JP2007177103A - Electrically conductive coating material and process for producing electrically conductive coating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrically conductive coating material that has an electrically conductive powder of a very small particle size dispersed in a good state therein, causes no change with time in physical properties such as viscosity increase or the like, is easy to redisperse after a long period of storage, can be used for forming a fine circuit by thick film printing and forming a wiring pattern with a high printing density and good electrical conductivity and achieves the improvement in bending durability. <P>SOLUTION: The electrically conductive coating material comprises 100 pts.mass powder having a surfactant adsorbed on the surface of particles composed mainly of silver or a silver compound, 0.1-1.0 pt.mass carbon nanotube, 1-10 pts.mass resin as a binding agent and a solvent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a conductive coating material that can be used for printed wiring used in electronic devices and the like and has excellent conductivity and printing accuracy, and a method for manufacturing the same.

The conductive paint is a paste-like paint containing conductive fine particles as a solid content. Generally, metal particles such as gold, platinum, silver, and palladium that are not oxidized in air are used as the conductive fine particles. Conventionally, conductive paints can be broadly classified as follows: (1) High conductivity by conductive bonding between conductive particles can be realized, but the base material is limited to ceramic or the like, and ( 2) Widely applicable from glass and epoxy printed circuit boards to films, but there are polymer-type conductive paints with relatively high electrical resistance in order to obtain conduction through contact between conductive particles due to heat shrinkage during binder curing .
For example, when a conductive circuit is formed on a support for a flexible printed circuit board using a polymer-type conductive paint, the polymer-type conductive paint is applied to a plastic film such as polyethylene terephthalate or polyimide by screen printing or the like. The conductive circuit pattern is formed, and the binder in the formed pattern coating film is heat-cured to improve the conductivity and durability, and to secure the adhesion on the film.

In particular, polymer-type conductive paints using silver or silver compound particles as conductive particles are easy to achieve stable conductivity and have good heat conduction characteristics, so various wiring inside or between electronic components It is used to form electronic circuit patterns.
In the process of printing a conductive circuit pattern, it is required to increase the printing density and printing accuracy as much as possible along with the miniaturization of the circuit and to reduce the resistance between terminals.

However, the printing density and printing accuracy are limited by the average particle diameter of the conductive particles. Therefore, in order to obtain good printing accuracy, the conductive particles in the conductive paint are dispersed to primary particles, and the primary particles are completely covered with a resin or the like, that is, highly dispersed. It is required to be in the state.
If the coating of resin or the like around the highly dispersed primary particles is insufficient, the particles become more active as the particle size becomes finer. Viscosity was likely to increase over time, and in some extreme cases gelled.

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 high printing density, it is important to increase the coating thickness of the fine wires used for wiring, as well as the selection of conductive particles. 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 particles of the conductive powder as good as possible.

In order for such a fine wiring pattern to be formed accurately and stably, the conductive particles need to be stably dispersed to primary particles and each particle must be coated with a resin. If the surrounding resin coating is too thick, the resin component remaining between the particles tends to hinder the electrical conduction between the particles, and thus there is a tendency that good conductivity cannot be obtained. The tendency becomes remarkable. 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 it is preferable that the dispersion of conductive particles, the adhesion of the conductive coating material to the substrate, and the film formability become better with a smaller amount of resin.

Conventionally, in producing conductive paints by dispersing conductive particles in a resin, in order to improve the dispersibility, many kinds of higher fatty acid ethylene oxide, propylene oxide addition ester compounds, sorbitan and fatty acid ester compounds, sorbitan, etc. Nonionic dispersants such as ethylene oxide of prophydric alcohol, propylene oxide addition ether compound, ethylene oxide of alkylbenzene, propylene oxide adduct, alkylbenzene sulfonic acid alkali salt, higher alcohol sulfate alkaline salt, phosphate ester compound, higher fatty acid, higher fatty acid Various dispersants such as anionic dispersants such as sulfate alkali salts of ethylene oxide and propylene oxide adducts, and quaternary ammonium salt type cationic dispersants are used.
However, even when these dispersants are used, the conventional method of dispersing conductive particles in a resin using, for example, a disperser or a kneader, maintains the conductivity of the conductive paint while maintaining good dispersibility. It could not be improved sufficiently.

  In particular, when silver particles are used as the conductive particles, it is difficult to disperse the silver particles having a true specific gravity of 10.5 by avoiding sedimentation, the amount of resin to be mixed is as large as possible, and the amount of solvent is Although it is preferable that the amount be as small as possible, it is not easy to proceed with the dispersion, and even if the dispersion proceeds, 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 has been made to obtain good dispersibility and stability over time by using an anionic surfactant comprising an organic vehicle and a sulfosuccinate containing an alkyl group (Patent Literature). 1). However, the use of the method described in Patent Document 1 is insufficient to improve the redispersibility of the settled particles. Further, the amount of resin used for dispersion is not reduced to the minimum necessary, and the conductivity is insufficient.

  In particular, in recent years, in order to reduce the electrical resistance of the conductor circuit formed from the conductive paint, the particle diameter of the silver particles has been made very fine, or a particulate silver compound containing particulate silver oxide or tertiary fatty acid silver has been used. For example, it has been studied to use a conductive paint that can be fired at a low temperature. In these low-temperature firing type conductive paints, when finely divided silver powder is used, adjacent silver particles are fused together by heating at 300 ° C. or lower, and the electrical resistance of the conductive circuit is lowered. When a particulate silver compound is used, the silver compound is reduced by heating at 300 ° C. or lower or in the presence of a reducing agent to form metallic silver, and adjacent silver particles are fused to form a conductive circuit. Electric resistance is reduced (see, for example, Patent Document 2).

  Conventionally, polymer-type conductive paints have a spherical or flake-like conductivity by adding 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. The particles were dispersed and mixed, and the conductivity was obtained by contact between the conductive 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 a conductor circuit or the like formed using a polymer-type conductive paint Has the disadvantage that it is likely 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, silver fine particles 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, and the dry reaction rate is very high. May be difficult to handle. In particular, when an alcohol or the like is used as a dispersion solvent, reduction proceeds during dispersion of the conductive coating material, and silver particles may not be dispersed, but conversely, fusion between silver particles may occur. For this reason, it is further required to disperse these silver and silver compound particles to primary particles to coat and stabilize the surface of each particle.
Furthermore, in these conductive paints, in order to obtain the original high electrical conductivity, the silver particles in the conductive paint must be well dispersed while maintaining a high silver content, and in addition to the necessary minimum It is necessary to perform the stabilization by using a limited resin so that the coating thickness on the surface of the particles is as thin as possible so that adjacent particles can be easily fused 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. However, if the coating amount formed on the particle surface of silver or the like is too thick due to a large amount of resin, adjacent particles are difficult to fuse together, and the thixotropy decreases, resulting in a decrease in height after printing. The actual electrical resistance becomes high. 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.

Also, in recent years, in order to solve the sedimentation of conductive particles and the increase in the thickness of the coating film that can occur when the conductive particles are highly filled in the resin, even if the filling rate of the conductive particles in the coating film is low, high conductivity As a conductive resin composition capable of obtaining a high rate, a paste in which conductive particles, carbon nanotubes, and a thermoplastic resin are dispersed in an organic solvent is known (see Patent Document 3).
As described above, generally, fine conductive particles are liable to settle and aggregate and are difficult to uniformly disperse. Therefore, it is necessary to add a sufficient amount of resin and organic solvent for dispersibility and coating property. However, in the low-temperature firing type conductive paint, as described above, it is desirable to add the resin and the organic solvent to the minimum necessary from the viewpoints of improving the printing density and printing accuracy and ensuring the conduction state between the particles. .

  Furthermore, the flexible printed circuit board is required to have a small increase in specific resistance without being disconnected by bending. In order to meet the above-mentioned demands for circuit miniaturization, conductivity improvement, etc., if a fine circuit is formed using a conductive paint with a high silver content and a small amount of resin, it can be easily broken by bending and further durable. There was a problem that the performance decreased.

For this reason, these low-temperature firing type conductive paints are stabilized by coating each particle, improved dispersibility, improved conductivity by low-temperature firing, and conductivity to satisfy the durability against bending at the same time. Development of the composition of the paint was a more important issue.
JP 2000-231828 A JP 2003-309337 A JP 2004-168966 A

  The object of the present invention is that the conductive particles having a fine particle size are well dispersed, there is no change over time in physical properties such as viscosity increase, and re-dispersion after long-term storage is easy, and a thick film of a fine circuit An object of the present invention is to provide a conductive paint capable of printing, capable of forming a wiring pattern with high printing density and good conductivity, and capable of improving durability against bending, and a method for producing the conductive paint.

  The conductive paint of the present invention comprises 100 parts by mass of powder in which a surfactant is adsorbed on the surface of particles mainly composed of silver or a silver compound, 0.1 to 1.0 part by mass of carbon nanotubes, and a binder. It consists of 1 to 10 parts by mass of a resin and a solvent.

  The method for producing a conductive paint according to the present invention includes a dispersion production process for producing a dispersion in which particles containing silver or a silver compound as a main component are dispersed in a dispersion solvent in the presence of a surfactant. Drying step for freeze-drying in vacuum, and 0.1 to 1.0 part by weight of carbon nanotubes and 1 to 10 parts by weight of binder resin for 100 parts by weight of the product of the drying step are mixed with a solvent to form a paint It is characterized by having a paint-making process for producing.

  According to the conductive paint of the present invention, particles having conductivity with a small particle size are well dispersed, there is no change with time in physical properties such as increase in viscosity, and redispersion after long-term storage is easy, Circuit thick film printing can be performed, and excellent conductivity and durability against bending can be satisfied at the same time.

  According to the method for producing a conductive paint of the present invention, particles of silver or a silver compound are dispersed to fine primary particles, and a surfactant is adsorbed on the surface of each particle and is satisfactorily coated. As a result, conductive particles with a small particle size are 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 circuit printing of fine circuits is possible. Conductive paint can be manufactured. Further, by adding carbon nanotubes having conductivity, excellent conductivity and durability against bending can be satisfied at the same time.

  The present invention is described in further detail below. In the present invention, “sintering of particles” refers to melting and fusing particles together by heating a substance (for example, powder or paste) containing the particles. “Baking of conductive paint” means heating the conductive paint to cure the contained resin and bringing adjacent conductive particles into contact with each other by shrinkage of the resin or fusing the contacted parts. “Dispersion” refers to a phenomenon in which other phases are dispersed in the continuous phase in the form of fine particles.

The conductive paint of the present invention comprises 100 parts by mass of powder in which a surfactant is adsorbed on the surface of particles mainly composed of silver or a silver compound, 0.1 to 1.0 part by mass of carbon nanotubes, and a binder. It consists of 1 to 10 parts by mass of a resin and a solvent.
The carbon nanotube (CNT) is a shape in which a graphite sheet is rounded like a tube. The layer structure is classified into single layer (called SWNT), two layer (called DWNT) and multilayer (called MWNT). The cross-sectional diameter of the tube is about 0.4 to 3 nm for a single layer, 1 to 5 nm for a double layer, and 10 nm or more for a multilayer. It is commercially available from Mitsui & Co., Ltd. and Yamamoto Tsusan Co., Ltd. Many of the properties of carbon nanotubes have not yet been fully elucidated.

In addition, the method for producing a conductive paint according to the present invention includes (1) a dispersion production process for producing a dispersion in which particles containing silver or a silver compound as a main component are dispersed in a dispersion solvent in the presence of a surfactant. (2) A drying step of freeze-drying the dispersion, and (3) 0.1 to 1.0 parts by mass of carbon nanotubes and 1 to 1 binder resin with respect to 100 parts by mass of the product of the drying step. It has a paint forming step of preparing a paint by mixing 10 parts by mass with a solvent.
The form of the carbon nanotube used in the present invention is not particularly limited, but a multi-layer type (MWNT) is preferable from the viewpoint of price and availability. The aspect ratio is preferably 10 to 1000. If the aspect ratio is less than 10, conduction between particles such as silver is difficult. On the other hand, when the aspect ratio exceeds 1000, conduction between particles such as silver tends to be obstructed, and uniformity of the obtained coating film tends to be obstructed. The aspect ratio of the carbon nanotube in the present invention refers to the ratio (length / diameter) of the length and diameter of the carbon nanotube having a cylindrical shape. The method of blending the carbon nanotubes in the coating step is preferably a method of preparing a master batch in which carbon nanotubes are kneaded into a resin and adding the master batch.
Hereinafter, the conductive paint of the present invention and the production method thereof will be described in more detail in the order of the production steps.

(Particles with silver or silver compound as the main component)
As silver particles used as a raw material in the present invention, pure silver particles, metal particles surface-coated with silver, or a mixture thereof can be used. As the silver particles, particles having any shape such as a spherical shape, a scale shape, a needle shape, or a dendritic shape can be used. The method for producing silver particles 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 particles made of a metal other than silver by a method such as plating. For example, a copper particle whose surface is coated with silver is commercially available. As the silver particles, spherical silver particles and scaly silver particles made of only silver are preferable from the viewpoint of conductivity and cost.
The volume average particle diameter of the silver particles is preferably about 0.01 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 the silver particles.

  As particles of the silver compound, particles of silver-containing organic compounds such as silver oxide, silver aliphatic carboxylate, silver alicyclic carboxylate and silver aromatic carboxylate can be used. As these silver compound particles (particulate silver compound), 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 silver compound particles having an average particle size of 0.5 μm or less because the speed of the reduction reaction is increased. In order to produce silver compound particles 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 that has been produced by a reaction between the silver compound and another compound with stirring. It can manufacture by the method of making it react and obtaining silver oxide particle.

It is preferable to use particles capable of setting the firing temperature of the conductive paint to 300 ° C. or less as the raw material of silver or silver compound as a main component. The low-temperature firing type conductive paint having such a low firing temperature can, for example, fire a wiring pattern formed on a polyimide film or a PET film as it is. Generally, the more finely conductive particles are dispersed in the conductive paint, the lower the heat capacity of the conductive paint, and the firing temperature of the conductive paint is closer to the intrinsic firing temperature of the conductive particles themselves. Become. Furthermore, since the packing density is improved as the conductive particles are finely dispersed, generally the higher the dispersion, the better the conductivity after firing.
In addition, the conductive paint according to the present invention can reduce the resin component, and the resin coating the conductive particles is thin, so that adjacent particles are easily fused after firing. For this reason, when using low-temperature sintering type silver or silver compound particles having a sintering temperature of 300 ° C. or lower as the silver or silver compound particles subjected to the surface treatment with the surfactant, the surface treatment with the surfactant is performed. After that, it is possible to obtain a low-temperature firing type conductive paint by fully exhibiting its original low-temperature sinterability, and to obtain a wiring pattern with good conductivity after firing the conductive paint. .

  As silver particles having a low sintering temperature, silver particles having a volume average particle diameter of 0.01 to 10 μm can be used. It is more preferable to use silver particles having a volume average particle diameter of 0.05 to 5 μm. In the dispersion manufacturing process (described later) in the manufacturing method of the present invention, when particles of silver or a silver compound are manufactured in the liquid phase, these particles having a small volume average particle size and high activity are effectively used. Since the particles can be surface-treated in the presence of a surfactant in a state in which they are dispersed in the liquid phase when they are produced, the treatment is easy, and these particles having a low sintering temperature are inherent to the particles. The characteristics can be fully exhibited. Examples of the method for producing silver fine particles include a gas evaporation method (Japanese Patent Laid-Open No. 3-34211) and a reduction precipitation method using an amine compound for reduction (Japanese Patent Laid-Open No. 11-319538).

  Furthermore, silver particles having a low crystallinity can be used as the silver particles having a low sintering temperature. If the crystallinity of the silver particles is low, the crystallite size is usually small. Therefore, by reducing the crystallite size, the fusion temperature (sintering temperature) between the silver particles can be significantly reduced. 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, silver particles in which a part of the particles are treated with silver oxide can be used as silver or silver compound particles having a low sintering temperature. In addition to the method of oxidizing the surface of the silver particle from silver to silver oxide by partially oxidizing the surface of the silver particle, the silver oxide-treated silver particle is coated with a silver oxide layer on the surface of the silver particle It can be obtained by the method to do.

  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 particle whose particle surface is coated with silver oxide, the silver oxide on the particle surface may be in a state in which first silver oxide, second silver oxide, and the like are mixed. In these silver particles whose surface is coated with silver oxide, the 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 at a low temperature. Silver particles having a surface subjected to silver oxide treatment 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 particles treated with silver oxide is preferably about 0.01 to 10 μm, more preferably about 0.05 to 5 μm. In particular, the use of particles having an average particle size of 0.5 μm or less is preferable because the speed of the reduction reaction is increased.

  When silver particles surface-treated with silver oxide are used, the oxygen released during the reduction of silver oxide to silver oxidizes the organic matter around the particles and generates heat. A lowering effect is obtained. Therefore, in the silver particles surface-treated with silver oxide, the content of silver oxide and silver is preferably 40 to 5% by mass of silver oxide (60 to 95% by mass of silver), and 30 to 5% by mass of silver oxide (70% of silver). -95 mass%) is more preferred, and 20-10 mass% (80-90 mass% silver) of silver oxide is particularly preferred.

  These silver oxide-treated silver particles are coated with the surface of the particles using a surfactant to produce a conductive paint with good conductivity and a low firing temperature. These particles with easy properties can be stored stably, and since the silver particles are stably dispersed as fine particles (primary particles) even in the conductive paint, the aggregates are unnecessary due to the fusion of the particles during the reduction. Can be prevented, and there is no problem in fine printing.

(Conductive powder with surfactant adsorbed on particle surface)
In the present invention, in order to improve the dispersibility of silver or a silver compound powder in a resin, etc., a powder comprising conductive particles in which a surfactant is adsorbed on the surface of the above-mentioned particles containing silver or a silver compound as a main component Is used. Such a conductive powder includes: (1) a dispersion production process for producing a dispersion in which silver or silver compound particles are dispersed in a dispersion solvent in the presence of a surfactant; and (2) the dispersion. It is possible to manufacture by a manufacturing process having a drying process of vacuum freeze drying.

(1) Dispersion Production Process In the dispersion production process, particles containing silver or a silver compound as a main component (sometimes collectively referred to as “particles such as silver”) are dispersed in the presence of a surfactant. A dispersion liquid dispersed therein is produced.
Here, the surfactant used for the surface treatment of particles such as silver 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 mentioned.

  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, those that can be particularly preferably used in the present invention include alkylamine-based, alkylamine salt-based, and phosphate ester-based surfactants.

(Surfactants of alkylamines and alkylamine salts)
Alkylamines and alkylamine salts are suitable as surfactants used for surface treatment (coating) of particles such as silver in the present invention. 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.

(A and b are each an integer of 1 to 20, and R represents an alkyl or 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).

(R represents an alkyl group having 8 to 20 carbon atoms or an 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 the alkylamine surfactant and the alkylamine salt-based cationic surfactant are used alone or in combination, the total amount of the surfactant with respect to the particles such as silver is the particles such as silver. However, it is preferably 0.01 to 3.00 parts by mass, more preferably 0.05 to 1.50 parts by mass with respect to 100 parts by mass of particles such as silver. 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, when the amount exceeds 3.00 parts by mass, the surface of particles such as silver is thick and coated with an organic component of a surfactant, making it difficult to obtain contact between the particles after drying, and the conductivity tends to decrease.
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. The phosphoric ester surfactant is a surfactant mainly composed of phosphoric monoester or phosphoric diester. The phosphate ester 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).

(In Formula (3), R represents an alkyl group having 1 to 20 carbon atoms or an alkylaryl group, n is an integer of 1 to 20, and 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 addition, it is preferable that the carbon number of R is 1-10, n is 1-10, and the sum of the carbon number of R and n is 7-15. The weight average molecular weight of the phosphate ester surfactant is preferably 100 to 10,000, and more preferably 150 to 5,000. The P content is preferably 0.5% to 10%, particularly preferably 2% to 6%.
Further, it is preferable to use a phosphate ester surfactant having an HLB of 10 or more, or adding a basic compound to neutralize the acid value.

  The type and amount of the phosphate ester surfactant can be appropriately selected depending on the type of particles such as silver. The amount of the phosphate ester-based surfactant needs to be adjusted as appropriate depending on the type of particles such as silver, but is preferably 0.01 to 3.00 parts by mass with respect to 100 parts by mass of particles such as silver, 0.05-0.50 mass part is still more preferable. If the surfactant is less than 0.01 parts by mass, sufficient dispersibility tends to be difficult to obtain. On the other hand, when the amount exceeds 3.00 parts by mass, the surface of particles such as silver is thick and coated with an organic component of a surfactant, making it difficult to obtain contact between the particles after drying, and the conductivity tends to decrease.

(Dispersing solvent)
The dispersion solvent (dispersion medium) used for dispersion of particles such as silver is not particularly limited as long as it is suitable for dissolution of the surfactant. For example, water; ethanol, isopropyl alcohol, etc. Lower alcohols: 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. Of these dispersing solvents, water is preferred.
These dispersing solvents are not limited to those listed here. The dispersing solvent can be used alone or in admixture of two or more (for example, as an aqueous solution or a mixed solvent).

(Dispersion production method)
As a dispersion manufacturing method,
A method in which particles such as silver and a surfactant are added to a dispersion solvent, and the particles such as silver are pulverized into fine particles (primary particles) and mixed with the surfactant using a stirrer or a disperser. Is mentioned. In this case, for example, silver particles, a dispersion solvent, and a surfactant are mixed in a desired ratio, and the silver particles are disintegrated into primary particles by a disperser or the like and dispersed in the dispersion solvent. Thus, a dispersion of silver particles can be obtained. The same applies when silver compound particles or silver oxide-treated silver particles are used instead of silver particles. When powder (dry powder) is used as the raw material such as silver particles when added to the dispersion solvent, it is easy to optimize the amount of silver particles used, and undesirable components are mixed from the raw material in the dispersion process. This is preferable because it has the advantage that it can be prevented.
Usable stirrers or dispersers can be appropriately selected from known stirrers or dispersers described later.

  When silver or a silver compound powder is dispersed in a dispersion solvent, it is preferable that a silver or silver compound powder is blended after the surfactant is sufficiently dissolved in the dispersion solvent. If necessary, the solubility of the surfactant in the dispersion 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 secondary particles (aggregated particles) in the silver powder or silver compound powder are crushed into primary particles, and the surfactant and silver or silver compound 1 Secondary particles reach adsorption equilibrium.

As another dispersion manufacturing method, particles such as silver are synthesized in a liquid phase, and then particles such as silver are filtered from the mother liquor, and the particles such as silver are washed and then dispersed in a dispersion solvent. In this method, it is desirable not to dry particles such as silver, and the presence or absence of a treatment such as filtration or washing can be appropriately set.
In addition, a mother liquor solvent (for example, water) obtained by synthesizing particles such as silver can be used as a dispersion solvent in the dispersion as it is. In this case, the process of separating particles such as silver from the mother liquor by filtration can be omitted. Further, when unnecessary components coexist in the mother liquor, a process for removing the unnecessary components is performed as necessary. And after adding a required amount of surfactant with respect to the dispersion liquid in which particles, such as silver, were disperse | distributed, it uses for a freeze-drying process. When a suitable surfactant has already been added to the mother liquor, this can be used for lyophilization treatment, or a surfactant may be further added.
According to this method, since particles such as silver produced in the liquid phase are primary particles, a dispersion liquid in which particles such as silver are dispersed together with a surfactant is obtained while suppressing aggregation of particles such as silver. Can do. In this case, treatment using a stirrer or a disperser for crushing secondary particles such as silver into primary particles is unnecessary, and even if the degree of stirring and mixing is moderate, the particles such as silver A desirable dispersion state in which the primary particles are dispersed in the dispersion solvent can be obtained.

  The dispersion liquid of particles such as silver containing a surfactant produced by the dispersion production method exemplified above is subjected to a lyophilization treatment in the next step. The range of the solid content concentration in the dispersion liquid of particles such as silver when freeze-drying in the next step is preferably 0.5 to 80%, and particularly preferably 1 to 50%.

  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 surface of particles such as silver via the surfactant, and dispersion stability is obtained. In addition, in the phosphate ester system and the alkylamine or alkylamine salt system, the charge when the hydrophilic group portion is ionized is opposite, so repulsive force between the particles depends on the sign of the surface charge of the particles such as silver. It is preferable to select and use any of the surfactants so that.

  For example, in the case of silver particles 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. is there. In the case of pure silver particles (silver particles whose surface is not subjected to silver oxide treatment), phosphate ester type surfactants are preferable, and conductive paints based on this combination have excellent dispersibility in the binder resin. There is a feature.

(2) Drying step After particles such as silver are sufficiently dispersed in the dispersion solvent in the presence of a surfactant, the dispersion solvent is removed from the dispersion by a vacuum freeze-drying method.
In the present invention, since a vacuum freeze-drying method is used as the drying method, it is preferable to select and use a solvent that is easily frozen from the above-mentioned dispersing solvents. Considering that the cooling capacity of a generally available apparatus for performing vacuum freeze-drying is up to about −40 ° C., selecting a solvent having a freezing point of −40 ° C. or higher as a solvent for dispersion This is preferable because it can reduce the cost.

In the vacuum freeze-drying method used in the present invention, only the dispersion solvent is sublimated and removed from a dispersion basically frozen at a low temperature. According to this method, when the dispersion solvent is removed, the surfactant is not eluted and lost in the dispersion solvent, so that almost all of the added surfactant remains in the processed powder. be able to.
In the dispersion, the surfactant is localized near the surface of the particles such as silver, and when the vacuum freeze-drying is performed in which only the dispersing solvent is removed, the surfactant remains on the surface of the particles such as silver. In addition, the particles such as silver and the surface-treated particles are agglomerated as in the case of removing the dispersing solvent by a normal method other than vacuum freeze-drying. This is an extremely efficient processing method. All the surfactants used in this way remain on the surface of particles such as silver, giving surface-treated particles such as silver in a high yield, making it easy to grasp the relationship between the effect of surfactants and the amount used. Easy to optimize for usage.
The surfactant molecule adsorbs to the surface of the particle such as silver at the end of the hydrophilic group, so 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 particles such as silver is improved. Moreover, aggregation of particles is suppressed and the state dispersed in the primary particles can be maintained.

Freeze-vacuum drying may be performed, for example, by pre-freezing the dispersion liquid below the freezing point of the dispersing solvent at atmospheric pressure and controlling the degree of vacuum at a pressure lower than the vapor pressure of the dispersing solvent at the freezing point. Thus, in theory, the molecules of the solvent for dispersion can be sublimated from the solid mixture in the frozen state.
For example, in the case of a dispersion using water as a dispersion solvent (a dispersion containing silver or silver compound particles, water, and a surfactant), it is pre-frozen to 0 ° C. or less at atmospheric pressure, and theoretically The degree of vacuum may be controlled so that the water vapor pressure at 0 ° C. does not exceed 4.5 mmHg (= 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.

  As described above, the surface of the particles containing silver or a silver compound as a main component is surface-activated by subjecting the dispersion in which particles such as silver are dispersed in a solvent for dispersion in the presence of a surfactant to vacuum freeze-drying. A powder composed of particles adsorbed with the agent is obtained.

(3) Coating process A conductive coating is produced using a product (particles such as surface-treated silver) in which a surfactant is adsorbed on the surface of silver or silver compound particles by the dispersion manufacturing process and the drying process. In order to manufacture, the product is mixed with a solvent, carbon nanotubes (MWNT) and a binder resin to prepare a paint.

Binder resins include acrylic resin, butyral resin, polyvinyl alcohol resin, acetal resin, phenol resin, urea resin, vinyl acetate emulsion, polyurethane resin, polyvinyl acetate resin, epoxy resin, melamine resin, alkyd resin, nitrocellulose resin Natural resins can be used alone or in admixture of two or more. When the production method of the present invention is used, since particles such as silver are surface-treated with a surfactant in advance, particles such as silver 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.
Of these binder resins, polyurethane resins are preferred.

Solvents used in the coating process include alcohols such as methanol, ethanol, n-propanol, benzyl alcohol, and terpineol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, isophorone, and acetylacetone; N, N-dimethylformamide, Amides such as N, N-dimethylacetamide; ethers such as tetrahydrofuran, dioxane, methyl cellosolve, diglyme, butyl carbitol; methyl acetate, ethyl acetate, diethyl carbonate, TXIB (1-isopropyl-2,2-dimethyltrimethylene Diisobutyrate), esters such as carbitol acetate, butyl carbitol acetate; sulfoxides and sulfones such as dimethyl sulfoxide, sulfolane; methylene chloride, chloroform, carbon tetrachloride 1,1,2 aliphatic halogenated hydrocarbons trichloroethane; benzene, toluene, o- xylene, p- xylene, m- xylene, monochlorobenzene, aromatics dichlorobenzene, and the like. These solvents are not limited to those listed here, and can be used alone or in admixture of two or more.
These organic solvents added for dispersibility and coatability can be used as long as they are liquid at room temperature. However, from the viewpoint of suppressing a decrease in printability due to volatilization of the solvent, a solvent having a boiling point of 200 ° C. or higher ( Also called a plasticizer).

The composition of the conductive paint of the present invention comprises 0.1 to 1.0 parts by mass of carbon nanotubes with respect to 100 parts by mass of a powder in which a surfactant is adsorbed on the surface of particles mainly composed of silver or a silver compound. In addition, 1 to 10 parts by mass of a binder resin and an appropriate amount of a solvent are added.
A more preferable range of the blending amount of the binder resin is 3 to 10 parts by mass with respect to 100 parts by mass of the powder.

  The conductive paint with excellent dispersion stability and adhesion to the substrate is obtained by adding a binder resin to the particles such as silver surface-treated in the dispersion manufacturing process and the drying process in addition to the solvent. Can be manufactured.

If particles such as silver surface-treated by the dispersion manufacturing process and the drying process are used as raw materials, a simple dispersion process such as stirring using a solvent and a binder resin when a conductive paint is required It is possible to quickly produce a good conductive paint simply by performing the above. That is, since a good conductive paint can be obtained by performing a simple stirring operation with the solvent and the binder resin immediately before printing, a large amount of equipment for manufacturing the paint is not required as equipment accompanying the printing apparatus.
However, in order to perform the dispersion more reliably, the following dispersion machine may be used for the dispersion process.

  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 conductive paint after kneading and dispersing is generally printed as a paste-like composition on an insulating film or an insulating substrate by a known and commonly used coating method or printing method, and this is heated to form a conductor circuit. Can be formed.
The conductive paint of the present invention can form a coating 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 application 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 is formed on the film with a predetermined pattern. It is possible to print on the substrate and heat-cure after drying the printed matter.
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 particles or silver particles whose surface is treated with silver oxide are used as the particles such as silver, the heat treatment reduces the silver oxide to silver along with hardening by the heat treatment, and the oxygen released along with the reduction reaction The surrounding surfactant and resin can be oxidized to generate heat. As a result, the silver particles in which the silver oxide has been reduced can be fused by a heat treatment at a lower temperature (for example, 200 ° C. or less) than when pure silver particles are used. Therefore, conductive paints using silver oxide particles or silver oxide-treated silver particles can reduce the requirement for heat resistance of the base material during application or printing, so PET, PI, other plastics, etc. It is particularly suitable for a substrate made of

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, this invention is not limited only to these Examples. In the following examples, “%” and “part” are based on mass unless otherwise specified.

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 using a low resistivity meter Lorester EP (manufactured by Mitsubishi Chemical Corporation) of a four-terminal measurement method. The volume resistivity was determined from the film thickness of the test piece film.

Production of CNT paint:
MWNT (diameter 40 to 80 nm) 10.0 parts by mass, urethane elastomer EDL555 (solid content 50%, manufactured by Dainippon Ink & Chemicals, Inc.) 26.0 parts by mass and butyl carbitol acetate are added as appropriate. Then, the mixture was kneaded with a vertical kneader, and finally blended so that the charged amount of butyl carbitol acetate was 64.0 parts by mass to produce a master batch of CNT paint.

  As the silver powder, silver powder obtained by treating the surface of a silver powder FHD (crystallite diameter <10 nm, manufactured by Mitsui Kinzoku Co., Ltd.) having a center particle diameter of 0.3 μm with 10% silver oxide was used. With respect to 100 parts by mass of the silver powder treated with silver oxide, 5.1 parts by mass of EDD523 (solid content 68.2%), 5.1 parts by mass of EDL555 (solid content 50%), and EDL524 (solid content 74.6) %) 1.3 parts by mass, butyl phthalyl glycolate butyl (manufactured by Wako Pure Chemical Industries, Ltd., BPBG (plasticizer)) 0.35 parts by mass, carbitol acetate 6.1 parts by mass, A silver paste was prepared by kneading and dispersing with a kneader.

(State of film after bending)
In Table 1, the criteria for determining the state of the film after bending are as follows.
A: No cutting is observed at the bent portion by visual observation.
○: Slight cutting is observed at the bent part by visual observation.
Δ: A part of the bent portion is clearly cut.
X: The bent part is completely cut.

Example 1
The conductive paste according to Example 1 was prepared by kneading 20 g of the silver paste and 0.26 g of the CNT master batch. The obtained conductive paint was applied to a PET film and dried at 160 ° C. for 30 minutes to obtain a conductive film according to Example 1. The state of this conductive film was cream color, and the volume resistivity was 1.93 × 10 ⁻⁵ Ω · cm. After the conductive film of Example 1 was folded, the volume resistivity was measured and found to be 1.93 × 10 ⁻⁴ Ω · cm.

(Example 2)
The conductive paste according to Example 2 was prepared by kneading 20 g of the silver paste and 0.78 g of the CNT master batch. The obtained conductive paint was applied to a PET film and dried at 160 ° C. for 30 minutes to obtain a conductive film according to Example 2. The state of this conductive film was cream to gray and the volume resistivity was 2.91 × 10 ⁻⁵ Ω · cm. After the conductive film of Example 2 was bent, the volume resistivity was measured and found to be 1.02 × 10 ⁻⁴ Ω · cm.

(Comparative Example 1)
20 g of the silver paste was applied to a PET film and dried at 160 ° C. for 30 minutes to obtain a conductive film according to Comparative Example 1. The state of this conductive film was cream color, and the volume resistivity was 1.62 × 10 ⁻⁵ Ω · cm. After the conductive film of Comparative Example 1 was bent, the volume resistivity was measured and found to be 1.43 × 10 ⁻² Ω · cm. When the state of the film after bending was observed, it was completely cut.

(Comparative Example 2)
A conductive film according to Comparative Example 2 was prepared by kneading 20 g of the silver paste and 0.10 g of EDL555 (solid content: 50%), applying the obtained paint to a PET film, and drying at 160 ° C. for 30 minutes. Obtained. The state of this conductive film was cream color, and the volume resistivity was 1.75 × 10 ⁻⁵ Ω · cm. After the conductive film of Comparative Example 2 was folded, the folded film was completely cut, and the volume resistivity was not measurable.

(Evaluation results and discussion)
The results of the above test are summarized in Table 1.

  As is apparent from the results shown in Table 1, the films produced using the conductive paints of the examples are strong against bending by the addition of CNTs, and suppress the decrease in volume resistivity of the film after bending. did it.

  The conductive paint of the present invention is excellent in conductivity and printing accuracy, and can be used for printed wiring used in electronic devices and the like.

Claims (12)

  100 parts by mass of a powder in which a surfactant is adsorbed on the surface of particles mainly composed of silver or a silver compound, 0.1 to 1.0 parts by mass of carbon nanotubes, 1 to 10 parts by mass of a binder resin, A conductive paint comprising a solvent.   The conductive paint according to claim 1, wherein the binder resin is polyurethane.   3. The conductive paint according to claim 1, wherein a volume average particle diameter of the silver or silver compound as a main component is in a range of 0.01 to 10 μm.   4. The conductive paint according to claim 1, wherein the particles containing silver or a silver compound as a main component are silver particles having a surface coated with silver oxide and a silver oxide content of 40% or less.   The conductive paint according to claim 1, wherein the surfactant is an alkylamine or an alkylamine salt.   The conductive paint according to claim 1, wherein the surfactant is a phosphate ester-based surfactant.   A dispersion manufacturing process for manufacturing a dispersion in which particles containing silver or a silver compound as a main component are dispersed in a dispersion solvent in the presence of a surfactant, a drying process for freeze-drying the dispersion in vacuum, and the drying It is characterized by having a paint forming step of preparing a paint by mixing 0.1 to 1.0 part by mass of carbon nanotubes and 1 to 10 parts by mass of a binder resin with a solvent with respect to 100 parts by mass of the product of the process. A method for producing a conductive paint.   The method for producing a conductive paint according to claim 7, wherein the binder resin is polyurethane.   The method for producing a conductive paint according to claim 7 or 8, wherein a volume average particle diameter of the silver or silver compound as a main component is in a range of 0.01 to 10 µm.   The method for producing a conductive paint according to claim 7, wherein the particles containing silver or a silver compound as a main component are silver particles having a particle surface coated with silver oxide and a silver content of 60% or more. .   The method for producing a conductive paint according to claim 7, wherein the surfactant is an alkylamine or an alkylamine salt.   The method for producing a conductive paint according to claim 7, wherein the surfactant is a phosphate ester-based surfactant.