JPH0689069B2 - Conductive microsphere - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive microsphere having a high crush strength, which is composed of a resin microsphere having excellent adhesion to each other and a conductive plating layer.

(Prior Art) As a conductive material such as a conductive paste, a conductive adhesive or an anisotropic conductive film, a composition composed of conductive particles and a resin is used. The conductive particles generally include metal particles such as gold, silver and nickel. However,
Such metal particles have a larger specific gravity than resin,
Since the shape is also irregular, it tends to exist unevenly in the resin. Therefore, uneven conductivity occurs. In order to solve such a drawback, in Japanese Patent Laid-Open No. 59-28185, instead of metal particles, the surface of non-conductive particles such as glass beads, glass fibers, plastic balls having a uniform particle size, The conductive particles coated with gold, silver, tin, copper, nickel, etc. by plating are disclosed. However,
The conductive particles lack the adhesion between the non-conductive particles and the conductive plating layer, and have extremely low crush strength. Although the adhesion can be improved by etching the non-conductive particles, the crush strength cannot be reduced. Therefore, when such conductive particles are used as the conductive material, peeling of the conductive plating layer and crushing of the conductive particles due to pressure are unavoidable. The peeling of the conductive plating layer and the crushing of the conductive particles hinder the conductivity of the material.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a resin microsphere and a conductive plating layer, and both have excellent adhesion. The purpose is to provide electrically conductive microspheres. Another object of the present invention is to provide a conductive microsphere having high crush strength.

(Means for Solving Problems) The conductive microspheres of the first aspect of the present invention are a resin microsphere obtained by pearl polymerization of a monomer represented by the following formula, and a conductive plating formed on the surface thereof. The conductive microspheres of the second aspect of the present invention include a resin microsphere obtained by pearl polymerization of a monomer represented by the following formula, and a conductive microsphere formed on the surface thereof. Conductive microspheres comprising a plating layer, the surface of the resin microspheres being conductive microspheres in which the ester bond derived from the pearl polymer is hydrolyzed by etching.

Here, R is a methylol group or an alkyl group; and m is an integer of 4 or less.

Examples of the monomer include tetramethylolmethane tetraacrylate, tetramethylolmethane triacrylate, tetramethylolmethane diacrylate, tetramethylolmethane monoacrylate, trimethylolethane triacrylate, and trimethylolpropane triacrylate. Preferably, tetramethylolmethane tetraacrylate, tetramethylolmethane triacrylate, trimethylolpropane triacrylate is used. These may be used alone or as a mixture. Further, these monomers may be copolymerized with other polymerizable comonomer. Examples of the comonomer include styrene, α-methylstyrene, methyl methacrylate, methyl acrylate, ethyl acrylate, methacrylonitrile, acrylonitrile, vinyl chloride, tetrafluoroethylene, ethylene, propylene, divinylbenzene,
Hexatriene, divinyl ether, divinyl sulfone, diallyl phthalate, diallyl carbinol, triallyl isocyanurate. The comonomer is usually used in a proportion of 500 parts by weight or less based on 100 parts by weight of the above monomer. If it exceeds 500 parts by weight, the properties of the obtained polymer depend on the comonomer, and it is not possible to obtain resin microspheres having excellent adhesion to the conductive plating layer.

These monomers become resin microspheres by pearl polymerization with a radical initiator. Radical initiators include lauroyl peroxide, benzoyl peroxide, acetyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, t-butyl peroxy octoate, t-butyl peroxy. Acetate, t-butyl peroxyisobutyrate,
All known initiators such as azobisisobutyronitrile and azobisisovaleronitrile are used. The radical initiator is added in an amount of 0.5 to 15 parts by weight with respect to 100 parts by weight of the monomer. When the amount is less than 0.5 part by weight, the polymerization rate of the monomer is remarkably reduced. It is not necessary to use more than 15 parts by weight of initiator.

A suspension stabilizer is preferably added to the monomer and the initiator. The suspension stabilizer is an additive for stably allowing the resin microspheres formed by the polymerization reaction to exist in the reaction system, and examples thereof include polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, gelatin, methylcellulose, and polymethacryl. Amide, polyethylene glycol,
There are polyethylene oxide monostearate, sorbitan tetraoleate, and glyceryl monooleate.

A mixture containing these monomers, an initiator and a suspension stabilizer is dispersed in a suitable liquid medium, atomized with vigorous stirring, and heated to become a polymer. Water is usually used as the liquid medium. The polymerization reaction is continued until the end reaction monomer disappears. The resulting polymer becomes resin microspheres. A fine crosslinked layer is formed on the resin microspheres, and therefore the crush strength is excellent. Also, at least the surface of the microsphere has many ester bonds. Therefore, when the microspheres are etched, the ester bond is easily hydrolyzed by the etching solution and the adhesion with the conductive plating layer is improved.

The particle size of the resin microspheres is adjusted by the stirring speed and stirring time of the mixture in the above step. Particle size is 1-10
0 μm is preferable. More preferably, 3 to 20 μm is used. More preferably, it is 5 to 15 μm. Since there is dispersion in the particle size, it is preferable to classify by a usual method. Alternatively, classification may be performed after forming the conductive plating layer.

On the surface of such a resin microsphere, for example, a conductive plating layer is formed as follows.

The conductive plating layer forming process is divided into etching, activation and chemical plating processes.

The etching process is a process for forming irregularities on the surface of the resin microspheres to provide the adhesion of the conductive plating layer, and the etching solution is, for example, caustic soda aqueous solution,
Concentrated hydrochloric acid, concentrated sulfuric acid or chromic anhydride is used.

The activation step is a step of forming a contact layer on the surface of the etched resin microspheres and activating this catalyst layer. The activation of the catalyst layer promotes the deposition of metal in the chemical plating process described below. As a catalyst, Pd ²⁺ and Sn ²⁺ are adsorbed on the surface of resin microspheres. Concentrated sulfuric acid or concentrated hydrochloric acid is made to act on this catalyst layer to cause Sn ²⁺
Only Pd ²⁺ is metallized by dissolution and removal. Metallized palladium is activated and sensitized by a palladium activator such as concentrated caustic soda solution.

The chemical plating step is a step of further forming a conductive plating layer on the surface of the resin microsphere on which the catalyst layer is formed. By immersing the resin microspheres in a chemical plating solution containing metal ions, a conductive plating layer is formed on the surface of the resin microspheres. By chemical plating, the metal adheres sufficiently to the resin surface, so there is no need for further electroplating. The metals used include, for example, nickel, gold, silver, copper and cobalt. The thickness of the conductive plating layer is adjusted by the concentration of the chemical plating solution. The thickness of the plated layer is preferably 0.02 to 5 μm. If it is less than 0.02 μm, it is difficult to obtain the desired conductivity. When the thickness exceeds 5 μm, the conductive plating layer is easily separated from the surface of the resin microsphere due to the difference in thermal expansion coefficient between the resin microsphere and the conductive plating layer.

The conductive microspheres thus obtained have good conductivity and excellent adhesion between the resin microspheres and the conductive plating layer. Moreover, the deformation and crushing of the particles due to the pressure does not occur. Therefore, it is suitably used for applications such as conductive pastes, conductive adhesives, conductive adhesives, anisotropic conductive films, fillers for electromagnetic wave shielding resins, and magnetic materials.

(Examples) The present invention will be described below with reference to Examples.

Example 1 Tetramethylolmethane tetraacrylate (NH ester A-TMMT, manufactured by Shin-Nakamura Chemical Co., Ltd.) 320 g as a monomer
192 g of divinylbenzene, 128 g of ethylvinylbenzene and 18 g of benzoyl peroxide as a polymerization initiator were mixed and uniformly dissolved.

Into a 5 volume separable flask, 2400 ml of a 5% aqueous solution of polyvinyl alcohol was added, and this mixture was further injected, and atomized while stirring. After about 8 hours, stirring was stopped when the average particle size of the droplets reached 9 μm. Then, while injecting nitrogen gas into the vessel, the polymerization reaction was carried out by gently stirring in a water bath at 80 ° C. The reaction was stopped after 10 hours.

The reaction product was separated from the aqueous polyvinyl alcohol solution by filtration through a glass filter. The reaction product was thoroughly washed on a glass filter with hot water at 80 ° C.

10 g of the resin microspheres were immersed in a powder coating pre-dip solution (Okuno Pharmaceutical Co., Ltd.) for 30 minutes at room temperature for etching. It was washed with water, then immersed in 10 ml of Catalyst C liquid (Okuno Pharmaceutical Co., Ltd.), 10 ml of 37% hydrochloric acid, and 10 ml of methanol at room temperature for 30 minutes for activation. Further, it was washed with 5% sulfuric acid and then thoroughly washed with water. After immersing in 50 ml of electroless nickel plating solution (Top Nicolon VS, Okuno Chemical Industries Co., Ltd.) at 70 ° C for 10 minutes, it was taken out and dried to form a conductive plating layer.

As a result of observing a cross section of the conductive microspheres thus obtained with a scanning electron microscope, it was found that a plating layer having a thickness of about 0.3 μm was uniformly formed. The conductive microspheres were scattered on a glass plate at a density of 30 to 40 pieces / mm ² , and a pressure of 15 kg / cm ² was applied from above the glass plate with another glass plate placed.
However, the conductive plating layer was not damaged.

Example 2 Tetramethylolmethane triacrylate (NK ester A-TMM-3, manufactured by Shin-Nakamura Chemical Co., Ltd.) 320 g as a monomer,
192 g of divinylbenzene, 128 g of ethylvinylbenzene and 18 g of benzoyl peroxide as a polymerization initiator were mixed and uniformly dissolved. Using this mixture, Example 1
Resin microspheres were synthesized in the same manner as described above and subjected to electroless nickel plating.

On the thus obtained conductive microspheres, a plating layer having a thickness of about 0.3 μm was uniformly formed by observation with a scanning electron microscope. When the conductive microspheres were subjected to the same pressure test as in Example 1, the conductive plated layer was not damaged.

Comparative Example 1 327 g of divinylbenzene, 248 g of ethylvinylbenzene as a monomer and 18 g of benzoyl peroxide as a polymerization initiator were mixed and uniformly dissolved. Using this mixture, resin microspheres were synthesized in the same manner as in Example 1 and subjected to electroless nickel plating.

On the thus obtained conductive microspheres, a plating layer having a thickness of about 0.3 μm was formed by observation with a scanning electron microscope. However, there were some areas where the plating layer was peeled off. When this conductive microsphere was subjected to the same pressure test as in Example 1, peeling of the conductive plating layer was observed.

Comparative Example 2 After dissolving 2 g of polyvinyl alcohol in 300 g of ion-exchanged water in a 500 ml beaker, 20 g of methyl methacrylate, 20 g of methyl acrylate, 20 g of ethylene glycol dimethacrylate, 1 g of benzoyl peroxide were charged and irradiated with ultrasonic waves for 10 minutes, A monomer dispersion was prepared. This preparation is
200 in a 500 ml four-necked flask equipped with a squid-type stirring blade
Suspension polymerization was carried out at 75 ° C. for 12 hours at a stirring speed of rpm. The obtained microspheres were subjected to electroless nickel plating treatment.

On the conductive microspheres thus obtained, a plating layer was formed by observation with a scanning electron microscope, but a part of the plating layer was partially peeled off. . When this conductive microsphere was subjected to the same pressure test as in Example 1, peeling of the conductive plating layer was observed.

Comparative Example 3 In the same manner as in Comparative Example 2, suspension polymerization of the following raw material composition was carried out. That is, 300 g of ion-exchanged water, 1 polyvinyl alcohol
g, styrene 50 g, divinylbenzene 10 g, and lauroyl peroxide 1 g. The obtained microspheres were subjected to electroless nickel plating treatment.

On the conductive microspheres thus obtained, a plating layer was formed by observation with a scanning electron microscope, but a part where the plating layer was peeled off was observed. When this conductive microsphere was subjected to the same pressure test as in Example 1, peeling of the conductive plating layer was observed.

(Effects of the Invention) In the conductive microspheres of the present invention, the resin microspheres forming the microspheres and the conductive plating layer have excellent adhesion as described above. High crush strength. Therefore, this conductive microsphere is
It is useful as a conductive material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-90019 (JP, A) JP-A-59-219303 (JP, A) JP-A-54-137398 (JP, A) JP-A-59- 28185 (JP, A)

Claims (8)

[Claims] 1. A conductive microsphere comprising a resin microsphere obtained by pearl polymerization of a monomer represented by the following formula, and a conductive plating layer formed on the surface thereof. Here, R is a methylol group or an alkyl group; and m is an integer of 4 or less. 2. The monomer is at least one of tetramethylol methane tetraacrylate, tetramethylol methane triacrylate, tetramethylol methane diacrylate, tetramethylol methane monoacrylate, trimethylol ethane triacrylate and trimethylol propane triacrylate. The conductive microsphere according to claim 1, which is a kind. 3. The conductive plating layer comprises nickel, gold, silver,
The conductive microsphere according to claim 1, comprising at least one of copper and cobalt. 4. The conductive plating layer has a thickness of 0.02 to 5 μm.
The conductive microsphere according to claim 1, which is in the range of. 5. A conductive microsphere comprising a resin microsphere obtained by pearl polymerization of a monomer represented by the following formula, and a conductive plating layer formed on the surface of the resin microsphere. Conductive microspheres on the surface of which ester bonds derived from the pearl polymer are hydrolyzed by etching treatment; Here, R is a methylol group or an alkyl group; and m is an integer of 4 or less. 6. The monomer is at least one of tetramethylolmethane tetraacrylate, tetramethylolmethane triacrylate, tetramethylolmethane diacrylate, tetramethylolmethane monoacrylate, trimethylolethane triacrylate and trimethylolpropane triacrylate. The conductive microsphere according to claim 5, which is a kind. 7. The conductive plating layer comprises nickel, gold, silver,
The conductive microsphere according to claim 5, which is composed of at least one of copper and cobalt. 8. The conductive plating layer has a thickness of 0.02 to 5 μm.
The conductive microsphere according to claim 5, which is in the range of.