JPS5854649B2 - Method for manufacturing heat-shrinkable tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a heat-shrinkable tube made of an organic polymer material and having an extremely small degree of shrinkage in the axial direction during heat-shrinking.

Heat-shrinkable tubes have traditionally been used to cover and protect various articles.

For example, as described in Japanese Patent Publication No. 31-10088, a material tube with one end sealed is inserted into a formed tube with a larger diameter, and then heated and pressed to stretch it. It is manufactured by the method described in Japanese Patent No. 29-2843, in which a heated material tube is inserted onto an expanding mandrel having a diameter smaller than that, and then passed through and stretched.

However, in such conventional methods, when the material tube is stretched in the radial direction, no special means for suppressing the stretching in the axial direction is taken, so that the material tube is stretched in the radial direction and simultaneously in the axial direction. Stretching occurs, and the resulting tube becomes relatively thick (shrinks) in the axial direction as well when heated.

If such a tube is placed at a predetermined position on an object and heated to a temperature above the softening point of the material, the tube will shrink in the axial direction, exposing the end of the object to be covered or damaging the covered portion. It often happens that the numbers are not aligned.

In addition, in some cases, tension may act in the axial direction of the coating, bending the object, or if the coating is left under tension for a long time, deterioration of the coating may be accelerated from that part. Inconveniences such as cracks may occur.

Therefore, there have been significant restrictions on its application to electrical device parts that require excellent insulation, precision mechanical parts that require high precision, and the like.

Japanese Patent Publication No. 5,114,547 proposes a method of manufacturing a heat-shrinkable tube intended to improve the disadvantages of the conventional products.

In this method, a material tube made of an organic polymer material with a length-to-diameter ratio of 20 or more is inserted into a molded tube having a larger diameter, and then both open ends of the material tube are inserted into the molded tube. The material tube is then heated to the appropriate temperature for stretching, and a differential pressure is applied to it to perform the stretching process.By fixing both open ends of the material tube to the forming tube, the axis during the stretching process is Stretching in this direction is suppressed.

According to this method, it is possible to suppress stretching in the axial direction, but the thermal expansion force in the axial direction due to heating during the stretching process cannot be released, and meandering and constriction frequently occur, resulting in a decrease in diameter. A new layer of difficulty has arisen in obtaining uniform heat shrinkable tubing.

In view of the above-mentioned current situation, the inventors of the present invention have conducted intensive research and found that a material tube inserted into a forming tube and fixed at one end to the forming tube is heated to an appropriate temperature for stretching in advance to thermally expand it in the axial direction. By fixing the other end of the material tube in contact with the stopper of the forming tube to regulate the length of the material tube before stretching, it is possible to effectively prevent the occurrence of meandering and constriction during the stretching process, as well as the stretching in the axial direction. This discovery led to the completion of the present invention.

That is, the method for manufacturing a heat-shrinkable tube according to the present invention involves inserting a material tube made of an organic polymer material into a forming tube having a stopper, fixing one end of the material tube to the forming tube, and heating the material tube to an appropriate temperature for stretching. The material tube is thermally expanded in the axial direction, the other end is brought into contact with the stopper of the forming tube to regulate the length of the material tube during stretching, and then a differential pressure is applied to change the outer wall surface of the material tube to the inner wall surface of the forming tube. This method is characterized by stretching in the radial direction so as to bring the material into contact with the material, and then cooling the material.

The material tube used in the present invention is made of an organic polymeric material, such as natural rubber, synthetic rubber, thermoplastic plastic, or a mixture thereof, and optionally a vulcanizing agent.

It is obtained by adding additives such as anti-aging agents and pigments and molding it into a tubular shape using a predetermined method.

Of course, a two-layer type tubular product having an adhesive layer on the inner wall can also be used.

In the present invention, the material tube is first inserted into a forming tube having a larger diameter and having a stopper, and one end thereof is fixed to the forming tube.

The fixation of the material tube to the forming tube is often done indirectly through a support consisting of two rings that can fit together as shown in Figure 1. If the elongation rate is large, one end of the material tube can be folded back at the opening of the forming tube, guided onto the outer wall of the forming tube, and directly fixed thereon by tightening with adhesive tape or the like.

In addition, in order to suppress stretching in the axial direction when the material tube is stretched in the radial direction, a stopper such as a wire crossed in a criss-cross shape, a net-like body, or a plate-like body is arranged on the forming tube. However, if the stopper is of a type that is fixed at a predetermined position on the forming tube, when fixing one end of the material tube to the forming tube as described above, the stopper at the other end of the material tube is When the material tube is heated to an appropriate temperature for stretching, a constant distance corresponding to the thermal expansion of the material tube in the axial direction must be maintained.

Since the amount of thermal expansion described above varies depending on the material, length, wall thickness, heating temperature, etc. of the material tube used, it is preferable to calculate the thermal expansion length in advance numerically or to determine it based on actual measured values.

Furthermore, even if the stopper is movable within the forming tube or removable from the forming tube, the same precautions as for fixed types are required when placing the stopper in a predetermined position within the forming tube before thermal expansion of the material tube. It is.

After one end of the material tube is fixed to the molded tube in this manner, the material tube is heated to an appropriate temperature for stretching (from the softening point to the melting point of the material tube) and heated in the axial direction.

The thermal expansion is preferably carried out at a temperature equal to or slightly higher than the temperature during the subsequent stretching operation, and even if the temperature at the time of thermal expansion is between the softening point and melting point of the material tube, the temperature during the stretching operation If the temperature is significantly lower than the temperature, thermal expansion in the axial direction will occur during the stretching process, causing meandering and constriction, making it impossible to achieve the desired purpose, so care must be taken to control the temperature. .

The material tube can be heated to the appropriate temperature for stretching by (1) heating from the outside of the formed tube with electric heat, heating fluid, etc., (method of feeding heating fluid into the double-shaped tube or into the material tube, etc.) However, when using a method of feeding heated fluid into the material tube, care must be taken to ensure that the feeding pressure is sufficiently low and that the material tube is not stretched in the axial direction.

In addition, if the forming tube is installed horizontally in the factory and the diameter, wall thickness, and length of the material tube are large, the material tube may droop downward during thermal expansion work, but this should be avoided. In order to prevent this, it is preferable to attach a donut-shaped position holder or the like to the other end of the material tube so that it can slide inside the forming tube as the material tube thermally expands.

In the present invention, the other end of the material tube that has been thermally expanded in the axial direction as described above is brought into contact with the stopper of the formed tube,
A differential pressure is then applied to effect radial stretching.

The differential pressure for this stretching process can be achieved by (1) sealing one end of the material tube and pressurizing a pressurized fluid such as air, nitrogen gas, water, etc. from the other open end; (2) one end of the material tube; Or a method of sealing both ends and reducing the pressure between the molded tube and the material tube, (
3) A method in which both ends of the material tube are sealed and the entire material tube is placed in a vacuum chamber to reduce the pressure; (4) a method in which the material tube is pressurized and the pressure between the formed tube and the material tube is reduced, etc.

The opening end of the material tube can be sealed by (1) heat fusion method, (2) adhesive method, (3) method of winding adhesive tape or string-like material, (
4) This is done by means such as stoppering.

Of course, it is also possible to seal the tube before inserting it into the forming tube.

In addition, when applying differential pressure to the material tube and stretching the material tube in the radial direction as described above, small holes are provided in the formed tube to facilitate the discharge of internal fluid existing between the material tube and the formed tube. It is preferable to provide an internal fluid evacuation means by arranging thin metal wires over the entire length, or by arranging grooves or protrusions.

The material tube stretched in the radial direction in this manner is cooled while applying a differential pressure, and is pulled out from the formed tube to obtain a heat-shrinkable tube.

What is important in the present invention is that +-4, before the stretching process, the material tube is heated to an appropriate temperature for stretching to thermally expand in the axial direction, and then stretched only in the radial direction.

By thermally expanding the tube in the axial direction before stretching, it is possible to prevent meandering and constriction during the stretching process, and by suppressing the stretching in the axial direction, the resulting tube can shrink in the axial direction during thermal contraction. The ratio can be made extremely small.

Next, an example of the present invention will be explained with reference to the drawings.

First, as shown in FIG. 1, a material tube 2 whose one open end has been sealed with a stopper 1 is inserted into a molded tube 3 having a diameter larger than that, and the other open end is fitted with an inner ring 4 and an outer ring 4. It is fixed to the forming tube 3 by a ring 5 and a pin 6.

The fixing is carried out by providing a gap between the sealed end of the material tube 2 and the stopper 7, which is sufficient for the thermal expansion of the material tube 2 in the axial direction when the material tube 2 is heated to an appropriate temperature for stretching.

Reference numeral 8 is a fluid inlet pipe, 9 is a large number of small holes provided in the molded tube 3 as internal fluid discharge means, and 10 is a donut-shaped position holder.

The material tube 2 inserted and fixed into the forming tube 3 in this way is heated to an appropriate temperature for stretching to thermally expand in the axial direction, and its sealed end is brought into contact with the stopper 7 as shown in FIG. The length of the material tube 2 is regulated so that it is not stretched.

Next, a pressurized fluid is introduced into the material tube 2 from the fluid inlet tube 8 and stretched in the radial direction as shown in FIG.

After stretching, the tube is cooled while maintaining the pressurized state, returned to normal pressure, and pulled out from the molded tube 3 to obtain a heat-shrinkable tube.

In this example, the stopper 7 is fixed to the end of the forming tube 3, but it is of a type that can be moved within the forming tube 3 or can be removed from the forming tube 3, and after thermally expanding the material tube 2, it contacts the sealed end of the material tube 2. It is also possible to do so.

The present invention does not require complicated and expensive equipment, and the process is short.
Moreover, the resulting tube has features such as an extremely small shrinkage rate in the axial direction, and a uniform diameter without meandering or constriction.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Ethylene propyne rubber (manufactured by Mitsui Petrochemicals, trade name EP)
T1045) 75 parts by weight, polyethylene (manufactured by Sumitomo Chemical Co., Ltd., trade name Sumikasen G201) 25 parts by weight, carbon black 80 parts by weight, paraffin oil 20 parts by weight, zinc white 5
parts by weight, 1 part by weight of stearic acid, 2.4 parts by weight of vulcanizing agent (
A mixture of (manufactured by Iriuchi Shinko Kagaku Co., Ltd., trade names: 1 part by weight Tsukusela DM, 4 parts by weight Tsukusera TRAl) was extruded and vulcanized in a heating furnace to obtain a long tube with an outer diameter of 22 mm and a wall thickness of 1.5 mg. The long tube is cut into a length of 577L to obtain a material tube.

One end of the material tube was sealed by heat fusion, and a metal formed tube (inner diameter 65 mm, length 5.3 mm) with the same structure as shown in FIG.
m) and fix the open end to the molded tube with a support.

At this time, the distance between the sealed end of the material tube and the fixed stopper of the forming tube is adjusted to 10 degrees.

Next, the formed tube is placed in a heating furnace at 150° C. and heated for 20 minutes to thermally expand the material tube in the axial direction and bring it into contact with the stopper.

Then, pressurized air (pressure 1.5 kg/
crrt) is introduced and stretched in the radial direction, the formed tube is taken out from the heating furnace while being pressurized, cooled by immersion in running water at 20°C for 10 minutes, then pulled out, the pressure is returned to normal pressure, and the formed tube is pulled out. A heat-shrinkable tube with a diameter of 58 IIN and a wall thickness of 0.5 mm was obtained.

No meandering or constriction was observed in the heat-shrinkable tube.

length 3 to measure the shrinkage rate in the axial direction of the tube.
Prepare 20 pieces cut to QQm, and cut them into an outer diameter of 24
A 1L/11L metal tube was coated with the mixture and heated at 150°C for 15 minutes to shrink it.

The shrinkage rate in the axial direction at this time is -1 to 4% (average 2.1%)
Met.

Note that the shrinkage rate was calculated using the following formula.

Example 2 Polyethylene (manufactured by Nippon Unicar Co., Ltd., trade name DFD200)
5) 100 parts by weight of an anti-aging agent (manufactured by Kawaguchi Kagaku Co., Ltd., trade name: ANTAGE RC) was added and mixed, formed into a tube by extrusion molding, cross-linked by irradiating it with an electron beam at 25 M rad, and then A long tube with a diameter of 19 mm and a wall thickness of l□□□ was cut into 5 lengths to obtain a material tube.

The material tube was inserted into the same molded tube used in Example 1, the distance between the sealing end of the material tube and the stopper was set to 12 cr/L, and the work was carried out in the same manner as in Example 1 (however, the pressure of pressurized air was 0.
．． 8 kg/crii), and a heat-shrinkable tube with an outer diameter of 65 cm and a wall thickness of 0.3 mrnO was obtained.

No meandering or constriction was observed in the tube.

Further, when the shrinkage rate in the axial direction was measured in the same manner as in Example 1, it was -1.5 to 4% (average 1.8%).

Comparative Example 1 When inserting the two types of material tubes used in Examples 1 and 2 into the same molded tube used in each of the above examples, the sealed end was brought into contact with the stopper, and the open end was inserted into the molded tube with a support. Use to fix.

Next, thermal expansion, stretching, and cooling were performed under the same conditions as in each example to obtain tubes, but each tube had meandering and constrictions, and a tube with a uniform diameter could not be obtained.

Comparative Example 2 The stopper of each of the above-mentioned molded tubes was removed, the same material tubes used in Examples 1 and 2 were used, the stretching in the axial direction was not restricted, and the other conditions were the same as in each Example. When the shrinkage rate of the tube was measured in the same manner as in Example 1, it was 8 to 25.
% (average 17%) and 10-22% (average 14%), which were significantly large.

As is clear from the above Examples and Comparative Examples, the heat-shrinkable tube obtained by the present invention has a small shrinkage rate in the axial direction during heat-shrinking, and is free from meandering and constriction.

[Brief explanation of drawings]

Figures 1 to 3 show an example of the method for manufacturing a heat-shrinkable tube according to the present invention, and Figure 1 is a cross-sectional view showing a state in which a material tube is inserted into a molded tube and one end thereof is fixed to the molded tube. , Figure 2 is a cross-sectional view showing a state in which the material tube is heated to an appropriate temperature for stretching, thermally expanded in the axial direction, and the sealed end is in contact with the stopper.
The figure is a sectional view showing a state in which the material tube is stretched in the radial direction. 2... Material pipe, 3... Molded pipe, 7...
...Stopper, 8...Fluid feed pipe, 9.
...Small hole, 10...Position holder.

Claims (1)

[Claims] 1. Insert a material tube made of an organic polymer material into a molded tube with a stopper, fix one end of the material tube to the molded tube, heat the material tube to an appropriate temperature for stretching, thermally expand the material tube in the axial direction, and open the other end. A heat-shrinkable tube that is brought into contact with a stopper of a formed tube, then stretched in the radial direction so that the outer wall surface of the material tube contacts the inner wall surface of the formed tube by applying a differential pressure, and then cooled. Production method.