JPS5854647B2 - 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.

The tube can be produced, for example, by a method of inserting a material tube with one end sealed into a formed tube having a diameter of 100 mm, followed by heating and pressing and stretching, as described in Japanese Patent Publication No. 31-10088, or by a special method. It is manufactured by the method described in Japanese Publication No. 29-2843, in which a heated material tube is inserted over a core for expansion having a larger diameter, passed through it, 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 also shrinks relatively significantly in the axial direction 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, causing the object to bend, 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. 51-14547 proposes a method of manufacturing a heat-shrinkable tube intended to improve the disadvantages of the conventional products.

This method involves inserting a material tube made of an organic polymer material with a length-to-diameter ratio of 20 or more into a forming tube having a larger diameter, and then inserting both open ends of the material tube into the forming 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, stretching in the axial direction can be suppressed, but the thermal expansion force in the axial direction due to heating during the stretching process cannot be released, resulting in frequent meandering and constriction, resulting in a uniform diameter. A new problem has arisen in that it is difficult to obtain heat-shrinkable tubing.

In view of the above-mentioned current situation, the inventors of the present invention conducted extensive research and found that, before stretching, the material tube inserted into the formed tube is heated to an appropriate temperature for stretching in advance to thermally expand in the axial direction. If the outer wall of the material tube is tightened and stretched using two supports placed at a distance from each other, stretching in the axial direction can be suppressed, and it is possible to prevent meandering or constriction caused by thermal expansion force in the axial direction. They discovered that there is no such thing and completed 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 molded tube, heating the material tube to an appropriate temperature for stretching, and then thermally expanding it in the axial direction. , the outer wall of the material tube is tightened by two supports placed at a predetermined interval inside the forming tube, and then a differential pressure is applied to the material tube so that the outer wall surface of the stretching part of the material tube between the supports is tightened. After stretching in the radial direction so as to contact the inner wall surface,
It is characterized by cooling.

The material tube used in the present invention is made by adding additives such as a vulcanizing agent, anti-aging agent, pigment, etc. to an organic polymer material, that is, natural rubber, synthetic rubber, thermoplastic plastic, or a mixture thereof, as desired, and forming it into a tubular shape by a predetermined method. Obtained by molding into.

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 above-mentioned material tube is first inserted into a formed tube having a larger diameter, and stretched at an appropriate temperature (from the softening point of the material tube to
melting point) and thermally expand in the axial direction.

It is preferable that the thermal expansion is carried out at a temperature equal to or slightly higher than the temperature during the drawing operation that will be carried out later. If the temperature is significantly lower than the temperature, a thermal expansion phenomenon in the axial direction will occur during the stretching process, resulting in meandering and constriction. It won't happen.

The material tube can be heated to the appropriate stretching temperature by (1) heating from the outside of the formed tube with electric heat, heated fluid, etc., (2) method of feeding heated fluid into the formed tube or 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.

Furthermore, when carrying out the above-mentioned thermal expansion work, if supports are arranged in advance at a predetermined interval within the forming tube, and the material tube is slidably supported by the supports, the following steps can be taken: This is preferable because the outer wall of the material tube can be easily tightened using a support during the process, but thermal expansion can also be carried out without support using a support.

In the present invention, after the material tube is thermally expanded in the axial direction as described above, two
Its outer wall is tightened by means of several supports, and a differential pressure is then applied to the material tube to cause it to stretch in the radial direction.

The tightening is made strong so that no axial stretching occurs during the stretching process.

In addition, the differential pressure for stretching can be achieved by (1) sealing one end of the material tube and pressurizing a pressurized fluid such as air, nitrogen gas, or water from the other open end, or (2) closing the material tube. A method of sealing one end or both ends and reducing the pressure between the forming tube and the material tube. (3) A method of sealing both ends of the material tube and placing the entire material tube in a vacuum chamber to reduce the pressure. (4) A method of pressurizing the material tube and reducing the pressure. and the material pipe, 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) It is carried out by means such as stoppering method.

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 make it easier to drain the internal fluid that exists between the material tube and the formed tube. In addition, it is preferable to provide an internal fluid discharge means by arranging thin metal wires over the entire length, or by providing 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 shrinkable tube.

What is important in the present invention is to heat the material tube to an appropriate temperature for stretching and thermally expand it in the axial direction before the stretching process, and at the time of the stretching process performed after the thermal expansion, two locations on the outer wall of the material tube are The purpose is to tighten the parts at intervals to restrict the length of the part that requires stretching and to prevent stretching in the axial direction.

By doing this, it is possible to eliminate the meandering and constriction of the material tube during the stretching process, and to suppress stretching in the axial direction, thereby obtaining a heat-shrinkable tube with an extremely small shrinkage rate in the axial direction during heat shrinkage. be able to.

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

Figure 1 shows the material tube inserted into the forming tube.
Supports 2 and 3 are arranged at a predetermined interval within the forming tube 1, one end of which is sealed with a stopper 4 and a string-like material 5, and a material tube 6 is slidably supported between the supports 2 and 3. .

Note that 7 is a large number of small holes drilled in the molded tube 1 as internal fluid discharge means.

After the material tube 6 inserted into the forming tube 1 is stretched and heated to an appropriate temperature to thermally expand in the axial direction, the pin 8 is inserted as shown in the second figure.
, 9 to tighten the outer wall of the material tube 6, and then pressurized fluid is introduced from the open end 10 side of the material tube 6 to stretch it in the radial direction, as shown in FIG. The outer wall surface of the stretching portion A of the material tube 6 is brought into contact with the inner wall surface of the forming tube 1.

After the stretching process, the tube is cooled under pressure and returned to normal pressure, and the support 2.3 is removed from the formed tube 1 to obtain a heat-shrinkable tube.

In this example, the supports 2 and 3 are detachable from the forming tube 1, but one of them may be of a non-removable type.

Incidentally, a long product is used as the material tube 6, a predetermined portion is stretched according to the method of the present invention, and after the stretched portion is pulled out from the formed tube, the unstretched portion adjacent to the stretched portion is subsequently treated with the method of the present invention. By applying the method, heat-shrinkable tubes can also be obtained continuously.

As described above, the present invention does not require complicated and expensive equipment, is easy to operate, has a short process, and can continuously produce heat-shrinkable tubes by using long material tubes. It has the characteristics that the shrinkage rate in the axial direction during heat shrinkage is extremely small, and it has a uniform diameter without meandering or constriction.

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

Example polyethylene (manufactured by Nippon Unicar Co., Ltd., product name DFD200
5) Add and mix 0.2 parts by weight of an anti-aging agent (Antage RC manufactured by Kawaguchi Kagaku Co., Ltd.) to 100 parts by weight, form a tube by extrusion molding, and crosslink with electron beam (irradiation dose: 25 Mrad).
) A long material tube with an outer diameter of 61 m and a wall thickness of 1 iog was obtained.

The material tube is a metal formed tube (with the same structure as shown in Fig. 1).
It is inserted into a tube with an inner diameter of 13 m and a length of 6 vg, and is slidably supported by two supports arranged at an interval of 5.9 m.

Next, a string-like material is tied to one end of the material tube to seal it, and the material tube is placed in a heating furnace at 150° C. to thermally expand the material tube in the axial direction.

After 20 minutes, tighten the outer wall of the material tube with two supports,
Pressurized air (pressure: 1.0 kg/cyyD) is introduced to stretch it in the radial direction, and the outer wall surface of the portion requiring stretching is brought into contact with the inner wall surface of the formed tube.

After that, the formed tube was taken out of the heating furnace and kept under pressure for 20 minutes.
The material tube is immersed in running water for 10 minutes to cool it, then pulled out of the water and returned to normal pressure, the support at the sealing end of the material tube is removed from the formed tube, and the stretched material tube is pulled out of the tube.

Next, the removed support was placed in the molded tube again and the same operation as above was repeated to obtain a connected article having a large number of stretched parts.

The extended portion of the connected product was cut at intervals of 30 cm to obtain a heat-shrinkable tube with an outer diameter of 13 and a wall thickness of 0.41 m without meandering or constriction.

Twenty of these tubes were used as samples, and the metal rods with five outer diameters were coated and heated at 160°C for 10 minutes to shrink.The shrinkage rate in the axial direction was measured.The results were -1 to 4% (average 1.9%). Met.

The shrinkage rate was calculated using the following formula.

For comparison, the shrinkage rate in the axial direction was measured in the same manner as in the above example without using the support tool, and the shrinkage rate in the axial direction was 10 to 22% (average 15%). %
) was significantly larger.

Furthermore, when the outer wall of the material tube was tightened with a support before thermal expansion, meandering and constriction occurred, making it impossible to obtain a tube with a uniform diameter.

[Brief explanation of the drawing]

Figures 1 to 3 show the implementation of the method for manufacturing a heat-shrinkable tube according to the present invention, and Figure 1 shows a state in which a material tube is inserted into a molded tube and slidably supported by a support. 2 is a sectional view showing a state in which the outer wall of the material tube that has been thermally expanded in the axial direction is tightened by a support; FIG. 3 is a sectional view showing the state immediately after the material tube is stretched. 1... Formed tube, 2, 3... Support tool, 6
...Material pipe, 7...Small hole.

Claims (1)

[Claims] 1. Insert a material tube made of an organic polymer material into a forming tube, heat the material tube to an appropriate temperature for stretching, and thermally expand it in the axial direction. The outer wall of the material tube is tightened with a tool, and then a differential pressure is applied to the material tube to stretch it in the radial direction between the supports so that the outer wall surface of the portion of the material tube that needs to be stretched contacts the inner wall surface of the forming tube, and then the material tube is cooled. A method for producing a heat-shrinkable tube, the method comprising: