Acidic zinc plating bath and manufacturing method for zinc plating component

Abstract

To provide a technique that reduces the need for acid-based activation treatment that is usually carried out prior to the chemical conversion treatment after acidic zinc plating, and in a preferred aspect, that can omit acid-based activation treatment.SOLUTION: There is provided an acidic zinc plating bath including a bath-soluble zinc-containing substance and a chelating agent comprising a bath-soluble hydroxycarboxylic acid substance, where the hydroxycarboxylic acid that provides the bath-soluble hydroxycarboxylic acid substance is one or more selected from the group consisting of gluconic acid and citric acid, and when a depth profile is obtained for a zinc plating film formed using the acidic zinc plating bath, the thickness of an oxide layer that is defined as a region on the surface side with an oxygen concentration of 5 atom% or more, is 7 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acidic zinc plating bath containing a film quality improver that is added to the acidic zinc plating bath to modify the zinc plating film formed from the bath, a zinc plating apparatus that is an apparatus for performing zinc plating in the acidic zinc plating bath, and a method for producing a member (zinc-plated member) provided with a zinc plating film with improved film quality. [Background technology]

[0002] Zinc plating films are widely used for everyday materials, including steel plates for automobiles and machine parts made of steel, such as bolts and nuts, to improve functionality such as corrosion resistance and heat resistance.

[0003] A zinc plating film is formed by electroplating, in which electrolysis is performed while the member to be plated is immersed in a plating bath for forming the zinc plating film (also referred to as a "zinc plating bath" in this specification). This zinc plating bath is roughly classified into alkaline baths (e.g., Patent Document 1, etc.) and acidic baths (e.g., Patent Document 2, etc.), with the alkaline baths being cyanide baths and zincate zinc plating baths, and the acidic baths being zinc chloride baths and zinc sulfate baths. An appropriate bath is selected from these zinc plating baths, taking into consideration various conditions such as the desired hardness and gloss of the zinc plating film, the shape and size of the member to be plated, and the working environment.

[0004] Members coated with a zinc plating film (zinc-plated members) are rarely used as they are, and are often subjected to a chemical conversion treatment to form a chemical conversion film, as disclosed in Patent Document 3, for example. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 1-298192 [Patent Document 2] Patent No. 4307810 [Patent Document 3] Patent No. 7133889 Summary of the Invention [Problem to be solved by the invention]

[0006] As disclosed in the examples of Patent Document 3, when a chemical conversion treatment is performed on a zinc-plated member using a chemical conversion treatment solution, an activation treatment (acid-based activation treatment) including contact with an inorganic acid such as hydrochloric acid or nitric acid may be performed as a pretreatment. If this acid-based activation treatment is omitted, there is a concern that the reaction of the chemical conversion treatment will be insufficient, resulting in a decrease in the corrosion resistance of the member that has been subjected to the chemical conversion treatment.

[0007] From the viewpoint of increasing the productivity of zinc-plated members, it is effective to reduce the number of processes. However, as described above, acid-based activation treatment has been practically essential until now, and therefore, the process control of the acid (concentration, temperature, contact time) for the acid-based activation treatment has been an obstacle to improving productivity.

[0008] In view of the current situation, the present invention aims to provide a technique that reduces the need for an acid-based activation treatment that is usually performed prior to chemical conversion treatment after acid zinc plating, and in a preferred embodiment, makes it possible to omit the acid-based activation treatment. Specifically, the present invention aims to provide an acidic zinc plating bath containing a film quality improver that is added to an acidic zinc plating bath to modify a zinc plating film formed from the bath (reducing the need for an acid-based activation treatment as a pretreatment for chemical conversion treatment), a zinc plating apparatus that is an apparatus for performing zinc plating in the acidic zinc plating bath, and a method for manufacturing a member (zinc-plated member) having a modified zinc plating film. [Means for solving the problem]

[0009] The present invention provided to solve the above problems includes the following aspects. (1) An acidic zinc plating bath comprising a bath-soluble zinc-containing substance and a chelating agent comprising a bath-soluble hydroxycarboxylic acid substance, wherein the hydroxycarboxylic acid that gives the bath-soluble hydroxycarboxylic acid substance is at least one selected from the group consisting of gluconic acid and citric acid, and wherein, when a depth profile is obtained for a zinc plating film formed using the acidic zinc plating bath, the thickness of an oxide layer, which is defined as a surface region having an oxygen concentration of 5 atomic % or more, is 7 nm or less. (2) The acidic zinc plating bath according to (1) above, wherein the bath-soluble hydroxycarboxylic acid substance has a content of 4 mmol / L or more calculated as hydroxycarboxylic acid. (3) The acidic zinc plating bath according to (1) above, which is a boric acid-free chloride bath. (4) The acidic zinc plating bath according to the above (1), which contains at least one of a primary brightener and a secondary brightener. (5) A zinc plating apparatus for forming a zinc plating film on a plated member having a portion made of an iron-based material by using the acidic zinc plating bath according to any one of (1) to (4) above, the zinc plating apparatus having a removal section that brings a removal member for removing iron ions into contact with the acidic zinc plating bath. (6) A method for producing a zinc-plated member comprising a plated member having a portion made of an iron-based material and a zinc plating film provided on the plated member, the method comprising forming a zinc plating film on the plated member using an acidic zinc plating bath described in any one of (1) to (4) above, and subjecting the zinc plating film to a chemical conversion treatment without subjecting the plated member to an acid-based activation treatment. (7) A method for producing a zinc-plated member as described in (6) above, comprising forming a zinc plating film on the member to be plated using the zinc plating apparatus as described in (5) above. Effect of the Invention

[0010] The film quality improver according to the present invention can reduce the need for an acid-based activation treatment in a chemical conversion treatment performed after acid zinc plating. Therefore, for a zinc-plated member obtained using an acid zinc plating bath containing such a film quality improver, the treatment conditions for the acid-based activation treatment before the chemical conversion treatment can be relaxed compared to conventional conditions, and in a preferred example, the acid-based activation treatment does not need to be performed. Even in such a case, the member after the chemical conversion treatment can maintain an appropriate corrosion resistance. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram showing the results of XPS analysis of the surface of a zinc-plated member according to an example. [Figure 2A] FIG. 1 is a view showing the appearance of a zinc-plated member produced in Example 57. [Figure 2B] FIG. 1 is a view showing the appearance of a zinc-plated member produced in Example 58. [Figure 2C] FIG. 1 is a view showing the appearance of a zinc-plated member produced in Example 65. [Figure 3A] FIG. 13 shows the depth profile of the zinc-plated member produced in Example 57. [Figure 3B] FIG. 13 shows the depth profile of the zinc-plated member produced in Example 58. [Figure 3C] FIG. 13 shows the depth profile of the zinc-plated member produced in Example 65. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below.

[0013] 1. Film quality improver for acidic zinc plating bath A film quality improver for an acidic zinc plating bath according to one embodiment of the present invention (the present modifier) ​​contains, as an active ingredient, a chelating agent (also referred to as "chelating agent (A)" in this specification) consisting of one or more selected from the group consisting of bath-soluble hydroxycarboxylic acid substances and bath-soluble EDTA substances, or a chelating source which is a substance capable of generating the chelating agent (A) in an acidic zinc plating bath. The present modifier may be a liquid containing the chelating agent (A), or when the chelating source is a solid, the present modifier may be a solid or liquid dispersion containing the chelating source.

[0014] In this specification, the term "bath-soluble hydroxycarboxylic acid substance" refers to one or more substances selected from the group consisting of hydroxycarboxylic acids, which are carboxylic acids having a hydroxyl group, and substances based thereon, which are soluble in an acidic zinc plating bath, and specific examples include hydroxycarboxylic acids (including associations and hydrates) and hydroxycarboxylic acid ions. Examples of substances (hydroxycarboxylic acid sources) that serve as raw materials for bath-soluble hydroxycarboxylic acid substances include derivatives of hydroxycarboxylic acids, such as hydroxycarboxylic acid (including associations), hydroxycarboxylic acid salts, and hydroxycarboxylic acid esters. When the hydroxycarboxylic acid has optical isomers, it may be any of D-, L-, and DL-isomers.

[0015] The hydroxycarboxylic acid that gives the soluble hydroxycarboxylic acid substance contained in the present modifying agent is at least one selected from the group consisting of gluconic acid and citric acid. Hereinafter, the soluble hydroxycarboxylic acid substance based on gluconic acid may be referred to as the "chelating agent (A-1)" and the soluble hydroxycarboxylic acid substance based on citric acid may be referred to as the "chelating agent (A-2)."

[0016] In this specification, the "bath-soluble EDTA substance" refers to one or more substances selected from the group consisting of substances containing ethylenediaminetetraacetic acid and substances based thereon and soluble in an acidic zinc plating bath, specific examples of which include ethylenediaminetetraacetic acid (including associated compounds) and ethylenediaminetetraacetate ions. Examples of substances that can be used as raw materials for the bath-soluble EDTA substance (EDTA sources) include ethylenediaminetetraacetic acid (including associated compounds), ethylenediaminetetraacetate salts, and derivatives of ethylenediaminetetraacetic acid. Hereinafter, the bath-soluble EDTA substance may be referred to as the "chelating agent (A-3)".

[0017] A zinc plating film obtained from an acidic zinc plating bath containing the chelating agent (A) is unlikely to produce zinc hydroxide on its surface. Therefore, when the zinc plating film is subjected to a chemical conversion treatment, the need for subjecting the zinc plating film to an acid-based activation treatment is reduced, and in a preferred example, the acid-based activation treatment is substantially unnecessary. Therefore, in a zinc plating film and a zinc-plated member having a chemical conversion film, poor appearance and deterioration in corrosion resistance caused by improperly performing an acid-based activation treatment are unlikely to occur. The reason why zinc hydroxide is unlikely to form on the surface of a zinc plating film obtained from an acidic zinc plating bath containing the chelating agent (A) is unclear, but as described later, the oxidation of zinc near the surface of the plating film is suppressed (it is metallic) to the same extent as when an acid-based activation treatment is performed, so that even after the zinc ions complexed with the chelating agent (A) are precipitated as plating (by reduction), the chelating agent (A) may be located near the zinc and function as an antioxidant for zinc.

[0018] The present modifier may contain components other than the chelating agent (A), such as primary brighteners, secondary brighteners, antioxidants, antifoaming agents, and sequestering agents.

[0019] 2. Acidic zinc plating bath The zinc plating bath according to one embodiment of the present invention is acidic, and therefore has a higher current efficiency and is more productive than an alkaline zinc plating bath. The zinc plating bath according to one embodiment of the present invention contains a bath-soluble zinc-containing substance and a chelating agent (A) as an active ingredient of the modifier. For this reason, the zinc plating film formed from the zinc plating bath according to this embodiment can be subjected to chemical conversion treatment without reducing the need for an acid-based activation treatment, and in a preferred example, without performing an acid-based activation treatment. The zinc plating member provided with the chemical conversion film thus obtained is likely to have a good appearance and excellent corrosion resistance.

[0020] (1) Metallic components The zinc plating bath according to this embodiment contains a bath-soluble zinc-containing substance. In this specification, the bath-soluble zinc-containing substance is a supply source of zinc to be deposited as a zinc plating film, and refers to one or more components selected from the group consisting of zinc cations and bath-soluble substances containing the same. Since the zinc plating bath according to this embodiment is acidic, an example of a bath-soluble zinc-containing substance is zinc ion (Zn 2+ Examples of raw materials (also referred to as "zinc sources" in the present invention) for supplying bath-soluble zinc-containing substances to the plating bath include zinc chloride, zinc sulfate, zinc oxide, etc., and zinc chloride (chloride bath) may be particularly preferred.

[0021] The zinc-equivalent content of the bath-soluble zinc-containing substance in the zinc plating bath according to the present embodiment (the zinc-equivalent content of the soluble zinc-containing substance in the bath) is not limited. If this content is too low, the zinc plating film may be difficult to deposit, so the above-mentioned zinc-equivalent content is preferably 5 g / L or more, more preferably 10 g / L or more, and particularly preferably 15 g / L or more. If the zinc-equivalent content of the soluble zinc-containing substance is too high, poor appearance and reduced throwing power may easily occur, so the above-mentioned zinc-equivalent content is preferably 200 g / L or less, more preferably 150 g / L or less, and particularly preferably 120 g / L or less.

[0022] (2) Additive components The zinc plating bath according to one embodiment of the present invention contains the above-mentioned chelating agent (A), which is the active ingredient of the present modifier, and may contain other additive components.

[0023] (2-1) Chelating agent (A) (2-1-1) Chelating agent (A-1) In the case where the zinc plating bath according to one embodiment of the present invention contains a chelating agent (A-1), a non-limiting example of the gluconic acid-based content of the chelating agent (A-1) in the zinc plating bath is 0.5 mmol / L or more and 50 mmol / L or less. When the gluconic acid-based content of the chelating agent (A-1) is 0.5 mmol / L or more, the effect of including the chelating agent (A-1) is easily obtained. From the viewpoint of stably obtaining the effect of including the chelating agent (A-1), the gluconic acid-based content of the chelating agent (A-1) may be preferably 1 mmol / L or more, more preferably 2 mmol / L or more, particularly preferably 4 mmol / L or more, and extremely preferably 4.6 mmol / L or more. On the other hand, if the gluconic acid-based content of the chelating agent (A-1) is 50 mmol / L or less, the substance can be sufficiently dissolved in the plating bath, and the possibility of excessive load on wastewater treatment is not particularly increased. In setting the composition of the zinc plating bath, from the viewpoint of minimizing the influence on the adjustment range of the contents of other components, the content of the chelating agent (A-1) calculated as gluconic acid may be preferably 30 mmol / L or less, and more preferably 20 mmol / L or less.

[0024] (2-1-2) Chelating agent (A-2) In the case where the zinc plating bath according to one embodiment of the present invention contains a chelating agent (A-2), a non-limiting example of the content of the chelating agent (A-2) in the zinc plating bath in terms of citric acid is 2 mmol / L or more and 200 mmol / L or less. When the content of the chelating agent (A-2) in terms of citric acid is 2 mmol / L or more, the effect of including the chelating agent (A-2) is easily obtained. From the viewpoint of stably obtaining the effect of including the chelating agent (A-2), the content of the chelating agent (A-2) in terms of citric acid may be preferably 4 mmol / L or more, more preferably 8 mmol / L or more, and particularly preferably 16 mmol / L or more. On the other hand, if the content of the chelating agent (A-2) in terms of citric acid is 200 mmol / L or less, the substance can be sufficiently dissolved in the plating bath, and the possibility of excessive load on wastewater treatment is not particularly increased. In setting the composition of the zinc plating bath, from the viewpoint of minimizing the influence on the adjustment range of the contents of other components, the content of the chelating agent (A-2) in terms of citric acid may be preferably 150 mmol / L or less, and more preferably 100 mmol / L or less.

[0025] (2-1-3) Chelating agent (A-3) In the case where the zinc plating bath according to one embodiment of the present invention contains a chelating agent (A-3), a non-limiting example of the EDTA-equivalent content of the chelating agent (A-3) in the zinc plating bath is 2 mmol / L or more and 200 mmol / L or less. When the EDTA-equivalent content of the chelating agent (A-3) is 2 mmol / L or more, the effect of containing the chelating agent (A-3) is easily obtained. From the viewpoint of stably obtaining the effect of containing the chelating agent (A-3), the EDTA-equivalent content of the chelating agent (A-3) may be preferably 4 mmol / L or more, more preferably 8 mmol / L or more, and particularly preferably 16 mmol / L or more. On the other hand, if the EDTA-equivalent content of the chelating agent (A-3) is 200 mmol / L or less, the substance can be sufficiently dissolved in the plating bath, and the possibility of excessive load on wastewater treatment is not particularly increased. In setting the composition of the zinc plating bath, from the viewpoint of minimizing the influence on the adjustment range of the contents of other components, the content of the chelating agent (A-3) in terms of EDTA may be preferably 150 mmol / L or less, and more preferably 100 mmol / L or less.

[0026] (2-2) Other additives The zinc plating bath according to one embodiment of the present invention may contain, as an additive component, a substance other than the above-mentioned chelating agent (A). Examples of such additive components or materials that provide additive components in the zinc plating bath include the following.

[0027] (2-2-1) Primary gloss agent The zinc plating bath according to one embodiment of the present invention may contain a primary brightener as one type of additive component. Examples of such primary brighteners include anionic surfactants, nonionic surfactants, and water-soluble organic compounds such as water-soluble cationic polymer compounds, which are used in various zinc plating baths.

[0028] The primary brightener may have both structures contained in anionic surfactants such as sulfonic acid groups and structures contained in nonionic surfactants such as polyethers. Such compounds include alkali metal salts of aromatic or aliphatic polyether sulfates.

[0029] In the case where the zinc plating bath according to an embodiment of the present invention contains a primary brightener, it may be preferable that the primary brightener is a nitrogen-free surfactant, specific examples of which include the above-mentioned aromatic or aliphatic polyether sulfate alkali metal salts and polyether compounds of acetylenic dialcohols.

[0030] In the case where the zinc plating bath according to one embodiment of the present invention contains a primary brightener, the content of the primary brightener in the zinc plating bath is not limited. It is appropriately set depending on the type of primary brightener, the type and content of components other than the primary brightener contained in the zinc plating bath, the composition of the zinc plating film formed from the zinc plating bath, etc. As an example, the content of the primary brightener is preferably 0.1 g / L or more and 100 g / L or less, and more preferably 0.5 g / L or more and 20 g / L or less.

[0031] (2-2-2) Secondary gloss agent The zinc plating bath according to one embodiment of the present invention may contain a secondary brightener as one type of additive component. In particular, from the viewpoint of improving the brightness, the secondary brightener may contain an aromatic compound having a carbonyl group. Examples of such compounds include aromatic aldehydes such as anisaldehyde, veratraldehyde, o-chlorobenzaldehyde (OCAD), salicylaldehyde, vanillin, piperonal, and p-hydroxybenzaldehyde; and acetones having an aromatic ring such as benzylideneacetone.

[0032] In the case where the zinc plating bath according to one embodiment of the present invention contains a secondary brightener, the content of the secondary brightener in the zinc plating bath is not limited. It is appropriately set depending on the type of secondary brightener, the type and content of components other than the secondary brightener contained in the zinc plating bath, the composition of the zinc plating film formed from the zinc plating bath, etc. As an example, the content of the secondary brightener is preferably 0.001 g / L or more and 10 g / L or less, and more preferably 0.005 g / L or more and 1 g / L or less.

[0033] (2-2-3) Other The zinc plating bath according to one embodiment of the present invention may contain additive components other than the above-mentioned components. Examples of such additive components include antioxidants, antifoaming agents, and sequestering agents.

[0034] Examples of the antioxidant include hydroxyphenyl compounds such as phenol, catechol, resorcin, hydroquinone, and pyrogallol, L-ascorbic acid, and sorbitol.

[0035] Examples of the defoaming agent include silicone-based defoaming agents and organic defoaming agents such as surfactants, polyethers, and higher alcohols.

[0036] Examples of the sequestering agent include silicates (a specific example is sodium silicate) and silica (a specific example is colloidal silica). The content of the sequestering agent in the zinc plating bath is not limited. It may be set appropriately taking into consideration the type of sequestering agent, the composition of the solvent, and the like. As an example, the content of the sequestering agent is preferably 0.1 g / L or more and 100 g / L or less, and more preferably 0.5 g / L or more and 20 g / L or less.

[0037] (3) Inorganic electrolytes, buffers The zinc plating bath according to one embodiment of the present invention may contain an inorganic electrolyte. Examples of inorganic electrolytes include chloride ions, sulfate ions, nitrate ions, phosphate ions, sodium ions, potassium ions, magnesium ions, and aluminum ions, which may be mixed into the zinc plating bath as salts consisting of cations and anions. As such salts, potassium salts such as potassium chloride may be preferable in terms of ease of dissolution. The total content of inorganic electrolytes contained in the zinc plating bath according to one embodiment of the present invention is not limited. It is appropriately set according to the type of inorganic electrolyte, the type and content of components other than the inorganic electrolyte contained in the zinc plating bath, plating conditions, and the like. For example, the total content of inorganic electrolytes contained in the zinc plating bath is preferably 10 g / L or more and 1000 g / L or less, and more preferably 50 g / L or more and 500 g / L or less. When the acidic zinc plating bath contains chloride ions, from the viewpoint of ensuring the stability of the bath, it may be preferable that the concentration of chloride ions in the bath is 100 g / L or more and 400 g / L or less, and it may be more preferable that the concentration is 120 g / L or more and 280 g / L or less.

[0038] The zinc plating bath according to one embodiment of the present invention may contain a substance having a buffering effect as a buffering agent. By containing the buffering agent, the pH near the surface of the plated member is prevented from becoming excessively high. As a result, the deposition form of metals such as zinc on the plated member is stabilized, and abnormal deposition is less likely to occur.

[0039] In the case where the zinc plating bath according to one embodiment of the present invention contains a buffer, the type of the buffer is not limited. Specific examples of the buffer include an ammonia-containing substance that contains at least one of ammonia and ammonium ions, a boric acid-containing substance that contains at least one of boric acid and borate ions, and an acetic acid-containing substance that contains at least one of acetic acid and acetate ions. The ammonia-containing substance may be composed of the inorganic electrolytes listed above, such as ammonium chloride.

[0040] From the viewpoint of reducing the environmental load, the content of the boric acid-containing substance in the zinc plating bath according to one embodiment of the present invention is preferably 5 g / L or less, more preferably 1 g / L or less, and even more preferably 0.1 g / L or less, calculated as boric acid, and it is particularly preferable that the zinc plating bath according to one embodiment of the present invention is substantially free of the boric acid-containing substance (boric acid-free). In this specification, boric acid-free means that boric acid and borate ions are not contained to an extent that they function as a buffer in the plating bath.

[0041] (4) Solvents and liquid properties The solvent of the zinc plating bath according to one embodiment of the present invention is mainly water. As a solvent other than water, an organic solvent having high solubility in water, such as alcohol, ether, or ketone, may be mixed in. In this case, from the viewpoint of the stability of the entire plating bath and the reduction of the burden on wastewater treatment, the ratio of the organic solvent is preferably 10% by volume or less with respect to the total solvent.

[0042] The zinc plating bath according to one embodiment of the present invention is acidic, and its pH is preferably 4 or more and 6.5 or less, and more preferably 5.0 or more and 6.0 or less. The type of material used to adjust the pH of the plating bath is not particularly limited. Known materials such as hydrochloric acid, sulfuric acid, nitric acid, and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide may be used.

[0043] (5) Preparation method The method for preparing the zinc plating bath according to this embodiment is not particularly limited. The zinc plating bath can be prepared by dissolving a zinc source and a chelating agent (A) or a chelating source that is a substance capable of producing a chelating agent (A) in a zinc plating bath in a solvent mainly composed of water. If necessary, a metal source, the above-mentioned other additive components as optional added components, a buffer, an inorganic electrolyte, etc. may be dissolved in the solvent.

[0044] 3. Zinc plating film A zinc plating film formed on a plated member (one specific example of which has a portion made of an iron-based material such as steel) using the acidic zinc plating bath according to this embodiment has a thin oxide layer formed near the surface, so that treatment unevenness is unlikely to occur when the zinc plating film is subjected to a chemical conversion treatment. Therefore, with the zinc plating film formed using the acidic zinc plating bath according to this embodiment, it is possible to omit the acid activation treatment that is generally performed before the chemical conversion treatment.

[0045] In this specification, a plating step is carried out to form a zinc plating film on a plated member using an acidic zinc plating bath, followed by a water washing step (washing with running ion-exchanged water for 30 seconds) and a drying step (holding at 80°C for 10 minutes), and the resulting member is subjected to depth analysis using an XPS (X-ray photoelectron spectroscopy) to define the thickness of the "oxide layer" from the obtained depth profile. A specific example of depth analysis is elemental analysis performed in 1 nm steps while performing argon gas etching. In this specification, the oxide layer refers to the surface side region in the depth profile where the oxygen concentration is 5 atomic % or more. Therefore, in this specification, the thickness of the oxide layer of the zinc plating film is the thickness from the surface to the part where the oxygen concentration reaches 5 atomic %.

[0046] The thickness of the oxide layer of the zinc plating film obtained using the acidic zinc plating bath according to the present embodiment is 7 nm or less. When the thickness of the oxide layer is 7 nm or less, an acid-based activation treatment is not required. As specifically shown in the examples described later, the acid-based activation treatment is a process for removing at least a part of the oxide layer of the zinc plating film, and the thickness of the oxide layer of the zinc plating film after the acid-based activation treatment is appropriately performed is 7 nm or less. From the viewpoint of more stably satisfying the requirement that an acid-based activation treatment is not required, the thickness of the oxide layer of the zinc plating film of the plated member obtained using the acidic zinc plating bath according to the present embodiment is preferably 6 nm or less, more preferably 5 nm or less, and particularly preferably 4 nm or less.

[0047] 4.Zinc plating equipment A zinc plating apparatus according to one embodiment of the present invention is an apparatus for forming a zinc plating film on a plated member having a portion made of an iron-based material such as steel by using an acidic zinc plating bath, and has a removal section that brings a removal member for removing iron ions into contact with the acidic zinc plating bath. The removal section is, for example, a section that brings an ion exchange resin or a chelating resin into contact with the plating solution, and can be disposed in a part of a plating solution circulation line for stirring the plating solution in the bath.

[0048] When the member to be plated is made of an iron-based material, when acid zinc plating is performed, iron ions are diffused in the zinc plating bath due to partial dissolution of the member to be plated. Since these iron ions may affect the speed and quality of zinc plating, it is preferable to remove them. The simplest method for removing iron ions is to generate and precipitate a substance that has low solubility in the zinc plating bath, such as an iron oxide or hydroxide. However, since the zinc plating bath according to this embodiment contains a chelating agent (A), the chelating agent (A) and the iron ions form a complex, which is likely to remain in the zinc plating bath. Therefore, by providing the above-mentioned removal section and actively recovering the iron ions present in a dissolved state in the zinc plating bath, it is possible to suppress the influence of the iron ions remaining in the zinc plating bath on the zinc plating.

[0049] The basic configuration of the zinc plating apparatus according to one embodiment of the present invention, except for the removal unit, is the same as that of a general zinc plating apparatus. For example, a member to be plated as a cathode may be placed in a zinc plating bath so as to face a plate-shaped or rod-shaped anode, and a zinc plating film may be formed on the member to be plated by electrolysis while appropriately stirring the liquid in the zinc plating bath. In this case, the liquid may be stirred using a liquid circulation pump, aeration, or by moving the member to be plated in the plating bath.

[0050] Another specific example of a zinc plating device is a barrel plating facility in which a barrel containing a plated member such as a bolt is immersed in a zinc plating bath and electrolysis is performed while rotating the barrel to form a zinc plating film on the plated member. Specific examples of plated members using the barrel plating facility include bolts, nuts, screws, etc.

[0051] 5. Manufacturing method of zinc-plated members The zinc-plated member can be obtained by bringing the zinc plating bath according to the present embodiment into contact with a member to be plated and performing electrolysis using the member to be plated as a cathode (negative electrode). The method of bringing the zinc plating bath into contact with the member to be plated is not limited. Specific examples of the contact method include immersing the member to be plated in the zinc plating bath and spraying the plating solution constituting the zinc plating bath onto the member to be plated.

[0052] The material of the member to be plated is not particularly limited as long as it has electrical conductivity. Examples of the material include conductive materials, typically metal-based materials such as iron-based materials, and non-conductive materials such as resin-based materials and ceramic-based materials, on whose surfaces a layer of a conductive material is formed by electroless plating or the like. The shape of the member to be plated is also not particularly limited. Examples include primary processed products such as plates, bars, and wires; cut and ground products such as screws, bolts, and dies (which may be further polished); press processed products such as vehicle frames and device casings; and secondary processed products such as cast products such as brake calipers and engine blocks. In addition, when the member to be plated is a cast product made of an iron-based material, a zinc plating film may not be formed from an alkaline zinc plating bath due to the influence of components contained to improve castability.

[0053] The material constituting the anode (positive electrode) is not particularly limited. A metallic material containing zinc may be used as a soluble anode, or an insoluble anode may be used to supply a bath-soluble zinc-containing substance to the acidic zinc-based plating bath.

[0054] The current density in electrolysis is not particularly limited. If the current density is too low, the deposition rate of the resulting zinc plating film may be low, resulting in poor productivity, whereas if the current density is too high, the appearance of the resulting zinc plating film may deteriorate, and the uniform electrodeposition and throwing power may decrease. Taking this into consideration, the current density may be appropriately set. From the viewpoint of achieving both high productivity and high quality of the plating film, a current density of 0.1 A / dm 2 More than 15A / dm 2 It is preferable to set it to 0.5A / dm or less. 2 More than 13A / dm 2 It is more preferable to set it as follows:

[0055] The temperature of the plating bath in the electrolysis (plating bath temperature) may be in the range of about 15°C to about 50°C, and may be about room temperature (about 25°C).

[0056] The electrolysis time (plating time) is appropriately set based on the deposition rate of the plating film and the desired thickness of the plating film, which are determined by the composition of the zinc plating bath, the above-mentioned current density, the plating bath temperature, etc.

[0057] The member obtained by plating (post-plating member) is washed with water to remove the plating solution adhering to the surface. When a zinc plating bath according to the conventional technology is used, a part of the zinc located near the surface of the plating film of the post-plating member is oxidized to form hydroxides or the like due to contact with the plating solution after electrolysis and the washing process. Since this hydroxide becomes an inhibitor of the chemical reaction in the subsequent chemical conversion treatment, an acid-based activation treatment is usually performed at this stage. In the acid-based activation treatment, the plating film of the post-plating member is contacted with an aqueous solution of an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid (acid aqueous solution) with a concentration of, for example, 0.5% for, for example, 1 minute or less. The contact method is arbitrary, and examples include immersing the post-plating member in the acid aqueous solution and spraying the post-plating member with the acid aqueous solution.

[0058] In contrast, in the plating film formed using the zinc plating bath according to one embodiment of the present invention, even if a water washing step is performed, the zinc located on the surface of the plating film is not easily oxidized. Therefore, the above-mentioned acid-based activation treatment is not essential. Specifically, after water washing, a chemical conversion treatment may be performed without an acid-based activation treatment, or after water washing, an activation treatment may be performed under weaker conditions than usual, and then a chemical conversion treatment may be performed. Specific examples of "weak conditions" include a low concentration of inorganic acid in the acid aqueous solution, a low temperature of the acid aqueous solution brought into contact with the plating film, and a short contact time with the acid aqueous solution. Specific examples of weak conditions include treatment conditions in which the nitric acid concentration in the acid aqueous solution is 0.01%, the temperature of the acid aqueous solution is 10°C, and the contact time with the acid aqueous solution is 20 seconds.

[0059] By not requiring an acid-based activation treatment in this way, the possibility of occurrence of defects due to the plated member being affected by an acid aqueous solution is reduced, and in particular, when an acid-based activation treatment is not performed, the possibility of occurrence of the above-mentioned defects can be eliminated. For example, when the plated member has a bolt shape and the plating treatment is performed under conditions that reduce the thickness of the plating film from the viewpoint of improving productivity, the current density is locally low in the groove of the screw, and the plating film may become thin or may not be formed substantially on the plated member. If an acid-based activation treatment is performed on the plated member in this state, there is a concern that the plated member may come into contact with the acid aqueous solution and corrode. Even in such a case, if a plating film is formed using a zinc plating bath according to one embodiment of the present invention, the possibility of the plated member coming into contact with the acid aqueous solution can be reduced, and in a preferred example, the plated member does not come into contact with the acid aqueous solution.

[0060] The composition of the chemical conversion treatment solution in the chemical conversion treatment is not particularly limited, and it is sufficient that a zinc dissolution reaction occurs when the zinc-containing plating film comes into contact with the chemical conversion treatment solution, and hydrogen is generated based on this reaction, causing an increase in the pH of the chemical conversion treatment solution in the vicinity of the plating film, resulting in the deposition of substances containing the elements contained in the chemical conversion treatment solution.

[0061] The zinc-plated member obtained by the chemical conversion treatment may be further subjected to a surface treatment such as painting. Specific examples of such surface treatment include application of a liquid treatment agent containing an organic material such as polyvinyl alcohol and / or an inorganic material such as lithium silicate, and powder coating containing an epoxy resin.

[0062] The above-described embodiments are described for the purpose of facilitating understanding of the present invention, and are not described for the purpose of limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. EXAMPLES

[0063] The effects of the present invention will be described below based on examples, but the present invention is not limited to these.

[0064] (Examples 1 to 48) A zinc plating bath (ammonium chloride bath) having the following composition and a pH of 5.6 was prepared. Zinc chloride: 104g / L (zinc concentration: 50g / L) Ammonium chloride: 220g / L Gloss agent (Yuken Kogyo Co., Ltd. "Metas FZ-77M1"): 45ml / L Gloss agent (Yuken Kogyo Co., Ltd. "Metas FZ-77GC1"): 0.2ml / L Additives: See Tables 1 and 2

[0065] In addition, sodium gluconate is a type of chelating agent (A-1), citric acid monohydrate is a type of chelating agent (A-2), and EDTA·2Na is a type of chelating agent (A-3) shown in Tables 1 and 2. The chloride ion concentration in the above plating bath was 200g / L, and the ammonium ion concentration was 74g / L.

[0066] For each of the prepared plating baths, a steel sheet (SPCC, 50 mm x 100 mm x 0.8 mm thick) was used as the material to be plated, and the bath temperature was 30°C, the current density was 4 A / dm 2The plating treatment was carried out for 10 minutes to obtain a plated member.

[0067] After the plating process, the member was subjected to a water rinsing process (rinsing with ion-exchanged water for 30 seconds, this process is referred to as the "water rinsing process" in this specification), and then chemical conversion treatment was performed with or without an acid-based activation treatment, as shown in Tables 1 and 2. The composition of the chemical conversion treatment solution used in the chemical conversion treatment and the treatment conditions are as follows. Note that a water rinsing process was performed after the acid-based activation treatment and after the chemical conversion treatment, and a drying process (maintained at 80°C for 10 minutes, this process is referred to as the "drying process" in this specification) was performed after the water rinsing process after the chemical conversion treatment. A transfer time of 30 seconds was provided between each process, during which the member after each process was in a room temperature (25°C) environment. This transfer time was set equally between all of the following processes. composition Yuken Kogyo Co., Ltd. "Metas YFA-CFH2": 40ml / L Yuken Industrial Co., Ltd. "Metas YFA-35HR": 40ml / L Processing conditions Temperature: 40℃ pH:3.1 Time: 30 seconds

[0068] [Table 1]

[0069] [Table 2]

[0070] The corrosion resistance of the zinc-plated members obtained by the chemical conversion treatment was evaluated under the same conditions as those of the JIS Z2371 salt spray test, except that ion-exchanged water was used instead of salt water. The details of the test conditions were as follows: Spray water temperature: 35℃ Spray amount: 1.5ml / 80cm 2 / hr Test duration: 72 hours

[0071] After the test, the zinc-plated members were visually observed and evaluated for the incidence of black corrosion according to the following criteria. The evaluation results are shown in Tables 1 and 2. 1: Virtually no black corrosion has occurred. 2: Black corrosion has occurred, but the area ratio of black corrosion is less than 5%. 3: Black corrosion has occurred, and the area ratio of black corrosion is 5% or more and less than 20%. 4: Black corrosion has occurred, and the area ratio of black corrosion is 20% or more.

[0072] As shown in Table 1, it was confirmed that the zinc-plated member obtained by performing chemical conversion treatment without performing acid-based activation treatment on a plated member formed from a zinc-plating bath containing the chelating agent (A) has excellent corrosion resistance. In contrast, it was confirmed that the zinc-plated member obtained by performing chemical conversion treatment without performing acid-based activation treatment with additives other than the chelating agent (A) does not have excellent corrosion resistance. In addition, it was confirmed that, under the above test conditions, the chelating agent (A-1) can reduce the incidence of black corrosion on the zinc-plated member to less than 5% when added in an amount of 2.3 mmol / L, and does not substantially cause black corrosion on the zinc-plated member when added in an amount of 4.6 mmol / L or more. It was confirmed that, under the above test conditions, the chelating agent (A-2) and the chelating agent (A-3) can reduce the incidence of black corrosion on the zinc-plated member to less than 5% when added in an amount of 4.6 mmol / L, and does not substantially cause black corrosion on the zinc-plated member when added in an amount of 18.3 mmol / L or more.

[0073] In order to further confirm the effect of the present invention, surface analysis was performed using an XPS (X-ray photoelectron spectroscopy) on the members before chemical conversion treatment in Example 1 (activation treatment with nitric acid), Example 16 (no acid-based activation treatment using chelating agent (A-1)), and Example 4 (no additives, no acid-based activation treatment). The results are shown in Figure 1.

[0074] As shown in FIG. 1, the zinc peak values ​​are clearly different between Example 1 and Example 4, and Example 4, in which no acid activation treatment was performed, had a higher binding energy value, and zinc oxidation was observed. Specifically, the peak value of Example 4, 1022.75 eV, was outside the range (1020.8 eV to 1022.1 eV) that can be taken by the peak value of binding energy of general metallic zinc. On the other hand, in Example 16, which is an example of the present invention, although no acid activation treatment was performed, the degree of zinc oxidation was close to that of Example 1, in which acid activation treatment was performed, and it was confirmed that oxidation of zinc (generation of hydroxide) located on the surface of the plating film did not progress.

[0075] The plating film according to each Example was argon gas etched, and the oxygen content depth analysis was performed in 1 nm steps. In Example 1, where zinc oxidation was not advanced, the oxygen peak substantially disappeared at a depth of about 2 nm from the surface, but in Example 4, where zinc oxidation was advanced, the oxygen peak could be confirmed at a depth of 9 nm from the surface. In Example 16, which is an example of the present invention, the oxygen peak disappeared at a depth of 4 nm from the surface, and it was confirmed that the surface condition was equivalent to that of Example 1, where an acid-based activation treatment was performed, even though an acid-based activation treatment was not performed.

[0076] (Example 49 to Example 56) Two types of acidic zinc plating baths were prepared with the compositions shown in Table 3. The plating bath with bath number 1 was a potassium chloride bath containing boric acid (potassium borate bath), and the plating bath with bath number 2 was a boric acid-free potassium chloride bath (boric acid-free potassium bath) that did not contain boric acid. Note that "Metas FZ-500A" and "Metas FZ-77GC1" in Table 3 are both brighteners manufactured by Yuken Kogyo Co., Ltd.

[0077] [Table 3]

[0078] Using compositions prepared by adding the additives shown in Table 4 to these plating baths, a plating process was carried out for 10 minutes on steel sheets (SPCC, 50 mm × 100 mm × thickness 0.8 mm) as the plated members in the same manner as in Examples 13 to 16, to obtain plated members.

[0079] After the plating treatment, the member was subjected to a chemical conversion treatment with or without an acid-based activation treatment, as in Examples 13 to 16, as shown in Table 4. The composition of the chemical conversion treatment solution used in the chemical conversion treatment and the treatment conditions were the same as in Examples 13 to 16. Note that a water rinsing step was performed after the plating treatment, the acid-based activation treatment, and the chemical conversion treatment, and a drying step was performed after the water rinsing step after the chemical conversion treatment.

[0080] [Table 4]

[0081] The zinc-plated members obtained by the chemical conversion treatment were subjected to a corrosion resistance test using ion-exchanged water under the same conditions as in Examples 13 to 16, and the zinc-plated members after the test were evaluated according to the same criteria as in Examples 13 to 16. The evaluation results are shown in Table 4. As shown in Table 4, by using a zinc plating bath not containing boric acid, zinc-plated members having excellent corrosion resistance were obtained, similar to the case of a plating bath containing boric acid.

[0082] (Example 57 to Example 75) An acidic zinc plating bath was prepared having the composition shown in Table 5. In addition, "METAS FZ-77M1" and "METAS FZ-77GC1" in Table 5 are both brighteners manufactured by Yuken Kogyo Co., Ltd.

[0083] [Table 5]

[0084] This plating bath was used as it was, or a composition obtained by adding the additives shown in Table 6 to this plating bath was used to perform a plating process for 10 minutes on a steel plate (SPCC, 50 mm × 100 mm × thickness 0.8 mm) as a plated member in the same manner as in Examples 13 to 16, to obtain a plated member.

[0085] After the plating process, the members were washed with water, and then some members were subjected to an acid activation process followed by a washing process, while other members were directly subjected to a drying process, as shown in Table 6. For Examples 57 to 75, no chemical conversion treatment was performed in order to properly evaluate the oxide film of the plating film. Specifically, the results were as follows.

[0086] For Examples 57 to 64, plating was performed in a plating bath containing no sodium gluconate. For Example 57, no acid activation treatment was performed. For Examples 58 to 64, the acid activation treatments shown in Table 6 were performed.

[0087] For Examples 65 to 72, plating was performed in a plating bath containing 9.2 mmol / L sodium gluconate. For Example 65, no acid activation treatment was performed. For Examples 66 to 72, the acid activation treatment shown in Table 6 was performed.

[0088] In Examples 73 to 75, plating was performed in a plating bath containing 2.3 mmol / L to 18.3 mmol / L of sodium gluconate, and no acid activation treatment was performed in any of the examples.

[0089] [Table 6]

[0090] The appearance of the zinc-plated members after the drying process was evaluated. The evaluation criteria were whether or not white stains were visible. In addition, argon gas etching was performed using an XPS (X-ray photoelectron spectroscopy) to perform depth analysis of the oxygen and zinc content in 1 nm steps to obtain a depth profile. In the obtained depth profile, the region on the surface side where the oxygen concentration was 5 atomic % or more was defined as the oxide layer, and the thickness of the oxide layer was measured. These results are summarized in Table 6.

[0091] The appearance (FIGS. 2A to 2C) and depth profile (FIGS. 3A to 3C) are shown for Example 57, Example 58, and Example 65. The tables that are the source data for these depth profiles are shown below (Table 7: Example 57, Table 8: Example 58, Table 9: Example 65).

[0092] [Table 7]

[0093] [Table 8]

[0094] [Table 9]

[0095] As shown in Tables 6 to 9 and Figures 2A to 2C and Figures 3A to 3C, white stains were observed as dry stains for members having an oxide layer of 9 nm or more. For members on which white stains occur, the chemical conversion treatment is not performed appropriately, and there is a high possibility that a member on which black corrosion occurs, that is, a member with poor corrosion resistance, is formed.

[0096] On the other hand, when the thickness of the oxide layer was less than 9 nm, specifically 5 nm or less, no white stains were formed. For such members that do not have white stains, a chemical conversion treatment can be performed to stably form a member that is less susceptible to black corrosion and has excellent corrosion resistance. Considering the measurement accuracy of the oxide film thickness, it can be said that if the oxide film thickness is 7 nm or less, no white stains are formed and a chemical conversion film with excellent corrosion resistance can be stably formed. Therefore, it was confirmed that a zinc plating film with an oxide film thickness of 7 nm or less can be stably formed by using an acidic zinc plating bath containing an appropriate content of the chelating agent (A-1).

Claims

1. 1. An acidic zinc plating bath comprising a bath-soluble zinc-containing substance and a chelating agent comprising a bath-soluble hydroxycarboxylic acid substance, the hydroxycarboxylic acid that provides the bath-soluble hydroxycarboxylic acid substance is at least one selected from the group consisting of gluconic acid and citric acid; When a depth profile is obtained for a zinc plating film formed using the acidic zinc plating bath, the thickness of an oxide layer, defined as a surface region having an oxygen concentration of 5 atomic % or more, is 7 nm or less.

1. An acidic zinc plating bath comprising:

2. 2. The acidic zinc plating bath according to claim 1, wherein the bath-soluble hydroxycarboxylic acid substance has a content of 4 mmol / L or more calculated as hydroxycarboxylic acid.

3. 2. The acidic zinc plating bath according to claim 1, which is a boric acid-free chloride bath.

4. 2. The acidic zinc plating bath according to claim 1, containing at least one of a primary brightener and a secondary brightener.

5. A zinc plating apparatus for forming a zinc plating film on a plated member having a portion made of an iron-based material by using the acidic zinc plating bath according to any one of claims 1 to 4, A zinc plating apparatus having a removal section that brings a removing member for removing iron ions into contact with the acidic zinc plating bath.

6. A method for manufacturing a zinc-plated member comprising a plated member having a portion made of an iron-based material and a zinc plating film provided on the plated member, comprising: A zinc plating film is formed on the plated member by using the acidic zinc plating bath according to any one of claims 1 to 4, The zinc plating film is subjected to a chemical conversion treatment on the plated member without performing an acid-based activation treatment. A method for producing a zinc-plated member, comprising the steps of:

7. The method for producing a zinc-plated member according to claim 6, further comprising forming a zinc plating film on the member to be plated by using the zinc plating apparatus according to claim 5.

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