JPH05217422A - Conductive paste and conductive coating - Google Patents

Abstract

PURPOSE:To improve the environmental stability and printing characteristic of a conductive paste to a large degree, and to provide the conductive paste that has an excellent feature in every aspect by improving adhesion without reducing conductivity by using benzoic acid and/or its derivative. CONSTITUTION:In a conductive paste including conductive powder, an organic binder, an additive, and a solvent, a thermosettimg resin is an essential component for an organic binder of the conductive paste, while benzoic acid indicated by a formula I and/or its derivative are included as the additive. The conductive paste is applied on a basic material as a conductive coating, or it is hardened after printing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste containing an organic material as a binder and a conductive coating film using this conductive paste. More specifically, it is more suitable for paper / phenol resin substrates, glass / epoxy resin substrates, etc. By coating on a circuit board by screen printing, etc., and then heating and curing, a conductive coating film with excellent conductivity, adhesiveness, and printability is formed to prevent electromagnetic noise from the circuit board or wiring of the circuit board. TECHNICAL FIELD The present invention relates to a conductive paste suitable for use as a conductor or the like, and a conductive coating film obtained by coating or printing the conductive paste and curing the conductive paste.

[0002]

2. Description of the Related Art Generally, a conductive paste is basically composed of an organic binder such as epoxy resin, saturated polyester resin, acrylic resin, phenol resin, amino resin (hereinafter sometimes abbreviated as a binder), a conductive powder and a solvent. Is configured. This conductive paste has been conventionally used as a conductor for a circuit board. Recently, attempts have also been made to use a conductive paste as an electromagnetic wave shielding material for printed circuit boards. That is,
This application is a printed wiring board formed by forming a conductive layer having a circuit pattern including a ground pattern on the board,
An insulating layer is printed on the substrate so as to cover the conductive layer except for the portion of the ground pattern on the surface on which the conductive layer of the substrate is provided, and the conductive layer is formed so as to cover the insulating layer of the substrate and connect to the ground pattern. By printing a paste, an electromagnetic wave shield layer is formed and used as a conductor of a circuit board for preventing electromagnetic noise (JP-A-63-15).
497 and Japanese Utility Model Publication 55-29276).

[0003]

Among the above-mentioned conductive pastes, the conductive copper paste has recently been attracting attention as a conductor replacing the conductive silver paste because it is cheaper than the conductive silver paste. .. This conductive copper paste is required to have various physical properties such as high conductivity, adhesiveness, durability, and printability, but copper is essentially more easily oxidized than silver, and an electrically insulating oxide film is formed by the oxidation. Since it has a drawback of being formed, it has been a practically large problem in terms of maintaining conductivity for a long period of time in a paste state or a heat-cured film state.

To cope with this drawback, various kinds of additives such as antioxidants, reducing agents and metal chelating agents have been added so far. For example, a method using salicylic acid and its derivative as an antioxidant for a conductive copper paste (JP-A-1-158081) and a method using γ-aminoisopropyltriethoxysilane as a reducing agent (JP-A-50-6638). Publication) and 2-hydroxy-
A method using 3-phenoxypropyl phosphite (JP-A-52-24936), a method using monoethanolamine, diethanolamine and the like (JP-A-62-230869), and acetylacetone etc. are used as the metal chelating agent. Method (JP-A-2-66802)
No. gazette) is proposed. However, in the conductive copper paste containing the above additive, although improved in terms of improving or maintaining conductivity, other physical properties, that is, adhesion with the copper foil surface (particularly metal copper surface),
The screen printability was poor, and further improvement was strongly demanded. In particular, the relationship between conductivity and adhesion is generally a trade-off relationship, which has been a major obstacle to the development of conductive pastes.

Therefore, in the industry, it is expected to develop a conductive copper paste having excellent conductivity and adhesion, and also having excellent overall performance such as durability and printability. The object of the present invention is to solve this problem, which is exactly at this point, in the conductive paste, in particular, the conductivity, adhesion, durability, printing even when using a metal that is easily oxidized as the conductive powder. The purpose of the present invention is to provide a conductive paste having excellent properties such as excellent properties.

[0006]

Means for Solving the Problems In view of the present situation, the present inventors have diligently studied to maintain and improve the conductivity of the conductive paste, improve the adhesion with the copper foil surface, and improve the screen printability, It was found that the above problems can be solved by using benzoic acid and / or its derivative,
The present invention has been completed.

That is, according to the present invention, in a conductive paste containing a conductive powder, an organic binder, an additive, and a solvent, the organic binder contains a thermosetting resin as an essential component,
The present invention relates to a conductive paste containing the benzoic acid represented by the general formula (I) and / or a derivative thereof as the additive, and the present invention relates to a conductive paste coated on a substrate. Alternatively, the present invention relates to a conductive coating film obtained by curing after printing.

[0008]

[Chemical 2]

(In the formula, R ^a is a hydrogen atom or has 1 carbon atom.
-24 are linear or branched alkyl groups or alkoxyl groups. R ^b represents a hydrogen atom, an alkali metal, an alkaline earth metal, a transition metal, ammonium, alkylammonium or hydroxyalkylammonium. )

The additive in the present invention is characterized by containing the benzoic acid represented by the above general formula (I) and / or its derivative. Here, R ^a is a hydrogen atom, an alkyl group or an alkoxyl group, and may be linear or branched. The carbon number of the alkyl group or alkoxyl group is usually 1 to 24, preferably 3 to 20. When the number of carbon atoms of the alkyl group or the alkoxyl group exceeds 24, only those having reduced conductivity are obtained, which is not preferable.

Specific examples of benzoic acid and / or its derivative in the present invention include benzoic acid, methylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, butylbenzoic acid, hexylbenzoic acid, octylbenzoic acid, nonylbenzoic acid, Decylbenzoic acid, dodecylbenzoic acid, tetradecylbenzoic acid, hexadecylbenzoic acid, octadecylbenzoic acid, methoxybenzoic acid, ethoxybenzoic acid, butoxybenzoic acid, octyloxybenzoic acid, tetradecyloxybenzoic acid and the like.

As a salt of benzoic acid and / or its derivative in the present invention, R ^b is usually an alkali metal such as sodium, potassium or lithium, an alkaline earth metal such as calcium, magnesium or barium, or a copper or the like. Examples include transition metal, ammonium, or alkylammonium formed by alkylamine such as triethylamine, hydroxyalkylammonium formed by hydroxyalkylamine such as triethanolamine, preferably sodium,
Examples include potassium, copper, ammonium, triethylamine and triethanolamine. These benzoic acid and /
Alternatively, the derivatives thereof may be used alone or in combination of two or more.

The content ratio of benzoic acid and / or its derivative in the conductive paste of the present invention is 0.05 to 25% by weight, preferably 0.1 to 1 based on the total weight excluding the solvent.
It is 0% by weight, more preferably 0.2 to 5% by weight.
When the compounding weight is less than 0.05% by weight, the absolute amount of benzoic acid and / or its derivative is insufficient, and the conductivity, adhesion, or printability is deteriorated. Insufficient binding effect, conductivity, adhesion,
Durability decreases.

The method for synthesizing the derivative of benzoic acid used in the present invention may be carried out, for example, by the usual Friedel-Crafts acylation reaction and haloform reaction. In particular,
Anhydrous aluminum chloride and acetyl chloride are added to dichloromethane, and acetyl chloride and alkylbenzene or alkoxybenzene are quickly added while cooling and stirring. It is decomposed with a mixture of concentrated hydrochloric acid and ice, the dichloromethane layer is separated, neutralized and washed, the solvent is removed, and vacuum distillation is carried out to obtain p-acetylalkylbenzene or p-acetylalkoxybenzene. Next, bromine and sodium hydroxide are added to water and dioxane to prepare an alcal hypobromous acid solution, and the above substance is added dropwise while stirring at 0 ° C. Then, it is acidified with an excess of hydrochloric acid, the precipitate formed is filtered off, and purified by recrystallization from benzene to obtain a benzoic acid derivative. In addition, the salt of benzoic acid and / or its derivative can be obtained by neutralizing with excess metal hydroxide, ammonia, alkylamine, alkanolamine and the like.

In the present invention, by using such benzoic acid and / or its derivative as an additive, high conductivity is exhibited and the cured coating film thereof is excellent in environmental stability. Furthermore, it exhibits good adhesion regardless of the surface state (particularly the oxidized state) of the copper foil. In addition, the flow characteristics of the conductive paste are improved, and good printing becomes possible.

The organic binder of the conductive paste of the present invention contains a thermosetting resin as an essential component. The thermosetting resin effectively used in the present invention, phenol resin, urea resin, amino resin, xylene resin, alkyd resin, silicon resin, furan resin, unsaturated polyester resin, epoxy resin, polyurethane resin, polyester polyol resin, Known thermosetting resins such as acrylic resins, methylolated hydroxystyrene polymers and / or derivatives thereof can be used, but phenol resins, amino resins and xylene resins are particularly preferable. The above-mentioned thermosetting resins used in the present invention may be used alone or in combination of two or more.

As the phenol resin, generally known products and commercially available products can be used. For example, phenol, cresol, xylenol, p-alkylphenol, chlorophenol, bisphenol A, phenolsulfonic acid, resorcin, various modified phenols and the like phenolic resin can be used. Resins obtained by adding and condensing aldehydes such as formalin and furfural to those having a hydroxyl group can be mentioned. Resol type phenolic resin is particularly preferable. When a novolac type phenolic resin is used, it is preferable to use hexamethylenetetramine together.

As the amino resin, generally known products and commercially available products can be used, but those having a weight average molecular weight of 500 to 50,000 are preferable. For example, urea, melamine, guanamine, aniline, a resin obtained by addition condensation of formalin to an amino group such as sulfonamide, or an epoxy-modified melamine resin, a phenol-modified melamine resin,
Examples thereof include acrylic modified melamine resin, butylated urea resin, butylated urea melamine co-condensed resin, butylated melamine / guanamine co-condensed resin, amino / alkyd co-condensed resin, and alkyl etherified melamine resin. Alkyl etherified melamine resin is preferable. Examples of the alkyl etherified melamine resin include methyl etherified melamine resin, n-butyl etherified melamine resin, iso-butyl etherified melamine resin, and the like, for example, Super Beckamine (trade name) manufactured by Dainippon Ink and Chemicals, or Mitsui Toatsu There is a chemical company U-ban (trade name). Among these alkyl etherified melamine resins, preferred are those having a weight average molecular weight (Mw) in the range of 500 to 50,000 and an etherification degree of 10 to 95% (at 100%, 6 units per 1 unit of triazine ring). Alkyl ether group is introduced), more preferably Mw of 1000-2.
In the range of 50,000 and the degree of etherification is 20 to 80%,
Most preferably, the melamine resin has an Mw of 1000 to 10,000 and an etherification degree of 30 to 60%. Mw
Is less than 500, the flexibility of the cured coating film is insufficient, and if it exceeds 50,000, the adhesion and conductivity are deteriorated. When the degree of etherification is less than 10%, the melamine resin is unstable, and the pot life of the conductive paste is shortened, and when it exceeds 95%, the curing speed decreases and a sufficient dense coating film cannot be obtained under normal curing conditions. This is because it becomes difficult to obtain good adhesion and conductivity.

As the xylene resin, generally known products and commercially available products can be used, and examples thereof include resins obtained by adding and condensing aldehydes such as formalin and furfural to xylene and modified xylene.

As the organic binder of the conductive paste of the present invention, it is preferable to use a thermoplastic resin together with the thermosetting resin. The thermoplastic resin effectively used in the present invention is a hydroxystyrene polymer and / or its derivative, saturated polyester resin, polyurethane resin,
Known thermoplastic resins such as polyamide resin, acrylic resin, butyral resin, novolac type phenol resin, and thermoplastic xylene resin can be used, but a hydroxystyrene polymer and / or its derivative is particularly preferable. The above-mentioned thermoplastic resins used in the present invention may be used alone or in combination of two or more.

The hydroxystyrene polymer and / or its derivative more preferably contains a weight average molecular weight of 1,000 to 2,000,000. The addition of this binder component improves performances such as conductivity, adhesiveness, durability and printability. The hydroxystyrene polymer and / or its derivative are preferably those described in JP-A-3-2283, JP-A-3-2248 and JP-A-3-173007. For example, those represented by the following general formula (II) can be mentioned.

[0022]

[Chemical 3]

[Wherein l and m are l ≧ 0 and m ≧ 3, and the average molecular weight of the organic polymer of the general formula (II) is 1000, respectively.
Up to 2 million, k, p, and u represent average values in the polymer, and their ranges are 0 ≦ k ≦ 2 and 2, respectively.
0 ≦ p ≦ 2, 0 <u ≦ 2, but k + p + u> 0, R ¹
To R ³ are hydrogen atoms or alkyl groups having 1 to 5 carbon atoms, Q is a polymerizable vinyl-based monomer, Y and Z are the same or different, and

[0024]

[Chemical 4]

Alternatively, it is selected from an alkyl group or an aryl group having 1 to 18 carbon atoms (wherein M is a hydrogen atom, an organic cation such as an alkali metal, an alkaline earth metal or an amine, Y ¹ , Y ² Is halogen, Y ³ is a counter ion such as a halogen ion, an organic acid anion and an inorganic acid anion, W is S or O, and R ^{4 to} R ⁸ are the same or different and are linear or branched alkyl groups or hydroxyalkyl groups. Such as an alkyl derivative, an aromatic group or a hydrogen atom, and R ⁶ and R ⁷ may form a ring together with an N group, and R ^{9 to} R ¹⁵ are the same or different and are linear or branched alkyl. Group, or an alkyl derivative such as a hydroxyalkyl group, an aromatic group, or a hydrogen atom, q, s, and t represent 0 or 1, and r represents 0, 1 or 2.

The hydroxystyrene-based polymer represented by the general formula (II) and its derivative are hydroxystyrene having or not having a substituent represented by Y or Z in the general formula (II). , Hydroxy-α-methylstyrene, or a copolymer of hydroxystyrene-based monomers such as hydroxy-α-ethylstyrene, or these hydroxystyrene-based monomers and other polymerizable vinyl-based monomers It may be a copolymer with (Q). The hydroxystyrene monomer of the polymerized unit is
It may be an ortho body, a meta body, a para body or a mixture thereof, but a para body or a meta body is preferable.

Other vinyl-based monomers (Q) in the case of copolymers include anionic or cationic ionic monomers, nonionic monomers, methacrylates, vinyl esters, vinyl ethers, Known compounds such as malate and α-olefin can be mentioned. In the present invention, as described above, the copolymerization of the hydroxystyrene-based monomers may be carried out, but when the copolymerization with the other polymerizable vinyl-based monomer (Q) is carried out, the hydroxystyrene-based monomer may be used. The ratio of the monomer / other vinyl-based monomer (Q) is appropriately 1/10 to 20/1 in terms of molar ratio.

If the proportion of the vinyl-based monomer (Q) exceeds 10 times the molar amount of the hydroxystyrene-based monomer (molar ratio), the effect of the hydroxystyrene-based monomer will not be exhibited, which is not preferable, and the vinyl-based monomer When the ratio of the body (Q) is less than 1/20, the effect of copolymerization is not exhibited, so it is not necessary to purposely copolymerize with the vinyl-based monomer (Q). Therefore, in the present invention, such vinyl monomer (Q)
The number of is m ≧ 0.

These hydroxystyrene-based polymers and their derivatives can be easily prepared by known methods (CG Overberger, JC Salamone, S. Yaroslavsk.
y, J.Am.Chem.Soc., 89,6231 (1967); DIPackham, J.Chem.
Soc., 2617 (1964); M.Kato, J.Polym.Sci., Part A-1,7,217
5 (1969)).

The blending ratio of the binder in the conductive paste of the present invention is 5 to 50% by weight, preferably 5 to 40% by weight, based on the total weight excluding the solvent. Absolute amount is insufficient and adhesion decreases,
Further, the fluidity of the obtained composition is deteriorated, the printability is deteriorated, and the conductive powder is easily oxidized at the time of heating and curing, resulting in deterioration of flexibility and conductivity. On the contrary, when the amount of the binder exceeds 50% by weight, the absolute amount of the conductive powder is insufficient and the conductivity required for forming a circuit cannot be obtained.

Examples of the conductive powder used in the present invention include metal powders such as copper powder, silver powder, nickel powder and aluminum powder, and powders having a coating layer of the above metal on the surface, but copper powder is particularly preferable. .. The form of the conductive powder may be any of dendritic, flake-like, spherical, and indefinite, but is preferably dendritic electrolytic copper powder produced by electrolysis or spherical powder. Average particle size is 30
The dendritic powder having a particle size of 1 to 10 μm is more preferable in view of high density and multiple contact point filling. However, the average particle size referred to here is "LA-5 manufactured by Horiba Ltd.
The volume-based median diameter determined by "00 type laser diffraction type particle size distribution measuring device". This is because if the average particle size exceeds 30 μm, it becomes difficult to densely fill the conductive powder, the conductivity is lowered, and the printability is deteriorated. Further, when the surface-treated copper powder is used, particularly excellent conductivity, durability and printability are easily obtained. Since it is not necessary to attach solder to the surface of the copper paste and its coating film of the present invention, an organic surface treatment agent may be used. The conductive powder may be used alone or in a mixed system. It is preferable that the purity of the metal powder is high. Particularly, the copper powder is most preferably the one having the same purity as that of the copper foil or the plated copper layer used for the conductor of the circuit board.

In the present invention, the action and effect of benzoic acid and / or its derivative is more remarkably exhibited when the metallic copper powder is used, so the present invention is particularly important for the production of the conductive copper paste. The content of the conductive powder in the conductive paste of the present invention is 50 to 95% by weight based on the total weight excluding the solvent, and preferably 70 to
90% by weight, more preferably 80 to 90% by weight. If the blending amount is less than 50% by weight, sufficient conductivity cannot be obtained. Conversely, if the blending amount exceeds 95% by weight, the conductive powder is not sufficiently bound, the coating film obtained becomes brittle, and the moisture resistance decreases and the conductivity decreases. It also becomes worse.

In the conductive paste of the present invention, one or more known reducing agents or chelating agents may be used, if necessary, for the purpose of preventing the oxidation of the conductive powder (for example, Japanese Patent Application No. Hei 2). -341074, Japanese Patent Application No. 2-341076
And the known compounds).
In the present invention, as preferable reducing agents, for example, inorganic reducing agents such as phosphorous acid and hypophosphorous acid, and hydroquinone, catechols, ascorbins, hydrazine compounds, formalin, borohydride compounds, reducing sugars. Examples include organic and inorganic compounds such as

Preferred chelating agents include, for example, alkanolamines such as triethanolamine, alkylamines such as triethylamine and palmitylamine,
o-aminophenol, 2-amino-4-methylphenol, o-aminothiophenol, 8-hydroxyquinoline, 2-methyl-8-hydroxyquinoline, 1-nitroso-2-naphthol, 1- (2-pyridylazo)- Two
-Aromatic amino compounds such as naphthol, EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid),
CDTA (t-1,2-cyclohexanediamine-N,
N, N ′, N′-tetraacetic acid hydrate), polyaminocarboxylic acids such as DTPA (diethylenetriaminepentaacetic acid), polyvinylamine and vinylamine / vinyl alcohol copolymer derivatives, o-nitrophenol resin, polymer ester Polymers obtained by reacting hydroxylamine with carboxylic acids such as hydroxamic acid, succinic acid, propionic acid, humic acid, citric acid, hydroxycarboxylic acids such as ascorbic acid, salicylic acid, sulfonylsalicylic acid, salicylamide, salicylhydroxysamic acid Salicylic acid compounds such as phenylalanine, tyrosine, anthranilic acid and aspartic acid, imino acids such as proline, pyridinecarboxylic acids such as nicotinic acid, hydrazines such as hydrazine and phenylhydrazine, benzoylacetone, acetone β-diketones such as Ruaseton, lauryl mercaptan, and the like.

In the present invention, the compounding amount of the reducing agent or the metal chelating agent is usually 0.1 to 2 with respect to the total weight excluding the solvent.
It is 0% by weight, preferably 0.5 to 10% by weight. If the blending amount is less than 0.1% by weight, the effect of addition is not sufficient,
If it exceeds 20% by weight, the adhesion and the migration resistance are deteriorated, which is not preferable.

Known thixotropic agents and leveling agents may be used, if necessary, for the purpose of improving the dispersibility of the copper powder and the screen printability of the paste.
In order to produce the conductive paste of the present invention, it is prepared by sufficiently uniformly kneading with a disper, a ball mill, a triple roll or the like.

As the solvent that can be used here,
Benzene, toluene, hexanone, methyl isobutyl ketone, methyl amyl ketone or butyl carbitol, butyl carbitol acetate, butyl cellosolve, butyl cellosolve acetate, propylene glycol monomethyl ether acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, etc. Known solvents include propylene glycol ethers, diester salts of dibasic acids such as dimethyl adipate, dimethyl glutarate and dimethyl succinate. The blending amount of the solvent varies depending on the type of kneading machine, the kneading conditions and the type of solvent. It is preferable to adjust the amount of the solvent so that the paste viscosity after the kneading can be screen-printed.

As a method for producing a circuit board for electromagnetic wave noise prevention in which an electromagnetic wave shield layer is provided on the circuit board using the conductive paste of the present invention, for example, there are the following methods. That is, a heat-curable or UV-curable organic insulator is applied on a conductive circuit formed by a metal-clad laminate by an etched-for method except the ground pattern portion to form an insulating layer, and the insulating layer is provided on the insulating layer. Using the conductive paste according to the present invention, the conductive paste is applied to almost the entire surface of the insulating layer so as to be connected to the ground pattern by screen printing, and the conductive paste is heated and cured to form an effective electromagnetic wave shield layer. It is possible to fabricate the circuit board for electromagnetic wave noise protection. This circuit board can also be effectively used as an electrostatic shield layer.

The metal-clad laminated substrate that can be used is a printed circuit technology handbook such as a glass / epoxy resin substrate, a paper / phenol resin substrate, a ceramic substrate, a polyimide resin substrate, and a flexible substrate (Nikkan Kogyo Shimbun, Showa 6).
Any known substrate described in, for example, 2 years publication) may be used. Further, as a method of using the conductive paste of the present invention as a conductor for wiring of a circuit board, the same method as a conventional method can be used. The insulating substrate to be applied may be any known or commercially available substrate as described above. As a wiring forming method, a method of applying by screen printing, intaglio printing, spraying or brush coating can be used. In the present invention, the conductive coating film means a cured product or a cured coating film obtained by drying and curing the conductive paste of the present invention and having a volume resistivity of 1 × 10 ⁻² Ω · cm or less. ..

[0040]

The present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited to these examples. In the examples and comparative examples, "%" in the blending amount means "% by weight".

Examples 1 to 18 Preparation of Pastes The conductive powders shown in Table 1, benzoic acid or its derivatives shown in Table 2, organic binders shown in Table 3, and other additives shown in Table 4 are shown in Tables 5 and 6. Blended to give a composition,
A conductive paste is prepared by kneading with a disper or three rolls sufficiently uniformly.

Substrate Preparation Using a glass / epoxy resin substrate (CEM-3), an organic insulating layer (S-222, HR-6 or MF made by TAIYO INK CO., LTD. -100S, TS-17)
Printed and cured. For the pretreatment of the copper foil, a 10% aqueous solution of sulfuric acid / ammonium citrate (1: 3) was used.
After dipping at 60 ° C. for 60 seconds to dissolve the surface oxide film, it was air dried with jet air.

Paste printing Using each of the obtained conductive pastes, the adhesion test portion and the conductivity measurement pattern (2 mm × 360 mm) were printed on the organic insulator by a screen printer equipped with a 180-250 mesh Tetoron screen. Or printed on copper foil. Next, it was heated and cured at 140 to 160 ° C. for 10 to 30 minutes to obtain a paste cured coating film having a thickness of 20 to 30 μm.

Approximately 20μ of overcoat printed organic insulation layer (MF-200, TS-91E made by Taiyo Ink)
Printed on a paste-cured coating with a thickness of m, UV-cured (high pressure mercury lamp, 1200 mj / cm ² ) and 150 ° C x 2
It was cured by heating in 0 minutes. The results of examining various characteristics of the conductive circuit obtained in the above process are shown in Tables 5 and 6.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

[Table 6]

Conductivity Measurement The conductivity of a coating film means the volume resistivity of a coating film which has been cured by heating with a digital multimeter (R655 manufactured by Advantest).
It is the value measured by the two-terminal method using 1). In addition,
The formula for calculating the volume resistivity is shown below. Volume resistivity (Ω · cm) = (R × t × W) / L R: Resistance value between electrodes (Ω) t: Thickness of coating film (cm)
W: coating width (cm) L: distance between electrodes (cm)

Moisture resistance test The humidity resistance of the coating film is 5 at 60 ° C. and 95% relative humidity.
A standing test was carried out for 00 hours, and the change rate W _R of the resistance value before and after the test was determined by the following formula. Resistance change rate W _R (%) = (R ₅₀₀ −R ₀ ) / R ₀ R ₀ : Resistance value of coating film before test (Ω) R ₅₀₀ : Resistance value (Ω) W _R value after 500 hours test Shows the moisture resistance of the coating film as follows. A: W _R is less than 30% B: W _R is 30% or more and less than 100% C: W _R is 100% or more

Adhesion Test A humidity resistance test (60 ° C., 95% relative humidity) was applied for 96 hours, and then immersion was conducted in a solder bath at 260 ° C. for 5 seconds × 2 times, and then evaluation was performed. According to JIS K 5400 (1979) cross-cut cellophane tape peeling test method, the number of cross-cuts of the coating film remaining on the copper foil or the organic insulating layer was determined. The judgment criteria are as follows. A: 100/100 B: 90/100 or more and less than 100/100 C: 50/100 or more and less than 90/100 D: 0/100 or more and less than 10/100

The evaluation criteria for printability are as follows. ◯: Good printability Δ: Temporarily printable ×: Unprintable

Comparative Examples 1 to 4 Conductive pastes having the compositions shown in Table 6 were prepared as comparative products and evaluated in the same manner as in the examples. The results are also shown in Table 6.

Tables 5 and 6 show various characteristics of the conductive paste and the conductive coating film according to the present invention together with comparative examples. As shown in Examples 1 to 18, the conductive paste of the present invention has excellent printability and high conductivity (10 ⁻³ to
The adhesion to the metallic copper surface is greatly improved while maintaining 10 ⁻⁵ Ω · cm). Further, it can be seen that these physical properties are also excellent in environmental stability such as moisture resistance and solder heating resistance.

On the other hand, a conductive paste containing no benzoic acid or its derivative (Comparative Example 1) or a conductive paste containing a derivative of benzoic acid having an alkyl group or an alkoxyl group having more than 24 carbon atoms (Comparative Example) In 2), it is difficult to comprehensively satisfy various physical properties (conductivity, moisture resistance, adhesion and printability), and when the compounding amount of benzoic acid or its derivative used in the present invention is not appropriate. It is also difficult for (Comparative Example 3) to comprehensively satisfy various physical properties. Further, also in the example (Comparative Example 4) in which salicylic acid which has been conventionally used as an additive is blended, it is similarly difficult to comprehensively satisfy various physical properties. Also,
The conductive paste of the present invention showed good adhesion even on the surface of a copper foil which was oxidized at a high temperature of 100 to 250 ° C. Although the mechanism of action is unknown, the conductive paste containing the hydroxystyrene polymer and / or its derivative as the organic binder had good migration properties.

[0058]

INDUSTRIAL APPLICABILITY In the present invention, by using benzoic acid and / or a derivative thereof, the adhesion can be improved without lowering the conductivity, and the environmental stability and printability thereof can be greatly improved. It is possible to provide a comprehensively superior conductive paste. Therefore, by using the conductive paste of the present invention, it is possible to easily and stably form an electromagnetic wave shield layer having extremely high reliability and high effect on a circuit board. Further, even when it is used as a conductor for wiring of a circuit board, wiring with high reliability can be formed. Further, it can be effectively used for electrodes of electronic equipment parts, circuit parts, etc., and these effects are extremely large in industry.

Claims (5)

[Claims] 1. A conductive powder, an organic binder, an additive,
In a conductive paste containing a solvent and a solvent, the organic binder contains a thermosetting resin as an essential component, and contains benzoic acid represented by the general formula (I) and / or a derivative thereof as the additive. Sex paste. [Chemical 1] (In the formula, R ^a represents a hydrogen atom, or a linear or branched alkyl group or alkoxyl group having 1 to 24 carbon atoms. R ^b represents a hydrogen atom, an alkali metal, an alkaline earth metal, a transition metal, ammonium, an alkyl group. Indicates ammonium or hydroxyalkyl ammonium.) 2. The conductive paste according to claim 1, wherein the organic binder contains a thermoplastic resin. 3. The conductive material according to claim 1, wherein the organic binder contains at least one selected from the group consisting of phenol resins, amino resins, xylene resins, hydroxystyrene polymers and their derivatives. paste. 4. The conductive paste according to claim 1, wherein the conductive powder is a metal powder or a solid powder having a metal layer on the surface. 5. A conductive coating film obtained by applying the conductive paste according to claim 1, 2, 3 or 4 on a substrate, or printing and curing the conductive paste.