Use of swellable hot-melt adhesives

The invention relates to the use of a water-swellable hot-melt adhesive based on a non-water-soluble component, a water-soluble or dispersible component and a water-swellable component. The invention further relates to the use of this hot-melt adhesive for the production of waterproof constructions, in particular for the production of longitudinally watertight cable constructions.

For a variety of constructions such as pipelines and, in particular, cables laid in the ground or under water. There is a need to protect these structures at the junctions or damage to their outer shell against penetrating water. In particular, energy and / or telecommunications cables are long-lived investment goods whose operational safety must be ensured over a very long lifetime. In the case of damage in the outer insulation and / or in faulty transition points, water penetrates into the interior of such cable structures, which can lead to considerable damage to the cables. This can lead to a rapid spreading of the water along the cable longitudinal axis and render a cable of this kind unusable on long distances.

In order to prevent the penetration of water into such constructions, water-swellable sealing materials or sealing structures have already been used for some time. The<patcit id="pcit0001" dnum="JP5821533483A"><text>JP-A-58-215334 (83</text></patcit>) Describes in general form thermosetting sealants based on rubbers and a water-swellable polyurethane resin based on ethylene oxide propylene oxide copolymers.

According to the prior art, multi-layered sealing systems are used for the production of longitudinally watertight energy or telecommunication cables. So describe<nplcit id="ncit0001" npl-type="s"><text>W. Schäfer and P. Graber in "Draht und Kabelpanorama", Mail June / July 1988, pages 64 to 68</text></nplcit> Source fluids from an extremely homogeneous source layer. Consisting of a mixture of a synthetic hydrogel former (source powder) with chemically pure cellulose pulp as filler and a carrier layer with high mechanical strength of polyester fibers with polyester threads as an additional reinforcing element. These two layers are thermally bonded together by high pressure and temperature without the use of low-melting thermoplastics. Swellable bandages are then produced from such fluids or yarns, which are bandaged around the bundle, possibly in combination with a plastic inner sheath.

The <patcit id="pcit0002" dnum="US5179611A"><text>U.S. Patent No. 5,179,611</text></patcit> Teaches a water-swellable thermoplastic mass of cable seal. The components of this mass are always dissolved or dispersed in a solvent and then applied. Melting adhesives are not mentioned.

The <patcit id="pcit0003" dnum="EP188959A"><text>EP-A-188959</text></patcit> Describes a multilayer sealing tape consisting of a carrier of paper. Textile materials or plastics which is coated with a layer of a water-swellable polymer powder and a water-soluble binder and optionally a surfactant.

The <patcit id="pcit0004" dnum="US5020875A"><text>US-A-5020875</text></patcit> Describes cable constructions in which the layer, which is intended to prevent water penetration by swelling, consists of a multilayer laminate. This laminate consists of two backing bands made of hydrophobic material such as polyester. A water-swellable polymer or copolymer of the superabsorber type is interposed between these two carrier bands.

The <patcit id="pcit0005" dnum="US5188883A"><text>US-A-5188883</text></patcit> Describes a multilayer composite structure of a metal strip as a layer and a layer of a swellable water-blocking material wherein the two layers and surfaces are bonded by means of an adhesive.

The use of the above-mentioned multilayer composite materials for producing longitudinal water-proof cable constructions is complex and cost-intensive owing to the multiplicity of the associated working steps. There was therefore a need. Which allows a simpler manufacture of longitudinally watertight cable constructions.

According to the invention, this object is achieved by the use of a water-swellable hotmelt adhesive essentially consisting of three components:<ol><li>A.) A non-water-soluble component comprising at least one water-insoluble polymer or copolymer and at least one further resin which is substantially insoluble in water and has a saponification number different from O.</li><li>(B) a water-soluble or water-dispersible component, which component contains at least one water-soluble or water-dispersible oligomer and / or polymer or copolymer,</li><li>C.) a water-swellable component consisting of a water-swellable homo- or copolymer,</li></ol>Wherein the components A, B and C are mixed homogeneously as hot-melt adhesives and surfacers or coating compositions for the production of waterproof construction. For the purposes of this invention, "homogeneously mixed" is understood to mean that the matrix of the mass has no macroscopic inhomogeneities. This does not mean that, in the microscopic range, different phases consist of the non-water-soluble component and the water-soluble component or water-swellable component. In particular, homogeneously mixed does not mean that the water-swellable homo- or copolymer of component C is to be present in one or both other components in molecularly dissolved form.

The melt-swellable adhesives, which are swellable with water, therefore constitute hot-melt adhesives, which can be used, in particular, in cable constructions

As a water-insoluble homo- or copolymer of component A, it is possible in principle to use all thermoplastic polymers known per se for use in hot-melt adhesives, for example polyamides, copolyamides, polyaminoamides, polyesters, polyacrylates, polymethacrylates, polyolefins and in particular ethylene vinyl acetate Copolymers or mixtures of one or more of the abovementioned polymers.

As a further resin of component A, all the known tackifying resins, with the exception of the pure hydrocarbon resins, can be used to increase the tackiness of the melt. The resins to be used according to the invention therefore have a saponification number different from 0. Particularly suitable for this purpose are the various rosin derivatives, ie, in particular the resin esters of abietic acid, but other polyterpenes and terpenephenol resins are also suitable.

For the constituents of component B, a large number of water-soluble or water-dispersible oligomers or homo- or copolymers are suitable. Examples which may be mentioned are polyethylene glycols in the molecular weight range between 400 and 20000, polyvinyl methyl ether, polyvinylpyrrolidone, copolymers of vinyl methyl ether or of vinylpyrrolidone, polyvinyl alcohols, water-soluble or water-dispersible polyesters or copolyesters, water-soluble or water-dispersible acrylate polymers.

The water-swellable component C can be formed by all those homo- and / or copolymers which, as hydrophilic materials, can absorb large amounts of water and also retain them under pressure. Without being immediately dissolved in the water. Such hydrophilic materials are also known as "superabsorbers". Examples which may be mentioned here are graft copolymers of starch or cellulose with acrylonitrile, acrylic acid or acrylamide, carboxymethylcellulose, maleic anhydride-poly-α-olefin copolymers, polyacrylamide. Polyacrylic acid and salts of the polyacrylic acid and optionally copolymers of acrylic acid or acrylamide with acrylate esters.

Depending on the use of the hot-melt adhesives according to the invention, these can have surface-adhesive properties or tack-free surfaces for so-called "block-free" versions. The latter compositions contain per se known wax additives, in particular bis-stearamide waxes. Furthermore, both versions of the hotmelt adhesives according to the invention can contain known commercially available stabilizing agents, which ensure a temperature stability of the formulations.

Particularly preferred surface-tacky swellable hot-melt adhesive compositions contain the following ingredients: 15 to 45% by weight of rosin ester or terpene phenol resins 15 to 40% by weight of thermoplastic copolymer, in particular ethylene vinyl acetate copolymers, 5 to 20% by weight of acrylate copolymers 5 to 30% by weight of polyethylene glycols, 5 to 15% by weight of polyvinyl ethyl ether, water-soluble or water-dispersible acrylate polymers or water-soluble or water-dispersible copolyesters 15 to 50% by weight of powdered polyacrylic acid salt, polyacrylamide or similar pulverulent superabsorbers 0.2 to 2.0% by weight of commercial stabilizers.

Particularly preferred swellable melt adhesive formulations in the block-free version include: 15 to 45% by weight of rosin ester, terpene phenol resin or the like 15 to 40% by weight of thermoplastic (co) polymer, in particular ethyl vinyl acetate copolymer 5 to 25% by weight of polyethylene glycols 15 to 50% by weight of powdered superabsorber, in particular polyacrylic acid salt 0.2 to 2.0% by weight of stabilizing agent 0.5 to 5.0% by weight of waxes, in particular ethylene bis-stearamide.

These inventive uses of the water-swellable hot-melt adhesives are suitable, for example, as coating of metal foils or glass-fiber-reinforced reinforcing elements made of plastic in the cable construction. A particularly preferred application is, for example, the direct coating of the central reinforcing element of optical waveguide cables.

This central element can be coated with the non-surface-adhesive version of the adhesive and then rolled up and interposed. The individual optical waveguides are arranged concentrically around this central element in conventional optical fiber cables. After reactivation of the non-surface-adhesive version of the adhesive on the central element, these optical fibers can be adhesively fixed directly on the central element and can then continue through further production steps. If necessary, The plastic tubes (tubes) which contain the optical waveguide (s) may be used. Can also be coated on the outer side with the hotmelt adhesive according to the invention. A covering of the optical waveguides with a water-swellable multi-layered adhesive tape or multi-layered flow material and additional longitudinal water sealing of the cavities between the central element and the tubes with a fat (petrojelly), which is necessary according to the prior art, can be dispensed with in the use of the hot-melt adhesives according to the invention. The construction-related cavities can be left in the cable construction as the water-swellable hot-melt adhesive completely fills these cavities as a result of the swelling process when entering the water, thus ensuring a reliable longitudinal water seal. This type of construction results in simplified connection technology, the possibility of fat-free work and a significant weight saving of the cable construction. In addition, a higher production speed is possible compared to the processing of source flows.

In the case of the use of the surface-adhesive version of the hot-melt adhesive according to the invention, this is applied directly to the central element and / or the optical waveguides in the cable construction line, in this case no reactivation of the hot-melt adhesive is necessary.

FIG. 1 shows schematically the cross-section through a light-waveguide cable, using the swellable hot-melt adhesives according to the invention. The central element<b>1</b> Is from several tubes <b>2</b> With light waveguides. A wrapping was shown<b>3</b> Of the optical waveguide with the swellable hotmelt adhesive. The end of the cable to the outside forms the cable jacket<b>4</b>.

The water-swellable hot-melt adhesives are prepared as follows:

Resin esters, ethylene vinyl acetate and acrylate copolymers are melted and homogenized at from 140 to 160 ° C. Subsequently, the polydiol or polydiols is added and homogenized. Thereafter, the polyvinyl methyl ether and the stabilizing agent are added and homogenized. Finally, the powdery polyacrylic acid salt is incorporated and homogenized. In the case of the block-free versions, the wax is then added last and homogenized again. Subsequently, the homogeneous melt is discharged into the corresponding packaging units and cooled to room temperature.

The following test is carried out in order to test the functionality of the water-swellable hot-melt adhesive:

A 0.1 mm thick polyester film is coated on both sides with the hotmelt adhesive in a layer of 0.2 mm to a maximum of 0.4 mm per side. The total layer thickness of the coated film must not exceed 1 mm. This film coated on both sides is wound around a Teflon rod (200 ml long, 19 mm diameter) with a maximum overlap of 2 mm at the longitudinal seam. A glass tube with an inner diameter of 23 mm and a length of 350 mm is provided with a loose cotton plug at its lower outlet, then the Teflon rod, which is wrapped with the coated film, is placed in the center of the glass tube, and the upper end of the vertical glass tube, Further loose cotton wool stoppers. A dropping funnel containing 250 ml of deionized water is placed above the glass tube.

If the water is slowly dripped dropwise from above into the glass tube, the hot melt adhesive swells within a short time in such a way that only a few milliliters of water flow out from the glass tube during a short initial phase. After this, no more water can penetrate.

The water-swellable hot-melt adhesive used for the above practice test according to the invention had the following composition:<ul><li>19.5 parts of pentaerythritol ester of abietic acid</li><li>29.8 parts of ethylene vinyl acetate</li><li>10.0 parts of a copolymer of ethylene, acrylic acid, vinyl acetate and vinyl alcohol</li><li>0.2 parts sterically hindered phenol as antioxidant</li><li>19.5 parts of polyethylene glycol, molecular weight 12,000</li><li>20.0 parts Sodium salt of polyacrylic acid (swelling agent)</li><li>1.0 part of ethylenebisstearamide (antiblocking agent).</li></ul>