Composite plating film

Abstract

To provide a technique for providing a plating film having a small coefficient of friction without using an organofluorine compound (hereinafter referred to as "PFAS") since a polytetrafluoroethylene resin ("PTFE") compound plating technique can be used to obtain the plating film having the small coefficient of friction, but may not be usable in future because of environmental regulation trends with respect to PFAS.SOLUTION: There is provided an electroless nickel plating film having a eutectoid of silicone resin powder, and the silicone resin powder is caused to form a eutectoid in electroless nickel phosphorous plating instead of PTFE. The silicone resin power can be dispersed in a plating solution by using a surface active agent not corresponding to PFAS, and is taken in the plating film to form a plating film having a small coefficient of friction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a composite plating film. [Background technology]

[0002] Composite plating, in which polytetrafluoroethylene resin (hereinafter referred to as "PTFE") is co-deposited with a plating film, has been investigated as a surface treatment technology with a low coefficient of friction and excellent durability. These composite platings are used in, for example, sliding components (e.g., Patent Documents 1 and 2). The plating films that form the matrix of the composite plating films described in Patent Documents 1 and 2 are mainly made of electrolytic nickel plating or electroless nickel-phosphorus plating, which are inexpensive and have excellent hardness.

[0003] Fluorine-containing compounds such as PTFE (Per- and Polyfluoroalkyl Substances, commonly known as "PFAS") are widely used materials due to their many excellent properties, such as low adhesion, low coefficient of friction, and chemical stability. However, due to their chemical stability, they do not decompose in nature, and it has been pointed out that they remain and accumulate in the environment for long periods of time.

[0004] Perfluorooctylic acid (PFOA) and perfluorooctylsulfonic acid (PFOS), which are types of PFAS, have long been a source of concern due to their toxicity, and their use has been banned under many chemical substance regulations, including REACH.

[0005] In recent years, there has been a growing movement to expand these chemical substance restrictions to cover all PFAS, raising the possibility that most fluorine-containing materials, including PTFE, may become unusable in the future.

[0006] Given this background, it is expected that there will be a strong demand for PFAS-free materials to replace PTFE. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2001-049449 A (Patent No. 3419354) [Patent Document 2] JP-A-09-149998 (Patent No. 3215627 specification) Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a composite plating film that does not use PTFE or PFASs, has the low friction coefficient and water repellency required for PTFE composite plating, and can be used as an alternative to PTFE composite plating. [Means for solving the problem]

[0009] The present invention provides a plating film in which a silicone resin powder is co-deposited with electroless nickel plating, and can impart to the plating film the characteristics expected of PTFE composite plating, such as water repellency and a low coefficient of friction, without using surfactants such as PTFE and PFAS. That is, the present invention provides an electroless nickel composite plating film according to the present invention, which solves the above technical problems. The electroless nickel composite plating film according to the present invention comprises: [1] It is characterized by being formed from a dispersion liquid in which a silicone resin powder is co-deposited with an electroless nickel plating in the presence of a cationic surfactant. Furthermore, the electroless nickel composite plating film according to the present invention has the following features: [2] The content of the silicone resin powder is 3.0 vol% or more; [3] The average particle size of the particles constituting the silicone resin powder is 0.1 to 3.0 μm. [4] A preferred solution is an abrasion-resistant electroless nickel composite plating film obtained by heat treating the electroless nickel composite coating described in the above [1] to [3] in a temperature range of 200 to 500°C.

[0010] The present inventors discovered that silicone resin powder can be dispersed in an electroless nickel plating solution using any cationic surfactant that does not fall under the category of PFASs, and that a composite plating can be obtained in which a silicone resin with a silicone resin content of 3 to 45 vol% is co-deposited with an electroless nickel plating, thereby arriving at the present invention. [Effects of the Invention]

[0011] According to the present invention, it is possible to obtain a plating film having properties such as a low friction coefficient and water repellency, which are required for conventionally proposed PTFE composite plating, without using any substances that fall under the PFAS category. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a surface microscope image of the composite plating film produced in Example 5. [Figure 2] 1 is a cross-sectional microscope image of a composite plating film produced in Example 5. [Figure 3] 1 is a surface microscope image of the composite plating film produced in Example 7. [Figure 4] 1 is a cross-sectional microscope image of a composite plating film produced in Example 7. [Figure 5] 10 is a graph showing the relationship between the heat treatment temperature after plating and the film hardness for Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail. Note that the drawings are schematic and may differ from the actual embodiments. Furthermore, the following embodiments exemplify devices and methods for embodying the technical idea of the present invention, and are not intended to limit the configuration to the following. In other words, the technical idea of the present invention can be modified in various ways within the technical scope described in the claims.

[0014] [First embodiment] The composite plating film according to the first embodiment will be described. The composite plating film according to this embodiment is a plating film in which 3 vol% or more, more preferably 5 vol% or more of silicone resin powder is co-deposited with an electroless nickel plating matrix. By combining 3 vol% or more, a sufficient reduction in the wear coefficient can be achieved. The silicone resin powder used in the present invention has an average particle size of 0.1 to 3.0 μm, preferably 0.1 to 1.0 μm. Particles smaller than 0.1 μm or larger than 3.0 μm are not effectively incorporated into the composite plating film, and the particle content in the film does not increase sufficiently. Examples of materials constituting the silicone resin powder include polydimethylsiloxane and its derivatives. The composite plating film according to the present invention can be further heat-treated at 200 to 500°C to improve its film hardness. The heat treatment temperature is preferably 200 to 500°C, more preferably 250 to 450°C. Heat treatment at a temperature of 200°C or higher improves film hardness and abrasion resistance. Temperatures above 500°C are not preferred because they may accelerate decomposition of the silicone resin, resulting in a loss of properties such as water repellency, and may accelerate softening of the electroless nickel plating matrix, resulting in a decrease in hardness. The composite plating film according to this embodiment is characterized in that a composite plating film with a low coefficient of friction is obtained by adding a dispersion of silicone resin powder to an electroless nickel plating solution containing a water-soluble metal salt, a reducing agent, and organic acids.

[0015] <Dispersion of silicone resin powder> The silicone resin powder is preferably dispersed in water using a cationic surfactant. A silicone resin powder dispersion containing a silicone resin powder and a cationic surfactant has a powder concentration of 50 g / L or more and 700 g / L or less. A powder concentration of 700 g / L or less is preferable because a fluid silicone resin powder dispersion can be prepared, and a powder concentration of 50 g / L or more is preferable because the particles constituting the silicone resin powder settle quickly and storage stability is not compromised. The incorporation of silicone resin powder into electroless nickel plating films proceeds through the following process: 1. A cationic surfactant adsorbs to the hydrophobic surface of the silicone resin powder, positively charging the particles and dispersing them in the plating solution. 2. The dispersed, positively charged particles are adsorbed and held on the surface of the electroless nickel plating film by electrostatic or hydrophobic interactions. 3. As the plating reaction progresses, the particles are incorporated into the plating film, becoming embedded therein.

[0016] Examples of cationic surfactants include alkyltrimethylammonium salts, alkylbenzyldimethylammonium salts, and alkyltriethylammonium salts.

[0017] <Electroless nickel plating solution> The water-soluble metal salt used in the electroless nickel plating solution is not particularly limited as long as it is one that is commonly used in plating baths, and for example, nickel sulfate, nickel chloride, etc. can be used.

[0018] The reducing agent used in the electroless nickel plating solution is hypophosphite, dimethylamine borane, or the like.

[0019] Examples of organic acids that can be used include alkylcarboxylic acids such as acetic acid and propionic acid, hydroxycarboxylic acids such as lactic acid and malic acid, and amino acids such as glycine and alanine. Furthermore, the pH of the electroless nickel plating solution is adjusted to 4 to 9 using sodium hydroxide, potassium hydroxide, aqueous ammonia, etc.

[0020] The electroless nickel plating solution may contain stabilizers such as water-soluble lead compounds, water-soluble bismuth compounds, iodates, bromates, vanadates, molybdates, and tungstates.

[0021] Furthermore, the coating composition may contain organic sulfur compounds such as thiourea, thioglycol, and thiodiglycol as plating accelerators, and various ionic and nonionic surfactants as wettability improvers.

[0022] A plating solution for composite plating films was prepared by adding a predetermined amount of the silicone resin powder to the electroless nickel plating solution prepared in this manner. After heating this seacorn resin powder-dispersed electroless nickel plating solution to 60°C to 90°C, a substrate that had been appropriately pretreated was immersed in the silicone resin powder-dispersed electroless nickel plating solution to obtain a silicone resin powder composite electroless plating film. The substrate may be any substrate that can be electrolessly plated as a matrix, and the pretreatment may be similar to that for electroless plating. Examples of substrates include internal components of small machines, sliding parts such as washers, and sliding parts such as gears and bearings. In other words, the composite plating film of the present invention is suitable for use on components, such as sliding parts, that have excellent film hardness and friction coefficient.

[0023] The composite plating film obtained in this manner contains 3 vol % to 45 vol % of silicone resin powder, and has a low coefficient of friction.

[0024] The resulting composite plating film can be further heat-treated at 200 to 500°C to increase the film hardness and improve its wear resistance. [Example]

[0025] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0026] <Examples 1 to 6> 1) Preparation of plating solution Chemicals were dissolved in pure water according to the composition shown below to prepare an electroless plating solution. [Plating solution composition] Nickel sulfate: 0.1 mol / L Sodium hypophosphite: 0.3 mol / L Sodium lactate: 0.11 mol / L Sodium malate: 0.15 mol / L Bisulfite: 0.003 mmol / L pH: 5.0, temperature: 85°C (stirrer stirring)

[0027] 2) Preparation of silicone resin dispersion 5 g of cationic surfactant (benzyl dimethyl stearyl ammonium chloride, Tokyo Chemical Industry Co., Ltd.) was dissolved in 500 ml of water, and 300 g of silicone resin powder (X52-854, Shin-Etsu Chemical Co., Ltd.) was added to the solution. After thorough stirring and dispersion, pure water was added to adjust the liquid volume to 1 liter.

[0028] 3) Preparation of composite plating solution <Plating Experiment> A specified amount of the silicone resin powder dispersion prepared using the method described in the previous section was added to the electroless plating solution, and the mixture was thoroughly stirred and dispersed to conduct a plating experiment. An iron Hull Cell cathode plate (B-60-P01A, Yamamoto Plating Tester Co., Ltd.) was used as the substrate, and after degreasing with a steel degreasing solution (Nickel Boomer HCR Prople V, Nippon Chemical Industry Co., Ltd.), it was activated by immersion in 5% hydrochloric acid, and then immersed in a plating solution heated to 85°C for 20 minutes to form a plating film.

[0029] 4) Evaluation of the coating The silicone resin content of the resulting plating film was measured using an X-ray fluorescence analyzer (Rigaku, ZSX100e), the hardness of the plating film was measured using a micro Vickers hardness tester (Mitutoyo, HM-200), and the friction coefficient of the film was measured using a friction and wear tester (Trinity Lab, TL-201Tt). The water contact angle was also measured using an automatic contact meter (Kyowa Interface Science, MD-301).

[0030] <Examples 7 to 11> Silicone resin dispersions were produced in the same manner as in Examples 1 to 6, except that the composition of the silicone resin dispersions produced was changed. Specifically, the type of surfactant contained in the silicone resin dispersion, the concentration of particles contained in the plating solution, and the particle content in the plating film were changed, and composite plating films were produced, and then the composite plating films were evaluated. The results are shown in Tables 1 and 2.

[0031] <Comparative Examples 1 and 2> In Comparative Examples 1 and 2, the amount of powder added to the plating solution was varied to examine the change in the content in the film and the resulting changes in film properties. Comparative Example 1 is an example where the powder addition amount is 0 g / L (electroless nickel plating film that becomes the matrix), and Comparative Example 2 is an example where the powder addition amount is 1.5 g / L, and the content in the film is less than 3 vol%. Table 1 shows the conditions and particle content in the film.

[0032] [Table 1]

[0033] Photographs of the surface and cross section of the coating of Example 5 (addition amount 8 g / L) are shown in Figures 1 and 2. It can be seen that particles are uniformly incorporated throughout the entire coating. Furthermore, photographs of the surface and cross section of the coating of Example 6 (addition amount 34.5 g / L) are shown in Figures 3 and 4. Similarly, it can be seen that particles are incorporated uniformly throughout the entire coating.

[0034] The relationship between the content in the plating film and the film hardness and friction coefficient is shown in Table 2. For comparison, data on a PTFE composite electroless nickel plating film (PTFE 30 vol%) is also shown.

[0035] [Table 2]

[0036] In Examples 1 to 11, the friction coefficient is significantly reduced compared to Comparative Example 1 (electroless nickel plating film). Comparative Example 2, which has a low content, does not have an adequate effect of reducing the friction coefficient. Furthermore, Examples 3 to 11 show similar friction coefficients, and the effect of reducing the friction coefficient does not change much when the particle content is 10 vol% or more. As with PTFE composite coatings, the hardness of the coating decreases with the particle content. At high particle content, the Vickers hardness is around 200.

[0037] The water contact angle and the water droplet sliding angle are shown in Table 3. The water droplet sliding angle was measured by placing the plating sample on a plate fixed at one end with double-sided tape, placing a predetermined amount of water droplet on it, and then gradually lifting the other end of the plate, and recording the angle of the plate when the water droplet ran down.

[0038] [Table 3]

[0039] The electroless nickel plating film has a small contact angle of water, making it difficult for droplets to slide off. Example 4 was slightly inferior to the PTFE composite plating film in water repellency, but still exhibited water sliding properties comparable to those of the PTFE composite plating film.

[0040] FIG. 5 shows the hardness of the coating when the coating of Example 5 was heat treated. The higher the heat treatment temperature, the higher the hardness of the coating, reaching a maximum at 450°C, thereby improving wear resistance.

[0041] As described above, the present invention involves codepositing a silicone resin powder onto an electroless nickel plating film, and can provide a plating film with the low friction coefficient and water repellency expected of conventional PTFE composite plating, without using any substances that fall under the PFAS category.

Claims

1. Electroless nickel composite plating film made by co-depositing silicone resin powder into electroless nickel plating solution.

2. 2. The electroless nickel composite plating film according to claim 1, wherein the content of the silicone resin powder is 3 vol % or more.

3. 2. The electroless nickel composite plating film according to claim 1, wherein the silicone resin powder has an average particle size of 0.1 to 3.0 μm.

4. 2. The electroless nickel composite plating film according to claim 1, wherein the plating is followed by a heat treatment at a temperature of 200 to 500°C.

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