Method for forming metal oxide films

Abstract

To extend the lifespan of plating baths used for forming metal oxide films and to enable more efficient use of the plating baths. [Solution] The method for forming a metal oxide film comprises the steps of forming a metal oxide film on the surface of a plated object using a plating bath containing a metal compound that forms the film and a boron compound that acts as a reducing agent, and regenerating the plating bath using an adsorption filter that adsorbs boric acid.

Description

[Technical Field]

[0001] This disclosure relates to a method for forming a metal oxide film and a plating tank therefor. [Background technology]

[0002] A known method for forming a metal film on a non-conductive surface to be plated, such as a glass substrate, involves first forming a zinc oxide film on the surface of the plated object, and then performing electroless plating of a metal film such as copper or gold. While methods such as vapor deposition, sputtering, and sol-gel methods are known for forming a zinc oxide film on the surface of the plated object, electroless plating is attracting attention because it can easily form a zinc oxide film on the surface of the plated object.

[0003] The electroless plating method for zinc oxide coatings is performed using a plating bath containing zinc nitrate and a boron-based reducing agent such as dimethylaminoborane (DMAB). Since the process can be carried out simply by immersing the object to be plated in the plating bath, a zinc oxide coating can be easily formed (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-278437 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, plating baths for zinc oxide coatings have a problem: they have a short lifespan. Boron-based reducing agents such as DMAB rapidly decompose in the plating bath to produce boric acid. Electroless plating of zinc oxide coatings proceeds with the involvement of hydroxide ions. Boric acid in the plating bath inhibits the formation of hydroxide ions and zinc hydroxide, so even though sufficient zinc ions and reducing agents remain in the plating bath, the ability to deposit zinc oxide coatings rapidly decreases. For this reason, the plating bath needs to be replaced frequently.

[0006] Such problems can occur not only with zinc oxide films but also in the formation of other metal oxide films using boron-containing reducing agents.

[0007] The objective of this disclosure is to extend the lifespan of a plating bath used for forming metal oxide films and to enable efficient use of the plating bath. [Means for solving the problem]

[0008] One embodiment of the method for forming a metal oxide film according to the present disclosure comprises the steps of forming a metal oxide film on a surface to be plated using a plating bath containing a metal compound for forming the film and a boron compound as a reducing agent, and regenerating the plating bath using an adsorption filter that adsorbs boric acid.

[0009] One method for forming a metal oxide film involves regenerating the plating bath using a filter that adsorbs boric acid. This allows the boric acid concentration in the plating bath to remain low, enabling the plating bath to be used for extended periods. This significantly improves productivity. [Effects of the Invention]

[0010] The method for forming a metal film according to this disclosure significantly extends the lifespan of the plating bath and enables efficient film formation. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an example of a plating tank used in the method for forming a metal oxide film according to the present disclosure. [Modes for carrying out the invention]

[0012] The method for forming the metal oxide film according to this embodiment can be carried out using a plating bath 100 as shown in FIG. 1. The plating bath 100 includes a bath main body 101 containing a plating solution 104 and a circulation circuit 102 for circulating the plating solution 104 contained in the bath main body 101. The circulation circuit 102 includes a circulation pump 121, a first filter 122, and a second filter 123. The first filter 122 is a normal filtration filter for removing foreign substances such as aggregates in the plating solution 104. The second filter 123 is a column filled with chelating resin beads that selectively remove boric acid. The plating solution 104 is an electroless plating solution for a zinc oxide film containing zinc nitrate as a metal source and DMAB as a reducing agent.

[0013] By immersing a plating object 106 such as a glass substrate in the plating solution 104 in the plating bath 100, a zinc oxide film can be formed on the surface of the plating object 106. In the deposition of the zinc oxide film in the plating solution 104, boric acid and electrons (e , , - , 2+ ) are generated from DMAB, which is a reducing agent (Equation 1). Zinc nitrate dissociates into zinc ions and nitrate ions (Equation 2). Nitrate ions generate nitrite ions and hydroxide ions with water and electrons (Equation 3). Zinc ions combine with hydroxide ions to form zinc hydroxide, and further, as zinc hydroxide changes to zinc oxide, a zinc oxide film is deposited on the surface of the plating object 106 (Equations 4 and 5).

[0014] (CH3)2NHBH3 + 3H2O → H3BO3 + (CH3)2H2N + +5H + +6e - ···(Equation 1) Zn(NO3)2 → Zn 2+ +2NO3 - ···(Equation 2) NO3 - +H2O + 2e - →NO2 - +2OH - ···(Equation 3) Zn 2+ +2OH - →Zn(OH)2 ···(Equation 4) Zn(OH)2 → ZnO + H2O ··· (Equation 5)

[0015] Since the boric acid generated from DMAB has a buffering function, it inhibits the reaction of Equation (4). Therefore, as the plating reaction progresses, the boric acid concentration in the plating bath 104 increases, and the film-forming ability rapidly decreases. Usually, it is necessary to replace the plating bath 104 every time. However, in this embodiment, the boric acid in the plating bath 104 is continuously removed by the second filter 123. For this reason, since the increase in the boric acid concentration in the plating bath 104 is suppressed, the life of the plating bath 104 can be extended and it can be used efficiently.

[0016] The generation of boric acid due to the decomposition of DMAB proceeds even when the plating object 106 is not immersed in the plating bath 104. For this reason, it is preferable to continuously operate the circulation pump 121 to remove boric acid. However, the circulation pump 121 can be operated intermittently. Also, the boric acid concentration in the plating bath 104 can be monitored, and the circulation pump 121 can be operated when the boric acid concentration exceeds a predetermined value. It is also possible to alternately perform the plating cycle in which the plating object 106 is immersed in the plating bath 104 and the regeneration cycle in which the circulation pump 121 is operated to remove the boric acid in the plating bath 104 and regenerate the plating bath 104.

[0017] The configuration of the plating tank 100 for removing boric acid by circulating the plating bath 104 in the tank body 101 by the circulation pump 121 has been shown. However, it is also possible to use a batch-type plating tank in which the plating bath 104 is withdrawn from the tank body 101 for regeneration and the regenerated plating bath 104 is returned to the tank body 101 again.

[0018] The second filter 123 for removing boric acid is a column filled with chelating resin beads that selectively remove boric acid. By using a column, handling becomes easy and it can efficiently come into contact with the plating bath, so the removal efficiency of boric acid can be increased. It is not limited to beads, and a column filled with powder, fiber, etc. can be used. A column filled with beads having a large particle size is preferable because clogging and the like are less likely to occur. Porous resin beads or resin fibers can also be used. This can increase the liquid contact area and improve the removal efficiency of boric acid.

[0019] As the chelating resin, one having a chelating formation part that selectively forms a chelate with boric acid can be used. The chelating formation part can use a structure such as a polyhydric alcohol or catechol having a plurality of hydroxyl groups. Among them, those having a glucamine group (N-methylglucamine group) as the chelating formation part are preferable. The carrier for supporting the chelating formation part is not limited to resin, and inorganic particles such as silica can also be used. Also, a column filled with cerium hydroxide, hydrotalcite, etc. can be used as the second filter 123.

[0020] The first filter 122 is not particularly limited, and a non-woven fabric filter or the like can be used. Also, the first filter 122 may be provided as necessary or may not be provided. The first filter 122 can also be provided on the downstream side of the second filter 123.

[0021] Although an example was shown where the metal source of the plating bath 104 is zinc nitrate, other zinc-containing compounds such as zinc chloride, zinc carbonate, and zinc sulfate can be used, not just zinc nitrate. When forming a metal oxide film other than zinc oxide, compounds such as cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), aluminum (Al), titanium (Ti), zirconium (Zr), tin (Sn), and silicon (Si) can be used. The concentration of the metal compound used as the metal source can be appropriately selected depending on the type and application of the film, but is preferably 0.01 mol / L or higher, more preferably 0.05 mol / L or higher, more preferably 0.2 mol / L or lower, and more preferably 0.09 mol / L.

[0022] The reducing agent is not limited to DMAB; boron-based reducing agents can be used. For example, sodium borohydride, trimethylaminoborane (TMAB), etc., can be used. The concentration of the reducing agent can be appropriately selected depending on the type of film and its application, but is preferably 0.0001 mol / L or higher, more preferably 0.0005 mol / L or higher, even more preferably 0.001 mol / L or higher, preferably 0.5 mol / L or lower, more preferably 0.3 mol / L or lower, and even more preferably 0.2 mol / L or lower.

[0023] In addition to the metal source and reducing agent, the plating bath 104 may optionally contain pH adjusting agents such as nitric acid, hydrochloric acid, and sulfuric acid. The pH of the plating bath 104 is not particularly limited, but is preferably around 4 to 6. The plating bath 104 can be used at a temperature of preferably 10°C or higher, more preferably 50°C or higher, preferably 90°C or lower, and more preferably 80°C or lower. The immersion time of the object to be plated 106 in the plating bath 104 can be selected depending on the type, thickness, and application of the required coating, but is preferably 10 minutes or more, more preferably 15 minutes or more, preferably 200 minutes or less, more preferably 100 minutes or less, and even more preferably 30 minutes or less.

[0024] In the metal oxide film formation method of this embodiment, the concentration of boric acid in the plating bath 104 during use is preferably maintained at 1.0 g / L or less, more preferably at 0.5 g / L or less, and even more preferably at 0.3 g / L or less. By maintaining such a concentration and forming the metal oxide film, a metal oxide film with excellent peel strength can be formed.

[0025] When the plating bath 104 is used continuously, the consumed metal source and reducing agent can be replenished so that the concentrations of the metal source and reducing agent do not fluctuate significantly over time. From the viewpoint of forming a consistent film, it is preferable to maintain the concentrations of the metal source and reducing agent at the initial values, preferably 90% to 110%, and more preferably 95% to 105%. In addition, the pH can be adjusted by adding acid or alkali as appropriate.

[0026] In this embodiment, the material to be plated can be a material having hydroxyl groups (-OH) on its surface, such as glass. It is not limited to glass; it can also be a non-conductive material such as ceramics or resin having hydroxyl groups on its surface. Furthermore, it can be a material that normally does not have hydroxyl groups but has been surface-treated to introduce them. The shape of the material to be plated is not limited to a flat plate such as a substrate; it can also have a three-dimensional shape.

[0027] The metal oxide formed in the metal oxide film formation method of this embodiment can be used as an adhesion-improving layer for materials that are difficult to plate (such as glass) and cannot be adhered to at all by conventional methods.

[0028] Although this embodiment describes a method for forming a zinc oxide film, the same method can be used to form other metal oxide films using a boron-based reducing agent. For example, the same method can be used to form oxide films of cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), aluminum (Al), titanium (Ti), tin (Sn), and silicon (Si). [Examples]

[0029] The present invention will be described in more detail below with reference to examples. The following examples are illustrative and are not intended to limit the present invention.

[0030] <Measurement of zinc concentration> The zinc concentration in the plating bath was measured by chelation titration.

[0031] <Measurement of reducing agent concentration> The concentration of the reducing agent in the plating bath was measured by redox titration.

[0032] <Measurement of boric acid concentration> The concentration of boric acid in the plating bath was measured by neutralization titration.

[0033] <Measuring film thickness> The thickness of the coating was calculated by measuring the difference between the mass before and after plating, and then considering the substrate area and the density of zinc oxide.

[0034] <Measurement of Peel Strength> The peel strength of the coating was measured using an Autograph (Shimadzu Corporation, Autograph AGS-X).

[0035] <Evaluation of the effects of boric acid> The peel strength of the resulting film was measured after adding different amounts of boric acid to the plating bath and immersing a glass substrate (5cm x 5cm) at 80°C for 20 minutes.

[0036] The plating bath was prepared with a zinc nitrate (hexahydrate) concentration of 14.9 g / L (0.05 mol / L) and a DMAB concentration of 1.2 g / L (0.02 mol / L). Boric acid was added in amounts of 1.1 g, 3.1 g, 5.1 g, and 10.1 g per liter of the plating bath.

[0037] The peel strength was 900 gf / cm without boric acid, and 401 gf / cm with 1.1 g of boric acid added. When 3.1 g of boric acid was added, film precipitation was observed, but blistering occurred and the film peeled off immediately, making it impossible to measure the peel strength. When 5.1 g and 10.1 g of boric acid were added, no film precipitation was observed.

[0038] (Example 1) In a plating tank configured as shown in Figure 1, 2.8 L of zinc nitrate (hexahydrate) solution (14.9 g / L, 0.05 mol / L) was added, and the solution was circulated at a flow rate of 450 mL / min at a temperature of 80°C. The first filter was a nonwoven fabric filter (manufactured by Nippon Filter, FSG-1 cartridge filter). The second filter was a column packed with 300 g of chelate resin containing N-methylglucamine (manufactured by Mitsubishi Chemical Corporation, Diaion CRB-05) as the chelate-forming element.

[0039] DMAB was added to the plating bath at a concentration of 1.2 g / L (0.02 mol / L), and a glass substrate was immersed in it. After 20 minutes, the substrate was removed, and the zinc and DMAB concentrations were measured. The consumed zinc nitrate and DMAB were replenished. Five minutes after removing the first glass substrate, it was immersed again to perform the second coating process. This coating process was repeated 15 times.

[0040] From the first to the fifteenth immersion, the film thickness after 20 minutes of immersion remained almost constant at approximately 0.2 μm. The peel strength of the film ranged from approximately 600 gf / cm to 900 gf / cm. Good film formation was achieved from the first to the fifteenth immersion. The boric acid concentration after film formation in the fifth and tenth immersions was 5.4 ppm, and after film formation in the fifteenth immersion was 20.8 ppm. The results are summarized in Table 1.

[0041] [Table 1]

[0042] (Comparative Example 1) Film formation on the glass substrate was carried out in the same manner as in Example 1, without circulating the solution through a filter. The first film had a thickness of 0.2 μm and a peel strength of 902 gf / cm. However, blistering occurred during the second application, making it impossible to measure the peel strength. [Industrial applicability]

[0043] The method for forming a metal oxide film according to this disclosure stabilizes the plating bath and enables efficient film formation, making it useful in the field of film formation. [Explanation of Symbols]

[0044] 100 plating tanks 101 Tank body 102 Circulation circuit 104 Plating bath 106 Plating targets 121 Circulation pump 122 First filter 123 Second filter

Claims

1. A process of forming a metal oxide film on the surface of a plated object using a plating bath containing a metal compound that forms the film and a boron compound that acts as a reducing agent, A method for forming a metal oxide film, comprising the step of regenerating the plating bath by adsorbing the boric acid produced by the decomposition of the reducing agent using an adsorption filter that adsorbs boric acid.

2. The method for forming a metal oxide film according to claim 1, wherein the adsorption filter comprises a chelating resin that selectively adsorbs boric acid.

3. The method for forming a metal oxide film according to claim 2, wherein the chelate resin is a resin having methylglucamine as a chelate-forming portion.

4. The process of forming the aforementioned film is carried out by immersing the object to be plated in a plating tank containing the plating bath. The method for forming a metal oxide film according to claim 1, wherein the regeneration step is performed by circulating the plating bath in the plating tank by passing it through the adsorption filter.

5. The method for forming a metal oxide film according to claim 4, wherein the step of forming the film and the step of regeneration are performed simultaneously and in parallel.

6. The method for forming a metal oxide film according to claim 1, wherein the reducing agent comprises dimethylaminoborane (DMAB).

7. The method for forming a metal oxide film according to claim 1, wherein the metal is zinc.

8. A plating tank containing a plating bath containing a metal compound that forms a film and a boron compound that acts as a reducing agent, into which a plated object is immersed to form a metal oxide film on the surface of the plated object, The system includes a plating bath regeneration unit that regenerates the plating bath in the plating tank by adsorbing boric acid produced by the decomposition of the reducing agent, The plating bath regeneration unit comprises an adsorption filter for adsorbing boric acid and a pump for returning the plating bath in the plating tank to the plating tank through the adsorption filter.

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