JPH0662911B2 - Conductive paste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive paste using copper powder as a conductive material.

[Prior Art] Conventionally, a conductive paste has been used to form an electric circuit by printing, and as its conductive material, copper is easily oxidized and its conductivity is lowered. Although noble metals are used, they are expensive and cannot be used for general electronic devices in terms of cost.

Therefore, recently, conductive pastes using copper powder as a conductive material have been extensively researched, and conductive pastes containing anthracene derivative as a reducing agent have been added in order to suppress the oxidation of the copper powder (JP-A-56 No. 103260) is proposed.

However, this paste has a drawback that skin is likely to be formed on the surface (hereinafter referred to as “skinning property”, which means that it is difficult to skinnable is said to have good skinning property), and it is difficult to put it into practical use. It was

[Problems to be solved by the invention]

In view of the above-mentioned drawbacks, an object of the present invention is to provide a conductive paste using copper powder as a conductive material, which has good skin-tightness and excellent conductivity when applied and cured.

[Means for solving problems]

The thermosetting resin binder (A) used in the present invention is a condensate of cresol and formaldehyde, contains 3 to 7 phenol nuclei and at least 3 methylol groups, and the phenol nuclei are dimethylene ether. It is mainly composed of bound phenol oligomers. When the number of phenol nuclei decreases, the strength of the cured film decreases, and when the number of phenol nuclei decreases, the solubility in the diluent decreases, the viscosity of the paste increases, and the printability decreases. Limited to individual. When the number of methylol groups decreases, the skin-tightness deteriorates, so three or more are necessary, and the number is preferably 4 to 6.

If the bonds between the phenol nuclei are bonds other than the dimethylene ether bond, the skin tension becomes poor.

The copper powder (B) used in the present invention cannot be made into a fine electric circuit when the average particle size is large, and even if it is prepared, the stability of conductivity with time is deteriorated. Yes, and preferably 30 μm or less. Further, the shape of the copper powder may be arbitrary, and examples thereof include a spherical shape, a flake shape, and a dendritic shape. A dendritic electrolytic copper powder having an average particle size of 15 μm or less is preferable, and the surface may be washed with an acid or the like before use.

The amount of the binder (A) and the copper powder (B) blended becomes difficult when the amount of the binder (A) is small, and even if the binder (A) is applied, the copper powder is easily oxidized and the stability of conductivity with time deteriorates. Since the conductivity decreases as the amount of the copper powder (B) decreases, it is used in a weight ratio range of 15 to 25:85 to 75.

The diluent (C) used in the present invention may be any solvent capable of dissolving the binder (A), but if the boiling point is low, it will volatilize during storage or coating, and the viscosity will change or the skin will stick. Therefore, alcohols having a boiling point of 160 ° C. or higher are preferable, and examples thereof include solvents such as ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether. .

The amount of the diluent (C) added may be appropriately determined depending on the use of the conductive paste, but generally 5 to 50 parts by weight is added to 100 parts by weight of the total amount of the binder (A) and the copper powder (B). It

Any method may be adopted as the method for producing the conductive paste of the present invention. For example, a predetermined amount of the thermosetting resin binder (A), the copper powder (B) and the diluent (C) are supplied to a three-roll mill or the like. And a method of kneading and dispersing.

It goes without saying that a leveling agent, a color of a binder, etc. may be added to the conductive paste of the present invention as required.

Any method may be adopted as the method of using the conductive paste of the present invention, for example, after applying or printing in a predetermined position,
The binder may be cured by heating at 0 to 200 ° C.

〔The invention's effect〕

Since the configuration of the conductive paste of the present invention is as described above,
It is inexpensive and easy to manufacture, has good skin-tightness during storage and use, has a low settling property of copper powder, has excellent redispersion even when it settles, and has excellent conductivity of the coating film. There is.

〔Example〕

Next, examples of the present invention will be described. Hereinafter, "part" means "part by weight". In addition, the following "condensate" means "a condensate of cresol and formaldehyde having four phenol nuclei and four methylol groups (manufactured by Gunei Chemical Co., Ltd., trade name REGITOP XTL-4262D)", "Copper powder" means "dendritic electrolytic copper powder having an average particle size of 8 µm".

Examples 1 to 3 and Comparative Examples 1 to 4 A predetermined amount of the condensate, resol type phenol resin, copper powder, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether and anthracene shown in Table 1 were supplied to a three roll mill and mixed. To obtain a conductive paste. The obtained conductive paste is sealed and kept at 20 ℃, 65
It was supplied to a RH thermostatic chamber, and the skin and sedimentation properties were observed for up to 3 months. The sedimented product was stirred with a glass rod and the redispersibility was observed. The results are shown in Table 1.

In addition, the conductive paste that was introduced was screen-printed (250
Mesh, Tetron screen) and applied to the surface of the glass epoxy laminate having a width (W) of 1 mm and a length (l) of 50 mm, and heated at 150 ° C. for 1 hour to be cured to form a conductive layer. After cooling, the resistance (R) was measured with a resistor (Digital Multimeter ME-530, manufactured by Soara Co., Ltd.), and the volume resistivity (ρ) was calculated by the following formula and shown in Table 1. Note that t is the thickness of the conductive layer.

Claims (1)

[Claims] 1. (A) A condensate of cresol and formaldehyde, containing 3 to 7 phenol nuclei and at least 3 methylol groups, and the phenol nuclei are mainly dimethylene ether-bonded phenol oligomers. And (B) a copper powder having an average particle size of 200 μm or less and (C) a diluent, and the weight ratio of the binder (A) to the copper powder (B) is
15-25: 85-75, a conductive paste.