JP2017059334A - Conductive resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive resin composition excellent in printability during application, shape retention property after application and before drying and conductivity when made as a coated film.SOLUTION: A conductive resin composition contains 2 kinds of silver coated particle A and silver coated particle B having different average particle diameter as conductive fillers and a binder resin C. Both of variation coefficient of particle diameter of the silver coated particle A (CV) and variation coefficient of particle diameter of the silver coated particle B (CV) are 15% or less, specific gravity of the silver coated particle A (d) and specific gravity of the silver coated particle B (d) are in a range of 2.0 to 6.0 respectively, a ratio D/Dof average particle diameter of the silver coated particle A (D) to average particle diameter of the silver coated particle B (D) is 1.2 to 5.0, a ratio W/Wof mass of the silver coated particle A (W) to weight of the silver coated particle B (W) is 0.5 to 3.0, and a ratio (W+W)/Wof total mass of the silver coated particles A and B (W+W) to mass of the binder resin C (W) is 3.0 to 8.0.SELECTED DRAWING: None

Description

  The present invention relates to a conductive resin composition excellent in printability at the time of coating and shape retention before drying after coating, and excellent in conductivity when formed into a coating film.

  Conventionally, a composition for forming a conductive part containing silver particles and a binder resin has been disclosed (see, for example, Patent Document 1). Moreover, the electroconductive resin composition which has silver covering silica particle, an epoxy resin, and a hardening | curing agent as an essential component is disclosed (for example, refer patent document 2). Patent Document 2 describes that the specific gravity of silver-coated silica particles is 2.4 to 3.6.

JP 2014-67492 A (Claims 1 and 3) Japanese Patent Laying-Open No. 2015-26519 (Claims 1 and 2)

  When silver particles are used as the conductive filler as in the conductive part forming composition of Patent Document 1, since the specific gravity of the silver particles is larger than that of the binder resin, before drying after applying this composition, There exists a malfunction which settles in the composition apply | coated by the dead weight of an electroconductive filler, a shape becomes easy to become unstable, and shape retainability is low. Moreover, like the conductive resin composition of patent document 2, when the silver covering particle | grains whose specific gravity is small compared with silver particle are used as a conductive filler, when the variation coefficient of the particle size of a conductive filler is large, a particle size of Due to the variation, the filling rate of the conductive filler in the coating film cannot be increased, and there is a problem that voids are generated in the coating film and the conductivity of the coating film is lowered.

  An object of the present invention is to provide a conductive resin composition that is excellent in printability at the time of coating and shape retention before drying after coating, and excellent in conductivity when formed into a coating film.

The first aspect of the present invention includes two kinds of silver-coated particles A and silver-coated particles B having different average particle diameters as a conductive filler, and a binder resin C. Both the coefficient (CV _A ) and the coefficient of variation (CV _B ) of the particle diameter of the silver-coated particles B are 15% or less, and the specific gravity (d _A ) of the silver-coated particles A and the specific gravity (d of the silver-coated particles B) _B ) is in the range of 2.0 to 6.0, respectively, and the ratio of the average particle diameter (D _A ) of the silver-coated particles A to the average particle diameter (D _B ) of the silver-coated particles B (D _A / D _B ) is 1.2 to 5.0, and the ratio (W _A / W _B ) of the mass (W _A ) of the silver-coated particles A to the mass (W _B ) of the silver-coated particles B is 0.5. is 3.0, the total weight _(W a + W _B) and the mass of the binder resin C of the silver-coated particles a and the silver-coated particles B (W _{Ratio) ((W A + W B} ) / W C) is a conductive resin composition is 3.0 to 8.0.

  The 2nd viewpoint of this invention is the method of apply | coating the conductive resin composition based on a 1st viewpoint to a base material, and forming a conductive coating film.

In the conductive resin composition of the first aspect of the present invention, the coefficient of variation (CV _A ) of the particle diameter of the silver-coated particles _A and the coefficient of variation (CV _B ) of the particle diameter of the silver-coated particles B are both 15% or less. Therefore, local voids due to the variation in particle size are reduced compared to the case where the coefficient of variation of the particle size of silver-coated particle A and / or silver-coated particle B exceeds 15%. At the same time, agglomeration derived from the difference in surface energy of silver-coated particles having different particle diameters is reduced, the uniform dispersibility in the resin composition is improved, and a coating film excellent in conductivity is obtained. In the conductive coating film, the specific gravity (d _A ) of the silver-coated particles _A and the specific gravity (d _B ) of the silver-coated particles B are values in the range of 2.0 to 6.0, respectively. There is no difference in sedimentation due to the weights of both particles A and B in the composition before the removal, and the particles exist uniformly. The ratio (D _A / D _B ) of the average particle diameter (D _A ) of the silver-coated particles _A and the average particle diameter (D _B ) of the silver-coated particles B is 1.2 to 5.0, and the silver-coated particles since the ratio of the mass of particles a _{(W a)} and the silver-coated particles B mass _{(W B) (W a /} W B) is 0.5 to 3.0, the particles B a gap generated between the particles a By filling the film, a coating film having no voids and high packing density and excellent conductivity can be obtained. Furthermore, the ratio ((W _A + W _B ) / W _C ) of the total mass (W _A + W _B ) of the silver-coated particles A and the silver-coated particles B to the mass (W _C ) of the binder resin C is 3.0 to 8.0. Therefore, the coating film obtained by applying the composition onto the substrate and drying it has many contact points with the silver-coated particles and is excellent in conductivity.

  In the method for forming a conductive coating film according to the second aspect of the present invention, in a coating process such as screen printing, the conductive resin composition can be finely printed due to the excellent thixotropic property of the conductive resin composition. It becomes possible. Before drying after applying the conductive resin composition, the shape is maintained, and a coating film having a predetermined shape can be formed. Moreover, when it is set as a coating film, the coating density with high packing density of silver coating particle A and B and low volume resistivity can be formed.

  Next, the form for implementing this invention is demonstrated.

[Silver coated particles]
The silver-coated particles of this embodiment are composed of two types of silver-coated particles A and silver-coated particles B having different average particle sizes. Both particles A and B each include a core particle and a silver coating layer formed on the surface of the core particle. The core particles include resin particles and inorganic particles. Examples of the resin particles include acrylic resin particles, styrene resin particles, phenol resin particles, silicone resin particles, silicone rubber particles, melamine resin particles, fluororubber particles, polyamide resin particles, and polyimide resin particles. Examples of inorganic particles include silica particles, glass particles, mica particles, alumina particles, aluminum particles, talc particles, and mixed powders thereof. These particles may be classified so as to obtain a required particle size and CV value. The two particles A and B are preferably manufactured to have the same composition, but they may have different compositions. It is preferable that the quantity of silver contained in a silver coating layer exists in the range of 45-90 mass parts with respect to 100 mass parts of silver-coated particles in both particles A and B. The thickness of the silver coating layer is preferably in the range of 0.05 to 0.70 μm for both particles A and B. Depending on the amount of silver contained in the silver coating layer and the thickness of the silver coating layer, the specific gravity dA of the silver-coated particles A and the specific gravity dB of the silver-coated particles B are in the range of 2.0 to 6.0. These specific gravities were measured by a liquid immersion method using an organic solvent used for the conductive resin composition.

  The silver coating amount (content) is determined by the average particle size of the resin and the required conductivity. When the amount of silver contained in the silver coating layer is less than the lower limit of 45 parts by mass, and when the thickness of the silver coating layer is less than 0.05 μm, the silver-coated contacts are dispersed when the silver-coated particles are dispersed as the conductive filler. However, it is difficult to obtain sufficient conductivity. On the other hand, when the silver content exceeds 90 parts by mass, and when the thickness of the silver coating layer exceeds 0.70 μm, the specific gravity of the silver-coated particles increases, the cost increases, and the conductivity is saturated. The silver content is more preferably 50 to 88 parts by mass. The silver coating amount is obtained by, for example, ICP emission spectrometry after acid-decomposing silver-coated particles.

  The average particle diameter of the core particles of the silver-coated particles A is preferably in the range of 1.0 to 20 μm, and more preferably in the range of 1.5 to 5.0 μm. The average particle size of the core particles of the silver-coated particles B is smaller than the average particle size of the core particles of the silver-coated particles A, preferably in the range of 0.3 to 12 μm, and in the range of 0.5 to 3 μm. More preferably. For both particles A and B, the core particles are preferably single particles without aggregation. If the lower limit of 0.3 μm of the core particle of the silver-coated particle B is less than 0.3 μm, the core particle is likely to aggregate, the surface area of the core particle is increased, and the amount of silver for obtaining the necessary conductivity as a conductive filler is increased. This is because it is difficult to form a good silver coating layer. On the other hand, when the average particle diameter of the core particles of the silver-coated particles A exceeds 20 μm, problems such as a decrease in the surface smoothness of the resin electrode film, a decrease in the contact ratio of the conductive particles, and an increase in the resistance value occur. In the present specification, the average particle diameter of the core particles is a magnification of 5000 times by software (product name: PC SEM) using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation: model name: S-4300SE). Then, the diameter of 300 silver-coated resins is measured and the calculated average value is referred to. The values other than the true sphere mean the average of the long sides. The core particle may be a spherical particle, or may be a non-spherical shape, such as a flat shape, a plate shape, or a needle shape.

The average particle size _{D A} of the silver-coated particles A, in addition to the thickness of the silver coating layer on the particle size of the core particles is preferably in the range of 1.1～21Myuemu, range 1.6~5.1μm More preferably, The average particle size _{D B} of the silver-coated particles B are likewise smaller than the average particle size of the core particles of the silver-coated particles A, preferably in the range of 0.4～3.5Myuemu, 0.8 to 2 More preferably, it is in the range of 0.0 μm. The ratio D _A / D _B of the average particle diameter D _B of the silver-coated particles B to the average particle diameter D _A of the silver-coated particles _A is 1.2 to 5.0. If it is less than 1.2, the difference between the average particle sizes of the particles A and B becomes too small, and the particle B cannot fill the gap formed between the particles A. On the other hand, if it exceeds 5.0, the difference between the average particle diameters of the two particles A and B becomes too large, and the particle B cannot fill the gap formed between the particles A. _A preferable range of the ratio D _A / D _B is 1.5 to 3.0.

The coefficient of variation CV _B of grain size distribution variation coefficient of the grain size of the silver-coated particles A CV _A and silver-coated particles A is less than both 15.0%, preferably have uniform particle size. This is because if the coefficient of variation exceeds 15.0% and the particle diameter is not uniform, the reproducibility of imparting conductivity when used as a conductive filler is impaired. The coefficient of variation (CV value, unit:%) is determined from the particle size of the 300 resins by the formula: [(standard deviation / average particle size) × 100].

[Method for producing silver-coated particles]
The silver-coated particles A and B of this embodiment are each produced by the following method. First, the core particle is added to an aqueous solution of a tin compound kept at 25 to 45 ° C. to form a tin adsorption layer on the surface of the core particle. Next, an electroless silver plating solution containing no reducing agent is brought into contact with the tin adsorption layer formed on the surface of the core particle, and the tin adsorption layer formed on the surface of the core particle and the silver in the electroless plating solution A silver substitution layer is formed on the surface of the core particle by a substitution reaction. Next, by adding a reducing agent to the electroless silver plating solution, a silver coating layer is formed on the surface of the silver replacement layer of the core particles.

[Method of forming silver coating layer by electroless silver plating]
A silver coating layer is provided on the surface of the core particle. Generally, when electroless plating is performed on the surface of a nonconductor such as an organic material or an inorganic material, it is necessary to perform a catalyst treatment on the surface of the nonconductor in advance. In the present embodiment, as a catalyst treatment, a treatment for providing a tin adsorption layer on the surface of the core particles is performed, and then an electroless silver plating treatment is performed to form a silver coating layer. Specifically, the silver coating layer of this embodiment is manufactured by the following method. First, the core particle is added to an aqueous solution of a tin compound kept at 25 to 45 ° C. to form a tin adsorption layer on the surface of the core particle. Next, an electroless silver plating solution not included in the tin adsorption layer is brought into contact, and a silver substitution layer is formed on the surface of the core particle by a substitution reaction between the tin adsorption layer formed on the surface of the core particle and silver in the electroless plating solution. Form. Next, by adding a reducing agent to the electroless silver plating solution, a silver coating layer is formed on the surface of the silver replacement layer of the core particles.

  In order to form the tin adsorption layer, the core particles are added to an aqueous solution of a tin compound and stirred, and then the core particles are filtered or centrifuged and washed with water. Although stirring time is suitably determined by the temperature of the following aqueous solution of a tin compound and the content of the tin compound, it is preferably 0.5 to 24 hours. The temperature of the aqueous solution of the tin compound is 25 to 45 ° C, preferably 25 to 35 ° C, and more preferably 27 to 35 ° C. When the temperature of the aqueous solution of the tin compound is less than 25 ° C., the temperature is too low and the activity of the aqueous solution becomes low, and the tin compound does not sufficiently adhere to the core particles. On the other hand, when the temperature of the aqueous solution of the tin compound exceeds 45 ° C., the tin compound is oxidized, so that the aqueous solution becomes unstable and the tin compound does not sufficiently adhere to the core particles. When this treatment is carried out with an aqueous solution at 25 to 45 ° C., divalent ions of tin adhere to the surface of the core particles, and a tin adsorption layer is formed.

Examples of the tin compound include stannous chloride, stannous fluoride, stannous bromide, stannous iodide, and the like. When using stannous chloride, the content of stannous chloride in the aqueous solution of the tin compound is preferably ³⁰ to 100 g / dm ³ . If the content of stannous chloride is 30 g / dm ³ or more, a uniform tin adsorption layer can be formed. If the stannous chloride content is 100 g / dm ³ or less, the amount of inevitable impurities in stannous chloride is suppressed. Note that stannous chloride can be contained in an aqueous solution of a tin compound until saturation.

  After a tin adsorption layer is formed on the surface of the core particle, an electroless plating solution containing no reducing agent is brought into contact with the tin adsorption layer, and a silver substitution layer is formed on the surface of the core particle by a substitution reaction of tin and silver. Subsequently, a reducing agent is added to the electroless silver plating solution to perform electroless plating, thereby forming a silver coating layer on the surface of the core particles to produce silver coated particles. The electroless silver plating method includes (1) a method in which core particles having a silver substitution layer formed on the surface are immersed in an aqueous solution containing a complexing agent, a reducing agent, and the like, and (2) silver salt aqueous solution is dropped. A method in which core particles having a silver substitution layer formed on the surface thereof are immersed in an aqueous solution containing a salt and a complexing agent, and a reducing agent aqueous solution is dropped; (3) an aqueous solution containing a silver salt, a complexing agent, a reducing agent, etc. And a method of immersing core particles having a silver substitution layer on the surface and dropping a caustic aqueous solution.

  As the silver salt, silver nitrate or silver dissolved in nitric acid can be used. Complexing agents include salts such as ammonia, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, nitrotriacetic acid, triethylenetetraamminehexaacetic acid, sodium thiosulfate, succinate, succinimide, citrate or iodide salt Can be used. As the reducing agent, formalin, glucose, imidazole, Rochelle salt (sodium potassium tartrate), hydrazine and its derivatives, hydroquinone, L-ascorbic acid or formic acid can be used. As the reducing agent, formaldehyde is preferable because of its strong reducing power, a mixture of two or more reducing agents containing at least formaldehyde is more preferable, and a mixture of reducing agent containing formaldehyde and glucose is most preferable.

  In the previous step of the electroless silver plating process, tin in the tin adsorption layer releases and elutes electrons by coming into contact with silver ions in the solution, while silver ions receive electrons from tin and core as metal. Displacement deposits on the portion of the particles where the tin was adsorbed. Thereafter, when all the tin is dissolved in the aqueous solution, the substitution reaction of tin and silver is completed. Subsequently, a reducing agent is added to the electroless plating solution, and a silver coating layer is formed on the surface of the core particles by a reduction reaction with the reducing agent, thereby producing silver-coated particles.

[Conductive resin composition]
The conductive resin composition of this embodiment contains two types of silver-coated particles A and silver-coated particles B having different average particle diameters as a conductive filler, and a binder resin C. These compositional ratio of the mass of the silver-coated particles A and _{W A,} the mass of the silver-coated particles B and _{W B,} when the mass of the binder resin C and _{W C,} W A / _{W B} are 0.5 in the range of 3.0, it is in the range of _{3.0~8.0 (W a + W B)} / W C. The range of W _A / W _B is determined by the ranges of the average particle diameter and specific gravity of both particles A and B described above. (W _{A +} W _B) / If W _C is less than 3.0, the contact of the particles is inhibited because the binder resin is too large, conductivity decreases. Moreover, when it exceeds 8.0, there are too few binder resins and it is inferior to the coating property and adhesiveness to the base material of a composition.

[Method for producing conductive resin composition]
The binder resin C contained in the conductive resin composition is any one of an epoxy resin, a phenol resin, a urethane resin, an acrylic resin, a silicone resin, or a polyimide resin. In addition to the silver-coated particles A, the silver-coated particles B, and the binder resin C, the conductive resin composition contains a curing agent and a solvent.

[Ratio of silver-coated particles in the conductive resin composition]
The total ratio of the silver-coated particles A and B in the conductive resin composition is preferably 70 to 90% by mass, and 75 to 85% by mass in 100% by mass of the conductive resin composition. More preferably. If it is less than 70% by mass, the resistance value of an electrode or wiring formed by applying and curing the conductive resin composition is increased, and it becomes difficult to form an electrode or wiring having excellent conductivity. On the other hand, if it exceeds 90% by mass, a composition having good fluidity tends to be not obtained, and it becomes difficult to form a good electrode in terms of printability.

[Binder resin in conductive resin composition]
Examples of the epoxy resin as the binder resin to be included in the conductive resin composition include bisphenol type, biphenyl type, biphenyl mixed type, naphthalene type, cresol novolac type, dicyclopentadiene type, trisphenolethane type, tetraphenolethane type epoxy. Resin. Examples of epoxy resin curing agents include commonly used imidazoles, tertiary amines or Lewis acids containing boron fluoride, or compounds thereof, phenol resin curing agents, acid anhydride curing agents, dicyandiamide, and the like. The latent curing agent is preferred. Examples of imidazoles include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4. -Methyl-5-hydroxymethylimidazole, 2-phenylimidazole isocyanuric acid adduct and the like. Tertiary amines include piperidine, benzyldiamine, diethylaminopropylamine, isophoronediamine, diaminodiphenylmethane, and the like. The Lewis acid containing boron fluoride includes an amine complex of boron fluoride such as boron fluoride monoethylamine.

  Examples of the phenolic curing agent include phenol novolac resin, paraxylylene phenol resin, and dicyclopentadiene phenol resin. Examples of the acid anhydride curing agent include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride and the like. Moreover, you may add a hardening accelerator as needed. Curing accelerators include imidazoles such as 1-benzyl-2-methylimidazole and salts thereof, tertiary amines such as 1,8-diazabicyclo [5.4.0] undec-7-ene and salts thereof, triphenyl, and the like. Examples thereof include organic phosphine compounds such as phosphine and salts thereof, organic metal salts such as zinc octylate, tin octylate and alkoxytitanium, and noble metals such as platinum and palladium.

  The phenol resin as the binder resin to be included in the conductive resin composition may be of any structure as long as the thermosetting phenol resin is a thermosetting type, but the molar ratio of formaldehyde / phenol is 1-2. A range is preferable. The thermosetting phenol resin preferably has a weight average molecular weight of 300 to 5,000, more preferably 1,000 to 4,000. If it is less than 300, the amount of water vapor generated during heat curing is large, and voids are easily formed in the film, and it is difficult to obtain sufficient film strength. If it is greater than 5000, the solubility is insufficient and it becomes difficult to form a paste. A part of the thermosetting phenol component used in the present invention may be replaced with another compound having a phenolic hydroxyl group.

  As the urethane resin as the binder resin to be included in the conductive resin composition, those generally used for bonding can be used. Specific examples include polyol-based urethane resins, polyester-based urethane resins, polycaprolactam-based urethane resins, polyether-based urethane resins, polycarbonate-based urethane resins, and urethane acrylate resins. These may be used alone or in combination. Can do. Moreover, hardening | curing agents, such as isocyanate and block isocyanate, can be added as needed.

  As the silicone resin as the binder resin to be included in the conductive resin composition, any structure of addition type or condensation type can be used as long as it is generally used for bonding. Specific examples of the silicone resin include various organopolysiloxanes, modified polysiloxanes, elastomer-modified polysiloxanes, room temperature curable silicone rubbers, and the like, and these can be used alone or in combination.

  As the acrylic resin as the binder resin to be included in the conductive resin composition, generally used thermosetting, photopolymerization, and solvent evaporation types can be used. For example, acrylic-melamide resin, polymethyl methacrylate resin, acrylic-styrene copolymer, silicon-modified acrylic resin, epoxy-modified acrylic resin and the like can be used, and these can be used alone or in combination. If necessary, a thermosetting agent such as isocyanate, an alkylphenone photopolymerization initiator, or the like can be used as the curing agent.

  Generally used polyimide resin can be used as the binder resin to be included in the conductive resin composition. For example, aromatic polyimide, alicyclic polyimide, polyimide siloxane, epoxy-modified polyimide, photosensitive polyimide and the like can be mentioned, and these can be used alone or in combination.

  The above-mentioned epoxy resin, phenol resin, urethane resin, acrylic resin, silicone resin or polyimide resin can suppress deterioration in quality due to aging of the conductive resin composition, and at the same time has a rigid skeleton in the main chain and a cured product. Since it is excellent in heat resistance and moisture resistance, durability of an electrode or the like to be formed can be improved. When the ratio of the binder resin is less than the lower limit, problems such as poor adhesion occur. Exceeding the upper limit causes problems such as a decrease in conductivity.

[Solvent in conductive resin composition]
As the solvent, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, Ether alcohol solvents such as dipropylene glycol monobutyl ether and tripropylene glycol monomethyl ether and their acetate solvents, ethylene hydrocarbon, propylene glycol, terpineol, mineral spirits, aromatic hydrocarbon solvents such as toluene, fats such as dodecane, etc. Group hydrocarbon solvents, dimethylformamide, N-methyl-2- Pyrrolidone, dimethyl sulfoxide, diacetone alcohol, dimethylacetamide, .gamma.-butyrolactone. These are selected depending on the compatibility with the binder resin. In the case of silicone resin, mineral spirit and toluene, in the case of polyimide resin, N-methyl 2-pyrrolidone, phenol resin, urethane resin, and epoxy resin, ethyl carbitol acetate and butyl carbitol acetate. Α-terpineol is particularly preferred. These solvents can be used alone or in combination of two or more.

  With respect to the binder resin and the mixture thereof, additives can be mixed as long as the conductivity, adhesion, and shape retention are not impaired. Examples of the additive include a silane coupling agent, a titanium coupling agent, silver nanoparticles, a thickener, a dispersant, a flame retardant, an antifoaming agent, and an antioxidant.

[Method for preparing conductive resin composition]
The conductive resin composition is prepared by first mixing the binder resin with the solvent under the conditions of a temperature of preferably 50 to 70 ° C, more preferably 60 ° C. At this time, the ratio of the binder resin is preferably 5 to 50 parts by mass and more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the solvent. Next, if necessary, the curing agent is mixed in an appropriate amount, and the conductive filler is further added. The kneading machine is preferably kneaded for 0.1 to 1 hour, for example, using a kneader such as a three-roll mill or a reiki machine. The conductive resin composition is prepared by making a paste. At this time, in order to give the prepared conductive resin composition suitable viscosity and necessary fluidity, and for the reasons described above, the conductive filler occupies the coating film formed by the conductive resin composition. Mix to 75-89% by mass. Moreover, the usage-amount of binder resin is adjusted so that mass ratio with an electroconductive filler may become the above-mentioned ratio from the reason mentioned above. As a result, the viscosity is preferably adjusted to 0.5 to 3.0 Pa · s. By adjusting the viscosity within this range, the printability of the conductive resin composition is improved and the printed pattern shape after printing is also kept good.

  The conductive resin composition thus prepared is applied onto, for example, a 4 × 4 cm alumina substrate as a base material, and dried at a predetermined temperature, fired, or the like to form a coating film. Firing is performed, for example, by holding at a temperature of 150 to 250 ° C. for 0.5 to 1 hour using an apparatus such as a hot air circulating furnace.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, 15 g of stannous chloride and 15 cm ³ of hydrochloric acid having a concentration of 35% were diluted to 1 dm ³ with water using a 1 dm ³ volumetric flask and kept at 30 ° C. To this aqueous solution, 5.0 g of core particles A having the types and average particle diameters shown in Table 1 as core particles serving as a base are added and stirred for 1 hour, and then these core particles A are filtered and washed with water. The pretreatment was performed.

Next, a silver coating layer was formed by electroless plating on the surface of the core particle A on which the tin adsorption layer was formed on the surface by the pretreatment. Specifically, first, 40 g of ethylenediaminetetraacetate as a complexing agent, 20.0 g of sodium hydroxide as a pH adjusting agent, and 15 cm ³ of formalin (formaldehyde concentration 37% by mass) as a reducing agent are added to 2 dm ³ of water. By dissolving these, an aqueous solution containing a complexing agent and a reducing agent was prepared. Next, a slurry was prepared by immersing the pretreated core particles A in this aqueous solution.

Then, silver nitrate 30 g, 25% ammonia water 35 cm ^3, water 50 cm ³ were mixed to prepare a silver nitrate-containing aqueous solution, while stirring the slurry, it was added dropwise the silver nitrate-containing aqueous solution. Further, a sodium hydroxide aqueous solution was dropped into the slurry after dropping the silver nitrate-containing aqueous solution to adjust the pH to 12, and the silver was deposited on the surface of the core particles A by stirring while maintaining the temperature at 25 ° C. . Then, washing | cleaning and filtration were performed, and it was made to dry at the temperature of 60 degreeC finally with the vacuum dryer, and the silver coating particle A was obtained.

  Also for the core particles B 5.0 g having the types and average particle sizes shown in Table 1, the same operation as that for the core particles A was performed in another system to obtain silver-coated particles B. Table 4 shows the physical properties of the silver-coated particles A and B of Example 1, and Table 5 shows the ratio (mass%) of silver in the silver-coated particles A and B of Example 1.

  As a binder resin, 5.0 g of a 1: 1 mass ratio mixture of a bisphenol F type epoxy resin (JER807 manufactured by Mitsubishi Chemical Corporation) and a biphenyl type epoxy resin (NC-3000 manufactured by Nippon Kayaku Co., Ltd.) shown in Table 2, a curing agent Dicyandiamide (DICY7, manufactured by Mitsubishi Chemical Corporation) 0.3 g, 3- (3,4-dichlorophenyl) -1,1-dimethylurea 0.1 g, dipropylene glycol monobutyl ether 5.0 g as a solvent Was used to prepare a binder varnish.

  Using the above-prepared binder varnish with 20.0 g of silver-coated particles A and 15.0 g of silver-coated particles B of Example 1 having the physical properties shown in Table 4 as conductive fillers, each using foam removal Netaro (Sinky Corporation) Mixed. This mixture was kneaded with a three-roll mill (EXAKT) to obtain a conductive resin composition of Example 1.

<Examples 2 to 10 and Comparative Examples 1 to 12>
The silver-coated particles A and B are obtained by classifying the core particles A and B of the type shown in Table 1 by the sedimentation method to obtain the average particle size shown in Table 1, and then the silver particles as shown in Table 5 The amounts of silver nitrate, ethylenediaminetetraacetic acid sodium salt, sodium hydroxide, and formalin were adjusted so that the ratio (mass%) was obtained, and the other components were produced in the same manner as in Example 1. The obtained silver-coated particles A and B were kneaded with the binder resins of the types shown in Tables 2 and 3 at the blending ratios shown in Table 4 in the same manner as in Example 1, and Examples 2 to 10 and The conductive resin composition of Comparative Examples 1-12 was obtained.

<Comparison test and evaluation>
About the conductive resin composition obtained in Examples 1-10 and Comparative Examples 1-12, the printability at the time of application | coating, the shape retainability before drying after apply | coating, and the electroconductivity when it was used as a coating film ( The volume resistivity was evaluated by the methods shown below. These results are shown in Table 5.

(1) Printability at the time of application The conductive resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 12 were subjected to L / S (line and line) using a 250 mesh screen plate with a screen printer. -Space) = 300 μm comb-shaped wiring pattern was printed on a glass substrate. The printed pattern was observed and measured with a 20 × objective lens with a laser microscope (Keyence), and appearance observation and surface roughness (Ra value) such as bleeding and blurring during printing were measured. The case where there was no blur or blur and the Ra value was less than 10 μm was judged as “good”, and the case where there was blur, blur or the like or the Ra value was 10 μm or more was judged as “bad”.

(2) Shape retention before drying after coating The conductive resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 12 were screened using a 250-mesh screen slab. Ten sets of 10 patterns of S = 300 μm comb wiring were printed on a glass substrate. Of these, 5 sets were dried within 5 minutes immediately after printing in an air atmosphere in a baking furnace at 150 ° C. for 1 hour using a baking furnace to dry the volatile components and cure the binder resin to obtain a conductive coating film. The remaining 5 sets were allowed to stand inside the desiccator for 1 hour, and then the volatile components were dried and the binder resin was cured under the same conditions to obtain a conductive coating film. The line width of the comb portion of the conductive coating film was measured with a laser microscope (Keyence) using a 20 × objective lens. The average value of 10 sets of 10 comb-shaped wirings in each measurement was calculated, and the line width expansion due to shape collapse was compared. The line width after standing was less than 1.05 times the line width without standing, and “good” and 1.05 or more times “bad”.

(3) Conductivity when used as a coating (volume resistivity)
The conductive resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 12 were printed on a glass substrate in a 10 × 10 mm square pattern using a screen printing machine, and 1 at 150 ° C. in an air atmosphere. The volatile components were dried using a time firing furnace and the binder resin was cured to obtain a conductive coating film. The surface resistance of the coating film was measured with a Loresta resistance meter, and the volume resistivity was calculated from the film thickness of the conductive coating film obtained with a laser microscope. Volume resistivity is determined that there is conductivity of less than 1.0 × ^{10 -3} Ω · cm, and determine when more than 1.0 × ^{10 -3} Ω · cm and no conductive.

  As is clear from Tables 4 and 5, in Examples 1 to 10 in which the average particle size ratio, CV value, specific gravity, and mixing ratio of appropriate silver-coated particles were used, the printability, shape retention, and volume resistivity were improved. It was excellent. On the other hand, in Comparative Examples 1 and 2 in which only a single type of silver-coated particles was mixed, printability was deteriorated due to insufficient thixotropic property, and a sufficient volume due to voids generated in the coating film. The resistivity was not obtained. With respect to Comparative Examples 3 and 4 in which the CV value of the silver-coated particles was greater than 15%, the silver-coated particles in the coating film were not sufficiently filled and sufficient volume resistivity could not be obtained due to the formation of voids. It was. With respect to Comparative Example 5 in which the specific gravity of the silver-coated particles A was less than 2.0, the shape retention decreased due to the difference in the specific gravity balance with the other particles. Regarding Comparative Example 6 in which the specific gravity of the silver-coated particles B exceeded 6.3, the printability, shape retention, and volume resistivity were lowered due to the loss of the specific gravity balance with the other particles. Regarding Comparative Examples 7 and 8 in which the average particle size ratio of the silver-coated particles was out of the range of 1.2 to 5.0, the printability was deteriorated due to insufficient thixotropic property, and occurred in the coating film. A sufficient volume resistivity could not be obtained due to the voids.

  Regarding Comparative Examples 9 and 10 in which the mass ratio of the silver-coated particles A and B in the resin composition was outside the range of 0.5 to 3.0, a sufficient volume resistivity was obtained due to the voids generated in the coating film. It was not obtained. With respect to Comparative Example 11 in which the ratio of the total mass of silver-coated particles in the resin composition to the mass of the binder resin exceeded 8.0, sufficient volume resistivity was obtained due to insufficient contact between the silver-coated particles. It was not obtained. Regarding Comparative Example 12 in which the ratio of the total mass of the silver-coated particles in the resin composition to the mass of the binder resin was less than 3.0, the fluidity of the resin composition and the adhesiveness of the coating film were reduced due to insufficient binder content. However, sufficient printability, shape retention and volume resistivity were not obtained.

  The conductive resin composition of the present invention can be used for paste-like, film-like, and ink-like conductive adhesives, anisotropic or isotropic conductive films, and conductive spacers.

Claims (2)

Including two kinds of silver-coated particles A and silver-coated particles B having different average particle diameters as a conductive filler, and a binder resin C;
The coefficient of variation (CV _A ) of the particle diameter of the silver-coated particles A and the coefficient of variation (CV _B ) of the particle diameter of the silver-coated particles B are both 15% or less,
The specific gravity (d _A ) of the silver-coated particles A and the specific gravity (d _B ) of the silver-coated particles B are in the range of 2.0 to 6.0, respectively.
The ratio (D _A / D _B ) of the average particle size (D _A ) of the silver-coated particles _A and the average particle size (D _B ) of the silver-coated particles B is 1.2 to 5.0,
The ratio (W _A / W _B ) of the mass (W _A ) of the silver-coated particles _A and the mass (W _B ) of the silver-coated particles B is 0.5 to 3.0,
The ratio ((W _A + W _B ) / W _C ) of the total mass (W _A + W _B ) of the silver-coated particles A and the silver-coated particles B to the mass (W _C ) of the binder resin C is 3.0 to 8 Conductive resin composition which is 0.0.   A method for forming a conductive coating film by applying the conductive resin composition according to claim 1 to a substrate.