JPH0113731B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive resin composition with improved heat resistance and particularly good adhesion to lead. Conventionally, for example, a high voltage rubber or plastic insulated power cable has a conductor 1, an inner conductive layer 2, an insulator layer 3 made of polyethylene or ethylene propylene rubber, an outer semiconducting layer 4, copper, etc., as shown in FIG. The basic configuration includes a metal shielding layer 5 made of tape or copper wire, and a protective sheet 6 made of vinyl chloride or the like, provided in this order. If water intrudes into the cable from the outside for some reason in such rubber or plastic insulated power cables, so-called water trees will occur in the insulator, each semiconducting layer, etc., resulting in a decline in insulation performance, etc. This becomes a serious cause of deterioration of various characteristics of the cable. In addition, during cable manufacturing, storage, cable pulling work, etc., moisture may infiltrate through the conductor from the cable terminal or joint, etc.
It is well known that water intrusion from the conductor side into the internal semiconducting layer and further into the insulating layer causes water trees. As described above, rubber and plastic insulated power cables are strongly required to (a) prevent water from entering from the outside and (b) prevent water from entering from the conductor. In response to such requests, the applicant has developed a water-shielding cable in which a laminate tape made by laminating a conductive plastic thin film on one or both sides of a lead foil tape with a thickness of 10 to 200 μm is installed on the conductor or between the insulator and the metal shielding layer. I have proposed a structure. On the other hand, the present inventors have disclosed in Japanese Patent Application No. 152,119/1986 that an ethylene-acrylic acid copolymer is used as a conductive composition suitable for obtaining a conductive plastic thin film to be laminated on a metal foil tape. We proposed a resin composition in which electrically conductive carbon black is blended into a resin mixture in which a polyolefin resin selected from the group of polyethylene, EVA, EEA, and non-polar polyolefin crystalline resins is mixed. However, when a thin film made of the above resin composition is laminated with lead foil and used for a long time at high temperatures, deterioration due to oxidation progresses, and peeling occurs at the bond between the lead foil and the conductive thin film. There were problems in maintaining quality over a long period of time as cracks occurred in the thin thallus itself. In order to prevent oxidative deterioration of polyolefin polymers, it has conventionally been done to add antioxidants. It has been difficult to find inhibitors. In view of the above points, and as a result of intensive studies, the present invention has been developed to prevent oxidative deterioration of the conductive thin film material even when used for a long period of time at high temperatures, e.g., 50 to 90°C, It has been possible to develop a conductive resin composition that exhibits extremely good adhesion to lead foil without cracking and without deteriorating the peel strength of the bonded portion with the lead foil tape. That is, as a result of intensive research, the present inventors have found that various types of sulfur-based compounds, which have sulfur atoms in their molecules and are classified as sulfur-based compounds that have functions such as radical suppression and peroxide decomposition, have been found in the conductive composition described above. Commercially available sulfur-based antioxidants, such as bis[2-methyl-
4-(3-n-alkylC ₁₂ -C ₁₄ )thiopropionyloxy)-5-t-butylphenyl] sulfide (trade name Mark AO-23, manufactured by Adeka), dilauryl-3,3'thiodipropionic acid ester (cypropionyloxy)-5-t-butylphenyl] Kaseisha product name: Seenox DL), ditridecyl-
3,3' thiodipropionic acid ester (Sumitomo Chemical Co., Ltd. trade name: Sumilizer TL), dimyristyl-3,3'-
Thiodipropionic acid ester (Cipro Kasei Co., Ltd. trade name: Seenox DM), distearyl-3,3'-thiodipropionic acid ester (Sumitomo Chemical Co., Ltd. trade name)
Sumilizer TPS), lauryl stearyl-3,
3′thiodipropionic acid ester (Yoshitomisha brand name)
Compounds selected from the group such as LSTP Yoshitomi), 2-mercaptobenzimidazole, and tetramethylthiuram monosulfide can be used, but Adeka's Mark AO-23 is particularly suitable because it does not bleed when molded. Can be used for It was discovered that these sulfur-based antioxidants have a great effect of significantly improving the heat resistance of conductive compositions mainly composed of EAA, and also stabilize the adhesive strength with lead, and this led to the completion of the present invention. He guided it. That is, the conductive resin composition of the present invention comprises (a) an ethylene-acrylic acid copolymer (hereinafter referred to as EAA).
polyethylene, ethylene-vinyl acetate copolymer, (hereinafter referred to as
100 parts by weight of a mixture substituted with one or more polyolefins selected from the group of ethylene-ethyl acrylate copolymer (hereinafter abbreviated as EVA) and non-polar polyolefin crystalline resins (hereinafter abbreviated as EEA). (b) one or more substances selected from the group of carbon black and carbon fiber graphite.
~140 parts by weight and (c) 0.1 to 5 parts by weight of a sulfur-based antioxidant are uniformly mixed. Even if the cable is used for a long period of time in the presence of moisture and at the same temperature as the cable is used, the original properties (adhesive strength, mechanical strength, etc.) will not be significantly impaired. As the EAA used in the present invention, various kinds of EAAs manufactured by conventional methods such as high pressure method or emulsion polymerization method under high pressure can be used so that the content of acrylic acid is 1 to 20% by weight. Preferably, one having an acrylic acid content of 3 to 15% by weight is used. As the polyethylene used in the present invention, high density polyethylene and low density polyethylene (hereinafter abbreviated as LDPE) can be used. In addition, the above-mentioned ethylene-vinyl acetate copolymer (EVA) has a vinyl acetate content of 5 to 48
% by weight is preferable, and the acetoxy group is
You may use one in which 70% or more is hydrolyzed to hydroxyl groups. Further, as the above-mentioned EEA, it is preferable to use one having an ethyl acrylate content of 5 to 25% by weight. The above-mentioned non-polar polyolefin crystalline resin is a polyolefin resin that contains almost no polar groups such as chlorine, acetate groups, or double bonds, and is made with elasticity so that the elongation at break is 400 to 1000%. For example, Tafmer A series (trade name, manufactured by Mitsui Petrochemical Industries, Ltd.), which is a nonpolar ethylene α-olefin copolymer, can be suitably used. Also, a mixture of two or more of these resins may be used. As the carbon black, various acetylene blacks, furnace blacks, etc. can be used, but Kettien black (trade name manufactured by AKZO) is used.
A material with particularly excellent conductivity, such as , is most suitable. The reason why a sulfur-based antioxidant is specifically specified as an antioxidant in the present invention is that antioxidants other than sulfur-based antioxidants do not have the above-mentioned effect. Although the details of the reason for this are unknown, when the antioxidant sulfur exists at the interface between lead and the conductive thin film, it becomes PbS, which strengthens the adhesion with the conductive thin film and makes it stable. At the same time, the heat resistance of the conductive thin film itself is increased,
It is thought that this is due to these superimposed effects. Next, regarding the proportions of the above-mentioned components in the present invention, (a) the resin containing EAA as the main component;
If the amount of the conductive material (b) exceeds 140 parts by weight per 100 parts by weight, the film formability and flexibility will deteriorate and the mechanical properties will deteriorate;
The required electrical properties of ~10 ⁷ Ω-cm resistance cannot be obtained. Furthermore, if the sulfur-based antioxidant (c) is less than 0.1 part by weight, it is ineffective in improving the heat resistance of the conductive composition of the present invention. On the other hand, if it exceeds 5 parts by weight, the mechanical properties of the electrically conductive composition of the present invention will be impaired. Furthermore, in the present invention, polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-
The reason for limiting the blending ratio of polyolefins such as ethyl acrylate copolymer and non-polar polyolefin crystalline resin to 60% by weight or less is that if the blending ratio of these resins exceeds 60% of the total resin amount, the resulting composition This is because the film formability, flexibility, and adhesion to the lead foil tape deteriorate. The conductive resin composition of the present invention may further contain various additives, if desired, in addition to the above-mentioned essential components.
For example, various stabilizers, lubricants, flame retardants, reinforcing agents, etc. may be added as appropriate. The present invention will be further explained below with reference to Examples and comparison with Comparative Examples. Examples 1 to 12 Comparative Examples 1 to 10 A 0.1 mm thick film consisting of the conductive resin composition of the present invention and the conductive resin composition of the comparative example shown in Table 1 was placed on both sides of a 50 μ thick lead foil tape at a temperature of 160°C. ℃ and a pressure of 5 kg/cm ² for 1 minute to produce a chemical-resistant, water-shielding thin film for electrical cables. Volume resistivity of the above sample, adhesive strength with lead foil,
After measuring the tensile properties, immersed in 80℃ warm water for one month,
The adhesive strength and tensile properties with lead foil were measured. The obtained results are also listed in Table 1. In addition to the above tests, the samples were heat treated in a gear oven at 120°C for one month and then subjected to a tensile test. The obtained results are also listed in Table 1. Of the various raw materials used in the Examples and Comparative Examples, LDPE was used with MI=7, EVA was used with a vinyl acetate content of 19%, EEA was used with an ethyl acrylate content of 12%, and Toughmer was used with an ethyl acrylate content of 12%. The carbon black used was A4085 (trade name) manufactured by Mitsui Petrochemical Industries, Ltd. and had an MI of 4, and the carbon black was manufactured by AKZO Co., Ltd. (trade name) KETSUCHEN BLACK EC. The sulfur-based antioxidants are Examples 1, 2, 3, 4,
5 is dilauryl-3,3'-thiodipropionic acid ester (Cipro Kasei Co., Ltd. trade name: Seenox DL),
Examples 6, 7, 8, 9, 10, and 11 are bis[2-methyl-4-(3-n-alkyl (C ₁₂ -C ₁₄ ) thiopropionyloxy)-5-t-butylphenyl] sulfide (ADEKA Company product name Mark AO―
23), Comparative Examples 1 and 2 are triphenyl phosphorite, Comparative Examples 3 and 4 are 2,2′-methylenebis(4methyl-6-tertiarybutylphenol), and Comparative Examples 5 and 6 are 2,6-di-tert-butyl p-cresol (BHT), Comparative Examples 7 and 8 were
2,6-di-tertiary-butyl-4-ethylphenol was used, and in Comparative Examples 9 and 10, N,N'-diphenyl-p-phenylenediamine was used. As is clear from the examples above, the lead-conductive composition thin film using the conductive composition of the present invention can be used for a long period of time under the temperature conditions used for cables in the presence of moisture. It can prevent oxidative deterioration of the conductive rubber plastic thin film without deteriorating its adhesion to the film, and can be made into a conductive thin film for use in water-shielding electric cables with extremely excellent chemical resistance in practical use.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic structure of a high voltage rubber/plastic insulated power cable. DESCRIPTION OF SYMBOLS 1...Conductor, 2...Inner conductive layer, 3...Insulator layer, 4
...outer conductive layer, 5...metal shielding layer, 6...corrosion protection layer.

Claims (1)

[Scope of Claims] 1 (a) Up to 60% by weight of the ethylene-acrylic acid copolymer is added to polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, non-polar polyolefin-based crystalline (b) one or more substances selected from the group of carbon black, carbon fiber, and graphite per 100 parts by weight of the mixture substituted with one or more polyolefins selected from the group of resins; 5 to 140 parts by weight, and (c) 0.1 to 5 parts by weight of a sulfur-based antioxidant are uniformly mixed.