JPS6130897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a so-called heat-shrinkable resin tube that shrinks upon heating and returns to its original diameter.

[Conventional technology]

Heat-shrinkable resin tubes are manufactured by expanding the tube to a predetermined size using a certain type of expansion means in a heated state, and then cooling and fixing the tube.Various expansion methods have been proposed in the past. has been and is being implemented.

By the way, when such a heat-shrinkable tube is used as a protective cover for a cable joint, it is required to have a large shrinkage rate and a small shrinkage rate in the length direction.

This is because cable joints often have to joint cables with significantly different diameters, and in such cases, a large shrinkage ratio is required in order to fit both cables.

Furthermore, even if a cable having a high contraction rate in the radial direction can successfully fit cables of different diameters, if the contraction rate in the longitudinal direction is large, problems such as the joint portion being exposed after contraction will occur.

We conducted various studies in order to obtain a shrinkable tube with a large shrinkage rate in the radial direction and a small shrinkage rate in the longitudinal direction.

As a result, a large number of metal pins were inserted into the tube in advance, the tube was heated to below the melting temperature, and then these metal pins were expanded to almost double the diameter with an expanding core bar. If you use the method of expanding into a polygon, then heat-shrinking it onto a cylinder with an outer diameter that is inscribed in this polygon, and then drawing out the cylinder after cooling, the shrinkage rate in the radial direction is large and the length is large. It has been found that a heat-shrinkable tube with a small directional shrinkage rate can be obtained. We also tried a method of making a heat-shrinkable tube by spreading multiple layers of high-temperature stretched film and heat-sealing them, and this method also yielded a shrinkable tube with a high shrinkage rate in the radial direction and a small shrinkage rate in the length direction.

[Problem that the invention seeks to solve]

In the method of making a heat-shrinkable tube by spreading multiple layers of stretched film and heat-sealing them, there remains a problem with integration (for example, the tubes come apart when immersed in xylene).

In addition, the tube is placed inside the formed tube, which is conventionally widely used, and the formed tube and the tube are immersed in a heated melt tank, and then internal pressure is applied to expand the tube to about twice its diameter until it tightly contacts the formed tube, while the tube is expanded into a cooling bath. When the tube was placed in a tube and cooled and fixed, a constriction formed and the desired uniform expansion of the tube was not possible.

[Means for solving problems]

The present invention is to manufacture a tube having a shrinkage rate larger than that of a conventional heat-shrinkable tube (for example, 50%, that is, shrinkage to 1/2) in the radial direction, and The purpose of the present invention is to manufacture a tube which is circular in shape, has a uniform adhesive layer on its inner surface, and has almost no uneven thickness.

In order to achieve the above object, the present invention employs a process of (i) inserting a large number of pins into the tube and pushing the pins apart with an expanding core mold to expand the tube into a polygonal shape; In addition to manufacturing a tube with a large shrinkage rate, the disadvantages due to the polygonal cross section of the tube obtained by this manufacturing method, that is, uneven thickness that is thought to be due to uneven heating, are eliminated in subsequent steps. That is, the problem was solved by (ii) a step of inserting the tube into a cylinder having an outer diameter that is inscribed in the polygonal tube, shrinking it by heating, and pulling out the cylinder after cooling.

However, this still inevitably causes some unevenness in thickness, and in the present invention, further (iii) the tube is inserted into a cylinder wrapped with a plastic tape that can flow at the heat contraction temperature of the tube. In step (ii), an adhesive layer is simultaneously provided on the inner wall of the tube, and the slight unevenness in thickness that has still occurred is almost completely eliminated. In other words, the present invention provides step (ii) in addition to step (i).
By configuring step (iii), a large shrinkage rate in the radial direction can be obtained, and since an adhesive layer is simultaneously provided on the inner wall of the tube in the step of circularizing, one step can be simplified. In addition, it is possible to produce a heat-shrinkable resin tube that hardly causes uneven thickness.

Example A polyethylene tube with an inner diameter of 20 mmφ and a thickness of 4.0 mm was made by extrusion and irradiated with an electron beam of 30 Mrad.

The apparatus used to inflate this tube is shown in FIG.

1 is a plate for fixing the metal pin 2 at a position corresponding to the inner diameter of the tube after expansion, and the pin can be moved up and down by rotating the screw 3.

4 is a core bar for expansion, and a groove is cut to prevent the pin from shifting in the circumferential direction when moving up and down.

As 2, fix eight 2.0mmφ steel rods in the designated positions in 1, align them with the expansion core with an outer diameter of 90mmφ at the largest part, then insert the aforementioned tube as shown in step 5, and insert the expansion core. The gold was fixed on a fixed stand 6.

Tube 5 was heated, and when the temperature reached 130 to 150°C, the metal pin fixing plate 1 was lowered.
According to the metal pin fixing plate, the metal pin is also below,
At that time, it was expanded by the expanding core bar, and at the same time, the tube was also expanded by the amount that the pin was expanded. This expanded octagonal tube was cooled and fixed as it was.

The octagonal heat-shrinkable tube thus obtained was placed over the joint of the cable, etc., and an attempt was made to heat-shrink it with a burner, etc., but the shrinkage was extremely high, and since it was polygonal, it was thought that the heating would be uneven. It was found that this causes an unbalanced contraction, which tends to cause uneven thickness, and is extremely unstable. Therefore, an attempt was made to make the tube into a circular shape by placing the tube over a cylindrical mandrel with an outer diameter of 82 mmφ, heating and shrinking it with a burner, cooling it, and then punching out the cylinder, but this also resulted in a slight unevenness in thickness.

Therefore, a non-crosslinked and relatively small molecular weight ethylene ethyl acrylate copolymer or ethylene vinyl acetate copolymer was sprinkled on the aforementioned cylinder in advance, and the tube was placed on top of the ethylene ethyl acrylate copolymer, which was heated to integrate and cooled. When the rear cylinder was cut out, we succeeded in obtaining a highly shrinkable shrink tube with an adhesive layer and a circular shape of 80 mm diameter with almost no uneven thickness.

〔Effect of the invention〕

The shrinkage tube obtained in this way has a high shrinkage rate, and it goes without saying that the shrinkage rate in the length direction is small, and even if it is placed over the joint and heated and shrunk with a burner, the shrinkage will not be unbalanced and will be almost uniform. I was able to shrink it to a certain thickness.

In addition, similarly good heat-shrinkable tubes were obtained with tubes made of polyvinyl chloride resin compositions, ethylene vinyl acetate copolymers, and ethylene ethyl acrylate copolymers.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the expansion device used in making the deflation tube of the present invention. 1 is a metal pin fixing plate, 2 is a metal pin, 3 is a screw for moving the metal pin fixing plate up and down, 4
Reference numeral 5 indicates a core bar for expansion, numeral 5 indicates an article to be expanded, and numeral 6 indicates a fixing base for the core bar for expansion.

Claims (1)

[Claims] 1. Insert a large number of pins into the tube, and expand the pins with an expanding core mold to expand the tube into a polygon. Production of a heat-shrinkable resin tube, which is characterized by inserting the tube into a cylinder having a diameter and pre-wrapping an adhesive tape that melts at a temperature lower than the heat-shrinking temperature of the tube, shrinking it by heating, and pulling out the cylinder after cooling. Method.