JP2619348B2 - Heat shrink tube manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a heat-shrinkable tube having a high shrinkage and a high fusibility.

[0002]

2. Description of the Related Art Insulated rubber / plastic cables 1
In general, as shown in a cross section in FIG. 7, a structure in which an inner conductive layer 3, an insulator 4, and an outer conductive layer 5 are sequentially formed concentrically outside a central conductor 2 is shown. In such a rubber / plastic insulated cable 1, when a long line is laid, the cable length must be limited on the site because the cable length is restricted in manufacturing, transportation, and laying.

As shown in FIG. 8, the cables are connected on site by removing the coating on the ends of the cables 1 and 1 to be connected, exposing the conductors 2 and abutting the end faces of each other. After the conductor connection sleeve 6 is put on the outer circumferences of the two conductors 2 in this state, an inner conductive semiconductive tube 7 as a substitute for the inner semiconductive layer 3 is put on the outside of the conductor connection sleeve 6. Multiple layers of insulating tape made of uncrosslinked thermoplastic resin are wrapped around the outside, and cable 1
An insulating layer 8 as a substitute for the insulator 4 is formed, and a semiconductive tube for external conduction 9 as a substitute for the external semiconductive layer 5 is provided on the outside thereof. The inner conductive semiconductive tube 7 and the outer conductive semiconductive tube 9 are previously covered on the outer periphery of one of the cables 1 at the time of cable connection, and after the conductor connection sleeve 6 is attached, the conductor The outer conductive semiconductive tube 9 is moved to the outside of the insulating layer 8 after the insulating layer 8 is formed, and is contracted by being moved to the outside of the connection sleeve 6 and contracted to adhere to the outer periphery. Close to the outer periphery.

Accordingly, in many cases, a heat-shrinkable tube is used for the inner conductive semiconductive tube 7 in order to make it adhere to the outside of the conductor connection sleeve 6. Insulating layer 8 formed outside
It is necessary to prevent the entry of dust and foreign matter into the interface with the interface, and to fuse them so that projections, peeling and voids (bubbles) are not formed at the interface, to prevent the occurrence of electric field irregularities.
Similarly, the semiconductive tube 9 for external conduction needs to be fused to the interface with the insulating layer 8 so that dust and foreign matter are not mixed, peeled, and voids are not generated. Therefore, the semiconductive tube for inner conduction 7 is a heat-shrinkable tube having a high shrinkage rate, and has a smooth outer peripheral surface that is in contact with the insulating layer 8 and has the insulating layer 8.
It is necessary to make it easy to fuse. Similarly, the semiconductive tube for external conduction 9 is a heat-shrinkable tube having a high shrinkage rate,
In addition, it is necessary that the inner peripheral surface in contact with the insulating layer 8 is smooth and easily fused to the insulating layer 8.

[0005]

The semiconductive heat-shrinkable tube is made of a resin composition comprising a thermoplastic resin such as polyethylene or ethylene-ethyl acrylate copolymer as a base polymer and a conductive carbon powder added thereto. Is extruded into a tube having a predetermined thickness. Then, the semiconductive tube is manufactured by irradiating, for example, an electron beam to crosslink, and then expanding the diameter while heating to a melting temperature, and the expansion rate at this time is almost equal to the heat shrinkage rate. Become.
However, the extruded semi-conductive tube has a large amount of conductive carbon powder and the like, so the elongation performance in the heated state is reduced, and the thickness of the tube is uneven. However, there is a problem that the heat-shrinkable tube cannot be formed into a heat-shrinkable tube having a high surface shrinkage rate, although the tube is easily broken and the diameter cannot be increased so much. In addition, since the semiconductive tube is used after being electronically cross-linked, if the degree of cross-linking is high, there is a problem that the fusion property with the insulating layer is poor.

Therefore, as a method of producing a semi-conductive heat-shrinkable tube having a high shrinkage ratio, a resin compound to which conductive carbon powder and other fillers are added is extruded into a sheet shape.
After cross-linking the sheet by, for example, irradiating an electron beam, the sheet is cut into a tape having a predetermined width and is first-stretched, and the first-stretched stretched tape is wrapped around the outer circumference of the heating mandrel in multiple layers. By heating and fusing the layers of the stretched tape together to form a cylindrical body integrally, the cylindrical body is heated and expanded in diameter (secondarily stretched) to obtain a semiconductive heat-shrinkable tube having a high shrinkage rate. The way has been done.

However, in the method for manufacturing a semiconductive heat-shrinkable tube using this stretched tape, the wall thickness can be made uniform and a high shrinkage rate can be obtained. This causes a problem that voids and peeling are liable to occur when fused to the insulating layer. Further, since the stretched tape is subjected to primary stretching after being electronically crosslinked, the degree of crosslinking is high, and therefore, there has been a problem that the adhesiveness to the insulating layer is low.

The present invention has been made in view of the above circumstances, and is intended to produce a heat-shrinkable tube having a high shrinkage rate, at least one of an inner peripheral surface and an outer peripheral surface being smooth, and easily fused to an insulating layer. It is intended to provide a way.

[0009]

Means for Solving the Problems As a means for solving the above-mentioned problems, the method of the first invention is to overlap a stretching tape of a thermoplastic resin which has been stretched after crosslinking on the outer periphery of a heating mandrel. After covering the outside with an uncrosslinked extruded tube made of the same material as the stretched tape, the temperature of the heating mandrel is increased, and when the extruded tube is heated and softened, the extruded tube is extruded. Wrap a holding tape with low thermal expansion around the outside of the molded tube, further raise the temperature of the heating mandrel, heat the stretched tape and the extruded tube to the melting temperature, fuse them together to form a cylindrical body, and then cool it Then, after removing the presser tape, the temperature of the heating mandrel is raised again, and the integrated cylindrical body is heated to a melting temperature and expanded to a predetermined size. To have.

According to a second aspect of the present invention, an uncrosslinked extruded tube of a thermoplastic resin is placed over the outer periphery of the heating mandrel, and then the heating mandrel is heated to soften the extruded tube by heating. At this point, a stretching tape that has been subjected to a stretching process after crosslinking is wrapped around the outside thereof, and a holding tape having a low thermal expansion is further wrapped around the outside thereof, and then the heating mandrel is further heated to obtain the stretching tape and extrusion molding. The tube was heated to the melting temperature and fused together to form a cylindrical body, then cooled once, the holding tape was removed, and then the heating mandrel was heated again to bring the integrated cylindrical body to a melting temperature. It is characterized in that it is heated to a predetermined size and heated to a predetermined size.

[0011]

As described above, in the first invention, a stretching tape of a thermoplastic resin stretched after crosslinking is wound around the outer periphery of the heating mandrel, and the outside is formed of the same material as the stretching tape. After covering the uncrosslinked extruded tube, the temperature of the heating mandrel is increased, and when the extruded tube is heated and softened, a pressing tape having a small thermal expansion is wound around the outside of the extruded tube and heated. When the temperature of the heating mandrel is further increased while preventing sagging, the stretched tape and the extruded tube are melted and fused together to form a cylindrical body. After cooling the cylinder once, removing the holding tape wound outside, the heating mandrel is heated again to heat the cylinder to the melting temperature, and if the diameter is expanded to a predetermined size, the cylinder is heated. The inner peripheral part of the cylinder is subjected to secondary stretching of the stretched tape, so the shrinkage is large, and the outer peripheral part of the cylindrical body to be fused to the insulator is formed by an extruded tube, so that it is smooth and uncrosslinked. Therefore, it is easy to fuse.

Further, in the second invention, an uncrosslinked extruded tube of a thermoplastic resin is placed over the outer periphery of the heating mandrel, and then the heating mandrel is heated, and the extruded tube is heated and softened. At this point, a stretched tape that has been subjected to a stretching process after cross-linking is wrapped around the outside, and a holding tape with low thermal expansion is further wrapped around the outside to prevent heat dripping, and then the heating mandrel is further heated. Then, the stretched tape and the extruded tube are heated to a melting temperature and fused together to form a cylindrical body, then cooled once, the holding tape is removed, and then the heating mandrel is heated again and integrated. If the cylindrical body is heated to a melting temperature to expand the diameter to a predetermined size, the outer peripheral portion of the cylindrical body is subjected to secondary stretching of the stretched tape, so that the shrinkage is large, and the cylindrical body is fused to the insulator. That the inner peripheral portion of the cylindrical body, with a smooth because it is formed by extrusion tube, fused because uncrosslinked easily.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the method of the present invention is applied to the production of a semiconductive heat-shrinkable tube used for coating a cable connecting portion will be described below with reference to FIGS.

FIG. 1 shows an example of an apparatus for manufacturing a heat-shrinkable tube using a heat pipe type heating mandrel used for carrying out the method of the present invention.
Reference numeral 1 denotes a heating mandrel 12 on which a material tube or the like is mounted on the outside thereof, and a detachably mounted outer surface of the heating mandrel 12 with a predetermined space, and melts and softens the material tube to blow air. At this time, it has an expansion restriction pipe 13 for restricting the expansion limit of the material tube so as to have a predetermined outer diameter and preventing adhesion of dust and the like.

The heating mandrel 12 is a container 1 made of a metal pipe such as copper or copper alloy having excellent heat conductivity.
A wick (not shown) is provided on the inner peripheral surface of 4, and
Only the condensable working fluid is sealed in the inside thereof to provide a heat pipe function. Both ends of the container 14 are formed to have a small diameter by narrowing the outer diameter, and one end formed to this small diameter is provided. A portion (the left end in FIG. 1) is a heating / cooling portion 15 that is heated when the heating mandrel 12 is heated and is cooled during cooling, and a central portion of the heating mandrel 12 has a fixed outer diameter. Processing part 1
6 are formed.

A workpiece W such as a material tube is mounted on the processing portion 16 of the heating mandrel 12 with the outer expansion regulating pipe 13 removed. At the end (right end in FIG. 1) of the heating mandrel 12 on the side opposite to the heating / cooling section 15, an air blowing port 17 provided with a connector is provided. An air passage 17 a communicating with the air blowing port 17 and having the other end opened to the surface of the processing portion 16 is formed.

The heating / cooling unit 15 of the heating mandrel 12 includes a high-frequency coil 18 connected to a high-frequency power supply.
When the heating mandrel 12 is heated, the high-frequency coil 18 is energized and the heating / cooling unit 15 is induction-heated. When the heating mandrel 12 is cooled, the high-frequency coil 18 is removed and the exposed heating / cooling unit 15 is blown with cool air to cool the heating mandrel 12.

On the other hand, the expansion regulating pipe 13 is formed of a transparent resin pipe made of polycarbonate or the like having excellent mechanical strength and heat resistance, and the inner diameter thereof matches the outer diameter of the completed semiconductive heat shrinkable tube. A large number of small-diameter air vent holes 19 are formed in the circumferential surface of the air vent hole. And
The expansion restricting pipe 13 is supported by ring-shaped clampers 20, 20 attached to engage with step portions near both ends formed on the small diameter of the heating mandrel 12, and is concentric with the outer periphery of the heating mandrel 12. It is mounted in the shape. On the surfaces of the clampers 20 and 20 facing each other,
Each of the expansion guide tapered recesses 20a is formed in a mortar shape.

The air compressor 17 is provided at the end of the heating mandrel 12 with an air blower 17.
The connector 17 is provided at one end of an air passage 17 a having one end opened to the surface of the processing portion 16.

The manufacturing apparatus 11 configured as described above includes:
When heating, the heating mandrel 12 is set so that the heating and cooling unit 15 side is lowered, and then the high-frequency coil 1
When the induction heating is performed by energizing 8, the heating / cooling section 15 serves as an evaporating section of the heat pipe, the processing section 16 serves as a condensing section, and the entire processing section 16 is rapidly and uniformly heated. When the heated mandrel 12 is cooled, the heating mandrel 12 is set so that the heating / cooling unit 15 is higher, and the cooling / cooling unit 15 is blown with cool air. Reference numeral 15 denotes a condensing section, and the heat of the high-temperature processing section 16 is transferred to the vapor of the working fluid and radiated by the condensing section, whereby the entire processing section 16 is rapidly cooled.

The material of the semiconductive heat-shrinkable tube W4, that is, the material of the stretched tape W1 and the extruded tube W2 is polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, or the like as the base polymer. A thermoplastic resin such as an ethylene-propylene copolymer or a silicone resin is used, and a conductive carbon powder is added thereto to impart semiconductivity. In addition, powdered calcium carbonate and aluminum hydroxide are used. And a compounding agent such as a filler, a stabilizer, and the like are kneaded and used as a resin compound. Then, the resin composition is formed into a sheet shape, cut into a tape shape having a predetermined width, crosslinked by electron beam irradiation or the like, and then primarily stretched to prepare a stretched tape W1. The resin composition is extruded into a tube having a predetermined thickness to prepare an uncrosslinked semiconductive extruded tube W2. Therefore, the stretched tape W1 and the extruded tube W2 to be prepared have a reduced stretchability during heating due to the addition of a large amount of conductive carbon powder and other fillers, and are easily broken at the time of diameter expansion. .

Next, a case where the method of the first invention is applied to the production of a semiconductive heat-shrinkable tube for use in covering a cable connecting portion will be described with reference to FIGS. .

When manufacturing the semiconductive heat-shrinkable tube W4 for inner conduction, first, the expansion restricting pipe 1 of the manufacturing apparatus 11 is used.
3 is drawn on the outer periphery of the heating mandrel 12 with a stretching tape W1 of a thermoplastic resin stretched after crosslinking.
And a non-crosslinked extruded tube W2 made of the same material as the stretched tape W1 is covered on the outside thereof, and then the heating / cooling unit 15 of the heating mandrel 12 is induction-heated by the high-frequency coil 18 to obtain Heating and cooling unit 1
5 is heated to become an evaporating portion of the heat pipe, and the working fluid enclosed therein is heated and evaporated to become a working fluid vapor, which moves to the processing portion 16 which is a condensing portion of the heat pipe, and serves as latent heat of evaporation. The transported heat is released, and as a result, the entire processing section 16 is uniformly heated by the characteristics of the heat pipe, and the stretched tape W1 and the extruded tube W2 which are in close contact with the outer periphery thereof are uniformly heated. Then, when the extruded tube W2 is softened, a pressing tape T having a small thermal expansion is wrapped around the extruded tube W2 to prevent the heat dripping (the state of FIG. 2).

After the pressing tape T is wound, the heating mandrel 12 is further heated to heat the stretched tape W1 and the extruded tube W2 to a melting temperature and are fused together to form a cylindrical body W3. Thereafter, the pressing tape T is once cooled and the pressing tape T is removed. The expansion restricting pipe 13 is provided outside the heating mandrel 12 in a state where the cylindrical body W3 is covered.
Is mounted, and both ends of the cylindrical body W3 are clamped between the surfaces of the heating mandrel 12 by the clampers 20 and 20, and then the heating mandrel 12 is heated again to bring the cylindrical body W3 to a melting temperature. Heat (state of FIG. 3). Then, when the cylindrical body W3 is heated to the melting point, the compressor 21 is started and air is supplied from the air blowing port 17, so that air is injected between the cylindrical body W3 and the heating mandrel 12, and the cylindrical body W3 is compressed. Swell. At this time, since the heating mandrel 12 is a heat pipe, the entire cylindrical body W3 is uniformly heated and uniformly softened, so that the diameter can be increased at a high magnification. The air in the expansion regulating pipe 13 is discharged from the air vent hole 19 with the expansion of the cylindrical body W3.

When the cylindrical body W3 is expanded and reaches a predetermined diameter, the cylindrical body W3 comes into contact with the inner surface of the expansion restricting pipe 13 so that further expansion is restricted and the predetermined diameter is maintained (FIG. 4). Status). When the cylindrical body W3 is expanded to a predetermined diameter in this manner, the high-frequency coil 18 is removed from the heating / cooling unit 15, and the heating / cooling unit 15 side of the manufacturing apparatus 11 is reset to a high position. The cooling mandrel 12 is cooled by blowing cool air to the cooling unit 15 with a blower or the like. Therefore, since the heating / cooling unit 15 serves as a condensing unit of the heat pipe and the processing unit 16 serves as a heating unit of the heat pipe, the processing unit 16 and the air around the processing unit 16 are rapidly cooled. Then, it is cooled and fixed in the expanded state. Therefore, after sufficiently cooled, the air compressor 21 is stopped to stop the supply of air, and the expansion control pipe 13 is removed. The heat-shrinkable tube W4 is obtained (see FIG. 5).

Accordingly, the semiconductive heat-shrinkable tube W4 for inner conduction manufactured by the method of the first invention is composed of a stretched tape W1 which has been subjected to primary stretching after crosslinking, and an uncrosslinked tape which has been superimposed thereon. The extruded tube W2 is heated to the melting point by a heat pipe type heating mandrel 12 and then fused and integrally fused, and the cylindrical body W3 is secondarily stretched by heating and expanding. It is possible to manufacture a semiconductive heat-shrinkable tube W4 for the inner conductor, which can be made large and has a smooth and uncrosslinked outer peripheral surface on the side of the extruded tube W2 before fusion. Therefore, if the semiconductive heat-shrinkable tube W4 for the inner conductor is used for the inner semiconductive layer for the cable connection, the insulating layer formed outside the semiconductive heat-shrinkable tube W4 for the inner conductor can be used. No protrusions are formed at the interface of, and it is possible to fuse them tightly without generating voids or peeling.

FIG. 5 shows a semiconductive heat-shrinkable tube for external conduction manufactured by the method of the second invention.
The semiconductive heat-shrinkable tube W5 for external conduction is the first type.
It is manufactured using the same manufacturing apparatus 11 as used in the embodiment of the present invention, and the manufacturing process will be described below in order. As the material of the semiconductive heat-shrinkable tube W5 for external conduction, that is, the material of the stretched tape W1 and the extruded tube W2, polyethylene, ethylene-vinyl acetate copolymer, ethylene −
A resin-based mixture of a thermoplastic resin base polymer such as ethyl acrylate copolymer and conductive carbon powder for imparting semi-conductivity or calcium carbonate as an extender is molded into a sheet. And then cross-linked by electron beam irradiation or the like, and then subjected to primary stretching to prepare a stretched tape W1. The resin composition is extruded into a tube having a predetermined thickness to prepare an uncrosslinked, semiconductive extruded tube W2. Therefore,
Prepared stretched tape W1 and extruded tube W
In No. 2, since conductive carbon powder and the like are added in a large amount, the extensibility during heating is reduced, and it is easily broken at the time of expanding the diameter.

Next, a case where the method of the second invention is applied to the production of a semiconductive heat-shrinkable tube for external use used for coating a cable connecting portion will be described.

When manufacturing the semiconductive heat-shrinkable tube W5 for external conduction, first, the expansion restricting pipe 1 of the manufacturing apparatus 11 is used.
After covering the outer circumference of the heating mandrel 12 with an uncrosslinked extruded tube W2 of thermoplastic resin, the heat pipe type heating mandrel 12 is heated, and the heated extruded tube is heated. When W2 is softened, a stretched tape W1 stretched after cross-linking is wound around the outside thereof, and a pressing tape T with low thermal expansion is wound around the outside to prevent heat sag. The heating mandrel 12 is further heated and the extruded tube W2
Then, the stretched tape W1 is heated to a melting temperature, and is integrally fused to form a cylindrical body, and then cooled once to remove the pressing tape T.

Then, after the expansion restricting pipe 13 is attached to the outside of the heating mandrel 12 with the cylindrical body mounted thereon to seal both ends of the cylindrical body, as in the case of the above-described embodiment, the heating mandrel is formed. When the temperature of the cylinder 12 is raised again and the cylinder is heated to the melting temperature, the cylinder 21 expands when the compressor 21 is started and air is supplied from the air inlet 17. At this time, since the entire cylinder is uniformly heated and uniformly softened, the diameter of the cylinder is increased at a high magnification. When the cylindrical body is expanded and reaches a predetermined diameter, the expansion regulating pipe 13
A further increase in diameter is regulated to maintain a predetermined diameter. When the cylindrical body is expanded to a predetermined diameter in this way, the high-frequency coil 18 is removed from the heating / cooling unit 15, and the heating / cooling unit 15 side of the manufacturing apparatus 11 is set to a higher position. The cooling mandrel 12 is cooled by blowing cool air to the cooling unit 15 with a blower or the like. Therefore, the cylinder is cooled and fixed in an expanded state. After sufficiently cooling in this state, the air compressor 21 is stopped to stop the air supply, and the expansion control pipe 13 is removed. As shown in FIG. 6, a semi-conductive heat-shrinkable tube W5 having a high shrinkage ratio and having a high shrinkage ratio and having a large diameter is obtained.

In the method of the second invention, the stretched tape W1 subjected to the primary stretching after the crosslinking and the uncrosslinked extruded tube W2 superimposed on the stretched tape W1 are connected to each other by the heat pipe type heating mandrel 12. The cylindrical body heated to the melting point and fused together is stretched secondarily by heating and expanding, so that the heat shrinkage can be increased,
It is possible to manufacture an uncrosslinked semiconductive heat-shrinkable tube W5 for external conduction, which has a smooth inner peripheral surface on the side of the extruded tube W2, and is therefore formed inside when used for cable connection. No protrusion is formed between the insulating layer and the insulating layer, so that fusion can be performed densely without causing separation or voids.

Therefore, if the extruded tube is formed on the outside, a cable connecting tube suitable for an inner heat shrink tube is manufactured, and if the extruded tube is formed on the inside, a cable connecting tube suitable for an outer heat shrink tube is manufactured. it can.

[0033]

As described above, the method for manufacturing a heat-shrinkable tube according to the present invention is characterized in that the two conditions required for the heat-shrinkable tube, that is, the high shrinkage rate and the fusibility, are determined by subjecting the stretched tape to secondary stretching. Along with having a high shrinkage rate, this stretched tape and the extruded tube with a flat surface are fused together in an uncrosslinked state to maintain the fusibility, so that a high shrinkage rate and fusibility An excellent heat-shrinkable tube having both of the above can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus used for the method of the present invention.

FIG. 2 is a diagram showing a pressing tape winding step of the method of the present invention.

FIG. 3 is a view showing a heating step.

FIG. 4 is a view similarly showing a diameter expanding step.

FIG. 5 is a perspective view of a semiconductive heat-shrinkable tube for inner conduction manufactured by the method of the first invention.

FIG. 6 is a perspective view of a semiconductive heat-shrinkable tube for external conduction manufactured by the method of the second invention.

FIG. 7 is a cross-sectional view of a rubber / plastic insulated cable.

FIG. 8 is a cross-sectional view of a connection portion between rubber and plastic insulated cables.

[Description of Signs] 11 ... Manufacturing equipment, 12 ... Mandrel for heating, 13 ...
Expansion control pipe, 15: heating / cooling section, 16: processing section, 17: air blowing port, 17a: ventilation path, 18
... High frequency coil, 20 ... Clamper, 21 ... Air compressor, 22 ... Piping, T ... Tightening tape, W1 ... Stretched tape, W2 ... Extruded tube, W3 ... Cylinder, W4 ... Semiconductive heat shrinkage for inner conduction Tubes, semi-conductive heat-shrinkable tubes for external conduction.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 9:00 23:00

Claims (2)

(57) [Claims] 1. A stretching tape of a thermoplastic resin stretched after crosslinking is wound around an outer periphery of a heating mandrel, and an uncrosslinked extruded tube made of the same material as the stretching tape is covered on the outside thereof. Thereafter, the temperature of the heating mandrel is increased, and when the extruded tube is heated and softened, a pressing tape having a small thermal expansion is wound around the outside of the extruded tube, and the heating mandrel is further heated. The stretched tape and the extruded tube were heated to the melting temperature and fused together to form a cylindrical body, then cooled once, the holding tape was removed, and then the heating mandrel was heated again to be integrated. A method for manufacturing a heat-shrinkable tube, comprising heating the cylindrical body to a melting temperature and expanding the diameter to a predetermined size. 2. An uncrosslinked extruded tube made of a thermoplastic resin is placed on the outer periphery of the heating mandrel, and then the heating mandrel is heated to a temperature at which the extruded tube is heated and softened. Then, wind a stretched tape subjected to a stretching process after cross-linking, and further wrap a pressing tape having a small thermal expansion around the outside, and then further raise the heating mandrel to raise the stretching tape and the extruded tube to a melting temperature. After heating and fusing together to form a cylindrical body, it is cooled once, the holding tape is removed, then the heating mandrel is heated again, and the integrated cylindrical body is heated to a melting temperature to a predetermined temperature. A method for producing a heat-shrinkable tube, characterized in that the diameter is expanded to a dimension.