JPH0213616B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-shrinkable tube using fluororubber as the main material, and in detail, 100 parts by weight of fluororubber and 12 to 12 parts of ethylene-ethyl acrylate copolymer resin containing 8 to 20% by weight of ethyl acrylate. This invention relates to a heat-shrinkable tube characterized in that it is made by crosslinking a mixture with 100 parts by weight and then 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 whose main material is 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 found. Not yet. 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. As a result of consideration to obtain a heat shrink tube,
This led to the present invention. 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 EEA, which has a SP value of 8.5 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 EEA with a high content of ethyl acrylate, that is, a large SP value, was used as a crystalline polymer. It was found that the compatibility with fluororubber is better. As a result of experiments, it was confirmed that the ethyl acrylate content in EEA in this case was 8% or more. However, when the content of ethyl acrylate increases in EEA, EEA loses its crystallinity and becomes rubber-like, so that even when mixed with fluororubber, no memory effect is imparted. Therefore, from this point of view, the appropriate content of ethyl acrylate in EEA is 8 to 20% by weight. Further, the amount of EEA to be mixed with respect to 100 parts by weight of fluororubber 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 EEA 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. At that time, the dimensional change rate was measured, and the heat setting 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 EEA resins. Furthermore, heat setting properties were tested when the mixing ratio of fluororubber and EEA was varied, and the results shown in Table 2 were obtained. In addition, in this test, the EEA
DPDJ-6169 was used.

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

Claims (1)

[Claims] 1. A mixture of 100 parts by weight of fluororubber and 12 to 100 parts by weight of an ethylene-ethyl acrylate copolymer resin containing 8 to 20% by weight of ethyl acrylate is crosslinked and then expanded into a tube shape. A heat-shrinkable tube whose main ingredient is fluorocarbon rubber.