Zinc plating solution and zinc plating treatment method

Abstract

Provided are a zinc plating solution and a zinc plating method that can suppress the occurrence of black spot stains and form zinc plating with good appearance and corrosion resistance. The zinc plating solution contains zinc ions, chloride ions, a buffer, and a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant as a brightener, and sodium ions or potassium ions.

Description

[Technical Field]

[0001] The present invention relates to a zinc plating solution and a zinc plating method. [Background technology]

[0002] Zinc chloride plating is often used on cast iron (brake calipers), which is difficult to electrodeposit, due to its very high deposition rate. Zinc chloride plating is broadly divided into two types: ammonium chloride baths, as described in Patent Document 1, and potassium chloride baths. Generally, the majority of plating solutions used on cast iron are ammonium chloride baths.

[0003] However, the ammonia contained in ammonium chloride baths is subject to wastewater regulations, which places a burden on wastewater treatment, and in some countries it is designated as a regulated substance, so zinc plating is sometimes performed using a potassium chloride bath. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-143360 Summary of the Invention [Problem to be solved by the invention]

[0005] When zinc plating is performed using a bath containing potassium or sodium ions, such as a potassium chloride bath, a problem arises where black spots (commonly known as alkali spots) appear on the surface of cast iron within a short period (1-2 days) if the surface is left to stand after the zinc plating has formed. These black spots impair the appearance of the plating and can also lead to a deterioration of corrosion resistance.

[0006] An object of the present invention is to provide a zinc plating solution and a zinc plating method that can suppress the occurrence of black spots and form zinc plating that has good appearance and corrosion resistance. [Means for solving the problem]

[0007] It has been believed that countless pores exist in cast iron material, and that alkaline chemicals such as alkaline degreasing agents penetrate these pores, causing alkaline components to leach out of the pores and appear as black spots after a certain period of time. However, when the inventors actually observed the surface of black spots on products treated in a potassium chloride bath, they detected a large amount of potassium, leading to the discovery that potassium hydroxide incorporated in the plating film absorbs moisture from the ambient air and leaches out of the plating film, causing the black spots. After extensive research, the inventors have found that the above-mentioned problems can be solved by the zinc plating solution and zinc plating method specified below.

[0008] (1) Zinc ions, chloride ions, buffering agent, and a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant as a brightening agent, Sodium ions or potassium ions, A zinc plating solution containing [the specified ingredient]. (2) The zinc plating solution according to (1) further comprising metal ions other than zinc and a chelating agent. (3) The zinc plating solution according to (2), wherein the chelating agent is a water-soluble carboxylic acid or a water-soluble amine. (4) The zinc plating solution according to any one of (1) to (3) above, wherein the buffer is one or more of ammonia, boric acid, formic acid, acetic acid, gluconic acid, citric acid, malic acid, and amines. (5) A zinc plating method comprising a plating step of forming a zinc plating on the surface of a metal substrate using a zinc plating solution described in any of (1) to (4) above. (6) The zinc plating method according to (5), further comprising a pickling step of pickling the surface of a metal substrate with a pickling solution before forming the zinc plating. (7) The zinc plating method according to (6), further comprising a desmutting step between the pickling step and the plating step, wherein ultrasonic treatment is performed with a treatment solution containing an alkaline agent and a chelating agent. (8) The zinc plating method according to (7) above, wherein the chelating agent contained in the treatment solution is a water-soluble carboxylic acid or a water-soluble amine. (9) The zinc plating method according to any one of (5) to (8), further comprising, after the plating step, a trivalent chromium chemical conversion treatment step of treating the plated surface of the metal base material with a hexavalent chromium-free chemical conversion treatment solution containing trivalent chromium ions, nitrate ions, and colloidal silica. (10) The method for zinc plating treatment according to any one of (5) to (9), wherein the metal substrate is cast iron. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a zinc plating solution and a zinc plating method that can suppress the occurrence of black spots and form zinc plating that has good appearance and corrosion resistance. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, the embodiments for carrying out the present invention will be described in detail. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0011] <Zinc plating solution> Traditionally, the cause of black spots that occur when zinc plating is formed on the surface of cast iron is potassium hydroxide or sodium hydroxide. Since the source of these spots is potassium ions or sodium ions contained in the plating, the occurrence of black spots is caused by the plating process. Cast iron contains many impurities, including carbon, resulting in a low hydrogen overpotential, i.e., low plating current efficiency. Therefore, some of the potassium ions or sodium ions contained in the plating solution are generated as potassium hydroxide or sodium hydroxide and incorporated into the plating film. Normally, the electrodeposition reaction of acid zinc plating is simplified and proceeds as follows. When the plating current efficiency decreases, reaction 2 is accelerated, and as a result, potassium hydroxide or sodium hydroxide is more easily generated, making it easier for black spots to occur. Zn 2+ + 2e - →Zn (Reaction 1: Main reaction) 2H2O → H2+ 2OH - (Reaction 2: Increase in pH produces potassium hydroxide or sodium hydroxide)

[0012] In contrast, the zinc plating solution according to the present invention contains zinc ions, chloride ions, a buffer, a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant as a brightener, and sodium ions or potassium ions. This configuration, in which the β-naphthol-based anionic surfactant or the cumylphenol-based anionic surfactant is added as a brightener, densifies the zinc plating film without reducing plating current efficiency by electrodeposition along the surface of the metal substrate. As a result, even though the solution contains sodium ions or potassium ions, sodium hydroxide or potassium hydroxide is less likely to be produced, thereby suppressing the occurrence of black spots.

[0013] (zinc ions) Examples of sources of zinc ions in the zinc plating solution include zinc chloride, zinc sulfate, and zinc oxide. Of these, zinc chloride is preferred. The zinc ion concentration in the zinc plating solution is preferably 20 to 100 g / L. When the zinc ion concentration in the zinc plating solution is 20 g / L or more, the current efficiency is improved. When the zinc ion concentration in the zinc plating solution is 100 g / L or less, the throwing power of the plating is improved. The zinc ion concentration in the zinc plating solution is more preferably 30 to 60 g / L.

[0014] (chloride ions) Examples of sources of chloride ions in zinc plating solutions include potassium chloride, sodium chloride, and ammonium chloride. The chloride ion concentration in the zinc plating solution is preferably 160 to 250 g / L. When the chloride ion concentration in the zinc plating solution is 160 g / L or more, the throwing power of the plating is improved. When the chloride ion concentration in the zinc plating solution is 250 g / L or less, the salt concentration in the plating bath is reduced, thereby preventing salting out of the plating solution. The chloride ion concentration in the zinc plating solution is more preferably 180 to 220 g / L.

[0015] (buffering agent) The buffer in the zinc plating solution may be one or more of ammonia, boric acid, formic acid, acetic acid, gluconic acid, citric acid, malic acid, and amines, of which ammonia, boric acid, or acetic acid is more preferred.

[0016] The concentration of the buffer in the zinc plating solution is preferably 10 to 100 g / L. When the concentration of the buffer in the zinc plating solution is 10 g / L or more, it is effective in preventing kogation of the plating and improving the adhesion of the plating film. When the concentration of the buffer in the zinc plating solution is 100 g / L or less, the salt concentration in the plating bath is reduced, thereby preventing salting out of the plating solution and improving the current efficiency. The concentration of the buffer in the zinc plating solution is more preferably 20 to 90 g / L.

[0017] (Gloss agent) Examples of β-naphthol-based anionic surfactants used as brighteners in zinc plating solutions include polyoxyethylene β-naphthol sulfonates, polyoxypropylene β-naphthol sulfonates, etc. As the polyoxyethylene β-naphthol sulfonates, sodium polyoxyethylene β-naphthol sulfonate is particularly preferred.

[0018] The concentration of β-naphthol-based anionic surfactant as a brightener in the zinc plating solution is preferably 0.5 to 5 g / L. A concentration of β-naphthol-based anionic surfactant as a brightener in the zinc plating solution of 0.5 g / L or higher improves the adhesion of the plating and densifies the plating film. A concentration of β-naphthol-based anionic surfactant as a brightener in the zinc plating solution of 5 g / L or lower improves the cloud point (cloudiness) of the plating solution. A concentration of β-naphthol-based anionic surfactant as a brightener in the zinc plating solution of 1 to 3 g / L is more preferable.

[0019] Examples of cumylphenol-based anionic surfactants used as brighteners in zinc plating solutions include polyoxyethylene-p-cumylphenyl ether sulfate and polyoxypropylene-p-cumylphenyl ether sulfate. Among polyoxyethylene-p-cumylphenyl ether sulfates, sodium polyoxyethylene-cumylphenyl ether sulfate is particularly preferred.

[0020] The concentration of cumylphenol-based anionic surfactant as a brightener in a zinc plating solution is preferably 0.5 to 5 g / L. A concentration of cumylphenol-based anionic surfactant as a brightener in a zinc plating solution of 0.5 g / L or higher improves the adhesion of the plating and densifies the plating film. A concentration of cumylphenol-based anionic surfactant as a brightener in a zinc plating solution of 5 g / L or lower improves the cloud point (turbidity) of the plating solution. A concentration of cumylphenol-based anionic surfactant as a brightener in a zinc plating solution of 1 to 3 g / L is more preferable.

[0021] In zinc plating solutions, the brightener more preferably contains one or more of the following brighteners in addition to a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant. Examples of such brighteners include polyoxyethylene alkyl ether sulfonates, aromatic carboxylates (benzoates, salicylates, cinnamic acid, m-chlorobenzoic acid, p-chlorobenzoic acid, etc.), aromatic aldehydes (vanillin, pyrogallol, anisaldehyde, benzaldehyde, o-chlorobenzaldehyde, etc.), aromatic ketones (benzylideneacetone, etc.), aromatic chlorides (benzoyl chloride, etc.), and the like.

[0022] The concentration of polyoxyethylene alkyl ether sulfonate in the zinc plating solution is preferably 1 to 10 g / L, and more preferably 3 to 9 g / L. The concentration of benzoates such as sodium benzoate in the zinc plating solution is preferably 1 to 10 g / L, and more preferably 1 to 8 g / L. The concentration of aromatic aldehydes, aromatic ketones, and aromatic chlorides in the zinc plating solution is preferably 0.01 to 1.0 g / L, and more preferably 0.01 to 0.4 g / L.

[0023] Furthermore, when forming a zinc alloy plating using a zinc plating solution, in addition to the above components, metal ions other than zinc and chelating agents may also be included. Alternatively, the brightener may be used in two parts: a primary brightener, which serves as a base agent for smoothing the plating, and a secondary brightener, which serves as a brightener for increasing the glossiness of the plating.

[0024] (metal ions other than zinc) Other metal ions besides zinc include ions of metals that form alloy plating with zinc, such as nickel ions, aluminum ions, copper ions, magnesium ions, iron ions, lead ions, and tin ions, which are commonly used in zinc alloy plating. Sources of these metal ions include chlorides, sulfates, and oxides of these metals.

[0025] The concentration of metal ions other than zinc in the zinc plating solution is preferably 10 to 40 g / L. When the concentration of metal ions other than zinc in the zinc plating solution is 10 g / L or more, the throwing power is improved and the co-deposition rate is easily controlled. When the concentration of metal ions other than zinc in the zinc plating solution is 40 g / L or less, the co-deposition rate is easily controlled. The concentration of metal ions other than zinc in the zinc plating solution is more preferably 12 to 25 g / L.

[0026] (Chelating agent) The chelating agent is preferably a water-soluble carboxylic acid or a water-soluble amine. Examples of water-soluble carboxylic acids include gluconic acid, citric acid, malic acid, and tartaric acid. Of these, gluconic acid or citric acid is particularly preferred. Examples of water-soluble amines include triethanolamine, ethanolamine, ethylenediamine, diethylenetriamine, triethylenetetramine, or ethylene oxide reactants thereof. Of these, diethylenetriamine or ethylene oxide reactants are particularly preferred.

[0027] The concentration of the chelating agent in the zinc plating solution is preferably 5 to 50 g / L. When the concentration of the chelating agent in the zinc plating solution is 5 g / L or more, the effects of improving plating adhesion and facilitating control of the co-deposition rate are achieved. When the concentration of the chelating agent in the zinc plating solution is 50 g / L or less, the effects of improving current efficiency are achieved. The concentration of the chelating agent in the zinc plating solution is more preferably 10 to 40 g / L.

[0028] <Zinc Plating Method> The zinc plating method according to the embodiment of the present invention includes a step of forming a zinc plating on the surface of a metal substrate using the zinc plating solution according to the embodiment of the present invention (plating step). Furthermore, the zinc plating method according to the embodiment of the present invention preferably includes an alkaline degreasing step, an acid pickling step, and a desmutting step, in this order, as pretreatments for the plating step, and preferably includes a trivalent chromium chemical conversion treatment step as posttreatments for the plating step. Each step will be described in detail below.

[0029] (metal base material) The metal substrate to be treated in the zinc plating method according to the embodiment of the present invention is, for example, steel, which is iron containing carbon and which may develop black spots during zinc plating. In particular, when cast iron, which has traditionally been problematic due to the development of black spots, is used as the metal substrate, the development of black spots after zinc plating is effectively suppressed, and the effects of the present invention can be more clearly confirmed. Examples of cast iron include gray cast iron and ductile cast iron.

[0030] (Alkaline degreasing process) In the alkaline degreasing process, there are no particular limitations on the conditions, and the processing temperature and processing time can be adjusted as appropriate depending on the condition of the metal substrate. The processing solution used for alkaline degreasing can be prepared by dissolving a commercially available alkaline degreasing agent in sodium hydroxide as a solvent.

[0031] (pickling process) In the pickling step, the metal substrate after alkaline degreasing is immersed in a treatment bath of a pickling treatment solution and pickled. The pickling is preferably carried out under the following conditions. Type of acid: 35% by mass hydrochloric acid aqueous solution or 75% by mass sulfuric acid aqueous solution, preferably 35% by mass hydrochloric acid aqueous solution Acid concentration: 150-500 mL / L, preferably 250-400 mL / L Inhibitor: Compounds containing hexamethylenetriamine or reaction products of epichlorohydrin with amine compounds Inhibitor concentration: 0.1 to 3.0 g / L, preferably 1.5 to 2.5 g / L Processing temperature: 20~40℃ Processing time: 1 to 15 minutes, preferably 3 to 10 minutes

[0032] (Desmutting process) In the desmutting process, the pickled metal substrate is immersed in a treatment solution containing an alkaline agent and a chelating agent, followed by ultrasonic treatment. Here, smut refers to a fine powder substance composed of carbon and metal oxides that adheres to the surface of the metal substrate. Examples of alkaline agents include sodium hydroxide, potassium hydroxide, and sodium carbonate, with sodium hydroxide being preferred. The concentration of the alkaline agent is 40 to 90 g / L, preferably 50 to 80 g / L. The chelating agent is a water-soluble carboxylic acid such as gluconic acid, ethylenediaminetetraacetic acid (EDTA), or citric acid, or a water-soluble amine such as triethanolamine or diethylenetriamine. Of these, gluconic acid, ethylenediaminetetraacetic acid (EDTA), citric acid, or triethanolamine is preferred. The concentration of the chelating agent is 5 to 80 g / L, preferably 20 to 80 g / L. The conditions for the desmutting treatment are as follows: Processing temperature: 25 to 70°C, preferably 40 to 60°C Processing time: 1 to 10 minutes, preferably 2 to 10 minutes Ultrasonic frequency: 28kHZ~40kHZ

[0033] The above-mentioned pickling and desmutting processes can reduce smut on the surface of the metal substrate, thereby normalizing the electrodeposition in the subsequent plating process and suppressing the occurrence of defective coatings, thereby more effectively suppressing the occurrence of black spots. Traditionally, anodic electrolysis has been recommended for desmutting steel products, especially high-carbon steel. The anodic electrolysis method removes smut through the generation of oxygen gas by electrolysis of water and the electrolytic dissolution of the metal substrate. However, when the metal substrate is cast iron, the high impurity content makes anodic electrolysis more likely to result in smut due to dissolution of the cast iron than through electrolytic dissolution of the cast iron. Furthermore, the silicon in cast iron causes anodic oxidation, resulting in poor plating adhesion and the development of black spots, making it difficult to enhance smut removal with anodic electrolysis. Besides electrolysis, immersion desmutting processes are also known. However, the chemicals used in the immersion method are strong oxidizers, which, when introduced into the plating solution, oxidize the plating solution, leading to plating defects. Furthermore, the presence of oxidizers places a strain on wastewater treatment, making their use impractical. On the other hand, immersion-based desmutting processes that do not contain oxidizers are completely ineffective. From this perspective, in the present invention, it is appropriate to remove smut using a method that utilizes a physical action other than anodic electrolysis. After extensive research, the inventors have found that smut can be effectively removed by performing ultrasonic treatment in a solution containing an alkaline agent and a chelating agent. After the desmutting step, an acid activation step may be carried out in which the material is immersed in an aqueous solution of hydrochloric acid for a predetermined time in order to neutralize the alkaline components on the surface of the material and to activate the surface of the material.

[0034] (Plating process) In the plating step, the metal substrate is immersed in a zinc plating bath using the zinc plating solution according to the embodiment of the present invention described above, and electrolytic plating is performed under the following plating conditions: The thickness of the formed zinc plating is 1 to 50 μm. Temperature of plating solution: 20 to 50°C, preferably 25 to 40°C pH of plating solution: 4.5 to 6.0, preferably 5.0 to 5.8 (pH is preferably adjusted with hydrochloric acid or potassium hydroxide) • Cathode current density of the plating bath: 1.0~4.0 A / dm 2, preferably 1.5 to 4.0 A / dm 2

[0035] According to the above-mentioned plating process, the zinc plating solution contains a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant as a brightener, and by electrodeposition along the surface of the metal substrate, the zinc plating film can be densified and the plating current efficiency can be improved. As a result, potassium hydroxide is less likely to be produced, and the occurrence of black spots can be suppressed. After the plating step, an activation step may be carried out in which the plated surface is immersed in an aqueous solution of nitric acid or hydrochloric acid for a predetermined time in order to activate the plated surface.

[0036] (Trivalent chromium conversion coating process) After the plating step, the plated surface of the metal substrate is treated with a hexavalent chromium-free chemical conversion treatment solution containing trivalent chromium ions, nitrate ions, and colloidal silica.

[0037] Examples of sources of trivalent chromium ions contained in the chemical conversion treatment solution include chromium nitrate, chromium chloride, chromium sulfate, chromium acetate, and chromium hydroxide. Of these, chromium nitrate, chromium sulfate, and chromium chloride are preferred. The concentration of trivalent chromium ions in the chemical conversion treatment solution is 0.5 to 5.0 g / L, and preferably 1.0 to 4.0 g / L.

[0038] Sources of the nitrate ions contained in the chemical conversion treatment solution include nitric acid, nitric acid compounds such as sodium nitrate, ammonium nitrate, etc. The nitrate ion concentration is 1.5 to 30 g / L, and preferably 3 to 20 g / L.

[0039] Anions other than nitrate ions may be added to the chemical conversion treatment solution as needed. Sources of anions other than nitrate ions may include sulfate compounds such as sulfuric acid, sodium sulfate, and ammonium sulfate, halogen compounds such as hydrochloric acid, sodium chloride, potassium chloride, and ammonium fluoride, phosphoric acid compounds, or organic sulfonic acid compounds. The concentration of anions other than nitrate ions is 0 to 15 g / L, and preferably 0 to 10 g / L.

[0040] The colloidal silica contained in the chemical conversion treatment solution can be a commercially available common colloidal silica, and the particle size is not particularly limited. Examples of colloidal silica that can be used include Snowtex XS (hereinafter, Snowtex is a registered trademark), Snowtex OXS, Snowtex CXS, Snowtex C, Snowtex OX, Snowtex OS, Snowtex UP, and Snowtex OUP, manufactured by Nissan Chemical Industries, Ltd. The concentration of colloidal silica in the chemical conversion treatment solution is 0.5 to 8.0 g / L, preferably 1.0 to 6.0 g / L, in terms of Si.

[0041] The chemical conversion treatment solution may contain cobalt ions, if necessary, generated from sources such as cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt hydroxide, etc. The cobalt ion concentration is 0 to 5.0 g / L, and preferably 0 to 3.0 g / L.

[0042] The chemical conversion treatment solution may contain other metal ions as needed. Examples of other metal ions include zinc ions, aluminum ions, titanium ions, zirconium ions, molybdenum ions, tungsten ions, vanadium ions, and cerium ions. These metal ions are preferably water-soluble. Sources of these metal ions include vanadium sulfate, vanadium chloride, vanadium oxalate, aluminum chloride, aluminum sulfate, and Orgatix TC-310, Orgatix TC-300, and Orgatix ZC-126 (manufactured by Matsumoto Fine Chemical Co., Ltd.), ammonium titanium fluoride, ammonium zirconium fluoride, and fluorozirconic acid. The concentration of the other metal ions is 0 to 5.0 g / L, preferably 0 to 3.0 g / L.

[0043] The chemical treatment solution may contain a chelating agent as needed. Examples of chelating agents include dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid; oxycarboxylic acids such as citric acid, malic acid, tartaric acid, and gluconic acid; and aminocarboxylic acids such as nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and glycine. Of these, oxalic acid, malonic acid, succinic acid, tartaric acid, malic acid, and citric acid are preferred as chelating agents. The concentration of the chelating agent is 0 to 20 g / L as an organic acid, and preferably 0 to 10 g / L.

[0044] The trivalent chromium chemical conversion treatment is carried out by immersing the plated metal substrate in the above chemical conversion treatment solution and performing electrolytic treatment under the following conditions. pH of chemical conversion treatment solution: 1.5 to 5.0, preferably 1.8 to 4.5 Processing temperature: 20 to 50°C, preferably 25 to 40°C Processing time: 20 to 120 seconds, preferably 30 to 90 seconds

[0045] As described above, by treating the plated surface of a metal substrate with a hexavalent chromium-free chemical conversion treatment solution containing trivalent chromium ions, nitrate ions, and colloidal silica, a two-layer film consisting of a Cr layer and a Si layer can be formed on the plated surface of the metal substrate. Furthermore, by appropriately adjusting the conditions of the chemical conversion treatment solution, the Cr layer and Si layer can be formed to be thick and dense. With this configuration, the chemical conversion film does not peel off or discolor over time, and the occurrence of black spots caused by the chemical conversion film can be suppressed more effectively. [Example]

[0046] The following are examples of the present invention, provided to better understand the invention and not intended to limit it.

[0047] (Examples 1 to 13, Reference Example 1, Comparative Examples 2 to 5) A disc brake cylinder (material: FCD-450 (cast iron), size: 10cm (depth) x 21cm (width) x 16cm (height)) was prepared as the material to be treated. As shown in Tables 1 to 18, the alkaline degreasing process, pickling process, desmutting process, acid activation process, plating process, activation process, post-treatment process (trivalent chromium conversion treatment process), and drying process were carried out on the material in this order. Note that the desmutting process was not performed for Reference Example 1, Comparative Examples 3 and 5. A rinsing step was performed after each processing step. In addition, the pH of the plating solution was adjusted with hydrochloric acid or potassium hydroxide, and the pH of the post-treatment solution was adjusted with nitric acid or sodium hydroxide. Tables 1 to 18 also show the chemicals and processing conditions used in each step. Table 19 shows details such as the classification of raw materials and raw material components of the drugs used in Tables 1-18.

[0048] [Table 1]

[0049] [Table 2]

[0050] [Table 3]

[0051] [Table 4]

[0052] [Table 5]

[0053] [Table 6]

[0054] [Table 7]

[0055] Table 8

[0056] Table 9

[0057] Table 10

[0058] Table 11

[0059] Table 12

[0060] Table 13

[0061] Table 14

[0062] Table 15

[0063] Table 16

[0064] Table 17

[0065] [Table 18]

[0066] [Table 19-1] [Table 19-2] [Table 19-3]

[0067] <Evaluation test> • Appearance evaluation The samples prepared in Examples 1-13, Reference Example 1, and Comparative Examples 2-5 were visually inspected for appearance and color tone, and their gloss was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 20. A: Glossy appearance (glossy appearance) B: Less glossy than A but has a semi-glossy appearance

[0068] • Black spot / stain evaluation The samples prepared in Examples 1-13, Reference Example 1, and Comparative Examples 2-5 were left for one month at 30°C (room temperature) and 95% RH (relative humidity). Afterward, the appearance of the samples was evaluated, and the presence or absence of black spots was observed and evaluated according to the following criteria. The evaluation results are shown in Table 20. A: No black spots or stains C: Black spots present

[0069] • Corrosion resistance evaluation The samples prepared in Examples 1-13, Reference Example 1, and Comparative Examples 2-5 were left for 48 hours, after which a salt spray test was performed according to JIS Z 2731. The samples were then visually inspected, and the time at which white rust and red rust developed was evaluated. The evaluation results are shown in Table 20.

[0070] [Table 20]

[0071] <Consideration> The samples of Examples 1 to 13 were treated with a zinc plating solution containing zinc ions, chloride ions, a buffer, a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant as a brightener, and sodium ions or potassium ions. Furthermore, the samples were treated by optimizing the pretreatment (pickling process and desmutting process) and post-treatment (two-layer coating of Cr and Si). As a result, the occurrence of black spots was suppressed, and zinc plating with good appearance and corrosion resistance was formed. In Reference Example 1, the plating solution did not contain a brightener such as a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant, but since the plating solution did not contain potassium ions or sodium ions, which cause black spots, no black spots occurred. In Comparative Example 2, the plating solution did not contain a brightener related to a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant, and black spots occurred. In Comparative Examples 3 to 5, the conditions of Comparative Example 2 were the same as those of Comparative Example 2, and the pretreatment was not optimized, and the post-treatment was only a Cr coating, so black spots occurred.

Claims

1. zinc ions, chloride ions, a buffer, and a β-naphthol-based anionic surfactant or a cumylphenol-based anionic surfactant as a brightener; sodium ions or potassium ions, A zinc plating solution comprising:

2. 2. The zinc plating solution according to claim 1, further comprising metal ions other than zinc and a chelating agent.

3. 3. The zinc plating solution according to claim 2, wherein the chelating agent is a water-soluble carboxylic acid or a water-soluble amine.

4. 2. The zinc plating solution according to claim 1, wherein the buffer is at least one of ammonia, boric acid, formic acid, acetic acid, gluconic acid, citric acid, malic acid, and amines.

5. A zinc plating method, comprising a plating step of forming a zinc plating on a surface of a metal substrate using the zinc plating solution according to any one of claims 1 to 4.

6. The zinc plating method according to claim 5, further comprising a pickling step of pickling the surface of the metal substrate with a pickling solution before forming the zinc plating.

7. 7. The zinc plating method according to claim 6, further comprising a desmutting step between the pickling step and the plating step, in which ultrasonic treatment is carried out in a treatment solution containing an alkaline agent and a chelating agent.

8. 8. The zinc plating method according to claim 7, wherein the chelating agent contained in the treatment solution is a water-soluble carboxylic acid or a water-soluble amine.

9. 6. The zinc plating method according to claim 5, further comprising, after the plating step, a trivalent chromium chemical conversion treatment step of treating the plated surface of the metal base material with a hexavalent chromium-free chemical conversion treatment solution containing trivalent chromium ions, nitrate ions, and colloidal silica.

10. 6. The method of claim 5, wherein the metal substrate is cast iron.

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