JP7232053B2 - Method for manufacturing glossy plating film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a glossy plating film and an electronic component having the same.

Among connecting parts such as low-current (signal system) switches and connectors used in electrical and electronic equipment, those that are repeatedly used with a low contact load require high connection reliability. A conductive metal member whose surface is plated with a noble metal is used.

In addition, the plating film is required to have moderate gloss and excellent ductility, as well as to have nonporosity, corrosion resistance, low friction, and low contact resistance.

Patent Literature 1 describes rolling a plated film to smooth the surface. However, the problem was that the manufacturing method was complicated.

Also known is a method of adding a leveling agent to the plating bath to smooth the surface of the resulting plating film. For example, Patent Document 2 describes that by using an aminosulfonic acid-based polymer as a leveling agent, small lumps of metal crystals are reduced and a plated film with high glossiness is obtained.

However, the glossiness of the plated film is still insufficient, and it has been desired to further increase it.

JP 2015-117424 A JP 2016-148023 A

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a plating film having high glossiness and a method for producing the same.
Another object of the present invention is to provide an electronic component having a plated film with high glossiness.
Another object of the present invention is to provide a novel brightening agent that imparts high gloss to a plated film.

As a result of intensive studies by the present inventors in order to solve the above problems, when a plating bath containing nanodiamond particles is used, the growth of precious metal crystals is inhibited by the nanodiamond particles and the surface is smoothed by miniaturization. It was found that a plating film having a high glossiness was obtained. The present invention has been completed based on these findings.

That is, the present invention provides a plating film containing a noble metal matrix and nanodiamond particles dispersed in the noble metal matrix, the plating film having a glossiness of 250 GU or more at an incident angle of 60°.

The present invention also provides the aforementioned plated film, which is a plated film obtained using a plating bath containing noble metal ions and nanodiamond particles.

The present invention also provides the plating film having a glossiness at an incident angle of 60° that is 20 GU or more higher than a plating film obtained using a plating bath having the same composition except that it does not contain nanodiamond particles. do.

The present invention also provides the plating film having a surface roughness (Ra) of 0.5 μm or less.

The present invention also provides the above plating film, wherein the particle size (D50) of the nanodiamond particles dispersed in the noble metal matrix is in the range of 4 to 100 nm as determined by the SEM method.

The present invention also provides the above plating film, wherein the nanodiamond particles are nanodiamond particles provided with a surface modification group containing a steric repulsion group.

The present invention also provides the above plating film, wherein the nanodiamond particles are nanodiamond particles having surface modification groups containing polyglycerol chains.

The present invention also provides the above plating film, wherein the content of nanodiamond particles is 0.5 to 25% by area of the plating film.

The present invention also provides a plating bath containing noble metal ions and nanodiamond particles, the content of the nanodiamond particles is 0.001 to 1.0 g/L, and the light transmittance of light with a wavelength of 600 nm is 95%. Provided is a method for producing a plated film by electrolytic plating using the above plating bath.

The present invention also provides an electronic component comprising the plating film described above.

The present invention also provides a plating film brightener comprising nanodiamond particles having surface modification groups comprising polyglycerol chains.

The plated film of the present invention has a structure in which nanodiamond particles are highly dispersed in a noble metal matrix, and the nanodiamond particles inhibit the growth of crystals of the noble metal and refine the crystal grains, so that the surface is extremely smooth. have sex. Therefore, the plating film of the present invention has high glossiness. In addition, as described above, since it contains nanodiamond particles, it is also excellent in oxidation resistance. Therefore, the plating film of the present invention is suitably used for connecting parts for electronic devices, ornaments, and the like.
In addition, since the plated film of the present invention has a smooth surface, it has a low coefficient of friction. Therefore, it has low contact resistance, excellent conductivity, and low current (signal system) connection parts (or electrical contacts) such as low current (signal system) switches and connectors used in electrical and electronic equipment that are repeatedly used with a low contact load. Suitable for parts.

FIG. 2 is an enlarged schematic diagram showing an example of ND particles [1] having surface modification groups according to the present invention, in which surface modification groups [3] are provided on the surface of ND particles (parts) [2]. 3 is a diagram showing the results of SEM observation of the cross section of the plated film obtained in Example 1. FIG. 3 is a diagram showing the results of SEM observation of the cross section of the plated film obtained in Comparative Example 1. FIG. FIG. 10 is a view showing the results of SEM observation of the cross section of the plated film obtained in Comparative Example 2;

[Plating film]
The plated film of the present invention is a plated film containing a noble metal matrix and nanodiamond particles (hereinafter sometimes referred to as "ND particles") dispersed in the noble metal matrix. In the plated film of the present invention, the plated film obtained only by plating and not subjected to surface flattening treatment or the like has a glossiness of 250 GU or more at an incident angle of 60°. and

The glossiness of the plating film of the present invention at an incident angle of 60° is 250 GU or more, preferably 300 GU or more, more preferably 400 GU or more, still more preferably 500 GU or more, still more preferably 550 GU or more, particularly preferably 600 GU or more, most preferably 600 GU or more. is greater than or equal to 700 GU. Incidentally, the upper limit of the glossiness is 1000 GU.

In addition, the same plating film as the plating film of the present invention except that it does not contain ND particles, that is, a plating bath having the same composition except that it does not contain ND particles, is used, and the plating treatment conditions are the same except that the plating bath is different as described above. Compared to the plated film obtained in , the plated film of the present invention has a glossiness at an incident angle of 60 °, for example, 20 GU or more (for example, 20 to 500 GU) higher, preferably 50 GU or more, more preferably 100 GU or more, and particularly preferably is higher than 150 GU, most preferably higher than 300 GU, most preferably higher than 400 GU.

Furthermore, since the plating film of the present invention contains ND particles (particularly, hydrophilic ND particles described later), it has excellent oxidation resistance, and the plating film immediately after production is not exposed to direct sunlight (at a temperature of 25 ° C., The increase in the amount of noble metal oxide in the plated film after storage for 7 days at 50% humidity is, for example, less than 1% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.3% by weight, most preferably Less than 0.1% by weight.

In the plating film of the present invention, the surface roughness (Ra) of the plating film obtained by performing only plating treatment and not subjected to surface flattening treatment or the like is, for example, 0.5 μm or less, preferably It is 0.4 μm or less, more preferably 0.3 μm or less, still more preferably 0.29 μm or less, still more preferably 0.2 μm or less, particularly preferably 0.15 μm or less, and most preferably 0.1 μm or less.

In the plating film of the present invention, the surface roughness (Ra) of the plating film obtained by performing only plating treatment and not subjected to surface flattening treatment etc. (for example, when the film thickness is 1 μm or more) The surface roughness, preferably the surface roughness when the film thickness is 1.5 μm or more) is, for example, 0.5 μm or less, preferably 0.4 μm or less, more preferably 0.3 μm or less, further preferably 0.29 μm or less. , more preferably 0.2 μm or less, particularly preferably 0.15 μm or less, and most preferably 0.1 μm or less.

In the plated film of the present invention, the particle diameter (D50) of the ND particles dispersed in the noble metal matrix by the SEM method is, for example, in the range of 4 to 100 nm, preferably 10 to 80 nm, particularly preferably 20 to 60 nm, and most preferably. is 30-50 nm.

In addition, in the plating film of the present invention, the content of ND particles is, for example, 0.5 to 25 area %, preferably 2 to 20 area %, particularly preferably 5 to 15 area % of the area of the plating film. The plated film of the present invention contains ND particles in the above range, and therefore has excellent glossiness. If the ND particle content is less than the above range, glossiness tends to decrease. On the other hand, even if the content of ND particles exceeds the above range, the effect of further improving the glossiness is not obtained, and rather the adhesion between the plating film and the substrate deteriorates, and there is a tendency for the plating film to peel off easily.

The ND particles are fine particles having a primary particle size of 10 nm or less. Since ND particles have a large proportion of surface atoms, the sum of van der Waals forces that can act between surface atoms of adjacent particles is large, and aggregation is likely to occur. In addition to this, a phenomenon called agglutination can occur in which coulomb interactions between crystal planes of adjacent crystallites contribute to bring them together very strongly. ND particles have such a unique property that superimposed interactions can occur between crystallites or primary particles.

Accordingly, ND particles having a hydrophilic surface (=hydrophilic ND particles) are preferable as the ND particles in the present invention because they are easily dispersed in the plating bath.

Hydrophilic ND particles include (1) ND particles coated with a hydrophilic polymer and (2) ND particles modified with a hydrophilic polymer. In the present invention, among others, (2) ND particles modified with a hydrophilic polymer have steric repulsion (= effect of physically preventing aggregation due to steric hindrance) of the surface-modifying hydrophilic polymer. , is particularly preferable in that excellent dispersibility can be obtained.

Examples of the hydrophilic polymer include polyglycerin, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, poly(meth)acrylic acid, polyacrylamide, polyethyleneimine, vinyl ether polymers, water-soluble polyesters (e.g., polydimethylolpropionic acid esters, etc.), natural polymer polysaccharides such as cellulose, dextrin, and starch, and derivatives thereof (eg, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, etc.). In the present invention, among others, at least one selected from polyglycerin, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and poly(meth)acrylic acid is preferred, and polyglycerin is particularly preferred.

Therefore, the ND particles in the present invention are preferably ND particles provided with a surface modifying group containing a hydrophilic polymer-derived steric repulsive group. It is preferred to use ND particles (=ND particles with surface modification groups containing polyglycerol chains).

ND particles equipped with a surface modification group containing a hydrophilic polymer-derived steric repulsive group or ND particles modified with a surface modification group containing a polyglycerol chain are more favorable than ND particles without a hydrophilic surface modification group. In the plating bath, the surface-modifying groups act as steric hindrance, thereby suppressing the aggregation of the ND particles and exhibiting excellent dispersibility.

An ND particle modified with a surface modifying group containing a polyglycerol chain has, for example, a structure in which a polyglycerol chain represented by the following formula (1) is bonded to the surface functional group of the ND particle. In the formula below, n represents the number of glycerin units constituting the polyglycerin chain and is an integer of 1 or more.
HO—(C ₃ H ₆ O ₂ ) _n —H (1)

C ₃ H ₆ O ₂ in parentheses in formula (1) has a structure represented by formula (2) and/or (3) below.
-CH ₂ -CHOH-CH ₂ O- (2)
-CH( _CH2OH ) _CH2O- (3)

The polyglycerin chains include linear, branched, and cyclic polyglycerin chains.

The amount of the surface modification group introduced is, for example, about 0.4 to 1.0 parts by mass, preferably 0.5 to 0.9 parts by mass, and particularly preferably 0.6 to 0.6 parts by mass, per 1 part by mass of the ND particle portion. It is 0.8 parts by mass. If the amount of surface-modifying group introduced is less than the above range, it tends to be difficult to prevent aggregation of the ND particles. On the other hand, if the amount of the surface modifying group introduced exceeds the above range, the ND particles tend to aggregate due to the entanglement of the surface modifying groups. The mass ratio of the surface modification group portion and the ND particle portion can be obtained by measuring the mass change during heat treatment or the composition ratio by elemental analysis using a differential thermal balance analyzer (TG-DTA).

[Manufacturing method of plating film]
The plated film of the present invention can be produced by a well-known and commonly used electrolytic plating method (preferably electrolytic composite plating method). More specifically, a member to be plated (for example, a conductive substrate such as a copper substrate) is immersed in a plating bath containing noble metal ions and ND particles, and electrolysis is performed to remove the noble metal ions and ND particles from the surface of the member. ND particles can be incorporated into the coating of the noble metal, and by continuing this process until a desired thickness is achieved, the plating film (or noble metal- A plated film made of an ND particle composite material) can be produced.

The thickness of the plated film can be appropriately set according to the application. When used for coating the surface of a conductive metal member in connection parts such as switches and connectors or ornaments, the thickness of the plating film is, for example, about 0.1 to 50 μm, preferably 0.5 to 30 μm, particularly preferably 0.5 to 30 μm. 1-20 μm, most preferably 1.5-10 μm.

(plating bath)
The plating bath in the present invention contains a plating solution and ND particles. The content of ND particles in the plating bath is, for example, 0.001 to 1.0 g/L (the lower limit is preferably 0.003 g/L, more preferably 0.006 g/L, and still more preferably 0.01 g/L). L, particularly preferably 0.03 g/L, most preferably 0.06 g/L.The upper limit is preferably 0.5 g/L, particularly preferably 0.3 g/L. If the ND particle content is less than the above range, the glossiness of the obtained plating film tends to decrease. On the other hand, even if the content of ND particles exceeds the above range, the effect of further improving the glossiness of the obtained plating film cannot be obtained, and rather the adhesion between the plating film and the substrate deteriorates, and there is a tendency that peeling tends to occur. There is

The plating bath contains ND particles in a highly dispersed (or colloidally dispersed) state, and thus has excellent transparency. is, for example, 95% or more. Also, the haze value (cloudiness) is, for example, 0 to 5, preferably 0 to 2, particularly preferably 0 to 1, most preferably 0 to 0.5, particularly preferably 0 to 0.4. A perfect transparency has a haze value of 0, and the haze value increases as the haze increases. The haze value can be measured by a method conforming to JIS K7136.

The particle size (D10) of the ND particles in the plating bath is, for example, 100 nm or less, preferably 60 nm or less, particularly preferably 50 nm or less, and most preferably 40 nm or less. The lower limit of the particle size (D10) of ND particles is, for example, 10 nm.

The particle size (D50) of the ND particles in the plating bath is, for example, 100 nm or less, preferably 70 nm or less, particularly preferably 60 nm or less, and most preferably 50 nm or less. The lower limit of the particle size (D50) of ND particles is, for example, 10 nm.

The particle size (D90) of the ND particles in the plating bath is, for example, 100 nm or less, preferably 90 nm or less, and particularly preferably 80 nm or less. The lower limit of the particle size (D90) of ND particles is, for example, 10 nm.

Incidentally, the particle size of the ND particles in the plating bath can be measured by a dynamic light scattering method.

The pH of the plating bath is, for example, about 2 in the case of a plating bath containing gold ions as noble metal ions, and is, for example, about 1 in the case of a plating bath containing rhodium ions as noble metal ions. It is preferable in that a plating film having Incidentally, the pH can be adjusted using a pH adjuster or the like.

Since the plating bath contains hydrophilic ND particles having excellent dispersibility as described above, it is not necessary to contain a surfactant. The content of the surfactant in the plating bath (for example, a nonionic surfactant having a molecular weight of 30,000 to 200,000) is, for example, less than 0.5 g/L, preferably 0.1 g/L or less, and particularly preferably is 0.05 g/L or less, most preferably 0.01 g/L or less, and is particularly preferably substantially free of the surfactant.

The plating bath can be prepared, for example, by adding an ND particle dispersion to a plating solution described below.

(Plating solution)
The plating solution in the present invention contains essential components for preparing a plating film and does not contain the ND particles described above. The plating solution contains at least noble metal ions (for example, at least one selected from gold ions, silver ions, platinum ions, palladium ions, rhodium ions, iridium ions, ruthenium ions, and osmium ions).

The plating solution can be prepared by blending, for example, a noble metal salt, a conductivity salt, a complexing agent, an additive for adjusting the appearance and physical properties of the film, and the like. The noble metal salt exists as noble metal ions in the plating bath. In addition, it may exist as a noble metal oxyacid ion or a noble metal complex ion combined with a complexing agent.

The noble metal salt concentration contained in the plating solution is, for example, 0.01 to 0.5 mol/L, preferably 0.05 to 0.2 mol/L.

Examples of the complexing agent include citric acid, lactic acid, malic acid, glycolic acid, and salts thereof. The concentration of the complexing agent contained in the plating solution is, for example, 0.02 to 1.0 mol/L, preferably 0.1 to 0.5 mol/L.

Plating solutions for gold plating include, for example, mixtures of gold salt such as gold potassium chloride; and conductivity salt such as sulfuric acid. In the present invention, for example, commercially available products such as the product name "Aurobond XPH20" (manufactured by Nippon Electroplating Engineers Co., Ltd.) can be used.

Plating solutions for rhodium plating include, for example, rhodium salts such as rhodium sulfate and rhodium phosphate; sulfuric acid and phosphoric acid as conductivity salts; and mixtures such as sulfamic acid and organic carboxylic acids as stress reducers. be done. In the present invention, for example, commercially available products such as the trade name "Rhodex" (manufactured by Nippon Electroplating Engineers Co., Ltd.) can be used.

(ND particle dispersion)
The ND particle dispersion liquid is obtained by dispersing ND particles in a dispersion medium (preferably water). The ND particle concentration in the ND particle dispersion liquid is, for example, about 1 to 100 g/L.

As the ND particles, hydrophilic ND particles are preferable in terms of excellent dispersibility, ND particles modified with a hydrophilic polymer are particularly preferable, and surface modification containing a steric repulsive group derived from a hydrophilic polymer is most preferable. ND particles with groups, particularly preferably ND particles with surface modification groups containing polyglycerol chains.

The particle size (D50) of the ND particles in the ND particle dispersion is, for example, 100 nm or less, preferably 70 nm or less, particularly preferably 60 nm or less, and most preferably 50 nm or less. The lower limit of the particle size (D50) of ND particles is, for example, 10 nm. The particle size of the ND particles in the ND particle dispersion can be measured by a dynamic light scattering method.

Conventionally, surfactants have been used to disperse ND particles that tend to agglomerate. For example, for the purpose of dispersing ND particles into which polyethylene glycol chains have been introduced, nonionic surfactants (especially alkylphenol surfactants such as polyethylene glycol-4-octylphenyl ether, etc.) having a molecular weight of 30,000 to 200,000 can be used. ) was used. However, there has been a problem in that quality deterioration such as reduction in glossiness and increase in contact resistance value is caused when the surfactant is mixed in the plating film as an impurity.

However, since the hydrophilic ND particles have excellent dispersibility as described above, it is not necessary to add the surfactant to the ND particle dispersion. Therefore, the content of the surfactant (in particular, a nonionic surfactant having a molecular weight of 30,000 to 200,000) in the ND particle dispersion of the present invention is, for example, less than 0.5 g/L, preferably 0 0.1 g/L or less, particularly preferably 0.05 g/L or less, most preferably 0.01 g/L or less, and it is particularly preferred that the surfactant is substantially free.

By adding the ND particle dispersion to the plating bath, it is possible to impart gloss to the obtained plating film. In addition, the effect of suppressing oxidation of the noble metal forming the plating film (oxidation resistance) can be imparted. Therefore, it can be used, for example, as a brightening agent for plating films.

(Method for preparing ND particle dispersion)
For the hydrophilic ND particles, for example, ND particles having surface functional groups such as OH, COOH, and _NH2 groups are used, and a hydrophilic polymer is directly attached to the surface functional groups of the ND particles, or a linker (such as , ester bond, amide bond, imide bond, ether bond, urethane bond, urea bond, etc.). The linker can be formed by a method such as reacting the surface functional groups of the ND particles with a condensing agent.

Then, according to the detonation method, ND particles having surface functional groups such as OH groups, COOH groups, and NH ₂ groups are obtained. In addition, ND particles having a smaller average particle size can be obtained as compared with the impact compression method. Therefore, in the present invention, the detonation method is preferred as the method for producing ND particles.

An example of a method for producing a dispersion of ND particles having surface modification groups containing polyglycerol chains is described below, but the ND particle dispersion used in the present invention is not limited to that obtained by the following production method. .

(Generation process)
First, an explosive with an electric detonator attached is placed inside a pressure-resistant container for detonation, and the container is sealed in a state in which a normal-pressure gas of atmospheric composition and the explosive used coexist in the container. The container is, for example, made of iron and has a volume of, for example, 0.5 to 40 m ³ . As an explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitroamine or hexogen (RDX) can be used. The mass ratio of TNT and RDX (TNT/RDX) is, for example, in the range of 40/60 to 60/40.

In the production process, an electric detonator is then detonated to detonate the explosive within the container. At the time of detonation, ND particles are generated by the action of the pressure and energy of the shock wave generated by the explosion, using the carbon liberated by partial incomplete combustion of the explosive used as a raw material. Adjacent primary particles or crystallites of the produced ND particles are very strongly aggregated to form an aggregate due to the effect of the van der Waals force and the contribution of the Coulomb interaction between the crystal planes.

In the production step, the mixture is then left at room temperature for about 24 hours to allow the temperature of the container and its interior to drop. After this standing to cool, the ND particles are removed by scraping with a spatula the coarse ND particles adhering to the inner wall of the container (including the agglomerate of ND particles and soot produced as described above). A crude product is obtained.

(Acid treatment step)
The acid treatment step is a step of applying a strong acid to the crude ND particles, which is a raw material, in a water solvent, for example, to remove metal oxides. The ND particle coarse product obtained by the detonation method tends to contain metal oxides, and the metal oxides are oxides of Fe, Co, Ni, etc. derived from the container or the like used in the detonation method. For example, metal oxides can be dissolved and removed from the crude ND grains by applying a predetermined strong acid in an aqueous solvent. The strong acid used in this acid treatment is preferably a mineral acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and mixtures thereof. The concentration of strong acid used in acid treatment is, for example, 1 to 50% by mass. The acid treatment temperature is, for example, 70-150.degree. The acid treatment time is, for example, 0.1 to 24 hours. Moreover, the acid treatment can be performed under reduced pressure, normal pressure, or increased pressure. After such an acid treatment, it is preferable to wash the solid content (including ND aggregates) with water, for example, by decantation until the pH of the precipitate reaches, for example, 2 to 3. When the content of metal oxides in the ND grain coarse product obtained by the detonation method is small, the above acid treatment may be omitted.

(Oxidation treatment step)
The oxidation treatment step is a step of removing graphite from the ND grain coarse product using an oxidizing agent. Graphite (black lead) is included in the ND particle crude product obtained by the detonation method, but this graphite did not form ND crystals out of the carbon liberated due to partial incomplete combustion of the explosive used. Derived from carbon. For example, graphite can be removed from the ND grain crude product by reacting a predetermined oxidizing agent in a water solvent after the acid treatment. Also, oxygen-containing groups such as carboxyl groups and hydroxyl groups can be introduced to the ND surface by applying an oxidizing agent.

Examples of oxidizing agents used in this oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, mixtures thereof, and at least one acid selected from these. and other acids (for example, sulfuric acid, etc.), and salts thereof. In the present invention, among others, it is preferable to use a mixed acid (especially a mixed acid of sulfuric acid and nitric acid) because it is environmentally friendly and has an excellent effect of oxidizing and removing graphite.

The mixing ratio of sulfuric acid and nitric acid in the mixed acid (former/latter; mass ratio) is, for example, 60/40 to 95/5, even under pressure near normal pressure (for example, 0.5 to 2 atm). , for example, at a temperature of 130° C. or higher (particularly preferably 150° C. or higher; the upper limit is, for example, 200° C.), because graphite can be efficiently oxidized and removed. The lower limit is preferably 65/35, particularly preferably 70/30. Also, the upper limit is preferably 90/10, particularly preferably 85/15, most preferably 80/20.

When the ratio of nitric acid in the mixed acid exceeds the above range, the content of sulfuric acid having a high boiling point is reduced, so that the reaction temperature becomes, for example, 120° C. or lower under pressure near normal pressure, and the graphite removal efficiency tends to decrease. There is On the other hand, when the ratio of nitric acid in the mixed acid is below the above range, the content of nitric acid, which greatly contributes to the oxidation of graphite, is reduced, so the efficiency of removing graphite tends to decrease.

The amount of the oxidizing agent (especially the mixed acid) used is, for example, 10 to 50 parts by weight, preferably 15 to 40 parts by weight, and particularly preferably 20 to 40 parts by weight, per 1 part by weight of the crude ND grains. The amount of sulfuric acid used in the mixed acid is, for example, 5 to 48 parts by mass, preferably 10 to 35 parts by mass, and particularly preferably 15 to 30 parts by mass, based on 1 part by mass of the crude ND particles. The amount of nitric acid used in the mixed acid is, for example, 2 to 20 parts by weight, preferably 4 to 10 parts by weight, particularly preferably 5 to 8 parts by weight, per 1 part by weight of the crude ND grains.

Moreover, when using the said mixed acid as an oxidizing agent, you may use a catalyst with a mixed acid. By using a catalyst, the graphite removal efficiency can be further improved. Examples of the catalyst include copper (II) carbonate and the like. The amount of the catalyst used is, for example, about 0.01 to 10 parts by mass with respect to 100 parts by mass of the crude ND particles.

The oxidation treatment temperature is, for example, 100-200.degree. The oxidation treatment time is, for example, 1 to 24 hours. The oxidation treatment can be performed under reduced pressure, normal pressure, or increased pressure.

(Drying process)
In this method, it is preferable to provide a drying step next. Residual solids are dried by heat drying in a drying oven. The heat drying temperature is, for example, 40 to 150.degree. ND powder is obtained through such a drying process.

(Oxygen oxidation process)
In the oxygen oxidation step, a gas atmosphere furnace is used to heat the ND powder in a gas atmosphere containing oxygen and having a predetermined composition. Specifically, ND powder is placed in a gas atmosphere furnace, an oxygen-containing gas is supplied or flowed to the furnace, and the inside of the furnace is heated to a temperature condition set as a heating temperature, and oxygen An oxidation treatment is performed.

The temperature conditions for the oxygen oxidation treatment are, for example, 250 to 500.degree. In order to obtain ND particles having a negative zeta potential, the temperature condition for this oxygen oxidation treatment is preferably relatively high, eg, 400-450.degree. Also, the oxygen-containing gas is a mixed gas containing an inert gas in addition to oxygen. Inert gases include, for example, nitrogen, argon, carbon dioxide, and helium. The oxygen concentration of the mixed gas is, for example, 1 to 35% by volume.

(Hydrogenation process)
Also, if ND particles with a positive zeta potential are desired, a hydrogenation step is performed after the oxygen oxidation step described above. In the hydrogenation step, the ND powder that has undergone the oxygen oxidation step is heated in a gas atmosphere of a predetermined composition containing hydrogen using a gas atmosphere furnace. Specifically, a hydrogen-containing gas is supplied or flowed to a gas atmosphere furnace in which the ND powder is arranged, and the temperature inside the furnace is raised to the temperature condition set as the heating temperature to hydrogenate. Processing is performed. The temperature condition for this hydrogenation treatment is, for example, 400 to 800.degree. Moreover, the hydrogen-containing gas is preferably a mixed gas containing an inert gas in addition to hydrogen. Inert gases include, for example, nitrogen, argon, carbon dioxide, and helium. The hydrogen concentration of the mixed gas is, for example, 1 to 50% by volume.

(Crushing process)
Even after being purified through the series of processes described above, ND particles may take the form of agglomerates (secondary particles) in which primary particles interact very strongly and aggregate. There are many. Therefore, it is preferable to perform a crushing step to separate the primary particles from the aggregate. Specifically, first, ND powder that has undergone an oxygen oxidation step or a subsequent hydrogenation step is suspended in pure water to prepare a slurry containing ND particles. In preparing the slurry, centrifugation may be performed to remove larger aggregates from the ND particle suspension, and the ND particle suspension may be subjected to ultrasonic treatment. Then, the slurry is subjected to a wet crushing treatment. Disintegration can be performed using, for example, a high shear mixer, high shear mixer, homomixer, ball mill, bead mill, high pressure homogenizer, ultrasonic homogenizer, or colloid mill. The crushing treatment may be carried out by combining these methods. From the viewpoint of efficiency, it is preferable to use a bead mill.

An aqueous dispersion of ND particles containing primary ND particles can be obtained through such a pulverization step. The dispersion liquid obtained through the pulverization step may be subjected to a classification operation to remove coarse particles.

(Drying process)
In this method, it is preferable to then provide a drying step. For example, after evaporating the liquid component from the ND particle aqueous dispersion obtained through the above steps using a spray dryer, an evaporator, or the like, The resulting residual solids are dried by heat drying in a drying oven. The heat drying temperature is, for example, 40 to 150.degree. Through such a drying process, ND particles are obtained as powder.

(Modification process)
ND particles having surface modification groups containing polyglycerol chains can be obtained, for example, by directly subjecting the ND particles obtained through the above steps to ring-opening polymerization of glycidol. ND particles have carboxyl groups and hydroxyl groups on their surfaces generated during the manufacturing process, and by reacting these functional groups with glycidol, the surface of NDs can be modified with polyglycerin chains.

The reaction (ring-opening polymerization) between ND particles and glycidol can be carried out, for example, by adding glycidol and a catalyst to ND particles under an inert gas atmosphere and heating to 50 to 100°C. As the catalyst, an acidic catalyst or a basic catalyst can be used. Examples of the acidic catalyst include trifluoroboron etherate, acetic acid, and phosphoric acid, and examples of the basic catalyst include triethylamine, pyridine, dimethylaminopyridine, triphenylphosphine, and the like.

The amount of glycidol used in the ring-opening polymerization is, for example, 20 parts by mass or more, preferably 20 to 150 parts by mass, per 1 part by mass of the ND particles. If the amount of glycidol used is less than the above range, it tends to be difficult to obtain sufficient dispersibility.

Therefore, as the ND particles in the present invention, the surface of the ND particles is provided with 20 parts by mass or more (preferably 20 to 150 parts by mass) of a ring-opening polymer of glycidol with respect to 1 part by mass of the ND particles. ND particles with surface modification groups comprising glycerol chains are preferred.

After completion of the reaction, the resulting reaction product is preferably subjected to purification treatment by, for example, filtration, centrifugation, extraction, washing with water, neutralization, or a combination thereof. As a result, an ND particle dispersion (preferably an aqueous ND particle dispersion) in the present invention is obtained.

[Electronic parts]
An electronic component according to the present invention includes the plating film described above. The electronic component of the present invention may have a plating film other than the plating film described above, and may have, for example, one or more layers of Ni/Au plating film or the like as a base plating film. . The electronic parts of the present invention include, for example, connection parts (for example, connectors, etc.) for electronic devices such as personal digital assistants (PDAs) and mobile phones.

[Brightener]
The plating film brightener of the present invention is characterized by containing nanodiamond particles having a surface modification group containing the polyglycerol chain.

The brightener may contain other components in addition to the nanodiamond particles having surface modification groups containing polyglycerol chains, but the ratio of the nanodiamond particles to the total amount of the brightener is, for example, 50%. % by mass or more, preferably 60% by mass or more, particularly preferably 70% by mass or more, most preferably 80% by mass or more, and particularly preferably 90% by mass or more.

The brightener does not require the addition of surfactants conventionally used to disperse ND particles as described above. Therefore, the content of the surfactant (for example, a nonionic surfactant having a molecular weight of 30,000 to 200,000) in the leveling agent in the present invention is, for example, less than 0.5 g/L, preferably 0.1 g/L. L or less, particularly preferably 0.05 g/L or less, most preferably 0.01 g/L or less, and it is particularly preferred that the surfactant is substantially free.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. The ND particle concentration, particle size, and zeta potential were measured by the following methods.

<ND particle concentration>
The ND particle concentration of the ND particle aqueous dispersion is obtained by weighing the weighed value of 3 to 5 g of the weighed dispersion and the dry matter (powder) remaining after evaporating water from the weighed dispersion by heating with a precision balance. calculated based on

<Particle size>
The particle size (median diameter, D10, D50, and D90) of the ND particles contained in the ND particle aqueous dispersion and the plating bath is measured using an apparatus manufactured by Malvern (trade name "Zetasizer Nano ZS"). It was measured by a dynamic light scattering method (non-contact backscattering method).

<Zeta potential>
The zeta potential of the ND particles contained in the ND particle aqueous dispersion was measured by laser Doppler electrophoresis using an apparatus manufactured by Malvern (trade name “Zetasizer Nano ZS”). The ND particle aqueous dispersion subjected to the measurement was diluted with ultrapure water so that the ND particle concentration was 0.2% by mass, and then subjected to ultrasonic irradiation by an ultrasonic cleaner. The temperature is 25°C.

Preparation example 1
An aqueous dispersion of ND particles was prepared through the following steps.
(Generation process)
First, a molded explosive to which an electric detonator was attached was placed inside a pressure-resistant container for detonation (made of iron, volume: 15 m ³ ), and the container was sealed. As an explosive, 0.50 kg of a mixture of TNT and RDX (TNT/RDX (mass ratio) = 50/50) was used. An electric detonator was then detonated to detonate the explosive within the container. Next, the temperature of the container and its interior was lowered by allowing it to stand at room temperature for 24 hours. After this cooling, the crude ND particles adhering to the inner wall of the container (including the ND particle agglomerate and soot produced by the detonation method) were recovered to obtain the crude ND particles. .

(Acid treatment step)
Next, the ND grain coarse product obtained in the above step was subjected to an acid treatment. Specifically, a slurry obtained by adding 6 L of 10% by mass hydrochloric acid to 200 g of the ND grain crude product was heat-treated under reflux under normal pressure conditions for 1 hour (heating temperature: 85 to 100° C. ) was performed. Next, after cooling, the solid content (including ND aggregate and soot) was washed with water by decantation. The solid content was repeatedly washed with water by decantation until the pH of the precipitate reached 2 from the low pH side.

(Oxidation treatment step)
Next, a mixed acid treatment was performed. Specifically, 6 L of a 98% by mass sulfuric acid aqueous solution and 1 L of a 69% by mass aqueous nitric acid solution are added to a precipitate (including ND aggregates) obtained through decantation after an acid treatment to form a slurry. This slurry was subjected to heat treatment (heating temperature: 140-160° C.) for 48 hours under normal pressure conditions and under reflux. After cooling, the solid content (including the ND aggregate) was washed with water by decantation. Although the supernatant liquid at the beginning of water washing was colored, washing of the solid content with water by decantation was repeated until the supernatant liquid became visually transparent.

(Drying process)
Next, 1000 mL of the ND particle-containing liquid obtained through the above water washing treatment was subjected to spray drying using a spray drying apparatus (trade name “Spray Dryer B-290” manufactured by Nippon Buchi Co., Ltd.). This gave 50 g of ND powder.

(Oxygen oxidation process)
Next, 4.5 g of the ND powder obtained as described above was left still in the core tube of a gas atmosphere furnace (trade name “Gas Atmosphere Tube Furnace KTF045N1” manufactured by Koyo Thermo Systems Co., Ltd.). After continuing to flow nitrogen gas at a flow rate of 1 L/min for 30 minutes, the flowing gas is switched from nitrogen to a mixed gas of oxygen and nitrogen, and the mixed gas is flowed through the furnace core tube at a flow rate of 1 L/min. continued. The oxygen concentration in the mixed gas is 4% by volume. After switching to the mixed gas, the temperature inside the furnace was raised to 400° C., which is the heating set temperature. The heating rate was 10°C/min up to 380°C, which is 20°C lower than the heating set temperature, and 1°C/min from 380°C to 400°C thereafter. Then, while maintaining the temperature condition in the furnace at 400° C., the ND powder in the furnace was subjected to an oxygen oxidation treatment. The treatment time was 3 hours.

After the oxygen oxidation treatment, oxygen-containing functional groups such as carboxy groups in the ND particles were evaluated by the following FT-IR analysis. From the spectrum obtained by this analysis, absorption near 1780 cm ⁻¹ attributed to C═O stretching vibration was detected as a main peak. From this, it was confirmed that the ND powder mainly contained ND particles (ND-COOH) having a carboxyl group as a surface functional group.
<FT-IR analysis conditions>
Fourier transform infrared spectroscopy (FT-IR) was performed using an FT-IR device (trade name “Spectrum 400 type FT-IR”, manufactured by PerkinElmer Japan Co., Ltd.). In this measurement, the infrared absorption spectrum was measured while heating the sample to 150° C. in a vacuum atmosphere. For heating under vacuum atmosphere, Model-HC900 type Heat Chamber and TC-100WA type Thermo Controller manufactured by ST Japan Co., Ltd. were used together.

(Crushing process)
First, 0.3 g of ND powder that has undergone the oxygen oxidation process and 29.7 mL of pure water were mixed in a 50 mL sample bottle to obtain about 30 mL of slurry. Next, after adjusting the pH of the slurry by adding a 1N sodium hydroxide aqueous solution, an ultrasonic irradiator (trade name “Ultrasonic Cleaner AS-3”, manufactured by AS ONE) was used. was subjected to ultrasonic irradiation for 2 hours. After that, bead milling was performed using a bead milling device (trade name: “parallel four-cylinder sand grinder LSG-4U-2L type”, manufactured by Imex Co., Ltd.). Specifically, 30 mL of the slurry after ultrasonic irradiation and zirconia beads with a diameter of 30 μm were enclosed in a 100 mL mill vessel Vessel (manufactured by Imex Co., Ltd.), and the apparatus was driven to perform bead milling. In this bead milling, the input amount of zirconia beads is about 33% with respect to the volume of the mill vessel, the rotation speed of the mill vessel is 2570 rpm, and the milling time is 2 hours.

Next, the slurry that had undergone the pulverization step was subjected to centrifugal separation using a centrifugal separator (classification operation). The centrifugal force in this centrifugation treatment was 20000×g, and the centrifugation time was 10 minutes.

Next, 25 mL of the supernatant liquid of the ND particle-containing solution that had undergone the centrifugation treatment was collected to obtain an ND particle aqueous dispersion (ND-COOH). The ND particle concentration in the ND particle aqueous dispersion was 11.8 g/L. Further, the pH was 9.33 when measured using a pH test paper (trade name "Three Band pH Test Paper", manufactured by AS ONE Corporation). The particle size D50 was 3.97 nm, the particle size D90 was 7.20 nm, and the zeta potential was -42 mV.

Crystal structure analysis was performed on the obtained particles in the ND particle aqueous dispersion using an X-ray diffractometer (trade name “SmartLab”, manufactured by Rigaku Corporation). As a result, a strong peak was observed at the analysis peak position of diamond, that is, at the diffraction peak position from the (111) plane of the diamond crystal. This confirmed that the obtained particles were diamond particles.

(Modification process)
The ND particle aqueous dispersion obtained above was dried using an evaporator to obtain a black dry powder. The obtained dry powder (100 mg) was added to 12 mL of glycidol placed in a glass reactor, and washed in an ultrasonic cleaner (trade name "BRANSON 2510", manufactured by Marshall Scientific) at room temperature for 2 hours. sonicated for hours to dissolve. This was reacted at 140° C. for 20 hours while stirring under nitrogen atmosphere. After cooling the reaction mixture, 120 mL of methanol was added, and after ultrasonic treatment, the mixture was centrifuged at 50400 G for 2 hours to obtain a precipitate. 120 mL of methanol is added to this precipitate, and the same washing-centrifugation process is repeated 5 times. Pure water dialysis was performed, residual methanol was replaced with water, and freeze-drying was performed to obtain gray powder of ND particles modified with polyglycerin (PG-ND particles).
TG-DTA thermal analysis measured the ratio of the ND particles and the surface modification groups, and the result was ND particles:surface modification groups=1:0.7.
PG-ND gray powder and water were added and the concentration was adjusted to 10 g/L based on the mass of ND particles to obtain a PG-ND particle aqueous dispersion.

Further, the obtained PG-ND gray powder was subjected to small-angle X-ray scattering measurement (SAXS method) using an X-ray diffractometer (trade name "SmartLab", manufactured by Rigaku), and particle size distribution analysis software ( Using a product name "NANO-Solver" manufactured by Rigaku Corporation), the primary particle size of PG-ND was estimated for the scattering angle range of 1° to 3°. In this estimate, we assumed that the PG-ND primary particles were spherical and had a particle density of 3.51 g/cm ³ . As a result, the average particle size of PG-ND was 7 nm.

Here, ND particles obtained by the impact compression method and modified ND particles obtained by modifying the surface of the ND particles with PG in the same manner as the ND particles obtained by the detonation method are also average particles. diameter was measured. As a result, the average particle size of the unmodified ND particles obtained by the impact compression method was 20 nm, and the average particle size of the modified ND particles was 23 nm. For this reason, the PG-ND particles obtained using the ND particles obtained by the detonation method have a smaller particle diameter, and the detonation PG-ND particles are used for dispersing in the noble metal matrix that constitutes the plating film. was found to be superior.

[Example 1]
The aqueous dispersion of PG-ND particles obtained in Preparation Example 1 was added to a plating solution having a rhodium concentration of 5 g/L (trade name “Rodex”, manufactured by Nippon Electroplating Engineers Co., Ltd.) to form a plating bath. (1) (PG-ND particle concentration in plating bath: 0.1 g/L) was obtained.
When the particle size of the PG-ND particles in the plating bath (1) was measured, the particle size (D10) was 30 nm, the particle size (D50) was 44 nm, and the particle size (D90) was 76 nm.
Plating bath (1) was transparent (light transmittance for light with a wavelength of 600 nm when measured in a quartz glass cell with an optical path length of 1 cm was 95% or more) and no turbidity (haze value = 0).

A copper plate (purity 99.9%, length 20 mm x width 20 mm x thickness 2 mm) as a member to be plated film is degreased and washed, and then subjected to electrolytic Ni/Au plating treatment to obtain a copper plate with a base plating film. Obtained.
This copper plate with a base plating film is plated for 15 minutes with stirring under the conditions of pH 1, solution temperature 50 ° C., current density 1.3 A / dm ² using plating bath (1), and plating on the base plating film A plated film (ND particle content: 12 area %, film thickness: 5 μm, see FIG. 2) made of a metal rhodium-ND particle composite material was formed on the substrate. The resulting plated film had ND particles highly dispersed uniformly and had a smooth surface.

[Example 2]
Plating bath (2) (PG-ND particle concentration in plating bath: 0.05 g/L) was prepared in the same manner as in Example 1, except that the amount of the PG-ND particle aqueous dispersion obtained in Preparation Example 1 was changed. ) was obtained, and a plating film was obtained in the same manner as in Example 1 except that the obtained plating bath (2) was used.

[Example 3]
Plating bath (3) (PG-ND particle concentration in plating bath: 0.02 g/L) was prepared in the same manner as in Example 1 except that the amount of the PG-ND particle aqueous dispersion obtained in Preparation Example 1 was changed. ) was obtained, and a plating film was obtained in the same manner as in Example 1 except that the obtained plating bath (3) was used.

[Example 4]
Plating bath (4) (PG-ND particle concentration in plating bath: 0.01 g/L) was prepared in the same manner as in Example 1, except that the amount of the PG-ND particle aqueous dispersion obtained in Preparation Example 1 was changed. ) was obtained, and a plating film was obtained in the same manner as in Example 1 except that the obtained plating bath (4) was used.

[Example 5]
Plating bath (5) (PG-ND particle concentration in plating bath: 0.005 g/L) was prepared in the same manner as in Example 1, except that the amount of the PG-ND particle aqueous dispersion obtained in Preparation Example 1 was changed. ) was obtained, and a plating film was obtained in the same manner as in Example 1 except that the obtained plating bath (5) was used.

[Example 6]
Plating bath (6) (PG-ND particle concentration in plating bath: 0.002 g/L) was prepared in the same manner as in Example 1 except that the amount of the PG-ND particle aqueous dispersion obtained in Preparation Example 1 was changed. ) was obtained, and a plating film was obtained in the same manner as in Example 1 except that the obtained plating bath (6) was used.

[Comparative Example 1]
A plating bath (7) was prepared in the same manner as in Example 1 except that the aqueous dispersion of ND particles (ND-COOH) obtained through the oxygen oxidation step of Preparation Example 1 was used instead of the aqueous dispersion of PG-ND particles. got The ND particles in the plating bath (7) aggregated into large clumps.

A plated film was obtained in the same manner as in Example 1 except that plating bath (7) was used instead of plating bath (1) (see FIG. 3). The resulting plated film had an uneven surface.

[Comparative Example 2]
Instead of the plating bath (1), a plating bath ( A plated film was formed in the same manner as in Example 1 except that 8) was used (see FIG. 4). The resulting plated film had an uneven surface.

<Gloss measurement>
The glossiness (GU) of the plating films obtained in Examples and Comparative Examples was measured using a measuring instrument (trade name “High Gloss Gloss Checker IG410”, manufactured by Horiba, Ltd.). The reflectance at an incident angle of 60° was measured, and the glossiness (GU) was calculated. The results are summarized in the table below.
From the table below, it was found that the glossiness (GU) of the plating film increased according to the amount of ND particles added.

[Example 7]
The PG-ND particle aqueous dispersion obtained in Preparation Example 1 was obtained by removing the brightener from a plating solution [trade name “Aurobond XPH20” (manufactured by Nippon Electroplating Engineers Co., Ltd.) with a gold concentration of 2 g/L. Plating bath (9) (PG-ND particle concentration in plating bath: 0.1 g/L) was obtained.
When the particle size of the PG-ND particles in the plating bath (9) was measured, the particle size (D10) was 35 nm, the particle size (D50) was 52 nm, and the particle size (D90) was 97 nm.
The plating bath (9) was transparent (light transmittance for light with a wavelength of 600 nm when measured in a quartz glass cell with an optical path length of 1 cm was 95% or more), and there was no turbidity.

A copper plate with an underlying plating film obtained in the same manner as in Example 1 was subjected to plating bath (9) under the conditions of pH 2, liquid temperature 55°C, and current density 1 A/dm ² for 12 minutes while stirring. A plated film (ND particle content: 7 area %, film thickness: 1.6 μm) made of a gold-ND particle composite material was formed on the underlying plated film by plating. The resulting plated film had ND particles highly dispersed uniformly and had a smooth surface.

[Comparative Example 3]
Instead of the plating bath (9), a plating bath ( A plated film (thickness: 0.97 μm) was formed in the same manner as in Example 7, except that No. 10) was used. The resulting plated film had an uneven surface.

The glossiness (GU) of the plating films obtained in Example 7 and Comparative Example 3 was measured in the same manner as described above. The results are summarized in the table below.

From Table 2, it was found that the addition of ND particles increased the glossiness (GU) of the plating film.

1 Nanodiamond particles with surface modification groups 2 Nanodiamond particles (part)
3 surface modification group

Claims (6)

A plating film containing a noble metal matrix and nanodiamond particles dispersed in the noble metal matrix and having a glossiness of 250 GU or more at an incident angle of 60° is produced by an electrolytic plating method using the following plating bath . manufacturing method.
Plating bath: contains nanodiamond particles having surface modification groups containing noble metal ions and polyglycerol chains, the content of said nanodiamond particles is 0.001-1.0 g/L, and said nanodiamond particles in the plating bath The particle size (D50) by the dynamic light scattering method is 100 nm or less 2. The plating film according to claim 1 , wherein the glossiness at an incident angle of 60° is 20 GU or more higher than a plating film obtained using a plating bath having the same composition except that it does not contain nanodiamond particles. A method for producing a plating film. 3. The method for producing a plated film according to claim 1, wherein the plated film has a surface roughness (Ra) of 0.5 [mu]m or less. The method for producing a plated film according to any one of claims 1 to 3 , wherein the nanodiamond particles dispersed in the noble metal matrix of the plated film have a particle diameter (D50) of 4 to 100 nm as measured by an SEM method. The method for producing a plated film according to any one of claims 1 to 4 , wherein the content of nanodiamond particles in the plated film is 0.5 to 25% by area of the plated film. A method of manufacturing an electronic component, comprising a step of manufacturing a plated film by the method of manufacturing a plated film according to any one of claims 1 to 5 , to obtain an electronic component provided with the plated film.

Images