JPH0244082B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrically insulating composition with excellent water resistance. Polyolefin insulated cables, especially cross-linked polyethylene insulated vinyl sheathed cables (CV cables), are currently in widespread use, and are expected to become even higher in voltage in the future, and there is great interest in their long-term performance stability. It is being said. However, with this CV cable, slow deterioration of cable performance is observed after long-term use, and in particular, when the cable is used underwater or under wet conditions, the progress of deterioration is accelerated, and the insulation deteriorates. Deterioration marks that extend in the direction of the electric field centering on minute voids and foreign matter (bow tree), and deterioration marks that extend in the direction of the electric field in a crown shape starting from protrusions and gaps at the interface between the insulating layer and the semiconducting layer (water tree) The disadvantage is that this occurs. The above-mentioned water tree causes a decline in the overall insulation performance of the cable, and ultimately becomes a cause of dielectric breakdown of the cable, but the cause of its occurrence is still not clear. However, since this water tree is a phenomenon that is observed only when water exists within the cable insulation layer, the inventors of the present invention have thoroughly investigated the characteristics of the water tree and found that the existing water is pure water. In this case, the occurrence and extension of water trees is slight, but if the water is contaminated, especially if it contains metal ions, the occurrence and extension of water trees is greatly accelerated, and the degree of deterioration of the cable becomes remarkable. I discovered that. Normally, the water that CV cables come into contact with during actual use, that is, the water that may enter the insulator, is groundwater, tap water, rainwater, sewage, seawater, etc., and these contain various metal ions, which can cause contamination. We found that the interaction between water and local high electric fields is a major factor in the development and spread of water trees. In addition, in such cases, 0.005 to 5
parts, preferably from 0.05 to 1 part of 4-hydroxyimidazole, 4-hydroxythiazole, and
The present inventors have discovered that by adding -hydroxyoxazole or a mixture thereof, the occurrence of water trees in a polyolefin insulator when it comes into contact with contaminated water can be significantly improved, and the present invention has been completed. In other words, the feature of the present invention is that the compound added to the insulator prevents metal ions contained in contaminated water that are harmful to water tree deterioration from entering the insulator. Its purpose is to trap and stabilize it as an organometallic complex, thereby eliminating the cause of water tree deterioration in polyolefin insulators. Polyolefins used in the composition of the present invention include non-crosslinked, crosslinked, or partially crosslinked high-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene ethyl acrylate copolymer, polypropylene, and ethylene-propylene copolymer. Alternatively, there are ethylene-propylene-diene copolymers or blends thereof, especially
For CV cable insulation, low-density polyethylene (for example, Mitsubishi Yuka, Yucalon EH-30, ZF
-35, Nippon Unicar NUC-9025, etc.) are preferred. In addition, as a crosslinking method when using the above-mentioned polyolefin after crosslinking or partially crosslinking, in addition to crosslinking by electron beam or radiation, a chemical crosslinking method using a crosslinking agent can be used.A typical example of the chemical crosslinking method is organic peroxide. Examples include crosslinking. Examples of the peroxide in this case include dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di(tert-
butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,1,3-bis(tert-butyloxy)isopropylbenzene, tert-butylperoxyisopropyl carbonate, etc. Organic peroxides can be suitably used. The amount of these organic peroxides used is 0.05 to 10 parts, preferably 0.1 parts per 100 parts of polyolefin.
~5 parts. 4-hydroxyimidazole, 4-hydroxythiazole and 4-hydroxyoxazole used in the present invention have the following general formula: (In the formula, X is N, O, or S, and R is H, an alkyl group or an aryl group having 10 or less carbon atoms), and particularly preferred specific examples are illustrated below.

【formula】

【formula】

【formula】

【formula】

【formula】

【formula】

【formula】

[Formula] The amounts used of these 4-hydroxyimidazole, 4-hydroxythiazole, and 4-hydroxyoxazole are as described above, but if the amount used is less than the above range, the effect of improving water resistance will be poor, or if the amount used is too much. In such cases, it may cause discoloration and bleeding, which are both undesirable. In addition to the above-mentioned additives, the present invention also uses various additives commonly used in polyolefins, such as crosslinking aids (triallyl isocyanurate,
There is no harm in adding ordinary amounts of anti-aging agents, ultraviolet absorbers, copper damage inhibitors, etc. (trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, etc.). The electrical insulating composition of the present invention can be easily subjected to a series of necessary processing operations such as mixing, extrusion, crosslinking, etc. by ordinary processing methods in the rubber and plastic industries, and can be used as an electrical insulating composition for electric wires and cables. When used as a coating layer, water-tree deterioration can be effectively prevented and improved, and therefore it can be particularly suitably used for power cables that are likely to suffer from water-tree deterioration.
Furthermore, the composition of the present invention can be used not only for extrusion coating, but also for forming an insulating layer in any shape by injection molding, or by wrapping and molding after being processed into a tape. Needless to say, it can also be used for parts or accessories. Examples 1 to 10, Comparative Example 1 Low density polyethylene (manufactured by Mitsubishi Yuka Co., Ltd., Yucalon
ZF-30) 100 parts to 2 parts of dikyumyl peroxide,
and 0.1 part of 325 mesh copper powder as a bowtite nucleating agent, and each compound of the present invention shown in Table 1 were kneaded with a roll at 115°C, and then at 170°C.
Press molding crosslinking was performed for 45 minutes to obtain a sheet-like sample with a thickness of 3 mm. A semiconductive paint was applied to the front and back of this sheet in a circular area with a diameter of 25 mm to form electrodes. Next, install this sheet horizontally, attach a PE pipe with a diameter of 60 mm to the top of the sheet, and insert it inside the pipe.
Filled with 22 mmol 1 copper sulfate solution. Then, after applying AC 1200Hz and 10KV to the electrode for 240 hours, the electrode-coated part of the sample sheet was cut into slices with a thickness of 200 μm, and then boiled in tap water for 2 hours.
The length of the bow tie tree generated from the copper powder in the sample was observed using a microscope. Three slices of each sample were observed, and the maximum length and minimum length of the bow-tied trees generated therein and the arithmetic mean value thereof were each expressed as the bow-tied tree length. The results obtained are shown in Table 1.

【table】

Claims (1)

[Claims] 1. Electrically insulating polymer and the following general formula (In the formula, X is N, O, or S, R is H, and the number of carbon atoms is
4-hydroxyimidazole, 4-hydroxythiazole, and 4-hydroxyoxazole represented by 10 or less alkyl or aryl groups, and mixtures thereof. 2. The composition of claim 1, wherein the electrically insulating polymer is a non-crosslinked, crosslinked, or partially crosslinked polyolefin. 3. The electrically insulating composition according to claim 1, wherein the electrically insulating polymer is crosslinked low density polyethylene.