JP2007262495A - Electroconductive electroless-plated powder and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroconductive electroless-plated powder that has a plated film which is formed on fine particles without using such chromic acid or permanganic acid as to cause environmental pollution, and which has excellent adhesiveness even though the fine particles have an average size of 20 μm or smaller, and to provide an industrially advantageous production method therefor. <P>SOLUTION: The electroconductive electroless-plated powder has a melamine resin coated on the surface of its core powder, and further has a metallic film electroless-plated thereon. The production method comprises the steps of: preparing a core powder coated with the melamine resin by bringing the core powder in contact with an initial condensate of the melamine resin and polymerizing the initial condensate through a reaction; subsequently, making the surface of the core powder coated with the melamine resin carry a noble metal; and subsequently, electroless-plating the core powder having the noble metal carried thereon with a metal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conductive electroless plating powder and a method for producing the same.

  Conventionally, when producing electroless plating products such as conductive electroless plating powders, when the object to be plated is hydrophobic, the surface is hydrophilized so that the metal film and the object to be plated It is necessary to improve adhesion. Conventionally, strong oxidizing agents such as chromic acid and permanganic acid have been used as means for improving adhesion.

  However, these oxidizing agents have the disadvantage that the environmental burden is large. With proper reduction and cleaning treatment, chromium and manganese will hardly remain in the plated product, but complete removal is very difficult.

  Therefore, as a hydrophilization treatment method with a small environmental load, for example, in Patent Document 1 below, an unsaturated fatty acid such as an aminosilane compound, a glycol compound, a nitrile compound, a titanate compound, a butadiene polymer, linoleic acid, or linolenic acid is used as a synthetic resin material. A method has been proposed in which the synthetic resin material is coated with a noble metal-trapping surface treatment material selected from the above to carry noble metal ions, and then electroless plating treatment is performed.

However, in the method described in Patent Document 1, it is difficult to obtain a material having excellent plating adhesion particularly for fine particles having an average particle diameter of 20 μm or less, and it is difficult to use for fine pitch connection, for example.
JP 61-64882 A

  Accordingly, an object of the present invention is to provide an electroless electroless plating powder that has excellent plating adhesion even if it is a fine particle having an average particle diameter of 20 μm or less, without using chromic acid or permanganic acid that causes environmental pollution. It is to provide a body and an industrially advantageous production method thereof.

  The object of the present invention is to provide a conductive electroless plating powder characterized in that the surface of the core powder is coated with a melamine resin and a metal film is formed by electroless plating. Achieved.

  According to the present invention, a conductive electroless plating powder having excellent plating adhesion even for fine particles having an average particle diameter of 20 μm or less, even without using chromic acid, permanganic acid, or the like for the hydrophilic treatment. The conductive electroless plating powder of the present invention can be applied to, for example, an anisotropic conductive film (ACF), a heat seal connector (HSC), or an electrode of a liquid crystal display panel on a circuit board of a driving LSI chip. It is suitably used for conductive materials for connection, applications of polarizing plates, and the like.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The conductive electroless plating powder of the present invention (hereinafter also simply referred to as plating powder) is obtained by coating the surface of a core material powder with a melamine resin and further forming a metal film by electroless plating. is there.

  There is no restriction | limiting in particular in the kind of core material powder used by this invention, Both organic substance powder and inorganic substance powder are used. The surface of the core material powder may be hydrophobic or hydrophilic. However, the method of this embodiment is particularly effective for the core material powder having a hydrophobic surface. The core powder is preferably substantially insoluble in water, more preferably not dissolved or denatured in acid or alkali.

  There is no restriction | limiting in particular in the shape of core material powder. In general, the core powder may be granular, but may have other shapes, for example, a fiber shape, a hollow shape, a plate shape, a needle shape, a particle having a large number of protrusions on the particle surface, or an irregular shape. It may be a thing. In the present invention, among these, spherical ones are particularly preferable in that they have excellent filling properties when used as conductive fillers.

  Specific examples of the core powder include metal (including alloys), glass, ceramics, silica, carbon, metal or non-metal oxides (including hydrates), and metal silicates including aluminosilicates as inorganic materials. Metal carbide, metal nitride, metal carbonate, metal sulfate, metal phosphate, metal sulfide, metal acid salt, metal halide and carbon. Organic materials include natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester and other thermoplastic resins, alkyd resins, phenol resins, Examples include urea resin, benzoguanamine resin, melamine resin, xylene resin, silicone resin, epoxy resin, or diallyl phthalate resin. These may be used alone or in a mixture of two or more.

  Another preferable physical property of the core powder used in the present invention is that the average particle size is 0.5 to 100 μm, particularly 0.8 to 80 μm, especially 1 to 20 μm to suppress aggregation during the plating process. The conductive particles after electroless plating are particularly preferable from the viewpoint of adapting to narrow pitch. In addition, the average particle diameter of core material powder shows the value measured using the electrical resistance method.

Furthermore, there is a range in the particle size distribution of the core material powder measured by the method described above. In general, the width of the particle size distribution of the powder is represented by a coefficient of variation represented by the following calculation formula (1).
Coefficient of variation (%) = (standard deviation / average particle size) × 100 Formula (1)
A large coefficient of variation indicates that the distribution is wide, while a small coefficient of variation indicates that the particle size distribution is sharp. In the present embodiment, it is preferable to use a core material powder having a coefficient of variation of 50% or less, particularly 30% or less, especially 20% or less. This is because when the plating powder obtained by the present invention is used as conductive particles in an anisotropic conductive film, there is an advantage that the effective contribution ratio for connection is increased.

  The coating amount of the melamine resin varies depending on the type and shape of the core material powder to be used, but in many cases it is 0.1 to 15% by weight, preferably 0.5 to 10% by weight. The reason for this is that when the coating amount of the melamine resin is less than 0.1% by weight, the coating amount is insufficient and a plating powder excellent in plating adhesion tends to be not obtained. This is because in the step 1) of obtaining the core material powder coated with the melamine resin, the fine particle melamine resin is generated alone and remains as a foreign substance. The melamine resin may be a modified one.

  The metal film in the electroless electroless plating powder is usually a single metal single layer structure, but may be a multilayer structure of two or more different kinds of metals if desired. The metal film may be crystalline or amorphous depending on the type and plating conditions. Furthermore, the metal film may be magnetic or non-magnetic. The metal here includes not only a simple metal but also an alloy (for example, nickel-phosphorus alloy or nickel-boron alloy). Usable metals include Ni, Fe, Cu, Co, Pd, Ag, Au, Pt, and Sn. The thickness of the metal film is preferably 0.001 to 2 μm, particularly preferably 0.005 to 1 μm. The thickness of the metal film can be calculated from the amount of nickel ions added and chemical analysis.

  Ni is preferable from an economical viewpoint. In the following embodiment, nickel will be described as an example of the metal, but the metal that can be used is not limited to this.

  The production method of the present embodiment includes a step of bringing a core material powder and an initial condensate of melamine resin into contact with each other to perform a polymerization reaction of the initial condensate to obtain a core material powder coated with melamine resin, and then the melamine resin Including a step of supporting a noble metal on the surface of the core material powder coated with, and then a step of electroless plating the core material powder supporting the noble metal, particularly (1) coated with a melamine resin. By including a step of obtaining a core powder, (2) a catalytic treatment step, (3) an initial thin film forming step, and (4) an electroless plating step, a stable quality plating powder is advantageously obtained industrially. be able to.

  The melamine resin coating step of the core material powder of (1) is performed by bringing the core material powder and the melamine resin into an initial condensate so that the initial condensate undergoes a polymerization reaction to coat the core material powder coated with the melamine resin. It is a process to obtain.

  In the present invention, the initial condensate of melamine resin refers to a product in which a condensation reaction is caused by heating or addition of an acid catalyst to produce a melamine resin. The initial condensate of the melamine resin may be a commercially available product, or a product obtained by reacting a melamine compound and an aldehyde compound may be used as the initial condensate of the melamine resin.

  Examples of the melamine compound include melamine, a melamine compound in which the amino group hydrogen of melamine is substituted with an alkyl group, an alkenyl group, or a phenyl group (see, for example, Japanese Patent Application Laid-Open No. 09-143238), and the hydrogen of the melamine amino group. Substituted with a hydroxyalkyl group or an aminoalkyl group (for example, see JP-A No. 5-202157). However, melamine is preferable because it is easily available industrially and is inexpensive. . Some melamine compounds are substituted with ureas such as urea, thiourea and ethylene urea, guanamines such as benzoguanamine and acetoguanamine, phenols such as phenol, cresol, alkylphenol, resorcin, hydroquinone and pyrogallol, and aniline. It may be.

  Examples of the aldehyde compound include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, furfural and the like, and formaldehyde and paraformaldehyde are preferable from the viewpoint of reactivity with the melamine compound. The addition amount of the aldehyde compound is 1.1 to 6.0 times mol, preferably 1.2 to 4.0 times mol in terms of a molar ratio to the melamine compound.

  As a solvent that can be used, water is particularly preferable, but it may be used as a mixed solvent of water and an organic solvent. In this case, the organic solvent that can be used is preferably a solvent that can dissolve the initial condensate of the melamine resin. For example, alcohols such as methanol, ethanol, and propanol, dioxane, tetrahydrofuran, and 1,2 -Ethers such as dimethoxyethane, and polar solvents such as dimethylformamide and dimethylsulfoxide.

  The reaction between the melamine compound and the aldehyde compound is carried out at a pH of 8 to 9, and the reaction can be carried out by adding a base if necessary. Usable bases such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and aqueous ammonia can be used as the base that can be used. An initial condensate of melamine resin having a reaction temperature of 25 to 100 and a molecular weight of about 200 to 700 can be obtained.

  Further, by reacting the initial condensate of melamine resin with alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol in the presence of a small amount of acidic substance, an initial condensate of melamine resin modified with alcohol is obtained. Obtainable.

  The amount of the initial condensation product of the melamine resin varies depending on the kind of the core material powder to be used, but in many cases it is 0.1 to 15% by weight, preferably 0.5 to 10% by weight.

  In the present invention, the reaction operation in the step (1) of obtaining the core material powder coated with the melamine resin comprises preparing a solvent containing the core material powder, and adding the initial condensate of the melamine resin to the solvent. A method of adding and conducting a polymerization reaction of the initial condensate, a method of adding the core material powder to a solvent containing the initial condensate of the melamine resin and performing a polymerization reaction of the initial condensate, or a core material powder A predetermined amount of the melamine compound and the aldehyde compound, an alkali agent as necessary, and a polymerization reaction of the initial condensate of the melamine resin in a solvent can be used. In addition, an acid catalyst is added to the polymerization reaction as necessary, and the reaction is carried out at 40 to 100 ° C. under heating, and after the completion of the reaction, solid-liquid separation is carried out by a conventional method, followed by drying at 60 to 180 ° C. By spray-drying the liquid as it is, a core powder coated with melamine resin can be obtained.

  The acid catalyst that can be used in the polymerization reaction is not particularly limited. For example, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, methanesulfonic acid, benzenesulfonic acid, paratoluenesulfonic acid, alkylbenzenesulfonic acid, sulfamine. Sulfonic acids such as acids, and organic acids such as formic acid, oxalic acid, benzoic acid, and phthalic acid can be used.

  The catalytic treatment step (2) includes capturing the noble metal ions in the core powder having the ability to capture noble metal ions or imparting the ability to capture noble metal ions by surface treatment, and then reducing the noble metal ions. This is a step of supporting a noble metal on the surface of the core powder. In the initial thin film forming step (3), the core material powder carrying the noble metal is dispersed and mixed in an initial thin film forming liquid containing nickel ions, a reducing agent and a complexing agent, and the nickel ions are reduced to reduce the core material. This is a step of forming an initial thin film of nickel on the surface of the powder. The electroless plating step (4) is a step of producing a plating powder having a nickel coating on the surface of the core material powder by electroless plating. Hereinafter, each process is explained in full detail.

(2) Catalytic treatment step The core powder coated with the melamine resin obtained in the step (1) has a surface capable of capturing noble metal ions, or has a capability of capturing noble metal ions. Surface modified. The noble metal ions are preferably palladium or silver ions. Having a precious metal ion scavenging ability means that the precious metal ion can be captured as a chelate or salt.

Next, the core powder is dispersed in a dilute acidic aqueous solution of a noble metal salt such as palladium chloride or silver nitrate. As a result, noble metal ions are trapped on the powder surface. The noble metal salt concentration is sufficiently in the range of 1 × 10 ⁻⁷ to 1 × 10 ⁻² mol per 1 m ² of the surface area of the powder. The core powder with the precious metal ions captured is separated from the system and washed with water. Subsequently, the core material powder is suspended in water, and a reducing agent is added thereto to reduce the noble metal ions. As a result, the noble metal is supported on the surface of the core powder. Examples of the reducing agent include sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, formalin and the like.

  Before capturing the noble metal ions on the surface of the core powder, a sensitization treatment for adsorbing tin ions on the powder surface may be performed. In order to adsorb tin ions on the powder surface, for example, the surface-modified core material powder may be put into an aqueous solution of stannous chloride and stirred for a predetermined time.

(3) Initial thin film forming step The initial thin film forming step is mainly performed for the purpose of smoothing uniform precipitation of nickel on the core material powder. In the initial thin film forming step, first, the core material powder supporting the noble metal is sufficiently dispersed in water. For the dispersion, a shearing dispersion device such as a colloid mill or a homogenizer can be used. In dispersing the core powder, for example, a dispersant such as a surfactant can be used as necessary. The aqueous suspension thus obtained is dispersed and mixed in an initial thin film forming liquid containing nickel ions, a reducing agent and a complexing agent. Thereby, the reduction reaction of nickel ions is started, and an initial thin film of nickel is formed on the surface of the core material powder. As described above, since the initial thin film forming step is mainly performed for the purpose of uniform precipitation, the formed initial thin film of nickel may be thin enough to smooth the surface of the core powder. From this viewpoint, the thickness of the initial thin film is preferably 0.001 to 2 μm, particularly preferably 0.005 to 1 μm. The thickness of the initial thin film can be calculated from the amount of nickel ions added and chemical analysis.

From the viewpoint of forming the initial thin film having the thickness described above, the concentration of nickel ions in the initial thin film forming liquid is 2.0 × 10 ^{−4 to} 1.0 mol / liter, particularly 1.0 × 10 ^{−3 to} 0.1. Mole / liter is preferred. As the nickel ion source, a water-soluble nickel salt such as nickel sulfate or nickel chloride is used. From the same viewpoint, the concentration of the reducing agent in the initial thin film forming solution is preferably 4 × 10 ^{−4 to} 2.0 mol / liter, particularly 2.0 × 10 ^{−3 to} 0.2 mol / liter. As the reducing agent, those similar to those used for the reduction of the noble metal ions described above can be used.

The initial thin film forming liquid preferably contains a complexing agent. The complexing agent is a compound having a complex forming action on the metal ion to be plated. In this embodiment, an organic carboxylic acid or a salt thereof such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid or gluconic acid, or an alkali metal salt or ammonium salt thereof can be used as the complexing agent. Further, amine compounds such as glycine, alanine, ethylenediamine, diethylenetriamine, triethylenetetramine, pentaethylenehexamine and other compounds having an amino group can also be used. These complexing agents can be used alone or in combination of two or more. From the viewpoint of the solubility of the complexing agent, the amount of the complexing agent in the initial thin film forming liquid is preferably 0.003 to 10 mol / liter, particularly preferably 0.006 to 4 mol / liter.
From the viewpoint that an initial thin film can be easily formed, the concentration of the core material powder in the aqueous suspension is preferably 0.1 to 500 g / liter, particularly preferably 0.5 to 300 g / liter.

The aqueous suspension obtained by mixing the aqueous suspension containing the core powder and the initial thin film forming liquid is then subjected to an electroless plating process described later. In the aqueous suspension before being subjected to the electroless plating step, the ratio of the total surface area of the core powder contained in the aqueous suspension to the volume of the aqueous suspension (this ratio is generally a load). (Referred to as “amount”) is preferably 0.1 to 15 m ² / liter, particularly 1 to 10 m ² / liter from the viewpoint that a nickel film having a film having excellent adhesion can be easily formed. If the load is too high, the reduction of nickel ions in the liquid phase will be significant in the electroless plating process described later, and a large amount of nickel fine particles will be generated in the liquid phase, which will adhere to the surface of the core powder. Therefore, it becomes difficult to form a uniform nickel film.

(3) Electroless plating step In the electroless plating step, (a) an aqueous suspension containing the core material powder on which an initial thin film is formed and the complexing agent, (b) a nickel ion-containing liquid, and (c) Three liquids containing a reducing agent are used. As the aqueous suspension (a), the aqueous suspension obtained in the above-described initial thin film formation step may be used as it is.

  Separately from the aqueous suspension of (a), two liquids, a nickel ion-containing liquid (b) and a reducing agent-containing liquid (c), are prepared. The nickel ion-containing liquid is an aqueous solution of a water-soluble nickel salt such as nickel sulfate or nickel chloride, which is a nickel ion source. The concentration of nickel ions is preferably 0.1 to 1.2 mol / liter, particularly 0.5 to 1.0 mol / liter because a nickel film having excellent adhesion can be easily formed. .

  The nickel ion-containing liquid preferably contains a complexing agent of the same type as the complexing agent contained in the aqueous suspension. That is, it is preferable that the same kind of complexing agent is contained in both the aqueous suspension (a) and the nickel ion-containing liquid (b). As a result, a nickel film having excellent adhesion can be easily formed. The reason for this is not clear, but by adding a complexing agent to both the aqueous suspension (a) and the nickel ion-containing liquid (b), the nickel ions are stabilized, and the reduction reaction is rapid. It is presumed that this is hindered from proceeding to the next stage.

  The concentration of the complexing agent in the nickel ion-containing liquid (b) affects the formation of the nickel film in the same manner as the concentration of the complexing agent in the aqueous suspension (a). From this viewpoint and the viewpoint of the solubility of the complexing agent, the amount of the complexing agent in the nickel ion-containing liquid is preferably 0.006 to 12 mol / liter, particularly 0.012 to 8 mol / liter.

  The reducing agent-containing liquid (c) is generally an aqueous solution of a reducing agent. As the reducing agent, those similar to those used for the reduction of the noble metal ions described above can be used. It is particularly preferable to use sodium hypophosphite. Since the concentration of the reducing agent affects the reduction state of nickel ions, it is preferably adjusted to a range of 0.1 to 20 mol / liter, particularly 1 to 10 mol / liter.

  Two liquids, the nickel ion-containing liquid (b) and the reducing agent-containing liquid (c), are added individually and simultaneously to the aqueous suspension (a). As a result, nickel ions are reduced, and nickel is deposited on the surface of the core powder to form a film. The addition rate of the nickel ion-containing liquid and the reducing agent-containing liquid is effective in controlling the nickel deposition rate. The deposition rate of nickel affects the formation of a nickel film with good adhesion. Therefore, it is preferable to control the deposition rate of nickel by adjusting the addition rate of both solutions to 1 to 10,000 nm / hour, particularly 5 to 300 nm / hour. The deposition rate of nickel can be obtained by calculation from the addition rate of the nickel ion-containing liquid.

While the two liquids are added to the aqueous suspension, it is preferable to keep the loading in the range of 0.1 to 15 m ² / liter, particularly 1 to 10 m ² / liter. Thereby, nickel is deposited uniformly. For the same reason, it is also preferable that the loading amount at the time when the addition of the two liquids is completed and the reduction of nickel ions is completed is within this range.

  Depending on the type of reducing agent used, during the nickel ion reduction reaction, the pH of the aqueous suspension is maintained in the range of 3 to 13, particularly 4 to 11, in order to form a water-insoluble precipitate of nickel. It is preferable from the point which prevents. In order to adjust the pH, for example, a predetermined amount of a pH adjusting agent such as sodium hydroxide may be added to the reducing agent-containing liquid.

  The obtained plating powder is separated after filtration and water washing are repeated several times. Further, as an additional process, a gold plating layer as the uppermost layer may be formed on the nickel film. The gold plating layer can be formed according to a conventionally known electroless plating method. For example, by adding an electroless plating solution containing ethylenediaminetetraacetic acid tetrasodium, trisodium citrate and potassium gold cyanide, adjusted to pH with sodium hydroxide, to an aqueous suspension of plating powder, A gold plating layer is formed on the film. The thickness of the gold plating layer is generally about 0.001 to 0.5 μm. The thickness of the gold plating layer can be calculated from the amount of gold ions added and chemical analysis.

  In this way, a plating powder is obtained in which a nickel film is formed on the surface of the core powder. The nickel film in the plating powder has excellent adhesion to the core material powder. The thickness of the nickel film has a considerable influence on its adhesion and heat resistance, and if the film is too thick, it tends to fall from the core powder and the conductivity tends to decrease. On the contrary, even if the film is too thin, desired conductivity cannot be obtained. From these viewpoints, the thickness of the nickel coating is preferably about 0.005 to 10 μm, particularly about 0.01 to 2 μm. The thickness of the nickel film can be measured, for example, by observation with a scanning electron microscope, or can be calculated from the amount of nickel ions added or chemical analysis.

  The plating powder of the present invention thus obtained includes, for example, an anisotropic conductive film (ACF), a heat seal connector (HSC), a conductive material for connecting electrodes of a liquid crystal display panel to a circuit board of a driving LSI chip, a polarizing plate It is suitably used for such applications.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1-3]
(1) Melamine resin coating step In a four-necked flask equipped with a condenser, 100 parts by weight of the core powder shown in Table 1, 100 parts by weight of water, 3 parts by weight of melamine, and 8 parts by weight of 37% formalin were charged and stirred under 5 parts. % Aqueous sodium carbonate solution was added to adjust the pH to 9.0. Next, the temperature was raised to 75 ° C., and the reaction was conducted with stirring for 2 hours. After completion of the reaction, the mixture was cooled, filtered, washed with water, and dried and cured at 150 ° C. for 6 hours under reduced pressure (5 mmHg or less) to obtain a core material powder coated with 2.1% by weight of melamine resin.

(2) Catalytic Treatment Step 200 ml of stannous chloride aqueous solution was added to 200 ml of an aqueous slurry containing 7.5% by weight of the melamine-coated core material powder obtained in the step (1). The concentration of this aqueous solution was 5 × 10 ⁻³ mol / L. The mixture was stirred at room temperature for 5 minutes, and sensitization treatment was performed to adsorb tin ions to the surface of the melamine-coated core material powder. Subsequently, the aqueous solution was filtered, repulped once and washed with water. Next, 400 mL of an aqueous slurry containing 3.75% by weight of melamine-coated core material powder was prepared and maintained at 60 ° C. While stirring the slurry using ultrasonic waves, 2 mL of an aqueous 0.11 mol / L palladium chloride solution was added. The state of stirring as it was was maintained for 5 minutes, and an activation treatment for trapping palladium ions on the surface of the melamine-coated core material powder was performed. The aqueous solution was then filtered and washed once with repulp hot water. Next, 200 ml of an aqueous slurry containing 7.5% by weight of melamine-coated core material powder was prepared. The slurry was stirred while using ultrasonic waves, and 20 mL of a mixed aqueous solution of 0.017 mol / liter dimethylamine borane and 0.16 mol / liter boric acid was added thereto. The mixture was stirred for 2 minutes while using ultrasonic waves at room temperature to reduce palladium ions.
(3) Initial thin film formation process

200 mL of an aqueous slurry containing 7.5% by weight of the melamine-coated core powder treated in the step (2) was mixed with 0.087 mol / L sodium tartrate, 0.005 mol / L nickel sulfate and 0.012 mol / L. An aqueous suspension was obtained by adding to the initial thin film-forming solution composed of sodium hypophosphite while stirring. The initial thin film forming liquid was heated to 75 ° C., and the liquid volume was 2 L. Immediately after the slurry was introduced, hydrogen generation was observed, confirming the start of initial thin film formation.
(4) Electroless plating process

  Nickel ion-containing liquid consisting of 0.86 mol / L nickel sulfate and 0.17 mol / L sodium tartrate and 2.57 mol / L hypophosphorous acid in the aqueous suspension obtained in the initial thin film formation step Two solutions of a reducing agent-containing solution consisting of sodium and 2.6 mol / L sodium hydroxide were added at an addition rate of 8 mL / min. The amount of the added solution was adjusted so that the deposited film thickness was 0.2 microns. Generation of hydrogen was observed immediately after the addition of the two liquids, confirming the start of the plating reaction. After the addition of the two liquids was completed, stirring was continued while maintaining the temperature at 75 ° C. until hydrogen bubbling stopped. Subsequently, the aqueous suspension was filtered, and the filtrate was washed with repulp three times and then dried with a vacuum dryer at 110 ° C. Thereby, the plating powder which has a nickel- phosphorus alloy plating film was obtained.

[Comparative Example 1-3]
In Examples 1 to 3, plated powder was obtained by the same operation except that the step (1) was not performed.

[Comparative Examples 4 to 6]
In Example 1, the plating powder was obtained by the same operation as Example 1-3 except having replaced the process of (1) with the following (1-1) process.
(1-1) Step 10 parts by weight of the same styrene resin used in Example 1 was added to 100 parts by weight of an aqueous solution containing 1.0% by weight of the surface treatment agent shown in Table 1, and immersed for 1 hour at room temperature. Next, the core material powder which dried by 110 degreeC and coat | covered the surface treating agent was prepared.

[Comparative Example 7]
In Example 1, plating powder was obtained by the same operation as Example 1 except having replaced the process of (1) with the following (1-2) process.
(1-2) Step 100 parts by weight of core material powder is charged in 2 L of an etching solution consisting of 2.0 mol / L of chromic anhydride and 3.6 mol / L of sulfuric acid, heated to 70 ° C., and stirred for 10 minutes. did. Subsequently, filtration and washing were repeated to obtain an etching-treated core material powder.

  About the obtained plating powder, the thickness of the plating film and the adhesion of the plating film were measured and evaluated by the following methods. The results are shown in Table 2. Further, the amount of chromium remaining in the plating powder was measured, and the results are also shown in Table 2.

[Thickness of plating film]
The plating powder was immersed in nitric acid to dissolve the plating film, the film components were quantified by ICP or chemical analysis, and the thickness was calculated by the following equation.
A = [(r + t) ³ −r ³ ] d ₁ / rd ₂
A = W / 100-W
In the formula, r is the radius of the core powder (μm), t is the thickness of the plating film (μm), d ₁ is the specific gravity of the plating film, d ₂ is the specific gravity of the core powder, and W is the metal content (weight). %).

[Adhesion of plating film]
Plating powder 2.2 g and zirconia beads 90 g having a diameter of 3 mm were placed in a 100 ml mayonnaise bottle. Further, 10 ml of toluene was added to the mayonnaise bottle using a whole pipette. The inside of the mayonnaise bottle was stirred for 10 minutes at 400 rpm using a stirrer (three one motor). After completion, the plating powder and zirconia beads were separated. The plating powder was observed with a scanning electron microscope, and the peeling degree of the plating film was evaluated according to the following criteria.
○: Peeling of the plating film was not observed.
X: Peeling of the plating film was observed.

[Chromium content]
The plating powder was immersed in nitric acid to dissolve the plating film, and further sulfuric acid was added for thermal decomposition. The amount of chromium was measured by ICP from the obtained decomposition solution.

注）表面処理剤１；γ―アミノプロピルトリエトキシシラン、表面処理剤２；Ｎ−β（アミノエチル）γ―アミノプロピルトリメトキシシラン、表面処理剤３；γ―メタアクリロキシプロピルトリメトキシシラン

Note) Surface treatment agent 1; γ-aminopropyltriethoxysilane, surface treatment agent 2; N-β (aminoethyl) γ-aminopropyltrimethoxysilane, surface treatment agent 3; γ-methacryloxypropyltrimethoxysilane

注）Ｎ．Ｄ．は検出限界０．００２ｍｇ／ｇ−めっき粉体以下であることを示す。

Note) N. D. Indicates that the detection limit is 0.002 mg / g or less of the plating powder.

  As is apparent from the results shown in Table 2, it can be seen that the plating powders of the respective examples (products of the present invention) are excellent in the adhesion of the plating film and are substantially free of chromium. On the other hand, although the plating powder of Comparative Examples 1-6 does not contain chromium, it turns out that plating is easy to peel off. Moreover, although the plating powder of the comparative example 7 is excellent in the adhesiveness of a plating film, it turns out that chromium is contained in plating powder.

Claims (6)

  A conductive electroless plating powder, wherein the surface of a core powder is coated with a melamine resin, and further a metal film is formed by electroless plating.   The conductive electroless plating powder according to claim 1, wherein the core material powder is hydrophobic.   The conductive electroless plating powder according to claim 1 or 2, wherein the core material powder has an average particle size of 0.5 to 100 µm.   The conductive electroless plating powder according to claim 1 or 2, wherein the core material powder has an average particle diameter of 1 to 20 µm.   The conductive electroless plating powder according to claim 1, wherein a spherical powder is used as the core material powder.   A step of bringing a core material powder and an initial condensate of melamine resin into contact with each other to carry out a polymerization reaction of the initial condensate to obtain a core material powder coated with melamine resin; A method for producing a conductive electroless plating powder, comprising: a step of supporting a noble metal on a surface; and a step of subjecting a core powder carrying the noble metal to electroless plating.