JPH1166956A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste for electrode membrane which is excellent in resistivity, printing fitness, and peeling-off resistance, by using a suitable amount of mixed conductive noble metal particles having different diameters and shapes and using thermoplastic synthetic resin as adhesives. SOLUTION: This conductive paste consists of conductive noble metal particles, synthetic resin, and organic solvent, whereas the conductive noble metal particles are silver particles, a combination of 10-30 pts.wt. of flake-shaped particles whose diameter is 0.2-5 μm and 30-90 pts.wt. of spherical particles whose diameter is 0.2-10 μm is used. The synthetic resin is polyester resin, acrylic series resin, cellulose series resin or the like, and contains thermoplastic synthetic resin whose softening point is 180 deg.C or over of 5-14 pts.wt. to the conductive noble metal particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for forming an electric circuit, and more particularly to a conductive paste having a small specific resistance, which is suitable for fine line printing by a synthetic resin curing type.

[0002]

2. Description of the Related Art In recent years, the application technology of noble metal pastes for the electronics industry has been rapidly expanding, and various kinds of noble metal particles are used singly or in combination as a paste material. Noble metal paste, noble metal powder or noble metal resinate as a conductive functional material, organic or inorganic binder,
It is kneaded and dispersed in a viscosity imparting medium composed of a metal oxide to form a paste.

As a method of forming a metal film on electrodes, conductors and resistors as electronic parts, a method of forming a metal film from a base metal or a precious metal organometal (ink), or a thin film by wet plating typified by electroplating. , A method of forming a thin film by dry plating such as a vacuum evaporation method, a chemical vapor deposition method, and sputtering, and a thick film method of forming a metal film using a base metal or a noble metal paste.

[0004] Synthetic resin-curable conductive pastes widely used in the field of electronic parts are generally used as conductive adhesives for electronic equipment parts. The adhesive component contains silver particles as conductive noble metal particles and thermosetting resins such as phenol resin and epoxy resin as synthetic resins, but is not suitable for forming wiring as a conductor by printing, such as screen printing. Yes, the specific resistance is not taken into account too much. Conventionally, in general, a hard type such as an epoxy reinforced glass fiber plate is mainly used as a base material.

As a conventional example, see, for example,
No. 658 discloses a conductive adhesive composed of a thermosetting resin and a thermoplastic resin. However, no consideration is given to wiring formation such as printability and electrical resistivity as a conductive material. I see it only from the aspect of the agent.

A conductive paste using a thermosetting resin such as a phenolic resin or an epoxy resin is not considered in terms of printability in the process, and is left at room temperature during printing, resulting in a change in viscosity and unstable viscosity. In particular, fine lines cannot be achieved in the formation of wiring. Further, the specific resistance is as high as about 10 ⁻⁴ Ωcm, and there is a problem that the conductive layer is peeled off from the substrate due to deformation of the base material of some flexible substrates other than the hard type such as an epoxy reinforced glass fiber plate.

On the other hand, a conductive paste using a thermoplastic resin can correspond to a flexible base material, but has a specific resistance of 10 ⁻⁴ Ωc.
In order to obtain a product having a thickness of about m, the drying condition must be set at 150 ° C. for 30 minutes or more, and thus thermal stability becomes a problem. In any case, under the current situation where flake-like silver particles are frequently used as conductive particles, mesh clogging during screen printing is likely to occur.

[0008]

SUMMARY OF THE INVENTION The present invention solves the problems of printability, electrical resistivity, and peeling from a substrate as described above in the prior art, and has a low specific resistance within a short drying time and a screen. It is an object to provide a conductive paste capable of achieving a fine line by printing.

[0009]

[Means for Solving the Problems]

1 A conductive paste comprising conductive noble metal particles, a synthetic resin, and an organic solvent, wherein the conductive noble metal particles comprise a mixture of flake-shaped and spherical silver particles. (2) The conductive paste according to the above (1), wherein the conductive noble metal particles comprise a mixture of flaky silver particles having a particle diameter of 0.2 to 5 μm and spherical silver particles having a particle diameter of 0.2 to 10 μm. 3. The conductive noble metal particle according to any one of the above items 1 and 2, wherein the particle shape is a mixture of silver particles exhibiting a flake shape of 10 to 30 parts by weight and a spherical shape of 30 to 90 parts by weight. Conductive paste. (4) The conductive paste according to the above (1), wherein the synthetic resin is a thermoplastic synthetic resin. (5) The conductive paste as described in any one of (1) and (4) above, wherein the synthetic resin is contained in an amount of 5 to 14 parts by weight based on the conductive noble metal particles. 6. Synthetic resins include polyester resin, acrylic resin,
6. The conductive paste as described in any one of the above items 1 to 4, which is a thermoplastic synthetic resin having a softening point of 180 ° C. or less, such as a cellulose resin.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention particularly relates to a flake silver particle having a conductive noble metal particle having a particle diameter of 0.2 to 5.0 μm,
Fine lines can be formed by screen printing due to the synergistic effect of using a mixture of spherical silver particles of 0.2 to 10 μm and using a thermoplastic synthetic resin as a binder. The silver particles have a particle diameter of 0.2 to 5.0.
The use of a mixture of flakes having a diameter of 0.2 μm and spheres having a diameter of 0.2 to 10 μm increases the degree of filling of the silver particle layer, and the specific resistance after drying at 150 ° C. for 5 minutes is 3 × 10 5
It was possible to achieve ^-5 Ωcm or less.

If the particle size of the flake silver particles is less than 0.2 μm, the resistance increases, and if it exceeds 5.0 μm, the viscosity (fluidity) of the paste becomes unstable and the intended purpose cannot be achieved. On the other hand, if the diameter is less than 0.2 μm, the resistance becomes high, and if it exceeds 10 μm, the screen is clogged, and the object cannot be achieved.

Regarding the mixing ratio of silver particles having different shapes, when the flake-shaped particles are not in the range of 10 to 30 parts by weight and the spherical particles are not in the range of 30 to 90 parts by weight, the following examples and conventional ones are used. The intended purpose of the present invention cannot be achieved with reference to Examples and Comparative Examples.

Next, the present invention will be described in detail with reference to an embodiment.
Examples of the thermoplastic synthetic resin used herein include ethyl cellulose, nitrocellulose, acrylate, methacrylate, and saturated polyester, and examples of the organic solvent include terpineol, butyl carbitol, and diethyl phthalate. Further, the conventional example and the comparative example are prior arts of the present invention.

[0014]

Example 1 Flaky silver particles (particle diameter: 0.2 to 5.0 μm) 20 parts by weight Spherical silver particles (particle diameter: 0.2 to 10 μm) 60 parts by weight Polyester resin 8 parts by weight Organic solvent 12 parts by weight Each component is mixed, mixed and dispersed with a three-roll mill to form a paste, and screen-printed on a PET substrate. Thereafter, the silver particles were dried in a batch dryer at 150 ° C. for 5 minutes, and the specific resistance and printability (line /
(Space 150 μm) was evaluated. The results are shown in Table 1 below.

[0015]

Example 2 Flaky silver particles (particle diameter 0.2 to 5.0 μm) 20 parts by weight Spherical silver particles (particle diameter 0.2 to 10 μm) 60 parts by weight Acrylic ester resin 8 parts by weight Organic solvent 12 parts by weight Except having the above-mentioned composition, all were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0016]

Conventional Example 1 Flaky silver particles (particle size: 0.2 to 5.0 μm) 70 parts by weight Epoxy resin 15 parts by weight Organic solvent 15 parts by weight The same procedure as in Example 1 was carried out except for the above composition. The results are shown in Table 1.

[0017]

Conventional Example 2 Flaky silver particles (particle size: 0.2 to 5.0 μm) 80 parts by weight Phenol resin 8 parts by weight Organic solvent 12 parts by weight The same procedure as in Example 1 was carried out except for the above composition. The results are shown in Table 1.

[0018]

Comparative Example 1 Flaky silver particles (particle diameter: 0.2 to 5.0 μm) 40 parts by weight Spherical silver particles (particle diameter: 0.2 to 10 μm) 40 parts by weight Polyester resin 15 parts by weight Organic solvent 5 parts by weight The above composition Other than that described above, the same procedure was performed as in Example 1. The results are shown in Table 1.

[0019]

Comparative Example 2 Flaky silver particles (particle diameter 0.2 to 5.0 μm) 20 parts by weight Spherical silver particles (particle diameter 0.2 to 10 μm) 60 parts by weight Acrylic ester resin 4 parts by weight Organic solvent 16 parts by weight Except having the above-mentioned composition, all were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0020]

[Table 1] * The resistance was measured by engraving a groove in the substrate

The bending resistance of the substrate was also evaluated. When the conventional thermosetting resin was used, the silver particle film was easily peeled off from the substrate. Also, when a thermoplastic resin was used, if the content thereof was small, the resin was easily peeled, and the suppression of the resistance value could not be expected. When a polyester resin or an acrylate resin is used as the thermoplastic resin, if the softening point is not 180 ° C. or less, the compactness of the silver particle film is low when dried at 150 ° C. for a short time. It became.

[0022]

As described in detail above, the particle size of silver particles in the conductive paste is 0.2 to 5.
By mixing and using 0 μm and spherical particles at a ratio of 0.2 to 10 μm, the drying condition of the paste is 150 ° C.
After drying for 5 minutes, a silver particle film having a specific resistance of 3 × 10 ⁻⁵ Ωcm or less can be obtained. In addition, since the use ratio of spherical particles to flake particle particles is increased, the denseness and printability of the silver particle film can be improved, and the use of a thermoplastic resin as an adhesive is possible. An excellent function and effect is obtained, such as a flexible conductive film without peeling of the conductive film printed on the flexible substrate.

Claims (6)

[Claims] 1. A conductive paste comprising conductive noble metal particles, a synthetic resin, and an organic solvent, wherein the conductive noble metal particles comprise a mixture of flake-shaped and spherical silver particles. 2. The conductive noble metal particles have a particle size of 0.2 to 0.2.
2. The conductive paste according to claim 1, comprising a mixture of 5 [mu] m flakes and 0.2 to 10 [mu] m spherical silver particles. 3. The conductive noble metal particles have a particle shape of 10 to 10.
3. A mixture of 30 parts by weight of flake-like silver particles and 30 to 90 parts by weight of spherical silver particles.
And the conductive paste according to any one of 2. 4. The conductive paste according to claim 1, wherein the synthetic resin is a thermoplastic synthetic resin. 5. The conductive paste according to claim 1, wherein the synthetic resin contains 5 to 14 parts by weight based on the conductive noble metal particles. 6. The synthetic resin according to claim 1, wherein the synthetic resin is a thermoplastic synthetic resin having a softening point of 180 ° C. or less, such as a polyester resin, an acrylic resin, and a cellulosic resin. The conductive paste as described in the above.