JPS598541B2 - Netshi Yushi Yukusei Plastic Tube Oyobi Sono Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a heat-shrinkable plastic tube.

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

0 In recent years, heat-shrinkable plastic tubes have come into use for anti-corrosion, electrical insulation, waterproofing, and other treatments.

This is because cable connections, various metal rods, and metal tubes can be processed very easily and uniformly for the above-mentioned purpose. 5. Heat-shrinkable plastic tubes used for these purposes, such as heat-shrinkable polyethylene tubes, are made by first forming a polyethylene tube using a molding machine, then crosslinking the polyethylene by electron beam irradiation, etc., and then stretching it. It's made well.

However, since this heat-shrinkable polyethylene tube consists only of a polyethylene layer, when it is applied to an adherend 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 combustion and melting of the tube surface occurs, the inside of the tube also easily burns and melts. Combustion and dissolution in the coating layer formed on the adherend by heat-shrinkable polyethylene tubes.7 Some of them have poor properties as a coating layer, which can lead to serious consequences such as corrosion of the adherend. Become.

Another drawback is that when cracks or weak points occur on the surface of the coating layer, they simply grow and propagate inside the coating layer, degrading various properties of the coating layer more than expected.

Furthermore, in the conventional method described above, when making a heat-shrinkable plastic tube with a large diameter (approximately 30 m or more in diameter), an extrusion die mold corresponding to the tube diameter is required, which not only increases manufacturing costs but also increases production costs. Another drawback was that it was difficult to obtain tubes with uniform wall thickness.

The present invention corrects the deficiencies of conventional products and methods and provides a new and useful method for producing heat-shrinkable plastic tubes.

That is, the method for producing a heat-shrinkable plastic tube according to the present invention comprises at least two layers, one plastic layer and the other plastic layer have different softening points, and at least one plastic layer S has heat-shrinkability. The plastic sheet is placed in a cylindrical mold body with a plastic layer having a high softening point as an outer layer, and the heat shrink direction of the plastic sheet is approximately aligned with the circumferential direction of the mold body to a predetermined thickness. Wrap it over and over until the ends are fixed,
Thereafter, the whole is heat-treated at a temperature higher than the softening point of each plastic layer to form a tube-shaped object, and after cooling, the tube-shaped object is removed from the cylindrical mold. Plastics used in the present invention include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene monovinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, chlorinated polyethylene, polyvinyl chloride,
Thermoplastic plastics such as polyester are mainly used, but synthetic rubbers such as silicone rubber and butyl rubber, natural rubber, or a mixture of the above-mentioned thermoplastic plastics and rubber can also be used, and if desired, anti-aging agents and fillers can also be used. , a predetermined amount of additives such as colorants may be added.

Further, the above-mentioned thermoplastic 4 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 J] S-K-7206), or if the plastics are of the same type, by appropriately changing the molecular weight, degree of polymerization, degree of crosslinking, etc. The softening points can be made different.

This difference in softening point is usually 3 to 150°C, especially 5 to 150°C.
15°C is preferred.

Furthermore, in the present invention, the plastic forming the outer layer of the tube has a higher softening point than the plastic forming the inner layer of the tube. 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 an embodiment thereof includes an embodiment in which all five plastic layers have different softening points. , 5 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 one layer, 6 The softening points of the specific multiple layers are the same, but , a mode in which the softening point of the remaining layers is different from that of the plurality of layers (the softening points of these layers are the same), and the like.

Furthermore, heat-shrinkability refers to the property of shrinking considerably when heat is applied. 1 In order to impart this property to plastics, commonly used methods are applied.

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 so,
The plastic exhibits heat shrinkability in the direction of stretching. Next, to describe an example of the manufacturing method of the present invention, the first method involves preparing two types of plastics with different softening points, and using a coextrusion device having two extruders and one die mold. ) A plastic sheet in which two layers are integrated is produced, and then one or both of the plastic layers is crosslinked by electron beam irradiation, etc., as desired, and then uniaxially or biaxially stretched to produce a stretched plastic sheet. .

Next, the stretched plastic sheet is placed into a cylindrical mold body (the outer circumferential surface is peeled off if necessary) having an outer diameter approximately equal to the inner diameter of the desired heat-shrinkable plastic tube. Wrap it in layers so that it is in contact with the mold.

In this case, the end (winding end) is fixed with adhesive, adhesive tape, etc. The number of windings is carried out two times or several times to + several times or more as necessary until the desired tube thickness is obtained. In the present invention, wrapping the plastic sheet around the cylindrical body involves overlapping two or more separate plastic sheets with different softening points so that the plastic sheet with a low softening point is in contact with the cylindrical body. This can also be done by wrapping the plastic sheets in layers (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 is shaped into a cylindrical mold so that the stretching direction (heat shrinkage direction) of the sheet substantially coincides with the circumferential direction of the cylindrical mold. Roll the sushi into sushi rolls or spiral rolls.

In addition, in the case of biaxially stretched products, it is preferable to wrap the stretched plastic sheet around the cylindrical mold in a sushi-wound or spiral manner so that the direction in which the stretched plastic sheet has a large stretching ratio substantially coincides with the circumferential direction of the cylindrical mold. be. As mentioned above, a tube-shaped object is obtained by wrapping a plastic sheet around a cylindrical body and then heat-treating the plastic sheet to maintain heat shrinkability at a temperature higher than the softening point of each plastic layer, thereby making these two bodies. A heat-shrinkable plastic tube is obtained by forming a heat-shrinkable plastic tube and then removing the tube-shaped 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, stretched, and then operated in the same manner as in the first method.

Further, as a third method, a predetermined number of two or more plastic sheets are crosslinked, the crosslinked plastic sheet is crimped with the remaining plastic sheet and stretched, and then the same process as in the first method is performed. There are several ways to work. Furthermore, as a fourth method, a predetermined number of two or more plastic sheets are cross-linked and stretched, and the remaining plastic sheets are left uncured and unstretched together with the cross-linked and stretched plastic sheets. There is a method in which the same method as the first method is used.

The thickness of the plastic sheet used in the present invention is usually about 0.1 to 0.5 m11 for an unstretched product,
The stretched product is about 0.05-0.3m7! It is about L.

Further, according to 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. You can also do it. When the heat-shrinkable plastic tube obtained by the method of the present invention is inserted into a metal tube or the like and heated with a gas burner, even if the outer plastic layer with a high softening point burns and melts, the next layer The plastic layer with a low softening point melts into a fluid state, and the temperature is uniformized and transmitted to the inside, so the plastic layer with a high softening point existing inside the low softening point layer does not burn and melt. , a good coating layer can be formed.

The present invention is constructed as described above, and has the characteristics that large-diameter products can be manufactured easily and inexpensively, and products with uniform wall thickness can be obtained.

Furthermore, as will become clear in the following examples, the heat-shrinkable plastic tube obtained by the method of the present invention has excellent shrinkage workability, and even if the surface burns and melts, the phenomenon does not extend to the inside. Moreover, the coating layer made of the tube has excellent stress crack resistance, weather resistance, electrical properties, etc. Example 1 In a coextrusion device, one side was made of a polyethylene layer with a thickness of 0.15 mm (density 0.935, M..1.01, softening point 110°C)
In addition, the other layer is made of ethylene vinyl monate copolymer (vinyl acetate content 10% by weight, density 0.9) with a thickness of O and 15 mm.
3, M. I. 6. Making a long plastic sheet with a thickness of 0.3 mm that has two integrated layers with a softening point of 73 ° C.
Next, this sheet is irradiated with an electron beam of 5 Mrad from the polyethylene layer side using an electron beam irradiation device to crosslink the polyethylene.

Next, the long plastic sheet is passed between two metal rolls, and then the long sheet is uniaxially stretched in the longitudinal direction by another roll installed in front of the sheet in the longitudinal direction. A long stretched plastic sheet having shrinkability and a thickness of 0.15 mm was made. Next, this elongated stretched plastic sheet was 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 opener 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 with an inner diameter of 680 mm and a wall thickness of 1.011 mm.
A heat-shrinkable plastic tube was obtained.

This heat-shrinkable plastic tube has a diameter of 609m1φ.
After inserting it into a steel pipe, the surface was heated with a gas burner to cause heat shrinkage.

After heat shrinking, the outermost polyethylene layer of the tube surface (covering layer) was burnt and melted, but the next layer, the ethylene monovinyl acetate copolymer layer, melted during heating and became fluid, making the temperature uniform. It was found that the polyethylene layer inside the copolymer layer was prevented from burning and dissolving as a result. Next, the stress crack resistance and weather resistance of the coating layer were tested.

The results are shown in Table 1. Example 2 A long polyethylene sheet with a thickness of 0.21t1t (density 0
．． 92, M. I. 2. Softening point: 95°C) was irradiated with an electron beam and stretched as in Example 1 to a thickness of 0.11! Obtain a long 5-stretched polyethylene sheet with a thickness of 0.1 m1L on one side.
unirradiated unstretched polyethylene sheet (density 0.91, M
．． I. 23, softening point 86°C), 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. Thickness 1.411!
A heat-shrinkable plastic tube 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.
J Example 3 In a coextrusion device, one side was made of an ethylene monoacetate pinyl copolymer layer with a thickness of 0.1 mm (
Vinyl acetate content 25% by weight, density 0.95, M. I.
3. Softening point: 45°C), 1. The other side has a thickness of 0. h1! A long piece with a thickness of 0.211 in which two layers of ethylene monovinyl acetate copolymer (vinyl acetate content 5% by weight, M..2, density 0.92, softening point 83°C) are integrated. A plastic sheet was prepared, and then an electron beam of 10 Mrab was irradiated from the side of the layer containing 5% by weight of vinyl acetate using an electron beam irradiation device to crosslink the layer.

Thereafter, stretching, winding (so that the low softening point layer is in contact with the mold), heat treatment, cooling, and ejecting were carried out in the same manner as in Example 1, resulting in a heat-shrinkable plastic with an inner diameter of 680 m, L, and wall thickness of 0.7 nm. Got 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 m1L (density 0.
92, M. I. 2. Softening point: 95°C) was irradiated with electron beam and stretched in the same manner as in Example 1 to obtain a long stretched polyethylene sheet with a thickness of 0.1 m, and on one side of the sheet was an unirradiated unstretched sheet with a thickness of 0.1 m71. Polyethylene sheet (density 0.935, M.
I. 1.0, 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 1.4V1L 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. I. Using a heat-shrinkable polyethylene tube consisting of only a layer of 1.5°C and a softening point of 97°C, 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. The present invention is as described above, and uses plastic sheets with different softening points,
When external factors such as heat and force act on a multilayer heat-shrinkable plastic tube made by wrapping these sheets over and over until they reach a predetermined thickness, weak points or cracks may occur in the outermost layer. Also, by absorbing heat and force internally, it is possible to prevent one weak point, cracks, etc. from propagating deep inside. In addition, a plastic layer with a low softening point is located in the inner layer, and during heat shrinking work, this plastic layer acts as if it were a hot melt adhesive. Needless to say, it also has strong adhesion between layers, so it has the feature of being able to impart complete corrosion-proofing, waterproofing, and electrical insulation to the adherend. On the other hand, single-layer conventional products do not have internal absorption capacity for external factors, so if weak points or cracks occur, they easily propagate internally and are destroyed.

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, is molded into a cylindrical mold. A plastic layer with a high softening point is used as an outer layer around the mold body, and the heat shrink direction of the plastic sheet substantially coincides with the circumferential direction of the mold body, and the plastic sheet is wrapped to a predetermined thickness, and the ends are fixed. The heat-shrinkable plastic tube is then heat-treated at a temperature higher than the softening point of each plastic layer to produce a tube-shaped object, and then, after cooling, the tube-shaped object is taken out from the cylindrical mold. Production method. 2. The method for manufacturing a heat-shrinkable plastic tube according to claim 1, wherein the plastic sheet is one in which one plastic layer and another plastic layer are integrated in advance. 3. The method for manufacturing a heat-shrinkable plastic tube according to claim 1, wherein the plastic sheet is made by laminating one plastic layer and another plastic layer that are separate from each other.