JPH0213615B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-shrinkable tube using fluorocarbon rubber as the main material.
~30% by weight ethylene-vinyl acetate copolymer resin 12
This invention relates to a heat-shrinkable tube characterized in that it is made by crosslinking a mixture of 100 parts by weight and expanding it into a tube shape. Heat-shrinkable tubes based on synthetic resins such as polyethylene, ethylene-vinyl acetate copolymer, polyvinyl chloride, and chlorinated polyethylene have been well known. It is also known to blend amorphous rubbery polymers with crystalline polymers to obtain shrinkable tubes. (Special Publication No. 51-39996) However, a heat-shrinkable tube based on fluorocarbon rubber, which has the best properties such as heat resistance and oil resistance among many synthetic resins and synthetic rubbers, has not yet been discovered. do not have. The present inventor has developed a heat-shrinkable tube that can be used at temperatures above 150°C by using fluorocarbon rubber, which has the above-mentioned properties, as a main material and is used as a heat-shrinkable tube for reconnecting communication cables and power cable connections and for corrosion protection of steel pipes. The present invention was developed as a result of studies aimed at obtaining a heat-shrinkable tube. The present invention will be explained in detail below. First of all, materials that have a memory effect (the property of returning to its original shape after a previously applied strain is removed by heating)
It is obtained by having crystals in the main polymer or by mixing a crystalline polymer. Examples of crystalline polymers include polyethylene, polypropylene, ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA), ethylene-ethyl acrylate copolymer (hereinafter abbreviated as EEA),
Polyvinylidene fluoride, polyamide, etc. are known, and polyethylene and polypropylene have particularly high crystallinity. In the present invention, when obtaining a heat-shrinkable tube using fluorocarbon rubber as the main material, the crystalline polymer to be mixed with the fluorocarbon rubber is polyethylene, polypropylene, etc. , hereinafter abbreviated as SP) shows a value close to 7.8 to 8.0 compared to 6.2 for fluororubber, and is considered to be easily compatible. However, when fluorine rubber and these crystalline polymers were actually mixed using a hot roll, the two did not mix but completely separated, making it impossible to mold them. Therefore, when EVA, which has a SP value of 8.3 to 9.4, which is quite different from that of fluoro rubber, was used as a crystalline polymer and mixed with a hot roll, the content of vinyl acetate in EVA was high, that is, the SP value was large.
It was found that EVA has better compatibility with fluororubber. As a result of experiments, it was confirmed that the vinyl acetate content in EVA in this case was 10% or more. However, this vinyl acetate content is EVA
If the amount increases, EVA loses its crystallinity and becomes rubbery, so that even when mixed with fluoro rubber, no memory effect is imparted. Therefore, from this point of view, the appropriate content of vinyl acetate in EVA is 10 to 30% by weight. Further, the amount of EVA to be mixed with respect to 100 parts by weight of fluorocarbon rubber is suitably 12 to 100 parts by weight from the viewpoint of heat setting properties after forming a sheet using this mixture. In addition, after mixing fluorocarbon rubber and EVA to create a sheet, it is necessary to give it sufficient shrinkage characteristics in order to use it as a heat-shrinkable tube, and for this purpose, the polymer must be crosslinked. It is important to keep the In addition to electron beam irradiation, the crosslinking method may be organic peroxide or silicon crosslinking. The thus obtained heat-shrinkable tube of the present invention had particularly excellent heat resistance and oil resistance compared to conventional shrinkable tubes made of other materials. The present invention will be explained below with reference to Examples. Example: A 1:1 ratio of the resin shown in Table 1 to fluorocarbon rubber (DuPont, Viton B) was heated at 140°C.
The mixture was kneaded using a hot roll. Then, a sheet was created from the mixture by hot pressing. Next, this was made into a tube shape, crosslinked by electron beam irradiation at 20 Mrad, and then expanded to obtain a heat-shrinkable tube. Further, a dumbbell-shaped test piece was punched out from the above sheet, stretched 100% in a 140°C oil bath, and then cooled in water. The dimensional change rate at that time was measured, and the heat set property was also examined, and the results are shown in Table 1.

[Table] From the above table, it was found that it is difficult to mix polyethylene and polyolefin with fluoro rubber, but it is possible to mix both EVA resins. It was also found that when mixed with this EVA resin, those containing a high vinyl acetate content lacked heat setting properties. Furthermore, we tested the heat setting property when the mixing ratio of fluoro rubber and EVA was changed, and the results shown in Table 2 were obtained. In this test, the above-mentioned Evatate H1011 was used as EVA.

[Table] *Heatset property was judged by deformation rate.
○: 5% or less, △: 10% or less, ×: 10% or more,
From the table above, the mixture of EVA to fluoro rubber is 12
It has been demonstrated that parts by weight or more are good.

Claims (1)

[Claims] 1 100 parts by weight of fluororubber and vinyl acetate content of 10
~30% by weight ethylene-vinyl acetate copolymer resin 12
1. A heat-shrinkable tube made of fluorocarbon rubber as a main ingredient, which is obtained by crosslinking a mixture of 100 parts by weight and expanding it into a tube shape.