JPH0214381B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a conductive paint used for forming a nonmetallic resistance conductor constituting a noise-preventing high-voltage resistance wire used as an ignition cable for automobiles and the like. [Prior Art] A nonmetallic resistance conductor constituting a high-voltage resistance wire for noise prevention, which is generally used as an ignition cable for automobiles, etc., has a structure as shown in FIG. 1 or 2. That is, the nonmetallic resistance conductor 1 is made by assembling a plurality of wires 2 made of glass fiber or the like to form an apparently single reinforcing core 3, and surrounding the reinforcing core 3 with a conductive paint or a conductive elastomer (the elastomer is The conductive material 4 is coated with a conductive material (general term for materials that have rubber-like elasticity at around room temperature), and the glass fibers 5 are further wound thereon (Fig. 1), or the glass fibers 7 are braided (Fig. 2). ), and its surrounding area is coated with a conductive coating film 6 made of conductive paint. Therefore, in this configuration, the conductive paint forming the conductive coating film 6 is made of synthetic resin or elastomer polymer as a binder.
Conductive particles such as carbon black, graphite or carbon fibers are added to this to give it conductivity, and then it is dissolved in an organic solvent such as toluene or methyl ethyl ketone to form a paint. However, when a synthetic resin polymer such as acrylic resin or phenolic resin is used as the binder, the binder does not have elasticity, so that it has sufficient flexibility to alleviate the strain that occurs between the glass fibers 5 or 7 and the conductive coating film 6. The adhesion between the glass fibers 5 or 7 and the conductive coating film 6 tends to decrease due to the addition of mechanical stress. In addition, the polymer as a binder rapidly softens at a relatively low heating temperature, which causes microscopic fluctuations in the dispersion state of the conductive particles blended, which tends to cause changes in the resistance value of the resistance conductor. , the change in the mechanical properties of the conductive coating film 6 is also large. Furthermore, in the case of using an elastomer-based polymer as a binder, polymeric rubber-like substances such as chloroprene and chlorosulfonated polyethylene are generally used, and these have elasticity and have some degree of adhesion with glass fibers. Approximately
When heated to a high temperature of 120°C or higher, the elasticity of the polymer is rapidly lost, the mechanical properties are also rapidly reduced due to thermal deterioration, and the resistance value changes significantly. Furthermore, elastomeric polymers that are heat resistant even at high temperatures of 120° C. or higher generally have low mechanical properties such as tensile strength, and have very low strength as a coating film. Some materials, like fluoro rubber, have a heat resistance temperature of 200℃.
As mentioned above, some of the coating film strengths are satisfactory to some extent, but since they are non-polar polymers, they do not show any adhesiveness to glass fibers. [Problems to be Solved by the Invention] Therefore, when using the conventional high-voltage resistance wire for noise prevention formed with the conventional conductive coating 6, there have been various drawbacks or problems as described below. That is, (a) as shown in FIG. 3, an insulating coating layer 8 is formed on the outer periphery of the nonmetallic resistance conductor 1, and a protective layer consisting of a braid 9 and a sheath 10 is coated thereon. Prevention When using the high-voltage resistance wire A, when stripping the insulation coating layer 8, braid 9, and sheath 10 from the nonmetallic resistance conductor 1, the conductive material may be removed from the glass fiber winding portion 5 or the glass fiber braid 7 of the nonmetallic resistance conductor 1. The coating film 6 adheres to the insulating coating layer 8 and peels off, making it unusable as a high-voltage resistance wire. (b) The resistance value of the nonmetallic resistance conductor 1 changes rapidly when it is placed in a place where the ambient temperature is about 120° C. or higher. (c) As shown in Figure 4, high voltage resistance wire A
When the ends of the nonmetallic resistance conductor 1 are peeled off, the nonmetallic resistance conductor 1 is exposed and bent, and the nonmetallic resistance conductor 1 is crimped and connected to the metal terminal 11, mechanical stress is suddenly applied to the nonmetallic resistance conductor 1 due to crimping. When the film 6 partially peels off and a high voltage is applied, a corona discharge occurs in the peeled part and the nonmetallic resistance conductor 1 may be burnt out. (d) Even during use, the conductive coating 6 undergoes thermal deterioration or softening due to heat received from the engine, etc., and partially peels off, causing corona discharge as in (c) above and causing the resistive conductor 1 to deteriorate. It may cause burnout. The present invention has been made focusing on the above-mentioned problems of conventional conductive paints used to form nonmetallic resistance conductors constituting noise-preventing high-voltage resistance wires for automobiles. The purpose of this project is to provide a variety of paints. In order to solve the problems of conventional conductive paints, the present inventors have developed a material that is highly elastic and flexible, has excellent adhesion to glass fibers, has good temperature characteristics of resistance value, and As a result of intensive study from the viewpoint that one of the requirements is to use a polymer with a high decomposition temperature and high thermal softening temperature as a binder for conductive particles, we found that ethylene-acrylic elastomer meets these requirements. The object of the present invention is to obtain a composition obtained by adding conductive particles to this polymer in a certain amount in a certain range and further blending an appropriate amount of silica powder and dissolving the composition in an organic solvent. The inventors have discovered that a coating material for forming a conductive coating film that is fully compatible with the above has been developed, and the present invention has been completed. [Means for Solving the Problems] That is, the present invention provides the following methods:
This is a conductive elastomer paint obtained by dissolving in an organic solvent a composition containing 5 to 50 parts by weight of conductive particles and 5 to 20 parts by weight of an inorganic filler consisting of silica powder. In the ethylene-acrylic copolymer used as the binder polymer of the conductive particles in the present invention, the ethylene monomer represented by ( _-CH2 - _CH2- )x is 5 to 95 mol%, preferably 30 to 70 mol% of the polymer. mole%,

〔Example〕

Next, the present invention will be specifically explained using examples. Example 1 Ethylene-acrylic elastomer VAMACG consisting of ethylene-methyl methacrylate copolymer as a binder polymer for conductive particles
(trade name of DuPont Co., Ltd.), carbon black was added in varying amounts as conductive particles, and silica powder Aerosil 200 (trade name of Nippon Aerosil Co., Ltd.) was added as an inorganic filler in varying amounts. Also, toluene (Reagent 1) was used as an organic solvent.
The conductive elastomer paints of the present invention shown in the upper column A to I were prepared using the above-mentioned conductive elastomer paints according to the blending ratios shown in Table 1. In this case, two types of carbon black made by different manufacturers were used separately. One of them is Ketsuchin Black EC (product name of Lion Akzo),
The other one is Vulcan XC-72 (product name of Kyabot Co., Ltd.), and the former has DBP oil absorption: 350ml/100g,
Surface area: 950m ² /g, PH: 9.5, the latter has DBP oil absorption: 230ml/100g, surface area: 220m ² /g, PH: 7.5
Both are conductive furnace blacks, and the latter contains less heavy metals than the former. Next, coating films were formed using the obtained paints A to I, and the electrical and mechanical properties were measured for the following items. (1) Volume resistivity (Ω-cm) Apply a thin layer of paint liquid onto a glass plate using a doctor knife to an even thickness, air dry at room temperature for 30 minutes, then place in a constant temperature bath and dry at 140℃ for 30 minutes. Then, the volume resistivity and its rate of change at each temperature were measured. The volume resistivity ρ is calculated by forming two plate-shaped silver electrodes 13 with a width W (cm) on the coating film 12 as shown in FIG.
The measurement was carried out using an apparatus in which the silver electrodes 13 were set upright at a distance of 1 (cm) and the upper ends of the silver electrodes 13 were connected to the Whitstone bridge circuit 14. Calculate the cross-sectional area S (cm ² ) of the coating film 12 by t × W from the thickness t (cm) of the coating film and the width W (cm) of the electrode 13, and calculate the length l (cm) between the electrodes and the measured resistance R
(Ω), the volume resistivity ρ was calculated using the following formula. ρ=t・W・R/l Also, the rate of change (%) of volume resistivity at each temperature is as follows: R ₁ is the initial resistance, and R ₂ is the resistance after a certain period of time.
In this case, ρ ₁ −ρ 2 /ρ ₁ ×100 was calculated from ρ ₁ =R ₁ S/l and ρ ₂ = _{R 2 S} /l. (2) Glass fiber shedding load (Kgf/2cm) Apply several layers of paint liquid on a polyester film, stretch the glass fibers straight on top of that, and then apply several layers of paint liquid on top of that. After air drying at room temperature for 5 hours, put it in a constant temperature machine, dry it at 140℃ for 1 hour, and test it at a speed of 200mm/
The glass fiber was pulled out in minutes, and the load required to pull it out was defined as the pullout load. (3) Coating film tensile strength (Kgf/cm ² ) Apply a thin layer of white Vaseline on a glass plate, then apply the paint liquid on top of it in several layers to a dry thickness of about 1 mm, and then leave it at room temperature. After air drying for 5 hours, it was placed in a constant temperature bath and dried at 140°C for 1 hour, and a tensile test was performed in accordance with the method of JISK6301. (4) Coating film elongation rate (%) Based on a sample prepared in the same way as the tensile strength.
Obtained in accordance with JISK6301. The above measurement results are shown in the lower column of Table 1. Further, the rate of change in volume resistivity is shown in FIG. Note that the solid content (%) in Table 1 indicates the amount of solid content in the paint in % by weight.

[Table] Furthermore, in order to compare the characteristic values of the coating material of the present invention and its characteristic values, the characteristic values of the conventional conductive coating material are shown in Table 2.

[Table] Comparing Tables 1 and 2, it can be seen that in the paint of the present invention, in particular, the glass fiber shedding load was improved by more than 2 kgf/2 cm compared to the conventional paint. The adhesion to glass fibers is significantly improved, and the tensile strength and elongation of the coating film are also significantly higher than that of the conventional paint (J) based on chlorosulfonated polyethylene. In this case, it has been found that excellent characteristic values can be obtained when the amount of conductive particles blended is 20 parts by weight or more based on 100 parts by weight of the elastomer, and the inorganic filler may not be added, but is preferably 10 parts by weight or more.
Furthermore, the tensile strength of the coating film tends to increase as the amount of conductive particles and inorganic filler added increases, and on the contrary, the elongation rate tends to decrease. Furthermore, as shown in Figure 6, the rate of change in volume resistivity at each temperature increases significantly with the increase in temperature for the conventional paint (J), whereas the rate of change in volume resistivity at each temperature increases significantly for the paints of the present invention.
It can be seen that it is very small at temperatures below 160-180°C. Example 2 Denka ER (trade name, Denka Kagaku Kogyo Co., Ltd.), an ethylene-acrylate elastomer made of an ethylene-methyl acrylate-vinyl acetate terpolymer, was used as a binder polymer for conductive particles, and conductive particles were added to this. As carbon black, buttchin black EC (product name of Lion Akzo Co., Ltd.),
GP60SKAI (Hitachi Powder Metallurgy Co., Ltd. product name) for graphite powder,
Torayca MLD-300 (trade name of Toray Industries, Inc.) was added to the carbon fibers separately, and graphite and carbon fiber were added in different amounts, and Aerosil 200 (trade name of Nippon Aerosil Corporation) was added as an inorganic filler. ,
Conductive elastomer paints of the present invention shown in L to R in the upper column of Table 3 were prepared using toluene (first grade reagent) as an organic solvent and at the compounding ratios shown in Table 3. Further, the above-mentioned characteristic values of the obtained paint are shown in the lower column of Table 3. Further, the rate of change (%) of the volume resistivity at each temperature is shown in FIG.

〔Effect of the invention〕

As shown in detail above, the conductive elastomer paint of the present invention uses an ethylene-acrylate elastomer as a binder for conductive particles, mixes conductive particles and an inorganic filler in a certain range of amounts, and mixes it with an organic solvent. Since it is a dissolved paint,
It has the advantage of being highly elastic and flexible, has good adhesion to glass fibers, has very little change in resistance due to temperature, and can form a durable conductive coating.

[Brief explanation of drawings]

Figures 1 and 2 are perspective views showing the structure of a non-metallic resistance conductor of a conventionally used noise-preventing high-voltage resistance wire for automobiles, and Fig. 3 is a perspective view showing an example of the structure of a noise-preventing high-voltage resistance wire for automobiles. Figure 4 is a front view showing the connection state between the automotive noise prevention high-voltage resistance wire and the metal terminal, Figure 5 is an explanatory diagram of the volume resistivity measurement device, and Figures 6 and 7 are volume resistivity. 2 is a graph showing the rate of change at each temperature. DESCRIPTION OF SYMBOLS 1... Nonmetal resistance conductor, 2... Element wire, 3... Reinforcement core, 4... Conductive material, 6... Conductive coating film, 8
...Insulating coating layer, 9... Braid, 10... Sheath.

Claims (1)

[Claims] 1. Ethylene-acrylic copolymer or ethylene-
5 to 50 parts by weight of conductive particles per 100 parts by weight of an elastomer made of an acrylic-vinyl monomer terpolymer.
1. A conductive elastomer paint characterized by dissolving in an organic solvent a composition containing 5 to 20 parts by weight of an inorganic filler made of silica-based powder. 2. The conductive elastomer paint according to claim 1, wherein the conductive particles are at least one selected from carbon black, graphite, and carbon fiber.