Background Art Generally cables laid underground are coated with various coating materials to prevent permeation of water into their joint. <BR> <P>For example, a heat shrinkable sleeve can be wrapped around a joint, fixed with a banding clip and adhered to the joint by being heated with a burner such as a torch lamp and so on.

Such heat shrinkable sleeves are classified into single layered type and composite layered type. Single layered heat shrinkable sleeves are used for small communication cable or a simple connector. The single layered heat shrinkable sleeves are prepared by heating and mixing high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE)'or polypropylene

(PP) with carbon black, silicon dioxide and other additives to yield a heat-melting sheet, which is then cross-linked, and drawn.

However said single layered heat shrinkable sleeve has a low heat shrinkage rate and cannot seal up completely joints of communication cable from the outside environment. Therefore, for joints of communication cable composed of multiple lines, composite layered heat shrinkable sleeves are used.

Said composite layered heat shrinkable sleeves can be explained with reference to Figure 5 as follows.

First, on an outer side or on both sides of a fabric (2) is extruded and coated a mixture of carbon black and a polymer of high melting point (1) (hereinafter referred to as"polymer of high m. p.") with a density of 0.94 to 0.96, which has been previously subjected to heat melting. Said polymer coated on the fabric is subsequently cross-linked to produce a complex composite of heat shrinkable fabric and polymer (hereinafter referred to as"the fabric composite"). Further a metal layer (5) on which a polymer of low melting point (3) (hereinafter referred to as "polymer of low m. p.") in the form of a film or an extruded product is laminated is coated on the inner side, and an adhesive having a low melting point (7) such as polyamide, ethylene vinylacetate (EVA) and the like is finally coated to complete the product. By using such a composite layered heat shrinkable sleeve, a disturbance of electromagnetic wave from the outside can be blocked,

a water resistant effect is remarkably enhanced and the joints of the communication cable can be sealed more efficiently.

With respect to techniques of conventional heat shrinkable sleeves, European Patent No. 112390 discloses a sleeve product having improved preservability and impermeability and British Patent No. 1604379 discloses a sleeve product in which a metal <BR> <BR> <BR> <BR> <BR> <BR> sheet of a thickness of 10 to 25 um is used. However, these products have drawbacks such as heat shrinkage of the sleeve is inhibited due to the use of a thick metal sheet. Further, neither the heat shrinkable sleeve of European Patent No. 116393, which employs a material for a polymeric matrix nor the heat shrinkable sleeve of British Patent Publication No. 2075991 which uses an adhesive such as polyamide and EVA resin has provided a satisfactory effect in complete sealing joints of communication cable. Korean Patent Publication No. 96-753, which is related to a conventional reinforcement for a heat shrinkable sleeve for sealing joints of communication cable, describes that, while the polymeric substance (1) disposed at the outer side of the fabric (2) should be desirably cross-linked so as to prevent it from being deteriorated or shifted in terms of physical properties particularly when the sleeve is heat-recovered by a torch, the polymer (la) disposed at the inner side should desirably not be cross-linked so as to be flown and combined with an adjacent strengthening layer during a heat recovery process. More

specifically, it is clearly described that said uncross-linked polymer (la) applied at the inner side of the fabric (2) can be flown and bond to a strengthening layer (3a, 4.5.8), and therefore enhancing its bonding to the strengthening layer. It is also described that the polymer (1) which is not cross-linked and disposed at the inner side, namely the meltable substance layer between the fabric composite and the strengthening layer should desirably have a thickness of 20 to 30 um and the reinforced layer may consist a single layered or double layers or more including for instance a"Mylar" (i. e., enriched polyester film) or nylon layer attached to a single side or both sides of the metal layer such as aluminum.

However, said conventional heat shrinkable sleeve has problems as the following.

Namely, in a conventional heat shrinkable sleeve, only the outer polymer of the heat shrinkable fabric is cross-linked and the inner materials are laminated after the outer polymer is cross-linked. Subsequently, the fabric composite is adhered to the strengthening layer by being subjected to a corona treatment and heat-melting, in order to strengthen the bonding between them.

Accordingly said process, which consists of cross-linking-- lamination--corona treatment, cannot be carried out simply.

Thus the process is complicated, and the production efficiency is lowered. Further it has a problem that the inner polymer is

often separated from the fabric or the sleeve is burst due to the lack of cross-linkage in the inner polymeric substance. A"Mylar", i. e., polyester layer (8), is employed to support the aluminum layer and a LLDPE layer (9) is used to prevent the oxidation of the aluminum layer. Since the LLDPE layer (9) has poor adhesiveness with adhesives having a low melting point (which is mostly polyamide), a film of ethylene acrylic acid (EAA) co-polymer should be coated between them by extrusion. Further an urethane adhesive should be coated between all these layers to adhere the respective layers. Consequently the number of layers of the reinforcement amounts to eight and the total thickness of the product becomes 100 to 105 um. Still further in respect to reinforcement of conventional heat shrinkable sleeves, a film of polymer of low m. p. (3a) is adhered to a polyester film through a urethane adhesive (4) by dry lamination and it should be aged at 40 to 50 C for 24 to 48 hours. And then polyester film (8) is adhered to the aluminum layer through a urethane adhesive (4) and it should be aged again at 40 to 50 C for 24 to 48 hours. <BR> <BR> <BR> <BR> <BR> <BR> <P>Subsequently the co-polymer of LLDPE and EAA is co-extruded and<BR> <BR> <BR> adhered to the aluminum layer (5) through a urethane adhesive and it is aged under the same condition as above and then the EAA layer is adhered to the polyamide adhesive layer. Accordingly, the process for production of said reinforcement has problems of being

complicated, time consuming, and expensive. Namely it has been a problem that the aging time itself requires 3 to 4 days for producing a reinforcement of the conventional heat shrinkable sleeve.

Disclosure of Invention The present invention is contrived to solve the aforementioned problems.

An object of the present invention is to provide a heat shrinkable sleeve for sealing junctions of the communication cable and a reinforcement for improving the functions of a sleeve. More particularly, an object of the invention is to provide a heat shrinkable sleeve and a reinforcement thereof, wherein, by cross-linking polymers of outer layer having high m. p., fabric composite, polymers of inner layer having high m. p., and a polymer layer having low m. p., the inner polymer of high m. p. does not flow during heat-recovery and remains to be bound to the fabric, therefore when it is applied to a heat shrinkable sleeve of air injection type, the sleeve becomes more resistant to the inner air pressure and the outside air, and bursting during heat recovery can be prevented. A further object of the invention is to provide a heat shrinkable sleeve and a reinforcement thereof, wherein, by lowering the total thickness of the reinforcement attached to the heat shrinkable sleeve to one-third of the thickness of

conventional products, the time for heat-recovery or contraction can be shortened remarkably.

Brief Description of Drawings Figure 1 is a cross section of a reinforcement for a heat shrinkable sleeve of the present invention, Figure 2 is a cross section of a heat shrinkable sleeve of the present invention, Figure 3 is a cross section of a heat shrinkable sleeve when it is applied to communication cable and is subjected to heat contraction, Figure 4 is a cross section of a conventional reinforcement for a heat shrinkable sleeve, Figure 5 is a cross section of a conventional heat shrinkable sleeve.

Best Mode for Carrying out the Invention In accomplishing the above objects, a reinforcement for a heat shrinkable sleeve of the present invention is characterized in that a polymer of low melting point (3), an oil-based or aqueous emulsion adhesive (4), a metal layer (5) and an emulsion co-polymer primer (6) are laminated successively to improve the function of the sleeve in sealing junctions of communication cable by heat contraction.

In the present invention, the polymer of low m. p. (3) means a thermoplastic polymer having a melting point of below 200C and an adhesiveness with a fabric.

Said oil-based or aqueous emulsion adhesive (4) includes all adhesives of emulsion type used for adhering films. Urethane adhesive is preferable. The thickness of the oil-based or aqueous emulsion adhesive (4) is desirably 0.5 to 1 um.

The metal layer (5) improves the pressure retaining ability and the creep performance of the heat shrinkable sleeve and prevents the permeation of other substances, and is desirable to haveatensile strengthofmorethanlOMPaetlO0 C. Particularly, aluminum is preferably used.

Said emulsion co-polymer primer (6) includes all primer materials of emulsion type which are used in the field of film coating to combine layers which are not by themselves adhesive to each other. Examples for such primer include a primer which consists principally of ethylene-acrylic acid co-polymer, propylene-acrylic acid co-polymer and butylene-acrylic acid co-polymer being dispersed in water. The emulsion co-polymer primer (6) is desirably coated with a coating of a thickness of 0.5 to 1um.

The heat shrinkable sleeve of the present invention is a heat shrinkable sleeve for adhering to junctions of the communication

cable by heat shrinkage, characterized in that the polymer of high melting point (1), fabric (2), the polymer of high m. p. (la), polymer of low m. p. (3), oil-based or aqueous emulsion adhesive (4), metal (5), emulsion co-polymer primer (6) and low m. p., adhesive (7) are successively laminated in turn.

The polymer of high m. p. (1) of the present invention signifies a polymeric substance having a melting point of over 200C, for instance ethylene/vinylacetate co-polymer, ethylene/ethyleneacrylate co-polymer, LLDPE, LDPE, MDPE, HDPE, polypropylene, polyester and polyamide can be used.

The fabric (2) of the present invention indicates a fabric shrinkable by heating, and any conventional fabrics used for heat shrinkable sleeves can be employed without restriction. To illustrate, a heat shrinkable fabric woven from glass fiber such as warp and HDPE such as weft may be used.

Said polymer of high m. p. (1), fabric (2), polymer of high m. p. (la) and polymer of low m. p. (3) are desirably to be cross-linked. All conventional methods for polymer cross-linking employed in the pertinent field may be adopted, particularly the radiation cross-linking method is preferred.

The present invention will be explained in the following, particularly with reference to the drawings attached.

Figure 1 is a cross-section of the reinforcement for the heat

shrinkable sleeve of the present invention, and Figure 2 is a cross-section showing the heat shrinkable sleeve with the reinforcement shown in Figure 1. As indicated in the figures, the reinforcement for the heat shrinkable sleeve of the present invention is prepared by coating the polymer of low m. p. (3) film with an amount of 1 to 3 g/m2 (thickness : 0.5 to 1 pm) of the oil-based or aqueous emulsion adhesive (4) to laminate the metal (5) layer and by coating the other surface of the metal (5) layer with an amount oflto3g/m2 (thickness: 0.5 to 1 um) of the emulsion co-polymer primer (6).

In addition, in the reinforcement for the heat shrinkable sleeve of the present invention, the polymer of high m. p. (1) is coated on the outer side of the fabric (2) by melt coating and, then the polymer of high m. p. (la) is coated by melt coating on the inner side of the fabric (2) to produce the fabric composite.

Apart from this, the oil-based or aqueous emulsion adhesive (4) is coated on the surface of the polymer of low m. p. (3) at the amount of 1 to 3 g/m2 (thickness: 0.5 to 1 pm) to laminate the metal (5) layer, on which the emulsion co-polymer primer (6) is coated at the amount of 1 to 3 g/m2 (thickness: 0.5 to 1 um) and the surface thereof is coated with the adhesive (7), to complete the reinforcement. The polymer of low m. p. (3) in the reinforcement for the heat shrinkable sleeve thus prepared is then adhered to the polymer of high m. p. (la), and the reinforcement is

subsequently coated with the adhesive layer (7) to complete the product.

In particular, a conventional heat shrinkable sleeve is disadvantageous in that in order to adhere the polyamide adhesive to the EAA film surface (10), the EAA film surface (10) should be treated with hot air of 100 to 130C by a high frequency corona treatment of 20,000 to 25,000V. However, the heat shrinkable sleeve of the present invention employing the emulsion co-polymer primer (6) coated on the surface of the aluminum layer (5) has excellent adhesiveness without any treatment or modification being applied to the polyamide adhesive (7) and can be used without aging.

Table 1 below shows the result of a test on physical properties of the reinforcement for the heat shrinkable sleeve of the present invention.

Table 1 Property Unit Value Remarks determined Adhesive force between kg/(25mm) Not exfoliated layers MD 5.75 Tensile MU 5.75 Strength CD 5. 40 Moisture Permeability 0. 0 KSM 3207 MD 74. 6 Extension rate on-ASTM D638 bursting CD 70.8 Adhesive force to Kg/mm Not exfoliated polymeric substance Adhesive force to Kg/mm Not exfoliated polyamide Temperature of thermal °C 80 ASTM D648 deformation

In the above test for physical properties, five samples were taken to give the mean value of each property, which was obtained to determine the adhesive force between the fabric composite and the reinforcement.

Table 2 shows the result of the test on the contraction time and contraction condition with respect to the entire structural thickness of the reinforcement for said heat shrinkable sleeve, when heated.

Table 2 Sheet of the interior Thickness of Time for after heat contraction Remarks reinforcement completing (Pleat internal of the contraction metal layer) (Unit : mm) 30 8 min and 17 sec 0.5~1.0 Contracted in a circular form 50 8 min and 49 sec 1.0-1.5 Contracted in a circular form 70 10 min and 6 sec 1.5~2.5 Unbalanced on one side 100 13 min and 11 sec 2. 0~2. 7 Irregular oval form 150 17 min and 32 sec Over 3.0 Irregular oval form

The data for the above test were obtained by attaching the reinforcement for the heat shrinkable sleeve of the present invention to a heat shrinkable sleeve and subsequently treating it by a torch method conventionally utilized in communication constructions. The changes in the thickness of the reinforcement

result from the changes in thickness of the film adhered to the metal layer.

As a result. it is understood that the thicker the reinforcement attached to the heat shrinkable tube is, the longer the processing time it takes, and the appearance becomes irregular after processing.

Table 3 below summarizes the comparison of the heat shrinkable sleeve of the present invention with a conventional heat shrinkable sleeve, wherein the sleeves and their effects clearly distinguished.

Table 3 Item The present invention Prior art Cross-linking Simultaneous execution on Execution on the polymer of the the polymer (1) of inner and outer layer only outer layer, fabric (2), (separate process) polymer of low m. p. (3) Number of 4 8 layers of the reinforcement Process for 1. Adhesion of the polymer of 1. Adhesion of the low density preparation low m. p. (3) to the aluminum polymeric film to polyester layer (5) 2. Adhesion of the aluminum 2. Coating of the aqueous layer emulsion primer (6) on the 3. Coating of the low density surface of aluminum layer (5) polyethylene by film extrusion 4. Coating of the EAA polymer by film extrusion Overall 30-40 100 ~ 105 thickness of the product (pm) Method of Adhesion by melting of the Adhesion of the reinforcement attaching to polymer of low m. p. by melting of the polymer of the sleeve high m. p. after the corona treatment Adhesion of Adhesion to the surface of Adhesion to a co-extruded film polyamide the aqueous emulsion primer of LLDPE and polymeric EAA or to layer having a thickness of a film of the same prepared by 0.1 to 0.005 um separate processes, having a (adhesive force-no thickness of 30-40 um exfoliation) (adhesive force-700g/15mm) Torch work No bursting of the sleeve on Bursting of the sleeve on heating heating

The present invention is not restricted to the above examples, and variations are allowed within the technical scope of the present invention.

Industrial Applicability As set forth herein above, the reinforcement for the heat shrinkable sleeve of the present invention has an overall thickness of a mere 30% of the thickness of conventional products. Thus, its effect on sealing up the joints of the communication cable by heat contraction is excellent. The adhesive force between the sheet layers is high and exfoliation of the layers does not occur even after torch treatment. Simplification of the process can be accomplished, and the production cost is lowered. Particularly, the time for contraction on processing is remarkably shortened.