JPH038046B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is particularly applicable to power cables.
This relates to power cables used as OF cables and POF cables of 500KV or higher. Recently, as insulators for such power cables, a laminate tape made by laminating polyolefin and kraft paper together, and a mixed paper made by mixing polyolefin fibers into kraft pulp have been developed, and have achieved some success. The present invention relates to a power cable using the former laminate structure tape as an oil-immersed insulating layer, but the following problems remain. That is, tapes made of kraft paper laminated with plastics such as silane-crosslinked polyethylene (PE), polypropylene (PP), poly4-methylpentene-1 (TP-X), tetrafluoroethylene/hexafluoropropylene (FEP), etc. as polyolefins. If an oil-immersed power cable is used as the insulating tape, or if PE is used as the plastic, the cable temperature may rise to around 120°C if an overload is transmitted to the cable due to an accident in a part of the power cable network. As expected, at such temperatures PE
There is a danger that most of it will melt and dissolve into the insulating oil.
This is undesirable because the oil flow resistance of the insulating layer increases. For this reason, the plastic used for laminated tape must have a melting temperature of at least 150°C or higher. FEP is preferable because it has a melting point of about 300°C and is a material that does not dissolve in insulating oil, but it is extremely expensive, has little versatility, and the cable price makes it difficult to put it into practical use economically. Therefore, the melting point is 150℃
Among the above-mentioned plastics, polyolefins such as PP.TP-X can be mentioned as economically viable materials, but they have the following problems. Since polyolefin is non-polar, the adhesive force on the bonded surface of polyolefin and kraft paper is poor, and there is no contribution from chemical affinity, but it is due to mechanical entanglement and frictional force, so impregnation with insulating oil is necessary. Furthermore, when exposed to high temperatures, the adhesive strength between kraft paper and polyolefin decreases significantly due to the difference in thermal expansion between the two, and in some cases, it may be difficult to bond them together. There is a risk of peeling on the surface, which poses a problem in terms of long-term reliability of the power cable. In addition, polyolefins are alkylbenzene oils (JIS C 2320 Type 2 Type 1 and 3) that are commonly used as insulating oils.
It has an affinity with other oils (such as No. 1 oil) due to the similarity of their chemical structures, and it is easy to absorb oil and swell, and the degree of swelling increases as the temperature increases. Therefore, in a power cable with an oil-immersed insulating layer made of a laminate of polyolefin and kraft paper, the compressive force between the tapes increases due to the swelling of the tapes.
Oil flow resistance also increases, which is undesirable. In view of the above-mentioned current situation, the present invention provides a power cable that does not cause the above-mentioned problems by using a material that has adhesive strength based on chemical affinity and has little oil absorption and swelling as a laminate used as an insulating tape. It was done for the purpose of That is, in the present invention, as an insulating tape constituting an oil-immersed insulating layer of a power cable, (1) a polyolefin sheet with a crystal melting point of 150°C or higher is coated with the general formula RR'SiY ₂ (where R is an olefinic unsaturated monovalent a hydrocarbon group or a hydrocarbonoxy group, or a hydrogen group and -NH-,

[Formula] SH group,

[Formula] A hydrocarbon containing one or more groups, Y is a hydrolyzable organic group, and R' is R or a group Y. cellulose-based insulating paper is laminated on one side of the silane-grafted polyolefin sheet, and (2) cellulose-based insulating paper is laminated on the silane-grafted polyolefin sheet by thermocompression bonding at a temperature equal to or higher than the Vikatsu softening point of the polyolefin according to ASTM D-1525. , (3) A power cable characterized by using a laminate tape that is cooled and held at a temperature in the range of 70 to 95% of the melting point of polyolefin expressed in absolute temperature (〓) for at least 5 seconds or more after thermocompression bonding. It is. More specifically, in the present invention, polypropylene (PP) and poly4-methylpentene-1 (TP-X) are materials that are economically acceptable as plastics with a crystalline melting point of 150°C or higher as insulating tape materials.
This polyolefin is used to laminate cellulose-based insulating paper, such as kraft paper, on one or both sides, but since this polyolefin is grafted by silane crosslinking, it is not compatible with cellulose-based insulating paper. are integrated by chemical affinity, and it is preferable to use an organic group as R in the general formula RR'SiY ₂ of silane that does not contain NH ₂ − or -SH groups because this will not deteriorate the dielectric loss tangent of the insulator. preferable. That is, when R is a vinyl group or a hydrocarbon group containing a vinyl group, this is preferable since the dielectric loss tangent does not decrease. Further, as Y, hydrolyzable organic groups such as
Groups such as CH ₃ O−, C ₂ H ₅ −, −OCH ₂ CH ₂ −OCH ₃ groups, etc.
It is preferable to use a material such as R-Si(OH) ₃ whose decomposition products, such as CH ₃ OH and O ₂ H ₅ OH, are easily vaporized during drying of the cable and do not adversely affect the cable. For example, Y is halogen, -
There are also silanes such as CO ₂ CH ₃ , but these are not preferable because they tend to be adsorbed and remain on kraft paper and deteriorate the dielectric loss tangent and insulation resistance of the cable. Silane grafting is carried out using an organic peroxide such as dicumyl peroxide under heating. For example, when a polyolefin tape is extruded in an extruder, grafting is carried out in the extruder using a silane that is blended. Next, even if silane-grafted polyolefin and cellulose-based insulating paper, such as graft paper, are bonded together under normal conditions, a strong bond does not form.The reason for this is that the proximity between the hydrolyzed silane and the kraft paper is insufficient, and This seems to be because it does not result in strong integration through bonding. In the present invention, polyolefin and cellulose insulating paper are strongly integrated by heat-pressing treatment at a temperature higher than the Vikato softening point (ASTM D-1525) of polyolefin. The Vikato softening point of the polyolefin used in the present invention is 135 to 155°C for PP;
TPX is approximately 180℃, and since the plastic deformation of the polyolefin is involved in adhesion, both temperature and pressure are conditions. When this temperature is low, a large pressure is required, and a small pressure is not enough. To improve adhesion, the temperature must be increased. By the way, as mentioned above, bonding of polyolefin and kraft paper is generally carried out by extrusion lamination, but since the extrusion temperature of polyolefin is considerably higher than the Vikato softening point of the polyolefin, it is difficult to use bonding. It is easy to perform heat and pressure treatment at the same time. In this case, the temperature of the bonding rolls may be set to about the Vikato softening point of the polyolefin. Further, bonding and heat-pressure treatment may be performed in separate steps. Next, heat-pressure treatment is carried out at a temperature higher than the Vikato softening point of the polyolefin, and since at this temperature a considerable portion of the polyolefin is melted, if it is rapidly cooled, the degree of crystallization of the polyolefin will be reduced. As a result, the degree of oil absorption and swelling of the laminate insulator becomes large. However, in the present invention, the cooling after the heat-pressure treatment is controlled, and the melting point of the polyolefin expressed in absolute temperature (〓) is lowered.
The temperature is maintained and cooled for at least 5 seconds in the range of 70 to 95%. For example, this temperature is controlled to be in the temperature range of 30 to 138℃ for PP and 86 to 214℃ for TP-X for at least 5 seconds to extremely increase crystallization and significantly improve the oil absorption and swelling phenomenon. This is what I did. As an example of the present invention, the present inventor has already proposed a method of blending hydrocarbon oil with polyolefin, but this method can naturally be applied to the polyolefin of the present invention, and the blending ratio is 100 parts by weight of polyolefin. , the initial distillation temperature
It can be used as a mixture containing 5 to 30 parts by weight of hydrocarbon oil having a temperature of 300°C or higher. Examples of the laminate tape used in the power cable of the present invention will be described below. Example 1 100 parts by weight of polypropylene homopolymer, CH ₂
= CHSi (OCH ₂ CH ₂ OCH ₃ ) ₃ A mixture of 2 parts by weight and 0.1 part by weight of benzoyl peroxide (BPO) was added to 220
Grafted PP pellets were obtained by extrusion at 280°C, and the grafted PP pellets were extruded into a film at 280°C, and 40 μm thick kraft paper was laminated on both sides to form a 150 μm thick laminated insulator.
For lamination, the roll temperature was 150°C, the cooling roll temperature was 80°C, and a 50°C air cooling tank was provided at the rear of the roll to form a laminated insulator. Comparative example 1 150μm using the same PP and kraft paper as Example 1
I made a thick laminate. In this case, the bonding roll was water-cooled, its surface temperature was 100° C. or less, and slow cooling was not performed. Example 2 Heavy alkylbenzene (JIS C
-2320 Type 2 No. 2 oil) 20 parts by weight, CH ₂ = CH-Si
(OCH ₂ CH ₂ OCH ₃ ) ₃ PP with silane grafted by extruding a blended powder of 3 parts by weight and 0.2 parts by weight of BPO at 220℃
(containing heavy alkylbenzene) and laminated with kraft paper in the same manner as in Example 1.
It was made of a laminate insulator with a thickness of 150 μm. The cooling conditions were also completely the same as in Example 1. The above three tapes were immersed in alkylbenzene oil (JIS C-2320 Type 2 No. 1 oil) for 10 days at 120°C, and the state of the tape was observed, and the adhesive strength of the PP-Kraft paper was measured. Adhesion strength was determined by peeling off the kraft paper from one end of a 15 mm wide tape and measuring the peeling conditions at 180°C. The results showed that in both Examples 1 and 2, there were no abnormalities such as peeling at the ends of the specimens, and the gap between the PP and kraft paper could not be peeled off, so the adhesive strength could not be measured. On the other hand, in the comparative example, one end of the sample partially peeled off due to oil immersion, and the adhesive strength of the five samples was 23 g/15 mm width on average. In addition, each sample was immersed in alkylbenzene oil (Type 2, No. 1) at 100℃ for 3 days, and the thickness swelling ratio (thickness after immersion - thickness before immersion)/( The thickness before immersion) x 100] was determined. The content of Example 1 of the present invention was 6.4%, the content of Example 2 was 3.2%, and the content of Comparative Example 1 was 10.5%. Example 3 100 parts by weight of TPX powder, 0.5 parts by weight of anti-aging agent,
25 parts by weight of heavy alkylbenzene (Type 2, No. 3) oil,
CH ₂ = CHSi (−OCH ₂ CH ₂ CCH ₃ ) ₃ 3 parts by weight, BP
0.2 parts by weight of the mixture was made into grafted TPX pellets at an extrusion temperature of 260°C. Using this pellet,
It was extruded at 270°C and 40 μm thick kraft paper was laminated on both sides to form a 150 μm thick laminate. The laminating roll temperature was 80℃, and the laminate was then heat-pressure treated under the conditions of a roll surface temperature of 230℃ and a compression force of 5Kg/cm roll length.
The temperature was set at 140°C, and then it was cooled in a slow cooling tank at a temperature of 100°C. Comparative Example 2 Same as Example 3, but a laminate was made without heat-pressure treatment and slow cooling (quenching). The above Example 3 and Comparative Example 2 were immersed in alkylbenzene (Type 2, No. 1) at 150° C. for 3 days, and the degree of adhesion was observed. In Example 3, there was no abnormality such as peeling and the TP-X and kraft paper could not be separated, so the adhesive strength could not be measured, but in Comparative Example 2, the TP-X and kraft paper were completely separated. was. Example 4 Contains 18% by weight of heavy alkylbenzene
100 parts by weight of PP, 2 parts by weight of CH ₂ =CHSi(OC ₂ H ₄ OCH ₃ ) ₃ and 0.1 parts by weight of BPO were blended and grafted at 220°C.
m-thick laminate insulator, 150μm with 50% PP fraction
We made a 220μm thick laminate insulator with a PP fraction of 70%. The thermocompression bonding and cooling conditions were the same as in Example 1. Example 5 TP containing 20% by weight of heavy alkylbenzene
-X100 parts by weight, CH ₂ =CHSi
(OC ₂ H ₄ OC ₂ H ₃ ) ₃ 2 parts by weight and 0.1 parts by weight of BPO were blended to make grafted pellets at 260°C.
A 220 μm thick laminate insulator with a TPX fraction of 70% was made. Thermocompression bonding is done at 200℃, cooling is at 150℃~
It was held at 100°C for 10 seconds. However, in the above, the PP and TP-X fractions are the ratio of the thickness of the polyolefin to the total thickness of the laminate insulator. Comparative Example 3 A laminate was made using the same materials and the same thickness as in Example 4 above. However, thermocompression bonding was not performed, and the roll was rapidly cooled by water cooling. Comparative Example 4 A laminate of the same thickness was made using the same materials as in Example 5 above. However, thermocompression bonding was not performed, and the roll was rapidly cooled by water cooling. The following power cables were manufactured using the laminate insulators shown in Examples 4 and 5 and Comparative Examples 3 and 4. In other words, the power cable has a conductor of 2500 mm ² (outer diameter approx.
68 mm), a shielding layer of carbon paper and metallized paper was provided, and on top of that, a 120 μm PP laminate of the above laminate was used as an insulating layer to give a layer thickness of about 2 mm, and a 150 μm PP laminate was used to a layer thickness of about 4 mm.
mm, using 220μm TP-X laminate with a layer thickness of approx.
An insulating layer with a total length of 25 mm was provided on 19 mm, and an external shielding layer was further provided using metallized paper. After deaeration and heating drying, the product was cooled to 40°C and impregnated with alkylbenzene oil (Type 2, No. 1). After that, an aluminum sheath was applied, and an anti-corrosion layer made of vinyl chloride compound was also provided. A cable of the present invention using the laminates shown in Examples 4 and 5 and a comparative cable using the laminates shown in Comparative Examples 3 and 4 for the insulating layer of the cable were made, and their performance was tested. The result is as follows.

[Table] The tan δ (20°C) value of the example of the present invention is extremely superior to that of the comparative example;
This is due to the effect that the dielectric dispersion of X is shifted to the lower temperature side due to impregnation with insulating oil. In addition, after keeping both cables in a pressurized condition of 100℃ for 5 days, bending them back and forth twice at 20 times the outer diameter of the cables, the cables were disassembled and the state of the insulation layer was examined. I investigated and found the following. In the cable of the example of the present invention, although changes in the gap due to the movement of the tape were observed, there was no peeling or wrinkles at the end of the tape and the cable was in good overall condition, whereas the cable of the comparative example was in good condition overall. Many peelings were observed at the end of the tape, wrinkles were observed in several places due to bending, and it was confirmed that the paper layer was torn in these areas.

Claims (1)

[Claims] 1. A power cable including a conductor, an oil-impregnated paper insulating layer, a metal sheath, and an oil passage, characterized in that the following is used as an insulating tape constituting the oil-impregnated paper insulating layer: and power cables. (a) A polyolefin sheet with a crystal melting point of 150°C or higher is coated with a polyolefin sheet having the general formula RR′SiY ₂ (wherein R is an olefinically unsaturated monovalent hydrocarbon group or a hydrocarbonoxy group, a hydrogen group, and -NH-,
A silane grafted with an organic silane represented by [Formula] SH group, a hydrocarbon group containing one or more [Formula] groups, Y is a hydrolyzable organic group, and R' is R or a group Y. Cellulose-based insulating paper is laminated on at least one side of the grafted polyolefin sheet, and (b) the silane-grafted polyolefin sheet and the cellulose-based insulating paper are bonded together by thermocompression at a temperature equal to or higher than the Vikat softening point of the polyolefin according to ASTM D-1525. (c) A laminate tape that is laminated with (c) thermocompression bonded and cooled at a temperature in the range of 70 to 95% of the melting point of the polyolefin expressed in absolute temperature (〓) for at least 5 seconds or more. 2. The power cable according to claim 1, wherein a hydrocarbon insulating oil having an initial distillation temperature of 300° C. or higher is blended as the polyolefin.