JP2007100062A - Method for producing electro conductive coating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electro conductive coating material comprising a well-dispersed conductive powder having a minute particle diameter, easy in redispersion after storing for a long period without such a variation with time in physical properties as the increase of viscosity and further capable of thick-film printing to form a circuit pattern having a narrow line and a small pitch between the lines and good conductivity; and to provide a method for producing the conductive coating material. <P>SOLUTION: The method for producing the conductive coating material is carried out by the followings. The conductive powders (a) are dispersed in an aqueous solvent in the presence of a surfactant (b), providing an aqueous dispersion. After surface-treating the conductive powders (a) prepared by vacuum-freeze drying the aqueous dispersion, the surface-treated conductive powders (c) are mixed with a solvent and an adhesive resin. Where the mass ratio of the resin/conductive powder is ≤0.1 and preferably the surfactant is an alkylamine, an alkylamine salt or a phosphate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a conductive paint that can be used for printed wiring used in electronic devices and the like and has excellent conductivity and printing accuracy.

The conductive paint is a paste containing conductive fine powder in a solid content. Generally, a metal such as gold, platinum, silver, palladium, etc. that is not oxidized in air is used as the conductive powder. Conventionally, conductive paints can be broadly divided into (1) high-temperature sintered conductive paints that can achieve good conductivity, but the base material is limited to ceramics, and (2) glass and epoxy prints. Although it can be widely applied from a substrate to a film, there is a polymer-type conductive paint having a relatively high electrical resistance in order to obtain conduction by contact between metal powder particles due to heat shrinkage during binder curing.
For example, when a conductive circuit is formed on a flexible printed circuit board support using a polymer-type conductive paint, the polymer-type conductive paint is used for screen printing on a plastic film such as polyethylene terephthalate or polyimide. Then, a conductive circuit pattern is formed, and the binder in the formed pattern coating film is heat-cured to improve conductivity and durability, and secure adhesion on the film.

In particular, polymer-type conductive paints using silver or silver compounds are easy to achieve stable conductivity and have good thermal conductivity, so they can be used to form various wiring and electronic circuit patterns inside or between electronic components. It has been.
In the process of printing a conductive circuit pattern, it is required to increase the printing density and printing accuracy as much as possible and to reduce the resistance between terminals as the circuit becomes finer.
Improvement in printing density and printing accuracy is limited by the average particle size of silver or silver compound powder. For this reason, in order to obtain good printing accuracy, it is necessary to disperse to primary particles. The primary particles of the silver or silver compound powder are completely covered with a resin or the like to be highly dispersed to produce a conductive paint. It is required to do.
If the primary particles of the silver or silver compound powder are highly dispersed and the coating of resin or the like is insufficient, the conductive paint becomes more active as the primary particle size becomes finer. If sufficient resin coating on the silver surface is not performed, the particles are quickly aggregated after production, the viscosity tends to increase with time, and in extreme cases, gelation may occur.

On the other hand, studies on reducing the resistance include (1) increasing the coating thickness or (2) reducing the specific resistance of the conductive paint. In particular, in order to reduce the resistance associated with wiring while maintaining a high printing density, it is important to increase the coating thickness of fine wires used for wiring, as well as the selection of conductive powder. Therefore, a paint having high thixotropy is required.
Furthermore, in order to reduce the specific resistance of the conductive paint, it is necessary to keep the resin coating of the conductive powder as thin as possible and keep the conduction state between the conductive particles as good as possible.

In order for such a fine wiring pattern to be formed accurately and stably, it is necessary that silver powder or the like is stably dispersed to primary particles and each particle is coated with a resin. On the other hand, the resin coating is too thick. In addition, the resin component remaining between the particles tends to hinder electrical conduction between the particles, so that good conductivity tends not to be obtained, and the tendency becomes more remarkable as the particle diameter of the silver powder to be used becomes smaller. . Furthermore, the thicker the resin coating, the higher the content of the resin component in the paint and the higher the thixotropy, making it impossible to increase the film thickness while preventing the printed film from sagging after printing. .
Therefore, the amount of resin used for dispersion is preferably the minimum necessary, and with a smaller amount of resin, the dispersibility of conductive powder such as silver powder, the adhesion of the paint to the substrate, and the film formability of the paint are improved. It is preferable.

Conventionally, in preparing a paint by dispersing conductive powder in a resin, in order to improve its dispersibility, higher fatty acid ethylene oxide, propylene oxide addition ester compound, sorbitan and fatty acid ester compound, polyhydric alcohol such as sorbitan Nonionic dispersants such as ethylene oxide, propylene oxide adduct ether compounds, ethylene oxide of alkylbenzene, propylene oxide adducts, alkylbenzene sulfonic acid alkali salts, higher alcohol sulfate alkali salts, phosphate ester compounds, higher fatty acids, higher fatty acid ethylene oxide, Various dispersing agents such as anionic dispersing agents such as sulfate alkali salts of propylene oxide adducts and quaternary ammonium salt type cationic dispersing agents are used.
However, even when these dispersants are used, the conventional method of dispersing conductive metal powder in a resin using, for example, a disperser or a kneader sufficiently improves conductivity while maintaining good dispersibility. I couldn't.

  In particular, it is difficult to disperse by avoiding sedimentation properties such as silver powder having a true specific gravity of 10.5. The amount of resin to be mixed is as large as possible, and the amount of solvent is preferably as small as possible, but the dispersion is advanced. Is not easy, and even if the dispersion progresses, the amount of resin is large, so that it behaves like a Newtonian fluid with low thixotropy. As a result, when the film thickness after printing was increased, the printed coating film was struck and the printed shape became a mountain shape, so that the printing accuracy was not improved and the specific resistance of the printed coating film was not lowered.

For such problems, for example, an attempt to obtain good dispersibility and stability over time by using an anionic surfactant comprising a conductive powder such as silver powder, an organic vehicle, and a sulfosuccinate containing an alkyl group. Has been done. (See Patent Document 1)
However, the use of the method described in Patent Document 1 is insufficient to improve the redispersibility of the precipitated silver powder and the like.
Further, the amount of resin used for dispersion is not reduced to the minimum necessary, and the conductivity is insufficient.

On the other hand, in the production of a dispersion using metal powder, a vacuum freeze-drying method is used. For example, in the production of a tantalum powder coating material for producing an anode element for an electrolytic capacitor, tantalum powder and a dispersant are contained in a solvent. And a method of adsorbing a dispersing agent on the tantalum surface by performing vacuum freeze drying (see Patent Document 2).
However, there is no example of applying vacuum freeze-drying to the production of conductive paints that have the same metal dispersion but differing in characteristics and applications, and no relationship between dispersibility and conductivity is suggested. Furthermore, there is no disclosure about the selection of a dispersant for developing good conductivity.

  In particular, in recent years, in order to reduce the electrical resistance of conductor circuits formed from conductive paints, the particle diameter of silver powder is made very fine, or particulate silver compounds containing particulate silver oxide and tertiary fatty acid silver are used. For example, it has been studied to use a conductive paint that can be fired at a low temperature. In this low-temperature firing type conductive paint, the finely divided silver powder is fused to each other by heating at 300 ° C. or lower, and the electrical resistance of the conductive circuit is lowered. In addition, the particulate silver compound is reduced to metal silver by heating at 300 ° C. or lower or in the presence of a reducing agent, and adjacent silver particles are fused together to reduce the electrical resistance of the conductive circuit (for example, And Patent Document 3).

  Conventionally, polymer-type conductive paints are added with a binder made of a thermoplastic resin such as acrylic resin or polyester resin or a thermosetting resin, an organic solvent, a curing agent, a catalyst, etc. as necessary, and spherical or flaky silver particles are added. Dispersed and mixed, conductivity was obtained by contact between silver particles due to curing shrinkage when the binder was thermally cured. For this reason, the electrical resistance becomes relatively high, and the cohesive force of the cured resin changes depending on the heating conditions, etc., and accordingly, the electrical resistance of the conductor circuit formed using the polymer type silver paint is reduced. It had the disadvantage of being easy to fluctuate.

The low-temperature firing type conductive coating material compensates for these drawbacks. By using this conductive coating material, a conductive circuit having good conductivity can be formed on a plastic film such as PET.
However, the finely divided silver powder and particulate silver compounds used in low-temperature firing type conductive paints must be stored in a solution such as water or a solvent having low reducibility because the reduction reaction rate is very fast. However, it may be difficult to handle with dry powder. In particular, when an alcohol or the like is used as a dispersion solvent, reduction proceeds during dispersion of silver or silver compound powder, and instead of being dispersed, fusion between silver particles may occur. For this reason, it is further required to disperse these silver and silver compound powders to primary particles to coat and stabilize the surface of each silver particle. Furthermore, in these conductive paints, in order to obtain the original high electrical conductivity, it is necessary that the silver particles in the paint be well dispersed while maintaining a high silver content. It is necessary to perform the stabilization by using a resin, to make the coating thickness on the silver surface as thin as possible, and to facilitate the fusion of adjacent resins by low-temperature firing.

If the resin is reduced as described above, the thixotropy increases, the thickness after printing can be increased, and there is an advantage that not only the specific resistance but also the substantial electrical resistance can be reduced. When the coating formed on the surface of silver and the silver compound is too thick, adjacent particles are difficult to fuse with each other, and the thixotropy is lowered, so that the height after printing is lowered and the substantial electrical resistance is increased. Furthermore, since the filling degree of silver or a silver compound is also lowered, the maximum characteristics of these low-temperature baking type conductive paints which are low-temperature baking and have good conductivity are diminished.
Therefore, for these low-temperature firing type conductive paints, the selection of a dispersant for simultaneously satisfying the stabilization by coating with individual silver particles, the improvement of dispersibility, and the improvement of conductivity by low-temperature firing, The manufacturing method was even more important.
As described above, in order to sufficiently bring out the characteristics of the conventional polymer-type conductive paint, there has been a demand for a dispersion method for realizing a conductive paint having a good dispersion state with a small amount of resin.
JP 2000-231828 A JP 2004006502 A JP 2003-309337 A

  The object of the present invention is that the finely divided conductive powder is well dispersed, there is no change over time in physical properties such as an increase in viscosity, redispersion after long-term storage is easy, and thick film printing is possible. Another object of the present invention is to provide a conductive paint capable of forming a wiring pattern having high printing density and good conductivity, and a method for producing the conductive paint.

  The present invention includes a dispersion step of producing an aqueous dispersion by dispersing conductive powder in a solvent comprising water and / or a water-soluble solvent in the presence of a surfactant, a drying step of freeze-drying the dispersion, and Production of a conductive paint characterized by comprising a paint-making process in which the product of the drying step is mixed with a solvent and a binder resin to produce a paint having a mass ratio of resin / conductive powder of 0.1 or less. Provide a method.

In the method for producing a conductive paint of the present invention, first, the conductive powder is dispersed as fine particles by the dispersion step and the drying step, and the surface of the particles of the conductive powder is alkylamine and alkylamine salt or phosphate ester type. The surface of the particles is satisfactorily coated.
The method for producing a conductive paint according to the present invention includes a dispersion step in which conductive powder is dispersed in a water-soluble solvent in the presence of a surfactant to produce an aqueous dispersion, and a drying step in which the dispersion is vacuum-lyophilized. Therefore, the surfactant can be effectively adsorbed on the surface of the conductive powder.
As a result, since the surface of the conductive powder is already surface-treated with a surfactant in the coating process, the amount of resin added as a dispersant can be suppressed to a small amount, and the mass ratio of resin / conductive powder. Thus, a conductive paint in which conductive powder is well dispersed with a resin component as small as 0.1 or less can be produced.
For this reason, the compounding quantity of electroconductive powder can be increased, thixotropy can be made high, a wiring pattern with a thick coating film thickness can be formed, and the resistance value of an electroconductive circuit can be lowered.

  Furthermore, since the resin coating covering the particle surface of the conductive powder is thin, silver or silver compound powder having a low sintering temperature, such as ultrafine fine silver powder, low crystallinity (crystallite diameter) silver powder Alternatively, when silver powder treated with silver oxide is applied, the contact resistance between the particles is low, and the specific resistance of the coating film forming the wiring pattern can be reduced. In particular, when a low-temperature sintering type conductive coating is manufactured by the method for manufacturing a conductive coating of the present invention, for example, the resin coating on the surface of the silver powder is thin. Therefore, the electrical resistance of the conductive circuit can be reduced, or it can be reduced by heating at 300 ° C. or lower, or by heating in the presence of a reducing agent, to form metallic silver, and adjacent silver particles can be reliably fused. Therefore, the electrical resistance of the conductive circuit can be reduced. Thus, by using the method for producing a conductive paint of the present invention, a wiring pattern having a low sintering temperature and good conductivity after sintering can be formed.

In addition, a metal powder such as silver having a large specific gravity usually tends to settle out in a normal processing method, and a concentration distribution tends to occur in the disperser, so that uniform processing is difficult. In the dispersion step and the drying step in the production method, the conductive powder is dispersed under a solvent containing a surfactant and then subjected to vacuum freeze-drying to treat the conductive powder. The particle surface can be treated.
When coating is performed using conductive powder surface-treated with such a surfactant, a dispersion having a wide range of viscosity can be produced only by mixing or kneading with a solvent or a resin and a solvent.

In general, since the paint viscosity is defined by the dispersing machine used, it is usual to readjust the paint viscosity after completion of dispersion to an optimum viscosity according to each printing method. For example, in order to set a high viscosity optimal for the screen printing method, the solvent amount of the sample after dispersion may have to be reduced.
However, in the coating process of the method for producing a conductive paint according to the present invention, the conductive powder that has been surface-treated with a surfactant, the solvent for forming the paint, and the resin are mixed and stirred, so that the conductive paint is obtained. Can be manufactured. For this reason, the degree of freedom of the blending ratio is high, and not only the viscosity adjustment by the amount of solvent but also the amount of resin can be prescribed in order to obtain thixotropy. As a result, it is possible to easily produce a conductive paint having silver powder content, viscosity, and flow characteristics most suitable for the printing means used for producing the conductor circuit.
The conductive paint produced by the method for producing a conductive paint of the present invention can be stored for a long period of time because a stable dispersion can be easily obtained by redispersion with stirring even if the standing period after coating is long. However, it is also stored in the state of conductive powder (conductive powder with conductive particles coated with a surfactant) that has been surface-treated in the dispersion process and drying process, and only the required amount of conductive powder is stored if necessary. It is also possible to produce a reactive paint.

  The method for producing a conductive paint of the present invention comprises (1) a dispersion step in which a conductive powder is dispersed in a water-soluble solvent in the presence of a surfactant to produce an aqueous dispersion, and (2) the dispersion is vacuum freeze-dried. And (3) a coating process for mixing the product of the drying process with a solvent and a binder resin to produce a paint having a resin / conductive paint mass ratio of 0.1 or less. Hereinafter, the manufacturing method of the conductive paint of this invention is demonstrated in detail in order of each manufacturing process.

(1) Dispersing Step In the dispersing step of the present invention, the conductive powder is dispersed in a solvent in the presence of a surfactant.

As the conductive powder used in the present invention, any metal powder treated as a general conductor can be used. For example, nickel, copper, gold, silver, aluminum, chromium, platinum, palladium, tungsten, molybdenum, etc., and an alloy of two or more of these, or a compound of these metals having good conductivity can be given.
In particular, silver powder made of silver or a silver compound is preferable because it can easily realize stable conductivity and has good heat conduction characteristics.

As the silver powder used in the present invention, pure silver powder, metal particles whose surface is coated with silver, or a mixture thereof can be used. As the silver powder, those having an arbitrary shape such as a spherical shape, a scale shape, a needle shape, and a dendritic shape can be used. The method for producing the silver powder is not particularly limited, and may be any method such as a mechanical pulverization method, a reduction method, an electrolysis method, or a gas phase method. The metal particle surface-coated with silver is obtained by forming a silver coating layer on the surface of a particle made of a metal other than silver by a method such as plating. As the silver particles, spherical silver powder and scaly silver powder consisting only of silver are preferable from the viewpoint of conductivity and cost.
The volume average particle diameter of the conductive powder such as silver particles is preferably about 0.05 to 10 μm, more preferably about 0.05 to 5 μm. As the silver particles, the conductivity of the conductive film may be improved by combining two or more kinds of particles having different volume average particle diameters or more to improve the packing density of silver.

  As a powder of a silver compound, powders of silver-containing organic compounds such as silver oxide, aliphatic carboxylate silver, alicyclic carboxylate silver, and aromatic carboxylate silver can be used. As these silver compound powders (particulate silver compounds), those produced industrially can be used, and those obtained by a reaction from an aqueous solution containing a silver compound may be used. In particular, it is preferable to use a silver compound powder having an average particle size of 0.5 μm or less because the speed of the reduction reaction is increased. In order to produce a silver compound powder having an average particle size of 0.5 μm or less, an aqueous alkali solution such as sodium hydroxide is added dropwise to an aqueous solution of silver nitrate produced by reaction of the silver compound with another compound with stirring. It can manufacture by the method of making it react and obtaining silver oxide powder.

  In the method for producing a conductive paint of the present invention, when silver or a silver compound powder is used as the conductive powder, the polymer-type conductive paint is heated even when the decomposition temperature of the resin is taken into consideration. It is preferable to use a material that can bring the firing temperature to 300 ° C. or lower. The conductive paint using the silver or silver compound powder having such a low firing temperature can, for example, sinter a wiring pattern formed on a polyimide film or a PET film as it is. Generally, the finer the conductive metal powder of the conductive paint is dispersed, the lower the heat capacity of the powder and the closer to the specific firing temperature of the powder. Furthermore, as the powder is finely dispersed, the close-packed form is easily obtained and the higher the dispersion, the better the conductivity after sintering. Moreover, the conductive paint produced by the production method of the present invention can reduce the blending amount of the resin, and the coating film of silver powder is thin, so that adjacent particles are easily fused after firing. For this reason, when low-temperature firing type silver or a silver compound having a firing temperature of 300 ° C. or less is used as the conductive paint of the present invention, the original low-temperature sinterability can be sufficiently exerted, and the conductive property after sintering A good wiring pattern can be obtained.

  As the silver powder having a low firing temperature, a silver powder having a volume average particle size of 0.05 to 10 μm can be used. It is more preferable to use silver powder having a volume average particle diameter of 0.05 to 5 μm. In the present invention, when silver powder is produced in a liquid phase, these highly active silver powders are effectively treated with the surface treatment in the presence of a surfactant in the liquid phase when the silver powder is produced. Therefore, the original characteristics of these silver powders can be fully exhibited. Examples of the method for producing fine particle silver powder include a gas evaporation method (JP-A-3-34211) and a reduction precipitation method using an amine compound for reduction (JP-A-11-319538).

  Furthermore, as the silver powder having a low sintering temperature, a silver powder having a low crystallinity can be used. When the crystallinity of the silver powder is low, the crystallite size is usually small. Therefore, by reducing the crystallite size, the fusion temperature between silver particles can be remarkably lowered. In order to lower the firing temperature of the conductive paint to 300 ° C. or less, the crystallite diameter is preferably 20 nm or less, and more preferably 10 nm or less.

Further, as a silver or silver compound powder having a low sintering temperature, silver powder in which some of the particles of the silver powder are treated with silver oxide can be used.
By the oxidation treatment on the silver particle surface, the silver on the particle surface is oxidized into first silver oxide, second silver oxide, and the like. In the silver whose particle surface is coated with silver oxide, silver oxide such as first silver oxide and second silver oxide may be mixed. In the silver powder whose surface is coated with silver oxide, silver oxide on the surface layer becomes silver by a reduction reaction in the absence of a reducing agent or in the presence of a reducing agent, and adjacent particles are fused together at a low temperature. The silver powder whose surface is treated with silver oxide can be appropriately selected from those having different compositions and shapes depending on the reduction reaction conditions; heating temperature, presence / absence of a reducing agent, reducing power of the reducing agent, and the like. The volume average particle diameter of the silver powder treated with silver oxide is preferably about 0.05 to 10 μm, more preferably about 0.05 to 5 μm. In particular, it is preferable to use a powder having an average particle size of 0.5 μm or less because the reduction reaction rate is increased. The silver content of the silver powder surface-treated with silver oxide is preferably 60% or more, more preferably 70% or more, and particularly preferably 80% or more.

  By using these silver oxide-treated silver powders as conductive powders in the method for producing conductive paints of the present invention, these particles having the property of being very easily reduced when dried are converted into fine particles even in conductive paints. Can be dispersed stably. For this reason, it is possible to prevent unnecessary agglomerates from being generated due to the fusion of the particles during the reduction, and no problem in fine printing occurs.

As the surfactant used in the method for producing a conductive paint of the present invention, it can be selected from many types of surfactants that are usually used, and can be used as an anionic surfactant or a nonionic surfactant. Surfactants, cationic surfactants, and amphoteric surfactants can be exemplified. Examples of the anionic surfactant include alkyl sulfate, polyoxyethylene alkyl sulfate ester salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, fatty acid salt, salt of naphthalene sulfonate formalin condensate, polycarboxylic acid type Examples thereof include polymeric surfactants, alkenyl succinates, alkane sulfonates, polyoxyalkylene alkyl ether phosphates and salts thereof, polyoxyalkylene alkyl aryl ether phosphates and salts thereof, and the like.
Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene derivatives, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxy Examples include ethylene fatty acid esters, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamines, polyoxyalkylene alkylamines, and alkyl alkanolamides.
Examples of the cationic surfactant include alkylamine salts and quaternary ammonium salts.
Examples of amphoteric surfactants include alkyl betaines and alkyl amine oxides.

  Among these surfactants, alkylamine-based, alkylamine salt-based, and phosphate ester-based surfactants are particularly preferable for use in the method for producing a conductive paint of the present invention. .

(Surfactants of alkylamines and alkylamine salts)
As the surfactant used in the present invention, alkylamines and alkylamine salts can be suitably used. This is particularly effective when silver powder is used as the conductive powder. Alkylamine-based nonionic surfactants and alkylamine-salt-based cationic surfactants are effective when used alone, but when used in combination, the dispersibility becomes better and the effect is remarkable. It is.
As the alkylamine surfactant, a polyoxyalkylene alkylamine type surfactant is preferable, and a polyoxyethylene alkylamine type surfactant is more preferable. Among them, those having the following chemical structure (1) are more preferable.

  In the formula (1), a and b are each an integer of 1 to 20, and R represents an alkyl group or an alkylaryl group having 8 to 20 carbon atoms.

  On the other hand, alkylamine salt surfactants are preferably alkylamine acetates, more preferably those having the following chemical structure (2).

  However, in Formula (2), R represents a C8-C20 alkyl group or alkylaryl group.

  In the formula (1) and the formula (2), the alkyl group having 8 to 20 carbon atoms may be a linear alkyl group or a branched alkyl group. For example, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, Examples include lauryl group, tetradecyl group, myristyl group, hexadecyl group, cetyl group, octadecyl group, stearyl group, and eicosyl group. Examples of the alkylaryl group having 8 to 20 carbon atoms include alkylphenyl groups such as octylphenyl group, nonylphenyl group, and dodecylphenyl group. The alkyl part of the alkylaryl group may be a linear alkyl group or a branched alkyl group.

When using an alkylamine surfactant and an alkylamine salt-based cationic surfactant alone or in combination, the total amount of surfactant to be added to the conductive powder depends on the type of conductive powder. Need to adjust. For example, although the compounding quantity with respect to silver powder needs to adjust a little with the kind of silver powder, 0.01-3.00 mass parts is preferable with respect to 100 mass parts of silver powder, and 0.05-1.50 mass parts is still more preferable. . When the total amount of the surfactant is less than 0.01 parts by mass, sufficient dispersibility tends to be difficult to obtain. On the other hand, if the amount exceeds 3.00 parts by mass, the silver surface is thick and coated with the organic component of the surfactant, making it difficult to obtain contact between the silver particles after drying, and the conductivity tends to be lowered.
When an alkylamine-based surfactant and an alkylamine salt-based cationic surfactant are used in combination, the mixing ratio of the alkylamine-based and alkylamine salt-based systems is in the range of 1:20 to 1: 5. preferable.

(Phosphate-based surfactant)
As the surfactant used in the present invention, a phosphate-based surfactant can also be suitably used. This is particularly effective when silver powder is used as the conductive powder.

  The phosphate ester surfactant used in the present invention is a surfactant mainly composed of phosphate monoester or phosphate diester. The phosphate ester-based surfactant as the main component is preferably a phosphate ester of polyoxyalkylene alkyl ether, and more preferably has a chemical structure represented by the following general formula (3).

  However, in Formula (3), R represents a C1-C20 alkyl group or an alkylaryl group, n is an integer of 1-20, x is 1 or 2.

  In the formula (3), the alkyl group having 1 to 20 carbon atoms may be a linear alkyl group or a branched alkyl group. For example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group, hexyl group , Heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, lauryl group, tetradecyl group, myristyl group, hexadecyl group, cetyl group, octadecyl group, stearyl group, eicosyl group and the like. Examples of the alkylaryl group having 20 or less carbon atoms include alkylphenyl groups such as octylphenyl group, nonylphenyl group, and dodecylphenyl group. The alkyl part of the alkylaryl group may be a linear alkyl group or a branched alkyl group.

In the formula (3), it is preferable that the carbon number of R is 1 to 10, n is 1 to 10, and the sum of the carbon number of R and n is 7 to 15. The weight average molecular weight of the phosphate ester surfactant is preferably 100 to 10,000, and more preferably 150 to 5,000. The phosphoric acid ester surfactant used in the present invention has a phosphorus content (P content) of preferably 0.5% to 10%, particularly preferably 2% to 6%.
Further, as the phosphate ester surfactant used in the production method of the present invention, it is preferable to use one having an HLB of 10 or more, or adding a basic compound to neutralize the acid value.

  The type and blending amount of the phosphate ester surfactant can be appropriately selected depending on the type of the conductive powder. The blending amount of the phosphate ester surfactant, for example, with respect to silver powder is preferably 0.01 to 3.00 parts by mass, more preferably 0.05 to 0.50 parts by mass with respect to 100 parts by mass of silver powder. If the surfactant is less than 0.01 parts by mass, sufficient dispersibility tends to be difficult to obtain. On the other hand, if the amount exceeds 3.00 parts by mass, the silver surface is thick and coated with the organic component of the surfactant, making it difficult to obtain contact between the silver particles after drying, and the conductivity tends to be lowered.

(Dispersing solvent)
In the method for producing a conductive paint of the present invention, in the dispersion step, a mixture of a conductive powder such as silver or a silver compound and a surfactant is added to a solvent, and the mixture is applied to a stirrer or a disperser to Crushing into fine powder and mixing with surfactant.
Thus, for example, silver powder, a solvent, and a surfactant can be mixed at a desired ratio to obtain a dispersion of silver powder dispersed by a dispersing means. However, when lyophilization is performed in the next step, The range of the solid content concentration in the silver powder dispersion is preferably 0.5 to 80%, and particularly preferably 1 to 50%.

Here, water, a water-soluble solvent, or a mixture of water and a water-soluble solvent (aqueous solution) is used as the solvent used for dispersing the conductive powder. Examples of the water-soluble solvent include lower alcohols such as ethanol and isopropyl alcohol; ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.
These solvents are not limited to those listed here, and can be used alone or in admixture of two or more.
Usable stirrers or dispersers can be appropriately selected from known stirrers or dispersers described later.

In the dispersion treatment with the surfactant for the conductive powder used in the present invention, it is preferable that the conductive powder is blended after the surfactant is blended and sufficiently dissolved in the solvent. If necessary, the solubility of the surfactant in the solvent can be increased by neutralization of the surfactant (for example, in the case of a phosphate ester surfactant, formation of a phosphate ester salt with an alkali or the like).
When dispersed for 0.5 to 4.0 hours after blending, the conductive powder such as silver powder is crushed into primary particles, and the surfactant and the conductive powder reach adsorption equilibrium.

  In the present invention, when a phosphate ester type surfactant is used, the dispersion is preferably set to acidic conditions (for example, pH 1 to 3), and when an alkylamine or alkylamine salt type surfactant is used, the dispersion is dispersed. It is preferable to make the liquid alkaline (for example, pH 12 to 14). Thereby, an interfacial electric double layer is generated on the particle surface of the conductive powder through the surfactant, and dispersion stability is obtained. In addition, in the phosphate ester system and the alkylamine or alkylamine salt system, since the charge when the hydrophilic group portion is ionized is opposite, depending on the sign of the surface charge of the silver powder or silver compound powder, It is preferable to select and use any surfactant so that repulsive force acts on the surface.

  For example, in the case of silver powder whose surface is treated with silver oxide, an alkylamine or alkylamine salt-based surfactant is preferable, and the conductive coating based on this combination is characterized by excellent thixotropy and a large amount. . In the case of pure silver powder (silver powder whose surface is not subjected to silver oxide treatment), a phosphate ester-based surfactant is preferable, and the conductive paint by this combination is excellent in dispersibility in the binder resin. There are features.

In the above-mentioned solvent, for example, a powder of silver or a silver compound and a cationic surfactant which is, for example, a polyoxyalkylamine type surfactant and an alkylamine acetate are sufficiently stirred and mixed. The solvent is removed from the mixture by vacuum lyophilization.
In the method for producing a conductive paint of the present invention, it is preferable to use a solvent that is easily frozen from the above-mentioned solvents because vacuum lyophilization is used as a drying method, and its freezing point is −40 ° C. or higher. It is preferable.

(2) Drying step In the vacuum freeze-drying method used in the method for producing a conductive paint of the present invention, basically only the aqueous solvent is sublimated and removed from the dispersion frozen at a low temperature. Since there is no surfactant lost by elution in the aqueous solvent, almost all of the added surfactant remains in the conductive powder after treatment. As shown in FIG. 1, the surfactant b is localized in the vicinity of the surface of the conductive powder particles a in the dispersion, and the surfactant is removed during vacuum lyophilization in which only the aqueous solvent is removed. It is highly possible that b is able to be taken out in a state of being uniformly adsorbed on the surface of the conductive powder particles a, and the conductive powder particles are removed as in the case of removing the aqueous solvent by a normal method other than vacuum freeze drying. It can be said that a and the surface-treated electroconductive powder particle | grains c do not aggregate, and can be said to be a very efficient processing method. Since all the surfactant b used in this way remains on the surface of the particles a of the conductive powder and gives the surface-treated conductive powder c with good yield, the relationship between the effect of the surfactant and the amount used is shown. Easy to grasp and easy to optimize for usage.
The molecule of the surfactant b is adsorbed on the surface of the conductive powder particle a at the end of the hydrophilic group, so that the end of the hydrophobic group faces the outside of the particle. Thereby, the affinity with the binder resin is improved, and the dispersibility of the surface-treated conductive powder c is improved. Moreover, aggregation of particles is suppressed and the state dispersed in the primary particles can be maintained.

For example, in the case of a dispersion of silver powder containing silver powder, water, and a surfactant, freeze-drying is pre-frozen to 0 ° C. or lower at atmospheric pressure, and theoretically, the vapor pressure of water at 0 ° C. is 4.5 mmHg ( The degree of vacuum may be controlled so as not to exceed 600 Pa). Considering the drying speed and ease of control, it is preferable to increase the temperature to 1 mmHg (= 133.32 Pa) or less and to the melting point (freezing point) at the vapor pressure.
Thus, in the drying method by vacuum freeze-drying, since it is sublimated and evaporated in vacuum and dried, the shrinkage due to drying is slight, and the structure and structure are not easily destroyed. Also, it is not dried by moving liquid components such as water in the sample at high temperature like hot air drying, but it is dried at low temperature in a solid frozen state, so partial components such as drying with movement of liquid components Concentration, partial component change, and almost no deformation are preferred.

(3) Coating process In order to produce a conductive coating using conductive powder such as silver or a silver compound in which a surfactant is adsorbed on the surface by the dispersion process and the drying process, the surface-treated conductive material is used. The powder, the solvent or binder resin, and the solvent are mixed, and the silver or silver compound powder is dispersed using an appropriate disperser.

  Solvents used in the coating process of the conductive paint production method of the present invention are alcohols such as methanol, ethanol, n-propanol, benzyl alcohol, and terpineol; acetone, methyl ethyl ketone, cyclohexanone, isophorone, acetylacetone, and the like. Ketones; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Ethers such as tetrahydrofuran, dioxane, methyl cellosolve, diglyme and butyl carbitol; Methyl acetate, ethyl acetate, diethyl carbonate, TXIB (1 -Isopropyl-2,2-dimethyltrimethylenediisobutyrate), esters such as carbitol acetate and butyl carbitol acetate; sulfoxides and sulfones such as dimethyl sulfoxide and sulfolane; methyl chloride Aliphatic hydrocarbons such as benzene, toluene, o-xylene, p-xylene, m-xylene, monochlorobenzene, dichlorobenzene, etc. Etc. These solvents are not limited to those listed here, and can be used alone or in admixture of two or more.

  The conductive powder such as silver or silver compound surface-treated with a surfactant in the dispersion step and the drying step is further added to the above-mentioned solvent in addition to a binder resin to form a conductive powder such as silver or silver compound. The dispersion stability is improved, and the adhesion to the substrate is improved, so that it is used as a conductive paint.

Examples of the binder resin that can be used in the method for producing the conductive paint of the present invention include acrylic resin, butyral resin, polyvinyl alcohol resin, acetal resin, phenol resin, urea resin, vinyl acetate emulsion, polyurethane resin, and polyvinyl acetate resin. Epoxy resin, melamine resin, alkyd resin, nitrocellulose resin, and natural resin can be used alone or in admixture of two or more. At this time, the mass ratio of the resin / conductive powder is 0.1 or less. At the stage of the coating step in the method for producing a conductive paint of the present invention, the conductive powder is preliminarily surface-treated with a surfactant, so that the conductive powder can be dispersed with a small amount of resin.
When the binder resin is an acrylic resin, the surfactant is preferably a polymer of acrylate and / or acrylic acid. Most preferred is an acrylate polymer containing 2-ethylhexyl acrylate.

The amount of the binder resin used is preferably in the range of 0.01 to 10 parts by mass per 100 parts by mass of conductive powder such as silver powder.
The amount of the solvent used varies depending on the coating method and the printing method, and the amount used may be appropriately selected.

If the conductive powder (for example, silver powder) surface-treated with a surfactant in the dispersion process and the drying process is used as a raw material, it can be easily stirred using a solvent or a solvent and a binder resin when used. A conductive paint (for example, a silver paint) can be obtained only by performing a proper dispersion treatment.
In other words, by conducting a simple stirring operation of the additive solvent or additive solvent and additive binder immediately before printing, a good conductive paint such as silver paint can be obtained. The paint adjustment equipment to be used can be simple.
Further, in order to perform the dispersion more reliably, the dispersion processing may be performed using the following disperser.

  Examples of dispersing means that can be used include two rolls, three rolls, ball mills, sand mills, pebble mills, tron mills, sand grinders, seg barrier strikers, high speed impeller dispersers, high speed stone mills, high speed impact mills, kneaders, It can be kneaded and dispersed by a homogenizer, an ultrasonic disperser or the like.

The dispersion liquid (conductive paint produced according to the present invention) that has been dispersed is generally printed as a paint on an insulating film or an insulating substrate by a commonly used application method or printing method, and this is heated. Thus, a conductor circuit can be formed.
As a coating method, it can form as a coated material by various coating methods. For example, known roll coating methods, such as air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat The coated product can be formed on the substrate by cast coating, spray coating or the like.
Various printing methods can also be applied. There are also printing methods in which the optimum viscosity region is in a relatively low viscosity region as in intaglio printing and in the high viscosity region in screen printing. Specifically, the coating material can be printed in a predetermined size on the substrate using a stencil printing method, an intaglio printing method, a lithographic printing method, or the like.

As a material of the substrate at the time of coating or printing, for example, a polyethylene terephthalate film (PET film), a polyimide film (PI film), or a green sheet (inorganic substrate) is used as a substrate, and a conductive paint such as a silver paint on the film. May be printed in a predetermined pattern, and the printed material may be dried and then heat-cured.
The thickness of the printed material varies depending on the printing method, but the wet thickness of the printed material is preferably in the range of 1 to 20 μm, particularly preferably 1 to 10 μm. In order to increase the electric resistance (volume resistivity) per unit volume after the printed matter is dried, press or calender treatment may be performed to such an extent that the substrate is not significantly deformed.

The coated product thus obtained is dried at, for example, about 160 ° C. for about 5 minutes, and then the binder resin is cured by a heat treatment step in the range of 150 ° C. to 250 ° C. Thereby, various electronic circuit boards are obtained.
In particular, when silver oxide fine particle powder or silver powder whose surface is subjected to silver oxide treatment is used as the conductive powder, it is reduced from silver oxide to silver along with curing by the heat treatment, and released along with the reduction reaction. Oxygen can oxidize surrounding surfactants and resins to generate heat. As a result, the silver powder particles in which silver oxide has been reduced can be fused together by a heat treatment at a lower temperature (for example, 200 ° C. or less) than when pure silver powder is used. Therefore, the conductive paint using conductive particles containing silver oxide can reduce the requirement for the heat resistance of the substrate material at the time of coating or printing, so that the substrate made of PET, PI, other plastics, etc. Particularly suitable for this.

Fig. 2 shows silver powder after surface treatment (freeze-drying treatment) with a surfactant prepared using silver powder to be sintered at low temperature (silver powder having a small crystallite diameter), and silver powder that has been subjected to silver oxide treatment at low temperature (oxidation) The result of the differential thermal analysis (DSC analysis) of the silver powder after the surface treatment (freeze-drying treatment) by the surfactant produced using the silver-treated silver powder having a small crystallite diameter) is shown.
The results of DSC analysis of the silver powder after surface treatment by lyophilization treatment in the presence of a surfactant prepared using silver powder having a small crystallite diameter (shown by a broken line in FIG. 2) show endotherm indicating melting of the silver powder. A peak appeared at 215 ° C. This indicates that the crystallite diameter of the silver powder is small, so that it melts at a lower temperature than before.
In addition, the result of DSC analysis of the silver powder after the surface treatment by freeze-drying treatment in the presence of a surfactant produced using silver oxide-treated silver powder (shown by a solid line in FIG. 2) shows melting of the silver powder. An endothermic peak appeared at 215 ° C and an exothermic peak appeared at 134 ° C. This exothermic peak is considered to be because the silver oxide of the silver powder was decomposed and oxygen was released, and the carbon component of the surface surfactant was oxidized to cause an exothermic reaction.
As is apparent from the above results, according to the silver powder after the surface treatment by the freeze-drying treatment in the presence of the surfactant, a silver paint that can be sintered and fired at a lower temperature than before can be produced. .

Hereinafter, the present invention will be described more specifically by way of examples in which the conductive powder is silver powder, but the present invention is not limited to the scope of these examples. Measuring methods for physical properties and the like are as follows.
(1) Film thickness: The film thickness was measured using a film thickness meter K402B (manufactured by Anritsu).
(2) Volume resistivity: The volume resistivity was measured with a low resistivity meter Lorester EP (manufactured by Mitsubishi Chemical Corporation) using a four-terminal measurement method. The volume resistivity was determined from the film thickness of the conductive film of the test piece. In addition, the volume resistivity was shown by the method of describing 8.8 * 10 < ^-6 > ohm * cm as "8.8E-06 ohm * cm", for example.

Example 1
50 g of 10% silver oxide-treated silver powder FHD (crystallite diameter <10 nm) manufactured by Mitsui Kinzoku Co., Ltd. with a center particle size of 0.3 μm, 10% by mass of coconut amine acetate as a cationic surfactant for alkylamine salt Put 5g of aqueous solution, 0.5g of 10% by weight aqueous solution of polyoxyethylene coconut alkylamine ether as surfactant for alkylamine, 50g of water as solvent, and 400g of 2mm zirconia beads into a 250cc plastic bottle. The mixture was mixed and kneaded for 4 hours using a rotating machine (ball mill) to obtain a silver powder dispersion (a1).

  100 g of this silver powder dispersion (a1) was transferred to a flat tray having a bottom dimension of 200 mmL × 150 mmW, pre-lyophilized, and then freeze-dried. As the freeze vacuum dryer, “DFM-05AS” manufactured by Nippon Vacuum Co., Ltd. was used. The pre-frozen silver powder dispersion (a1) is placed on a shelf previously cooled to about −40 ° C., freeze-dried for 20 hours at a degree of vacuum of 7 to 10 Pa, and then treated with silver powder as a bulky sponge-like dried product. 50 g of product (b1) was obtained. The particle size distribution of the silver particles at this time is shown in FIG.

Next, 50 g of a silver powder surface-treated product (b1), a binder resin (“Bernock DE-140-70” (manufactured by Dainippon Ink and Chemicals) as a polyol component) and “Bernock DB980” (Dainippon Ink Chemical Co., Ltd. ( Co., Ltd.), 4.17 g (solid content = 2.5 g) obtained by replacing the solvent component of the mixture of “Bernock DB980K” (Dainippon Ink Chemical Co., Ltd.) with carbitol acetate as an isocyanurate prepolymer component And 4.2 g of carbitol acetate were mixed in a 250 cc plastic bottle and mixed and stirred for 0.5 hour using a shaker (paint conditioner) to obtain silver paint B-1.
By screen printing using this silver paint B-1, a 50 mm × 80 mm rectangular printed coating film and a Line / Space = 40 μm / 40 μm printing pattern were formed on the PI film to obtain a screen printed coating film. The average thickness of the rectangular printed coating film was 12 μm. On the other hand, the thickness distribution in the printed pattern was measured with a laser microscope (manufactured by VK-9500 Keyence). The profile is shown in FIG. Here, the specifications of the screen plate are 640 mesh, a wire diameter of 15 μm, a calendar thickness of 22 μm, and an emulsion thickness of 10 μm. The average value of the peak height of the printed pattern was 11.9 μm.

  The rectangular printed coating was dried at 150 ° C. for 5 minutes. After drying, the volume resistivity after being placed in an oven at 160 ° C. and 250 ° C. for 60 minutes was measured to be 3.7E-05 Ω · cm and 7.5E-06 Ω · cm, respectively. The volume resistivity of the dried coating film decreases with time in the oven. The decrease in volume resistivity when the oven temperature is 160 ° C. and 250 ° C. is shown in FIG.

(Example 2)
Instead of the silver oxide-treated silver powder FHD in Example 1, as the conductive powder, silver powder FHD not processed with silver oxide manufactured by Mitsui Kinzoku Co., Ltd. was used, and the phosphorus content was 4.4% as the surfactant. The same polyoxyalkylene alkyl ether / phosphate ester as in Example 1 except that 5 g of a 10% by weight aqueous solution of a phosphate ester-based surfactant having a weight average molecular weight of 1750 and an HLB of 12 was used. By the method, a silver powder dispersion (a2) was obtained, and then 50 g of a silver powder surface-treated product (b2) was obtained. The average particle size of the silver particles at this time was 0.5 μm, and the particle size distribution was almost the same as in Example 1.

  Next, 58.3 g of silver paint B-2 was obtained from the surface treated product (b2) of the silver powder in the same manner as in Example 1. A rectangular print film and a print pattern were obtained in the same manner as in Example 1 by screen printing using the mask film on which the print pattern was formed and the silver paint B-2. A print pattern profile is shown in FIG. The average value of the peak height of the print pattern was 9.2 μm. After drying, the volume resistivity after being placed in an oven at 160 ° C. for 60 minutes was measured to be 4.5E−05 Ω · cm.

(Example 3)
In the same manner as in Example 2, except that silver powder AgC-G manufactured by Fukuda Metal Foil Powder Co., Ltd. was used in place of the silver powder FHD in Example 2, the silver powder dispersion (a3 Then, 50 g of a silver powder surface-treated product (b3) was obtained. The volume average particle diameter of the silver particles at this time was 0.2 μm, and a particle size distribution with a narrow distribution width was shown.
Next, 58.3 g of silver paint B-3 was obtained from the surface treated product (b3) of the silver powder in the same manner as in Example 1. The silver paint B-3 was stable without causing a viscosity increase or aggregation with time. Silver paint B-3 was screen-printed using the mask film in which the printing pattern was formed similarly to Example 1, and the printing coating film was obtained. Further, solid printing with a film thickness of 50 μm was performed by using the silver paint B-3 in the same manner as in Example 1, and after drying, the volume resistance after being placed in an oven at 160 ° C. and 250 ° C. for 60 minutes was measured. As a result, 4.5E-05 Ω · cm and 2.5E-05 Ω · cm were shown, respectively.

(Comparative Example 1)
As conductive powder, 50 g of silver powder FHD not manufactured by Mitsui Kinzoku Co., Ltd., 0.5 g of polyoxyalkylene alkyl ether / phosphate ester not converted into an aqueous solution as a surfactant, binder resin (polyol) “Bernock DE-140-70” (manufactured by Dainippon Ink & Chemicals, Inc.) and “Bernock DB980” (manufactured by Dainippon Ink & Chemicals, Inc.) as the components, and “Bernock DB980K” (large by the isocyanurate prepolymer component) (Replacement of the solvent component of Nippon Ink Chemical Co., Ltd.) with carbitol acetate) 4.17 g (solid content = 2.5 g) and 4.2 g of carbitol acetate in a 250 cc plastic bottle Mix and stir for 0.5 hour using a shaker (paint conditioner) I tried dispersed by, but it is impossible to make a good dispersion, it was not possible to obtain a silver paint.

(Comparative Example 2)
The same as Comparative Example 1 except that the amount of the binder resin (the solvent component of the mixture of the polyol component and the isocyanurate prepolymer component replaced with carbitol acetate) was 10.0 g (solid content = 6.0 g). Attempts were made to disperse the three rolls by the method to obtain silver paint B-4.
Next, a printed coating film and a printing pattern were obtained in the same manner as in Example 1 by screen printing using the mask film on which the printing pattern was formed and silver paint B-4. The profile of the print pattern is shown in FIG. The average peak height of the printed pattern was 8.4 μm. After drying, the volume resistivity after being placed in an oven at 160 ° C. for 60 minutes was measured and found to be 2.5E-03 Ω · cm.

As can be seen from FIG. 4, the surface of the conductive powder is obtained by adsorbing a surfactant such as alkylamine and alkylamine salt or phosphate ester to each silver powder or silver compound powder surface using freeze drying. When a conductive paint was prepared after the treatment, a conductive paint having a very high film thickness and a good dispersibility without causing clogging of a mask for printing a fine line of 40 μm was produced. Furthermore, when the silver powder whose surface is treated with silver oxide is used as the conductive powder in these conductive paints, or when a silver powder with a small particle size is used, the wiring pattern is formed by low-temperature firing, which is favorable. It can be seen that conductivity can be realized.
On the other hand, in Comparative Example 1 in which an attempt was made to produce a conductive paint with the same composition without using freeze-drying, a well-dispersed silver paint could not be obtained, and the amount of resin was increased. In Comparative Example 2, a silver paint was obtained, but since the resin component increased, good conductivity and high film thickness during screen printing could not be obtained.

(Relationship between silver content in coating film and volume resistivity)
In the conductive paint (silver paste) produced in Example 1 and Example 3, silver paints having various silver contents were prepared by changing the ratio of the surface-treated silver powder and the binder resin. Furthermore, the printed coating film was obtained by screen printing using the mask film which formed the printing pattern using these silver paints. The relationship between the silver content in the coating film at this time and the volume resistivity is shown in FIG.
In addition, “Conventional Technology 1” in FIG. 8 refers to a seminar “Conductive Paste Preparation with Nanoparticles and Circuit Formation Technology” (April 20, 2004, Kawasaki City Industrial Promotion Hall) sponsored by Information Technology Corporation. The 10th page of the abstract is a quote from data published by Toshiyuki Honda (Fujikura Kasei Co., Ltd.).

As can be seen from FIG. 8, in the conductive paint (silver paste) of the present invention, the higher the silver content in the coating film, the higher the conductivity, and the most when the silver content in the coating film is 90% or more. Good conductivity was shown. This is presumably because the silver powder was surface-treated with a surfactant, so that it was well dispersed in a small amount of binder resin and the conduction state between the silver powder particles was improved.
On the other hand, in the conventional silver paste described in the prior art 1, when the silver content in the coating film is 90% or more, the conductivity is reduced. This is thought to be because the dispersion state of the silver powder deteriorated when the amount of the binder resin was small.

It is explanatory drawing which illustrates typically the surface treatment method of the silver powder by the lyophilization process in surfactant presence. It is a figure showing an example of the measurement result of the DSC analysis of the silver powder after the surface treatment by the lyophilization process in the presence of a surfactant. It is a figure which shows the particle size distribution of the silver powder after the surface treatment used by manufacture of the electroconductive coating material of Example 1. FIG. It is a figure showing the profile of the fine line pattern produced by screen printing using the electroconductive coating material manufactured in Example 1. FIG. It is a figure showing the profile of the fine line pattern produced by screen printing using the electrically conductive paint manufactured in Example 2. FIG. It is a figure showing the profile of the fine line pattern produced by screen printing using the electrically conductive coating material manufactured by the comparative example 2. It is a figure which shows the relationship between the baking time when the fine line pattern produced in Example 1 was baked at 160 degreeC or 250 degreeC, and the volume resistivity of a fine line pattern. It is a figure which shows the relationship between the silver content rate and volume resistivity in the coating film produced using the electrically conductive coating material manufactured in Example 1 and Example 3, and in the silver paste described in the prior art 1. is there.

Explanation of symbols

a ... conductive powder (particles), b ... surfactant (molecules), c ... conductive powder (particles) surface-treated with a surfactant.

Claims (6)

  A dispersion step of producing an aqueous dispersion by dispersing the conductive powder in a solvent comprising water and / or a water-soluble solvent in the presence of a surfactant, a drying step of freeze-drying the dispersion, and a drying step A method for producing a conductive paint, comprising: a step of forming a paint by mixing a product with a solvent and a binder resin to produce a paint having a resin / conductive powder mass ratio of 0.1 or less.   The method for producing a conductive paint according to claim 1, wherein the conductive powder contains silver or a silver compound as a main component.   The method for producing a conductive paint according to claim 1, wherein the surfactant is an alkylamine or an alkylamine salt.   The method for producing a conductive paint according to claim 1, wherein the surfactant is a phosphate ester-based surfactant.   The method for producing a conductive paint according to claim 3 or 4, wherein the volume average particle size of the conductive powder is in the range of 0.05 to 10 µm.   The method for producing a conductive paint according to claim 5, wherein the conductive powder is a silver powder having a surface coated with silver oxide and a silver content of 60% or more.

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