JPH04214775A - Electrically conductive paste and electrically conductive coating film - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive paste having high electrical conductivity while keeping the adhesivity over a long period by compounding a hydroxystyrene copolymer (derivative) as an organic binder and a reducing agent as an additive. CONSTITUTION:The objective electrically conductive paste is produced by compounding, as essential components, (A) a hydroxystyrene copolymer (derivative) having a weight-average molecular weight of 1,000-2,000,000, preferably an organic polymer of formula (R<1> to R<3> are H or 1-5C alkyl; X is polymerizable vinyl monomer; Y and Z are 1-18C alkyl, -CH2OH, etc.; m>=0; n>=3) as an organic binder, (B) a reducing agent such as hydroquinone and L-ascorbic acid as an additive, (C) electrically conductive powder such as copper powder and (D) a solvent such as benzene.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive paste and a conductive coating film that have good conductivity while maintaining adhesion over a long period of time. More specifically, it is applied onto circuit boards such as paper/phenol resin boards, glass/epoxy resin boards, etc. by screen printing, and then heated and cured, thereby maintaining excellent adhesion to metals and insulating layers. The present invention relates to a conductive paste that has good conductivity over a long period of time and is suitable for use as a countermeasure against electromagnetic noise on a circuit board or as a conductor for wiring on a circuit board, and a conductive coating film.

[Conventional technology]

In general, a conductive paste is basically composed of an organic binder (hereinafter abbreviated as binder) such as an epoxy resin, a saturated polyester resin, an acrylic resin, or a phenol resin, a conductive powder, and a solvent.

This conductive paste has been conventionally used as a conductor for circuit boards. Recently, attempts have also begun to use conductive paste as an electromagnetic shielding material for printed circuit boards. That is, this application applies to a printed wiring board in which a conductive layer having a circuit pattern including a ground pattern is formed on the board, and a conductive layer is formed on the board except for the part of the ground pattern on the surface of the board on which the conductive layer is provided. An insulating layer is printed to cover the layer, and a conductive paste is printed to cover the insulating layer of the board and connect it to the ground pattern, thereby forming an electromagnetic shielding layer, which can be used as a conductor for a circuit board for electromagnetic noise countermeasures. (Japanese Unexamined Patent Publication No. 15497/1983 and Japanese Utility Model Application No. 29276/1983)
issue).

[Problem to be solved by the invention]

Among conductive pastes, conductive copper paste in particular is attracting attention as a conductor that can replace expensive conductive silver paste.

However, this conductive copper paste has the disadvantage that copper is inherently more easily oxidized than silver, and oxidation forms an electrically insulating oxide film, so it is less expensive than conductive silver paste. On the other hand, there remains a major practical problem in maintaining electrical conductivity over a long period of time in a paste state or a heat-cured film state.

To address this drawback, it has been attempted to add various additives such as antioxidants and metal chelating agents.

For example, it has been proposed to add an anthracene derivative or an organic titanium compound to a conductive copper paste, but sufficient conductivity and long-term stability of conductivity have not yet been achieved.

In addition, proposals have been made to prevent oxidation and maintain conductivity by adding monoethanolamine, diethanolamine, etc. as metal chelate forming agents (JP-A-62-230869, JP-A-62-252482), and metals such as acetylacetone. A proposal has been made to improve conductivity by adding a chelate compound (Japanese Unexamined Patent Publication No. 2-66802). However, when these metal chelate forming agents are added, although the effect of maintaining and improving conductivity can be obtained, on the other hand,
A problem has arisen in that the adhesion to the surface of a base material such as metallic copper is reduced.

Furthermore, various attempts have been made to maintain and improve electrical conductivity by reducing the oxide of the oxide film formed on metallic copper using a reducing agent.

For example, it has been proposed that conductivity can be improved by using γ-aminoisopropyltriethoxysilane as a reducing agent (Japanese Patent Application Laid-Open No. 1983-6638), 2-hydroxy-3-phenoxypropyl phosphite, etc. as a reducing agent. It has been proposed (Japanese Patent Publication No. 52-24936) that it is expected to improve conductivity and conductivity retention by using a reducing substance of copper.

However, even when adding a reducing agent, there remains the general problem that adhesion deteriorates due to the combination of low molecular weight substances, as in the case of adding metal chelate forming agents, etc.
Even in the above-mentioned proposals, these problems have not been sufficiently solved.

In this way, especially in the case of metals that easily form an electrically insulating oxide film through surface oxidation, such as metallic copper, it is possible to improve conductivity by reducing the oxides in the oxide film by adding a reducing agent. can.

However, conventional conductive pastes generally have adhesion to oxide films but lack adhesion to metal copper surfaces, etc., so conductivity is improved by reducing the oxide by adding a reducing agent. The actual situation was that the adhesion deteriorated as a result.

As described above, conventional conductive pastes generally do not have sufficient adhesion to metals and insulating layers on circuit boards, and are not used as conductors for electromagnetic shielding layers of circuit boards for electromagnetic noise countermeasures or as conductors for circuit board wiring. However, the problem of lack of reliability has been pointed out.

Various measures have been reported to improve adhesion. For example, as an example of improving the binder, improving the adhesion with metals and insulating layers by using melamine resin, polyol, polyester resin, and/or alkyd resin. (Japanese Unexamined Patent Publication No. 62-253675), an example where a mixture of melamine resin and acrylic resin was used to improve the adhesion to metal (Japanese Unexamined Patent Publication No. 63-83178), and poly-
An example of using p-hydroxystyrene to improve adhesion to an insulating layer and removability with a solvent (Japanese Unexamined Patent Publication No. 60-26
No. 0663), but in either method, the improvement in adhesion was still insufficient, and adhesion to metals and insulating layers could not be fully guaranteed.

In this way, conductivity and adhesion are generally in a trade-off relationship in conventional conductive pastes, so a conductive paste that can be expected to improve conductivity while maintaining adhesion has not yet been found. That is the reality.

However, in the industry, conductive pastes that maintain and improve conductivity by preventing oxidation of metal copper, etc., also have adhesion to metal copper, in other words, conductive pastes that maintain adhesion. The development of a conductive paste that can be expected to improve conductivity is expected.

[Means to solve the problem]

In view of the current situation, the present invention has been developed as a result of intensive studies to maintain and improve conductivity through oxidation stability of conductive paste and to improve adhesion to substrates. It was discovered that by using it as a component and blending a reducing agent as an additive, it is possible to increase the affinity and reactivity with the metal surface and the surface of the insulating layer, and the above object can be achieved, and the present invention was completed. Ta.

That is, the gist of the present invention is to provide a conductive paste containing a conductive powder, an organic binder, an additive, and a solvent as essential components, wherein the organic binder has a weight average molecular weight of 1,000 to 2.
The present invention relates to a conductive paste containing a hydroxystyrene copolymer and/or a derivative thereof, and a reducing agent as an additive, and a conductive coating film.

According to the present invention, by adjusting the type and density of substituents introduced into the organic polymer contained in the organic binder, the affinity and reactivity to the metal surface can be controlled, and the oxidation stability of the conductive powder can be improved. It is possible to increase the adhesion with metals and insulating layers.

In the present invention, the organic polymer contained in the organic binder is, for example, the following general formula (I): [where m≧0
, n≧3, respectively, an arbitrary number until the weight average molecular weight of the organic polymer of general formula (I) is 1,000 to 2,000,000; 0≦k≦2; 0≦p≦2; 0<u≦2, (However, k, p, and u indicate the average value in the polymer.); R1 and R2 are H or an alkyl group having 1 to 5 carbon atoms; X is a polymerizable vinyl monomer; ; Y and Z are the same or different, and or selected from alkyl groups or aryl groups having 1 to 18 carbon atoms (wherein, M is H, an alkali metal, an alkaline earth metal or Organic cations such as amines; Y1 and Y4 are halogens; Y2- and Y3- are halogen ions, organic acid anions,
A counter ion such as an inorganic acid anion; W is S or O; R4 to R8 are the same or different and are a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H
, Furthermore, R6 and R7 may form a ring with an N group.

; R9 to R15 are the same or different and are linear or branched alkyl groups, alkyl derivative groups, aromatic groups, or H; q, s, and t are 0 or 1; r is 0, 1, or 2) ] Hydroxystyrene copolymers represented by these and derivatives thereof are mentioned.

In the above general formula (I), m, n, k, p, and u are arbitrary numbers (real numbers) within a certain range.

If we consider the monomers that make up the polymer, k, p
is naturally an integer, if we consider each block of constituent units, m is an integer, and if we consider each molecule, n is an integer. However, polymers are essentially mixtures, and it is more appropriate to consider the properties of a polymer as a property of the mixture than with its individual constituent units. Therefore, in the present invention, m
, n, k, p, and u are expressed as average values in the polymer.

The hydroxystyrene copolymer represented by the above general formula (I) or its derivative has hydroxystyrene, which has or does not have a substituent represented by Y or Z in the general formula (I), A copolymer of only hydroxystyrene monomers such as hydroxy-α-methylstyrene or hydroxy-α-ethylstyrene,
Alternatively, it may be a copolymer of these hydroxystyrene monomers and another polymerizable vinyl monomer (X).

The hydroxystyrene monomer of the polymerized unit is ortho form,
It may be a meta-form, a para-form or a mixture thereof, but a para-form or a meta-form is preferable.

In addition, other vinyl monomers (X) in the case of a copolymer include ionic monomers such as anionic and cationic monomers, nonionic monomers, methacrylates, vinyl esters,
Known compounds such as vinyl ether, malate, fumarate, and α-olefin can be mentioned.

Specific examples of these compounds include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, or anhydrides thereof, and their monoalkyl esters and carboxyethyl vinyl ethers.
Unsaturated carboxylic acid monomers such as carboxypropyl vinyl ether, styrene sulfonic acid, allyl sulfonic acid, 2
- Acrylamide - Unsaturated sulfonic acid monomers such as 2-methylpropanesulfonic acid, unsaturated phosphoric acid monomers such as vinylphosphonic acid, vinyl phosphate, acrylic acid ethyl phosphate, methacrylic acid ethyl phosphate, acrylamide, methacrylamide, α,β-unsaturated carboxylic acid amides such as maleic acid amide and maleic acid imide;
Methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, perfluoroalkylethyl methacrylate, stearyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, 2-aminoethyl methacrylate hydrochloride, dimethyl Aminoethyl methacrylate, methoxymethyl methacrylate, chloromethyl methacrylate, dichlorotriazinyl aminoethyl methacrylate, and maleic acid, fumaric acid,
Diesters of itaconic acid, etc., esters of α,β-unsaturated carboxylic acids, substituted amides of unsaturated carboxylic acids such as methylol acrylamide, methylol methacrylamide, methoxymethyl acrylamide, acrylonitrile,
Nitriles of α,β-unsaturated carboxylic acids such as methacrylonitrile, vinyl acetate, vinyl chloride, vinyl chloroacetate, etc., divinyl compounds such as divinylbenzene, vinylidene compounds, aromatic vinyl compounds represented by styrene, vinyl Heterocyclic vinyl compounds such as pyridine and vinylpyrrolidone, vinyl ketone compounds, vinyl ether compounds, vinylamide compounds, monoolefin compounds such as ethylene and propylene, conjugated diolefin compounds such as butadiene, isoprene, and cloprene, allyl alcohol, allyl acetate, etc. One or more monomers selected from the group of monomers represented by allyl compounds, glycidyl methacrylate, etc. are used.

Among these monomers, any one can be used without any particular limitation, but specifically, the following monomers are preferably used.

In the present invention, copolymerization of only hydroxystyrene monomers may be performed as described above, but when copolymerizing with other polymerizable vinyl monomers (X), hydroxystyrene monomers may be copolymerized with each other. The ratio of monomer/other vinyl monomer (X) is suitably from 1/10 to 20/1 in terms of molar ratio.

If the proportion of the vinyl monomer (X) exceeds 10 times the amount (molar ratio) of the hydroxystyrene monomer, the effect of the polyhydroxystyrene monomer will not be exhibited, which is undesirable. If the ratio of X) is less than 1/20,
Since the effect of copolymerization is not exhibited, there is no need to intentionally copolymerize with the vinyl monomer (X).

Therefore, in the present invention, such vinyl monomers (
The number of X) is m≧0.

Regarding the substituents of hydroxystyrene monomers,
Examples include:

(a) Here, M is an alkali metal or an alkaline earth metal, and suitable examples include Li, Na, K, Mg, Ca, Sr, and Ba. Introduction of a sulfone group can be achieved by a conventional sulfonation method using fuming sulfuric acid or sulfuric anhydride as a sulfonation agent.

(b) Here, R4 to R8 may be the same or different, and may be a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H, and R6 and R7 may form a ring with an N group. do not have. Moreover, Y2- represents a counter ion such as a halogen ion, an organic acid anion, or an inorganic acid anion.

Here, examples of straight-chain or branched alkyl groups include those having 1 to 36 carbon atoms, and examples of alkyl derivative groups include hydroxyalkyl groups, aminoalkyl groups, phosphoalkyl groups, mercaptoalkyl groups, etc. Examples of the aromatic group include a benzyl group substituted with a straight chain or branched alkyl group having 1 to 16 carbon atoms. Preferred examples include straight-chain or branched-chain alkyl groups, hydroxyalkyl groups, or aromatic groups substituted with straight-chain or branched-chain alkyl groups having 1 to 5 carbon atoms. The above-mentioned tertiary amino group can be easily introduced by, for example, the Mannich reaction using a dialkylamine and formaldehyde, and the quaternary ammonium base can be easily introduced by, for example, the Menshutkin reaction of the above-mentioned tertiary aminated compound with an alkyl halide ( c) Here, R4 and R5 are the same as above, and R9 to R12 are the same or different and represent a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H. In addition, W is S or O, q is 0 or 1, r is 0 or 1
or 2. Here, straight-chain or branched-chain alkyl groups include those having 1 to 36 carbon atoms, examples of alkyl derivative groups include hydroxyalkyl groups, aminoalkyl groups, mercaptoalkyl groups, phosphoalkyl groups, etc., and aromatic groups include Examples include phenyl groups substituted with straight chain or branched alkyl groups having 1 to 16 carbon atoms. Preferred examples include a straight-chain or branched alkyl group having 18 carbon atoms, a hydroxyalkyl group, or an aromatic group substituted with a straight-chain or branched alkyl group having 1 to 5 carbon atoms. Formula (Ha-1
) is obtained by methylolizing a hydroxystyrene copolymer and then reacting it with a phosphoric acid or phosphate ester group-introduced product, as disclosed in JP-A-53-71190, for example. It will be done. The hydroxystyrene copolymer represented by formula (H-2) is obtained by first halogenating or halomethylating the hydroxystyrene copolymer, and then adding 3 Reacts with phosphorus compounds of valence (
Arpusov reaction) and then thermal rearrangement.

(d) Here, R4 and R5 are the same as above, and R13 and R14
, R15 are the same or different and represent a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H. Further, S represents 0 or 1. Moreover, Y3- represents a counter ion such as a halogen ion, an organic acid anion, or an inorganic acid anion.

The production of this hydroxystyrene copolymer containing a phosphonium group is, for example, as shown in JP-A No. 61-34444, by reacting hydrogen halide with formaldehyde, resulting in halogenomethylation (for example, -CH2Cl
) and then treated with trivalent phosphite.

(E) Here, Y1 and Y4 are halogens, and R4, R5, and R6 are the same as above. t indicates 0 or 1.

(f) Other examples include alkyl groups or aryl groups having 1 to 18 carbon atoms.

In the general formula (I), the number of substituents Y and Z of the hydroxystyrene monomer is an average value in the polymer, and is 0≦k≦2, 0≦p≦2, and The number of OH is 0<u≦2.

The hydroxystyrene copolymer and/or its derivative that can be used as the organic binder component in the present invention has a weight average molecular weight in the range of 1,000 to 2,000,000, preferably in the range of 1,000 to 1,000,000. .

The reason for this is that the molecular weight of the organic polymer affects the effect of the present invention, with low molecular weight substances having a molecular weight of less than 1,000, it is difficult to obtain oxidation stability of the conductive powder, while on the other hand, when the molecular weight exceeds 2 million, it is good. It is difficult to obtain good conductivity. In order to obtain such a product, the repeating unit represented by the general formula (I) is usually n≧3.

Polar groups such as amino groups, phosphoric acid groups, sulfone groups (hydroxyl groups,
(does not contain aromatic rings) is particularly important in terms of increasing the affinity and reactivity of organic polymers with metal powders, and the preferred range of polar group density is an average of 0.0 per 500 units of molecular weight.
Between 1 and 5. If the polar group density is less than 0.01, the affinity with the metal powder will be poor, which will cause a problem, and if it exceeds 5, the corrosion resistance of the resulting paste will decrease, which will cause a problem. From the point of view of improving the corrosion resistance of conductive powder, amino-based
A methylol group and a phosphorus-based polar group are preferred. The hydroxyl group is important for improving the corrosion resistance of the metal powder and the adhesion with the insulating layer, and it is preferable that the hydroxyl group is directly attached as a substituent, or that a large number of hydroxyl groups are attached because the effect is better exhibited.

Factors such as the molecular weight, structural unit, type and density of polar groups, and type of main chain of the organic polymer described above are important factors that play an essential role for the binder of the conductive paste of the present invention.

Since most of the hydroxystyrene copolymers and their derivatives are thermoplastic resins, it is preferable to use thermosetting resins in combination. The blending ratio when using a thermosetting resin varies depending on the purpose, but the hydroxystyrene copolymer and/or its derivative is preferably 0.1 to 60 parts by weight per 100 parts by weight of the conductive powder. 1 to 45 parts by weight,
More preferably, the amount is in the range of 5 to 35 parts by weight, and the sum of the thermosetting resin and the hydroxystyrene copolymer and/or its derivative is preferably 5 to 85 parts by weight.

Thermosetting resins that can be effectively used in the present invention include known thermosetting resins such as phenolic resins, urea resins, amino resins, alkyd resins, silicone resins, furan resins, unsaturated polyester resins, epoxy resins, and polyurethane resins. can be used.

Particularly preferred are phenolic resins, amino resins, and epoxy resins.

Examples of phenolic resins include phenol, cresol,
Examples include resins obtained by adding and condensing aldehydes such as formalin and furfural to those having a phenolic hydroxyl group such as xylenol, p-alkylphenol, chlorophenol, bisphenol A, phenolsulfonic acid, and resorcinol. Particularly preferred are resol type phenolic resins. When using a novolac type phenolic resin, it is preferable to use hexamethylenetetramine together.

Examples of the amino resin include resins in which formalin is added and condensed to amino groups such as urea, melamine, guanamine, aniline, and sulfonamide, and preferably melamine resins in which formalin is added and condensed with an alkyl ether.

Among amino resins, alkyl etherified melamine resins are effective, with a weight average molecular weight in the range of 500 to 50,000 and a degree of alkyl etherification of 10% to 95% (1
00%, six alkyl ether groups are introduced into one triazine ring unit).

When using the above amino resin, to accelerate the curing reaction,
A known acid catalyst may be used. As an acidic catalyst,
In addition to mineral acids such as hydrochloric acid and phosphoric acid, organic fatty acids such as linoleic acid and oleic acid, monohydric or polyhydric phenol adducts such as phenol oleate and phenol linoleate, oxalic acid,
Known acids include organic acids such as tartaric acid, para-toluenesulfonic acid, or amine salts thereof.

As the epoxy resin, bisphenol diepoxides are preferred, such as Epicoat 827 manufactured by Shell Chemical Co., Ltd.
, 828, 834, 1001, 1002, 1004, 1
007, 1009, DER 330 manufactured by Dow Chemical Company
, 331, 332, 334, 335, 336, 337,
660, 661, 662, 667, 668, 669, Ciba Geigy Araldite GY 250, 260,
280, 6071, 6084, 6097, 6099, J
EPI-RE 2510 manufactured by ONES DABNEY
, 5101, Epicron 810 manufactured by Dainippon Ink Chemical Co., Ltd.
There are 1000, 1010, 3010 (all product names) and the EP series manufactured by Asahi Denka. Further, as the epoxy resin, it is also possible to use a novolak epoxy resin having an average number of epoxy groups of 3 or more, for example. As these novolac epoxy resins, those having a molecular weight of 500 or more are suitable. Examples of industrially produced novolak epoxy resins include the following: Ciba Geigy Araldite EPN 11
38, 1139, ECN 1273, 1280, 129
9. DEN 431, 438 manufactured by Dow Chemical Company, Epicote 152, 154 manufactured by Shell Chemical Company, ERR-0100, ERRB-0447, E manufactured by Union Carbide Company.
RLB-0488, Nippon Kayaku Co., Ltd. EOCN series, etc. Moreover, a curing catalyst and a diluent for the epoxy resin can be further used as necessary.

Epoxy resin curing catalysts include aliphatic amines such as diethylene triamine, triethylene tetramine, and tetramethylene pentamine, aromatic amines such as benzyldimethylamine, diaminodiphenylmethane, and diaminodiphenylsulfone, maleic anhydride, and phthalic anhydride. , hexahydrophthalic anhydride, methylnadic anhydride, p-dimethylaminobenzaldehyde, boron trifluoride/piperidine complex, and the like can be used. Examples of diluents for epoxy resins include reactive diluents such as n-butyl glycidyl ether, octylene oxide, phenyl glycidyl ether, styrene oxide, allyl glycidyl ether, methacryl glycidyl, dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, Non-reactive diluents such as triacetate, xylene, castor oil, pine oil, semi-reactive diluents such as alkyl(nonyl)phenols, polyglycols, polysulfides, styrene diaryl phthalate, ε-caprolactam, butyrolactone can be used.

The above-mentioned thermosetting resins used in the present invention may be used alone or in combination of two or more.

The blending ratio of the binder in the present invention is 1 part conductive powder
00 parts by weight, 5 to 85 parts by weight, preferably 10 to 85 parts by weight
If the amount is less than 5 parts by weight, the absolute amount of the binder is insufficient, resulting in poor fluidity of the resulting composition, resulting in poor printability and the conductive powder being easily oxidized during heat curing. , leading to a decrease in conductivity. Conversely, when the amount of binder exceeds 85 parts by weight, the absolute amount of conductive powder is insufficient, and the conductivity required to form a circuit cannot be obtained.

As the reducing agent used as an additive in the present invention, one or more known reducing agents can be used. Specifically, for example, compounds having a dihydroxybenzene ring such as hydroquinone, vinylhydroquinone, methylhydroquinone, chlorohydroquinone, phenylhydroquinone, t-butylhydroquinone, and catechol;
Vinyl hydroquinone homopolymers and copolymers, hydroquinone/formaldehyde phenolic resins, catechol/formaldehyde phenolic resins, 1
, 4-dihydroxynaphthalene/formaldehyde resin, resin having a dihydroxybenzene ring such as polyvinylcatechol resin, o-aminophenol, m-aminophenol, 2-amino-4-methylphenol, 2-
Aminophenols such as amino-4-nitrophenol and 2-amino-4-chlorophenol, pyridyl derivatives such as 2,2'-dipyridyl, 2,2'-dipicolyl, and 2,2'-diquinolyl, L-ascorbic acid , phosphorous compounds such as phosphorous acid and hypophosphorous acid, phosphorous acid derivatives such as dimethyl phosphite, trimethyl phosphite, and phosphine derivatives.

Among these, compounds having a dihydroxybenzene ring, aminophenols, L-ascorbic acid and the like are preferred, although they are not particularly limited.

The amount of the reducing agent added is usually 0.01 to 10% by weight, preferably 0.1 to 5% by weight, and more preferably 0.1 to 2% by weight. If it exceeds 10% by weight, the adhesion will decrease and 0.
．． If it is less than 0.01% by weight, the effect of addition will be weak, so it is not preferable.

In the present invention, a metal chelating agent may be used as an additive. A metal chelating agent is one that selectively adsorbs metal ions, and is not particularly limited as long as it coordinates with metal ions to form a chelate compound. It can be used as is. For example, as various amines, o-
Cyclic amines such as aminophenol, aliphatic amines such as monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, triethylenediamine, triethylenetetramine, 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), glycidyl methacrylate copolymers such as divinylbenzene/glycidyl methacrylate/styrene copolymer, polyvinylamine and vinylamine/vinyl alcohol copolymers. Derivatives such as polymers, o-nitrophenol resin, polymer hydroxamic acid obtained by reacting polymer ester with hydroxylamine, succinic acid, acetic acid, propionic acid, tricarballylic acid, humic acid, ammonium humate, nitrofumic acid Carboxylic acids, citric acid, lactic acid, tartaric acid, glyceric acid, malic acid, gluconic acid, tropic acid, etc.
Hydroxycarboxylic acids such as benzylic acid, manideric acid, atrolactic acid, glycolic acid, ascorbic acid, salicylic acid, salicylamide, salicylhydroxysamic acid, salicylaldoxime, salicylhydrazide, N,N
Salicylic acid compounds such as '-bissalicyloylhydrazine, phenylalanine, tyrosine, anthranilic acid,
Amino acids such as tryptophan, histidine, aspartic acid, glutamic acid, lysine, arginine, proline,
Imino acids such as hydroxyproline, pyridine carboxylic acids such as nicotinic acid, hydrazines such as hydrazine, phenylhydrazine, and hydrazobenzene, hydrazine monohydrochloride,
Examples include hydrazinium salts such as hydrazine sulfate, lauryl mercaptan, and the like.

The metal chelating agent in the present invention is not particularly limited as described above, but preferably one that is easily soluble in the solvent used in the conductive paste of the present invention is used.

The amount of metal chelating agent added is usually 0.01 to 5% by weight, preferably 0.05 to 2% by weight, more preferably 0.1% by weight.
~1% by weight. If the amount added is less than 0.01% by weight, the addition effect will not be sufficient, and if it exceeds 5% by weight, this will lead to a decrease in adhesion and migration resistance, which is not preferable.

The conductive paste of the present invention contains one or more additives selected from saturated/unsaturated fatty acids, metal salts thereof, and higher aliphatic amines in order to prevent oxidation or impart dispersibility to the conductive powder. may also be used.

Preferred saturated fatty acids include, for example, palmitic acid, stearic acid, and arachidic acid, and preferred unsaturated fatty acids include, for example, oleic acid and linoleic acid. Examples of such metal salts include sodium salts and potassium salts. It is also possible to use vegetable oils containing 60% or more of unsaturated fatty acids, such as soybean oil, sesame oil, olive oil, and safflower oil. The additive amount is 0.1 to 20 parts by weight, preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the conductive powder.
．． It is 5 to 10 parts by weight. If the amount is less than 0.1 parts by weight, the effect of addition will hardly be seen, and if it exceeds 20 parts by weight, not only will the improvement in dispersibility commensurate with the amount added be not achieved,
On the contrary, the conductivity and durability of the resulting coating film are reduced.

Moreover, any organic compound having an amino group can be used as the higher aliphatic amine used in the present invention, and may have other substituents. For example, it may be an amine having a hydroxyl group derived from an α-olefin. However, because of the need to use it together with conductive powder, for example, solid materials that do not dissolve in solvents cannot be used. Preferred are higher aliphatic amines having 8 to 22 carbon atoms.

Such higher amines include saturated monoamines such as stearylamine, palmitylamine, phenylamine, cetylamine, octylamine, decylamine, laurylamine, unsaturated monoamines such as oleylamine,
Examples include diamines such as stearylpropylene diamine and oleylpropylene diamine.

In the present invention, the higher aliphatic amine is used as a conductive powder 10
It is preferable that the total amount is 0.1 to 10 parts by weight based on 0 parts by weight.

The conductive powder used in the present invention includes copper powder, silver powder,
Examples include metal powders such as solder powder, nickel powder, and aluminum powder, and powders having a coating layer of the above metal on the surface. The shape may be dendritic, flaky, spherical, or amorphous, but the average particle size is 100 μm.
It is preferably less than m, more preferably about 1 to 30 μm.

This is because if the thickness exceeds 30 μm, it becomes difficult to pack the conductive powder at a high density, resulting in decreased conductivity and poor printability. The above-mentioned conductive powder can be used alone or in a mixed system. The higher the purity of the metal powder, the better. In particular, the copper powder most preferably has a purity that matches the purity of the copper foil or plated copper layer used for the conductor of the circuit board.

Furthermore, the effects of the hydroxystyrene copolymer and/or its derivatives of the present invention are more pronounced when metallic copper powder is used, so the present invention is particularly important for the production of conductive copper pastes.

The amount of conductive powder is 50 to 9 in the cured coating state.
It is used in a range of 5% by weight, preferably 60 to 90% by weight, more preferably 70 to 85% by weight.

If the blending amount is less than 50% by weight, sufficient conductivity cannot be obtained,
On the other hand, when the amount exceeds 95% by weight, the conductive powder is not sufficiently bound and the resulting coating film becomes brittle, resulting in decreased durability and poor screen printability.

To produce the conductive paste of the present invention, for example, first dissolve the hydroxystyrene copolymer and/or its derivative in a solvent, then add the thermosetting resin and conductive powder, and process this using a disper, ball mill, or A conductive paste is prepared by sufficiently uniformly kneading with a triple roll or the like.

Solvents that can be used here include benzene, toluene, hexanone, dioxane, solvent naphtha,
Industrial gasoline, cellosolve acetate, cellosolve ethyl,
Known solvents include alcohols such as butyl cellosolve, butyl cellosolve acetate, butyl carbitol acetate, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, isopropyl alcohol, butanol, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. The amount of solvent blended varies depending on the type of kneader, cross-wire conditions, and type of solvent. It is preferable to adjust the amount of solvent so that the viscosity of the paste after kneading is within a range that allows screen printing.

A method for producing a circuit board for preventing electromagnetic noise by providing an electromagnetic shielding layer on a circuit board using the conductive paste of the present invention is, for example, to fabricate a circuit board for preventing electromagnetic noise by providing an electromagnetic shielding layer on the circuit board. An insulating layer is provided by applying a heat-curable or ultraviolet-curing organic insulator except for the ground pattern portion, and the conductive paste according to the present invention is used on the insulator layer and connected to the ground pattern by screen printing. By applying a conductive paste to almost the entire surface of the insulating layer and curing it by heating, it is possible to produce a circuit board for electromagnetic noise countermeasures having an effective electromagnetic shielding layer. This circuit board can also be effectively used as an electrostatic shield layer.

Further, the conductive paste of the present invention can be used as a conductor for wiring on a circuit board by a conventional method. The insulating substrates to be coated are glass/epoxy resin substrates,
Paper, phenolic resin substrate, ceramic substrate, polycarbonate resin substrate, polyethylene terephthalate resin substrate, polyimide resin substrate, polyolefin resin substrate, vinyl chloride resin substrate, polyester resin substrate, ABS resin substrate, polymethyl methacrylate resin substrate, melamine resin substrate, phenol Any of resin substrates, epoxy resin substrates, glass substrates, etc. may be used. As a wiring formation method, a coating method such as screen printing, intaglio printing, spraying, or brush coating can be used.

In the present invention, the conductive coating film refers to a cured body or cured coating film having a volume resistivity of 1×10 −2 Ω·cm or less obtained by drying and curing the conductive paste of the present invention.

[Effect]

The conductive paste of the present invention has the following characteristic effects 1) to 5).

1) The hydroxystyrene copolymer and/or its derivative used as a binder component has affinity with the metal surface,
Due to its excellent reactivity, a dense protective film is formed on the surface of the conductive particles other than the contact area during heat curing, increasing the rust prevention properties of the metal powder. In other words, conductivity can be maintained for a long period of time.

2) For the reason 1), when applied on a circuit board, the adhesion of the ground pattern portion to the copper foil is improved.

3) For the reason 2), even if the oxide of the electrically insulating oxide film is reduced by adding a reducing agent, the adhesion to the copper foil can be maintained. Therefore, when used in combination with a reducing agent, it is possible to maintain and improve conductivity while maintaining adhesion.

4) Adhesion to the organic insulating layer is improved by the action of the hydroxystyrene copolymer and/or its derivative.

5) The chelating action of the hydroxystyrene copolymer and/or its derivative improves the rust prevention properties of the metal powder in a paste state, making it possible to maintain electrical conductivity for a long period of time.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention is not limited only to these Examples. In Examples and Comparative Examples, "parts" means "parts by weight."

Paste Preparation/Printing Conductive powders shown in Table 1, hydroxystyrene copolymers and/or derivatives thereof shown in Table 2, thermosetting resins shown in Table 3, reducing agents shown in Table 4, and others. A conductive paste is prepared by thoroughly and uniformly kneading the additives shown in Table 5 using a disperser or a triple roll. Using each of the obtained conductive pastes, an organic insulating layer (S-2 manufactured by Taiyo Ink Co., Ltd.
22, HR-6) was printed to a thickness of 40 to 50 μm. hardened glass. A pattern with a width of 2 mm and a total length of 36 cm was printed on an epoxy resin substrate (CEM-3). Next 14
Heat cured at 0 to 160℃ for 10 to 30 minutes to a thickness of 20 to
A paste cured film of 30 μm was obtained.

Table 6 shows the results of examining various characteristics of the conductive circuit obtained through the above process.

Measurement of conductivity The conductivity of a paint film is measured by measuring the volume resistivity of a heat-cured paint film using a digital multimeter (Advantest R6).
551) by the two-terminal method.

Note that the formula for calculating the volume resistivity is shown in formula (1).

R: Resistance value between electrodes (Ω) t: Thickness of coating film (cm) W: Width of coating film (cm) L: Distance between electrodes (cm) Moisture resistance test Moisture resistance of a coating film is 60 A storage test was conducted for 500 hours in an environment of 95% relative humidity at 95% relative humidity, and the rate of change in resistance value WR before and after the test was determined using equation (2).

R0: Resistance value of the coating film before the test (Ω) R500: Resistance value after the 500 hour test (Ω) The moisture resistance of the coating film is expressed as follows based on the value of WR.

A: WR is less than 30% B: WR is 30% or more and less than 100% C: WR is 100% or more Initial adhesion test The adhesion of the coating film was determined using sulfuric acid/ammonium citrate (1:
After dissolving the surface oxide film by dipping in a 5% aqueous solution of 1) at 40°C for 30 seconds, a copper foil and organic insulating layer (manufactured by Taiyo Ink Co., Ltd. S-2) having a metallic copper surface was air-dried with jet air.
22, HR-6) with conductive paste of the present invention on top of 20~
Screen printed to a thickness of 30 μm and JIS K after curing
5400 (1979), 1 mm parallel lines of 11 vertical and horizontal lines perpendicular to each other were drawn on the coating film.
The coating film that remains on the copper foil or organic insulating layer when the coating film is peeled off using cellophane tape after making a grid-like cut so that there are 100 squares in 1 cm2. The number of pieces on the grid was calculated. The judgment criteria are as follows.

A: 100/100 B: 90/100 or more to less than 100/100 C: 50/
100 or more - less than 90/100 D: 0/100 or more - 1
Adhesion test after solder test less than 0/100 Organic acid flux was applied to the surface of the substrate with a brush, and then immersed in a molten solder bath at 260° C. for 10 seconds. After the substrate was left to cool to room temperature, an adhesion test was conducted using the method described above, and judgment was made according to the criteria described above.

Comparative Example After preparing a conductive paste with the composition shown in Table 6 and forming a conductor on a substrate in the same manner as in the example, the volume resistivity of the coating film was measured, and the moisture resistance, heat resistance, printability, and adhesion were measured. , the adhesion was investigated after the solder test. The results are also shown in Table 6.

(The following is a blank space) Table 6 shows various characteristics of the conductive paste and conductive coating film according to the present invention, together with comparative examples.

Invention Example No. Each of the conductive pastes Nos. 1 to 19 achieves high conductivity by adding a reducing agent, and has a PH of
It can be seen that the addition of S (polyhydroxystyrene) or its derivative suppresses the decrease in adhesion caused by the addition of the reducing agent, and maintains excellent adhesion.

Comparative example No. not including these. It can be seen that pastes Nos. 20 to 26 lack one of the above physical properties.

As described above, it is understood that high conductivity can be achieved while maintaining adhesion by using the novel conductive paste of the present invention.

〔Effect of the invention〕

The conductive paste of the present invention uses an organic polymer having a specific chemical structure as described above, that is, a hydroxystyrene copolymer and/or its derivative as a binder component, and contains a reducing agent as an additive. It has major characteristics. According to the present invention, the oxidation stability of the conductive powder can be improved by controlling the affinity and reactivity with the metal surface by adjusting the type and density of substituents introduced into the hydroxystyrene copolymer and/or its derivative. It is possible to improve the conductivity of the paste and maintain the conductivity of the paste for a long period of time. Furthermore, it is possible to significantly improve the adhesion between the copper foil surface and the insulating layer.

Therefore, for example, by using the conductive copper paste of the present invention, it is possible to significantly improve the durability (oxidation stability) and adhesion to the substrate, which were considered to be major drawbacks of conventional copper pastes. . By using this new copper paste,
An extremely reliable and highly effective electromagnetic shielding layer can be easily and stably formed on a circuit board.

Similarly, when used as a conductor for wiring on a circuit board, it is possible to form highly reliable wiring. It can also be effectively used as electrodes for electronic equipment parts and circuit parts. These effects are extremely significant industrially.

Patent applicant: Kao Corporation

Claims (3)

[Claims] 1. A conductive paste comprising a conductive powder, an organic binder, an additive, and a solvent as essential components, wherein the organic binder is a hydroxystyrene copolymer and/or a hydroxystyrene copolymer having a weight average molecular weight of 1,000 to 2,000,000. A conductive paste comprising a derivative thereof and a reducing agent as the additive. 2. The conductive paste according to claim 1, wherein the hydroxystyrene copolymer and/or its derivative is an organic polymer represented by the following general formula (I). General formula (I): [wherein m≧0, n≧3, each of which is an arbitrary number until the weight average molecular weight of the organic polymer of general formula (I) is 1,000 to 2,000,000, ;0 ≦k≦2, ;0≦p≦2, ;0<u≦2, (However, k, p, and u indicate the average value in the polymer.); R1 to R2 are H or carbon number 1 to 5 an alkyl group; ; ; M is H, an alkali metal, an alkaline earth metal, or an organic cation such as amines; Y1 and Y4 are halogens; Y2- and Y3- are halogen ions, organic acid anions,
A counter ion such as an inorganic acid anion; W is S or O; R4 to R8 are the same or different and are a linear or branched alkyl group, an alkyl derivative group, an aromatic group, or H
, Furthermore, R6 and R7 may form a ring with an N group. ; R9 to R15 are the same or different and are linear or branched alkyl groups, alkyl derivative groups, aromatic groups, or H; q, s, and t are 0 or 1; r is 0, 1, or 2) ] 3. A conductive coating film, which is obtained by coating or printing the conductive paste according to claim 1 or 2 on a substrate and then curing the paste.