JPH03247641A - Semiconductive composition - Google Patents

Abstract

PURPOSE:To obtain a semiconductive composition suitable as an inner (outer) semiconductive layer of a solid insulating cable by mixing ethylene-propylene- based copolymer rubber and ethylene-alkyl acrylate-based copolymer with carbon black. CONSTITUTION:100 pts.wt. polymer base material composed of (A) 5-70 pts.wt. ethylene-propylene-based copolymer rubber (EP rubber or EPT rubber) and (B) 95-30 pt.wt., preferably 90-40 pts.wt. ethylene-alkyl acrylate-based copolymer containing 1-35wt.%, preferably 2-25wt.% alkyl acrylate unit (preferably ethyl acrylate) having preferably <=30g/10min, especially 0.5-25g/10min is mixed with (C) 30-90 pts.wt. carbon black (preferably acetylene black) and lubricant, antioxidant, filler or crosslinking agent, etc., as necessary, to afford the aimed semiconductive composition.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a semiconducting composition suitable as an inner semiconducting layer and an outer semiconducting layer of a solid insulated cable whose insulator is crosslinked polyethylene or the like.

(Prior Art) The inner and outer semiconductive layers used in so-called C■ cables, which use cross-linked polyethylene or the like as an insulator, are generally made of a polymer base material mixed with a carbon blank. At this time, as the polymer base material, ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) is most often used because it is necessary to fill carbon black in a high concentration. Ethyl acrylate copolymer (hereinafter referred to as EEA) is used (Japanese Patent Application Laid-Open No. 63-205340).

(Problem to be Solved by the Invention) Conventionally, this type of semiconductive composition contains a component (polymer gel) with a very high molecular weight produced when EVA or EEA as a polymer base material is polymerized. Koto, and EVA
Also, when mixing EEA and carbon black, there are two reasons for the poor dispersion of carbon black, which causes the problem that small protrusions are formed at the interface between the insulating layer and the semiconductive layer when the cable is coated. Ta.

(Means for Solving the Problems) As a result of intensive studies on the above problems, the present inventors have developed an ethylene-propylene copolymer rubber with an ethylene alkyl acrylate-based copolymer as a polymer base material constituting a semiconductive layer. The present inventors have discovered that by using a specific olefin polymer blend, small protrusions do not occur at the interface between the insulating layer and the semiconducting layer, and the present invention has been completed.

That is, the present invention includes: (1) 5 to 70 parts by weight of ethylene-propylene copolymer rubber and 95 to 3 parts by weight of ethylene-alkyl acrylate copolymer;
The present invention provides a semiconductive composition comprising carbon black blended into a polymer base material containing 0 parts by weight, and is also characterized in that the carbon blank is acetylene black; (2) Another feature is that the melt flow rate of the ethylene-alkyl acrylate copolymer is 30 g/10 minutes or less.

Furthermore, the present invention will be specifically explained.

The ethylene-propylene copolymer rubber used in the present invention includes ethylene-propylene binary copolymer rubber called EP rubber, EPT rubber, and terpolymer ethylene-propylene conjugated or non-conjugated diene copolymer rubber. Examples include composite rubber.

In addition, examples of the diene component constituting the EPT rubber include 1,4-hexadiene, dicyclopentadiene, 5-
Non-conjugated dienes such as ethylidene-2-norpol-7one can be preferably used.

The ethylene-alkyl acrylate copolymer used in the present invention has an alkyl acrylate unit content of 1 to 35% by weight, preferably 2 to 25% by weight.
and ethylene-alkyl acrylate copolymer, as well as other third olefinic compounds (e.g., vinyl chloride, vinyl acetate, acrylic acid, maleic acid,
It also includes copolymers of maleic anhydride, etc.).

In addition, as the alkyl acrylate which is a copolymerization component,
Examples include methyl acrylate, ethyl, isopropyl, hexyl and the like, with ethylene-ethyl acrylate copolymer being particularly preferred.

Further, the above-mentioned ethylene-alkyl acrylate copolymer preferably has a melt flow rate (hereinafter referred to as MFR) of 30 g/10 minutes or less at 190°C and under a load of 2,160 g, particularly preferably 0. 5-25g/1
It takes about 0 minutes.

When the MFR exceeds 30 g/10 minutes, small protrusions are likely to form.

The composition ratio of the polymer base material constituting the semiconductive layer is 5 to 70 parts by weight of ethylene-propylene copolymer rubber, preferably 10 to 60 parts by weight, and 95 to 30 parts by weight of ethylene-alkyl acrylate copolymer. Parts by weight, preferably 90-40
A blend consisting mainly of parts by weight is desirable.

If the amount of ethylene-propylene copolymer rubber mixed is less than 5 parts by weight, a large amount of polymer gel will be produced from the ethylene-alkyl acrylate copolymer to be blended, forming protrusions on the semiconductive layer, and Carbon dispersibility also deteriorates.

Furthermore, if the amount of the ethylene-propylene copolymer rubber mixed exceeds 70 parts by weight, the semiconductive layer becomes highly sticky and difficult to handle.

In addition to the ethylene-propylene copolymer rubber and the ethylene alkyl acrylate copolymer, the polymer base material constituting the semiconductive layer may contain other polyolefins in small amounts that do not impair these functions. It may also contain a material such as polyethylene, ethylene vinyl acetate copolymer, etc.

In order to impart semi-S conductivity to such a polymer base material,
It is necessary to incorporate carbon black, for example conductive carbon black.

As the second carbon black, acetylene black can be particularly preferably used in order to reduce the aforementioned small protrusions.

The amount of carbon black to be blended is determined in consideration of the conductivity required of the semiconductive layer, but generally 30 to 90 parts by weight is used per 100 parts by weight of the polymer base material.

The semiconductive composition of the present invention may contain various additives such as a lubricant, an antioxidant, a filler, a crosslinking agent, and a crosslinking aid, if necessary.

In particular, as a lubricant, for example, stearic acid, zinc stearate, etc.; as an antioxidant, for example, 4,4"-
Thiobis (6-t-butyl-3 methylphenol), etc.; fillers include calcium carbonate, clay, magnesia, zinc oxide, etc.; crosslinking agents include dicumyl peroxide, 2.5-dimethyl-2, An organic peroxide crosslinking agent such as 5-di(L-butylperoxy)hexyne-3; As a crosslinking aid, triallyl isocyanurate, triallyl cyanurate, tetraallyloxyethane, m-phenylene bismaleimide etc. can be preferably used.

A semiconductive layer can be formed using the semiconductive composition of the present invention having such a composition by applying, for example, an extrusion coating method.

At this time, crosslinking may be carried out by chemical crosslinking using the above-mentioned organic peroxide or the like, or crosslinking by ionizing radiation may be carried out depending on the case.

(Function) ■ In the present invention, since ethylene-propylene copolymer rubber is used, the formation of polymer gel is different from that of conventional EVA.
, compared to EEA, etc., and less likely to cause poor dispersion of carbon when blending carbon.

■On the other hand, since an ethylene-alkyl acrylate copolymer was used, if only an ethylene-propylene copolymer rubber was used, when a semiconductive layer was formed with the obtained semiconductive composition, It becomes extremely sticky, which avoids practical handling problems.

In addition, since we selected an ethylene-alkyl acrylate copolymer without using EVA, the number of small protrusions increases compared to when EVA and ethylene-propylene copolymer rubber are mixed. , such a phenomenon does not occur.

Although the mechanism is not yet clear, it is thought to be due to the difference in compatibility between EVA or ethylene-alkyl acrylate copolymer and ethylene-propylene copolymer rubber.

(2) In the present invention, the carbon blank used is preferably an acetylene blank.

The reason for this is that furnace black, which is made from the most commonly used oil, has many impurities in the raw material, so there are many components that tend to cause poor dispersion when blended into a polymer base material.
This is also because small protrusions are easily formed.

■ MFR of ethylene-alkyl acrylate copolymer
is preferably 30 or less, preferably 0.5 to 25.

When the MFR exceeds 30 and the VFR increases (that is, when the molecular weight decreases), small protrusions are likely to be formed.

The reason for this is that the viscosity of the ethylene-propylene copolymer rubber and the ethylene-alkyl acrylate copolymer is too different during mixing, resulting in poor dispersion of the two, or This is thought to be because the molecular weight of the compound is low, making it easier to form a polymer gel during polymerization.

(Examples) The present invention will be explained in detail by the following examples, but these do not limit the scope of the present invention.

14m” stranded conductor with 1m+++ thick internal semi-conducting layer, 3mm thick XLPE (low density polyethylene) insulation layer,
and an outer semiconductive layer having a composition shown in Table 1 with a thickness of 1 ma+ was sequentially extruded and coated, heated at 140 ° C with an infrared heater,
A model cable was created.

Slices of 1 m thickness were cut from these model cables and the interface between the insulating layer and the external conductive layer was observed using an optical microscope6. The numbers are shown in Table 1.

In addition, the tackiness of the surface of the finished cable was examined by touch and is also shown in Table 1.

The materials used in the examples are as follows.

EVA-1: Mikata, manufactured by DuPont Polychemical, Evaflex EV450 (MFR15) EEA-1: Mikata,
Manufactured by DuPont Polychemical, Evaflex A-707 (
MFR25) EEA-2: Mikata, manufactured by DuPont Polychemicals, Evaflex A-701 (MFR5) EEA-3
: Mikata, manufactured by DuPont Polychemical, Evaflex A-
104 (MFR275) EP rubber: Manufactured by Susumu Kagaku ■, Nisprene 301 Acetylene blank: Manufactured by Denki Kagaku ■,
Denka black, Furnace black: Manufactured by Tokai Carbon ■, Geast SO
1 Antioxidant: Sumilizer WX-R, manufactured by Susumu Kagaku ■.

Lubricant: Zinc stearate, Nippon Yushi Corporation, dicumyl peroxide.

Comparing Comparative Examples 1 and 2 with Example 1, it is found that when the blend of EEA and EP rubber is used as a polymeric base material, the interface between the insulating layer and the semiconducting layer is smaller than when EVAl or EEA is used alone. It can be seen that the number of protrusions is significantly reduced.

However, it can be seen that in a blend in which the amount of EP rubber mixed with EEA is small, as in Comparative Example 4, the above effect is almost absent.

Next, when Comparative Example 7 and Example 1 are compared, it can be seen that Example 1, in which acetylene black is blended, has a very small number of small protrusions at the interface (and therefore, it is desirable to use acetylene black).

Furthermore, a comparison between Example 1.3 and Comparative Example 6 shows that it is desirable that the MFR value of the EEA used be as low as about 25 or less.

Furthermore, when the results of Example 4 are compared with other examples, it can be seen that there is no difference in the effect even if crosslinking is performed using an organic peroxide.

(Effects of the Invention) As explained above, in the semiconductive composition of the present invention, C
■The number of small protrusions existing between the cable insulator and the semiconducting layer can be reduced.

Therefore, especially in the field of ultra-high voltage C■ cables, the initial and long-term performance of the cable can be improved if used for the semiconducting layer thereof.

Claims (3)

[Claims] (1) 5 to 70 parts by weight of ethylene-propylene copolymer rubber and 95 to 95 parts by weight of ethylene-alkyl acrylate copolymer
1. A semiconductive composition comprising carbon black and a polymer base material containing 30 parts by weight of carbon black. (2) The semiconductive composition according to claim (1), wherein the carbon black is acetylene black. (3) The semiconductive composition according to any one of claims (1) and (2), wherein the ethylene-alkyl acrylate copolymer has a melt flow rate of 30 g/10 minutes or less.