JPH0516232A - Manufacture of heat-shrinkable tube - Google Patents

Abstract

PURPOSE:To easily manufacture a heat-shrinkable tube having a large shrinkage factor by a reduced number of processes by interposing a rubber tube almost uniform in elongation in the peripheral direction thereof between a heating mandrel and a material tube to integrally heat the same along with the material tube and subsequently introducing a fluid in the rubber tube to expand the diameter of the material tube. CONSTITUTION:The outer periphery of a heating mandrel 12 is covered with a rubber tube G and a material tube W composed of a crosslinked thermoplastic resin is superposed on the rubber tube G to cover the tube G and, after the rubber tube G and the material tube W are integrally heated by the heating mandrel 12, a fluid, for example, air is introduced into the rubber tube G. By interposing the rubber tube G, the diameter of the material tube W is equally expanded even when the material tube W is irregular in wall thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-shrinkable tube in which a crosslinked raw material tube made of a thermoplastic resin is expanded in a heat-softened state.

[0002]

2. Description of the Related Art As a method for producing a heat-shrinkable tube, for example, a material tube made of a cross-linked thermoplastic resin extruded in a circular cross section is used. A method is conceivable in which the above materials are injected under pressure, expanded and expanded to a predetermined size. However, the thickness of the extruded material tube is not completely uniform, and there are some parts that are thin. Therefore, if the material tube is softened by heating to near the melting point and then air or the like is pressed into the material tube, the part where the material tube easily expands, that is, the part where the wall thickness is thin, will precede the expansion. Therefore, there is a high possibility of breaking before reaching a predetermined diameter.

Therefore, as a method of expanding the diameter of the material tube substantially evenly even if the material tube has an uneven thickness and a part where the wall thickness is thin, for example, Japanese Patent Publication No. 61-3089.
The method described in Japanese Patent Publication No. 7 is performed. As shown in FIG. 5, this is eight metal pins 1 arranged in a circle.
The base end side (lower side in FIG. 3) of each is fixed to the fixing plate 2, and the free end side is converged. Next, after being extruded into a cylindrical shape, a polyethylene tube 3 which is irradiated with an electron beam and cross-linked is covered on the outer periphery of the eight metal pins 1 which are converged. Then, the diameter-expanding cored bar 4 arranged at a position closer to the fixed plate 2 inside the eight metal pins 1 arranged in a circle is moved while being rotated toward the convergent tip side. Since each of the metal pins 1 is pushed in the radial direction, the polyethylene tube 3 covered on the outer circumference is expanded into an octagonal shape by the eight metal pins 1. Then, although not shown, the octagonally expanded polyethylene tube 3 is put on the outer periphery of a cylinder coated with a non-crosslinked and relatively small molecular weight ethylene ethyl acrylate copolymer, and heated in this state. And heat-shrink, and after cooling, the cylinder is pulled out to produce a heat-shrinkable tube having a high shrinkage ratio.

[0004]

Therefore, in the conventional method for manufacturing a heat-shrinkable tube described above, since the polyethylene tube 3 is expanded into a polygonal shape, the polygonal polyethylene tube 3 is further covered with a cylindrical body to heat it. There is a problem that the process of shrinking and forming into a cylindrical tube is necessary, and the diameter of the heat shrinkable tube to be the product becomes smaller than the diameter expansion limit because the diameter is expanded to the maximum and then heat shrinks. It was Further, since the heat shrinkable tube 3 manufactured by this method has uneven thickness when heated and shrunk by a gas burner or the like, an adhesive layer made of a non-crosslinked ethylene ethyl acrylate copolymer or the like is formed inside the heat shrinkable tube. It has been necessary to suppress the increase in uneven thickness during shrinkage by forming, for example.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a heat-shrinkable tube which can easily manufacture a heat-shrinkable tube having a large shrinkage rate in a small number of steps.

[0006]

As a means for solving the above problems, the present invention is directed to covering a cross-linked material tube made of a thermoplastic resin on the outer periphery of a heating mandrel and heating the heated material tube. In the method of manufacturing a heat-shrinkable tube in which a fluid is pressed into the inside of the tube to expand it, and the material tube is expanded to a predetermined size and then cooled to fix the expanded state, between the heating mandrel and the material tube, A rubber tube having a substantially uniform circumferential extension is interposed, and after this rubber tube is heated integrally with the material tube, a fluid is press-fitted inside the rubber tube, and the material is passed through the rubber tube. It is characterized by expanding the diameter of the tube.

[0007]

A rubber tube having a substantially uniform circumferential extension is interposed between the heating mandrel and the material tube, and this rubber tube is heated and softened together with the material tube by the heating mandrel. After that, for example, gas is injected into the inside of the rubber tube to inflate it, so even if the outer material tube has uneven thickness, the inner rubber tube expands uniformly, so the material tube is expanded by the expanding rubber tube. It is pushed out from the inside and the diameter is expanded almost evenly. Therefore, even if there is unevenness in the wall thickness of the material tube, the diameter of the material tube can be expanded without breaking the unevenness of the thickness and without breaking to a predetermined size.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a method for manufacturing a high shrinkage semiconductive heat shrinkable tube will be described below with reference to FIGS.

FIG. 1 shows an example of a heat shrink tube manufacturing apparatus using a heat pipe type heating mandrel used to carry out the manufacturing method of the present invention. A mandrel 12 for covering a tube or the like, and a mandrel 12 that is detachably attached to the outer periphery of the mandrel 12 with a predetermined space so that the material tube has a predetermined outer diameter when heated and softened by blowing air. And an expansion control pipe 13 for restricting the expansion of the material tube.

Further, the mandrel 12 is a container 14 made of metal pipe such as copper or copper alloy having excellent heat conductivity.
A wick (not shown) is provided on the inner peripheral surface of the container, and only the condensable working fluid is enclosed inside to provide a heat pipe function. Both ends of the container 14 have a small outer diameter. The one end portion (the left end in FIG. 1) formed on the mandrel 12 is formed as a heating and cooling portion 15 that is heated when the mandrel 12 is heated and cooled when the mandrel 12 is cooled. A processed portion 16 having a constant outer diameter is formed in the central portion of the. Then, the processed portion 16 of the mandrel 12 is covered with a workpiece W such as a material tube in a state where the outer expansion regulating pipe 13 is removed (state of FIG. 2). Further, the end of the mandrel 12 opposite to the heating / cooling section 15 (see FIG.
At the right end), an air blowing port 17 having a connector for connecting an air hose (not shown) from an air compressor or the like is provided. One end of this air blowing port 17 is connected to this air blowing port 17. Communicate with each other, and the other end is the processing portion 16
An air passage 17a having an opening is formed on the surface of so as to blow air to the outer periphery of the processing portion 16.

The heating and cooling section 15 of the mandrel 12 is also provided.
A high-frequency induction coil 18 connected to a high-frequency power supply is detachably attached to the high-frequency power supply. When heating the mandrel 12, the high-frequency induction coil 18 is energized to induction-heat the heating / cooling unit 15. When the mandrel 12 is cooled, the high frequency induction coil 18 is removed to cool the exposed heating / cooling section 15 by cooling air. Further, the total length of the mandrel 12 can be increased within a range that does not impair the temperature-equalizing characteristic of the heat pipe, but when workability is taken into consideration, about 5 m is preferable as an example.

On the other hand, the expansion control pipe 13 is formed of a transparent resin pipe such as polycarbonate having excellent mechanical strength and heat resistance, and its inner diameter matches the outer diameter of the semiconductive heat-shrinkable tube when completed. A large number of small-sized air vent holes 19 are formed through the peripheral surface thereof. And
The expansion restricting pipe 13 is supported by ring-shaped clampers 20, 20 mounted so as to engage with the stepped portions near both ends of the mandrel 12 which are formed in a small diameter, and is concentrically mounted on the outer periphery of the mandrel 12. ing. Further, expansion guide tapered recesses 20a are formed in a mortar shape on the surfaces of the clampers 20, 20 facing each other.

The manufacturing apparatus 11 configured as described above is
When heating, the mandrel 12 is set so that the heating / cooling section 15 is lowered, and then the high-frequency induction coil 18 is energized to perform induction heating. Part 16 becomes the condensing part,
The entire processing portion 16 is rapidly and uniformly heated. Further, when the heated mandrel 12 is cooled, the mandrel 2 is set so that the heating / cooling unit 15 side becomes higher, and cold air is blown to the heating / cooling unit 15 to cause the heating / cooling unit 15 to condense. Therefore, the heat of the high temperature processing portion 16 is carried to the vapor of the working fluid and radiated in the condensing portion, whereby the entire processing portion 16 is rapidly cooled.

Next, the manufacturing apparatus 1 configured as described above.
An example of manufacturing a semiconductive heat-shrinkable tube by the method for manufacturing a heat-shrinkable tube performed by using No. 1 will be described with reference to FIGS. 3 and 4. As the material of the semiconductive heat-shrinkable tube, a thermoplastic resin such as polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene copolymer, or silicone resin is used as the base polymer. Then, conductive carbon powder is added to impart semiconductivity thereto. In addition to these, fillers such as calcium carbonate and aluminum hydroxide, stabilizers, and the like are blended and used as a resin blend. Then, this resin composition is molded into a tube having a predetermined wall thickness by an extrusion molding machine, and further irradiated with an electron beam to be crosslinked to prepare a semiconductive tube W.

A natural rubber tube is suitable as the rubber tube G used in the production of the semiconductive heat-shrinkable tube, and its circumferential expansion is substantially uniform.
In addition, the semiconductive tube W has heat resistance sufficient to withstand the heating temperature when expanding the diameter, and elasticity that allows it to easily expand to a predetermined size.
In addition, the outer surface of the rubber tube G is in close contact with the inner surface of the semiconductive tube W and is in a non-slip state.

The manufacture of the semiconductive heat-shrinkable tube is
First, the outer circumference of the mandrel 12 of the manufacturing apparatus 11 is covered with a rubber tube G, and the outer circumference of the rubber tube G is further covered with a semiconductive tube W which is a workpiece, and then the expansion of the mandrel 12 is restricted. The pipe 13 is attached, and an air hose (not shown) from an air compressor is connected to the air blowing port 17 in advance. At this time, both ends of the rubber tube G are hermetically sealed by the clampers 20, 20 inserted from both ends of the expansion restriction pipe 13, but both ends of the semiconductive tube W need not be sealed (see FIG. 3).

Next, when the heating and cooling section 15 side of the manufacturing apparatus 11 is lowered, the high frequency coil 18 is energized to induction-heat the heating and cooling section 15 of the mandrel 12, and the heating and cooling section 15 is heated. Is the evaporation part of the heat pipe, the working fluid enclosed inside is heated and evaporated,
It becomes the working fluid vapor, moves to the processing section 16 which is the condensing section of the heat pipe, and releases the heat transported as latent heat of vaporization. As a result, the entire processed portion 16 is uniformly heated due to the characteristics of the heat pipe, and the rubber tube G and the semiconductive tube W, which are provided on the outer periphery of the processed portion 16, are also uniformly heated and softened over the entire length thereof.

When the semiconductive tube W is heated to a predetermined temperature and softened together with the rubber tube G inside thereof, air is supplied from the air blowing port 17 at a preset pressure. .. The supplied air is supplied to the air passage 17
It is blown out from the surface of the mandrel 12 via a. As a result, air is injected between the mandrel 12 and the rubber tube G covering the surface of the mandrel 12, the rubber tube G sealed at both ends expands, and the outer semiconductive tube W expands in diameter. .. At this time, the rubber tube G expands substantially evenly in the circumferential direction and is made of a material that is intimately adhered to the inner surface of the semi-conductive tube W and is hard to slip. The semi-conductive tube W that expands and expands in diameter integrally with G has an evenly expanded diameter even if there is a portion with uneven thickness and a slightly thin wall thickness. Further, as the rubber tube G expands, the air in the expansion control pipe 13 is discharged from the air vent hole 19.

When the diameter of the semi-conductive tube W is expanded to reach a predetermined diameter, and the semi-conductive tube W comes into contact with the inner surface of the expansion restriction pipe 13 to restrict the further expansion, the air pressure in the rubber tube G is set. It is kept at a predetermined diameter in balance with the pressure.
After the semiconductive tube W has been expanded to have 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 high again. The mandrel 12 is cooled by blowing cold air onto the heating / cooling unit 15 with a blower or the like. Therefore, since the heating / cooling unit 15 serves as the condensing unit of the heat pipe and the processing unit 16 serves as the heating unit of the heat pipe, the processing unit 16 and the air around it are rapidly cooled, and as a result, the rubber tube G and the semi-conductive member. The flexible tube W is cooled in the expanded state, and the semiconductive tube W made of a thermoplastic resin is fixed in the expanded state.

When the pressure of the air supplied from the air blowing port 17 is released after the semi-conductive tube W has been sufficiently cooled, the expanded rubber tube G is elastically contracted to a expanded state. The semi-conductive tube W fixed to the inner wall of the expansion control pipe 13 is easily separated from the inner surface of the semi-conductive tube W.
By removing it, the semi-conductive heat-shrinkable tube W1 having a high shrinkage ratio and having a diameter increased to a predetermined size can be easily manufactured as a product of stable quality with almost no defective products.

As described above, in the method for manufacturing the semiconductive heat-shrinkable tube of this embodiment, since the mandrel 12 has the heat pipe function, the semiconductive tube W and the rubber tube G are uniformly heated. As a result, uniform diameter expansion is possible. Further, since air is press-fitted inside the rubber tube G and the diameter of the semiconductive tube W is indirectly increased through this rubber tube G, even if unheated air is injected, the semiconductive heat shrinkable tube W Since it is not rapidly cooled, the diameter can be expanded at a stretch even when the expansion ratio is large. Further, since the rubber tube G can be repeatedly used, it is economical, and the semi-conductive tube W can be easily attached because no seal is required.

In the above embodiment, air was pressed in to expand the diameter, but a gas such as nitrogen gas or a liquid such as water or warm water may be used instead of air.

[0023]

As described above, according to the method of manufacturing the heat shrinkable tube of the present invention, the rubber tube whose circumferential extension is substantially uniform is interposed between the heating mandrel and the material tube, and After heating the tube integrally with the material tube, pressurize the fluid inside the rubber tube to expand the diameter of the material tube through the rubber tube, so that even if the material tube has uneven thickness The diameter can be expanded, and even if there is a thin wall portion, the diameter can be expanded to a predetermined dimension without breaking, and a heat-shrinkable tube having a high shrinkage ratio can be manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional side view showing an example of an apparatus used in the method of the present invention.

FIG. 2 is a sectional side view showing a state in which the expansion restriction pipe of the same device is removed.

FIG. 3 is a partially enlarged sectional view showing a heating step of the method of the present invention.

FIG. 4 is a partially enlarged cross-sectional view showing the diameter expanding step.

FIG. 5 is a perspective view showing a diameter expansion step in a conventional manufacturing method.

[Explanation of symbols]

11 ... Manufacturing apparatus, 12 ... Mandrel, 13 ... Expansion control pipe, 15 ... Heating / cooling section, 16 ... Processing section,
17 ... Air blow-in port, 17a ... Ventilation path, 18 ... High frequency induction coil, G ... Rubber tube, W ... Semi-conductive tube, W1 ... Semi-conductive heat-shrinkable tube.

Claims (1)

Claim: What is claimed is: 1. A crosslinked material tube made of a thermoplastic resin is put on the outer circumference of a heating mandrel and heated, and a fluid is press-fitted inside the heated material tube to expand the material tube. In the method for manufacturing a heat-shrinkable tube in which the tube is expanded to a predetermined size and then cooled to fix the expanded state, a rubber tube having a substantially uniform circumferential expansion is interposed between the heating mandrel and the material tube. While wearing
After heating this rubber tube integrally with the material tube, a fluid is press-fitted inside the rubber tube to expand the diameter of the material tube through the rubber tube. ..