JPH09255900A - Thermosetting type carbon-based electroconductive coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject coating material useful for a printed circuit board with a carbon coated film, excellent in adhesivity, electrical conductivity, high-temperature stability of electrical conductivity, etc., by dispersing specific carbonaceous powder to a solution of a prescribed titonte-based coupling agent. SOLUTION: The coating material is obtained by dispersing (B) 30wt.% of carbonaceous powder as electroconductive particles composed of 12-18wt.% of natural flaky graphite having 10-30μm average particle diameter and 12-18wt.% carbon black to (A) a solution prepared by dissolving (A1 ) 0.7-2.5wt.% of a titanbate-based coupling agent composed of 25-30 wt.% of a resol type phenol resin having 3-10wt.% of a free phenol based on a resin in a nonvolatile component at 180 deg.C, 0.6-1.8wt.% of a polyvinyl butyral resin composed of >=60wt.% of a polyvinyl butyral resin having 1,000-1,800 degree of polymerization and an organotitanium compound in (A2 ) a solvent composed of butyl celloslove, butyl barbital (acetate) or its mixture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosetting carbon-based conductive paint for forming a printed conductive circuit of a printed circuit board.

[0002]

2. Description of the Related Art Conductive paints that are printed on substrates such as paper phenolic laminates and polyester films to form circuits are
Conductive particles are dispersed in an organic solvent with a dispersant as a main component of conductive particles such as metal or carbonaceous powder and a thermosetting resin as a binder and an organic solvent as a coating solvent. For example, Japanese Examined Patent Publication No. 60-58268 discloses a conductive copper paste containing copper powder, a thermosetting resin, an unsaturated fatty acid and an organic titanium compound.

However, as a conductive paint for a printed circuit board, a carbon-based paint using a carbonaceous powder is used rather than a paint using metallic conductive particles of copper or silver from the viewpoint of cost and migration. Many. That is, in comparison with metallic powders of noble metals and base metals such as silver and copper as conductive particles, carbonaceous powders such as graphite and carbon black are lower in price, and in printed circuit boards using a conductive coating of copper. , Because copper is easily oxidized,
A special anti-oxidation treatment needs to be applied to the formed copper printed conductive circuit coating. Further, in a printed circuit board using silver as a metallic powder, which has a remarkable migration due to electrochemical metal corrosion, a protective film is formed to prevent moisture and a halogen substance from contacting the formed film of the printed conductive circuit of silver. In the case of a coating material using metallic conductive particles, it is necessary to form a resistant coating film, which increases the cost of the circuit board as a product.

Furthermore, in recent years, even in the case of carbon-based conductive paints, the resistance value of the printed conductive circuit film formed has been reduced, and the sheet resistance value showing the conductivity of this kind of film is 3%.
Paints of about 0 to 50Ω / □ are commercially available. Such a carbon-based conductive coating material contains conductive particles made of carbonaceous powder such as graphite and carbon black, and a thermosetting resin such as phenol resin in a ratio of 1 to 1.5: 1, and butyl cellosolve or butyl carbitol. Conductive particles of carbonaceous powder are dispersed by using an ethylene glycol organic solvent such as butyl carbitol acetate as a solvent. Screen-print this paint on a printed circuit board, and at a temperature of 160 ° C or less to prevent deterioration of the board,
A heat-curing treatment is applied for 5 to 30 minutes to form a film of a printed conductive circuit on the substrate.

Subsequent substrate manufacturing processes include a soldering process and a hot water cleaning process. However, in the current commercial paint, a large increase / decrease in electric resistance value of about ± 20 to 100% occurs during these processes. However, there is a problem that the electric resistance value at the time of circuit design is not satisfied. This is because phenomena such as generation of cracks inside the printed conductive circuit coating, contraction of the coating, change in distribution of conductive particles, and modification of the material forming the coating of the printed conductive circuit are complicated.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention improves the electrical resistance of a printed conductive circuit coating formed from a carbon-based conductive paint by improving the composition of the paint material. It is something that we try to suppress.

[0007]

A thermosetting carbon type conductive coating material of the present invention is a solution of a titanate coupling agent composed of a resol type phenol resin, polyvinyl butyral and an organic titanium compound in a coating solvent. In a thermosetting carbon-based conductive paint in which carbonaceous powder of graphite and carbon black is dispersed as conductive particles,
(A) 30% by weight of carbonaceous powder consisting of 12 to 18% by weight of the graphite and 12 to 18% by weight of carbon black, 25 to 30% by weight of the resol type phenol resin, 0.6 to 1.8% by weight of the polyvinyl butyral resin. %, A titanate-based coupling agent consisting of the above-mentioned organic titanium compound.
The composition contains 7 to 2.5% by weight, and the balance of the coating solvent consisting of an organic solvent of a single or a mixture selected from butyl cellosolve, butyl carbitol and butyl carbitol acetate. Further, (b) the amount of free phenol in the nonvolatile content of the resol-type phenol resin at 180 ° C. is 3 to 10% by weight based on the resol-type phenol resin, and (c) the carbonaceous powder graphite is natural. Of phosphorus-like or flaky graphite particles having an average particle diameter of 10 to 30 μm,
(D) The polyvinyl butyral resin has a degree of polymerization of 10
It is characterized by containing 60% by weight or more in the range of 00 to 1800.

The present invention is achieved by the above configuration.
That is, it is preferable to use, as the graphite particles of the carbonaceous powder as the conductive particles, natural phosphorous or flaky graphite particles having a high crystallinity because a printed conductive circuit film having a low electric resistance value can be obtained. Natural graphite is classified into flake-like, phosphorus-like, and earth-like graphite according to the difference in crystallinity. Natural graphite suitable for this invention is a flake-like graphite that is closest to the crystallinity of true graphite. Graphite and phosphorous graphite having the next highest degree of crystallinity. The average particle size of the graphite particles is preferably in the range of 10 to 30 μm. When the average particle diameter is less than 10 μm, the contact resistance between particles becomes large and the electric resistance value of the printed conductive circuit film becomes high. Further, if the temperature of the thermosetting process for obtaining the printed conductive circuit is made higher than 150 ° C., the change rate of the electric resistance value becomes large. This is because the particles in the coating are in a filling state in which migration easily occurs. Also, when the average particle diameter of the graphite particles exceeds 30 μm, the filling rate of the conductive particles in the printed conductive circuit coating decreases, the electric resistance of the conductive coating increases, and the rate of change of the electric resistance increases. Furthermore, this type of conductive paint is mainly transferred to the printed substrate by screen printing,
Since the film of the printed conductive circuit is formed by heat curing, the maximum particle size of the graphite particles contained is 90 μm or less, which is smaller than the opening size of the screen mesh, from the viewpoint of preventing clogging of the screen mesh used for screen printing. It is necessary.

Since the carbon black particles are finer than the graphite particles, the combined use of the graphite particles as the conductive particles of the carbonaceous powder improves the packing state of the particles as compared with the case where only the graphite particles are used, and the obtained printed conductive particles can be obtained. The electric resistance of the coating is reduced. Among several types of carbon black, the one suitable for the conductive coating is acetylene black for conductivity. The blending weight ratio of graphite and carbon black is preferably graphite / carbon black = 40/60 to 60/40.
That is, when the amount of conductive particles in the coating material is 30% by weight, the amount of graphite particles is 12 to 18% by weight and the amount of carbon black particles is 12 to 18% by weight. This blending ratio is determined from the packed state of the particles described above. When the average particle size of the graphite particles is coarse and about 30 μm, the intergranular volume between the graphite particles is large, so that it is necessary to fill the intergranular spaces. The amount of carbon black increases. On the other hand, when the average particle size of the graphite particles is fine and is about 10 μm, the interparticle volume between the graphite particles is small, so that the amount of carbon black required to fill the intergranular particles is small. When the average particle diameter of the graphite particles is small, if the carbon black is added in an excessively large amount, the contact resistance between the particles will increase and the electrical resistance value will increase.

The dispersion state of the conductive particles in the coating material is closely related to the rate of change of the electric resistance value of the obtained printed conductive circuit film, and the better the dispersion state of the conductive particles in the coating material,
The rate of change of the electric resistance value becomes small. In order to improve the dispersed state of the conductive particles, it is desirable to use a polyvinyl butyral (hereinafter referred to as “PVB”) resin and a titanate coupling agent composed of an organic titanium compound in combination. Further, these materials can impart flexibility to the coating film of the printed conductive circuit obtained by thermosetting the coating material, so that the stress due to thermal shock is relieved and the change in electric resistance value is suppressed. Indicates. Among these, the amount of the PVB resin compounded is appropriately 2 to 6% by weight, preferably 3 to 5% by weight, more preferably 4% by weight based on the conductive particles of the carbonaceous powder.
% By weight. These values represent the amount of conductive particles in the paint to 3
Expressed as 0% by weight, the composition of the entire coating composition is 0.6 to 1.8% by weight, 0.9 to 1.5% by weight, and 1.
It becomes 2% by weight. When the PVB resin is less than 2% by weight with respect to the amount of conductive particles, the obtained printed conductive circuit coating has a high electric resistance value and a large change rate of the electric resistance value. This is because the conductive particles are not well dispersed in the paint, and the resulting printed conductive circuit coating does not have sufficient flexibility. On the other hand, if it exceeds 6% by weight, the electric resistance value of the obtained printed conductive circuit film is high and the rate of change of the electric resistance value is large. This is because the amount of resin coated on the carbonaceous conductive particles is large, and the influence of thermal denaturation, which is a characteristic of thermoplastic resins such as PVB resin, cannot be ignored.

PVB resin is a thermoplastic synthetic resin,
They are marketed by grade according to the difference in molecular weight, that is, the degree of polymerization. PVB blended with the conductive paint of this invention
As the resin, a single resin having a certain degree of polymerization may be used alone, or PVB resins having different degrees of polymerization may be appropriately mixed and used, but those having a degree of polymerization of 1000 to 1800 may be used as PVB. It is preferable to contain at least 60% by weight or more of the entire resin. When a low molecular weight PVB resin is used, the amount of conductive particles of carbonaceous powder coated increases, and the electrical resistance value of the resulting printed conductive circuit coating increases. In addition, the lower the molecular weight of the thermoplastic resin, the more easily it is subject to thermal denaturation, so that the rate of change of the electric resistance value increases. When a high molecular weight PVB resin is used, the dispersed state of the carbonaceous powder conductive particles, especially the graphite particles, deteriorates, and the electric resistance value of the obtained printed conductive circuit coating increases.

The titanate coupling agent used with the PVB resin is preferably an organic titanium compound having a benzene ring on the hydrophobic group side, and the compounding amount is 6 to 14% by weight based on the carbon black of the carbonaceous conductive particles. It is more preferably 8 to 12% by weight, and the most suitable amount is 10% by weight. This value is 12 ~ for carbon black
Expressed in terms of the composition of the entire 18% by weight blended material, it is 0.7 to 2.5% by weight, 1.0 to 2.2% by weight and 1.
It becomes 2 to 1.8% by weight. If the amount of the titanate coupling agent blended with the carbon black is less than 6% by weight, the change rate of the electric resistance value is large. This is because it is difficult to obtain a good dispersed state of carbon black in the coating material, and flexibility is not given to the film of the printed conductive circuit to be formed. On the other hand, the amount of titanate coupling agent to carbon black is 1
If it exceeds 4% by weight, the amount of coating on the carbonaceous conductive particles increases and the electric resistance value of the printed conductive circuit coating increases, which is not preferable. Furthermore, since the boiling point of the titanate-based coupling agent is 250 ° C. or higher, not only in the thermosetting process for obtaining the film of the printed conductive circuit, but also in the temperature range of the substrate manufacturing process such as the soldering process or the hot water washing process. It is in a liquid state. Therefore, in the case of a coating material containing a large amount of a titanate-based coupling agent, the heat history described above causes the adhesion of the formed printed conductive circuit coating to be significantly deteriorated.

As the organic solvent used as a solvent for the conductive paint, ethylene glycol butyl cellosolve, butyl carbitol or butyl carbitol acetate, which is a general solvent for this type of paint, may be used alone or in combination. Is appropriate. It is required that the solvent does not dry on the plate during screen printing, does not generate a peculiar irritating odor, and that the coating solvent does not remain inside the printed conductive film after the thermosetting process. However, the above solvents satisfy these conditions.

In the resol type phenol resin used in the present invention, at least about 2% of free phenol, which is usually used as a raw material for the phenol resin, remains. Since the boiling point of this free phenol is about 180 ° C., even if the heat curing treatment is carried out at a temperature of 160 ° C. or lower for heat curing the coating film,
Remains inside the printed conductive circuit coating. In this state, when exposed to an atmosphere of a temperature of 250 ° C. or higher as in the soldering process in the circuit board manufacturing process, the free phenol is rapidly volatilized to cause a crack in the coating film of the printed conductive circuit, which causes a change in the electric resistance value. Therefore, in the analysis of non-volatile matter at 180 ° C, it is desirable that the content of free phenol in the non-volatile matter is as low as possible, but 10 wt%
If it is below, even if it remains in the film of the printed conductive circuit, it does not have a great influence. It is one of the requirements for achieving the object of the present invention to use the phenol resin in which the content of the free phenol in the nonvolatile matter at 180 ° C is limited.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION 30% by weight of carbonaceous powder consisting of 12 to 18% by weight of natural phosphorus-like or scaly graphite having an average particle size of 10 to 30 μm and 12 to 18% by weight of carbon black, and nonvolatile at 180 ° C. The amount of free phenol in the fraction is 3 to 1 with respect to the resol type phenol resin.
25% to 30% by weight of resol type phenolic resin of 0% by weight, 0.6% to 1.8% by weight of polyvinyl butyral resin having a polymerization degree of 1000 to 1800 and more than 60% by weight, and a titanate coupling composed of an organic titanium compound. 0.7-2.5% by weight of the agent, and butyl cellosolve,
A thermosetting carbon-based conductive paint obtained by thoroughly mixing and kneading a raw material containing as a residual amount a paint solvent consisting of a single or mixed organic solvent selected from butyl carbitol and butyl carbitol acetate. The film of the printed conductive circuit obtained by using it has sufficient adhesion to the printed circuit board and has good electrical characteristics.

[0016]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples shown in Tables 1 to 4.

[Preparation of Paint] The samples of Examples and Comparative Examples were thoroughly mixed by a liquor machine, and then the mixture was sufficiently kneaded by a three-roll mill to prepare a paint, which was used for the study. Here, if the mixing and kneading are insufficient, the change rate of the electric resistance value of the obtained printed conductive circuit coating becomes large, so that care must be taken.

[Preparation of Sample] Using various paints prepared as described above, a solid surface pattern having a length of 50 mm and a width of 10 mm was printed on a printed circuit board by a screen printing machine, and after leveling, 150 A heat curing treatment was performed at 15 ° C. for 15 minutes.

[Evaluation of Samples] (1) Sheet Resistance Value The electric resistance value of the film of the printed conductive circuit formed by the above method was measured by the 2-short needle method, and the electric resistance value (R ₀ at the time of forming the printed conductive circuit film) was measured. ). The sheet resistance value (R _S ) was calculated from the measured electrical resistance value of this solid surface pattern by the following formula.

[0020]

[Equation 1]

Usually, in this calculation formula, it is necessary to consider the thickness of the coating of the printed conductive circuit, but the thickness of the printed conductive circuit coating formed by the paint described as the working sample and the comparative sample in the present invention is Since all were in the range of 19 to 21 μm, the comparison was performed without correcting the film thickness.

(2) Rate of change in resistance value Further, after the sample was immersed in a solder bath at 260 ° C. for 5 seconds, the electric resistance value was measured again to obtain the rate of change in the electric resistance value. The rate of change (ΔR) of the electric resistance value was calculated from the electric resistance value (R ₀ ) at the time of forming the film of the printed conductive circuit and the electric resistance value (R) after receiving heat by the following formula.

[0023]

[Equation 2]

(3) Adhesion In order to judge the adhesion state of the formed printed conductive film to the printed circuit board, the cellophane tape is attached to the solid surface pattern and then peeled off to check the adhesion state of the film to the cellophane tape. I observed.

<Example 1> (Examples 1 to 4 and comparative samples 1 to 3) -Regarding properties of graphite-Acetylene black was used as carbon black, and the compounding ratio of graphite and carbon black was 50/50.
PVB resin with a degree of polymerization of 1000 (manufactured by Sekisui Chemical Co., Ltd.,
Trade name: S-REC BH-S) 4% by weight with respect to conductive particles (graphite and carbon black), titanate coupling agent (manufactured by Ajinomoto Co., Inc., trade name: Planeact K)
R9SA) was blended in an amount of 10% by weight with respect to carbon black. Further, a resol-type phenol resin having a free phenol content of 4% by weight in a nonvolatile content at 180 ° C. was added so as to have the same weight as the conductive particles, and butyl cellosolve was added so as to be 30% by weight of the whole, and Conductive paints having different graphite properties were prepared according to the preparation method, and samples were prepared using the conductive paints. Table 1 shows the properties of graphite and the characteristic evaluation results of the printed conductive circuit coatings obtained from the coating materials prepared from the respective graphites.

[0026]

[Table 1]

Phosphorous or scaly graphite particles having an average particle diameter of 10 to 30 μm (conductive sample 1
The sheet resistance value of the printed conductive circuit coating obtained from 4) is 3
It is 0 Ω / □ or less, and the rate of change in electric resistance value is also within ± 10%. In contrast, if the average particle size of the phosphorous graphite particles is less than 10 μm (Comparative Sample 1), the sheet resistance value of the obtained printed conductive circuit coating is as high as 35 Ω / □, The rate of change is also large at 15%. This is because the graphite particles have a small particle diameter, so that the contact resistance between the conductive particles becomes large, and further, the conductive particles easily move when contacting with a high temperature atmosphere. The average particle size is 30μ
The sheet resistance value was as high as 32 Ω / □ even in Comparative Sample 2 of 40 μm larger than m, and the change rate of the electric resistance value was −.
It is as large as 25%. This is because the filling rate of the conductive particles in the printed conductive circuit coating is low and the coating shrinks when immersed in a solder bath. Further, even if the average particle diameter is 20 μm, the comparative sample 3 using the earth-like graphite has a sheet resistance value of 72 Ω / □, and the electric conductivity of the coating film is poor. This is because graphite having a low crystallinity, such as soil, has a high specific electric resistance, so that the electric resistance value of the obtained printed conductive circuit coating also becomes high.

<Example 2> (Examples 5 to 7 and comparative samples 4 to 5) -Regarding the compounding ratio of graphite and carbon black-Natural phosphorus-like graphite having an average particle size of 16 μm was used as graphite. Regarding materials, coating materials having different blending ratios of graphite and carbon black were prepared in the same manner as in Example 1, and samples were prepared using the coating materials. Table 2 shows the examined blending ratios of graphite and carbon black, and the characteristic evaluation results of the printed conductive circuit coatings obtained from the coating materials prepared by the respective blending ratios.

[0029]

[Table 2]

The blending ratio of graphite and carbon black is 4
The sheet resistance value of the printed conductive coating obtained from the conductive paint in the range of 0/60 to 60/40 (Examples 5 to 7) is 3
It is 0 Ω / □ or less, and the rate of change in electric resistance value is also within ± 10%. On the other hand, in Comparative Sample 4 (graphite / carbon black = 30/70) in which the blending ratio of graphite was low, the sheet resistance value was 40Ω / □, and the change rate of the electric resistance value was 40%, which is high. In the case of graphite / carbon black = 30/70, the amount of fine particles in the carbonaceous powder which is the conductive particles is large, the contact resistance between the conductive particles is increased and the electric resistance value is increased. Since the conductive particles easily move, the change in the electric resistance value increases. On the other hand, in the case of Comparative Sample 5 (graphite / carbon black = 70/30) in which the blending ratio of graphite is high, the sheet resistance value is low, but the change rate of the electric resistance value is large. This is because the filling rate of the conductive particles is low as in the comparative sample 2 of Example 1, and the printed conductive circuit coating shrinks due to heat.

<Example 3> (Examples 8 to 12 and comparative samples 6 to 7) -Regarding compounding amount of PVB (polyvinyl butyral) resin-Natural phosphorus-like graphite having an average particle size of 16 μm was used as graphite. For other materials, as in Example 1, P
A coating material having different VB resin compounding amounts was prepared, and this was used to prepare a sample. Table 3 shows the blended amount of the PVB resin examined (with respect to the carbonaceous powder) and the characteristic evaluation result of the printed conductive circuit coating film obtained from the coating material prepared according to each blended amount.

[0032]

[Table 3]

A sheet resistance value of a printed conductive coating film obtained from a conductive coating material (working samples 8 to 12) containing PVB resin in an amount of 2 to 6% by weight with respect to carbonaceous powder as conductive particles is 30 Ω /. □ or less, the rate of change in electrical resistance is ± 10
%. On the other hand, in Comparative Sample 6 having a PVB content of 1% by weight, the conductive particles, particularly graphite, were not sufficiently dispersed, and the filling state of the particles in the obtained printed conductive circuit coating was poor, resulting in a sheet resistance The value is as high as 55Ω / □. Also,
Since the printed conductive circuit coating does not have flexibility, when immersed in a solder bath, the coating cannot absorb the difference in thermal expansion from the printed circuit board, causing cracks in the coating, and The change in resistance becomes large. On the other hand, PV
In Comparative Sample 7 in which the content of B was more than 6% by weight and 7% by weight, the PVB resin excessively covered the surface of the carbonaceous powder which was the conductive particles, and as a result, the electric resistance value of the obtained printed conductive coating was high. became. Further, since the PVB resin is a thermoplastic resin, it is susceptible to modification by heat at a high temperature, so that the rate of change of the electric resistance value is as large as 35%.

<Example 4> (Examples 13 to 17 and comparative samples 8 to 9) -Regarding compounding amount of titanate coupling agent-Natural phosphorus-like graphite having an average particle size of 16 μm was used as graphite. As for the materials described in (1), in the same manner as in Example 1, coating materials having different titanate coupling agent compounding amounts were prepared, and samples were prepared using the coating materials. Amount of titanate coupling agent studied (against carbon black particles)
Table 4 shows the evaluation results of the characteristics of the printed conductive circuit film obtained from the coating materials prepared with the respective blending amounts.

[0035]

[Table 4]

A conductive coating material containing 6 to 14% by weight of a titanate-based coupling agent composed of an organotitanium compound based on carbon black particles (samples 13 to 1).
The sheet resistance value of the printed conductive film obtained from 7) is 30Ω.
/ □ or less, the rate of change of the electric resistance value is within ± 20%, and the electric resistance of the printed conductive coating film obtained from the conductive paint (implementation samples 14 to 16) in which the compounding amount is 8 to 12% by weight in particular. The rate of change of value is within ± 5%, which is good. When the blending amount is 5% by weight with respect to the carbon black particles (Comparative Sample 8), the sheet resistance value is high and the change rate of the electric resistance value is large. This is because the dispersed state of the carbon black particles is insufficient. On the other hand, if the blending amount exceeds 14% by weight, 1
At 5% by weight (Comparative sample 9), the rate of change in electrical resistance value was the same as that of sample 17, but the sheet resistance value was 40Ω / □.
And the adhesion of the printed conductive coating to the printed circuit board was poor, and the formed coating adhered to the cellophane tape side. This is because the amount of the titanate-based coupling agent is too large, so that the amount of the conductive particles to be coated is large, and even if the heat curing treatment at 150 ° C. is performed to obtain the printed conductive film, the titanate-based coupling agent is contained in the film. This is because the coating of the printed conductive circuit could not be sufficiently cured because the coupling agent remained in a liquid state.

Example 5 (Examples 18 to 21, Comparative Samples 10 to 12) -Polymerization Degree of PVB (Polyvinyl Butyral) Resin-Natural phosphorus-like graphite having an average particle size of 16 μm is used. With respect to the other materials, coating materials were prepared in the same manner as in Example 1 except that the blending amounts of PVB resins having different polymerization degrees were changed, and the coating materials were used to prepare samples. Table 5 shows the blending amounts of the PVB resins having different degrees of polymerization studied and the characteristic evaluation results of the printed conductive circuit coatings obtained from the coating materials prepared with the blending amounts.

[0038]

[Table 5]

The degree of polymerization of the PVB resin to be blended is from 1000 to
1800, and the conductive paint containing the PVB resin in an amount of 60% by weight or more (Examples 18 to 21),
The sheet resistance value of the obtained printed conductive coating is 30 Ω / □ or less, and the rate of change in electric resistance value is also within ± 10%. However, in the conductive paint containing 50% by weight of PVB resin having a degree of polymerization of 1000 and 50% by weight of PVB resin having a degree of polymerization of 800 (Comparative sample 10) and the conductive paint containing only PVB resin having a degree of polymerization of 800 (Comparative sample 11), Sheet resistance is 53
Ω / □ and 97Ω / □, which are high, and the rate of change in electric resistance value is also as large as 85% in Comparative Sample 10. This is because a resin having a low degree of polymerization has many active sites, so that the conductive particles are excessively coated and the electric conductivity of the obtained coating is impaired, and a thermoplastic resin having a low degree of polymerization has poor heat resistance. for,
This is because the electric resistance value is likely to change in a high temperature environment such as immersion in a solder bath. On the other hand, in the conductive paint containing only PVB resin having a degree of polymerization of 2100 (Comparative Sample 12), the dispersibility of the carbonaceous powder as the conductive particles, particularly the graphite particles, is poor, and the sheet resistance value becomes large.

Example 6 (Examples 22 to 25, Comparative Samples 13 to 14) -Amount of Free Phenol in Nonvolatile Content of Resol-Type Phenolic Resin-Graphite is a natural phosphorus-like compound having an average particle size of 16 μm. The same materials as in Example 1 were used for other materials.
A coating material was prepared using resol-type phenol resins having different amounts of free phenol in the non-volatile matter at 80 ° C., and this was used to prepare a sample. Table 6 shows the amount of free phenol examined and the evaluation results of the characteristics of the printed conductive circuit coatings obtained from the respective prepared coatings.

[0041]

[Table 6]

The amount of free phenol in the nonvolatile matter at 180 ° C. with respect to the phenol resin was 2% even after purification.
The degree remains. The amount of this free phenol is 10% by weight
The conductive paints up to (Examples 22 to 25) can suppress the rate of change of the electric resistance value within ± 10%. However, in the conductive paints in which the amount of free phenol exceeds 10% by weight (Comparative Samples 13 and 14), the rate of change in electric resistance value increases. This is because a large amount of free phenol remains in the coating of the printed conductive circuit that is heat-cured at 150 ° C, so the free phenol volatilizes from the coating in a high temperature environment such as when a sample is immersed in a solder bath, and the printed conductive This is because cracks are generated in the film of the circuit and the conductive contact of the conductive particles is broken.

[0043]

EFFECTS OF THE INVENTION Carbonaceous powder 3 comprising 12 to 18% by weight of natural phosphorous or scaly graphite having an average particle size of 10 to 30 μm and 12 to 18% by weight of carbon black.
25 wt% to 30 wt% of resol type phenolic resin whose amount of free phenol in the non-volatile matter at 0 ° C. and 180 ° C. is 10 wt% or less with respect to resol type phenolic resin, and whose polymerization degree is 1000 to 1800 is 60 wt% or more. 0.6 to 1.8% by weight of polyvinyl butyral resin present and a titanate coupling agent comprising an organic titanium compound.
A raw material containing 7 to 2.5% by weight and a coating solvent consisting of a single or a mixture of organic solvents selected from butyl cellosolve, butyl carbitol and butyl carbitol acetate as the balance is thoroughly mixed and kneaded. The obtained thermosetting carbon-based conductive paint is printed on a printed circuit board by a screen printing method, and is subjected to a thermosetting treatment at a temperature of 150 ° C. for at least 10 minutes to have sufficient adhesion to the printed circuit board. A coating of printed conductive circuitry is formed. Further, the sheet resistance value showing the electrical conductivity of this printed conductive circuit coating is 15 to 30.
It has a low value of Ω / □ and is extremely stable with a change rate of electrical resistance of ± 10% or less even in an environment at a temperature higher than the temperature when forming a printed conductive circuit film such as dipping in a solder bath. A printed conductive circuit having electrical properties is obtained. For this reason, it is possible to obtain a printed circuit board with a carbon coating that has little variation in circuit design.

Claims (1)

[Claims] 1. A solution in which a titanate coupling agent comprising a resol type phenol resin, polyvinyl butyral, and an organic titanium compound is dissolved in a coating solvent,
In a thermosetting carbon-based conductive coating in which carbonaceous powder of graphite and carbon black is dispersed as conductive particles,
(A) 30% by weight of carbonaceous powder consisting of 12 to 18% by weight of the graphite and 12 to 18% by weight of carbon black, 25 to 30% by weight of the resol type phenol resin, 0.6 to 1.8% by weight of the polyvinyl butyral resin. %, A titanate-based coupling agent consisting of the above-mentioned organic titanium compound.
7-2.5% by weight and a residual amount of a coating solvent consisting of a single or a mixture of organic solvents selected from butyl cellosolve, butyl carbitol and butyl carbitol acetate, and (b) containing the resol type phenolic resin. The amount of free phenol in the non-volatile matter at 180 ° C. is 3 to 10% by weight with respect to the resol type phenol resin, and (c) the carbonaceous powder graphite is a natural phosphorus-like or scaly graphite particle. And an average particle diameter of 10 to 30 μm, and (d) the polyvinyl butyral resin contains 60% by weight or more of a polyvinyl butyral resin having a degree of polymerization of 1000 to 1800. Carbon conductive paint.