Adhesive tube, composite tube and method for sealing using the same

Abstract: An adhesive tube, a composite tube comprising a heat-shrinkable tube having on the inner surface thereof the adhesive tube, and a method for sealing an object having an uneven surface comprising the steps of: inserting the object in the composite tube and then heating the composite tube. The adhesive tube comprises a double-layered thermoplastic resin layer comprising an outer layer and an inner layer, the outer layer having a melt index smaller than that of the inner layer.

Description: The present invention relates to an adhesive tube according to the precharacterising part of claim 1. An adhesive tube of this kind is to be inserted in a heat-shrinkable tube which is useful for waterproof sealing and/or insulation of a joint of wires or cables or for binding of a plurality of wires or cables. The present invention also relates to a composite tube comprising a heat-shrinkable tube having inserted therein the adhesive tube; and a sealing method using the composite tube. A tape-winding method is one of conventional methods for waterproof sealing or insulation of a joint of wires or cables or for binding a plurality of wires or cables. However, the tape-winding method has poor workability and does not always provide sufficient protection for a long period of time and is therefore lacking in reliability. Another method for binding a plurality of wires or cables comprises, as disclosed in JP-A-1-236268 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), providing a moisture-blocking arrangement for cables in a slit of a base material comprising a thermoplastic resin, making the base material into a coil, putting a heat-shrinkable sleeve on the coil, and heating the sleeve to shrink and to fluidize the base material in the sleeve thereby sealing the moisture-blocking arrangement. However, this method is poor in workability because insertion of the moisture-blocking arrangement into the base material requires much labor and time. Further, in the case where there is a great difference between the outer diameter of cables and the inner diameter of the heat-shrinkable sleeve to make a considerable gap therebetween, a possibility arises in that the thermoplastic resin does not thoroughly flow into the gap on heating and the gap remains unfilled, resulting in a failure of sufficient sealing. Another method for waterproof sealing or insulation of the joint of wires or cables comprises, as disclosed in JP-B-6-6341 (the term "JP-B" as used herein means an "examined published Japanese patent application"), putting a sealant and a heat-shrinkable tube having a hot-melt adhesive layer on the joint and heating the tube to shrink and to fluidize the hot-melt adhesive thereby sealing the gap. Where there is a great difference between the outer diameter of cables to be sealed and the inner diameter of the heat-shrinkable tube to make a considerable gap therebetween, this method also involves a possibility in that the thermoplastic resin does not thoroughly flow into the gap on heating leaving the gap unfilled, resulting in a failure of sufficient sealing. In order to avoid gap-formation between cables and a heat-shrinkable tube after shrinkage, it is preferred to increase the thickness of the hot-melt adhesive layer to sufficiently increase the amount of the adhesive which is fluidized on heating. However, a thermoplastic resin having high flowability has poor extrusion molding properties since it shows large variation in outer diameter, and the extruded tubing adheres to each other during the production. EP-A-481081 discloses a food packaging material comprising a composite constituted of a barrier substrate layer and a layer of an ethylene copolymer resin having carbon-carbon unsaturated bonds or of a composition comprising the same and a polyolefin. DE-A-3527436 discloses a tubular article comprising a double-layered thermoplastic resin tube, said tube comprising an inner sealing layer and an outer supporting layer. The melt indices of the inner layer and the outer layer are substantial equal, with the maximum difference being ± 8. EP-A-402841 discloses a food packaging material formed from a multilayer differentially crosslinked heat-sealable film. JP-A-3-227229 discloses a composite body of a nonfoamed film and a heat-shrinkable foamed film. The object of the present invention is to provide an improved adhesive tube capable of being inserted into a heat-shrinkable tube to form a composite tube for waterproof sealing and/or insulation of a joint of wires or cables or for binding a plurality of wires or cables. This object is solved by providing an adhesive tube (10) comprising a double-layered thermoplastic resin tube comprising an outer layer (12) and an inner layer (11) wherein the thermoplastic resin is not a crosslinked polymer, characterized in that said outer layer (12) has a melt index of from 0.1 to 10 g/10 minutes as measured at a temperature of 190°C and a load of 2,160 g according to JIS K6730 and said inner (11) layer has a melt index of from 20 to 140 g/10 minutes as measured at a temperature of 190°C and a load of 2,160 g according to JIS K6730. The present invention further provides a composite tube comprising a heat-shrinkable tube (20) having on the inner surface thereof an adhesive tube (10) as defined above. The present invention is also directed to a method for sealing an object having an uneven surface, said method comprising the steps of inserting said object into a composite tube as defined above, and then heating said composite tube. Preferred embodiments of the present invention are set forth in the dependent claims. Fig. 1 shows a cross section of one embodiment of an adhesive tube according to the present invention. Fig. 2 shows a cross section of one embodiment of a composite tube according to the present invention. A cross section of an embodiment of an adhesive tube according to the present invention is shown in Fig. 1. In this embodiment, the adhesive tube comprises a double-layered thermoplastic resin tube 10, which comprises an outer layer 12 and an inner layer 11. The melt index of the outer layer 12 is smaller than that of the inner layer 11. A cross section of an embodiment of a composite tube according to the present invention is shown in Fig. 2. In this embodiment, an adhesive tube 10 is laminated on the inner wall of a heat-shrinkable tube 20. The adhesive tube 10 has the same constitution as the above embodiment of the adhesive tube. When the composite tube of the present invention is sufficiently heated, the heat-shrinkable tube completely shrinks, and the adhesive tube inside the heat-shrinkable tube maintains its thermoplastic property, so that no unevenness takes place on the inner and outer surfaces of the heat-shrinkable tube after shrinkage. When the outer diameter of the inserted wire or cable to be sealed is approximately equal to the inner diameter of the completely shrunk heat-shrinkable tube, the inner layer maintaining its thermoplastic property is pressed out of the outer layer, covers the inserted wire or cable, and completely fills the gap between the wire or cable and the tube. Examples of the thermoplastic resin to be used as an adhesive tube includes a polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, a polyamide, and a polyester. Among these, a polyamide, an ethylene-vinyl acetate copolymer, and a polyester are preferably used, with a polyamide and an ethylene-vinyl acetate copolymer being more preferred. The thermoplastic resin is not a crosslinked polymer because it should be melted and fill the gaps on heating. The heat-shrinkable tube may comprise an electron radiation-crosslinked polyolefin, such as an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer. From the viewpoint of adhesion, the resin constituting the heat-shrinkable tube and that constituting at least the outer layer of the adhesive tube which comes into contact with the heat-shrinkable tube are preferably the same. However, these resins are not particularly limited in kind as long as they are brought into intimate adhesion to each other after shrinkage. The thermoplastic resins constituting the inner and outer layers of the adhesive tube are also not limited as long as they are brought into intimate adhesion to each other after shrinkage. The total thickness of the inner and outer layers of the adhesive tube is preferably 0.2 mm or more for sealing the object having an uneven surface. The thickness of the outer layer is generally from 0.1 to 10 mm, preferably from 0.2 to 0.5 mm, more preferably from 0.3 to 0.4 mm. The thickness of the inner layer is generally from 0.1 to 10 mm, preferably from 0.2 to 0.5 mm, more preferably from 0.3 to 0.4 mm. The adhesive tube can be produced by co-extrusion with high precision of its outer diameter in the longitudinal direction by selecting, as a thermoplastic resin for the outer layer, a resin having a melt index of from 0.1 to 10, preferably 1 to 10, more preferably from 2 to 7, and is lower than that of the resin for the inner layer. The melt index of the inner layer is generally from 20 to 140, preferably from 20 to 80. The melt index used herein means an amount (g) of molten resin effused per 10 minutes through a nozzle (specified in JIS K6730) at 190°C under a load of 2,160 g. The combination of the resulting adhesive tube and a heat-shrinkable tube provides a composite tube having an inner diameter of the innermost layer of from 0.3 to 25 mm, preferably from 2 to 7 mm, and the outermost diameter (i.e., the outer diameter of the heat-shrinkable tube) of 1.3 to 51 mm, preferably 5 to 15 mm. The difference between the outer diameter of the adhesive tube and the inner diameter of the heat-shrinkable tube is generally from 0.1 to 0.3 mm, preferably 0.2 mm. The inner layer of the adhesive tube may be endowed with adhesiveness to a polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, a polyamide, etc. by proper selection of the thermoplastic resin therefor. The present invention will be described in more detail by referring to the following examples. EXAMPLE 1 An uncrosslinked double-layered adhesive tube having an inner diameter of 5.8 mm, an outer diameter of 6.8 mm, and a length of several tens of millimeters in which the outer layer comprised an ethylene-ethyl acrylate copolymer having a melt index of 5 g/10min ("Evaflex A701" produced by Du Pont-Mitsui Polychemicals Co., Ltd.) and the inner layer had a thickness of 0.4 mm and comprised a polyamide having a melt index of 70 g/10min ("Versalon DPX-1301" produced by Henkel Hakusui Corporation) was completely inserted into a heat-shrinkable tube having an inner diameter of 7.1 mm and an outer diameter of 7.6 mm and having the same length as the adhesive tube, which comprised an ethylene-ethyl acrylate copolymer having a melt index of 5 g/10min before crosslinking ("Evaflex A701" produced by Du Pont-Mitsui polychemicals Co., Ltd.), capable of shrinking by half in its radial direction on heating. When the resulting composite tube was shrunk at 125°C, the gap in the heat-shrinkable tube was completely filled up with the inner layer of the adhesive tube. EXAMPLE 2 An uncrosslinked double-layered adhesive tube having an inner diameter of 5.8 mm, an outer diameter of 6.8 mm, and a length of several tens of millimeters in which the outer layer comprised a polyethylene having a melt index of 1.4 g/10min ("Sumikathene C215" produced by Sumitomo Chemical Co., Ltd.) and the inner layer had a thickness of 0.4 mm and comprised a polyamide having a melt index of 50 or more ("Versalon DPX-1301" produced by Henkel Hakusui Corporation) was completely inserted in a heat-shrinkable tube having an inner diameter of 7.1 mm and an outer diameter of 7.6 mm and having the same length as the adhesive tube, which comprised an ethylene-methyl acrylate copolymer having a melt index of 6 g/10min before crosslinking ("Yukalon XH-500M" produced by Mitubishi Chemical Co., Ltd.), capable of shrinking by half in its radial direction on heating. When the resulting composite tube was shrunk at 120°C, the gap in the heat-shrinkable tube was completely filled up with the inner layer of the adhesive tube. EXAMPLE 3 An uncrosslinked double-layered adhesive tube having an inner diameter of 5.8 mm, an outer diameter of 6.8 mm, and a length of several tens of millimeters in which the outer layer comprised an ethylene-ethyl acrylate copolymer having a melt index of 5 g/10min ("Evaflex A701" produced by Du Pont-Mitsui Polychemicals Co., Ltd.) and the inner layer had a thickness of 0.4 mm and comprised a polyamide having a melt index of 70 g/10min ("Versalon DPX-1301" produced by Henkel Hakusui Corporation) was completely inserted in a heat-shrinkable tube having an inner diameter of 7.1 mm and an outer diameter of 7.6 mm and having the same length as the adhesive tube, which comprised an ethylene-vinyl acetate copolymer having a melt index of 1.5 g/10min before crosslinking ("Evatate H2020F" produced by Sumitomo Chemical Co., Ltd.), capable of shrinking by half in its radial direction on heating. When the resulting composite tube was shrunk at 125°C, the gap in the heat-shrinkable tube was completely filled up with the inner layer of the adhesive tube. COMPARATIVE EXAMPLE 1 A polyamide having a melt index of 70 ("Versalon DPX-1301" produced by Henkel Hakusui Corporation) was extruded into a single-layered tube having an inner diameter of 5.8 mm and an outer diameter of 6.7 mm. The extruded tube showed considerable variation in diameter. The tube was cut to a length of several tens of millimeters and inserted into a heat-shrinkable tube having the same length having an inner diameter of 6.8 mm and an outer diameter of 7.7 mm comprising an ethylene-ethyl acrylate copolymer having a melt index of 5 g/10min before crosslinking ("Evaflex A701" produced by Du Pont-Mitsui Polychemicals Co., Ltd.). However, 50% or more of the tubes per lot could not be completely inserted, resulting in a poor yield. Since the extruded tube was so sticky to each other immediately after extrusion, it was necessary to cut the tube immediately after extrusion and keep the cut tubes separately, which required infinite labor. As described above, the adhesive tube of the present invention has excellent precision of outer diameter in its longitudinal direction and makes a great contribution to the improvements of workability and product quality. A composite tube comprising a heat-shrinkable tube having inserted therein the adhesive tube of the present invention can have desired adhesive strength and desired characteristics through proper choice of the resin materials for the inner and outer layers of the adhesive tube and the heat-shrinkable tube and is extremely effective in sealing an object with an uneven surface, for example, joints of wires or cables or a wire or cable bundle.

Claims: An adhesive tube (10) comprising a double-layered thermoplastic resin tube comprising an outer layer (12) and an inner layer (11) wherein the thermoplastic resin is not a crosslinked polymer, characterized in that said outer layer (12) has a melt index of from 0.1 to 10 g/10 minutes as measured at a temperature of 190°C and a load of 2,160 g according to JIS K6730 and said inner (11) layer has a melt index of from 20 to 140 g/10 minutes as measured at a temperature of 190°C and a load of 2,160 g according to JIS K6730. The adhesive tube (10) of claim 1, wherein said inner layer (11) has a melt index of from 20 to 80 g/10 minutes as measured at a temperature of 190°C and a load of 2,160 g according to JIS K6730. The adhesive tube (10) of claim 1, wherein said outer layer (12) and said inner layer (11) each comprises a polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, a polyamide or a polyester. The adhesive tube (10) of claim 1, wherein said outer layer (12) and said inner layer (11) each comprises a polyamide, an ethylene-vinyl acetate copolymer or a polyester. The adhesive tube (10) of claim 1, wherein said double-layered thermoplastic resin tube has a total thickness of at least 0.2 mm. A composite tube comprising a heat-shrinkable tube (20) having on the inner surface thereof an adhesive tube (10) as claimed in claim 1, 2, 3, 4 or 5. The composite tube of claim 6, wherein said heat-shrinkable tube (20) comprises an electron radiation-crosslinked polyolefin. A method for sealing an object having an uneven surface, said method comprising the steps of inserting said object into a composite tube as claimed in claim 6 or 7, and then heating said composite tube. The method of claim 8, wherein said object comprises a polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer or a polyamide.

Inventors: KISHIMOTO TOMOYOSHI, MATSUFUJI SHIGEO, KISHIMOTO, TOMOYOSHI, MATSUFUJI, SHIGEO, Kishimoto, Tomoyoshi, c/o Kumatori Works of, Matsufuji, Shigeo, c/o Kumatori Works of
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1995
Main classification: B29C61
IPC codes: F16L11, B29C61, B32B7