic and/or hydrocarbon resins, in the range, in particular of from 0 to 50 phr.
Depending on the intended use of the self-adhesive tape, all of these additives referred to can be employed either alone or in any desired combination with one another for preparing the styrene-butadiene copolymer 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 as is generally required by the industry.
The backing layer has a thickness of from 400 &mgr;m to 3000 &mgr;m, in particular from 500 &mgr;m to 1400 &mgr;m.
As a filler for modifying the properties of the backing it is possible to add solid microbeads to the backing formulation, in a volume proportion of from 1 to 50%, in particular from 10 to 30%, by volume. The solid microbeads present in the backing formulation bring about particularly advantageous properties of the self-adhesive tape of the invention if the solid microbeads are solid glass microbeads having a diameter of from 1 &mgr;m to 100 &mgr;m, in particular from 10 &mgr;m to 60 &mgr;m.
The backing mixture is preferably prepared in an internal mixer of the kind typical for elastomer compounding. In this case the styrene-butadiene copolymer is adjusted in particular to a Mooney value ML
1+3
(100° C.) in the range from 40 to 80. Processing takes place preferably without solvent. The desired fillers may be added to the styrene-butadiene copolymer at the same time. The styrene-butadiene copolymer can subsequently be extruded or calendered to the desired thickness on customary commercial machines. This gives a backing layer thickness that is within the ranges set out above.
Express reference is made here to the known technology of processing styrene-butadiene copolymers and to the known additives employed for this purpose, in accordance, for instance, with the book by Werner Kleemann (Werner Kleemann: “Mischungen für die Elastverarbeitung”, Deutscher Verlag für Grundstoffindustrie, Leipzig 1982).
Following the application of the interlayer and the elapsement of a certain waiting period within which the necessary diffusion takes place, the backing can be crosslinked by means of electron beams or by means of known chemical crosslinkers.
An alternative option is to laminate the polyphenlene ether-based interlayer onto the backing at temperatures higher than 120° C., using a calender, and to carry out in-line crosslinking of the backing immediately thereafter.
The thermodynamic state of the backing prior to contact with the interlayer allows the molecules and/or molecular segments the mobility required for diffusion. Preferably, the backing is not crosslinked until after the diffusion process has taken place.
The pressure-sensitive self-adhesive composition preferably includes known copolymers of methyl acrylate with 2-ethylhexyl acrylate and acrylic acid, preferably with a composition of from 20 to 40% by weight methyl acrylate, from 20 to 70% by weight 2-ethylhexyl acrylate and from 0 to 10% by weight acrylic acid.
It is possible to add further known components in order to obtain certain properties: crosslinkers, tackifier resins and anti-ageing agents are added in particular.
The self-adhesive composition can be applied directly from the solution, dispersion or melt o

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