JPS6147861B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked polyolefin electrical insulation composition that is heat resistant and has excellent flame retardancy. Conventional crosslinked polyolefin compositions that are heat resistant and difficult to refract include polyethylene or ethylene-based copolymers and halogen-containing flame retardants such as chlorinated polyethylene, perchlorocyclopentadecane, and tetrabromobisphenol A. A system in which a combination of antimony oxide and antimony oxide is added is known. When chlorinated polyethylene is used as a flame retardant, it is possible to provide heat resistance rated at 105°C by using an appropriate amount of heat stabilizer. However, it is insufficient in terms of thermal stability as a heat-resistant insulating material of about 120°C. On the other hand, when perchloropentacyclodecane or tetrabromobisphenol A is added, their compatibility with polyolefin is insufficient, and blooming occurs during short-term or long-term use, for example, in closed motor lead wires, etc. If used, there is a risk that it will adhere to the enamelled wire and cause insulation deterioration. For this reason, electrical insulators that can be used for long periods of time with ratings of 120°C and 130°C have been limited to expensive silicone rubber and fluorocarbon resins. Alternatively, although insufficient, electrical insulators using crosslinked polyolefins to which chlorinated polyethylene is added have been used. Therefore, if an electrical insulating composition can be obtained in which a flame retardant with excellent heat resistance and compatibility is added to a relatively inexpensive polyolefin, it would have an extremely large industrial contribution. An object of the present invention is to overcome the drawbacks of the prior art and to provide a crosslinked polyolefin electrical insulation composition that has excellent heat resistance and flame retardancy. Flame retardants with excellent thermal stability include bromine-containing compounds, chlorine-containing compounds, phosphorus-containing compounds, etc.
As a result of examining thermal stability and compatibility with polyolefin, it was found that decabromobiphenyl ether satisfies both conditions. Combining this with antimony oxide, like most halogen-containing flame retardants, provides efficient flame retardancy. However, although decabromo biphenyl ether is a stable substance with a high melting point, it has been found that when added to polyolefin, the volume resistivity decreases by two to three orders of magnitude.
When a method of preventing this decrease in volume resistivity was investigated, it was found that it is effective to use tribasic sulfate, epoxy resin, and organic phosphite alone or in combination. However, in order to maintain a high degree of heat resistance, it is important to select an antioxidant, and di-aryl-p-phenylenediamine was found to be effective as it inhibits crosslinking and volatilizes at high temperatures. . Other antioxidants may be used in combination with this. Crosslinking is carried out by well-known methods such as using an organic peroxide such as dicumyl peroxide or by irradiating with an electron beam. In addition to the above, there is no problem in adding inorganic fillers, carbon black, colorants, lubricants, etc., if necessary. The reason for setting limits on the combined amount of decabroviniphenyl ether and antimony oxide, which are Γ flame retardants, is that
If the amount added is small, a sufficient flame retardant effect cannot be obtained. This is because if the amount added is too large, it will have an adverse effect on physical properties, electrical properties, etc. The reason why the amount of the Γ stabilizer is limited to 0.1 parts by weight or more is because a small amount has no effect on improving the volume resistivity. The reason for limiting the amount of Γ di-aryl-p-phenylenediamine is that if it is less than 0.1 parts by weight, the heat resistance will be insufficient, and if it is more than 5 parts by weight, the crosslinking density will be greatly reduced, resulting in poor heat deformation and oil resistance. This is because it will drop significantly. The Γ polyolefin is as follows. Polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-methacrylate copolymer, ethylene-propylene copolymer, etc. with an ethylene content of at least 50%
% by weight. Next, examples of the present invention will be listed together with reference examples. In addition, various characteristics of each example will be listed below.

【table】

[Table] Γ Test method (1) Combustion test... Based on ASTM D635 (2) Heat aging properties A crosslinked sheet with a thickness of 1.0 mm was prepared by pressure molding for 10 minutes using a press at 180°C. This was punched out with a dumbbell No. 3 and placed in an aging tester at 180℃.
It was left for 10 days. After taking out the sample, it was cooled to room temperature and then the sheet was bent. At that time, the presence or absence of cracks was determined visually. (3) Volume resistivity Create a sheet with a thickness of 1.0 mm, use a super insulation resistance meter (Takeda Riken TR-16 model) to read the resistance value 1 minute after applying electricity, and convert it to volume resistivity. did. Measurements were performed at room temperature. (4) Heat deformation rate The amount of deformation of a sheet with a thickness of 2 mm was measured under the conditions of 120°C - 3 kg - 1 hr., divided by the original thickness, and then multiplied by 100. The effects of the electrical insulating composition of the present invention are clear from the above characteristic table, but the following points will be further detailed. Γ Previously, it was almost impossible to obtain electrical insulating materials based on cross-linked polyolefin that were rated at 120°C and had excellent heat resistance and flame retardancy. By using decabromo biphenyl ether as a flame retardant, adding a heat stabilizer to improve the volume resistivity, and adding diaryl-p-phenylenediamine, the desired heat resistance and flame retardance were achieved. We were able to obtain an excellent crosslinked polyolefin electrical insulator. Although Γ-decabromo biphenyl ether is a stable substance with a high melting point, some free bromine is generated during the high-temperature crosslinking process, which causes a decrease in volume resistivity. It is believed that the addition of a thermal stabilizer improves the volume resistivity because free bromine is captured and stabilized by these compounds. Although the mechanism of action of di-aryl-p-phenylenediamine is unknown, it is thought that it retains its efficacy well because it has low volatility at high temperatures.

Claims (1)

[Claims] 1. (a) decabromo biphenyl ether and (b) antimony oxide in a total amount of (a) + (b) based on 100 parts by weight of polyethylene or a copolymer mainly composed of ethylene. 15 to 60 parts by weight, the ratio of (a)/(b) is in the range of 0.1 to 30, and (c) 0.1 part by weight or more of a stabilizer to improve volume resistivity and thermal stability. d) G-
A heat-resistant flame-retardant crosslinked polyolefin electrical insulation composition containing 0.1 to 5 parts by weight of aryl-p-phenyleneamine.