JPH0675919B2 - Heat shrink tube - Google Patents

Description

The present invention relates to a heat-shrinkable tube having excellent heat resistance, transparency, and flame retardancy.

[Conventional technology]

Heat-shrinkable tubes are used for various purposes such as terminal treatment of wiring in various devices, joints of electric cables, corrosion protection of steel pipes, and the like. Among these applications, especially when it is used for connection of wiring in equipment or terminal treatment, it is required to be visible because the condition of the connection part is visible, or to use it as a capacitor cover, it is easy to judge the type of equipment used, so it is transparent. Excellent heat shrink tubing is required. For applications in this field, further, flame retardancy is required to be certified by UL standard, for example, and heat shrinkable tubes are required to have high flame retardancy. Therefore, a heat-shrinkable tube having a composition of a polyvinyl chloride (PVC) resin, which is superior in transparency, has been used for applications in this field. Other non-plastic polymers include chlorinated polyethylene (CPE), which is a polymer containing halogen in the same polymer as PVC, and EVA.
There is a graft copolymer grafted with PVC, and there is JP-B-59-17935 as a heat-shrinkable tube which is excellent in flame retardancy and transparency by combining these polymers.

[Problems to be solved by the invention]

Although the transparent PVC tube has excellent transparency, the plasticizer added to add flexibility exudes and contaminates the equipment surface, and plasticizes on the insulated wire that is the adherend of the tube. Since the agent often migrates, a so-called non-plastic type heat shrink tube that does not use a plasticizer has been desired. Non-plastic type resin, such as polyethylene (PE) resin, has poor flame retardancy and transparency, and ethylene-vinyl acetate copolymer (EVA), which has excellent transparency, is flammable and flame-retardant. Therefore, it becomes opaque if a flame retardant is added. Japanese Patent Publication No. 59-17935 has excellent flame retardancy and transparency, but is not necessarily sufficient in heat deformability (heat resistance) at high temperatures.

The present inventor has conducted intensive studies in order to obtain a heat-shrinkable tube which is unplasticized and has excellent heat resistance, transparency, and flame retardancy, and as a result, the present invention has been accomplished.

[Means for solving problems]

The gist of the present invention is to mold a resin composition obtained by adding silica having a particle size of 50 nm or less to chlorinated polyethylene having a crystallinity of 1 to 25% into a tube, and subjecting the tube to electron beam irradiation crosslinking. The heat-shrinkable tube is characterized by being expanded. The present invention will be described below along with the background of the invention.

The heat deformability can be solved by adding a filler to the resin composition, but the transparency decreases when the filler is added to the polymer. Among the fillers, silica is known as a filler that does not impair transparency, but it was better than other fillers but was ineffective against most polymers (eg polyethylene, polyvinyl chloride, etc.).

However, chlorinated polyethylene (hereinafter abbreviated as CPE)
It was found that the composition in which silica is added does not impair the transparency, but rather improves the transparency and the heat deformability.

The reason why the particle size (maximum value) of silica used in the present invention is 50 nm or less is that those having a particle size of 50 nm or less have excellent transparency.

In the present invention, the reason why the crystallinity of CPE is 1 to 25% is that if it is less than 1%, its shape retention after expansion is poor, and if it exceeds 25%, it becomes hard and its commercial value is lowered.

Especially when shape retention at room temperature is required, CPE having a crystallinity of 10% or more is preferable.

A heat shrinkable tube is manufactured by expanding the tube at a softening point temperature or melting point or higher and then cooling it as it is. However, at the softening point or melting point or higher, the resin used is melted to expand the tube. I can't. For this reason, crosslinking is performed so that the resin does not melt. There are chemical crosslinking, radiation crosslinking, and the like as this crosslinking method. In the chemical crosslinking, the resin composition is markedly colored because it is crosslinked at a high temperature. In the present invention, radiation crosslinking is most suitable. Furthermore, in order to improve the crosslinking efficiency of the resin composition of the present invention, it is preferable to add a polyfunctional monomer as a crosslinking aid. This is because the resin composition can be crosslinked with a smaller irradiation amount than that of the resin composition without addition, and thus the coloring due to irradiation can be further reduced. The polyfunctional monomers include acrylates (diethylene glycol diacrylate, etc.), dimethacrylates (diethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, etc.), triacrylates (trimethylolethane triacrylate, trimethylolpropane triacrylate). Etc.), trimethacrylates (trimethylolethane trimethacrylate,
Trimethylolpropane trimethacrylate, etc.), triallyl cyanurate, triallyl isocyanurate,
Diallymalate and the like.

The CPE according to the present invention contains halogen in the polymer, and the resin itself is flame retardant.

To impart a higher degree of flame retardancy to the heat-shrinkable tube of the present invention, for example, in order to pass the vertical combustion test of UL standard (UL-224), the resin alone lacks flame retardancy. Therefore, it is necessary to add a flame retardant. As a result of studying various flame retardants, powdered flame retardants such as decapromodiphenyl ether, chlorinated paraffin, and antimony trioxide
When added to the resin, the flame retardancy is significantly improved, but the transparency is impaired, and the liquid flame retardancy, for example, phosphoric acid ester, halogenated ester and the like have good transparency, but flame retardancy It is not good, and it can not be used because it oozes out on the surface of the tube, but if you use 2.2 di (4-bromoethoxy 3.5-dibromophenyl) propane,
It was found that it was excellent in transparency and had no bleeding at all.
Furthermore, the above-mentioned silica is effective for the sag of the sample, which is an evaluation item of the UL vertical test, and the flame retardancy is also improved by using 2.2 di (4-bromoethoxy 3.5-dibromophenyl) propane and silica together. It was found to pass the UL vertical test sufficiently.

Hereinafter, the present invention will be described with reference to specific examples.

〔Example〕

A tube having an inner diameter of 1.2 mm and a wall thickness of 0.45 mm was extruded from the resin composition consisting of the compositions 1, 2, and 3 shown in Table 1, irradiated with 5 Mrad using an electron beam accelerator of 1 MeV, and then the The tube was expanded to an inner diameter of 2.4 mm and cooled to produce a heat-shrinkable tube by a method (a method of heating a tube to a softening point or higher and reducing the internal pressure and / or the pressure around the tube).

Thermal deformability and flame retardancy comply with UL224, and transparency is
A sheet having a thickness of 0.2 mm was prepared from each of the resin compositions 1, 2, and 3, and 5 Mrad was irradiated with an electron beam accelerator of 1 MeV, and then a visible light transmission spectrum was measured.

The test results are shown in Table 2. From these results,
All of Examples 1, 2, and 3 were heat-shrinkable tubes having excellent heat resistance, transparency, and flame retardancy.

(Comparative Examples 1, 2, and 3) Using the resin compositions having the compositions 4, 5, and 6 shown in Table 1, a tube having the same size as that of the above-described example was prepared, and heat treatment was performed in the same manner as the example. A shrink tube was obtained. For these tubes, the same test method as in the example, heat resistance,
The transparency and flame retardancy were evaluated.

The results are shown in Table 2. Comparative Example 1 has good flame retardancy but poor heat resistance and transparency, and Comparative Example 2 has
Heat resistance and flame retardancy are good, but transparency is poor, and Comparative Example 3
Had good transparency and flame retardancy, but poor heat resistance.

[Advantages of the Invention] The heat-shrinkable tube of the present invention is excellent in heat resistance, transparency and flame retardancy, and is particularly useful for connection of in-device wiring and terminal treatment.

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Claims (3)

[Claims] 1. A resin composition obtained by adding silica having a particle diameter of 50 nm or less to chlorinated polyethylene having a crystallinity of 1 to 25% is molded into a tube, and the tube is subjected to electron beam irradiation crosslinking. A heat-shrinkable tube characterized by being expanded. 2. The heat-shrinkable tube according to claim 1, wherein the resin composition contains a polyfunctional monomer. 3. A resin composition containing 2.2 di (4-bromoethoxy)
The heat-shrinkable tube according to claim 1, which contains 3.5-dibromophenyl) propane.