JPH0689068B2 - Method for producing conductive microspheres - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a conductive microsphere having a high crushing 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 reduction of the crushing strength cannot be avoided. 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. It is an object to provide a method for producing a conductive microsphere. Another object of the present invention is to provide a method for producing a conductive microsphere having high crush strength.

(Means for Solving the Problems) The method for producing conductive microspheres of the present invention is a method in which a mixture containing at least a cross-linking reactive compound and a diluent is subjected to pearl polymerization, and after the polymerization reaction, from inside the produced resin microspheres. By separating the diluent, a step of forming fine pores sufficient to achieve the anchor effect in the following plating step from the inside to the surface of the resin microspheres and conductive plating on the surface of the resin microspheres It is a manufacturing method of a conductive microsphere including a process of forming a layer. Here, the cross-linking reactive compound is selected from at least one of divinylbenzene, divinyl ether, alkylene diacrylate, alkylene triacrylate and alkylene tetraacrylate, and the cross-linking reactive compound is the mixture 10
It is contained in the range of 5 to 95 parts by weight with respect to 0 parts by weight.

Further, the diluent is selected from at least one of benzene, toluene, ethylbenzene, diethylbenzene, xylene, pyridine, isopropyl alcohol, butyl alcohol, isoamyl alcohol, propyl acetate and butyl acetate, and the diluent is 100 parts by weight of the mixture. However, it is contained in the range of 2 to 50 parts by weight. Thereby, the above object is achieved.

The crosslinking reactive compound is contained in the range of 5 to 95 parts by weight with respect to 100 parts by weight of the mixture. If the amount is less than 5 parts by weight, the mechanical strength of the resin microspheres obtained by the pearl polymerization of the mixture is lowered. Moreover, when the microspheres are brought into contact with a liquid, a swelling phenomenon occurs. When it exceeds 95 parts by weight, the effect of the diluent is lost and it is difficult to obtain the desired resin microspheres even by pearl polymerization of the mixture.

The diluting agent means a compound which is not itself polymerizable, is soluble in the crosslinking reactive compound and the non-crosslinking monomer, and undergoes phase separation from the system after the reaction. After the polymerization reaction, this diluting agent escapes from the inside of the resin microspheres, whereby fine pores are formed from the inside to the surface of the resin microspheres. The diluent is contained in an amount of 2 to 50 parts by weight, preferably 5 to 45 parts by weight, based on 100 parts by weight of the mixture. Below 2 parts by weight, the number of fine holes formed in the resin microspheres is too small. Therefore, in the subsequent step of forming the conductive plating layer on the surface of the resin microspheres, the anchor of the conductive plating layer is formed. The effect decreases. As a result, the conductive plating layer is easily separated from the resin microspheres. If it exceeds 50 parts by weight, the holes formed in the resin microspheres are too large or there are too many voids, which easily deforms and becomes brittle against external pressure.

A non-crosslinking monomer is added to these mixtures, if necessary. The non-crosslinkable monomer in the present invention is a compound having one polymerizable double bond in the molecule, and examples thereof include styrene, α-methylstyrene, ethylvinylbenzene, methyl methacrylate, acrylic acid. Methyl, ethyl acrylate, methacrylonitrile, acrylonitrile,
There are vinyl chloride, ethylene tetrafluoride, ethylene and propylene. The non-crosslinkable monomer is contained in an amount of 90 parts by weight or less based on 100 parts by weight of the mixture. However, this non-crosslinkable monomer does not necessarily have to be added.

A polymerization initiator and a suspension stabilizer are further added to the mixture.

As the polymerization initiator, all known radical initiators are used, and examples thereof 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, azobisisobutyronitrile, azobisisovaleronitrile. The radical initiator is
Usually, 0.5 to 15 parts by weight is added to 100 parts by weight of the monomer. When it is less than 0.5 part by weight, the polymerization rate of the mixture is remarkably reduced. It is not necessary to use more than 15 parts by weight of initiator.

The suspension stabilizer is added to allow the resin microspheres formed by the polymerization reaction to exist stably in the reaction system. Suspension stabilizers include polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, gelatin, methyl cellulose,
Polymethacrylamide, polyethylene glycol, polyethylene oxide monostearate, sorbitan tetraoleate, glyceryl monooleate, etc. are used.

The mixture of the initiator and the suspension stabilizer is dispersed in a suitable liquid medium, and the mixture is vigorously stirred to be microspheres, which are then heated to form a polymer. In the liquid medium,
Water is usually used. The polymerization reaction is continued until the unreacted monomer and the crosslinkable compound disappear. The resulting polymer becomes resin microspheres. The mixture contains a diluting agent, and a large number of fine pores are formed from the inside to the surface of the resin microsphere due to volatilization of the diluting agent. The fine holes improve the adhesion between the plating layer and the resin microspheres due to the anchor effect in the subsequent step of forming the conductive plating layer. The hole diameter of the fine holes is, for example,
It is measured using a liquid chromatograph. The resin microspheres with micropores are filled in the column of the device, and standard polystyrene of various molecular weight is injected while flowing THF and the like. The column outflow count decreases with increasing molecular weight, but above a certain molecular weight, the outflow count becomes constant. This is because polystyrene larger than a certain size cannot be captured in the micropores. The relationship between the molecular weight and the outflow count is obtained, and the molecular weight at which there is no change in the outflow count is calculated. The pore diameter of the fine pores can be obtained from the calibration curve of the molecular weight and the pore diameter prepared in advance.

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 conventional 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. In the production method of the present invention, since a large number of fine holes are formed from the inside of the resin microsphere to the surface, the adhesion to the conductive plating layer is good. Therefore, the etching process is not always necessary. Alternatively, the minimum required is sufficient.
The preferred etching conditions are 2 to 36% hydrochloric acid at room temperature.
It is a process of 8 minutes.

The activation step is a step of forming a catalyst layer on the surface of the etched resin microspheres and activating the 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. Metal does not need to be further electroplated because it adheres sufficiently to the resin surface by chemical plating. 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 A mixture having the composition shown in the table was prepared. This mixture was stirred at room temperature and dissolved uniformly. Into a 5 volume separable flask, 2400 ml of a 5% aqueous solution of polyvinyl alcohol was placed, and 625 g of 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. A large number of fine holes were formed on the surface of the resin microspheres thus obtained. In order to determine the approximate size of the micropores, a column having a diameter of 7.9 mm and a length of 50 cm was packed with the resin microspheres, and the packed column was attached to a Shimadzu-Dupont Liquid Chromatograph Model 830. THF every minute
While flowing at a flow rate of 1 ml, standard polystyrene solutions having various molecular weights were injected, and the relationship between the outflow count and the molecular weight for each polystyrene was obtained. As a result, as shown in Fig. 1, the upper limit of the measurable molecular weight of the column using the resin microspheres is 40,000, which is "Experimental High Performance Liquid Chromatography" (Kagaku Dojin) 51
According to the page, the pore diameter was equivalent to 1000 angstrom.

10 g of the resin microspheres were etched by immersing them in a powder plating pre-dip solution (Okuno Pharmaceutical Co., Ltd.) at room temperature for 30 minutes. Wash with water, then Catalyst C liquid (Okuno Pharmaceutical Co., Ltd.)
It was activated by immersing it in 10 ml, 37% hydrochloric acid 10 ml, and methanol 10 ml at room temperature for 30 minutes. It was washed with 5% sulfuric acid and then thoroughly washed with water. After further immersing in 50 ml of electroless nickel plating solution (Top Nicolon VS, Okuno Pharmaceutical 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 conductive plating layer having a thickness of about 0.2 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 As shown in the table, resin microspheres were synthesized in the same manner as in Example 1 except that 23.5% by weight of diethylbenzene and 5% by weight of isoamyl alcohol were used as diluents. The resin microspheres thus obtained were found to have micropores with a pore size of 150 angstroms on the surface as measured by the same chromatography. Using this resin microsphere, electroless plating of nickel was performed in the same manner as in Example 1. As a result, a conductive plating layer having a thickness of about 0.3 μm was uniformly formed. When the conductive microspheres were subjected to the same pressure test as in Example 1, the plating layer was not damaged.

Example 3 As shown in the table, resin microspheres were synthesized in the same manner as in Example 1 except that 60% by weight of diallyl phthalate was used as the crosslinking reactive compound and 38.5% by weight of diethylbenzene was used as the diluent. The resin microspheres thus obtained were found to have micropores with a pore diameter of 2000 angstroms on the surface as measured by the same chromatography. Using this resin microsphere, electroless plating of nickel was performed in the same manner as in Example 1. As a result, a conductive plating layer having a thickness of about 0.2 μm was uniformly formed. When the conductive microspheres were subjected to the same pressure test as in Example 1, the plating layer was not damaged.

Comparative Example As shown in the table, resin microspheres were synthesized in the same manner as in Example 1 except that the diluent was not used. The weight ratio of divinylbenzene and ethylvinylbenzene is the same as in Example 1.
Is the same as. As a result of electroless plating of nickel using this resin microsphere in the same manner as in Example 1, a conductive plating layer having a thickness of about 0.3 μm was formed, but a peeled portion of the conductive plating layer was observed. . When the conductive microspheres were subjected to the same pressure test as in Example 1, peeling of the plating layer was observed.

(Effects of the Invention) According to the present invention, as described above, the conductive microspheres having a high crushing strength, which are composed of the resin microspheres and the conductive plating layer, which are excellent in mutual adhesion, can be obtained. Therefore, this conductive microsphere is useful as a conductive material.

[Brief description of drawings]

The figure shows the relationship between the molecular weight of standard polystyrene and the chromatographic outflow count in Examples 1, 2 and 3 of the present invention.

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Claims (6)

[Claims] 1. A mixture containing at least a cross-linking reactive compound and a diluent is subjected to pearl polymerization, and after the polymerization reaction, the diluent is separated from the inside of the resin microspheres formed, whereby the inside of the resin microspheres is separated. A method for producing conductive microspheres, which includes a step of forming fine pores sufficient to achieve an anchor effect in the following plating step on the surface and a step of forming a conductive plating layer on the surface of the resin microspheres;
Here, the crosslinking reactive compound is selected from at least one of divinylbenzene, divinyl ether, alkylene diacrylate, alkylene triacrylate and alkylene tetraacrylate, and the crosslinking reactive compound is 5 to 100 parts by weight of the mixture. It is contained in the range of 95 parts by weight, and the diluent is benzene, toluene,
It is selected from at least one of ethylbenzene, diethylbenzene, xylene, pyridine, isopropyl alcohol, butyl alcohol, isoamyl alcohol, propyl acetate and butyl acetate, and the diluent is 2 to 50 parts by weight per 100 parts by weight of the mixture. It is contained in the range. 2. The method for producing electrically conductive microspheres according to claim 1, wherein the mixture contains a non-crosslinking monomer. 3. The non-crosslinkable monomer is styrene, α-methylstyrene, ethylvinylbenzene, methyl methacrylate, methyl acrylate, ethyl acrylate, methacrylonitrile, acrylonitrile, vinyl chloride, tetrafluoroethylene. The method for producing a conductive microsphere according to claim 2, which is at least one of ethylene, ethylene and propylene. 4. The conductive plating layer comprises nickel, gold, silver,
The method for producing a conductive microsphere according to claim 1, comprising at least one of copper and cobalt. 5. The conductive plating layer has a thickness of 0.02 to 5 μm.
The method for producing a conductive microsphere according to claim 1, which is within the range. 6. The method for producing conductive microspheres according to claim 2, wherein the non-crosslinkable monomer is contained in a ratio of 90 parts by weight or less with respect to 100 parts by weight of the mixture.