JPH0368488B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a semiconductive mixture used for connecting power cables, and a semiconductive shrink tube made of the mixture. ``Prior Art'' Some power cables, particularly high-voltage power cables, are provided with a semiconducting mixture coated directly above the conductor wire and outside the insulation coating. Conventionally, semiconductive mixtures used for such purposes include conductive carbon black mixed with rubber or resin such as ethylene-vinyl acetate copolymer (EVA). There is. In addition, in order to form a semiconductive coating on the connection part when connecting the above cable, a tube-shaped semiconductive shrink tube that shrinks when heated is used to facilitate cable connection. It is widely used. This conventional semi-conducting shrink tube is
A semi-conductive mixture of EVA resin and other conductive carbon black is molded into a tube shape, and this semi-conductive shrink tube is fitted into a designated area, such as directly above the cable conductor connection or outside the insulation coating. The device is inserted and heated with a burner to cause it to shrink, forming a semiconductive coating on the target area. ``Problems to be solved by the invention'' By the way, power cables, especially high-voltage power cables, have excellent physical and mechanical performance, are highly reliable, and can handle a large amount of current. The trend is for CV cables (cross-linked polyethylene power cables) to be used more frequently. On the other hand, because conventional semiconductive mixtures are based on EVA resin, etc., they have poor adhesion with the polyethylene used as the insulating material for the CV cables mentioned above. A major problem was that the coating could not be tightly bonded. In addition, conventional semiconducting shrink tubes made of semiconducting compounds molded into tubes do not have a good shrinkage rate, making it difficult to tightly cover the target area when connecting cables. There was a problem. This invention solves the above-mentioned problems, and provides a semiconductive mixture that has good adhesion with polyethylene used in insulating materials such as CV cables, and also has good shrinkage when molded into a tube shape. It is an object of the present invention to provide a semiconductive shrink tube comprising the same. "Means for solving the problem" In this invention, the ethyl acrylate content is 10
~20% and 60 to 80 parts by weight of an ethylene-ethyl acrylate copolymer with an MFR of 2 or less, and linear low-density polyethylene with an MFR of 5 or less
A semiconductive mixture is prepared by blending 40 to 70 parts by weight of conductive carbon black with 100 parts by weight of a resin consisting of 40 to 20 parts by weight. The solution is to make a semiconductive shrinkable tube by crosslinking and forming it into a tube shape. Hereinafter, the semiconductive mixture of this invention (first invention)
and a semiconductive shrink tube (second invention) made of a mixture thereof will be explained in detail. Ethylene-ethyl acrylate copolymer (hereinafter referred to as EEA) used in the semiconductive mixture of the first invention
) has an ethyl acrylate content of 10 to 20% in EEA and an MFR of 2 or less. If the ethyl acrylate content is less than 10%, the elongation of the semiconductive mixture is insufficient, and
If the ethyl acrylate content exceeds 20%, the drawability of the semiconductive mixture deteriorates. Also,
If the EEA MFR exceeds 2, the elongation of the semiconductive mixture will be insufficient and the drawability will deteriorate. Linear low-density polyethylene (hereinafter referred to as L-LDPE) used for semiconductive mixtures is MFR
is 5 or less. If the MFR exceeds 5, the semiconductive mixture has insufficient elongation. The above EEA and L-LDPE are used by mixing 60 to 80 parts by weight of EEA and 40 to 20 parts by weight of L-LDPE. If the L-LDPE in the mixed resin exceeds 40 parts by weight, the elongation of the semiconductive mixture will be insufficient and the flexibility will deteriorate. Also, L-LDPE
If the amount is less than 20 parts by weight, the volume resistivity of the semiconductive mixture becomes high. The conductive carbon black (hereinafter abbreviated as carbon) used in the semiconductive mixture may be a commercially available product such as acetylene black or furnace black. Examples include Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and Vulcan XC. -72 (manufactured by Kiyubotsu)
etc. are preferably used. This carbon is
40 parts by weight of mixed resin of EEA and L-LDPE
~70 parts by weight is blended. If the carbon content 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 the flexibility will deteriorate. The semiconductive mixture of the first invention may contain the above-mentioned components in accordance with their respective compounding ratios, and in addition to the above-mentioned components, for example, a crosslinking agent, an anti-aging agent, a processing aid, etc. Other ingredients may also be mixed. The semiconductive mixture of the first invention is superior to conventional semiconductive mixtures in that it has good adhesion to polyethylene, good elongation, and good shrinkability when made into a shrink tube. It exhibits excellent performance especially as a semiconductive coating for cables coated with polyethylene insulation such as CV cables. Further, the purpose of use of this semiconductive mixture is not limited to the semiconductive coating of the above-mentioned cable; for example, this mixture can be formed into a sheet and used as an antistatic sheet. Next, the second invention will be explained with reference to the drawings. A second invention is a semiconductive shrink tube formed by forming the semiconductive mixture of the first invention into a sheet shape (or table shape), crosslinking this, and then forming it into a tube shape, and this shape is Any shape may be used as long as it is in the shape of a tube, and the method for forming the tube into the shape is not limited. Next, the second invention will be specifically explained by exemplifying the semiconductive shrinkable tube of the second invention. FIG. 1 shows an example of the semiconductive shrink tube of the second invention. In this figure, reference numeral 1 denotes a semiconductive shrink tube (hereinafter abbreviated as tube). This tube 1 is made of the semiconductive mixture described in the first invention, and includes a cylindrical tube body 2 and a locking protrusion integrally provided on the outer periphery of the tube body 2. It consists of 3. The locking protrusion 3 is attached to the tube body 2
It extends along the longitudinal direction and has a T-shaped cross section. Further, an incision 4 extending to the inner circumferential surface of the tube body 2 is formed in the center of the locking protrusion 3 along its longitudinal direction. This tube 1
The tube body 2 can be split by opening the incision 4, and the tube body 2 is spread out to cover the object such as a cable, conduit, or rod, and the fastener 5 is attached to the locking protrusion 3. By fastening and fixing the tube body 2 and heating it with a burner etc.,
The tube body 2 contracts to tightly cover an object such as a cable. Such a tube 1 is manufactured as shown in FIGS. 2 to 4. First, a long sheet 6 having a cross-sectional shape as shown in FIG. 2 is extruded using an extruder. Both ends of the sheet 6 in the width direction are bent into a hook shape to form locking portions 7, 7, which are one of the locking protrusions 3. This sheet 6 is then crosslinked. Crosslinking can be achieved by adding an organic peroxide crosslinking agent such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 or dicumyl peroxide and heating, or by electron beam. A method of irradiating with light can be adopted. This cross-linked sheet 6 was gripped by the locking parts 7, 7 at both ends thereof and pulled in the width direction of the sheet 6 to stretch the width by about 1.2 to 2 times, and this stretched state was maintained. This is then cooled to obtain a stretched sheet 8 as shown in FIG. Thereafter, this stretched sheet 8 is cut to an appropriate length, bent so that the locking parts 7, 7 are on the outside, and the locking parts 7, 7 are aligned to form an incision 4, and a fourth The tube 1 will be as shown in the figure. FIG. 5 shows another example of the semiconductive shrink tube of the second invention. The tube 9 shown in this figure is formed into a cylindrical shape using the semiconductive mixture of the first invention described above. This tube 9
can be inserted into objects such as cables, conduits, rods, etc.
The tube 9 is heated with a burner or the like to shrink and tightly cover an object such as a cable. This tube 9 is manufactured as follows.
First, the semiconductive mixture of the first invention described above is extruded into a film. This film is then crosslinked. Crosslinking can be carried out by adding the above-mentioned crosslinking agent and heating it, or by irradiating it with an electron beam. This crosslinked film is then stretched in the longitudinal direction to form a stretched film. Then,
This stretched film is cut into tape shapes and formed into tube shapes as shown in FIG. That is, the tape 10 is wound multiple times around the circular core metal 12 using a taping machine 11 to obtain a desired thickness. Next, the tape 10 is melted and integrated by heating above the melting point of the semiconductive mixture, and then cooled and the core bar 12 is removed to obtain the tube 9. The tubes 1 and 9 of the second invention are similar to the tubes 1 and 9 of the above-mentioned first invention.
Since the semiconductive mixture of the invention is molded into a tube shape, it has good adhesion to cables coated with polyethylene insulation, such as CV cables, which could not be tightly coated with conventional semiconductive shrink tubes. It is possible to form a semiconductive coating exhibiting properties. Further, since the tubes 1 and 9 have good shrinkability, it is possible to form a semiconductive coating tightly on the target location. Examples of this invention are shown below. "Example" Examples (3 examples) and comparative examples (2 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-1150 (ethyl acrylate content 15%,
MFR0.75), EEA is Nisseki Rexron EEA A-
270 (ethyl acrylate content 15%, MFR1.5),
EEA is Nisseki Rexron EEA A-4200 (ethyl acrylate content 20%, MFR5, each of the above
EEA is manufactured by Nippon Petrochemicals Co., Ltd.), EVA is manufactured by Mitsui-Dupont Polychemicals, L-LDPE is manufactured by Nippon Unicar (MFR3.8), carbon is Denka Carbon (manufactured by Denki Kagaku Kogyo Co., Ltd.), and anti-aging agent. Nokrac 300 (manufactured by Ouchi Shinko Co., Ltd.) was used, and zinc stearate was used as a processing aid. Each semiconductive mixture was manufactured by kneading the above components under heating using a Banbury mixer, and the following tests were conducted using each of the semiconductive mixtures obtained thereby. . Using these semiconductive mixtures, the elongation of each was first measured according to JIS K7113-1981. Next, each semiconductive mixture was processed into a sheet with a width of 0.5 mm, and then a irradiation crosslinking device was used to adjust the degree of crosslinking to approximately 50% (calculated without carbon components) in terms of gel fraction. was cross-linked. Each crosslinked sheet was then stretched using a stretching device. During this stretching operation, the maximum stretching ratio at which continuous and stable stretching was possible was measured, and this was taken as the stretchability. Next, shrink tubes were created using each sheet stretched at the maximum stretching ratio, and each shrink tube was heated at 200°C for 1 hour to determine the diameter of the tube after shrinkage (after heating) relative to the diameter of the tube before heating. The ratio was measured, and this was taken as contractility. Also, attach each of the above shrink tubes to the polyethylene insulation of the CV cable (6.6KV, 200mm ² ).
It was heated to about 0.degree. C. to shrink, and then heated to 200.degree. C. for 1 hour to adhere to the polyethylene insulator. The adhesion of the shrink tube was examined by making a 10 mm wide scratch on this and peeling off the shrink tube. The adhesion criteria were as follows: A sample in which the shrink tube did not peel off was considered good, and a sample in which the shrink tube peeled off was judged to be poor. The results of each of the above tests are shown in Table 2.

[Table] As is clear from Table 2, the semiconducting mixture of the present invention has better elongation than Comparative Example A, which was prepared with the intention of making a conventional semiconducting mixture, and was also made into a shrink tube. It was confirmed that the shrinkage properties and adhesion to polyethylene were also excellent. On the other hand, Comparative Example A, which was intended to be a conventional semiconducting mixture, had poor shrinkability when made into a shrink tube and failed to exhibit adhesion to polyethylene. In addition, Comparative Example B shows an example in which an EEA with an MFR of 2 or more is blended, but although the adhesiveness with polyethylene is good, sufficient shrinkability is not obtained, and a good shrink tube is not obtained. I can't get it. "Effects of the Invention" As explained above, the semiconductive mixture of the present invention and the semiconductive shrink tube formed from the mixture into a tube shape have excellent adhesiveness between the mixture and the polyethylene insulator. Since it can be obtained well, it is possible to form a semiconductive coating with good adhesion on polyethylene insulators, which has been difficult to coat with conventional semiconductive mixtures. In addition, the semiconductive shrink tube of this invention has good shrinkability, so it can be used when connecting cables, etc.
A tight coating can be easily applied to the target area.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of the semiconductive shrink tube of the present invention, FIGS. 2 to 4 are sectional views showing the manufacturing process of the semiconductive shrink tube shown in FIG. 1 in order of process, and FIG. 6 and 6 are views showing other examples of the semiconductive shrink tube of the present invention, in which FIG. 5 is a perspective view of the semiconductive shrink tube, and FIG. 6 is a side view showing the manufacturing process. . 1, 9...Tube (semi-conductive contraction tube),
6...Sheet.

Claims (1)

[Scope of Claims] 1. 60 to 80 parts by weight of an ethylene-ethyl acrylate copolymer having an ethyl acrylate content of 10 to 20% and an MFR of 2 or less, and a linear low density having an MFR of 5 or less. A semiconductive mixture comprising 40 to 70 parts by weight of conductive carbon black mixed with 100 parts by weight of a resin consisting of 40 to 20 parts by weight of polyethylene. 2 60 to 80 parts by weight of an ethylene-ethyl acrylate copolymer having an ethyl acrylate content of 10 to 20% and an MFR of 2 or less, and 40 to 20 parts by weight of linear low-density polyethylene having an MFR of 5 or less. A semiconductive shrink tube formed by molding a crosslinked sheet-like material of a semiconductive mixture, which is made by blending 40 to 70 parts by weight of conductive carbon black into 100 parts by weight of a resin consisting of the following, into a tube shape.