JPH0554203B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a power cable and a semiconductive mixture used for connection thereof. [Conventional technology] Power cables, especially high-voltage power cables,
A material coated with a semiconductive mixture directly above the conductor and outside the insulating coating is used. Traditionally, semiconductive mixtures used for such purposes include conductive carbon black mixed with rubber or resins such as ethylene-vinyl acetate copolymer (EVA). ing. Further, when connecting the above-mentioned cables, a semi-conductive tape or a semi-conductive tube made of the above-mentioned semi-conductive mixture is often used in order to form a semi-conductive coating on the connecting portion. This conventional semiconductive tape is made by extrusion molding a semiconductive mixture made of a resin such as EVA, conductive carbon black, and a crosslinking agent into a tape shape, and is placed directly above the conductor connection part of the cable. This anti-conductive tape is wrapped around a predetermined portion, such as the outside of the semi-conductive insulation coating, and is combustible to form a semi-conductive coating. The semi-conductive tube is formed by extruding the above-mentioned semi-conductive mixture into a tube shape, or by wrapping the above-mentioned semi-conductive tape around a circular core bar multiple times to obtain a desired thickness, and then forming the semi-conductive mixture into a tube shape. The tape is heated above the melting point of the cable to melt it into one piece, then cooled and the core bar is removed to form a tube. A semiconducting coating is formed on designated areas such as directly above the conductive connection of the cable and outside the insulation coating. I'm starting to do that. Here, the semiconductive mixture that forms this semiconductive coating should not only have sufficient adhesion with the crosslinked polyethylene but also have excellent moldability into tape or tube shapes as described above. It is also required to have properties such as good electrical and mechanical properties when a semiconductive coating is formed. [Problems to be Solved by the Invention] When connecting power cables, in order to form a semiconductive coating on the connection part, it is necessary to Due to constraints such as the melting point of the semiconductive mixture forming the conductive coating, it is desirable to keep the heating temperature of this connection part at about 130 to 160°C. Therefore, by heating in this temperature range, the crosslinking agent mixed in the semiconductive mixture exhibits its effect and forms a semiconductive coating with good electrical and mechanical properties. The crosslinking agent added to the resin has a relatively low decomposition temperature of 120 to 150℃ (half-life is 1
Temperature that indicates time). However, in conventional semiconducting mixtures,
If such a limited amount of crosslinking agent is blended, the crosslinking reaction will already proceed during the process of forming the material into a tape or tube shape, resulting in poor extrudability, resulting in the creation of a semiconductive member. A problem arose that made it difficult. Further, even if it is possible to create a semiconductive member, there is a problem that the electrical and mechanical properties of the semiconductive coating are not good. In particular, in addition to the above-mentioned problems, semiconductive mixtures based on conventional EVA resins also have
There was a major problem in that the adhesion to the crosslinked polyethylene used as the insulating material for CVA cables was poor, and the polyethylene insulator and semiconductive coating could not be tightly bonded. [Means for solving the problem] In this invention, the ethyl acrylate content is 15
~25% and 50 to 90 parts by weight of ethylene-ethyl acrylate copolymer having an MFR of 3 to 15, and linear low density polyethylene having an MFR of 2 to 10.
100 parts by weight of a mixed resin consisting of 50 to 10 parts by weight,
The solution is to mix 40 to 70 parts by weight of conductive carbon black and 0.2 to 5 parts by weight of an organic peroxide-based crosslinking agent whose half-life is 1 hour at a temperature of 120 to 150°C. shall be. Hereinafter, the semiconductive mixture of the present invention will be explained in detail. Ethylene-ethyl acrylate copolymer (hereinafter referred to as EEA) used in the semiconductive mixture of this invention
) has an ethyl acrylate content of 15 to 25% by weight in EEA and an MFR of 3 to 15. If the ethyl acrylate content is less than 15%, the elongation of the semiconductive mixture will be insufficient, and if the ethyl acrylate content exceeds 25%, the strength of the semiconductive mixture will be insufficient. Also,
If the EEA MFR is less than 3, the processability of the semiconductive mixture deteriorates, and if it exceeds 15, the elongation and strength of the semiconductive mixture are insufficient. Linear low-density polyethylene (hereinafter referred to as L-LDPE) used for semiconductive mixtures is MFR
is between 2 and 10. Those less than MFRGF2 are
The processability of the semiconductive mixture deteriorates, and if it exceeds 10, the elongation and strength of the semiconductive mixture are insufficient. The above EEA and L-LDPE are used by mixing 50 to 90 parts by weight of EEA and 50 to 10 parts by weight of L-LDPE. If the mixed resin contains more than 50 parts by weight of L-LDPE, the semiconductive mixture will not have sufficient elongation and will have poor flexibility. Also, L-
If the LDPE is less than 10 parts by weight, the volume resistivity of the semiconductive mixture will be high. In addition, conductive carbon black (hereinafter abbreviated as carbon) used in semiconductive mixtures is
Commercially available products such as acetylene black and furnace black may be used. For example, Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and Vulcan XC-72 (manufactured by Kabot Corporation) are preferably used. This carbon is
To 100 parts by weight of the mixed resin of the above EEA and L-LDPE,
Add 40 to 70 parts by weight. This carbon content is
If the amount is less than 40 parts by weight, the conductivity of the semiconductive mixture will be insufficient. Furthermore, if the carbon content exceeds 70 parts by weight, the elongation of the semiconductive mixture will be insufficient and workability will deteriorate. Next, the crosslinking agent added to the above semiconductive mixture is heated at a temperature of 120 to 150°C, at which its half-life is 1 hour.
It is an organic peroxide type product. This temperature
If the temperature is lower than 120°C, the decomposition reaction is rapid and the extrusion processability of the semiconductive mixture is deteriorated. If this temperature exceeds 150°C, the decomposition reaction will be slow and the extrusion processability of the semiconductive mixture will be good, but it will be difficult to crosslink the semiconductive coating, and the semiconductive mixture will have sufficient elongation and strength. No coverage is obtained. Examples of crosslinking agents that satisfy this condition include dicumyl peroxide (hereinafter abbreviated as DCP), 1,3
-bis-(t-butylperoxy-isopropyl)
Benzene is preferably used. This crosslinking agent was added to 100 parts by weight of the mixed resin of EEA and L-LDPE.
Add 0.2 to 5 parts by weight. Depending on the type of crosslinking agent,
Although the preferred amount varies, in general, if the amount is less than 0.2 parts by weight, crosslinking of the semiconductive coating will not be sufficient and satisfactory physical properties such as elongation and strength will not be obtained. Also,
If this amount exceeds 5 parts by weight, the extrusion processability of the semiconductive mixture will deteriorate. This semiconductive mixture may contain the above-mentioned components according to their respective compounding ratios, and may also contain other components such as anti-aging agents and processing aids in addition to the above-mentioned components. Also good. Compared to conventional semiconductive mixtures, this semiconductive mixture can be used as a semiconductive coating layer when forming the semiconductive coating by mixing an appropriate crosslinking agent when compounding the resin. Demonstrates excellent performance. That is, when a semiconductive mixture is formed into a tape or tube shape, a good semiconductive tape can be obtained without the disadvantages such as deterioration of extrusion processability due to crosslinking. In addition, unlike conventional semiconducting mixtures, there is no need to process it into a sheet or tape shape and then crosslink it using methods such as electron beam irradiation. The cross-linking reaction has progressed sufficiently, and there is sufficient electrical
A semiconducting coating with mechanical properties can be obtained. Moreover, it is superior to conventional semiconductive mixtures in terms of adhesion to crosslinked polyethylene. Such a semiconductive mixture is used as an internal or external semiconductive layer of a power cable by an extrusion coating method, and is also used as a semiconductive member formed into a tape or tube shape. This semiconductive tape is obtained by extruding it into a tape shape using an extruder, for example, and by wrapping it multiple times around the outside of an object such as a cable, conduit, or rod, and then heating the tape. Therefore, this semiconductive tape is used to cover objects such as cables while being crosslinked. Moreover, FIG. 1 shows an example of this semiconductive tube. The tube 1 shown in this figure is formed into a cylindrical shape using the above-mentioned semiconductive mixture. This tube 1 is inserted into an object such as a cable, conduit, or rod, and by heating the tube 1 with a burner or the like, the semiconductive tube 1 can be coated on the object such as a cable. It is something. Further, the semiconductive tape and semiconductive tube can be expanded by a method such as stretching to form a semiconductive tape or semiconductive tube that has shrinkability when heated. [Example] Examples (4 examples) and comparative examples (4 examples) of this invention
Each of the semiconducting mixtures in Example) was prepared according to the blending amounts shown in Table 1.

【table】

[Table] The EEA of each of the above ingredients is Nisseki Rexron.
EEA A-1100 (ethyl acrylate content 10%,
MFR0.4), EEA is Nisseki Rexron EEA A-
4200 (20% ethyl acrylate content, MFR5),
EEA is Nisseki Rexron EEA A-6170 (ethyl acrylate content 17%, MFR20, each of the above
EEA is manufactured by Nippon Petrochemical Co., Ltd.), L-LDPE
is Urtozex 3010F (MFR1.3), L-
LDPE is Ultxex 2020L (MFR2.1), L
-LDPE is Ultxex 20100J (MFR8), L
-LDPE is Ultzex 20200J (MFR18, each of the above L-LDPEs are manufactured by Mitsui Petrochemicals),
EVA is Evaflex 260 (manufactured by Mitsui, Dupont, Polychemical Co., Ltd.), carbon is Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.), and anti-aging agent is Nokuratsu.
300 (Ouchi Shinkosha), processing aid is zinc stearate,
Dicumyl peroxide (Percumil D, DCP, manufactured by Nippon Oil & Gas Co., Ltd.) was used as a crosslinking agent. Each semiconductive mixture was manufactured by kneading the above-mentioned components under heating using a mixing roll, and the following tests were conducted using each of the semiconductive mixtures thus obtained. Ivy. First, these semiconducting mixtures are pressed,
A sheet with a thickness of 1 mm was produced. The pressing conditions at this time were a temperature of 160°C and a time of 40 minutes. The volume resistivity at 60°C of each sheet obtained here,
Elongation (tensile elongation at break) and strength (tensile break strength) were measured according to JISK7113-1981. Next, from the above semiconducting mixture, a width of 150 mm,
A tape with a thickness of 0.2 mm was prepared, and its extrudability was examined based on the difficulty of extrusion. That is, those that could be continuously and stably extruded were classified as having "good" extrudability, and those that caused scorch in the T-die and could not be continuously extruded were classified as "poor" in extrudability. Next, for only those tape-shaped products obtained by the above-mentioned extrusion molding, each of the semiconductive tapes was wrapped around a cross-linked polyethylene insulator of a CV cable (6.6 KV, 200 mm ² ) and heated at 150°C for 90 minutes. .
After heating, the adhesiveness of the semiconductive tape was examined by peeling the tape. That is, when the tape adhered sufficiently and was difficult to peel off, the adhesion was rated as "good", and when the tape was easily peeled off, the adhesion was rated as "poor". The results of each of the above tests are shown in Table 2.

[Table] As is clear from Table 2, the semiconductive mixture of the present invention has better extrudability than Comparative Examples C and D, which were prepared with the intention of making a conventional semiconductive mixture. Furthermore, when made into a semiconductive tape, the adhesiveness was sufficient, and the mechanical properties such as elongation and strength, and the electrical properties were also good. In light of this, Comparative Example C, which was created with the intention of making a conventional EVA-based semiconductive mixture, had poor adhesion to polyethylene and a too high volume resistivity, as had been a problem in the past. The electrical characteristics were also poor. Comparative Example D is a mixture in which the amount of conductive carbon black is changed in order to improve the electrical properties of Comparative Example C, but this mixture lacks mechanical properties such as elongation and strength. Moreover, the extrudability was also poor, making it impossible to obtain a semiconductive tape. On the other hand, Comparative Example A is
It is a system consisting of EEA and L-LDPE.
This is an example in which the ethyl acrylate content in EEA is less than 15% and the MFR of L-LDPE is less than 2. In this case, the extrudability was poor and it was not possible to obtain a semiconductive tape. Comparative Example B shows an example in which EEA has an MFR of 15 or more and L-LDPE has an MFR of 10 or more. Although extrudability and adhesiveness are good, elongation and strength are poor. It was not possible to obtain a good semiconductive tape because of the lack of mechanical properties such as. [Effects of the Invention] As explained above, the semiconductive mixture of the present invention is an ethylene-ethyl acrylate copolymer having an ethyl acrylate content of 15 to 25% and an MFR of 3 to 15. 90 parts by weight and MFR 2
100 parts by weight of a mixed resin consisting of 50 to 10 parts by weight of linear low-density polyethylene of ~10 and 40 to 70 parts by weight of conductive carbon black at a temperature of 120 to 150°C with a half-life of 1 hour. Since this product contains a certain amount of an organic peroxide-based crosslinking agent, when extruding this semiconductive mixture, it is difficult to prevent extrudability from decreasing due to crosslinking during the extrusion process, as in conventional methods. A desired member can be obtained without any inconvenience. Further, when forming a semiconductive coating, crosslinking can be performed simultaneously under the same heating conditions as the coating, and therefore a semiconductive coating with good electrical and mechanical properties can be easily obtained.

[Brief explanation of the drawing]

The drawing is a perspective view showing an example of a semiconducting tube made of the semiconducting mixture of the present invention. 1...Tube (semi-conductive tube).

Claims (1)

[Claims] 1 50 to 90 parts by weight of an ethylene-ethyl acrylate copolymer having an ethyl acrylate content of 15 to 25% and an MFR of 3 to 15, and 50 to 10 parts by weight of linear low density polyethylene having an MFR of 2 to 10. 100 parts by weight of a mixed resin consisting of 40 to 70 parts by weight of conductive carbon black, and 0.2 to 5 parts by weight of an organic peroxide-based crosslinking agent whose half-life is 1 hour at a temperature of 120 to 150°C. A semiconductive mixture characterized by containing parts by weight.