JPS609899B2 - heat shrinkable plastic tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to heat-shrinkable plastic tubing.

One of the objects of the present invention is to provide a heat-shrinkable plastic tube that has excellent shrinkage workability during heat shrinkage, stress crack resistance, film resistance, electrical properties, etc.
Another object is to provide a relatively large diameter heat shrinkable plastic tube.

In recent years, heat-shrinkable plastic tubes have come to be used for treatments such as corrosion protection, electrical insulation, and waterproofing.

This is because cable connections, various metal rods, and metal tubes can be processed very easily and uniformly for the purpose mentioned above. Heat-shrinkable plastic tubes used for these purposes, such as heat-shrinkable polyethylene tubes, are made by first molding a polyethylene tube using a molding machine, then deconstructing the polyethylene by irradiating it with an electron beam, and then stretching it. ing.

However, since this heat-shrinkable polyethylene tube consists only of a polyethylene layer, when it is applied to an adhesive body such as a metal cylinder, heating with a gas burner or the like tends to cause local combustion and melting of the tube surface. Once the surface of the tube burns and melts, the inside of the tube also easily burns and melts. The combustion and melting portions in the coating layer formed on the adherend by the heat-shrinkable polyethylene tube have poor properties as a coating layer, and therefore lead to serious consequences such as corrosion of the adherend. Another disadvantage is that if cracks or weak points occur on the surface of the coating layer, they easily grow and propagate inside the coating layer, degrading various properties of the coating layer more than expected.

The present invention corrects the deficiencies of conventional products and provides a new and useful heat-shrinkable plastic tube.

That is, the heat-shrinkable plastic tube according to the present invention is
A plastic sheet consisting of at least two layers, one plastic layer and the other plastic layer having different softening points, and at least one plastic layer having heat shrinkability, with the plastic layer having a higher softening point as an outer layer. It has a cylindrical shape with a predetermined thickness and is fixed and integrated.

Plastics used in the present invention include polyethylene, polypropylene, ethylene-propylene copolymer,
Thermoplastic plastics such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, chlorinated polyethylene, polyvinyl chloride, and polyester are king, but silicone rubber, butyl rubber, etc. Synthetic rubbers, natural rubbers, or mixtures of the above thermoplastics and rubbers may also be used, and if desired, additives such as anti-aging agents, fillers, colorants, etc. may be added in predetermined amounts.

Further, the above thermoplastic plastics and rubbers can also be crosslinked and used. In the present invention, having different softening points means that the softening points (ASTM-D-
1525 or JIS-K-7206), and if the plastics are of the same type, the softening points can be made different by appropriately changing the molecular weight, degree of polymerization, degree of crosslinking, etc. I can do it.

This difference in softening point is usually 3 to 15,000, but especially 5
~15oo is preferred.

Further, in the present invention, as the plastic forming the outer layer of the tube, a material having a higher softening point than the plastic forming the inner layer of the tube is used. In addition, in the case where there are three or more plastic layers in the present invention, it is sufficient that two of the layers have different softening points, and the embodiments include: (1) an embodiment in which all the plastic layers have different softening points; ■ The remaining layers except one specific layer have the same softening point, but the softening point is different from the softening point of the specific layer, @ The softening point of multiple specific layers is the same, but the remaining layers have the same softening point. Examples include embodiments in which the softening point is different from that of multiple layers (the softening points of these layers are the same).

Furthermore, heat shrinkability refers to the property of shrinking when heat is applied, and commonly used methods can be applied to impart this property to plastics.

For example, in the case of polyethylene, crosslinking is carried out by irradiation with an electron beam or the like, followed by stretching with a roll. In addition, for polyvinyl chloride and the like, only roll stretching or the like is used. By doing this,
Plastic exhibits heat shrinkability in the stretching direction. Next, regarding an example of the method for manufacturing a heat-shrinkable tube according to the present invention, the first method involves preparing two types of plastics with different softening points, and using two extruders and one
A plastic sheet in which two layers are integrated is produced using a coextrusion device having two die molds, and then, if desired, one or both of the plastic layers is cross-linked by electron beam irradiation, etc., and then single-millimeter stretching or biaxial stretching is performed. Make a stretched plastic sheet.

Next, it is made into a cylindrical mold with an outer diameter approximately equal to the inner diameter of the desired heat-shrinkable plastic tube (the outer circumferential surface is peeled off if necessary). The stretched plastic sheets are wrapped in layers so that the low softening point plastic layer is in contact with the mold.

In this case, the end (winding end) is fixed with adhesive, adhesive tape, etc. The number of windings may be performed twice or several times to ten or more times as necessary until the desired tube thickness is achieved. In addition, when wrapping a plastic sheet around a cylindrical mold, two or more separate plastic sheets with different softening points are overlapped, and the plastic sheet with a low softening point is in contact with the cylindrical mold. It can also be carried out by a method of overlapping wrapping (at least one of the plastic sheets is heat-shrinkable).

In addition, when using a uniaxially stretched product as the stretched plastic sheet, the sheet should be shaped into a cylindrical mold so that the stretching direction (heat shrinkage direction) of the sheet approximately coincides with the circumferential direction of the cylindrical mold. Roll the sushi into sushi rolls or spiral rolls.

In addition, in the case of a double-stretched product, it is preferable to wrap the stretched plastic sheet in a sushi-wound or spiral manner around the cylindrical mold so that the direction in which the stretched plastic sheet has a large stretching ratio approximately coincides with the circumferential direction of the cylindrical mold. It is. As mentioned above, a tubular object is made by wrapping a plastic sheet around a cylindrical body and then heat-treating the plastic sheet to maintain its heat shrinkability at a temperature higher than the softening point of each plastic layer. A heat-shrinkable plastic tube is obtained by manufacturing and then removing the tubular object from the cylindrical mold after cooling.

The second method includes a method in which two or more plastic sheets are bonded together by thermocompression, crosslinked and stretched, and then operated in the same manner as the first method.

In addition, as a third method, a predetermined number of two or more plastic sheets are cross-linked, this cross-linked plastic sheet is crimped with the remaining plastic sheets and stretched, and then the same machine as the first method is used. Examples include methods of working. Furthermore, as a fourth method, a predetermined number of two or more plastic sheets are crosslinked and stretched, and the remaining plastic sheets are left uncrosslinked and unstretched and used together with the crosslinked and stretched plastic sheet. A method that operates in the same way as the first method can be mentioned.

The thickness of the plastic sheet used in the present invention is usually about 0.1 to 0.5 willow for an unstretched product, and about 0.05 to 0.3 willow for a stretched product.

Further, in the present invention, in order to reinforce the heat-shrinkable plastic tube, unstretched or stretched plastic fiber cloth, such as polyester or polyamide, may be enclosed between or within the plastic sheets. When the heat-shrinkable plastic tube of the present invention is inserted into a metal tube or the like and heated with a gas burner or the like, even if the outer plastic layer with a high softening point burns and melts, the next layer with a low softening point will not soften. The plastic layer with a high softening point melts and becomes a fluid state, and the temperature is uniformized and transmitted to the inside, so the plastic layer with a high softening point that exists inside the low softening point layer does not burn and melt, resulting in a good coating layer. can be formed.

The present invention is constructed as described above, and as will become clear in the following examples, it has excellent shrinkage workability, and even if the surface burns and melts, the phenomenon does not extend to the inside, and furthermore, the tube is coated with The layer also has excellent stress crack resistance, weather resistance, and electrical properties. In addition, large-scale products can be manufactured easily and inexpensively, and they can also be produced with uniform wall thickness.

Example 1 In a co-extrusion device, the polyethylene layer on the 0.15 thickness side (density 0.935, M. .15-legged ethylene-vinyl acetate copolymer (vinyl acetate content 10% by weight)
, density 0.93M. A long plastic sheet with a thickness of 0.3 is made by integrating two layers with a softening point of 1.0 (73°C), and then this sheet is irradiated with electrons with a regular ad direction from the polyethylene layer side using an electron beam irradiation device. The polyethylene is crosslinked by irradiation with radiation.

Next, the long plastic sheet is passed between two metal rolls, and another roll installed in front of the traveling direction uniaxially stretches the long sheet in the longest direction, and heats the sheet in the long direction. A long stretched plastic sheet having a shrinkage property and having a thickness of 0.15 mm was made.

Next, this elongated stretched plastic sheet is wrapped seven times (sheet (so that the longitudinal direction of the cylindrical mold body matches the circumferential direction of the cylindrical mold body), and the ends are fixed with commercially available fluororesin adhesive tape. Next, this was placed in an electric oven and heat-treated at 200°C for 1 hour to fix and integrate the sheets together, then cooled and taken out from the cylindrical mold. A heat-shrinkable plastic tube was obtained.

After inserting this heat-shrinkable plastic tube into a steel pipe on the 609-diameter side, the surface was heated with a gas burner to cause heat-shrinkage.

After heat shrinking, the outermost polyethylene layer on the tube surface (covering layer) was burned and melted, but the next layer, the ethylene-vinyl acetate copolymer layer, melted during heating and became fluid, equalizing the temperature and dissolving the inside. As a result, the polyethylene layer inside the copolymer layer was prevented from burning and dissolving. Next, the stress cracking resistance and aging resistance of the coating layer were tested.

The results are shown in Table 1. Example 2 The smallest polyethylene sheet with a thickness of 0.2 mm (density of 0.92 mm)
, M. 1.2, softening point 950C) as in Example 1,
Electron beam irradiation and stretching yielded a stretched polyethylene sheet with a maximum thickness of 0.1, and one side of the unirradiated unstretched polyethylene sheet with a thickness of 0.1 (density 0.91, M.1.23 softened) Points 8 and 0) were superimposed, and then wrapped in the same manner as in Example 1 (so that the unirradiated, unstretched polyethylene sheet was in contact with the mold), heated, cooled, and taken out.
A heat-shrinkable plastic tube with an inner diameter of 68 mm and a wall thickness of 1.4 mm was obtained.

This tube was heat-shrinked in the same manner as in Example 1 to form a coating layer. The properties of the coating layer are shown in Table 1. Example 3 One side was made of an ethylene-vinyl acetate copolymer layer with a thickness of 0.1 (vinyl acetate content: 25% by weight, density: 0) using a coextrusion device.
．． 95, M. 1.3, softening point 45 pm), and the other side is an ethylene-vinyl acetate copolymer layer with a thickness of 0.1 (vinyl acetate content 5% by weight, M.1.2, density 0.92, A long plastic sheet with a thickness of 0.2 ribs is made by integrating two layers with a softening point of 8yo), and then a plate Mr.
The layer is crosslinked by irradiation with an ad electron beam.

Thereafter, stretching, winding (so that the low softening point layer is in contact with the mold), heat treatment, cooling, and removal were performed in the same manner as in Example 1, and the heat shrinkage on the inner diameter 680 skin and wall thickness 0.7 side was Got a plastic tube.

This tube was heat-shrinked in the same manner as in Example 1 to form a coating layer. The properties of the coating layer are shown in Table 1. Example 4 A long polyethylene sheet with a thickness of 0.2 ribs (density of 0.92
, M. 1.1.2, softening point 9yo) was irradiated with an electron beam and stretched in the same manner as in Example 1 to obtain a stretched polyethylene sheet with a maximum thickness of 0.1 mm, and one side of the stretched polyethylene sheet with a thickness of 0.1 mm was Irradiated unstretched polyethylene sheet (density 0.935M.1.1.
(softening point: 110°C), and then wrapped in the same manner as in Example 1 (so that the stretched polyethylene sheet was in contact with the mold), heated, cooled, and taken out. A heat-shrinkable plastic tube with a thickness of 1.4 was obtained.

This tube was heat-shrinked in the same manner as in Example 1 to form a coating layer. The properties of the coating layer are shown in Table 1. Comparative Example Polyethylene with the same inner diameter and wall thickness as Example 1 (density 0.9
2.M. Using a heat-shrinkable polyethylene tube consisting only of layers (1.1.5, softening point: 97oo), this tube was heat-shrinked in the same manner as in Example 1 to form a coating layer.

The properties of the coating layer are shown in Table 1. 1. The method for measuring stress crack resistance is ASTM-D-16.
Equivalent to 93K.

Note 2 In accordance with ASTM--D-750, the elongation is halved in hours.

Claims (1)

[Claims] 1 A plastic sheet consisting of at least two layers in which one plastic layer and the other plastic layer have different softening points, and at least one plastic layer has heat shrinkability, with the plastic layer having a higher softening point as the outer layer. A heat-shrinkable plastic tube formed into a cylindrical shape with a predetermined thickness and fixedly integrated.