JPH0311486B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a carbon paste having excellent adhesion to substrates such as plastics and ceramics and high electrical conductivity. Prior Art and Problems to be Solved by the Invention Conventionally, in the electronic and electrical industry, carbon paste, which has been used for conductive plates, resistors, contacts, etc. of flexible wiring boards, is a combination of conductive carbon powder and a binder, such as polyvinyl. It is prepared by appropriately blending a mixture or copolymer of butyral resin and phenol resin or epoxy resin, and a solvent such as methyl ethyl ketone, ethanol, butyl carbitol, etc.
In particular, a carbon paste that has both excellent adhesion to substrates with excellent heat resistance such as polyester and ceramics and high conductivity has not been obtained. The present invention was made in order to provide a carbon paste that has both excellent adhesion to base materials and high conductivity and can be used in a wide range of applications. Means for Solving the Problems According to the present invention, per 100 parts by weight of a binder resin consisting of a polyvinyl butyral resin and a resol-type phenol formaldehyde resin, 10 to 65 parts by weight of carbon powder and a carbon powder selected from the group consisting of kaolinite, detsuite and illite are used. The present invention relates to a carbon paste containing 8 to 30 parts by weight of one or more inorganic fillers. The binder resin used in the present invention is composed of polyvinyl butyral resin and resol type phenol formaldehyde resin. The carbon powder can be one that has been commonly used in carbon pastes, such as highly conductive ones such as Kettchen Black EC or Acetylene Black, and the amount of carbon powder to be blended is the same as that of the binder resin mentioned above.
Approximately 10-65 parts by weight, depending on 100 parts by weight. When the amount of carbon powder blended exceeds about 65 parts by weight, conductivity increases, but adhesion or adhesion decreases, and
If the amount is less than 10 parts by weight, high conductivity cannot be obtained. The particle size of carbon powder is usually about 10 mμ to 100 mμ, but the secondary particle size, which is usually an aggregate of these particles, and the chain of these particles are important. Inorganic fillers used in the present invention include kaolinite, detsuite and illite;
Two or more of these may be used in combination if desired. These inorganic fillers can be added in relatively large amounts without increasing the viscosity of the system, and can also contribute to improving conductivity and adhesiveness. The amount of inorganic filler is the same as the binder resin described above.
The amount is about 8 to 30 parts by weight per 100 parts by weight, and if it is less than about 8 parts by weight, it is difficult to obtain the desired effect of the present invention, and if it is more than about 30 parts by weight, the clay content of the system increases and the conductivity also improves. It will disappear and the adhesion will also decrease. The viscosity diameter of the inorganic filler is usually preferably about 0.1~
It is 10μ. The carbon paste according to the present invention is prepared by kneading predetermined amounts of the binder resin, carbon powder, and inorganic filler using an appropriate solvent. The amount of solvent used should be kept to the minimum necessary, and examples of such solvents include a mixture of methyl ethyl ketone and ethyl alcohol. Butyl carbitol or the like is used as a diluent for carbon paste. Since the carbon paste prepared as described above usually contains about 30 to 80% volatile components, it can be applied to a desired substrate such as polyester film, ceramic tile, alumina plate, etc. to a desired thickness. After coating or printing to a thickness of about 1.3 to 3 times the thickness of the film, it is subjected to heat treatment. Heat treatment conditions may be selected appropriately depending on the properties of the carbon paste, purpose of use, type of substrate, etc., and are usually approximately
Process at 120-190°C for about 0.5-5 hours. For example, if the adherend substrate is a ceramic sintered body, 150 is 0.5
After heat treatment for ~1 hour, conductivity is improved by heat treatment at 400°C for 1 hour. Hereinafter, the present invention will be explained with reference to Examples. Example 1 60 parts by weight of polybutyral resin and 40 parts by weight of resol type phenolic resin were mixed with CH ₃ COC ₂ H _5.
C ₂ H ₅ OH mixed solvent [CH ₃ COC ₂ H ₅ :C ₂ H ₅ OH=
70:30 (weight ratio)] was added dropwise to 120 parts by weight at approximately room temperature to form a candy-like sticky mixture, and to this, 30 parts by weight of conductive carbon powder (Ketschen Black EC) was added.
Furthermore, 100 parts by weight of butyl carbitol was added, the mixture was kneaded while being crushed in a mortar, and 30 parts by weight of kaolinite (particle size: 5 μm) was further added to the kneaded mixture to prepare a carbon paste according to the present invention. The obtained carbon paste was printed on a polyester film (thickness: 50μ) (printing area: 16mm).
x 10mm; coating thickness: 0.1mm), heat treated at 150℃ for 1 hour to harden the conductive carbon film (thickness:
approximately 30μ) was formed. The adhesion strength and electrical resistance of this conductive carbon film were measured, and the results are shown in Table 1. Examples 2 to 4 According to the procedure of Example 1, the adhesion and electrical resistance of conductive carbon films formed under the conditions shown in Table 1 were measured, and the results are shown in Table 1. Comparative Examples 1 to 6 According to the procedure of Example 1, the adhesion and electrical resistance of conductive carbon films formed under the conditions shown in Table 1 were measured, and the results are shown in Table 1.

[Table] Comparative Example 7 Commercially available carbon paste containing carbon powder, phenolic resin binder, and mixed solvent of methyl ethyl ketone, ethanol, and butyl carbitol (composition ratio of ingredients is unknown, does not contain inorganic filler such as kaolinite) When the same operations and measurements as in Example 1 were carried out, the adhesion strength was evaluated as B, and the electrical resistance was 170KΩ. Effects of the Invention The carbon paste according to the present invention has electrical conductivity several times higher than that of conventional carbon pastes, and is effective for various adherent substrates, especially polyester films that have extremely excellent heat resistance, bending resistance, and weather resistance. Due to its good adhesion, it can be used as a material for, for example, conductors of flexible wiring boards, resistors, and contacts (for example, contacts on the fixed side and movable side of keyboard switches as described in JP-A-58-189919). In addition, it can be used as a flexible film heating element to prevent water pipes from freezing, and it can also be used as a heat ray absorber (for example, by applying carbon paste to a polyester container and curing it with infrared rays, it can be used in direct sunlight). It can be used as a water heater with high absorption capacity), and can also be used as a material for heating elements and resistors made of ceramic sintered bodies such as alumina substrates and tile plates.

Claims (1)

[Claims] 1. 10 to 65 parts by weight of carbon powder and one or more inorganic fillers selected from the group consisting of kaolinite, detsuite, and illite per 100 parts by weight of binder resin consisting of polyvinyl butyral resin and resol type phenol formaldehyde resin 8 A carbon paste characterized by containing ~30 parts by weight.