KR20110060884A

KR20110060884A - Method for forming metal coating film, and electrically conductive particle

Info

Publication number: KR20110060884A
Application number: KR1020117002980A
Authority: KR
Inventors: 히데카츠 쿠로다
Original assignee: 우베-니토 카세이 가부시키가이샤
Priority date: 2008-09-25
Filing date: 2009-09-18
Publication date: 2011-06-08
Also published as: TW201028498A; WO2010035708A1; JP5422563B2; TWI484066B; CN102124142A; JPWO2010035708A1; KR20160137589A; CN102124142B

Abstract

The metal film formation method is a method of forming a metal film on the surface of nonelectroconductive particle by electroless plating. Electroless plating is performed after the pretreatment of attaching the metal nuclei to the non-conductive particles, and at the same time, forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. Electroconductivity is provided to electroconductive particle by the metal film formed in the whole surface of nonelectroconductive particle. The metal film consists only of a silver film.

Description

METHOD FOR FORMING METAL COATING FILM, AND ELECTRICALLY CONDUCTIVE PARTICLE}

TECHNICAL FIELD This invention relates to the metal film formation method for forming a metal film in the electroconductive particle and nonelectroconductive particle which can be used, for example for a electrically conductive material, an electromagnetic wave shielding material, etc.

Electroless plating is known as a technique for forming a metal film on non-conductive particles. In order to promote the reaction of the electroless plating, pretreatment for attaching the catalyst initiating the electroless plating is performed on the surface of the non-conductive particles. In pretreatment, for example, the non-conductive particles are brought into contact with an aqueous solution of first tin chloride followed by contact with an aqueous palladium chloride solution. Then, the palladium colloid adsorb | sucks on the surface of a nonelectroconductive particle by the reduction effect of the tin ion adsorbed on the surface of a nonelectroconductive particle. Palladium colloids act as a catalyst to initiate electroless plating. The electroless plating bath contains metal salts, metal complexing agents, pH adjusting agents, reducing agents and the like.

However, there has been a problem that only an extremely non-uniform metal film can be obtained by electroless plating with the above-described pretreatment, and a continuous film is hardly formed. In Patent Document 1, the use of a metal plating powder having a homogeneous or strong coating power has been proposed. This metal plating powder can be obtained by a catalyzing step of supporting precious metal ions on the surface of the core material, and then by an electroless plating process of electroless plating on the core material. In the catalysis process, the noble metal ions are trapped in an organic or inorganic core, and the precious metal ions are reduced to carry the precious metal on the surface of the core. In electroless plating treatment, the electroless plating constituent liquid is divided into at least two or more liquids having different constituents, and then they are added separately or simultaneously.

On the other hand, substitution plating is known as a technique of forming a noble metal film in a nonelectroconductive particle (refer patent document 2 and 3). As a general substitution plating, there is a method of forming an electroless nickel plating as an underlayer and replacing the underlayer with a noble metal. In electroless nickel plating, sodium hypophosphite (monohydrate), citric acid, and the like are usually added to the plating liquid in order to properly adjust the pH of the plating liquid. In substitutional plating, cobalt is added to the plating liquid so as to have a concentration of several hundred ppm in order to control the crystal structure of the noble metal film. The metal film produced by substitution plating contains nickel which has higher electric resistance value than silver and gold, phosphorus, cobalt, etc. which are impurities.

Precious metals with high conductivity include gold and silver. Silver is more conductive and cheaper than gold. For this reason, the utilization value of the electroconductive particle which formed the metal film which consists of silver on the surface of a nonelectroconductive particle is high. However, when forming a silver film by substitution plating, it is necessary to form nickel plating as an underlayer. For this reason, the metal film is formed in at least two layers of the nickel layer and the silver layer. As described above, the metal film composed of a plurality of layers is disadvantageously costly because the amount of metal used increases or waste liquid treatment is required.

Therefore, it is conceivable to form a silver film by performing electroless plating after performing pretreatment using a coupling agent, for example to a nonelectroconductive particle. However, even if the above non-conductive particles were subjected to the above pretreatment, the silver film could not be formed from the micron-sized non-conductive particles or only a discontinuous film could be formed. As such, a technique of forming a silver film without the underlying plating on the micron-sized non-conductive particles is not practical yet. Further, there has been a problem that the smaller the particle diameter of the non-conductive particles, the more likely the aggregation of particles is likely to occur after the formation step or formation of the metal film.

[Patent Document 1] Japanese Patent Application Laid-Open No. 06-96771

[Patent Document 2] Japanese Laid-Open Patent Publication No. 2007-242307

[Patent Document 3] Japanese Laid-Open Patent Publication No. 2004-14409

The present inventor has invented a technique capable of forming a silver film without performing under plating on non-conductive particles having a micron size. An object of the present invention is to provide a metal film forming method capable of forming a silver film even if the particle size of the non-conductive particles is extremely small. Moreover, the objective of this invention is providing the electroconductive excellent particle | grains which are excellent in electroconductivity even if the particle diameter of a nonelectroconductive particle is extremely small.

In order to solve the said subject, according to the 1st Example of this invention, the metal film formation method which forms a metal film by electroless plating on the surface of nonelectroconductive particle is provided. Electroless plating is carried out after the pretreatment of attaching the metal nucleus to the surface of the non-conductive particles, and is carried out in the presence of a hydrophilic polymer having a pyrrolidone group to form a metal film made of silver.

In the above metal film forming method, it is preferable to prepare a dispersion liquid in which non-conductive particles are dispersed in an aqueous solution of a hydrophilic polymer having a pyrrolidone group, and then start electroless plating in the dispersion liquid.

In the above metal film forming method, the hydrophilic polymer having a pyrrolidone group preferably contains at least polyvinylpyrrolidone. In the above metal film forming method, it is preferable that electroless plating is performed by a silver diameter reaction.

In the above metal film forming method, the pretreatment is performed by contacting a non-conductive particle with a treatment liquid containing a silane coupling agent, a hydrolysis catalyst, and a metal salt, and then depositing a metal of the metal salt with a reducing agent. It is a process which attaches a nucleus, and it is preferable that a silane coupling agent has a functional group which forms a chelate with respect to the metal of a metal salt.

In the above metal film forming method, the metal of the metal core is preferably gold or silver.

In order to solve the said subject, according to the 2nd Example of this invention, the electroconductive particle provided with electroconductivity by the metal film formed in the whole surface of a nonelectroconductive particle is provided. The metal film consists only of a silver film.

In said electroconductive fine particles, it is preferable that only elements of gold and silver are detected as elements other than the element contained in a nonelectroconductive particle in the fluorescent X-ray analysis of electroconductive particle. In the conductive fine particles described above, it is preferable that the number of particles having an electric resistance value of 10 Ω or less after elapse of 240 hours in an environment of a temperature of 60 ° C. and a humidity of 90% RH is 80% or more.

In the conductive fine particles described above, the number of particles having the uncoated portion of the silver film is preferably 10% or less. In said electroconductive fine particles, it is preferable to be used as a sealant of a liquid crystal display element.

In said electroconductive fine particle, it is preferable to be used as an anisotropic conductive material.

In order to solve the said subject, according to the 3rd Example of this invention, the method of manufacturing electroconductive particle is provided by forming a metal film on the surface of nonelectroconductive particle by electroless plating. Electroless plating is carried out after the pretreatment of attaching the metal nucleus to the surface of the non-conductive particles, and simultaneously in the presence of a hydrophilic polymer having a pyrrolidone group to form a metal film made of silver.

In order to solve the said subject, according to the 4th Example of this invention, the electroconductive particle which can be obtained by forming a metal film on the surface of nonelectroconductive particle is provided. The metal coating is carried out after the pretreatment of attaching the metal nucleus to the surface of the non-conductive particles, and is formed by electroless plating to form a metal coating made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. In addition, a metal film consists only of a silver film.

According to the present invention, there is provided a metal film forming method which is easy to form a silver film even when the particle size of the non-conductive particles is extremely small. Further, according to the present invention, even when the particle diameter of the non-conductive particles is extremely small, excellent conductive particles and low-cost conductive particles are provided.

1 is a scanning electron micrograph showing silica particles used in Example 1. FIG.
2 is a scanning electron micrograph showing non-conductive particles subjected to pretreatment in Example 1. FIG.
3 is a scanning electron micrograph showing conductive particles of Example 1;
4 is a fluorescence X-ray analysis chart showing detection of silver with respect to the electroconductive particle of Example 1. FIG.
5 is a fluorescence X-ray analysis chart showing the detection of gold with respect to the electroconductive particle of Example 1. FIG.
6 is a scanning electron micrograph showing the conductive particles of Example 1 after the wet heat test.
7 is an optical micrograph showing the state in which the conductive particles of Example 1 are dispersed in a resin.
8 is a scanning electron micrograph showing conductive particles of Comparative Example 1. FIG.
9 is a scanning electron micrograph showing conductive particles of Comparative Example 2. FIG.
10 is an optical micrograph showing a state in which the conductive particles of Comparative Example 2 are dispersed in a resin.
11 is a scanning electron micrograph showing conductive particles of Comparative Example 3. FIG.
12 is a scanning electron micrograph showing the conductive particles of Comparative Example 3 after the wet heat test.

EMBODIMENT OF THE INVENTION Hereinafter, the Example which actualized this invention is described in detail. The metal film formation method of this embodiment is a method of forming a metal film by electroless plating on nonelectroconductive particle. Electroless plating is performed after the pretreatment of attaching the metal nucleus to the non-conductive particles, and simultaneously forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. First, nonelectroconductive particle is demonstrated.

The nonelectroconductive particle is comprised as a base material which forms a metal film. As a material of nonelectroconductive particle, at least 1 sort (s) chosen from silica, ceramics, glass, and resins is mentioned, for example. As silica, fully crystallized dry silica (cristobalite), water dispersion type silica (colloidal silica), etc. are mentioned, for example. Examples of the ceramics include alumina, sapphire, mullite, titania, silicon carbide, silicon nitride, aluminum nitride, zirconia, and the like. As glass, various shot glass, such as BK7, SF11, LaSFN9, optical crown glass, a soda glass, low-expansion borosilicate glass, etc. are mentioned, for example. Examples of the resins include silicone resins, phenol resins, natural modified phenol resins, epoxy resins, polyvinyl alcohol resins, cellulose resins, and the like, and modified substances such as polyolefin resins, styrene resins, acrylic resins, and coronas. The surface treatment goods by discharge etc. are mentioned. As nonelectroconductive particle, it is at least 1 sort (s) chosen from a silica, ceramics, and glass from a viewpoint that the dispersion | variation of a particle diameter is small, for example, More preferably, it is a silica. Examples of the shape of the non-conductive particles include spherical shape, bar shape, plate shape, needle shape, hollow shape, and the like. The shape of the non-conductive particles is preferably spherical in consideration of the water dispersibility of the non-conductive particles and the water dispersibility of the obtained conductive particles.

Although the particle diameter of a nonelectroconductive particle is not specifically limited, Preferably it is 0.5-100 micrometers, More preferably, it is 0.5-10 micrometers, More preferably, it is 1-5 micrometers. The particle diameter of the nonelectroconductive particle is measured in the photograph of a scanning electron microscope.

When using electroconductive particle especially for a member for liquid crystal display elements, it is necessary to adjust the particle diameter of electroconductive particle. Specifically, the particle size distribution of the non-conductive particles is preferably 10% or less, more preferably 5% or less, of the CV value required by the formula shown below.

CV value (%) = {[standard deviation of particle diameter (μm)] / [average particle diameter (μm)]} × 100

In the metal film formation method, pretreatment which makes a metal nucleus adhere to nonelectroconductive particle is performed. Next, this preprocessing is demonstrated.

In pretreatment, metal nuclei are attached to non-conductive particles. The metal nucleus serves to bring the metal film made of silver into close contact with the non-conductive particles. It is preferable that a metal core consists of gold or silver. The metal core made of gold or silver hardly adversely affects the conductivity of silver, which is a metal film, and can stably form a metal film.

As a pretreatment, for example, it is preferable to attach a metal nucleus by bringing a treatment liquid containing a silane coupling agent, a hydrolysis catalyst and a gold salt into contact with the nonconductive particles and then depositing metal ions with a reducing agent. Thereby, formation of the metal film by electroless plating advances uniformly.

The silane coupling agent has a hydrolysable functional group that generates a silanol group by hydrolysis. Examples of the hydrolyzable functional group include alkoxy (—OR) groups directly bonded to Si atoms. R constituting the alkoxy group is any linear, branched or cyclic alkyl group and preferably has 1 to 6 carbon atoms, specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n -Butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, cyclopentyl group, cyclohexyl group, etc. are mentioned.

The silane coupling agent used in the metal film formation method of this embodiment has a functional group which forms a chelate with respect to the metal of a metal salt. As a functional group which forms a chelate with respect to the metal of a metal salt, a polar group or a hydrophilic group is mentioned. It is preferable that it is a functional group which has at least 1 or more types of atom specifically, chosen from the atom of a nitrogen atom, a sulfur atom, and an oxygen atom. The functional group includes at least one functional group selected from the group consisting of -SH, -CN, -NH ₂ , -SO ₂ OH, -SOOH, -OPO (OH) ₂ and -COOH. The functional group may be a salt. When the functional group is an acid group such as -OH, -SH, -SO ₂ OH, -SOOH, -OPO (OH) ₂ , or -COOH, the salts include alkali metal salts such as sodium, potassium and lithium, or ammonium salts. have. On the other hand, in the case of a basic group such as -NH ₂ , inorganic salts such as hydrochloric acid, sulfuric acid and nitric acid, organic acid salts such as formic acid, acetic acid, propionic acid and trifluoroacetic acid are mentioned.

Specific examples of the silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, and N-2- (amino Ethyl) -3-aminopropyltriethoxysilane, and the like. 3-aminopropyltrimethoxysilane is particularly preferable in view of cost and ease of handling of the silane coupling agent.

The hydrolysis catalyst promotes hydrolysis of the hydrolyzable functional group of the silane coupling agent. Examples of the hydrolysis catalyst include organic anhydrides such as acetic anhydride, glacial acetic acid, propionic acid, citric acid, formic acid and oxalic acid, aluminum chelate compounds such as aluminum alkyl acetate, and inorganic alkaline compounds such as ammonia water. Among these hydrolyzable catalysts, ammonia water is preferred in consideration of the reactivity and cost for 3-aminopropyltrimethoxysilane, which is preferable as a silane coupling agent.

It is preferable that it is 0.5-5.0 mol, and, as for the usage-amount of the hydrolysis catalyst with respect to 1 mol of silane coupling agents, it is more preferable that it is 1.5-2.5 mol. Moreover, it is preferable that it is 0.005-0.05 mol, and, as for the usage-amount of the metal salt with respect to 1 mol of silane coupling agents, it is more preferable that it is 0.015-0.025 mol. Moreover, it is preferable that it is 0.025-0.25 mol, and, as for the usage-amount of the reducing agent with respect to 1 mol of metal salts, it is more preferable that it is 0.075-0.125 mol.

As a solvent or dispersion medium which comprises the processing liquid for pretreatment, water or an aqueous solvent is mentioned. An aqueous solvent is a mixed solvent of water and an organic solvent. As an organic solvent, lower alcohols, such as methanol, ethanol, a propanol, butanol, ketones, such as acetone, etc. are mentioned, for example. You may use these organic solvents individually or in combination of multiple types. Next, electroless plating will be described.

As electroless plating, the well-known electroless plating method using a metal salt, a reducing agent, etc. can be applied. Examples of the reducing agent include borohydrides such as sodium tetrahydroborate (alkali metal hydride borates such as sodium borohydride, ammonium hydride borates, etc.), hydrazine compounds, inorganic reducing agents such as hypochlorite, formaldehyde, Organic reducing agents, such as acetaldehyde, citric acid, sodium citrate, can be used. You may use these reducing agents individually or in combination of 2 or more types. The temperature conditions of the electroless plating, the reaction time are determined according to the conventional method of electroless plating. It is preferable that it is 0.025-0.25 mol, and, as for the usage-amount of the reducing agent with respect to 1 mol of metal salts, it is more preferable that it is 0.075-0.125 mol.

In electroless plating, it is preferable to use a silver diameter reaction from a viewpoint of being excellent in stability of reaction and reducing an impurity as much as possible. In other words, the substance involved in the silver mirror reaction is easily removed from the metal film by washing. For this reason, the metal film of extremely high purity can be formed. The silver ring reaction precipitates silver by reducing the ammine complex of silver with a reducing agent. Specifically, a reducing agent such as formalin is added to the aqueous ammonia solution of silver nitrate. Thereby, silver precipitates on the surface of a nonelectroconductive particle based on a metal nucleus.

Electroless plating forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. According to this film formation, a silver film can be continuously formed in the nonelectroconductive particle which performed the said preprocessing. Hydrophilic polymers having a pyrrolidone group include, for example, polyvinylpyrrolidone (PVP), poly (N-vinyl-2-pyrrolidone-g-citric acid), poly (N-vinyl-2-pyrrolidone) -co- itaconic acid), poly (N-vinyl-2-pyrrolidone-co-styrene), etc. are mentioned. You may use these hydrophilic polymers individually or in combination of multiple types.

Hydrophilic polymers having a pyrrolidone group have nitrogen atoms and oxygen atoms in their side chains. For this reason, the hydrophilic polymer which has a pyrrolidone group coordinates with the metal nucleus which adheres to nonelectroconductive particle, or silver which precipitates by electroless plating. The hydrophilic polymer coordinated in this way is supposed to increase the adhesion of the metal film to the non-conductive particles while uniformly advancing the film formation when silver precipitates around the metal nucleus to form the metal film. As a result, a high-adhesion and uniform metal film with nonelectroconductive particle is formed.

Regarding the hydrophilic polymer having a pyrrolidone group, polyvinyl alcohol (PVA), which is a kind of hydrophilic polymer, has an oxygen atom in the side chain. However, even if electroless plating is performed in the presence of polyvinyl alcohol, a continuous metal film is not formed on the surface of the non-conductive particles. From this, it is assumed that at least nitrogen atoms act on the formation of the continuous metal film. In addition, the presence of oxygen atoms and nitrogen atoms in the pyrrolidone skeleton is expected to act advantageously in the growth of the silver based on the metal nuclei adsorbed on the non-conductive particles and the formation of a continuous film.

The hydrophilic polymer having a pyrrolidone group preferably contains at least polyvinylpyrrolidone. In particular, it is assumed that polyvinylpyrrolidone which is a homopolymer is easier to coordinate with silver which precipitated than the copolymer which has a pyrrolidone group in a side chain. Therefore, the silver film is formed more stably. In particular, polyvinylpyrrolidone is assumed to be easy to coordinate with the metal nucleus in non-conductive particles with gold or silver attached as the metal nucleus. Therefore, the silver film is formed more stably.

The electroless plating of this embodiment is started in the dispersion after preparing a dispersion in which non-conductive particles are dispersed in an aqueous solution of a hydrophilic polymer having a pyrrolidone group. By dispersing the non-conductive particles in this manner, it is assumed that the hydrophilic polymer having a pyrrolidone group is uniformly and sufficiently coordinated with respect to the metal nucleus adsorbed on the non-conductive particles. That is, when electroless plating is started in the dispersion, the silver film is more stably formed because the hydrophilic polymer having a pyrrolidone group is fully functional. The dispersion medium in which the non-conductive particles are dispersed is an aqueous dispersion medium. The aqueous dispersion medium is water or a mixture of water and an organic solvent and serves as a solvent of a hydrophilic polymer having a pyrrolidone group. The organic solvent has compatibility with water. As an organic solvent, lower alcohols, such as methanol, ethanol, a propanol, butanol, ketones, such as acetone, etc. are mentioned, for example. You may use these organic solvents individually or in combination of multiple types.

After the start of the electroless plating, it is assumed that if the contact and dispersion between the non-conductive particles are repeated, it will be difficult to form a uniform metal film on the non-conductive particles. That is, the contact between the non-conductive particles may interfere with the uniform growth of the metal film or damage the metal film of the growth step, and may also cause the aggregation between the non-conductive particles. The viscosity of the dispersion is increased by a hydrophilic polymer having a pyrrolidone group. For this reason, the flow of nonelectroconductive fine particles is suppressed. Therefore, it is estimated that the frequency of collisions between the non-conductive fine particles is reduced, thereby making it difficult to prevent the uniform growth of the metal film in the dispersion. As a result, the metal film is formed uniformly. In addition, it is speculated that the molecular chain of the hydrophilic polymer having a pyrrolidone group becomes a three-dimensional obstacle when the non-conductive fine particles approach. Therefore, aggregation of non-conductive fine particles is suppressed.

Hydrophilic polymers having a pyrrolidone group are classified by the K value determined by the Pitcher method. For example, various kinds of polyvinylpyrrolidones having different K values are commercially available. K value is a value which becomes the reference | standard of the molecular weight of the hydrophilic polymer which has a pyrrolidone group. The lower the K value, the smaller the molecular weight of the hydrophilic polymer. In other words, the higher the K value, the higher the viscosity effect of the dispersion. In addition, the viscosity effect depends on the concentration of the hydrophilic polymer in the dispersion medium. That is, the higher the concentration of the hydrophilic polymer in the dispersion medium can improve the viscosity effect of the dispersion. In this embodiment, the K value and the concentration of the hydrophilic polymer having a pyrrolidone group are preferably K value of 30 to 120, or concentration of 0.5 to 10%, more preferably K value of 90 to 120, or The concentration is 2.0 to 5.0%. When the K value of the hydrophilic polymer is less than 30 or the concentration is less than 0.5%, there is a fear that the flow of the non-conductive fine particles may not be effectively suppressed. On the other hand, when the K value of the hydrophilic polymer is 120 or more and the concentration is 10% or more, the viscosity of the dispersion liquid becomes excessively high, and there is a fear that the precipitated silver becomes difficult to come into contact with the non-conductive particles. As a result, formation of a metal film may be delayed or silver particle may aggregate in a dispersion liquid.

The concentration (C) of the hydrophilic polymer having a pyrrolidone group in the dispersion is the concentration with respect to the aqueous dispersion medium, and is represented by the following formula.

Concentration (C) [%] = {[Hydrophilic Polymer (g)] / [Aqueous Dispersion Medium (mL)]} × 100

By such electroless plating, electroconductive particle which has a metal film in the whole surface of nonelectroconductive particle is formed. At this time, the hydrophilic polymer having a pyrrolidone group protects the surface of electroconductive particle by coordinating to a silver film. That is, the hydrophilic polymer having a pyrrolidone group alleviates the cohesion of silver constituting the metal film. Thereby, the electroconductive particle formed in the dispersion liquid becomes difficult to aggregate with each other.

Next, the obtained electroconductive particle is isolate | separated and wash | cleaned with a dispersion liquid, and then it can obtain the powder (electroconductive powder) of electroconductive particle by drying. Since aggregation of electroconductive powder is suppressed, the particle size distribution of electroconductive powder becomes narrow. It is preferable that it is 10% or less, and, as for CV value of electroconductive powder, it is more preferable that it is 5% or less. In addition, the method of stirring during electroless plating is not particularly limited, but, for example, in addition to the method of using stirring and dispersing means by a general stirring device such as a stirring blade, a magnetic stirrer, and the like, At the same time, a method using agitation and dispersion means by single ultrasonic irradiation can be used.

Next, the electroconductive particle which has a metal film formed by the said metal film formation method is demonstrated in detail.

Electroconductive particle is provided electroconductivity by the metal film formed in the whole surface of nonelectroconductive particle. The metal film consists only of a silver film. That is, electroconductive particle does not have the plating layer used as the base layer of a silver film.

The metal film consists of a collection of continuous silver fine particles. The metal film consists of a continuous film in which silver fine particles are densely arranged. The continuous aggregate of silver fine particles means the aggregate of silver fine particles arrange | positioned precisely to the level which cannot confirm a metal film which becomes discontinuous, when a metal film is observed with the magnification of 5000 times-10,000 times with a scanning microscope. It is preferable that the thickness of a metal film is 50 nm or more from a viewpoint of ensuring stable electroconductivity.

Impurities can be extremely reduced as electroconductive particle which has the said metal film. The purity of electroconductive particle can be confirmed here by fluorescent X-ray analysis. In the fluorescent X-ray analysis of the conductive particles, it is preferable that only gold and silver are detected as elements other than the elements contained in the non-conductive particles.

3 is an electron micrograph showing an example of conductive powder. It is confirmed in FIG. 3 that the continuous silver film has a petal shape. On the other hand, in the conventional electroconductive particle which formed the silver film, without using the hydrophilic polymer which has a pyrrolidone group, the uncoated part of the film has formed the crater shape. When the electroconductive particle of a present Example is electroconductive particle group, such as electroconductive powder, electroconductive particle dispersion liquid, etc., it is characterized by the extremely small even if there exists or does not exist the electroconductive particle which has an uncoated part of a silver film. In the case of an electroconductive particle group, the yield of the particle | grains which have an uncoated part of a silver film can be suppressed to 10% or less.

In addition, carbon is detected as the element other than an element contained in a nonelectroconductive particle by the said total organic carbon analysis method. In the conductive particles having the metal film, nitrogen is detected as an element other than the elements contained in the non-conductive particles by the Kjeldahl method. Carbon and nitrogen detected in electroconductive particle originate in the hydrophilic polymer which has a pyrrolidone group.

Electroconductive particle can be used suitably as various anisotropic conductive materials other than the sealant of a liquid crystal display element, for example. However, in recent years, miniaturization, high speed response, and the like are required for liquid crystal display panels. Therefore, the width | variety of the frame area in which the liquid crystal display panel seal part is arrange | positioned, the gap between an active matrix board | substrate and an opposing board | substrate, etc. are calculated | required. Therefore, in particular, the particle size of the electroconductive particle used for a liquid crystal display panel sealing part is calculated | required. The electroconductive particle of a present Example is 5 micrometers or less particle | grains, for example, and is especially applicable to a liquid crystal display panel seal part, and can respond to the said request | requirement.

Moreover, when using for the use as a sealant of a liquid crystal display element, an anisotropic conductive material, etc., the electroconductive particle of a present Example can exhibit stable electrical characteristics even in a high temperature, high humidity environment. Here, when the electroconductive particle of a present Example is electroconductive particle group, such as electroconductive powder, electroconductive particle dispersion, etc., 80% of the number ratio of the particle | grains whose electrical resistance value after 10 hours passes in the environment of the temperature of 60 degreeC, humidity 90% RH is 10 ohm or less. This can be done.

As mentioned above, according to this embodiment mentioned above, the following effects are exhibited.

(1) In the method for forming a metal film, electroless plating is performed after pretreatment of attaching a metal nucleus to non-conductive particles, and at the same time, a metal film made of silver is formed in the presence of a hydrophilic polymer having a pyrrolidone group. According to this method, even if it is a nonelectroconductive particle whose particle diameter is 5 micrometers or less, a silver film can be formed, without providing a plating layer as an underlayer.

Here, as the particle diameter of the non-conductive particles becomes smaller, the non-conductive particles tend to aggregate after the formation step of the metal film or the formation of the metal film. When the particle size of the nonelectroconductive particle is 5 μm or less, for example, the tendency of aggregation becomes remarkable, and when it is 3 μm or less, the tendency of aggregation becomes more significant. After formation of the metal film, although aggregated particles can be removed according to the classification, there is a fear of causing a decrease in productivity. Here, in the metal film forming method of the present embodiment, in order to form a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group, aggregation between the non-conductive fine particles is suppressed. As a result, the powder of electroconductive particle excellent in dispersibility can be obtained.

As described above, even when the particle size of the non-conductive particles is very small, there is provided a metal film forming method which is easy to form a silver film.

(2) In this embodiment, after preparing a dispersion liquid in which non-conductive particles are dispersed in an aqueous solution of a hydrophilic polymer having a pyrrolidone group, electroless plating is started in the dispersion liquid. Thereby, the metal film which consists of silver can be formed more stably.

(3) The hydrophilic polymer having a pyrrolidone group contains at least polyvinylpyrrolidone. Thereby, the metal film which consists of silver can be formed more stably.

(4) Electroless plating is performed by silver diameter reaction. Thereby, the impurity contained in electroconductive particle can be reduced as much as possible.

(5) As a pretreatment of electroless plating, it is preferable to contact a non-electroconductive particle with the processing liquid containing a silane coupling agent, a hydrolysis catalyst, and a metal salt, and to attach a metal nucleus by depositing the metal of a metal salt with a reducing agent. . Thereby, since a metal nucleus adheres more uniformly, the uniformity of a metal film can be improved further.

(6) The metal of the metal core is gold or silver. Thereby, it does not adversely affect the electroconductivity of the silver used as a metal film. Moreover, a metal film can be formed stably.

(7) The metal film of electroconductive particle consists only of a silver film. For this reason, the electroconductive particle excellent in electroconductivity can be provided. Moreover, it is cheaper than the metal film which consists only of a gold film.

(8) In the fluorescent X-ray analysis of electroconductive particle, only elements of gold and silver are detected as elements other than the element contained in a nonelectroconductive particle. In this case, the electroconductive particle which has a metal film with high purity can be provided. For this reason, the reliability about the electrical characteristic of electroconductive particle can be improved.

(9) The number of particles having an electrical resistance of 10 Ω or less after 240 hours in an environment of a temperature of 60 ° C. and a humidity of 90% RH with respect to the conductive particles is 80% or more. For this reason, the reliability of an electrical characteristic can be improved.

(10) The number of particles having an uncoated portion of the coated film is 10% or less. For this reason, the reliability of an electrical characteristic can be improved.

(11) Electroconductive particle is used suitably as a sealant or anisotropic conductive material of a liquid crystal display element, for example according to stable electrical conductivity and excellent electrical characteristic.

(12) As a method of forming a metal film on non-conductive particles, conventionally, substitution plating in which electroless nickel plating is formed as a base layer and the base plating layer is replaced with a metal has been generally performed. However, nickel has insufficient corrosion resistance under high temperature and high humidity conditions. The electroconductive particle of a present Example is comprised without using nickel plating as a base layer. For this reason, it is excellent in corrosion resistance on the conditions of high temperature and high humidity. By configuring the non-conductive particles in at least one selected from silica, ceramics and glass, the chemical stability of the non-conductive particles against heat or moisture can be improved, for example, than when the non-conductive particles are formed from a resin. Therefore, the practicality of electroconductive particle can be improved.

Further, the above embodiment may be modified as follows.

In the above example, after preparing a dispersion in which non-conductive particles were dispersed in an aqueous solution of a hydrophilic polymer having a pyrrolidone group, electroless plating was started in the dispersion. Alternatively, after starting electroless plating, for example, a hydrophilic polymer aqueous solution may be gradually added to the electroless plating solution to form a metal film.

The metal core to be attached in the pretreatment may be formed of a metal other than gold or silver. As metals other than gold or silver, noble metals, such as platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and iridium (Ir), are preferable.

The metal film may be formed by performing electroless plating in multiple steps. That is, the metal film may be composed of a multilayer film made of silver.

The particle diameter of the conductive particles is not particularly limited, but is preferably in the range of 0.5 to 5 µm.

Example

Next, the Example is described in more detail with reference to Examples and Comparative Examples.

Example 1

(A) pretreatment

Into a 500 mL Erlenmeyer flask, 10 g of silica particles (average particle size: 2.4 μm, CV value: 1.36%, the particle size of 70 particles was measured from a scanning electron micrograph) was added, and 65 mL of isopropyl alcohol (IPA) was added and sonicated for 10 minutes. It was. Next, 65 mL of methanol was added, the mixture was stirred for 10 minutes with a magnetic stirrer, 37 mL of 25% aqueous ammonia solution was added, and stirred for 60 minutes in an oil bath at 30 degrees (hereinafter, this solution was referred to as A liquid).

After adding 16 mL of methanol to 0.20 g of hydrochloric acid chloride (HAuCl ₄ · 4H ₂ O), the mixture was stirred with a magnetic stirrer for 10 minutes, and then 2.6 mL of 3-aminopropyl trimethoxysilane was added thereto, followed by further stirring for 10 minutes (this solution) Is called B liquid).

To 0.084 g of sodium tetrahydroborate (NaBH ₄ ), 50 mL of methanol was added, followed by stirring for 10 minutes with a magnetic stirrer (hereinafter, this solution was referred to as C liquid).

After adding B liquid to A liquid and stirring at 30 degreeC for 5 minutes, C liquid was dripped slowly, and the reaction system turned red. After C dropping, the oil bath was heated to 65 ° C and stirred for 3 hours. After stopping the stirring and performing methanol classification three times, filtration was carried out under reduced pressure to collect silica particles in which metal nuclei were formed, and dried in an oven at 80 ° C. for 24 hours. The powder of the obtained particle showed red color.

1 shows a scanning electron micrograph of silica particles. 2 shows a scanning electron micrograph of silica particles in which metal nuclei are formed. In Figure 2 it can be seen that the ultrafine gold particles are uniformly attached to the entire surface of the silica particles. The average particle diameter of 70 particle | grains was measured from the scanning electron micrograph, and the CV value which shows the spreading degree of particle size distribution was calculated | required. The results are shown in Table 1.

TABLE 1

(B) Formation of metal film (polyvinylpyrrolidone concentration (polyvinylpyrrolidone weight / water weight): 2.9% by weight)

475 mL of water was added to 10 g of the powder of particles obtained in the above "(A) pretreatment", followed by sonication for 10 minutes, and 28.65 g of silver nitrate was added, followed by stirring for 10 minutes with a magnetic stirrer. Thereafter, 28 g of polyvinylpyrrolidone (K-90) was added thereto, followed by further stirring for 60 minutes, followed by irradiation of ultrasonic waves for 15 minutes. Thereafter, 375 mL of a 25% aqueous ammonia solution was added, followed by 250 mL of an aqueous 3.57 mol / L formalin solution, followed by stirring for 10 minutes. The electroconductive particle was collect | recovered by the centrifugal separator, washed with distilled water, and dried in oven at 80 degreeC for 24 hours.

The scanning electron micrograph of electroconductive particle is shown in FIG. Referring to FIG. 3, it can be seen that a metal film is formed on the entire surface of the particle. The average particle diameter of 70 particle | grains was measured from the scanning electron micrograph, and CV value was calculated | required. The results are shown in Table 2.

TABLE 2

The thickness of the metal film was 0.14 μm. As a result of observing the number of particles having the uncovered portion in the crater shape in the micrograph shown in FIG. 3, the number of particles was 0/100.

Fluorescence X-ray Analysis

The electroconductive particle obtained in Example 1 was used for the fully automatic fluorescence X-ray spectrometer (the product of spectris, PW 2400 type, tube: Rh, measuring element: Na-U, irradiation area: 25 mm diameter). Qualitative analysis was performed. First, about 2 g of electroconductive particle was extract | collected, and it mounted uniformly on the 6 micrometer film made from polypropylene. Thereafter, the film was mounted on a fully automatic fluorescence X-ray analyzer to replace the measuring section with helium. The element was identified by scanning the wavelength range which can detect the fluorescent X-ray of the element of Na-U. As a result, the detected elements were two kinds of silver and gold. Elements other than silver and gold were not detected. Fluorescence X-ray analysis charts are shown in FIGS. 4 and 5.

The electrical resistance value of the 20 electroconductive particle of Example 1 was measured using the micro compression tester (made by Shimadzu Corporation), and the average was calculated | required. The results obtained are shown in Table 3 together with the standard deviation.

[Table 3]

The electrically conductive particles obtained in Example 1 were subjected to a wet heat test under conditions of 60 ° C., 90% RH, and 240 hours using a thermo-hygrostat (SPEC Co., Ltd. product). The scanning electron micrograph of electroconductive particle after a wet heat test is shown in FIG. As shown in Fig. 3 and Fig. 6, no change of state of the metal film was observed before and after the wet heat test.

The electric resistance value of 50 electroconductive particles was measured before and after a wet heat test, and the average of the number of electroconductive particles which can measure the electric resistance value, and the measured resistance value was calculated | required. The obtained results are shown in Table 4.

Table 4

In the electroconductive particle before and after a wet heat test, the difference of the electroconductive particle number which can measure an electrical resistance value was one. Moreover, the yield rate of the particle | grains whose electrical resistance value is 10 ohms or less was 86%. As a result, it turns out that the electroconductive particle obtained in Example 1 has sufficient moisture heat resistance.

Evaluation of Dispersibility in Resin

10 g of resin (brand name: STRUCT BOND) was stirred for 1 minute with a kneader. 0.2g of electroconductive particle of Example 1 was added to this resin, and it stirred for 1 minute. Resin which electroconductive particle was mix | blended was pressed to the slide glass, the cover glass was covered, and it observed with the optical microscope. An optical micrograph is shown in FIG.

As a result of optical microscopic observation, the number of particles to which two or more of the 317 particles were bonded was three (0.94%), and the dispersibility in the resin was considerably good.

(Comparative Example 1)

In Comparative Example 1, a metal film was formed without containing polyvinylpyrrolidone. In Comparative Example 1, first, 475 mL of water was added to 10 g of particles obtained in the same manner as in "(A) pretreatment" of Example 1, sonicated for 10 minutes, and 28.65 g of nitric acid was added thereto, followed by stirring for 10 minutes with a magnetic stirrer. Thereafter, 375 mL of 25% aqueous ammonia solution was added, followed by 250 mL of an aqueous 3.57 mol / L formalin solution, followed by stirring for 10 minutes. The precipitated silver layer coated silica particles were filtered under reduced pressure, washed with methanol, and dried in an oven at 80 ° C. for 24 hours.

The scanning electron micrograph of the electroconductive particle in which the metal film was formed is shown in FIG. As shown in FIG. 8, in the electroconductive particle of the comparative example 1, the metal film was not formed in a part of the surface. As a result of measuring the number of particles having an uncovered portion in the crater shape by the micrograph shown in FIG. 8, the number ratio of the particles was 53/100.

(Comparative Example 2)

In Comparative Example 2, polyvinylpyrrolidone was changed to polyvinyl alcohol. In Comparative Example 2, first, 475 mL of water was added to 10 g of particles obtained in the same manner as in "(A) pretreatment" of Example 1, sonicated for 10 minutes, and 28.65 g of nitric acid was added and stirred with a magnetic stirrer for 10 minutes. Thereafter, 28 g of polyvinyl alcohol (polymerization degree 400 to 600) was added and stirred for 60 minutes, followed by irradiation of ultrasonic waves for 15 minutes. Thereafter, 375 mL of a 25% aqueous ammonia solution was added, followed by 250 mL of an aqueous 3.57 mol / L formalin solution, followed by stirring for 10 minutes. The precipitated silver layer coated silica particles were collected, washed with distilled water, and dried in an oven at 80 ° C. for 24 hours.

The scanning electron micrograph of the electroconductive particle in which the metal film was formed is shown in FIG. As shown in FIG. 9, in the electroconductive particle of the comparative example 2, the metal film was not formed in the surface part. As a result of measuring the number of particles having an uncovered portion in the crater shape by the micrograph shown in FIG. 9, the number of particles was 33%.

Evaluation of Dispersibility in Resin

Evaluation of the dispersibility in resin of the electroconductive particle obtained by the comparative example 2 was performed similarly to the electroconductive particle of Example 1. The optical micrograph of the comparative example 2 is shown in FIG. As a result of the optical microscope observation shown in FIG. 10, eight or more adherent particles were observed and it was confirmed that dispersibility in resin is inferior to the electroconductive particle obtained in Example 1.

(Comparative Example 3)

In the comparative example 3, the powder of the electroconductive particle with substitution plating which forms electroless nickel plating as a base layer in the resin particle was prepared. The scanning electron micrograph of the electroconductive particle in which the metal film was formed is shown in FIG. As shown in FIG. 11, in the electroconductive particle of the comparative example 3, the metal film was not formed in a part of the surface. In the micrograph shown in FIG. 11, the number of particles having a crater-shaped uncoated portion was 57/100, and the number of particles was 57%.

Moist heat resistance evaluation similar to Example 1 was performed about the electroconductive particle obtained by the comparative example 3. The scanning electron micrograph after a wet heat test is shown in FIG. As shown in Figures 11 and 12, a change in the metal coating can be found after the wet heat test. As a result, in the electroconductive particle of the comparative example 3, corrosion | corrosion arises by oxidation of nickel, and it can be considered that the metal film which consists of gold peeled from the surface of a particle | grain.

The electrical resistance value of 50 electroconductive particles before and after a wet heat test was measured, and the average of the number of electroconductive particles which can measure the electrical resistance value, and the resistance value was calculated | required. The obtained results are shown in Table 5.

TABLE 5

The difference in the number of electroconductive particles which can measure an electrical resistance value in the electroconductive particle before and after a wet heat test is 39, The expression rate after a wet heat test is only 10% (5/50 piece), and the particle whose electrical resistance value is 10 ohm or less The yield of was 6%. As a result, it was confirmed that the electroconductive particle obtained by the comparative example 3 is inferior to moist heat resistance.

(Comparative Example 4)

Polyvinylpyrrolidone in Comparative Example 1 was changed to polyethylene glycol (molecular weight about 20,000). In Comparative Example 4, first, 475 mL of water was added to 10 g of particles obtained in the same manner as in "(A) pretreatment" of Example 1, sonicated for 10 minutes, and 28.65 g of nitric acid was added and stirred with a magnetic stirrer for 10 minutes. Thereafter, 28 g of polyethylene glycol was added thereto, followed by further stirring for 60 minutes, followed by irradiation of ultrasonic waves for 15 minutes. Thereafter, 375 mL of a 25% aqueous ammonia solution was added, followed by 250 mL of an aqueous 3.57 mol / L formalin solution, followed by stirring for 10 minutes. The precipitated silver layer coated silica particles were collected, washed with distilled water, and dried in an oven at 80 ° C. for 24 hours.

As a result of observing the electroconductive particle in which the metal film was formed with the scanning electron micrograph, the metal film was not formed in one part of the surface. As a result of measuring the number of particles having the uncovered portion of crater shape in the micrograph, the number of particles was 36/100 and the number of particles was 36%.

Evaluation of Dispersibility in Resin

Evaluation of the dispersibility in resin of the electroconductive particle obtained by the comparative example 4 was performed similarly to the electroconductive particle of Example 1. As a result of optical microscope observation, 8 or more adherent particles were observed and it was confirmed that dispersibility in resin is inferior to the electroconductive particle obtained in Example 1.

Claims

In the metal film formation method which forms a metal film by electroless plating on the surface of a nonelectroconductive particle,
The electroless plating is
After the pretreatment for attaching the metal nucleus to the surface of the non-conductive particles,
The metal film formation method characterized by forming the said metal film which consists of silver in presence of the hydrophilic polymer which has a pyrrolidone group.

The method for forming a metal film according to claim 1, wherein after preparing a dispersion in which the non-conductive particles are dispersed in an aqueous solution of a hydrophilic polymer having a pyrrolidone group, electroless plating is started from the dispersion.

The method of forming a metal film according to claim 1 or 2, wherein the hydrophilic polymer having a pyrrolidone group contains at least polyvinylpyrrolidone.

The method of any one of claims 1 to 3, wherein the electroless plating is performed by a silver diameter reaction.

The pretreatment according to any one of claims 1 to 4, wherein the pretreatment comprises contacting the non-conductive particles with a treatment liquid containing a silane coupling agent, a hydrolysis catalyst and a metal salt, to thereby precipitate the metal of the metal salt with a reducing agent. It is a process which makes a metal nucleus adhere to the surface of the said nonelectroconductive particle,
The said silane coupling agent has a functional group which forms a chelate with respect to the metal of the said metal salt, The metal film formation method characterized by the above-mentioned.

The metal film forming method according to any one of claims 1 to 5, wherein the metal of the metal core is gold or silver.

It is electroconductive particle provided electroconductivity by the metal film formed in the whole surface of a nonelectroconductive particle,
The said metal film consists of only a silver film, Electroconductive particle characterized by the above-mentioned.

The electroconductive particle of Claim 7 detected only the elements of gold and silver as elements other than the element contained in the said nonelectroconductive particle by the fluorescent X-ray analysis of the said electroconductive particle.

The electroconductive particle of Claim 7 or 8 whose yield of the particle | grains whose electrical resistance value is 10 ohms or less after 240 hours in the environment of temperature 60 degreeC, humidity 90% RH is 80% or more.

The electroconductive particle of any one of Claims 7-9 whose yields of the particle | grains which have an uncoated part of the said silver film are 10% or less.

The electroconductive particle of any one of Claims 7-10 used as a sealant of a liquid crystal display element.

The electroconductive particle of any one of Claims 7-11 used as an anisotropic conductive material.

In the method of manufacturing the electroconductive particle which formed the metal film by the electroless plating on the surface of a nonelectroconductive particle,
The electroless plating is
After the pretreatment for attaching the metal nucleus to the surface of the non-conductive particles,
A method for producing conductive particles, wherein the metal film made of silver is formed in the presence of a hydrophilic polymer having a pyrrolidone group.

It is electroconductive particle which can be obtained by forming a metal film on the surface of a nonelectroconductive particle,
The metal film is formed by electroless plating which is carried out after the pretreatment of attaching the metal nucleus to the surface of the non-conductive particles and simultaneously forms the metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group,
The said metal film consists of only a silver film, Electroconductive particle characterized by the above-mentioned.