JPWO2010035708A1 - Metal film forming method and conductive particles - Google Patents

Abstract

The metal film forming method is a method of forming a metal film on the surface of non-conductive particles by electroless plating. The electroless plating is performed after a pretreatment for attaching metal nuclei to non-conductive particles and forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. Conductivity is imparted to the conductive particles by a metal film formed on the entire surface of the non-conductive particles. The metal film consists only of a silver film.

Description

  The present invention relates to a conductive film that can be used for, for example, a conductive material, an electromagnetic shielding material, and the like, and a metal film forming method for forming a metal film on non-conductive particles.

  Electroless plating is known as a technique for forming a metal film on non-conductive particles. In order to accelerate the electroless plating reaction, a pretreatment for depositing a catalyst for starting the electroless plating is performed on the surface of the non-conductive particles. In the pretreatment, for example, non-conductive particles are brought into contact with an aqueous solution of stannous chloride and then brought into contact with an aqueous solution of palladium chloride. Then, the palladium colloid is adsorbed on the surface of the nonconductive particles by the reducing action of the tin ions adsorbed on the surface of the nonconductive particles. The palladium colloid acts as a catalyst that initiates electroless plating. The electroless plating bath contains a metal salt, a metal complexing agent, a pH adjusting agent, a reducing agent and the like.

  By the way, in the electroless plating accompanied by the pretreatment described above, there is a problem that only a very non-uniform metal film can be obtained and it is difficult to form a continuous film. Therefore, Patent Document 1 proposes the use of a metal plating powder having a uniform and strong covering power. This metal plating powder is obtained by a catalytic step for supporting noble metal ions on the surface of the core material, and then an electroless plating treatment for electroless plating on the core material. In the catalyzing step, after the noble metal ions are captured by the organic or inorganic core material, the noble metal ions are reduced and supported on the surface of the core material. In the electroless plating treatment, the electroless plating constituent liquid is divided into at least two liquids having different components, and then they are added separately and simultaneously.

  On the other hand, displacement plating is known as a technique for forming a noble metal film on non-conductive particles (see Patent Documents 2 and 3). As a general replacement plating, there is a method in which electroless nickel plating is formed as a base layer, and the base layer is replaced with a noble metal. In electroless nickel plating, sodium hypophosphite monohydrate, citric acid and the like are usually added to the plating solution in order to properly adjust the pH of the plating solution. In displacement plating, cobalt is added to the plating solution to a concentration of several hundred ppm in order to control the crystal structure of the noble metal film. The metal film produced by displacement plating includes nickel having a higher electrical resistance value than silver and gold, phosphorus, cobalt, and the like as impurities.

  Examples of the noble metal having high conductivity include gold and silver. Silver has a higher conductivity and is cheaper than gold. For this reason, the utility value of the electroconductive particle which formed the metal membrane | film | coat which consists of silver on the surface of a nonelectroconductive particle is high. However, when a silver film is formed by displacement plating, it is necessary to form nickel plating as an underlayer. For this reason, the metal film is formed of at least two layers of a nickel layer and a silver layer. As described above, the metal film composed of a plurality of layers is disadvantageous in terms of cost because the amount of metal used increases or the treatment of waste liquid is required.

  Therefore, it is conceivable to form a silver film by performing electroless plating on the non-conductive particles after, for example, pretreatment using a coupling agent. However, even if the non-conductive particles are subjected to the above-described pretreatment, the non-conductive particles of micron size cannot form a silver film or only a discontinuous film. Thus, a technique for forming a silver film on a micron-sized non-conductive particle without a base plating is not yet practical. Moreover, there is a problem that the smaller the particle size of the non-conductive particles, the more easily the particles are aggregated during or after the formation of the metal film.

Japanese Patent Publication No. 6-96771 JP 2007-242307 A JP 2004-14409 A

  The present inventor has found a technique capable of forming a silver film on a micron-sized non-conductive particle without applying a base plating. An object of the present invention is to provide a metal film forming method capable of forming a silver film even when the particle size of non-conductive particles is extremely small. Another object of the present invention is to provide conductive particles having excellent conductivity and low cost even if the particle size of the non-conductive particles is extremely small.

  In order to solve the above problems, according to a first aspect of the present invention, there is provided a metal film forming method for forming a metal film on the surface of non-conductive particles by electroless plating. The electroless plating is performed after a pretreatment for attaching metal nuclei to the surface of non-conductive particles, and forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group.

  In the above metal film forming method, it is preferable to prepare a dispersion 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.

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

  In the above metal film forming method, the pretreatment is such that the treatment liquid containing the silane coupling agent, the hydrolysis catalyst and the metal salt is brought into contact with the non-conductive particles, and then the metal of the metal salt is precipitated by the reducing agent. Therefore, it is preferable that the silane coupling agent has a functional group that forms a chelate with respect to the metal of the 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 above problems, according to the second aspect of the present invention, there are provided conductive particles imparted with conductivity by a metal film formed on the entire surface of the non-conductive particles. The metal film consists only of a silver film.

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

In the conductive fine particles described above, the number ratio of particles having an uncoated portion of a silver film is preferably 10% or less.
The conductive fine particles are preferably used as a sealing agent for liquid crystal display elements.

The conductive fine particles are preferably used as an anisotropic conductive material.
In order to solve the above problems, according to a third aspect of the present invention, there is provided a method for producing conductive particles formed by forming a metal film on the surface of nonconductive particles by electroless plating. The electroless plating is performed after a pretreatment for attaching metal nuclei to the surface of non-conductive particles, and forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group.

  In order to solve the above problems, according to a fourth aspect of the present invention, there are provided conductive particles obtained by forming a metal film on the surface of non-conductive particles. The metal film is formed by electroless plating that is performed after pretreatment to attach metal nuclei to the surface of non-conductive particles and forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. Is done. The metal film consists only of a silver film.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the particle size of a nonelectroconductive particle is very small, the metal film formation method which is easy to form a silver film is provided. In addition, according to the present invention, even when the particle size of the non-conductive particles is extremely small, it is possible to provide conductive particles that easily exhibit excellent conductivity and are low in cost.

2 is a scanning electron micrograph showing silica particles used in Example 1. FIG. The scanning electron micrograph which shows the nonelectroconductive particle which performed the pre-processing in Example 1. FIG. 2 is a scanning electron micrograph showing conductive particles of Example 1. FIG. 2 is a chart of fluorescent X-ray analysis showing detection of silver for the conductive particles of Example 1. FIG. The chart of the fluorescent X ray analysis which shows the detection of gold | metal | money about the electroconductive particle of Example 1. FIG. The scanning electron micrograph which shows the electroconductive particle of Example 1 after a wet heat test. The optical microscope photograph which shows the dispersion state in resin about the electroconductive particle of Example 1. FIG. 4 is a scanning electron micrograph showing conductive particles of Comparative Example 1. 6 is a scanning electron micrograph showing conductive particles of Comparative Example 2. The optical micrograph which shows the dispersion state in resin about the electroconductive particle of the comparative example 2. FIG. 6 is a scanning electron micrograph showing conductive particles of Comparative Example 3. The scanning electron micrograph which shows the electroconductive particle of the comparative example 3 after a wet heat test.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail.
The metal film forming method of this embodiment is a method of forming a metal film on non-conductive particles by electroless plating. The electroless plating is performed after a pretreatment for attaching metal nuclei to non-conductive particles, and forms a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. First, the nonconductive particles will be described.

<Non-conductive particles>
The non-conductive particles are configured as a base material that forms a metal film. Examples of the material of the nonconductive particles include at least one selected from silica, ceramics, glass, and resins. Examples of silica include completely crystallized dry silica (cristobalite) and water-dispersed silica (colloidal silica). Examples of ceramics include alumina, sapphire, mullite, titania, silicon carbide, silicon nitride, aluminum nitride, zirconia, and the like. Examples of the glass include various shot glasses such as BK7, SF11, and LaSFN9, optical crown glass, soda glass, low expansion borosilicate glass, and the like. Examples of the resins include silicone resins, phenol resins, naturally-modified phenol resins, epoxy resins, polyvinyl alcohol resins, cellulose resins, polyolefin resins, styrene resins, acrylic resins, and other modified products or corona discharge. And the like. The non-conductive particles are preferably at least one selected from silica, ceramics, and glass, more preferably silica, from the viewpoint of small variation in particle size. Examples of the shape of the non-conductive particles include a spherical shape, a rod shape, a plate shape, a needle shape, and a hollow shape. The shape of the non-conductive particles is preferably spherical considering the dispersibility of the non-conductive particles or the dispersibility of the obtained conductive particles.

  The particle size of the non-conductive particles is not particularly limited, but is preferably 0.5 to 100 μm, more preferably 0.5 to 10 μm, and still more preferably 1 to 5 μm. The particle size of the non-conductive particles is measured from a photograph of a scanning electron microscope.

  In particular, when using conductive particles for a liquid crystal display element member, it is necessary to make the particle diameters of the conductive particles uniform. Specifically, in the particle size distribution of the non-conductive particles, the CV value obtained by the following formula is preferably 10% or less, and more preferably 5% or less.

CV value (%) = {[standard deviation of particle diameter (μm)] / [average particle diameter (μm)]} × 100
In the metal film forming method, pretreatment for attaching metal nuclei to non-conductive particles is performed. Next, this preprocessing will be described.

<Pretreatment>
In the pretreatment, metal nuclei are attached to the non-conductive particles. The metal nucleus acts so that the metal film made of silver adheres to the non-conductive particles. The metal core is preferably made of gold or silver. A metal nucleus made of gold or silver hardly forms an adverse effect on the conductivity of silver that becomes a metal film, and can form a metal film stably.

  As the pretreatment, for example, after a treatment liquid containing a silane coupling agent, a hydrolysis catalyst, and a gold salt is brought into contact with non-conductive particles, a metal nucleus is deposited by depositing metal ions with a reducing agent. Is preferred. Thereby, formation of the metal film by electroless plating proceeds uniformly.

  The silane coupling agent has a hydrolyzable functional group that generates a silanol group by hydrolysis. Examples of the hydrolyzable functional group include an alkoxy (—OR) group directly bonded to a Si atom. R constituting the alkoxy group is preferably a linear, branched or cyclic alkyl group having 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 and the like can be mentioned.

The silane coupling agent used in the metal film forming method of the present embodiment has a functional group that forms a chelate with respect to the metal of the metal salt. Examples of the functional group that forms a chelate with respect to the metal of the metal salt include a polar group and a hydrophilic group. Specifically, a functional group having at least one atom selected from nitrogen atom, sulfur atom and oxygen atom is preferable. Examples of the functional group include 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 form a salt. When the functional group is an acidic group such as —OH, —SH, —SO ₂ OH, —SOOH, —OPO (OH) ₂ , —COOH, the salt includes alkali metal salts such as sodium, potassium, and lithium, Or ammonium salt etc. are mentioned. On the other hand, when it is a basic group such as —NH ₂ , examples of the salt include inorganic acid salts such as hydrochloric acid, sulfuric acid and nitric acid, and organic acid salts such as formic acid, acetic acid, propionic acid and trifluoroacetic acid.

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

  The hydrolysis catalyst promotes hydrolysis of the hydrolyzable functional group of the silane coupling agent. Examples of the hydrolysis catalyst include organic acids 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 aqueous ammonia. it can. Among these hydrolyzable catalysts, ammonia water is preferable in consideration of reactivity with 3-aminopropyltrimethoxysilane which is preferable as a silane coupling agent and cost.

  The amount of the hydrolysis catalyst used relative to 1 mol of the silane coupling agent is preferably 0.5 to 5.0 mol, and more preferably 1.5 to 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. Furthermore, 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.

  Examples of the solvent or dispersion medium constituting the treatment liquid for pretreatment include water and an aqueous solvent. The aqueous solvent is a mixed solvent of water and an organic solvent. Examples of the organic solvent include lower alcohols such as methanol, ethanol, propanol and butanol, and ketones such as acetone. These organic solvents may be used alone or in combination of two or more. Next, electroless plating will be described.

<Electroless plating>
As the electroless plating, a known electroless plating method using a metal salt, a reducing agent, or the like can be applied. Examples of the reducing agent include borohydrides such as sodium tetrahydroborate (alkali metal borohydrides such as sodium borohydride, ammonium borohydrides), hydrazine compounds, hypochlorite, and the like. An inorganic reducing agent such as an acid salt or an organic reducing agent such as formaldehyde, acetaldehyde, citric acid, or sodium citrate can be used. These reducing agents may be used alone or in combination of two or more. The temperature conditions and reaction time of electroless plating are set according to the conventional method of electroless plating. The amount of the reducing agent used relative to 1 mol of the metal salt is preferably 0.025 to 0.25 mol, and more preferably 0.075 to 0.125 mol.

  As the electroless plating, it is preferable to use a silver mirror reaction from the viewpoint of excellent reaction stability and reducing impurities as much as possible. That is, the substance involved in the silver mirror reaction is easily removed from the metal film by washing. For this reason, an extremely high-purity metal film can be formed. In the silver mirror reaction, silver is precipitated by reducing a silver ammine complex with a reducing agent. Specifically, a reducing agent such as formalin is added to an aqueous ammonia solution of silver nitrate. Thereby, silver is deposited on the surface of the non-conductive particles based on the 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 on the nonconductive particles subjected to the pretreatment. Examples of hydrophilic polymers having a pyrrolidone group include polyvinylpyrrolidone (PVP), poly (N-vinyl-2-pyrrolidone-g-citric acid), and poly (N-vinyl-2-pyrrolidone-co-itaconic acid). And poly (N-vinyl-2-pyrrolidone-co-styrene). These hydrophilic polymers may be used alone or in combination of two or more.

  The hydrophilic polymer having a pyrrolidone group has a nitrogen atom and an oxygen atom in its side chain. For this reason, the hydrophilic polymer having a pyrrolidone group is coordinated to a metal nucleus adhering to the non-conductive particles or silver deposited by electroless plating. The hydrophilic polymer coordinated in this way allows the formation of a metal film uniformly when silver deposits around the metal core to form a film, and the adhesion of the metal film to non-conductive particles. It is presumed to increase the nature. As a result, a highly uniform and uniform metal film is formed with non-conductive particles.

  In contrast to a 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 nonconductive particles. From this, it is presumed that at least nitrogen atoms act on the formation of a continuous metal film. Further, it is presumed that the presence of oxygen atoms and nitrogen atoms as a pyrrolidone skeleton has an advantageous effect in the growth of silver based on metal nuclei adsorbed on 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 presumed that polyvinylpyrrolidone, which is a homopolymer, is more easily coordinated with precipitated silver than a copolymer having a pyrrolidone group in the side chain. Thereby, the silver film is more stably formed. In particular, it is presumed that polyvinylpyrrolidone is easily coordinated to the metal nucleus in the non-conductive particles having gold or silver attached as the metal nucleus. Therefore, the silver film is more stably formed.

  The electroless plating of this embodiment is started in a 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 way, it is presumed that the hydrophilic polymer having a pyrrolidone group is uniformly and sufficiently coordinated with the metal nucleus adsorbed on the non-conductive particles. That is, when electroless plating is started in the dispersion, a hydrophilic polymer having a pyrrolidone group acts sufficiently, so that a silver film is more stably formed. The dispersion medium for dispersing the non-conductive particles is an aqueous dispersion medium. The aqueous dispersion medium is water or a mixed liquid of water and an organic solvent, and also serves as a solvent for a hydrophilic polymer having a pyrrolidone group. The organic solvent has compatibility with water. Examples of the organic solvent include lower alcohols such as methanol, ethanol, propanol and butanol, and ketones such as acetone. These organic solvents may be used alone or in combination of two or more.

  If contact and dispersion of nonconductive particles are repeated after the start of electroless plating, it is presumed that a uniform metal film is hardly formed on the nonconductive particles. That is, the contact between the nonconductive particles may hinder the uniform growth of the metal film or damage the metal film at the growth stage, and may also cause the nonconductive particles to aggregate. In this respect, the viscosity of the dispersion is increased by a hydrophilic polymer having a pyrrolidone group. For this reason, the flow of non-conductive fine particles is suppressed. Thereby, the collision frequency of nonelectroconductive fine particles is reduced. Therefore, it is presumed that uniform growth of the metal film in the dispersion is less likely to be hindered. As a result, a metal film is uniformly formed. Further, even when non-conductive fine particles approach each other, it is presumed that the molecular chain of the hydrophilic polymer having a pyrrolidone group becomes a steric hindrance. Thereby, aggregation of nonelectroconductive fine particles is suppressed.

  Hydrophilic polymers having a pyrrolidone group are classified according to the K value determined by the Fikencher method. For example, multiple types of polyvinylpyrrolidone having different K values are commercially available. The K value is a value serving as a reference for the molecular weight of a hydrophilic polymer having a pyrrolidone group. A lower K value means a smaller molecular weight of the hydrophilic polymer. That is, it means that the higher the K value, the higher the thickening effect of the dispersion. Further, the thickening effect also 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, the higher the thickening effect of the dispersion. In the present embodiment, the K value and the concentration of the hydrophilic polymer having a pyrrolidone group are preferably 30 to 120 and a concentration of 0.5 to 10%, more preferably 90 to 90%. -120, and the concentration is 2.0-5.0%. When the K value of the hydrophilic polymer is less than 30 and the concentration is less than 0.5%, the flow of the nonconductive fine particles may not be effectively suppressed. On the other hand, when the K value of the hydrophilic polymer exceeds 120 and the concentration exceeds 10%, the viscosity of the dispersion is excessively increased, so that the precipitated silver may not easily come into contact with the non-conductive particles. As a result, the formation of the metal film may be delayed or the silver particles may aggregate in the dispersion.

The concentration (C) of the hydrophilic polymer having a pyrrolidone group in the dispersion is represented by the following formula as the concentration with respect to the aqueous dispersion medium.
Concentration (C) [%] = {[Hydrophilic polymer (g)] / [Aqueous dispersion medium (ml)]} × 100
By such electroless plating, conductive particles having a metal film on the entire surface of the nonconductive particles are formed. At this time, the hydrophilic polymer having a pyrrolidone group protects the surface of the conductive particles by coordinating with the silver film. That is, the hydrophilic polymer having a pyrrolidone group relaxes the cohesive force of silver constituting the metal film. Thereby, the electroconductive particle formed in the dispersion liquid becomes difficult to aggregate each other.

  Next, the obtained conductive particles are separated from the dispersion, washed, and then dried to obtain conductive particle powder (conductive powder). Since the aggregation of the conductive powder is suppressed, the particle size distribution of the conductive powder is narrow. The CV value in the conductive powder is preferably 10% or less, and more preferably 5% or less. Further, the stirring method in the electroless plating is not particularly limited, for example, stirring by a general stirring device such as a stirring blade, a magnetic stirrer, etc., in addition to the dispersing means, simultaneously with stirring by the stirring device, Alternatively, stirring by ultrasonic irradiation alone, a method using a dispersing means, and the like can be mentioned.

<Conductive particles>
Next, the conductive particles having a metal film formed by the above metal film forming method will be described in detail.

  The conductive particles are given conductivity by a metal film formed on the entire surface of the non-conductive particles. The metal film consists only of a silver film. That is, the conductive particles do not have a plating layer that serves as an underlayer for the silver film.

  The metal film is composed of an aggregate of continuous silver fine particles. The metal film is composed of a continuous film in which silver fine particles are densely arranged. An aggregate of continuous silver fine particles refers to an aggregate of silver fine particles that are densely arranged to such a level that a discontinuous metal film cannot be confirmed when the metal film is observed at a magnification of 5000 to 10,000 times with a scanning microscope. It means the body. The thickness of the metal film is preferably 50 nm or more from the viewpoint of exhibiting stable conductivity.

  In the conductive particles having the metal film, impurities can be extremely reduced. In this regard, the purity of the conductive particles can be confirmed 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 nonconductive particles.

  FIG. 3 is an electron micrograph showing an example of the conductive powder. From FIG. 3, it is confirmed that the continuous silver film has a petal shape. On the other hand, in conventional conductive particles in which a silver film is formed without using a hydrophilic polymer having a pyrrolidone group, the uncoated portion of the film forms a crater shape. When the conductive particles of the present embodiment are a conductive particle group such as a conductive powder, a conductive particle dispersion, or the like, there are no conductive particles having an uncoated portion of the silver film, or It is characterized by very little, if any. In the case of the conductive particle group, the number ratio of particles having an uncoated portion of the silver film can be suppressed to 10% or less.

  Furthermore, in the conductive particles, carbon is detected as an element other than the elements contained in the nonconductive particles in the total organic carbon analysis. In the conductive particles having the metal film, nitrogen is detected as an element other than the elements contained in the nonconductive particles in the Kjeldahl method. Carbon and nitrogen detected in the conductive particles are derived from a hydrophilic polymer having a pyrrolidone group.

The conductive particles can be suitably used, for example, as various anisotropic conductive materials in addition to a sealing agent for liquid crystal display elements.
Incidentally, in recent years, liquid crystal display panels have been required to be small in size and fast in response. Therefore, it is desired to reduce the width of the frame region where the seal portion of the liquid crystal display panel is arranged, and to narrow the gap between the active matrix substrate and the counter substrate. Therefore, in particular, it is required to reduce the particle size of the conductive particles used for the seal portion of the liquid crystal display panel. In this regard, the conductive particles of the present embodiment can meet the above-described demands by being applied to, for example, a seal portion of a liquid crystal display panel as particles of 5 μm or less, for example.

  In addition, the conductive particles of this embodiment can exhibit stable electrical characteristics even in a high-temperature and high-humidity environment when used as a sealing agent for liquid crystal display elements, anisotropic conductive materials, and the like. In this regard, in the conductive particles of the present embodiment, 240 hours have passed in an environment of a temperature of 60 ° C. and a humidity of 90% RH when the conductive particles are a conductive powder, a conductive particle dispersion, or the like. The number ratio of particles having a subsequent electrical resistance value of 10Ω or less can be 80% or more.

As mentioned above, according to this embodiment explained in full detail, the following effects are exhibited.
(1) The electroless plating in the metal film forming method is performed after a pretreatment for attaching metal nuclei to non-conductive particles, and a metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. Form. According to this method, for example, a silver film can be formed without providing a plating layer as an underlayer even for non-conductive particles having a particle size of 5 μm or less.

  Here, the smaller the particle size of the non-conductive particles, the more easily the non-conductive particles are aggregated after the metal film is formed or after the metal film is formed. For example, when the particle size of the non-conductive particles is 5 μm or less, the tendency of aggregation is remarkable, and when the particle size is 3 μm or less, the tendency of aggregation is further remarkable. Although the aggregated particles can be removed by classification after the formation of the metal film, there is a possibility that productivity may be reduced. In this respect, in the metal film forming method of the present embodiment, since a metal film made of silver is formed in the presence of a hydrophilic polymer having a pyrrolidone group, aggregation of non-conductive fine particles is suppressed. As a result, a powder of conductive particles having excellent dispersibility can be obtained.

As described above, a method for forming a metal film that can easily form a silver film even when the particle size of the non-conductive particles is extremely small is provided.
(2) In this embodiment, after preparing a dispersion 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. 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 a silver mirror reaction. Thereby, impurities contained in the conductive particles can be reduced as much as possible.

  (5) In the pretreatment of electroless plating, after the treatment liquid containing the silane coupling agent, the hydrolysis catalyst and the metal salt is brought into contact with the non-conductive particles, the metal of the metal salt is precipitated by the reducing agent. It is preferable to attach metal nuclei. Thereby, since a metal nucleus adheres more uniformly, the uniformity of a metal membrane | film | coat can further be improved.

(6) The metal of the metal core is gold or silver. Thereby, it does not have a bad influence on the electroconductivity of silver used as a metal film. Moreover, a metal film can also be formed stably.
(7) The metal film of the conductive particles consists only of a silver film. For this reason, the electroconductive particle excellent in electroconductivity can be provided. Further, the cost is lower than that of a metal film made only of a gold film.

  (8) In the fluorescent X-ray analysis of the conductive particles, only gold and silver elements are detected as elements other than the elements contained in the nonconductive particles. In this case, conductive particles having a highly pure metal film can be provided. For this reason, the reliability regarding the electrical property of electroconductive particle can be improved.

  (9) For conductive particles, the number ratio of particles having an electrical resistance value of 10Ω or less after the elapse of 240 hours in an environment of temperature 60 ° C. and humidity 90% RH is 80% or more. Thereby, the reliability of electrical characteristics can be improved.

(10) The number ratio of the particles having an uncoated portion of the silver film is 10% or less. Thereby, the reliability of electrical characteristics can be improved.
(11) The conductive particles are preferably used as, for example, a sealing agent or an anisotropic conductive material for a liquid crystal display element due to its stable conductivity and excellent electrical characteristics.

  (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 metal has been generally performed. However, nickel has insufficient corrosion resistance under high temperature and high humidity conditions. The conductive particles of the present embodiment are configured without using nickel plating as an underlayer. For this reason, it is excellent in corrosion resistance under high temperature and high humidity conditions. In this regard, the non-conductive particles are composed of at least one selected from silica, ceramics, and glass, so that, for example, the non-conductive particles chemistry with respect to heat or moisture is more than when non-conductive particles are formed from a resin. Stability can be improved. Therefore, the practicality of the conductive particles can be improved.

The embodiment may be modified as follows.
In the embodiment, after preparing a dispersion 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. Instead of this, 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.

  -You may form the metal nucleus attached by pre-processing from metals other than gold | metal | money or silver. As the metal other than gold or silver, noble metals such as platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir) are preferable.

-The metal film may be formed by performing electroless plating in multiple stages. That is, the metal film may be composed of a multilayer film made of silver.
-Although the particle size of electroconductive particle is not specifically limited, Preferably, it is the range of 0.5-5 micrometers.

Next, the embodiment will be described more specifically with reference to examples and comparative examples.
Example 1
(A) Pretreatment In a 500 mL Erlenmeyer flask, 10 g of silica particles (average particle size: 2.4 μm, CV value: 1.36%, particle size of 70 particles measured from scanning electron micrograph) was added, and isopropyl alcohol was added. (IPA) 65 ml was added and sonicated for 10 minutes. Next, 65 ml of methanol was added and stirred with a magnetic stirrer for 10 minutes, 37 ml of 25% aqueous ammonia solution was added, and the mixture was stirred for 60 minutes in an oil bath at 30 ° C. (this solution is referred to as solution A).

To 0.20 g of chloroauric acid (HAuCl ₄ .4H ₂ O), 16 mL of methanol was added and stirred with a magnetic stirrer for 10 minutes, and then 2.6 mL of 3-aminopropyltrimethoxysilane was added and further stirred for 10 minutes (this solution) Is B liquid).

50 mL of methanol was added to 0.084 g of sodium tetrahydroborate (NaBH ₄ ), and the mixture was stirred for 10 minutes with a magnetic stirrer (this solution is referred to as solution C).
After adding B liquid to A liquid and stirring at 30 degreeC for 5 minute (s), when C liquid was dripped slowly, the reaction system changed to red. After dropping C droplets, the oil bath was heated to 65 ° C. and stirred for 3 hours. Stirring was stopped and methanol classification was performed three times, and then suction filtration was performed to collect silica particles on which metal nuclei were formed, followed by drying in an oven at 80 ° C. for 24 hours. The obtained powder of particles was red.

  FIG. 1 shows a scanning electron micrograph of silica particles. FIG. 2 shows a scanning electron micrograph of silica particles in which metal nuclei are formed. FIG. 2 shows that the ultrafine gold particles are uniformly attached to the entire surface of the silica particles. The average particle diameter of 70 particles was measured from a scanning electron micrograph, and the CV value indicating the extent of the particle size distribution was determined. The results are shown in 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 particle powder obtained in the above “(A) pretreatment” and subjected to ultrasonic treatment for 10 minutes. Then, 28.65 g of silver nitrate was added and stirred for 10 minutes with a magnetic stirrer. Next, after adding 28 g of polyvinylpyrrolidone (K-90) and stirring for another 60 minutes, ultrasonic waves were irradiated for 15 minutes. Then, after adding 375 mL of 25% ammonia aqueous solution, 250 mL of 3.57 mol / L formalin aqueous solution was added and stirred for 10 minutes. The conductive particles were collected with a centrifuge, washed with distilled water, and then dried in an oven at 80 ° C. for 24 hours.

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

The thickness of the metal film was 0.14 μm.
As a result of observing the number of particles having a crater-like uncoated portion with the micrograph shown in FIG. 3, it was 0/100, and the number ratio of the particles was 0%.

<Fluorescence X-ray analysis>
Qualitative analysis of the conductive particles obtained in Example 1 using a fully automatic X-ray fluorescence analyzer (Spectris PW2400, tube: Rh, measurement element: Na to U, irradiation area: 25 mmφ) Went. First, about 2 g of conductive particles were collected and mounted uniformly on a 6 μm film made of polypropylene. Next, the film was set in a fully automatic fluorescent X-ray analyzer, and the measurement part was replaced with helium. Elements were identified by scanning a wavelength range in which fluorescent X-rays of Na to U elements could be detected. As a result, the detected elements were two kinds of silver and gold. Elements other than silver and gold were not detected. The chart of fluorescent X-ray analysis is shown in FIGS.

<Measurement of electrical resistance value>
Using a micro compression tester (manufactured by Shimadzu Corporation), the electrical resistance value of 20 conductive particles of Example 1 was measured, and the average value was obtained. The results obtained are shown in Table 3 together with the standard deviation.

<Evaluation of heat and humidity resistance>
The electroconductive particles obtained in Example 1 were subjected to a wet heat test under the conditions of 60 ° C., 90% RH, and 240 h using a thermo-hygrostat (manufactured by Espec Corp.). A scanning electron micrograph of the conductive particles after the wet heat test is shown in FIG. As is clear from FIGS. 3 and 6, no change was observed in the state of the metal film before and after the wet heat test.

  The electrical resistance value of 50 conductive particles before and after the wet heat test was measured, and the number of electrical resistance values that could be measured and the average value of the resistance values were obtained. Table 4 shows the obtained results.

  In the conductive particles before and after the wet heat test, the difference in the number of measurable electric resistance values was one. The number ratio of particles having an electric resistance value of 10Ω or less was 86%. This result shows that the electroconductive particle obtained in Example 1 has sufficient heat-and-moisture resistance.

<Dispersibility evaluation in resin>
10 g of resin (trade name: STRUCT BOND) was stirred with a kneader for 1 minute. To this resin, 0.2 g of the conductive particles of Example 1 was added and stirred for 1 minute. The resin containing the conductive particles was pressed against a slide glass, covered with a cover glass, and observed with an optical microscope. An optical micrograph is shown in FIG.

As a result of observation with an optical microscope, the number of coalesced particles of 2 or more out of 317 particles was 3 (0.94%), and the dispersibility in the resin was very good.
(Comparative Example 1)
In Comparative Example 1, a metal film was formed without blending polyvinyl pyrrolidone. In Comparative Example 1, first, 475 mL of water was added to 10 g of the particles obtained in the same manner as “(A) pretreatment” in Example 1 and subjected to ultrasonic treatment for 10 minutes, and then 28.65 g of silver nitrate was added to magnetically. Stir with a stirrer for 10 minutes. Next, after adding 375 mL of 25% ammonia aqueous solution, 250 mL of 3.57 mol / L formalin aqueous solution was added and stirred for 10 minutes. The precipitated silver layer-coated silica particles were collected by suction filtration, washed with methanol, and then dried in an oven at 80 ° C. for 24 hours.

  A scanning electron micrograph of the conductive particles on which the metal film is formed is shown in FIG. As is clear from FIG. 8, in the conductive particles of Comparative Example 1, no metal film was formed on a part of the surface. As a result of measuring the number of particles having a crater-like uncoated portion with the micrograph shown in FIG. 8, it was 53/100, and the number ratio of the particles was 53%.

(Comparative Example 2)
In Comparative Example 2, polyvinyl pyrrolidone was changed to polyvinyl alcohol. In Comparative Example 2, first, 475 mL of water was added to 10 g of the particles obtained in the same manner as in “(A) pretreatment” of Example 1, and ultrasonic treatment was performed for 10 minutes, and then 28.65 g of silver nitrate was added to magnetically. Stir with a stirrer for 10 minutes. Next, after adding 28 g of polyvinyl alcohol (degree of polymerization 400-600) and stirring for 60 minutes, ultrasonic waves were applied for 15 minutes. Then, after adding 375 mL of 25% ammonia aqueous solution, 250 mL of 3.57 mol / L formalin aqueous solution was added and stirred for 10 minutes. The precipitated silver layer-coated silica particles were collected, washed with distilled water, and then dried in an oven at 80 ° C. for 24 hours.

  A scanning electron micrograph of the conductive particles on which the metal film is formed is shown in FIG. As is clear from FIG. 9, in the conductive particles of Comparative Example 2, no metal film was formed on a part of the surface. As a result of measuring the number of particles having a crater-like uncoated portion with the micrograph shown in FIG. 9, it was 33/100, and the number ratio of the particles was 33%.

<Dispersibility evaluation in resin>
Evaluation of dispersibility of the conductive particles obtained in Comparative Example 2 in the resin was performed in the same manner as the conductive particles of Example 1. An optical micrograph of Comparative Example 2 is shown in FIG. As a result of the optical microscope observation shown in FIG. 10, 8 or more coalesced particles were observed, and it was confirmed that the dispersibility in the resin was inferior to that of the conductive particles obtained in Example 1.

(Comparative Example 3)
In Comparative Example 3, a conductive particle powder was prepared in which substitution gold plating for forming electroless nickel plating as an underlayer on resin particles was performed. A scanning electron micrograph of the conductive particles on which the metal film is formed is shown in FIG. As is clear from FIG. 11, in the conductive particles of Comparative Example 3, no metal film was formed on a part of the surface. As a result of measuring the number of particles having a crater-like uncoated portion with the micrograph shown in FIG. 11, it was 57/100, and the number ratio of the particles was 57%.

<Evaluation of heat and humidity resistance>
The conductive particles obtained in Comparative Example 3 were subjected to the same wet heat resistance evaluation as in Example 1. A scanning electron micrograph after the wet heat test is shown in FIG. As is apparent from FIGS. 11 and 12, a change is observed in the metal film after the wet heat test. From this result, it is considered that in the conductive particles of Comparative Example 3, the metal film made of gold was peeled off from the surface of the particles due to corrosion caused by oxidation of nickel.

  The electrical resistance value of 50 conductive particles before and after the wet heat test was measured, and the number of electrical resistance values that could be measured and the average value of the resistance values were obtained. The results obtained are shown in Table 5.

  In the conductive particles before and after the wet heat test, the difference in the number of measurable electric resistance values is 39, the expression rate after the wet heat test is only 10% (5/50 particles), and the electric resistance value The number ratio of particles having a particle size of 10Ω or less was 6%. From this result, it was confirmed that the electroconductive particle obtained in the comparative example 3 was inferior in heat-and-moisture resistance.

(Comparative Example 4)
The polyvinyl pyrrolidone 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 the particles obtained in the same manner as in “(A) pretreatment” in Example 1, and ultrasonic treatment was performed for 10 minutes, and then 28.65 g of silver nitrate was added to magnetically. Stir with a stirrer for 10 minutes. Next, 28 g of polyethylene glycol was added and the mixture was further stirred for 60 minutes, and then irradiated with ultrasonic waves for 15 minutes. Then, after adding 375 mL of 25% ammonia aqueous solution, 250 mL of 3.57 mol / L formalin aqueous solution was added and stirred for 10 minutes. The precipitated silver layer-coated silica particles were collected, washed with distilled water, and then dried in an oven at 80 ° C. for 24 hours.

As a result of observing the conductive particles on which the metal film was formed with a scanning electron micrograph, the metal film was not formed on a part of the surface. As a result of measuring the number of particles having a crater-like uncoated portion by a micrograph, it was 36/100, and the number ratio of the particles was 36%.
<Dispersibility evaluation in resin>
Dispersibility evaluation of the conductive particles obtained in Comparative Example 4 in the resin was performed in the same manner as the conductive particles of Example 1. As a result of observation with an optical microscope, 8 or more coalesced particles were observed, and it was confirmed that the dispersibility in the resin was inferior to that of the conductive particles obtained in Example 1.

Claims (14)

A metal film forming method for forming a metal film on the surface of non-conductive particles by electroless plating,
The electroless plating is
Carried out after pretreatment to attach metal nuclei to the surface of the non-conductive particles,
A method for forming a metal film, comprising forming the metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. The electroless plating is started in the dispersion after preparing a dispersion in which the non-conductive particles are dispersed in an aqueous solution of the hydrophilic polymer having the pyrrolidone group. Metal film forming method. The method for forming a metal film according to claim 1 or 2, wherein the hydrophilic polymer having a pyrrolidone group contains at least polyvinylpyrrolidone. The metal film forming method according to any one of claims 1 to 3, wherein the electroless plating is performed by a silver mirror reaction. In the pretreatment, after the treatment liquid containing a silane coupling agent, a hydrolysis catalyst, and a metal salt is brought into contact with the nonconductive particles, the metal of the metal salt is precipitated by a reducing agent, whereby the nonconductive. Treatment to attach metal nuclei to the surface of the conductive particles
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 as described in any one of Claims 1-4 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. Conductive particles provided with conductivity by a metal film formed on the entire surface of the non-conductive particles,
The electroconductive particle, wherein the metal film is composed only of a silver film. 8. The conductive particle according to claim 7, wherein in the fluorescent X-ray analysis of the conductive particle, only an element of gold and silver is detected as an element other than an element contained in the non-conductive particle. 9. The number ratio of particles having an electric resistance value of 10Ω or less after 240 hours in an environment of a temperature of 60 ° C. and a humidity of 90% RH is 80% or more. Conductive particles. The conductive particles according to any one of claims 7 to 9, wherein the number ratio of the particles having an uncoated portion of the silver film is 10% or less. The conductive particles according to any one of claims 7 to 10, wherein the conductive particles are used as a sealant for a liquid crystal display element. The conductive particle according to claim 7, wherein the conductive particle is used as an anisotropic conductive material. In the method for producing conductive particles formed by forming a metal film on the surface of the non-conductive particles by electroless plating,
The electroless plating is
Carried out after pretreatment to attach metal nuclei to the surface of the non-conductive particles,
A method for producing conductive particles, comprising forming the metal film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. Conductive particles obtained by forming a metal film on the surface of non-conductive particles,
The metal coating is carried out after a pretreatment for attaching a metal nucleus to the surface of the non-conductive particles, and forms an electroless film made of silver in the presence of a hydrophilic polymer having a pyrrolidone group. Formed by plating,
The electroconductive particle, wherein the metal film is composed only of a silver film.