JPH0717007B2 - Method for producing heat-shrinkable tube - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a heat-shrinkable tube having a heat-melting type adhesive layer on the inner surface.

BACKGROUND OF THE INVENTION A heat-shrinkable tube having good workability is widely used for insulation treatment of electric wire connection portions, insulation treatment of lead portions of motors, and the like. In such a treatment, various composite tubes having an adhesive layer on the inner surface have been studied in order to improve the adhesion between the tube and the adherend and to provide watertightness.

However, it is difficult to provide an adhesive layer on the inner surface, and there is a problem that the manufacturing cost is high.

[Summary of Invention]

Therefore, we studied various methods for efficiently manufacturing a composite tube having an adhesive layer on the inner surface, made a tube with a specific plastic, that is, a thermoplastic resin or elastomer having a heat melting property, and used a low voltage accelerator to make the tube. The present invention was completed by finding that the target tube can be obtained by crosslinking only the outside of the.

[Detailed Description of the Invention] As the thermoplastic resin or elastomer having heat melting property used in the present invention, polyethylene, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, saponified ethylene vinyl acetate copolymer, Ionomer resin,
Polybutene-1 resin Polyamide resin, polyester resin, ethylene propylene elastomer, polyester elastomer, polyurethane elastomer, styrene-butadiene elastomer, etc., or a mixture of two or more thereof, preferably a polyolefin resin having an ethylene content of 50% by weight or more. Is good. These polyolefin resins include tackifiers and polybutene such as rosin, terpene resin, terpene phenol resin, alkylphenol resin and other petroleum resins to improve adhesiveness and tackiness.
Process oil, paraffin wax A resin mixed with a fluidity modifier such as polyethylene wax, a pigment, and an antioxidant is preferable. The thermoplastic resin or elastomer is preferably one that does not have tackiness at room temperature and can be molded into a tube by an extrusion molding machine.

The thermoplastic resin or elastomer molded into a tube was irradiated with an electron beam from the outer surface of the tube to crosslink the part from the outer surface of the tube to the middle of the tube to form the outer layer of the tube.

The electron beam irradiation apparatus used in the present invention has an accelerating voltage of 15
0 kV to 500 kV accelerators are preferred. This is because at an accelerating voltage of 150 kV or less, even a material with a low density, such as an ethylene content of 50% by weight or more, cannot be processed as a heat-shrinkable tube because it crosslinks only on the surface. When the wall thickness is about 1 mm, the electron beam penetrates and crosslinks not only the outer layer of the tube but also the inner surface of the tube, eliminating the heat melting property of the inner surface, making it possible to mold a heat-shrinkable tube with an inner layer agent. Because there is no.

As a method of bridging only the part from the outer surface of the tube to the middle of the tube (outer tube layer), a magnet is provided below the emission window of the electron beam speed governor as shown in FIGS. 1 and 2, for example. , By irradiating the electron beam so that the beam uniformly hits the entire surface of the bending tube.

FIG. 1 is a schematic view from the side of the electron beam irradiation device, and FIG. 2 is a plan view showing the outline from the top of the magnet of FIG.

In FIGS. 1 and 2, (1) is a particle emission source, and (2)
Is an accelerating tube, (3) is a scanning device, (4) is a beam derivation unit,
(5) is an emission window, (6), (7), (8), (9),
(10), (11), (12), and (13) are magnetic pole surfaces, (14) is an irradiated object, (15) is notches (16), (17), and (18) are particle beams.

A and B indicate magnets.

Further, the accelerator need not be limited to the scan type, and the curtain flow type may be used.

The thickness of the tube outer layer is largely determined by the acceleration voltage. When the accelerating voltage is low, only the outer surface is formed, and when the accelerating voltage is high, the inside can be crosslinked to a considerable extent, and the degree of crosslinking is determined by the irradiation dose of the electron beam.

FIG. 4 shows the relationship between the acceleration voltage of the electron beam irradiation apparatus used in the present invention and the thickness of the light transmitted from the outer surface. As the accelerating voltage becomes higher, the permeation thickness becomes thicker, and the gel fraction only changes depending on the irradiation amount, but does not affect the thickness. Further, the permeation thickness is affected by the density of the tube material, and the smaller the density, the easier the crosslinking. Based on these facts, the materials of various tubes and electron beam irradiation amount were examined, and the outer layer thickness and workability as a heat shrinkable tube were examined.

In the present invention, the thickness of the outer layer is 1/3 to 2 of the tube wall thickness.
/ 3 was excellent in heat expansion workability, and the degree of crosslinking was preferably such that the gel fraction was 30 to 80% by weight.

The tube thus cross-linked is heated to a temperature above the melting point of the tube, pressurized air is introduced into the tube to expand the tube to an arbitrary outer diameter by depressurizing the outside of the tube, and the tube is allowed to cool and solidify as it is, so that heat shrinkability is achieved. A tube is obtained. Since the inner surface of the heat-shrinkable tube is not cross-linked by the electron beam, the heat fusion property in the initial stage of the tube is maintained, and as shown in FIG. 3, the heat having the tube inner layer serving as the adhesive layer is apparently obtained. It becomes a shrinkable double tube. In FIG. 3, (19) is the outer tube layer, and (20) is the inner tube layer which is not crosslinked.

As described above, according to the present invention, one layer of a tube is extruded and molded by one material, so that the inner layer of the tube serves as an adhesive layer, and a heat-shrinkable tube similar to the heat-shrinkable tube with an adhesive can be easily molded.

A description will be given below based on examples.

Example 1. A thermoplastic resin prepared by kneading 60% by weight of low-density polyethylene, 30% by weight of ethylene ethyl acrylate copolymer, and 10% by weight of a terpene resin was extruded into a tube having an outer diameter of 10 mmφ and a wall thickness of 1.0 mm, and an acceleration voltage was applied. 24Mra with 300kV electron beam irradiation equipment
d irradiated. After that, the tube was heated to 150 ° C., the inside was pressurized, the outside was depressurized, and expansion molding was performed so as to have an outer diameter of 20 mmφ to obtain a heat-shrinkable tube.

In the obtained tube, the gel fractions of the outer layer and the inner layer were determined with a xylene solvent, and it was also examined how many millimeters the thickness was crosslinked. Further, the tube was heated and shrunk in an iron pipe having an outer diameter of 15 mmφ, and after cooling, a notch having a width of 10 mm was made in the tube, and its peel strength was determined. The results are shown in Table 1.

Example 2. A thermoplastic resin obtained by kneading 70% by weight of ethylene-vinyl acetate copolymer (vinyl acetate content 20% by weight) and 30% by weight of polyamide resin was molded in the same manner as in Example 1 to form a heat-shrinkable tube. Obtained and performance tested.

Example 3 A thermoplastic resin obtained by kneading 20% of a saponified ethylene vinyl acetate copolymer (acetic acid content 30% by weight), 30% by weight of an ionomer resin and 20% by weight of ethylene propylene elastomer in the same state as in Example 1 was used. It was molded and a heat-shrinkable tube was obtained, and the performance was tested.

As can be seen from the results in Table 1, a thermoplastic resin having a heat fusion property, which is obtained by kneading polyethylene and a polyethylene-based copolymer and a tackifier, cross-links only the outer layer portion of the tube at an appropriate irradiation dose and is heat-shrinkable. Expansion processing of the tube was easy.

The gel fraction of the outer layer portion was sufficiently obtained, the gel fraction of the inner layer portion was zero, and the thickness thereof was about 1/2. For this reason, sufficient adhesion to metal was obtained.

It was confirmed that the heat-shrinkable tube having a two-layer structure can be easily obtained from one material as described above, which is very economically advantageous and has no practical problem. This proves the superiority of the present invention.

[Brief description of drawings]

FIG. 1 is a side view showing the outline of an electron beam irradiation apparatus, and FIG. 2 is a plan view of a magnet and an irradiation object in the electron beam irradiation apparatus of FIG. FIG. 3 is a cross-sectional view of the heat-shrinkable tube obtained by the present invention. FIG. 4 is a diagram showing the relationship between the acceleration voltage of the electron beam irradiation apparatus used in the present invention and the thickness of the light transmitted from the outer surface. (1) …… Particle emission source, (2) …… Acceleration tube, (3) ……
Scanning device, (4) ... Beam derivation part, (5) ... Ejection window, A, B ... Magnet, (19) ... Tube outer layer, (20) ...
… Inner layer of tube

Continuation of front page (56) Reference JP-A-57-144716 (JP, A) JP-A-58-36407 (JP, A) JP-A-58-8609 (JP, A) JP-A-57-212024 (JP , A) JP-A-49-58174 (JP, A) JP-A-57-187214 (JP, A) Actually developed JP-A-56-176838 (JP, U)

Claims (1)

[Claims] 1. An electron beam irradiating device in which a magnet is provided from the outer surface of a tube mainly composed of a polyolefin resin having an ethylene content of 50% by weight or more so that the electron beam is bent to hit the entire surface of the tube. And irradiate with an output voltage that does not penetrate through the wall thickness of the tube to form a tube outer layer by bridging the part from the tube outer surface to the middle of the tube, and then expand the tube while heating it to a temperature above its melting point and then solidify by cooling. A method for producing a heat-shrinkable tube characterized by the above.