GB2167319A

GB2167319A - Shrink article

Info

Publication number: GB2167319A
Application number: GB08527933A
Authority: GB
Inventors: Hermann Uwe Voigt
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1984-11-15
Filing date: 1985-11-13
Publication date: 1986-05-29
Also published as: BE903648A; DE3441743A1; GB2167319B; DK165942C; ATA330785A; DE3441743C2; DK523685D0; IT8548786A0; DK523685A; AT389275B; NL8503115A; SE8505385L; FR2572995B1; SE8505385D0; CH665799A5; DK165942B; IT1182984B; FR2572995A1; GB8527933D0; SE466436B

Abstract

Shrink articles, e.g. tubing, caps, or sleeves, having at least one surface coated with a crosslinked hot melt adhesive, are so produced that at least one of the abutting layers of material is crosslinked, after grafting-on of an organosilane compound, by the action of moisture.

Description

SPECIFICATION Shrink article This invention relates to a shrink article, e.g.

shrink tubing, or a shrink cap, sleeve or tape, produced from a crosslinked material based on an olefin polymer or olefin copolymer, an elastomer or a thermoplastic rubber, which has at least one surface coated with a crosslinked hot melt adhesive.

It is already known that shrink articles of any desired shape can, where they are hollow articles, be coated on the inside with a hot melt adhesive, and also that a shrinkable tape may be provided with such an adhesive on one or both faces. Coating with such an adhesive has the advantage that, in the shrunk-on stage of the shrink article, the adhesion to its substrate is improved and also the gap between the shrink article and the substrate is sealed in a moisture-impermeable manner. The hot melt adhesives on the market at the present time develop their adhesive property through thermoplastic flow, the adhesion being the more favourable the better the adhesive flows and hence wets the surfaces. This adhesive property is lost, however, as soon as the material of the adhesive layer is crosslinked.On the other hand, it is possible to increase the shear strength of the adhesive by crosslinking it, or partially crosslinking it, so that the mechanical strength of the bonded surfaces is improved. With the object of combining these seemingly incompatible effects (i.e. the adhesiveness and mechanical strength just mentioned) certain adhesives are being used (German Offenlegungsschrift 3,111,064) having molecules which consist of functional groups and hydrocarbon sequences linking them, the latter being built up, prior to the crosslinking process required for the shrinkable material, from part-branched or multiplebranched (i. e. sidechain-bearing) molecular structural units. However, this known approach results in considerable restriction of the choice of the hot melt adhesives usable for practical purposes.

Setting out from this prior art, it is therefore an object of the invention to enable any desired crosslinkable hot melt adhesives to be used to give a secure bond in shrink methods.

According to the invention, there is provided a shrink article produced from a crosslinked material based on an olefin polymer or olefin copolymer, an elastomer or a thermoplastic rubber and having at least one surface coated with a crosslinked hot melt adhesive, wherein at least one of the abutting layers of material has been crosslinked, after the grafting-on of an organosilane compound, by the action of moisture. This arrangement ensures that production is simple even in the case of tubing and other hollow articles. Controlling the degree of crosslinking, which may range from low to high, is easily effected, and control of the crosslinking mechanism enables one to adjust as desired, for example, the viscosity of the adhesive.

The material of the shrink article itself can be crosslinked by the action of moisture. In cases in which the applied layer of adhesive is also moisture-crosslinkable after the graftingon of a silane, it is advantageous to choose different degrees of crosslinking for the adjoining layers.

It is also possible to arrange for the material of the shrink article to be crosslinkable by peroxide or by radiation, the hot melt adhesive being crosslinkable by the action of moisture, and in particular to different degrees of crosslinking according to the amount of the grafted-on silane compounds. In this way, the desired viscosity of the adhesive can be obtained by selecting a particular degree of crosslinking or degree of incipient crosslinking, and the adhesive can thereby be very readily adapted to a wide variety of requirements.

It is further possible to arrange for the material of the shrink article to be crosslinked by the action of moisture, the hot melt adhesive being crosslinked by peroxide. In that case it is possible, by subsequent addition of the crosslinking agent, to allow the crosslinking to take place only when the shrink article undergoes reshrinking by the action of heat. The effect of this is that only on the conclusion of assembly does the adhesive (or the material of the adhesive) undergo an abrupt change in viscosity, which increases its shear strength, whereas up to that stage the distension of the shrink article and the assembly is not hampered by an excessively viscous adhesive.

The hot melt adhesive can be applied to the shrink article by any desired applicable procedure; advantageously, the shrinkable shaped article and the adhesive layer are extruded together, or injection-moulded together. If the material of the shrink article is one to which one or more silane compounds have been grafted, then this material will be crosslinked by subsequent action of moisture, without the properties of the adhesive being changed. On subsequent distension with the intention of subsequent reshrinking on exposure to heat, the adhesive, whose flow has so far not been hampered by crosslinking, can follow the stretching movements of the tubing without flaking off therefrom.Only when the adhesive layer of the distended article is subsequently enriched with crosslinking agent for the purpose of causing crosslinking, does the adhesive (upon initiation of the reshrinking process) undergo an increase in viscosity at the shrink temperatures, which viscosity increase provides the shear strength of the adhesive layer which is required of the shrink bonds concerned.

A process which has proved particularly advantageous in this connection is one in which the silane compound is grafted on to the material of the shrink article, the grafted material is thereafter shaped into the desired configuration, and is coated, simultaneously or subsequently, with the hot melt adhesive, the grafted material is crosslinked by the action of moisture, and thereafter the crosslinking agent for the hot melt adhesive is introduced into the hot melt adhesive layer by diffusion.

For the purposes of the invention, any desired applicable materials can be used as the base for the hot melt adhesive, for example ethylene/vinyl acetate copolymers and acrylate polymers, as also materials based on polyamides, copolyamides, thermoplastic rubbers and polyesters.

These adhesive materials can also be foamable, to give resilience in the bond between a shrink article and a substrate.

As crosslinking agents, the familiar peroxides, e.g. dicumyl peroxide, cumyl tert.-butyl peroxide, or 2,5-dimethyl-2,5-di-(tert.-butyl)peroxyhexane, can be used, as also other free-radical initiators, e.g. 1,10decane-bis-sul- phanazide or p-quinonedioxime.

It will be understood that the invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

Claims

1. A shrink article produced from a crosslinked copolymer, an elastomer or a thermoplastic rubber and having at least one surface coated with a crosslinked hot melt adhesive, wherein at least one of the abutting layers of material has been crosslinked, after the grafting-on of an organosilane compound, by the action of moisture.

2. An article according to claim 1, wherein the abutting layers have been crosslinked by the action of moisture, but to different degrees of crosslinking.

3. An article according to claim 1, the material of which has been crosslinked by peroxide or by radiation, the hot melt adhesive having been crosslinked by the action of moisture.

4. An article according to claim 1, the material of which has been crosslinked by the action of moisture, the hot melt adhesive having been crosslinked by peroxide.

5. A process for the preparation of a shrink article according to claim 1, 2, 3 or 4, wherein the article and the adhesive layer are extruded together, or injection moulded together.

6. A process according to claim 5, wherein the silane compound is grafted on to the material of the shrink article, thereafter the grafted material is shaped into the desired configuration, and is coated, simultaneously or subsequently, with the hot melt adhesive, the grafted material is crosslinked by the action of moisture, and thereafter the crosslinking agent for the hot melt adhesive is introduced into the hot melt adhesive layer by diffusion.