JPH1081836A - Carbon black for semiconductive layer and resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin composition which gives a semiconductive layer having a necessary electric conductivity and good peeling strength as well as being satisfactory in mechanical properties, heat resistance, processability, etc., by adding a carbon black having specified properties to an ethylene copolymer resin. SOLUTION: This composition is obtained by adding 15-80 pts.wt. carbon black obtained by oxidizing common carbon black and having a specific surface area of 40m<2> /g or above, a DBP absorption of 120ml/100g or above and a pH of 4.5 or below to 100 pts.wt. resin based on an ethylene copolymer. The ethylene copolymer resin is desirably an ethylene/vinyl acetate copolymer having a content of comonomer units except ethylene units of 20wt.% or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon black used for a semiconductive layer of a power cable and a resin composition for the semiconductive layer.

[0002]

2. Description of the Related Art Insulated wires for cross-linked polyethylene insulated power cables are provided with an insulating layer for the purpose of alleviating electric field concentration and preventing partial discharge at the interface between the insulating layer and the conductor or between the insulating layer and the metal shielding layer. A semiconductive layer is provided inside and outside. This semiconductive layer is usually formed of a semiconductive resin composition obtained by mixing polyethylene or an ethylene-based copolymer as a base resin, carbon black as a conductivity-imparting material, and additives such as an antioxidant and a crosslinking agent. Is done. The semiconductive resin composition generally has a volume resistivity of about 1
It has a characteristic of having a 0 ⁵ Ω · cm or less conductive.

[0003] Regarding power cables, it is required that the outer semiconductive layer of a medium / high voltage cable of about 6 to 33 kV class can be relatively easily peeled off from the insulator with pliers or a peeling tool at the time of laying / constructing the cable. . As a method for this, means such as using a resin having low compatibility with the insulator as the base resin, using an additive that enhances the peeling effect, increasing the amount of carbon black added, and setting a low degree of cross-linking are available. It is possible. However, in any case, there were problems that mechanical properties and heat resistance were reduced, workability was deteriorated, and the composition was complicated.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, that is, it has the necessary conductivity while satisfying mechanical properties, heat resistance, workability, and the like. An object of the present invention is to provide a resin composition for a semiconductive layer having good releasability and a carbon black for a semiconductive layer which enables the resin composition.

[0005]

In order to solve the above-mentioned problems, the carbon black for a semiconductive layer of the present invention has a specific surface area of at least 40 m ² / g and a DBP oil absorption of 120 ml. / 100 g or more, and the pH is 4.
The carbon black for a semiconductive layer is 5 or less. Further, in order to solve the above-mentioned problem, the resin composition for a semiconductive layer of the present invention has a specific surface area of 40.
The ethylene copolymer contains carbon black having a m ² / g or more, a DBP oil absorption of 120 ml / 100 g or more, and a pH of 4.5 or less.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the specific surface area of carbon black for a semiconductive layer must be at least 40 m ² / g and the DBP oil absorption must be at least 120 ml / 100 g. If these values do not satisfy the conditions, it is not possible to impart sufficient conductivity to function as a semiconductive layer. The carbon black according to the present invention has a pH
Must be 4.5 or less. If the pH is higher than 4.5, the effect of the present invention, that is, good peelability cannot be obtained. Such carbon black for a semiconductive layer can be obtained by oxidizing ordinary carbon black (hereinafter referred to as “raw carbon black”). As the oxidation treatment, wet oxidation may be performed using an oxidizing agent such as hydrogen peroxide, permanganic acid, chlorite, sodium hypochlorite, bromine, or nitric acid, or air or specially adjusted. The gas phase oxidation treatment may be performed using a gas containing oxygen, a gas containing ozone, or the like.

The carbon black used as a raw material in the above oxidation treatment usually has a specific surface area of 1500 m ² / g.
Although it is known to a degree, it is desirably 400 m ² / g or less in terms of good dispersibility and easy kneading with a resin. Similarly, DBP oil absorption is 500ml
It is known that the weight is about 100 g / 100 g, but from the viewpoint of kneading with the resin, the weight is preferably 250 ml / 100 g or less.

[0008] The oxidation treatment needs to be performed under conditions adjusted so that the pH of the carbon black is 4.5 or less. The concentration, temperature, time and the like are appropriately adjusted to satisfy this condition. In addition, carboxyl groups, carbonyl groups, surface functional groups such as hydroxyl groups are introduced into the carbon black surface by the oxidation treatment, and these surface functional groups are
By appropriately selecting the oxidation treatment method (wet oxidation, gas phase oxidation) and its conditions (temperature, concentration, etc.), the abundance ratio can be adjusted to make the carbon black optimal for a semiconductive layer. is there.

[0009] A resin composition for a semiconductive layer of a power cable is prepared using the carbon black for a semiconductive layer obtained by performing the oxidation treatment as described above. Among the components constituting the resin composition for a semiconductive layer, an ethylene copolymer is preferable as the base resin in terms of good electrical properties, mechanical properties, and acceptability of additives. Here, examples of the ethylene copolymer include an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, and an ethylene-methyl acrylate copolymer. In addition, these ethylene copolymers can be used as a base resin by mixing two or more kinds.

In these ethylene copolymers, the content of comonomer units excluding ethylene units is 20%.
It is necessary that the content be at least% by weight. If it is less than 20% by weight, sufficient releasability cannot be obtained. Among these ethylene copolymers, it is desirable to use an ethylene-vinyl acetate copolymer in that it is relatively inexpensive, has low compatibility with polyethylene as an insulator, and easily imparts releasability. Add the oxidized carbon black to the base resin as described above and mix it to make a resin for the semiconductive layer. This work is performed using a Banbury mixer, kneader,
It can be performed using a screw kneading extruder or the like. In addition, it is also possible to improve the function as a semiconductive layer by adding an auxiliary agent such as a cross-linking agent or an antioxidant, in addition to the oxidized carbon black.

The amount of addition of the oxidized carbon black for the semiconductive layer is 100 base resin.
In terms of parts by weight, it must be more than 15 parts by weight and less than 80 parts by weight. When the amount is less than 15 parts by weight, a sufficient conductivity-imparting effect cannot be obtained. On the other hand, when the amount is more than 80 parts by weight, mechanical properties such as tensile elongation and workability deteriorate. In consideration of conductivity, mechanical properties, workability, and the like, a preferable range is 30 parts by weight or more and 70 parts by weight or less.

The thus prepared oxidized carbon black-containing resin composition for a semiconductive layer is prepared in the same manner as an ordinary resin composition for a semiconductive layer, that is, by using an extruder or the like. It can be formed on the insulated wire core of the power cable.

[0013]

【Example】

[Examples 1 to 9, Comparative Examples 1 to 12] Hereinafter, examples of the present invention will be described in comparison with comparative examples. The specific surface area is 40m ² /
g of carbon black having a DBP oil absorption of 120 ml / 100 g or more (hereinafter also referred to as "CB").
At room temperature with air containing 10 g / m ² of ozone
Carbon black (hereinafter also referred to as “CBox”) CB that has been subjected to an oxidation treatment (ozone oxidation) by performing a treatment for 0 to 70 minutes
ox1-CBox6 were obtained. Moreover, the specific surface area is 40 m ² / g.
Carbon black or DBP oil absorption of less than 12
Using carbon black of less than 0 ml / 100 g as a raw material,
Similarly, ozone oxidation was performed to obtain CBox7 and CBox8. The specific surface area is 58 m ² / g, and the DBP oil absorption amount is 170
Heat treatment (air oxidation) was performed at 250 ° C. in air using carbon black of 100 ml / 100 g to obtain CBox9.
I got The following study was performed on these and five types of carbon blacks CB1 to CB5 not subjected to oxidation treatment. Table 1 shows the specific surface area, DBP oil absorption and pH.

The specific surface area is measured according to ASTM D3037, and the DBP oil absorption and pH are measured according to JIS.
・ Measured according to K6221. Table 2 shows the resins, crosslinking agents, and antioxidants used in this study. Table 2
The thing indicated by "EVA" is an ethylene-vinyl acetate copolymer. The content of the vinyl acetate unit which is a comonomer unit excluding the ethylene unit of this copolymer is also shown. These CB1 to CB5 and CBox1
To CBox9, base resins 1-4, a crosslinking agent and an antioxidant were mixed at a mixing ratio (parts by weight) shown in Table 3 using a kneader to obtain a resin composition.

Next, these resin compositions (Examples 1 to 3)
9 and Comparative Examples 1 to 12) were laminated and formed on a crosslinked polyethylene sheet, and then the peel strength between the resin composition sheet and the crosslinked polyethylene sheet was measured. The peeling strength was determined by crosslinking and bonding a molded sheet made of a semiconductive resin composition having a thickness of 1 mm and a crosslinked polyethylene sheet having a thickness of 2 mm by a press molding machine at a pressure of 150 kg / cm ² and a temperature of 170 ° C. for 30 minutes. With respect to the portion made, a sample width of 12.7 mm and a tensile speed of 500 mm /
It was measured in min. The measured value at this time is converted into an AEIC (Association of Edison Illuminating Com
panies) ・ Value measured on an actual cable in accordance with C55-82 (1 in the cable length direction of the outer semiconductive layer)
The AEI was calculated using a calibration curve of 2.7 mm width incision, and peeling at a pulling speed of 500 mm / min while maintaining an angle of 90 °.
When the C / C55-82 conversion value was 4 kgf / 12.7 mm or less, it was evaluated as “○” as having good releasability, and as “x” when it was inferior to 4 kgf / 12.7 mm and more than 4 kgf / 12.7 mm.

Further, for the conductivity, a sheet sample was prepared from the above semiconductive resin composition, and their volume resistivity was measured by AS.
The measurement was carried out in accordance with TM.D991. When the conductivity was 10 ⁵ Ω · cm or less, it was evaluated as “○” having good conductivity, and when the conductivity was less than 10 ⁵ Ω · cm, it was evaluated as “X”.

Further, the mechanical properties are JIS C300
The tensile elongation (%) of the above sheet sample is measured according to the method described in 5, and the initial value of elongation (elongation measured immediately after the sample is manufactured) is 200% or more in consideration of deterioration in characteristics due to aging. Was evaluated as "O", and those less than that were evaluated as "X". (Normally, if the elongation of the wire material is 50% or more, it is considered that there will be no trouble such as cracking due to handling. However, considering the aging, it is considered that the elongation at the beginning of production is preferably 200% or more. Table 3 shows the results of these studies.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

From Table 3, it can be seen that the resin compositions for semiconductive layers of Examples 1 to 9 using carbon black according to the present invention are excellent ones satisfying all of releasability, conductivity and mechanical properties. . Furthermore, in Examples 1 to 9, no peeling failure such as carbon black remaining on the crosslinked polyethylene surface after peeling did not occur. Here, these examples 1
Regarding the semiconductive layer resin composition according to any one of Examples 9 to 9, the heat resistance and the workability when producing a cable were also investigated.
These results indicate that the material has sufficient performance to be used as a semiconductive layer of a power cable. In addition, Examples 5-8 of the resin composition for semiconductive layers of Examples 1-9.
Has a good balance between the releasability and other properties, and is optimal as a resin composition for a semiconductive layer.

Examples 10 to 12 The specific surface area was 58 m ^2.
/ G, DBP oil absorption 170ml / 100g, pH5.
Carbon black (hereinafter referred to as "CBa") is oxidized in the presence of air and ozone gas to have a specific surface area of 58 m ² / g and a DBP oil absorption of 170 ml / 100.
g and pH of 4.8, 4.3 and 3.0, respectively (hereinafter referred to as “CBb”, “CBc” and “C
Bd ").

Here, studies were actually conducted using these carbon blacks as a material for imparting conductivity to a resin composition. 55 parts by weight of each of the above four carbon blacks and 100 parts by weight of an ethylene-vinyl acetate copolymer (vinyl acetate unit amount = 30% by weight) used as a resin for a semiconductive layer of a crosslinked polyethylene cable, 55 parts by weight of an antioxidant,
By adding and mixing a crosslinking agent, the four types of resin compositions α, β, and γ
And δ were obtained. Next, using the sheets produced using these resin compositions for semiconductive layers, their volume resistivity was examined in accordance with ASTM D991. FIG. 2 shows the effect of the pH of carbon black on the volume resistivity. From FIG. 2, it can be seen that any of the carbon blacks was a good conductivity-imparting material in terms of volume resistivity characteristics.

Further, the relationship between the pH of carbon black and the peel strength was examined. That is, the crosslinked polyethylene (X
LPE) laminated and formed on the sheet composed of the above four types of resin compositions α, β, γ and δ,
The peel strength was measured. The results are shown in FIG. FIG. 3 shows that the crosslinked sheet made of the resin composition using carbon black having a low pH after being oxidized has low peel strength and excellent peelability.

Next, the degree of crosslinking (gel fraction) when these resin compositions α, β, γ and δ were crosslinked under the same conditions was measured. FIG. 4 shows the results. FIG. 4 shows that the degree of crosslinking decreases as the resin containing carbon black that has been oxidized and has a lower pH is reduced. This is considered to be caused by the acidic functional group of the carbon black inhibiting the crosslinking reaction. As described above, the effect (excellent peel strength) of the present invention is exhibited by inhibiting the crosslinking reaction.

Here, separately, these resin compositions α,
Using β, γ, and δ as the resin for the semiconductive layer, a power cable having a crosslinked polyethylene as an insulating layer was formed. These cross sections are modeled in FIG. These semiconductive layer resin compositions are applied to an outer semiconductive layer (reference numeral 4 in the figure), and an inner semiconductive layer and an insulating layer made of cross-linked polyethylene (reference numeral 3).
In addition, three layers of the outer conductive layer were co-extruded and heated in a nitrogen atmosphere to be chemically crosslinked to obtain three types of dry crosslinked power cables (6 kV-CV 60 mm ² ). In these power cables, the thickness (diameter) of the conductor portion, the thickness of the inner semiconductive layer, the thickness of the insulating layer, and the thickness of the outer semiconductive layer are respectively:
9.3 mm, 1 mm, 3 mm, and 0.7 mm.

The semiconductive layer of these power cables is AEIC
-When the peelability was examined in accordance with C55-82, the peel strength of the semiconductive layer of the power cable using CBa and CBb was more than 4 kgf / 12.7 mm, whereas CBc and CBd were used. It was found that both the semiconductive layers of the power cables had good peeling properties with a peel strength of 4 kgf / 12.7 mm or less. In addition, when a sensory evaluation of actually peeling the semiconductive layer of these power cables by hand was performed, the laminated sheet using the resin compositions γ and δ showed a half of the power cable using the resin compositions α and γ. It was confirmed that remarkably good releasability was obtained in both cases as compared with the releasability of the conductive layer.

[0028]

By using the carbon black according to the present invention, the semiconductive layer of the power cable can be peeled off while maintaining the same level of conductivity, mechanical properties, heat resistance and workability as the conventional power cable. As a result, it is possible to significantly reduce the time and effort required for connection of power cables and terminal processing, which are field operations.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a cross section of a power cable manufactured in an example.

FIG. 2 is a graph showing a relationship between a change in pH due to an oxidation treatment of carbon black and a volume resistivity in a molded product of a resin composition containing the same.

FIG. 3 is a graph showing a change in pH due to oxidation treatment of carbon black and a peel strength between a molded article and a crosslinked polyethylene by a resin composition containing the same.

FIG. 4 is a graph showing a relationship between a change in pH due to oxidation treatment of carbon black and a degree of cross-linking in a molded article of a resin composition containing the same.

[Explanation of symbols]

 Reference Signs List 1 conductor 2 inner semiconductive layer 3 insulating layer 4 outer semiconductive layer

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[Procedure amendment]

[Submission date] September 1, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

The semiconductive layer of these power cables is AEIC
-When the peeling property was examined based on C55-82, the peeling strength of the semiconductive layer of the power cable using CBa and CBb was more than 4 kgf / 12.7 mm, whereas CBc and CBd were used. It was found that both the semiconductive layers of the power cables had good peeling properties with a peel strength of 4 kgf / 12.7 mm or less. Incidentally, was subjected to sensory evaluation for actual manual peeling the semiconductive layer of a power cable, electric using the resin composition γ and δ
In the semiconductive layer of the power cable, it was confirmed that both of the semiconductive layers of the power cable using the resin compositions α and β exhibited remarkably good peelability as compared with the peelability of the semiconductive layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuneo Tani Inside 2771 Ooka Yazaki Electric Wire Co., Ltd., Numazu City, Shizuoka Prefecture (72) Inventor Kazuto Kataoka 2-3-2 Kitaaoyama, Minato-ku, Tokyo Tokai Carbon Co., Ltd. (72) Inventor Toshiaki Matsushima 1-3-2 Kitaaoyama, Minato-ku, Tokyo Tokai Carbon Co., Ltd.

Claims (6)

[Claims] 1. A specific surface area of 40 m ² / g or more, a DBP oil absorption of 120 ml / 100 g or more, and a pH of 4.
Carbon black for a semiconductive layer, wherein the carbon black is 5 or less. 2. The specific surface area is at least 40 m ² / g, the DBP oil absorption is at least 120 ml / 100 g, and the pH is 4.
A resin composition for a semiconductive layer containing carbon black of 5 or less. 3. The resin composition for a semiconductive layer according to claim 2, wherein the base resin is an ethylene copolymer.
The resin composition for a semiconductive layer according to the above. 4. The ethylene-based copolymer has a comonomer unit content of 20 excluding ethylene units.
The resin composition for a semiconductive layer according to claim 3, wherein the content is not less than% by weight. 5. The resin composition for a semiconductive layer according to claim 3, wherein the ethylene copolymer is an ethylene-vinyl acetate copolymer. 6. The resin composition for a semiconductive layer according to claim 4, wherein the ethylene copolymer is an ethylene-vinyl acetate copolymer.