JPS63239707A - Conductive composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a conductive composition used in conductive ink or conductive paint used in the production of electric circuits, etc.

(Prior art and problems) Carbon-based materials have been widely used as conductive materials that have shown superior reliability, but their area resistance is higher than that of metal-based materials, so the range of use is limited. It has the disadvantage of being limited.

When a conductive resin film composed of a conductive filler such as carbon black or graphite powder and a binder made of resin is formed on a substrate, the relationship between the proportion of the conductive filler and the sheet resistance value is generally A shown in Figure 1. (carbon black) and B (graphite powder). The horizontal axis indicates the conductive filler content in the total amount of conductive filler and resin solid content. As the proportion of the conductive filler increases, as shown in A and B in the figure, the sheet resistance value decreases and reaches a minimum region. For example, it shows a minimum value of about 15 to 20 Ω/mouth at a film thickness of 25 μm. In this state, the binder resin is insufficient, resulting in poor adhesion between the conductive filler layers.

If the proportion of conductive filler is further increased, the adhesion between the layers becomes worse, and the adhesion between the substrate and the resin film becomes worse.
The sheet resistance value increases.

Various attempts have been made to reduce the resistance value by increasing the packing density of conductive fillers. For example, the packing density has been improved by combining conductive fillers with different particle sizes: large, medium, and small. Ta.

However, since the contact resistance between each filler particle increases, a sheet resistance value lower than about 15 to 20 Ω/4 has not been achieved.

If a conductive filler with a large particle size is used, it is possible to reduce the resistance value to some extent, but on the other hand, the smoothness of the film and the precision of circuit printing are impaired, which limits the use of the filler.

(Purpose of the Invention) The inventors have conducted extensive studies with the aim of overcoming the above-mentioned drawbacks and finding a screen-printable carbon-based conductive filler that has excellent adhesion and flexibility and has a sufficiently low sheet resistance value. . As a result, they discovered that the above object could be fully achieved by using expanded graphite, and completed the present invention.

(Structure of the Invention) The present invention is a conductive composition characterized by containing expanded graphite and a carbon-based conductive filler such as carbon black and/or graphite powder.

That is, the conductive composition of the present invention includes conductive fillers and binders such as carbon black and graphite powder.

It has a structure in which expanded graphite is added to conventional carbon-based conductive compositions such as additives and solvents.

The expanded graphite used in the present invention can be produced by various methods. For example, natural scaly graphite with a well-developed layered structure is pulverized to a particle size of 5 μm or less, thoroughly impregnated with sulfuric acid solution, and then rapidly heated to 900 to 1100°C to expand and perpendicular to the layers. It is obtained by elongation in the C-axis direction. In addition, various compounds have been introduced into the interlayers of graphite under appropriate conditions and bonded to carbon atoms, resulting in rapid thermal expansion of the resulting graphite intercalation compound as described above.

The expansion ratio is generally 10 times or more, preferably 50 times or more. An example of expanded graphite is shown in FIG.

Carbon black and/or graphite powder, etc. are added as the carbon-based conductive filler of the present invention.

These particles have a diameter of 2 μm or less.

If the particle size exceeds 2 μm, high conductivity cannot be obtained.

The amount of expanded graphite used is usually 10 to 90% by weight, preferably 20 to 80% by weight of the total conductive filler, depending on the application. If it is less than 10% by weight or more than 90% by weight, high conductivity cannot be obtained.

In the present invention, conventional binders are used. Examples of resins include alkyd resins, phenolic resins, amine resins, aminoalkyd resins, unsaturated polyester resins, epoxy resins, polyurethane resins, and chlorinated rubber.

Acrylic resin, diallyl phthalate resin, vinyl chloride resin, vinyl acetate resin, nitrocellulose.

Examples include acetylcellulose and saturated polyester resin. Vinyl or allyl nail nails are used in combination with these, if necessary. Furthermore, elastomer-based materials can also be used if necessary. Additives include conductive filler dispersant and leveling agent.

Other various compounding agents used in the technical field may be used as necessary. The curing agent is appropriately selected depending on the type of binder used.

When the binder is a resin, the blending amount of the binder may be 25 to 85% by weight of the total amount as resin solid content. If it exceeds 85% by weight, sufficient conductivity cannot be obtained.

Conversely, if it is less than 25% by weight, the adhesion strength of the conductive filler is insufficient. The solvents are carpitol acetate, butyl cellosolve, cyclohexanone, and xylene.

Diacetone alcohol, ethyl cellosolve, butyl cellosolve, etc. are appropriately selected depending on the solubility, leveling property, adhesiveness, workability, etc. of the resin used. The amount of solvent used is adjusted depending on the application so that the viscosity of the composition is 100 to 400 poise.

For example, a conductive paste is produced using the conductive composition of the present invention as follows.

A predetermined amount of a solvent, a dispersant, a leveling agent, etc. is added to the binder resin in the chamber of a premixer and thoroughly stirred, and then a conductive filler such as carbon black or graphite powder is added and thoroughly stirred.

About 60% of the predetermined amount of expanded graphite is further added to this and thoroughly stirred. The resulting paste is kneaded using a roll mill.

Next, this is returned to the original premixer container, the remaining amount of expanded graphite is added, and after thorough stirring, kneading is carried out in a roll mill.

Next, the gap is sufficiently squeezed and kneaded further to create a paste. Ball mill instead of roll mill.

Ultrasonic dispersers and mixers for high viscosity can also be used.

An example of a screen ink prepared by dispersing expanded graphite and phenol resin is shown in FIG. 1C. The horizontal axis is the expanded graphite content (%) in the total amount of expanded graphite and resin solid content.
It shows. Compared to the case of using a carbon-based conductive filler such as carbon black or graphite powder (see A and B in Figure 1), the content range is 15 to 75%, which is a wide range of 15 to 2.
It can be seen that the same result as the conventional best resistance value of 0Ω/mouth was obtained. Compositions using expanded graphite have low contact resistance, large contact area, and can have extremely high packing density. The expanded graphite shown in FIG. 2 becomes a flat, flexible filler with a small thickness and a large particle size as shown in FIG. 3 as a result of crosstalk in a roll mill or the like. For example, it is possible to have a thickness of about 0.3 μm and a maximum particle size of 30 μm.

It is thought that the synergistic effect of the flat particles of expanded graphite and the conductive filler such as fine particles of carbon black allows the conductive composition of the present invention to achieve high conductivity of, for example, 10 Ω/mouth or less.

Add 2 more carbon blacks to expanded graphite and phenolic resin.
D of FIG. 1 shows an example of a screen ink that was prepared by adding % of the ink and dispersing it. The horizontal axis shows the total conductive filler content in the total amount. It shows high conductivity over a wide content range.

In order to create a resin film using the conductive composition of the present invention, various conventional methods such as screen printing, metal mask method, spraying method, two-reverse printing method, etc. can be used.

(Effects of the invention) 1. The conductive film using the expanded graphite of the present invention and other carbon-based conductive fillers has a smaller film thickness and extremely low resistance value than when using conventional carbon-based conductive fillers. It is possible to stably obtain

2. Expanded graphite itself shows low resistance in the planar direction and high resistance in the thickness direction, but by adding other carbon-based conductive fillers in the form of fine particles, the resistance in the thickness direction is improved and the overall conductivity is high. Show your gender.

3. Expanded graphite is loosened by dispersing it in a roll mill, for example, with a thickness of about 0.3 μm and a maximum particle size of 30 μm.
screen printing (150 mesh products) is possible.

4. Expanded graphite is stretched using a roll mill, so it can be given flexibility.

5. Expanded graphite is dispersed in a roll mill to form flat particles, and when applied to a substrate, the gap between the particles and the substrate becomes smaller. As a result, it exhibits sufficient adhesion with a smaller amount of binder than conventional carbon resin films. Furthermore, since the resistance value does not increase even if the binder amount is increased, the properties of the resin serving as the binder are exhibited.

For example, when a flexible resin is used as a binder, a greater amount of binder can be added than before without increasing the resistance value, resulting in a flexibility effect.

6. As a result of the present invention, the properties of the carbon-based conductive composition have been greatly improved, and as a result, its uses have increased dramatically. In particular, as a result of the development of an IC that operates even when the impedance of a conductive circuit is high, it has become possible to form a conductive circuit using the carbon resin film of the present invention.

In addition, it can be easily used for resistor two-sided heating elements, etc., which have been widely used as conventional carbon resin coatings.

This will be explained in more detail below with reference to Examples. The middle part of the example is based on weight.

Example 1 Expanded graphite (manufactured by Nippon Carbon Co., Ltd.) 65 parts Ketjenblack EC (manufactured by Lion Akzo Co., Ltd.) 35 Xylene resin (rPR-1440MJ made by Mitsubishi Gas Chemical Co., Ltd.) 300 Calpitol acetate 300 Dispersant ([Aramide OFJ made by Lion Akzo Co., Ltd.) ) 1 After sufficiently dispersing the above compound in a roll mill, it was mixed with a Bakelite plate (
It was printed with a 150-mesh screen to a size of 60 x 150 mm and dried in an oven at 150°C for 60 minutes. The area resistance value of this resin film is 6Ω/mouth (film thickness 2
0 μm). The adhesion of the film to the Bakelite plate was sufficient.

Comparative Example 1 Scale graphite (NC-1 manufactured by Nippon Crucible Co., Ltd.) 40 parts Artificial graphite (AF-40 manufactured by Oriental Carbon Co., Ltd.) 35 Ketjenblack EC (manufactured by Lion Akzo Co., Ltd.) 25 Saturated polyester (Byron 200 manufactured by Toyobo Co., Ltd.) io.

Carpitol acetate dispersant (Aramide OFJ, manufactured by Lion Akzo) 1 The above compound was thoroughly mixed in a premixer and passed through a roll mill 4 times to prepare a carbon paste.

The paste was printed on a Bakelite plate with a 150 mesh screen and dried in an oven at 150° C. for 60 minutes. The sheet resistance value of this resin film was 30Ω/hole (film thickness 25 μm).

Example 2 Expanded graphite (manufactured by Toyo Tanso Co., Ltd.) 65 parts Ketjenblack EC (manufactured by Lion Akzo Co., Ltd.) 35 Polyurethane (rtJcX904 J manufactured by Asahi Denka Co., Ltd.) 5
00 Dispersant (Armord OFJ, manufactured by Lion Akzo Co., Ltd.) 1 After sufficiently dispersing the above compound using a roll mill, it was printed on a 38 μm thick polyester film with a 150 mesh screen, and dried in an oven for 150 minutes. CX was dried for 60 minutes.The area resistance value of this resin film was 9Ω/mouth (film thickness 15μ).
m), the rate of change in resistance value due to bending was as small as 4.2%, and the tightness and flexibility with respect to the polynisder film were sufficiently maintained.

Example 3 A liquid B liquid Expanded graphite (manufactured by Toyo Tanso Co., Ltd.) 40 parts Ketjenblack EC (manufactured by Lion Akzo Co., Ltd.) 1010 7 Dekaspack S A-200 (manufactured by Asahi Denka Co., Ltd.) 250 - Azokasback SB-70 (manufactured by Asahi Denka Co., Ltd.) (manufactured by Asahi Denka) - 250 diluent sc-i (manufactured by Asahi Denka) 200 200
Dispersant ([Aramide OFJ, manufactured by Lion Akzo Co., Ltd.) 22 Two-component urethane paints A and B having the above composition were each prepared in a ball mill, and 100 parts of A and 21 parts of B were mixed to form ABS.
A plate (size: 150 x 50 x 3 mm) was sprayed with spray=.

The area resistance value of a sample of length 200 x width 10 mm is 2
, 4Ω/mouth (film thickness 36 μm). The shielding characteristics for magnetic field waves and electric field waves are measured using a shielding effectiveness evaluator ( rT
The results of the physical measurements were as shown in FIG. 4. High temperature storage 60'C X1500
The rate of change in resistance value after hours was -14%. Leave humidified 6
0°C x 95%RH x 1000 hours resistance change rate is +
It was 8.5%. Since there is little change in resistance value, it can also be used for electromagnetic shielding.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the conductive filler content of the conductive composition and the resistance value. FIG. 2 is an enlarged schematic diagram of expanded graphite, FIG. 3 is a dispersion state diagram of expanded graphite, and FIG. 4 is a shielding characteristic diagram. In Figure 1, A... Carbon black B... Graphite powder C... Expanded graphite

Claims (1)

[Claims] A conductive composition comprising expanded graphite and a carbon-based conductive filler such as carbon black and/or graphite powder.