JP2021042397A - Method of micronizing crystal grains in plating film - Google Patents

Abstract

To provide a method of micronizing crystal grains in a plating film, capable of modifying the surface of a plating film, hardly taking nanocarbon into the plating film.SOLUTION: A representative constitution of the method of micronizing crystal grains in a plating film according to the present invention, is to perform electroplating using a plating solution 104 which is in a state of being blended with an ion of plating metal 112, nanocarbon 114, and an anionic surfactant as a dispersant 116 for dispersing the nanocarbon.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for refining crystal grains of a plating film.

Conventionally, composite plating in which fine particles are co-deposited in a plating metal film has been known. For example, Patent Document 1 describes a zinc-nanocarbon composite plated product. In this composite plated product, a galvanized film is formed on the object to be plated by using a galvanized liquid to which nanocarbon and polyacrylamide as a dispersant for nanocarbon are added.

Further, Patent Document 1 describes that nanocarbon is mixed in the galvanized film and that the amount of nanocarbon added to the galvanized solution is preferably 0.5 to 5.0 g / L. ing. Further, Patent Document 1 states that since a part of nanocarbon is exposed from the galvanized film, it is possible to obtain a galvanized film having excellent sliding characteristics.

Japanese Unexamined Patent Publication No. 2008-2146667

Generally, it is considered that the surface of the plating film can be modified by incorporating nanocarbon into the plating film as in the technique described in Patent Document 1. As an example, it is said that when nanocarbon is incorporated into the plating film, the plating film becomes hard and the wear resistance during sliding is improved.

However, in reality, the plating film is not hard, but the nanocarbon particles on the surface layer are hard. The wear resistance of the plating film is not a simple property that depends only on the hardness of the plating film, but the surface roughness (slipperiness) of the plating, the lubricity, the toughness of the plated metal, and the size of the crystal grains. It is affected by multiple factors such as.

Specifically, even if the plating metal has high hardness and good slipperiness (plating metal with fine crystal grains), the plating surface is hard, so that the plating surface (contact surface) is chipped due to galling due to sliding (contact surface). Once a scratch) occurs, the friction coefficient of the plating surface rises sharply due to the scratch. As a result, the plated surface is further damaged and wear progresses rapidly. Such a phenomenon is likely to occur in a plating metal having a high hardness but a low toughness (a plating metal having a brittle grain boundary and a weak bonding force). On the other hand, in the case of a plated metal having a relatively low hardness, chipping does not occur, but due to the low hardness, the scraping speed becomes high and high wear resistance cannot be obtained.

Therefore, it cannot be said unconditionally that the surface of the plating film is modified by incorporating nanocarbon into the plating film. Moreover, when nanocarbon is incorporated into the plating film, it is very difficult to uniformly disperse the nanocarbon in the plating film and precisely control the content of nanocarbon in the plating film. Further, since nanocarbon is a non-conductor, when a plating film incorporating nanocarbon is used for electrical contacts, the electrical contact resistance becomes unstable and greatly increases.

In view of such a problem, an object of the present invention is to provide a method for refining crystal grains of a plating film, which can modify the surface of the plating film without incorporating nanocarbon into the plating film.

As a result of diligent studies to solve the above problems, the inventor of the present application can make the crystal grains of the plating film finer by making the nanocarbon function as if it were a catalyst without intentionally incorporating nanocarbon into the plating film. The present invention has been completed. That is, in order to solve the above problems, a typical configuration of the method for refining the crystal grains of the plating film according to the present invention is to disperse the ions of the plating metal, the nanocarbons, and the nanocarbons in the plating solution. It is characterized in that electroplating is performed in a state where an anionic surfactant is mixed as an agent.

According to the above configuration, since the dispersant is mixed in the plating solution, the nanocarbons are dispersed in the plating solution in a state where the molecules of the dispersant are adsorbed. Since an anionic surfactant is used as the dispersant, the nanocarbon dispersed in the plating solution is difficult to be incorporated into the surface of the component to be plated connected to the cathode. Further, on the surface of the part to be plated, epicapital growth of the plated metal proceeds to form crystal grains. On the other hand, nanocarbon affects the epicapital growth of the plating metal and makes the crystal grains of the plating film finer. Although the behavior at this time is not clearly known, nanocarbons are said to be miniaturized by the behavior of contacting the crystal grains and applying force to them due to the Brownian motion in the plating solution. Inferred. As described above, in the present invention, the surface of the plating film is modified by refining the crystal grains of the plating film without incorporating nanocarbon into the plating film.

It is preferable that the nanocarbon is positively charged in a state of being mixed with the plating solution. In this way, since the nanocarbon is positively charged in the plating solution, even when the molecules of the anionic surfactant are adsorbed on the nanocarbon, the surface of the part to be plated connected to the cathode is exposed. It is presumed to be attracted. Since the nanocarbon is attracted to the surface of the part to be plated, it is possible to reliably contact the crystal grains and apply a force to them, and the crystal grains of the plating film can be reliably refined.

The particle size of the above nanocarbon is preferably 2.6 ± 0.5 nm. In this way, if the particle size of the nanocarbons is within the above range, the nanocarbons in the plating solution will surely perform Brownian motion, and when they come into contact with the crystal grains, they will exert an appropriate force to make the crystal grains finer. Can be added to. If the particle size is larger than the above range, the miniaturization is insufficient because the Brownian motion is not sufficient and an appropriate force cannot be applied to the crystal grains. Further, if the particle size is smaller than the above range, the miniaturization becomes insufficient because the Brownian motion occurs, but the mass is so small that it is not possible to apply enough force to the crystal grains to make the crystal grains finer. Inferred.

The amount of the above-mentioned nanocarbon added to the plating solution is preferably 0.2 g / L or less. By setting the amount of nanocarbon added to a small amount of 0.2 g / L or less in this way, it is possible to prevent nanocarbon from being incorporated into the plating film.

The plated metal may be Ag, Ni, Sn, or Au. Therefore, a neutral or weakly acidic plating solution may be used.

According to the present invention, it is possible to provide a method for refining crystal grains of a plating film, which can modify the surface of the plating film with almost no incorporation of nanocarbon into the plating film.

It is a figure explaining the outline of the method of miniaturizing the crystal grain of a plating film in this embodiment. It is a micrograph which shows the plating film of FIG. 1 and a comparative example, respectively. It is a schematic diagram corresponding to each of the plating films of FIG. It is a graph which shows the durability and contact resistance of the plating film of FIG. 2, respectively. It is a micrograph which shows the plating film of another embodiment and comparative example respectively.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in such an embodiment are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to omit duplicate description, and elements not directly related to the present invention are not shown. To do.

FIG. 1 is a diagram illustrating an outline of a method for miniaturizing crystal grains of a plating film in the present embodiment. The miniaturization method in this embodiment is carried out using, for example, a plating apparatus 100. The plating device 100 is a device that performs electroplating, and is a power source that applies a voltage between the container 102, the plating solution 104 in the container 102, the cathode 106 and the anode 108 immersed in the plating solution 104, and both electrodes. It is equipped with 110.

The plating solution 104 is in a state in which the ions of the plating metal 112, the nanocarbon 114, and the dispersant 116 are mixed. The plated metal 112 is here a monovalent cation of Ag.

An anionic surfactant is used as the dispersant 116. As shown, when the surfactant molecule is adsorbed on the nanocarbon 114, the hydrophilic group 118a is arranged on the outside and the lipophilic group 118b is adsorbed on the nanocarbon 114. Therefore, the nanocarbon 114 is dispersed in the plating solution 104 by the dispersant 116 without agglomeration.

As an example, the amount of nanocarbon 114 added to the plating solution 104 was 0.2 g / L, and the particle size was 2.6 ± 0.5 nm. Further, the nanocarbon 114 is positively charged in a state of being mixed with the plating solution 104. The plating solution 104 is neutral because Ag is used as the plating metal 112.

In the plating apparatus 100, when a voltage is applied between the cathode 106 and the anode 108 by the power supply 110 and the plating process is started, epicapital growth of the plated metal 112 is performed on the surface of the component 120 to be plated connected to the cathode 106. Progresses to form crystal grains. As a result, the plating film 122 shown by hatching in the figure is formed on the surface of the component 120 to be plated.

FIG. 2 is a photomicrograph showing the plating films 122 and 122A of FIG. 1 and the comparative example, respectively. The plating film 122 shown in FIG. 2A is obtained by the miniaturization method of the present embodiment in which nanocarbon 114 is added to the plating solution 104. The plating film 122A of the comparative example shown in FIG. 2B was obtained without adding nanocarbon 114 to the plating solution 104.

When observing the micrographs of the plating films 122 and 122A, the crystal grains of the plating film 122 are clearly smaller than the crystal grains of the plating film 122A. Therefore, it is clear that the crystal grains of the plating film 122 can be miniaturized (nanocrystallized) by the miniaturization method of the present embodiment. Further, Table 1 below compares the carbon contents of the plating films 122 and 122A.

As shown in Table 1, the carbon content of the plating film 122 of the present embodiment to which the nanocarbon 114 is added is substantially the same as the carbon content of the plating film 122A of the comparative example to which the nanocarbon 114 is not added. .. Therefore, it is clear that the nanocarbon 114 is hardly incorporated in the plating film 122 formed by the miniaturization method of the present embodiment.

As described above, in the miniaturization method of the present embodiment, the crystal grains of the plating film 122 are miniaturized by making the nanocarbon 114 function as if it were a catalyst without incorporating the nanocarbon 114 into the plating film 122. There is. This phenomenon will be considered below.

First, since the nanocarbon 114 dispersed in the plating solution 104 uses an anionic surfactant as the dispersant 116, it is difficult to be incorporated into the plating film 122 on the surface of the component 120 to be plated connected to the cathode 106. In addition, since the amount of nanocarbon 114 added is as small as 0.2 g / L, it is difficult to be incorporated into the plating film 122 in the first place. Under such conditions, the nanocarbon 114 was actually hardly incorporated into the plating film 122.

Next, since the nanocarbon 114 is positively charged in the plating solution 104, the parts to be plated connected to the cathode 106 even when the molecules of the anionic surfactant are adsorbed on the nanocarbon 114. It is presumed that it is attracted to the surface of 120 and affects the epicapital growth of the plated metal 112.

Although the behavior of the nanocarbon 114 at this time is not clearly known, the nanocarbon 114 comes into contact with the crystal grains due to the Brownian motion in the plating solution 104 and applies a force to the crystal grains. It is presumed that the crystal grains will be refined. That is, the nanocarbon 114 positively charged in the plating solution 104 is attracted to the surface of the component 120 to be plated, and can be reliably contacted with the crystal grains to apply a force to the crystal grains of the plating film. It is presumed that it can be reliably refined.

Further, since the particle size of the nanocarbon 114 is set in the range of 2.6 ± 0.5 nm, the nanocarbon 114 in the plating solution 104 surely performs a brown motion, and when it comes into contact with the crystal grains, the crystal grains can be refined. It is presumed that an appropriate force can be applied to the crystal grains. On the other hand, if the particle size of the nanocarbon 114 is larger than the above range, the miniaturization becomes insufficient because the Brownian motion is not sufficient and an appropriate force cannot be applied to the crystal grains. On the other hand, if the particle size of the nanocarbon 114 is smaller than the above range, the miniaturization becomes insufficient because Brownian motion occurs, but the mass is small, so that a force sufficient to miniaturize the crystal grains can be applied to the crystal grains. It is presumed that it cannot be done.

By the way, the component 120 to be plated on which the plating film 122 is formed is used as an electrical contact. Therefore, the plating film 122 is required to have a low electrical resistivity (contact resistance) and to have high durability (that is, wear resistance during sliding) because it is repeatedly inserted and removed from a socket or the like. To.

Here, the crystal structure of the metal will be described with reference to FIG. FIG. 3 is a schematic view corresponding to the plating films 122 and 122A of FIG. 2, respectively.

The metal contains crystal grains and grain boundaries (crystal defects or impurities) surrounding the crystal grains, and can be regarded as an aggregate of crystal grains in which the crystal grains are bonded at the grain boundaries. The wear caused by the sliding of the metal may be that the crystal grains themselves are broken in the grains, or that the grain boundaries are broken and the crystal grains are chipped and scraped off in block units. One of the purposes of the present embodiment is to suppress the breakage of grain boundaries that are chipped off in crystal grain units and to improve durability. In a metal, when large crystal grains are scraped off due to grain boundary fracture, the lost volume, that is, the amount of scraping is large, and even if small crystal grains are scraped off, the scraping amount is small. Furthermore, since crystal grains of metal are bonded to each other at grain boundaries, it is presumed that the stronger the grain boundaries and the stronger the bonding force, the more difficult it is to scrape. Therefore, the crystal structure of the metal required to realize a highly durable plating film includes that the crystal grains are small and that the grain boundaries that bond the crystal grains are strong.

The plating film 122 shown in FIG. 3A has smaller crystal grains 124 than the crystal grains 124A and grain boundaries 126A of the plating film 122A shown in FIG. 3B, and the grain boundaries 126 that bond the crystal grains 124 to each other. Is increasing. Therefore, the plating coating 122 is less likely to be scraped due to sliding and has higher durability than the plating coating 122A.

Furthermore, it is generally said that metals become harder as the crystal grains become finer. In this regard, the plating film 122A of the comparative example in which the crystal grains 124A were not miniaturized had a Vickers hardness of 90 to 110 Hv. On the other hand, it was clarified that the plating film 122 of the present embodiment in which the crystal grains 124 were miniaturized had a Vickers hardness of 100 to 110 Hv and did not become hard even when the crystal grains 124 were miniaturized. As a result, the familiarity (lubricity) of the contact surface peculiar to Ag, which is the plated metal 112, can be maintained, so that the surface of the plating film 122 (contact surface during sliding) becomes smooth and friction even if sliding is repeated. There is no big change in the coefficient, and durability can be improved.

Next, the contact resistance of the plating film 122 will be described. It is generally said that the contact resistance of a metal increases because the grain boundaries increase as the crystal grains become finer. However, the plating film 122 of the present embodiment has a contact resistance of ^{about 3 to 3.5 × 10-6} Ωcm and does not increase even though the crystal grains 124 are small. The contact resistance of ultra-hard silver plating having the same grain size is 8 × ^10-6 Ωcm or more, which is high. The reason for this is that the plating film 122 does not alloy with dissimilar metals such as Sb to refine the crystal grains 124, and does not use an organic brightener that adsorbs in the film. It is presumed that there are few impurities at the grain boundaries 126.

FIG. 4 is a graph showing the durability and contact resistance of the plating films 122 and 122A of FIG. 2, respectively. In each graph, the horizontal axis represents the number of round trips (number of slides), and the vertical axis represents the frictional force (N) and the resistance value (mΩ), respectively. When the frictional force is high, the friction coefficient is large, so that the wear is likely to proceed and the wear resistance, that is, the durability is low.

Since the plating film 122 shown in FIG. 4A has a smaller frictional force as a whole than the plating film 122A shown in FIG. 4B, it has high wear resistance and is not broken even after 1000 round trips. On the other hand, since the plating film 122A has low wear resistance, it is broken after about 600 round trips as shown in FIG. 4 (b). Further, the plating film 122 is stable at a lower resistance value than the plating film 122A. On the other hand, the resistance value of the plating film 122A is unstable as a whole, and the resistance value rapidly increases as the plating film 122A breaks after about 600 round trips.

As described above, the plating film 122 formed by the miniaturization method of the present embodiment has lower contact resistance and durability as compared with the plating film 122A of the comparative example in which nanocarbon 114 is not added to the plating solution 104. It turned out to be expensive. That is, in the miniaturization method of the present embodiment, the crystal grains of the plating film 122 are miniaturized by adding the nanocarbon 114 to the plating solution 104 and hardly incorporating the nanocarbon 114 into the plating film 122. The surface of the plating film 122 is modified.

Examples and comparative examples when the amount of nanocarbon 114 added is changed will be described below. Table 2 is a diagram illustrating Examples and Comparative Examples. Examples 1 and 2 are examples in which the addition amount of nanocarbon 114 is 0.1 g / L and 0.2 g / L, and in Comparative Example 1, the addition amount of nanocarbon 114 is 0 and nanocarbon 114 is added. This is an example of not doing so. Comparative Example 2 is an example in which the amount of nanocarbon 114 added is 0.3 g / L.

As shown in Table 2, first, in Comparative Example 1 in which nanocarbon 114 was not added to the plating solution 104, the crystal grain size was “large”, the wear resistance (durability) was “NG”, and the volume resistance. (Electrical resistance) became "low". Next, in Comparative Example 2 in which the amount of nanocarbon 114 added was 0.3 g / L or more, the crystal grain size was “medium”, the wear resistance was “OK”, and the volume resistance was “high”. .. On the other hand, in Examples 1 and 2, the amount of nanocarbon 114 added was 0.2 g / L or less, the size of the crystal grains was "fine", the wear resistance was "OK", and the volume. All resistances were "low". Therefore, when the amount of nanocarbon 114 added is 0.2 g / L or less, the size of the crystal grains of the plating film 122 can be made minute, the wear resistance can be increased, and the size of the crystal grains can be further increased. It was revealed that the volume resistance did not increase and remained low despite the minute size.

FIG. 5 is a photomicrograph showing plating films 128 and 128A of other embodiments and comparative examples, respectively. The plating film 128 of the other embodiment shown in FIG. 5A differs from the plating film 122 in that the plating metal 112 is replaced with Ni instead of Ag. The plating film 128A of the comparative example shown in FIG. 5B was obtained by replacing the plating metal 112 with Ag with Ni and further, without adding nanocarbon 114 to the plating solution 104. Since Ni is used as the plating metal, the plating solution 104 is weakly acidic.

When observing the micrographs of the plating films 128 and 128A, the crystal grains of the plating film 128 are clearly smaller than the crystal grains of the plating film 128A. Therefore, it is clear that the crystal grains of the plating film 128 can be miniaturized by the miniaturization method of another embodiment. Further, Table 3 below shows the results of the sliding test of the plating films 128 and 128A.

The plating film 128A of the comparative example was formed by mixing nickel sulfamate as the plating solution 104 and without adding nanocarbon 114. As shown in Table 3, when the plating film 128A was repeatedly slid with a load of 50 g, it was destroyed with an average of 425.4 sliding times.

On the other hand, the plating film 128 of the other embodiment is formed by mixing nickel sulfamate as the plating solution 104 and further adding nanocarbon 114. As shown in Table 3, the plating film 128 was broken after 523.2 sliding times on average, and it was revealed that the plating film 128 had higher durability than the plating film 128A of the comparative example.

Therefore, according to the miniaturization method of the present embodiment, the crystal grains of the plating films 122 and 128 are miniaturized without incorporating nanocarbon 114 into the plating films 122 and 128, so that the surface of the plating films 122 and 128 can be refined. Modification can be realized.

In the above embodiment, the case where the plating metal 112 is Ag or Ni is illustrated, but the present invention is not limited to this, and the plating metal 112 may be Sn or Au. Even in such a case, the nanocarbon 114 is not intentionally incorporated into the plating film, and the nanocarbon 114 functions as if it were a catalyst, so that the crystal grains of the plating film are refined and the surface of the plating film is modified. It is presumed that the quality can be achieved.

Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, which naturally belong to the technical scope of the present invention. Understood.

The present invention can be used as a method for refining the crystal grains of the plating film.

100 ... Plating device, 102 ... Container, 104 ... Plating solution, 106 ... Cathode, 108 ... Anode, 110 ... Power supply, 112 ... Plating metal, 114 ... Nanocarbon, 116 ... Dispersant, 118a ... Hydrophilic group, 118b ... Parent oil Group, 120 ... Parts to be plated, 122, 122A, 128, 128A ... Plating film, 124, 124A ... Crystal grains, 126, 126A ... Grain boundaries

Claims (3)

This is a method for refining the crystal grains of the plating film.
Fine graining of the crystal grains of the plating film, which is characterized by performing electroplating in a state where ions of the plating metal, nanocarbon, and an anionic surfactant as a dispersant for dispersing the nanocarbon are mixed in the plating solution. Method. The method for refining crystal grains of a plating film according to claim 1, wherein the nanocarbon is positively charged in a state of being mixed with the plating solution. The method for refining crystal grains of a plating film according to claim 1 or 2, wherein the plating metal is Ag, Ni, Sn, or Au.

Images