JPH0244081B2 - - 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 the progress of deterioration is particularly accelerated when the cable is used underwater or under wet conditions.
Deterioration marks (bow trees) that extend in the direction of the electric field centering on minute voids and foreign matter in the insulator, 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 ( The disadvantage is that water trees) occur. The above-mentioned water tree causes a decline in the overall insulation performance of the cable, and is a contributing cause of eventually causing dielectric breakdown of the cable, but the cause of this occurrence is still not clear. However, since this water tree is a phenomenon that is observed only when water exists in the cable insulation layer, the inventors of the present invention have thoroughly studied the characteristics of the above water tree and found the following general formula: (In the formula, R is a phenyl group, an alkyl group or an alkenyl group having up to 20 carbon atoms, R' is a phenyl group, an alkyl group, an alkenyl group, or an alkoxy group having up to 20 carbon atoms, n is 1 or 0, and m is 2
By adding to the insulating layer a siloxane compound containing a mercaptoalkyl group and/or a hydroxyalkyl group (representing an integer of ~30, where X is S or O), the generation and extension of the water tree can be greatly suppressed. The present invention was completed based on the discovery that the deterioration tendency of CV cables due to water trees could be improved by this.
In addition, in such cases, polyolefin may be added to the insulator.
It has been found that it is most appropriate to add the mercaptoalkyl group- and/or hydroxyalkyl group-containing siloxane compound in an amount of 0.05 to 10 parts, preferably 0.1 to 5 parts, per 100 parts (by weight, hereinafter the same) of the mercaptoalkyl group- and/or hydroxyalkyl group-containing siloxane compound. That is, the present invention is characterized in that the siloxane compound added to the insulator eliminates the cause of water tree deterioration of the polyolefin insulator.The polyolefin used in the composition of the present invention may be non-crosslinked, crosslinked, or Partially crosslinked high density polyethylene, high pressure process and low pressure process, low density polyethylene, ethylene-vinyl acetate copolymer, ethylene ethyl acrylate copolymer, polypropylene, ethylene-propylene copolymer or ethylene-propylene-diene copolymer Or blends of these are available, especially low-density polyethylene (for example, Mitsubishi Yuka, Yucalon EH-30, ZF-35, Nippon Unicar) for CV cable insulation.
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 peroxides in this case include dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di(tert-butylperoxy)
Hexane, 2,5-dimethyl-2,5-di(tert
Organic peroxides such as -butylperoxy)hexane-3,1,3-bis(tert-butyloxy)isopropylbenzene and tert-butylperoxyisopropyl carbonate can be suitably used. The amount of these organic peroxides used is in the range of 0.05 to 10 parts, preferably 0.1 to 5 parts, per 100 parts of polyolefin. Among the siloxane compounds used in the present invention, preferred ones are those in the general formula where n is 1 or 0, X is an S atom, m is an integer of 5 to 20, and R and R' are phenyl groups, vinyl or an alkyl group or an alkoxy group having 8 or less carbon atoms. Particularly preferred siloxane compounds of the present invention are shown below. These siloxane compounds do not need to be particularly pure compounds, and may be a mixture of two or more types as long as they are within the range shown by the above general formula, and m (indicating the degree of polymerization) may also be a single one. do not need. The above compounds are examples thereof. The amount of these siloxane compounds to be used is as described above, but if the amount is less than the above range, the effect of improving water resistance will be poor, and if it is too much, 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,
A predetermined amount of the siloxane compound of the present invention shown in Table 1 was kneaded with a roll at 115°C, and then at 170°C.
Press molding and crosslinking were 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, this sheet was placed horizontally, a PE pipe with a diameter of 60 mm was attached to the top surface of the sheet, and the pipe was filled with deionized water. Then, after applying AC1200Hz and 10KV to the electrode for 240 hours, the electrode-coated part of the sample sheet was
After cutting into slices of 200 μm, rinse with tap water.
The sample was boiled for an hour and water trees generated in the sample were observed using a microscope. Three slices of each sample were observed, and the maximum and minimum lengths of the water trees generated therein and their arithmetic mean values were each expressed as the water tree length. The results obtained are shown in Table 1.

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【table】

Claims (1)

[Claims] 1. Electrically insulating polymer and the following general formula (In the formula, R is a phenyl group, an alkyl group or an alkenyl group having up to 20 carbon atoms, R' is a phenyl group, an alkyl group, an alkenyl group, or an alkoxy group having up to 20 carbon atoms, n is 1 or 0, and m is 2
a mercaptoalkyl group-containing and/or hydroxyalkyl group-containing siloxane compound represented by the following integer: ~30, X is S or O. 2. The composition of claim 1, wherein the electrically insulating polymer is a non-crosslinked, crosslinked, or partially crosslinked polyolefin. 3 The electrically insulating polymer is non-crosslinked, crosslinked or partially crosslinked high-density polyethylene, high-pressure low-density polyethylene, low-pressure low-density polyethylene, ethylene-hyphen vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene - The electrically insulating composition of claim 1, which is a diene terpolymer polypropylene and a mixture thereof. 4. The electrically insulating composition according to claim 1, wherein the electrically insulating polymer is crosslinked low density polyethylene.