Patent Application
20250207285
The present invention relates to an additive for an acidic zinc alloy plating bath, an acidic zinc alloy plating bath, and a zinc alloy plating film.
In the present specification, zinc alloy plating refers to plating composed of zinc, alloying components, and inevitable impurities. In the zinc alloy plating, the concentration (mass %) of zinc in the plating may be higher than the concentration (mass %) of any other alloying element, or an alloying element having a higher concentration (mass %) than the concentration (mass %) of zinc may be contained.
Plating films of zinc alloys such as zinc-nickel alloy, zinc-iron alloy, and tin-zinc alloy (also referred to as “zinc alloy plating films” in the present specification) are widely used for the purpose of improving functionalities such as corrosion resistance and heat resistance of members around us, including machine components composed of steel materials, such as steel sheets, bolts, and nuts for automobiles.
Zinc alloy plating films are formed by electroplating in which electrolysis is performed in a state where the members to be plated are immersed in a plating bath for forming the zinc alloy plating films (also referred to as a “zinc alloy plating bath” in the present specification). Such zinc alloy plating baths are roughly divided into alkaline baths (e.g., Patent Document 1, etc.) and acidic baths (e.g., Patent Document 2, etc.), and the alkaline baths include cyanide baths and zincate-based zinc alloy plating baths while the acidic baths include zinc chloride baths and zinc sulfate baths. An appropriate bath is selected from these zinc alloy plating baths in consideration of various conditions such as the desired hardness and brightness of the zinc alloy plating films, the shape and size of the members to be plated, and the working environment.
Patent Document 3 discloses a method for the deposition of a zinc-nickel alloy layer on a substrate. This method includes contacting a substrate of cast iron or steel with an electrolytic composition comprising a source of zinc ions, a source of nickel ions, aminoacetic acid, and an acetate selected from the group consisting of sodium acetate, potassium acetate, ammonium acetate, and mixtures thereof and applying a current to form the zinc-nickel alloy layer on the substrate. The zinc-nickel alloy layer has a nickel co-deposition ratio between 10 and 18 mass % and substantially no internal stress. The acetate and the aminoacetic acid are present in a molar ratio of acetate:aminoacetic acid within a range from about 0.35:1 to about 0.91:1.
Among these zinc alloy plating baths, the acidic zinc alloy plating bath has advantages of high current efficiency and excellent productivity. Unfortunately, however, the current density dependence of the film thickness and appearance is likely to increase, so if the member to be plated has a complicated shape, the deterioration in throwing power and poor appearance will be liable to occur. In recent years, from the viewpoint of improving the productivity, there is a tendency to increase the input amount in barrel plating and increase the applied voltage in rack plating. Such a tendency is likely to cause a local increase in the current density, resulting in a locally poor appearance.
An object of the present invention is to provide an additive used to obtain an acidic zinc alloy plating bath capable of obtaining a zinc alloy plating film with a good appearance. Another object of the present invention is to provide an acidic zinc alloy plating bath capable of obtaining a zinc alloy plating film with a good appearance. Still another object of the present invention is to provide a zinc alloy plating film that is formed using the above acidic zinc alloy plating bath and has a good appearance.
Note that a zinc alloy plated member refers to a member comprising a member to be plated and a zinc alloy plating film formed on the surface to be plated of the member to be plated. Note also that “good appearance” regarding a zinc alloy plating film refers to at least one of the following situations being satisfied in comparison with the prior art: a situation where the lower limit of the current density at which abnormal deposition is likely to occur in the zinc alloy plating film increases; and a situation where a zinc alloy plating film that was non-bright at a certain current density becomes bright or semi-bright even at the same current density.
An aspect of the present invention provided to solve the above problems is an additive for an acidic zinc alloy plating bath. The additive contains as active ingredients a glycine-containing water-soluble substance and an aliphatic polyamine whose carbon number is 12 or less.
The aliphatic polyamine contained in the above additive for an acidic zinc alloy plating bath may contain one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.
The glycine/polyamine ratio, which is a ratio of a glycine-equivalent molar concentration of the glycine-containing water-soluble substance contained in the above additive for an acidic zinc alloy plating bath to a molar concentration of the aliphatic polyamine, may be preferably 0.1 or more and 40 or less, more preferably 1 or more and 35 or less, and particularly preferably 4 or more and 34 or less.
Another aspect of the present invention is an acidic zinc alloy plating bath containing a bath-soluble zinc-containing substance, a bath-soluble metal-containing substance, and the active ingredients of the above additive.
The pH of the above acidic zinc alloy plating bath may be 4 or more and 6 or less.
The above acidic zinc alloy plating bath may be preferably boric acid-free.
The above acidic zinc alloy plating bath may be preferably ammonia-free.
The above acidic zinc alloy plating bath may preferably contain an acetic acid-containing substance.
The above acidic zinc alloy plating bath may contain a bath-soluble nickel-containing substance as the bath-soluble metal-containing substance, and in this case, the co-deposition ratio of nickel in a zinc alloy plating film formed from the acidic zinc alloy plating bath may be 5 mass % or more and 20 mass % or less.
The above acidic zinc alloy plating bath may contain a bath-soluble nickel-containing substance, and the glycine/nickel ratio, which is a ratio of a glycine-equivalent molar concentration of the glycine-containing water-soluble substance to a nickel-equivalent molar concentration of the bath-soluble nickel-containing substance may be preferably 0.1 or more.
The above acidic zinc alloy plating bath may contain at least one of a primary brightener and a secondary brightener.
Still another aspect of the present invention is a zinc alloy plating film of a zinc alloy plated member in which the zinc alloy plating film is formed on a member to be plated composed of an iron-based material, wherein when a depth profile of the zinc alloy plated member is measured, an alloying element-enriched region having a relatively high alloying element concentration is absent on a side proximal to the member to be plated in the zinc alloy plating.
The above zinc alloy plating film preferably contains nickel as an alloying element and is preferably formed from a plating bath that contains glycine and an aliphatic polyamine whose carbon number is 12 or less.
When it is defined in the depth profile of the above zinc alloy plating film that a position closest to an outermost surface and having a zinc concentration of 60 mass % or more is a surface-side end portion of the zinc alloy plating film, a position at which the zinc concentration is equal to an iron concentration derived from the member to be plated is a member-side end portion of the zinc alloy plating film, and a length of a region from the surface-side end portion to the member-side end portion is a thickness of the zinc alloy plating film,
[Ni1] and [Ni2] may preferably satisfy Expression (1) below:
where [Ni1] is an average value of nickel concentration in an intermediate region represented by a range of 40% to 60% of the thickness of the zinc alloy plating from the surface-side end portion, and [Ni2] is a maximum value of nickel concentration in an initial region represented by a range between the member-side end portion and a position moved from the member-side end portion to the surface side by 30% of the thickness of the zinc alloy plating film.
By using the acidic zinc alloy plating bath containing the additive according to the present invention, it is possible to obtain a zinc alloy plating film with a good appearance. Moreover, according to the present invention, a zinc alloy plated member having a zinc alloy plating film with a good appearance can be obtained.
Hereinafter, the present invention will be described in detail.
The additive for an acidic zinc alloy plating bath according to an embodiment of the present invention (the present additive) contains, as active ingredients, a glycine-containing water-soluble substance and an aliphatic polyamine having a plurality of amino groups and whose carbon number is 12 or less (which may be simply noted as “polyamine (A)” in the present specification).
In the present specification, the glycine-containing water-soluble substance refers to a glycine-based water-soluble substance generated in a plating bath from a glycine source that is a substance capable of giving glycine in the plating bath, such as glycine or glycine hydrochloride. Since the plating bath according to the present embodiment is acidic, glycinium ions represent a specific example of the glycine-containing water-soluble substance. Specific examples of the glycine source also include glycine derivatives such as the methyl ester of glycine.
The polyamine (A) is an aliphatic compound whose carbon number is 12 or less. Provided that the polyamine (A) has a plurality of amino groups, other structures of the polyamine (A) are not limited. The polyamine (A) may be any of primary amine, secondary amine, and tertiary amine. In the plating solution, the polyamine (A) may be ionized by being given one or more protons (H+). Specific examples of the polyamine (A) will be described later.
A zinc alloy plating film having a bright appearance can be easily obtained from an acidic zinc alloy plating bath that contains the glycine-containing water-soluble substance and the polyamine (A). Moreover, even when electroplating is performed under conditions of a high current density, for example, conditions exceeding 10 A/dm2, poor appearance due to abnormal deposition is less likely to occur in the obtained zinc alloy plating film. As will be described later, in a zinc-nickel alloy plating film having poor appearance, the nickel concentration of the plating in a region proximal to the end portion of the plating film on the side of the member to be plated, that is, the nickel concentration of the plating formed in the initial stage of a plating process (immediately after the start of energization) tends to be specifically higher than in other regions. If the nickel concentration increases in this manner, the deposited plating film will turn black, making it difficult to obtain a silver-white appearance. That is, the abnormal deposition of the plating film, particularly the poor appearance, is related to a phenomenon that nickel is preferentially deposited at the initial stage of plating (immediately after the start of energization) to form a nickel-enriched region (details will be described later).
By containing the glycine-containing water-soluble substance and the polyamine (A) as in the zinc alloy plating bath according to the present embodiment, the formation of a nickel-enriched region in the zinc alloy plating film is suppressed, and the poor appearance of the plating film is less likely to occur. The reason why the glycine-containing water-soluble substance and the polyamine (A) suppress the formation of nickel-enriched region is not clear. The present additive may contain amino acids other than glycine, but even if the present additive contains other amino acids (e.g., alanine, glutamine, glutamic acid, etc.), the same effect as glycine cannot be obtained. That is, other amino acids are not active ingredients of the present additive.
A zinc alloy plating film having a bright appearance can be readily and stably obtained from the acidic zinc alloy plating bath containing the present additive which contains the glycine-containing water-soluble substance and the polyamine (A) because a nickel-enriched region is less likely to be formed. For example, in barrel plating, a high current density plating process is intermittently repeated, so the appearance of the zinc alloy plating film formed by the barrel plating is readily affected by plating that is formed at the initial stage of plating (immediately after the start of energization). For this reason, if a plating bath according to the prior art is used in which the nickel-enriched region is readily formed, the appearance of the obtained plating film is liable to be poor. On the other hand, the nickel-enriched region is less likely to be formed in the plating bath according to the present embodiment, so the poor appearance is less likely to occur even in barrel plating.
Moreover, in the plating bath according to the present embodiment, even when electroplating is performed under conditions of a high current density, abnormal deposition is less likely to occur in the obtained zinc alloy plating film. In rack plating, the current density of plating tends to increase in order to increase the productivity, but with the plating bath according to the present embodiment, even when the current density is increased, poor appearance is less likely to occur in the obtained zinc alloy plating film.
The glycine/polyamine ratio, which is a ratio of the glycine-equivalent molar concentration of the glycine-containing water-soluble substance to the molar concentration of the polyamine (A), is preferably 0.1 or more and 40 or less, more preferably 1 or more and 35 or less, and particularly preferably 4 or more and 35 or less from the viewpoint of stably achieving a situation where a nickel-enriched region is less likely to occur in the zinc alloy plating film.
Thus, the glycine-containing water-soluble substance and the polyamine (A) have functions as primary brighteners, and it is therefore possible to reduce the content of surfactants usually used as primary brighteners. By reducing the content of surfactants in the plating bath, the problem of foaming that deteriorates the workability of zinc alloy plating can be alleviated.
When the zinc alloy plating bath is a zinc-nickel alloy plating bath, the zinc alloy plating bath contains the glycine-containing water-soluble substance and the polyamine (A), and a zinc-nickel alloy plating film may thereby be easily obtained in which the nickel co-deposition ratio is 10 mass % or more and 20 mass % or less, preferably 12 mass % or more and 18 mass % or less, and more preferably 14 mass % or more and 16 mass % or less.
Specific examples of the polyamine (A) of a primary amine include ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, dimethylaminopropylamine, diethylaminopropylamine, bis-(3-aminopropyl) ether, 1,2-bis-(3-aminopropoxy) ethane, 1,3-bis-(3-aminopropoxy)-2,2′-dimethylpropane, aminoethylethanolamine, 1,2-bisaminocyclohexane, 1,3-bisaminocyclohexane, 1,4-bisaminocyclohexane, 1,3-bisaminomethylcyclohexane, 1,4-bisaminomethylcyclohexane, 1,3-bisaminomethylcyclohexane, 1,4-bisaminoethylcyclohexane, 1,3-bisaminopropylcyclohexane, 1,4-bisaminopropylcyclohexane, hydrogenated 4,4′-diaminodiphenylmethane, 2-aminopiperidine, 4-aminopiperidine, 2-aminomethylpiperidine, 4-aminomethylpiperidine, 2-aminoethylpiperidine, 4-aminoethylpiperidine, N-aminoethylpiperidine, N-aminopropylpiperidine, N-aminoethylmorpholine, N-aminopropylmorpholine, isophoronediamine, menthanediamine, 1,4-bisaminopropylpiperazine, diethylenetriamine, iminobispropylamine, methyliminobispropylamine, bis(hexamethylene)triamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N-aminoethylpiperazine, N-aminopropylpiperazine, 1,4-bis(aminoethylpiperazine), and 1,4-bis(aminopropylpiperazine).
Specific examples of the polyamine (A) of a secondary amine include N,N′-dimethylethylenediamine, N,N′-dimethyl-1,2-diaminopropane, N,N′-dimethyl-1,3-diaminopropane, N,N′-dimethyl-1,2-diaminobutane, N,N′-dimethyl-1,3-diaminobutane, N,N′-dimethyl-1,4-diaminobutane, N,N′-dimethyl-1,5-diaminopentane, N,N′-dimethyl-1,6-diaminohexane, N,N′-dimethyl-1,7-diaminoheptane, N,N′-diethylethylenediamine, N,N′-diethyl-1,2-diaminopropane, N,N′-diethyl-1,3-diaminopropane, N,N′-diethyl-1,2-diaminobutane, N,N′-diethyl-1,3-diaminobutane, N,N′-diethyl-1,4-diaminobutane, and N,N′-diethyl-1,6-diaminohexane.
Specific examples of the polyamine (A) of a tertiary amine include tetramethylethylenediamine, N,N′-dimethylpiperazine, N,N′-bis((2-hydroxy) propyl) piperazine, hexamethylenetetramine, N,N,N′,N′-tetramethyl-1,3-butanamine, 2-dimethylamino-2-hydroxypropane, diethylaminoethanol, N,N,N-tris(3-dimethylaminopropyl)amine, 2,4,6-tris (N,N-dimethylaminomethyl) phenol, and heptamethylisobiguanide.
The polyamine (A) may have two or more of a primary amino group, a secondary amino group, and a tertiary amino group. Examples of such compounds include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and biguanides. Among them, the polyamine (A) preferably contains diethylenetriamine and more preferably is composed of diethylenetriamine from the viewpoint of high stability of the effect, high availability, etc.
The polyamine (A) may be composed of one type of compound or may also be composed of two or more types of compounds. When the polyamine (A) is composed of two or more types of compounds, the content ratio of these compounds is not limited. The content ratio is appropriately set according to the desired characteristics.
The carbon number of the polyamine (A) may be preferably 10 or less, more preferably 8 or less, and particularly preferably 6 or less.
Preferred examples of the polyamine (A) include ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, among which ethylenediamine, diethylenetriamine, and triethylenetetramine are more preferred as the polyamine (A).
The polyamine (A) may preferably have neither a carbonyl group nor a group containing a carbonyl group.
The present additive may contain components other than the polyamine (A). Examples of such components include a primary brightener, a secondary brightener, an antioxidant, a defoamer, and a sequestering agent. The polyamine (A) contained in the additive according to an embodiment of the present invention has a function as a primary brightener and/or a secondary brightener, so the present additive may not contain at least one of the primary brightener and the secondary brightener.
The zinc alloy plating bath according to an embodiment of the present invention is acidic and therefore has higher current efficiency and more excellent productivity than those of alkaline zinc alloy plating baths. The zinc alloy plating bath according to an embodiment of the present invention contains a bath-soluble zinc-containing substance, a bath-soluble metal-containing substance, and the above glycine-containing water-soluble substance and polyamine (A). Therefore, the silver-white zinc alloy plating film formed from the zinc alloy plating bath according to the present embodiment tends to have a good appearance.
The zinc alloy plating bath according to the present embodiment contains a bath-soluble zinc-containing substance. In the present specification, the bath-soluble zinc-containing substance is a supply source of zinc to be deposited as a zinc alloy plating film and refers to one or two components selected from the group consisting of zinc cations and bath-soluble substances containing zinc cations. Since the zinc alloy plating bath according to the present embodiment is acidic, an example of the bath-soluble zinc-containing substance is zinc ions (Zn2+). Examples of a raw material that supplies the bath-soluble zinc-containing substance to a plating bath (such a raw material is also referred to as a “zinc source” in the present invention) include zinc chloride, zinc sulfate, and zinc oxide.
The zinc-equivalent content of the soluble zinc-containing substance in the zinc alloy plating bath according to the present embodiment (the content of the soluble zinc-containing substance in the bath in terms of zinc) is not limited. If the content is unduly small, the zinc alloy plating film may be difficult to deposit, so the above 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 unduly large, poor appearance and decreased throwing power may occur, so the above zinc-equivalent content is preferably 100 g/L or less, more preferably 80 g/L or less, and particularly preferably 60 g/L or less.
The zinc alloy plating bath according to an embodiment of the present invention contains a bath-soluble metal-containing substance. In the present specification, the bath-soluble metal-containing substance is a supply source of metal other than zinc contained in the zinc alloy plating film and refers to one or more components selected from the group consisting of cations of metal elements and bath-soluble substances containing cations of metal elements. Examples of metal elements contained in the bath-soluble metal-containing substance include iron, nickel, and tin. In a preferred example, the metal element contained in the metal-containing substance is selected from the group consisting of iron, nickel, and tin.
A raw material that supplies the bath-soluble metal-containing substance to a plating bath (such a raw material is also referred to as a “metal source” in the present invention) may be appropriately selected according to the type of metal element contained in the bath-soluble metal-containing substance. For example, when the metal element contained in the bath-soluble metal-containing substance is iron, that is, when the zinc alloy plating bath contains a bath-soluble iron-containing substance, Fe2(SO4)3·7H2O, FeSO4·7H2O, Fe(OH)3, FeCl3·6H2O, FeCl2·4H2O, etc. are exemplified as iron sources. When the metal element contained in the bath-soluble metal-containing substance is nickel, that is, when the zinc alloy plating bath contains a bath-soluble nickel-containing substance, NiSO4·6H2O, NiCl2·6H2O, Ni(OH)2, etc. are exemplified as nickel sources. When the metal element contained in the bath-soluble metal-containing substance is tin, that is, when the zinc alloy plating bath contains a bath-soluble tin-containing substance, SnSO4, SnCl2, SnCl2·2H2O, etc. are exemplified as tin sources.
The metal-equivalent content of the bath-soluble metal-containing substance in the zinc alloy plating bath according to an embodiment of the present invention is appropriately set according to the composition of the target zinc alloy plating. When the zinc alloy plating bath contains a bath-soluble iron-containing substance, the iron-equivalent content of the bath-soluble iron-containing substance is exemplified to be about 1 g/L or more and 100 g/L or less. When the zinc alloy plating bath contains a bath-soluble nickel-containing substance, the nickel-equivalent content of the bath-soluble nickel-containing substance is exemplified to be about 0.1 g/L or more and 60 g/L or less. When the zinc alloy plating bath contains a bath-soluble tin-containing substance, the tin-equivalent content of the bath-soluble tin-containing substance is exemplified to be about 1 g/L or more and 100 g/L or less. The content ratio of an alloying element in the zinc alloy plating film (co-deposition ratio) is set according to the characteristics of the plating bath, the type of the alloying element, the application, etc.
When the alloying element contained in the zinc alloy plating bath according to an embodiment of the present invention is nickel, the co-deposition ratio of nickel in the zinc-nickel alloy plating film obtained from the zinc alloy plating bath is preferably 5 mass % or more and 20 mass % or less from the viewpoint of enhancing the corrosion resistance. A zinc-nickel alloy having a nickel content ratio of 10 mass % or more is particularly excellent in the corrosion resistance; therefore, when particularly excellent corrosion resistance is required, the co-deposition ratio of nickel in the zinc-nickel alloy plating film is preferably 10 mass % or more and 20 mass % or less, and from the viewpoint of enhancing the corrosion resistance and the uniformity of the film composition, the co-deposition ratio of nickel is more preferably 12 mass % or more and 18 mass % or less. When the application does not require particularly high corrosion resistance, the co-deposition ratio of nickel in the zinc-nickel alloy plating film may be preferably 5 mass % or more and less than 10 mass % in consideration of the balance between the corrosion resistance and the productivity (production cost). The co-deposition ratio of nickel can be adjusted by changing the bath composition and/or the current density.
The zinc alloy plating bath according to an embodiment of the present invention contains the aforementioned glycine-containing water-soluble substance and polyamine (A) as active ingredients. The bath may contain other additive components.
The zinc alloy plating bath according to an embodiment of the present invention contains the aforementioned glycine-containing water-soluble substance. The content of the glycine-containing water-soluble substance is appropriately set according to the type and content of components other than the glycine-containing water-soluble substance contained in the zinc alloy plating bath, the composition of the zinc alloy plating film formed from the zinc alloy plating bath, etc. An example of the glycine-equivalent content of the glycine-containing water-soluble substance in the zinc alloy plating bath according to an embodiment of the present invention may be, but is not limited to, 0.1 g/L or more and 100 g/L or less. When the glycine-containing water-soluble substance is 0.1 g/L or more, the effect of containing the glycine-containing water-soluble substance can be readily obtained. On the other hand, when the glycine-containing water-soluble substance is 100 g/L or less, the substance can be sufficiently dissolved in the plating bath. Upon setting of the plating bath composition, the glycine-containing water-soluble substance may be preferably 70 g/L or less from the viewpoint of reducing the influence on the adjustment range of the content of other components.
When the alloying element of the zinc alloy plating is nickel, as described above, the glycine-containing water-soluble substance and the polyamine (A) can suppress the preferential deposition of nickel at the initial stage of plating (immediately after the start of energization). From the viewpoint of stably achieving this function, the glycine-containing water-soluble substance in the zinc alloy plating bath may be preferably 1 g/L or more and more preferably 10 g/L or more.
The glycine/nickel ratio, which is a ratio of the glycine-equivalent molar concentration of the glycine-containing water-soluble substance to the nickel-equivalent molar concentration of the bath-soluble nickel-containing substance, may be preferably 0.1 or more, more preferably 0.5 or more, particularly preferably 1.2 or more, and extremely preferably 1.4 or more because the glycine-containing water-soluble substance is closely related to nickel deposition. The upper limit of the glycine/nickel ratio is not set from the viewpoint of improving the appearance of the plating film. If the content of the glycine-containing water-soluble substance is significantly excessive, it may be necessary to adjust the content of other components (e.g., potassium-containing component), so the glycine/nickel ratio may be preferably 3 or less and more preferably 2 or less. The glycine/nickel ratio has little effect on the co-deposition ratio of nickel in the zinc alloy plating film.
The zinc alloy plating bath according to an embodiment of the present invention contains the aforementioned polyamine (A). The content of the polyamine (A) is appropriately set according to the type of polyamine (A), the type and content of components other than the polyamine (A) contained in the zinc alloy plating bath, the composition of the zinc alloy plating film formed from the zinc alloy plating bath, etc. An example of the content of the polyamine (A) in the zinc alloy plating bath according to an embodiment of the present invention may be, but is not limited to, 0.1 g/L or more and 100 g/L or less. When the polyamine (A) is 0.1 g/L or more, the effect of containing the polyamine (A) can be readily obtained. On the other hand, when the polyamine (A) is 100 g/L or less, the possibility of generating insoluble substances in the bath is reduced.
Depending on the type of zinc alloy plating bath, the appearance of the zinc alloy plating film formed from the zinc alloy plating bath may be able to be more stably improved by setting the content of the polyamine (A) in the zinc alloy plating bath to a predetermined content or less. For example, when the zinc alloy plating is zinc-nickel alloy plating, good appearance of the zinc-nickel alloy plating film formed from the zinc-nickel alloy plating bath may be able to stably occur by setting the content of the polyamine (A) to 30 g/L or less. The content of the polyamine (A) may be preferably 20 g/L or less from the viewpoint of more stably improving the appearance of the zinc-nickel alloy plating film.
The zinc alloy plating bath according to an embodiment of the present invention may contain additive components other than the above polyamine (A). Such additive components or materials that provide additive components in zinc alloy plating baths will be exemplified as follows.
The zinc alloy plating bath according to an embodiment of the present invention may contain a primary brightener as one type of additive components. Examples of such a primary brightener include anionic surfactants, nonionic surfactants, and water-soluble organic compounds such as water-soluble cationic polymer compounds used in various zinc plating baths.
The primary brightener may have both the structure contained in anionic surfactants such as sulfonic acid groups and the structure contained in nonionic surfactants such as polyethers. Examples of such compounds include alkali metal salts of aromatic or aliphatic polyether sulfates.
When the zinc alloy plating bath according to an embodiment of the present invention contains a primary brightener, the primary brightener may be preferably a nitrogen-free surfactant. Specific examples of such surfactants include the above alkali metal salts of aromatic or aliphatic polyether sulfates and polyether compounds of acetylenic dialcohols.
When the zinc alloy plating bath according to an embodiment of the present invention contains a primary brightener, the content of the primary brightener in the zinc alloy plating bath is not limited. The content is appropriately set according to the type of primary brightener, the type and content of components other than the primary brightener contained in the zinc alloy plating bath, the composition of the zinc alloy plating film formed from the zinc alloy plating bath, etc. For 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.
As described previously, since the polyamine (A) has a function as a primary brightener, it is possible to reduce the content of the primary brightener composed of a surfactant. By reducing the content of the surfactant in the plating bath, it is possible to alleviate the problem of foaming that deteriorates the workability of zinc alloy plating.
The zinc alloy plating bath according to an embodiment of the present invention may contain a secondary brightener as one of additive components. In particular, from the viewpoint of improving brightness, etc., an aromatic compound having a carbonyl group may be contained as the secondary brightener. Examples of such compounds include aromatic aldehydes such as anisaldehyde, veratraldehyde, o-chlorobenzaldehyde (OCAD), salicylaldehyde, vanillin, piperonal, and p-hydroxybenzaldehyde; and acetone having an aromatic ring, such as benzylideneacetone.
When the zinc alloy plating bath according to an embodiment of the present invention contains a secondary brightener, the content of the secondary brightener in the zinc alloy plating bath is not limited. The content is appropriately set according to the type of secondary brightener, the type and content of components other than the secondary brightener contained in the zinc alloy plating bath, the composition of the zinc alloy plating film formed from the zinc-based plating bath, etc. For 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.
The zinc alloy plating bath according to an embodiment of the present invention may contain additive components other than the above components. Examples of such additive components include antioxidants, defoamers, and sequestering agents.
Examples of antioxidants include hydroxyphenyl compounds such as phenol, catechol, resorcinol, hydroquinone, and pyrogallol, L-ascorbic acid, and sorbitol.
Examples of defoamers include silicone-based defoamers and organic-based defoamers such as surfactants, polyethers, and higher alcohols.
Examples of sequestering agents include silicates (specific examples include sodium silicate) and silica (specific examples include colloidal silica). The content of the sequestering agent in the zinc alloy plating bath is not limited. The content may be appropriately set in consideration of the type of sequestering agent, the composition of solvent, etc. For 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.
The zinc alloy plating bath according to an embodiment of the present invention may contain a substance having a buffering action as a buffering agent. By containing the buffering agent, excessive increase in the pH in the vicinity of the surface of the member to be plated is suppressed. As a result, the deposition form of metal such as zinc on the member to be plated is stabilized, and abnormal deposition is less likely to occur.
When the zinc alloy plating bath according to an embodiment of the present invention contains a buffering agent, the type of buffering agent is not limited. Specific examples of buffering agents include acetic acid-containing substances that are substances containing at least one of acetic acid and acetate ions, ammonia-containing substances that are substances containing at least one of ammonia and ammonium ions, and boric acid-containing substances that are substances containing at least one of boric acid and borate ions. When the zinc alloy plating obtained from the zinc alloy plating bath is a zinc alloy plating, the inclusion of an acetic acid-containing substance as the buffering agent may stabilize the deposition of the zinc alloy plating. From the viewpoint of stabilizing the plating deposition, the alloying element in the zinc alloy plating is preferably nickel. Potassium acetate is preferred as the acetic acid source for supplying an acetic acid-containing substance to the plating bath.
From the viewpoint of reducing the environmental load, the acetic acid-equivalent content of the acetic acid-containing substance in the zinc alloy plating bath according to an embodiment of the present invention is preferably 200 g/L or less, more preferably 100 g/L or less, and further preferably 50 g/L or less. From the viewpoint of stably developing the function as the buffering agent, the acetic acid-equivalent content of the acetic acid-containing substance in the zinc alloy plating bath according to an embodiment of the present invention is preferably 1 g/L or more, more preferably 5 g/L or more, and particularly preferably 10 g/L or more.
From the viewpoint of reducing the environmental load, the ammonia-equivalent content of the ammonia-containing substance in the zinc alloy plating bath according to an embodiment of the present invention is preferably 100 g/L or less, more preferably 50 g/L or less, and further preferably 10 g/L or less, and it is particularly preferred that the zinc alloy plating bath according to an embodiment of the present invention should contain substantially no ammonia-containing substance (ammonia-free). In the present specification, “ammonia-free”means not containing ammonia or ammonium ions to such an extent that they function as buffering agents in the plating bath.
From the viewpoint of reducing the environmental load, the boric acid-equivalent content of the boric acid-containing substance in the zinc alloy plating bath according to an embodiment of the present invention is preferably 5 g/L or less, more preferably 1 g/L or less, and further preferably 0.1 g/L or less, and it is particularly preferred that the zinc alloy plating bath according to an embodiment of the present invention should contain substantially no boric acid-containing substance (boric acid-free). In the present specification, “boric acid-free” means not containing boric acid or borate ions to such an extent that they function as buffering agents in the plating bath.
Thus, even when the zinc alloy plating bath according to the present embodiment satisfies at least one of being boric acid-free and being ammonia-free, preferably both, provided that the zinc alloy plating bath contains an acetic acid-containing substance, the acetic acid-containing substance can serve as a buffering agent for the plating bath. Specific examples of acetic acid-containing substances include substances (acetic acid, acetate ion) based on acetic acid sources such as potassium acetate and sodium acetate. When the zinc alloy plating bath satisfies at least one of being boric acid-free and being ammonia-free, preferably both, and potassium acetate is used as the acetic acid source, the compounding amount of potassium acetate may be preferably 100 g/L or less and more preferably 70/L or less.
When the zinc alloy plating bath according to an embodiment of the present invention has a low content of ammonia-containing substances or boric acid-containing substances, and the zinc alloy plating bath has a low environmental load, this means that the zinc alloy plating bath according to an embodiment of the present invention has excellent wastewater treatment properties.
The zinc alloy plating bath according to an 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, and these may be compounded in the zinc alloy plating bath as salts composed of cations and anions. As such a salt, a potassium salt such as potassium chloride may be preferred from the viewpoint of ease of dissolution. The total content of the inorganic electrolytes contained in the zinc alloy plating bath according to an embodiment of the present invention is not limited. The total content 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 alloy plating bath, the composition of the zinc alloy plating film formed from the zinc alloy plating bath, the plating conditions, etc. For example, the total content of the inorganic electrolytes contained in the zinc alloy 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 alloying element of zinc alloy plating is nickel and the acidic zinc alloy plating bath contains chloride ions, the concentration of chloride ions in the bath may be preferably 100 g/L or more and 400 g./L or less and more preferably 120 g/L or more and 280 g/L or less from the viewpoint of ensuring the stability of the bath
The solvent of the zinc alloy plating bath according to an embodiment of the present invention contains water as the main component. As a solvent other than water, an organic solvent having high solubility in water, such as alcohol, ether, or ketone, may be mixed. In this case, from the viewpoint of the stability of the plating bath as a whole and the alleviation of the load on waste liquid treatment, the ratio is preferably 10 vol % or less with respect to the total solvent.
The zinc alloy plating bath according to an embodiment of the present invention is acidic, and its pH is preferably 4 or more and 6 or less and more preferably 5.0 or more and 5.8 or less. The type of material used for adjusting 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.
The method of preparing the zinc alloy plating bath according to the present embodiment is not particularly limited. The zinc alloy plating bath can be prepared by dissolving in a solvent a zinc source, a metal source, a glycine source, and a polyamine (A) source that is a substance capable of generating the polyamine (A) in the plating bath, and optionally the aforementioned other additive components, buffering agents, inorganic electrolytes, etc. as optional additive components. The glycine source contains glycine, and the polyamine (A) source contains polyamine (A).
A zinc alloy plated member can be obtained through bringing the zinc alloy 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 (cathodic electrode). The method of contact between the zinc alloy plating bath and the member to be plated is not limited. Typical examples of the method include bringing the member to be plated into contact with the zinc alloy plating bath, and the above contact may be performed by spraying a plating solution that constitutes the zinc alloy plating bath onto the member to be plated.
The material of a member to be plated is not particularly limited as long as it has conductivity. Examples of such materials include metal materials such as iron materials and those in which layers composed of conductive materials are formed by electroless plating or the like on the surfaces of non-conductive materials such as resin materials and ceramic materials. The shape of a member to be plated is also not particularly limited. Examples of members to be plated include primary products such as plate materials, rod materials, and wire materials; and secondary products such as screws, bolts, molds and other cut/ground products (which may be further subjected to a polishing process), vehicle body frames, equipment housings, and other pressed products, and brake calipers, engine blocks, and other castings. When the member to be plated is a casting composed of an iron-based material, there may be a case where a zinc alloy plating film cannot be formed from an alkaline zinc alloy plating bath due to the influence of components contained to improve the castability.
The material that constitutes the anode (anodic electrode) is not particularly limited. A metallic material containing zinc and/or an alloying element may be used as a soluble anode. An anode composed of a zinc-based material and another anode composed of a material containing an alloying element may be separately prepared as soluble anodes. Then, these anodes may be connected to different power sources and voltage application to each anode may be independently controlled.
The current density in electrolysis is not particularly limited. The current density may be appropriately set with consideration that if the current density is unduly low, the deposition rate of the zinc alloy plating film to be obtained may be low and the productivity may be poor while if the current density is unduly high, there may be concern that the appearance of the obtained zinc plating film deteriorates or the uniform electrodeposition and the throwing power deteriorate. From the viewpoint of improving both the productivity and the quality of the plating film, the current density is preferably 0.1 A/dm2 or more and 15 A/dm2 or less and more preferably 0.5 A/dm2 or more and 13 A/dm2 or less. As described above, since the acidic zinc alloy plating bath contains the glycine-containing water-soluble substance and the polyamine (A), a nickel-enriched region is not readily formed in the zinc-nickel alloy plating film even at a high current density, specifically at a current density exceeding 10 A/dm2, and the obtained plating film is therefore less likely to have poor appearance.
The temperature of the plating bath (plating bath temperature) in electrolysis may be within a range of about 15° C. to about 50° C., and the electrolysis may be performed at about room temperature (about 25° C.).
The electrolysis time (plating time) is appropriately set from the deposition rate of the plating film determined by the composition of the zinc alloy plating bath, the above current density and plating bath temperature, etc., and the desired thickness of the plating film.
The configuration of the plating equipment is not particularly limited. A member to be plated may be placed as a cathode in the zinc alloy plating bath so as to face a plate-shaped or rod-shaped anode and the electrolysis may be performed to form a zinc alloy plating film on the member to be plated while appropriately stirring the liquid in the zinc alloy plating bath. In this case, the liquid may be stirred by using a liquid circulation pump, by using aeration, or by moving the member to be plated and the like in the plating bath.
Examples of other plating equipment include barrel plating equipment in which a barrel containing members to be plated such as bolts are immersed in the zinc alloy plating bath and the electrolysis is performed while rotating the barrel to form zinc alloy plating films on the members to be plated. Specific examples of members to be plated using the barrel plating equipment include bolts, nuts, and screws. By using the zinc alloy plating bath according to an embodiment of the present invention, even when the members to be plated are those having high shape anisotropy (elongated), such as bolts, it is possible to prevent variations in the appearance, film thickness, and co-deposition ratio between the end portions and other portions in the obtained zinc alloy plating films. When an acidic zinc alloy plating bath having a high current efficiency is used rather than using an alkaline zinc alloy plating bath having a low current efficiency, it has conventionally been difficult to prevent variations in the appearance, film thickness, and co-deposition ratio between the end portions and other portions.
In the zinc-nickel alloy plating film formed using the present additive, when the depth profile of a zinc alloy plated member in which the plating film is formed on a member to be plated composed of an iron-based material is measured, a nickel-enriched region having a relatively high nickel concentration is less likely to be formed on the proximal side to the member to be plated.
The nickel-enriched region can be confirmed from a graph (depth profile) that represents changes in the component concentrations of the plated member in the thickness direction of the plating film. Specifically, when the depth profile of a zinc alloy plated member in which the plating film is formed on a member to be plated composed of an iron-based material is measured, a position closest to the outermost surface and having a zinc concentration of 60 mass % or more is defined as a surface-side end portion of the zinc alloy plating film. In addition, a position at which the zinc concentration is equal to an iron concentration derived from the member to be plated is defined as a member-side end portion of the zinc alloy plating film. Then, the length of a region from the surface-side end portion to the member-side end portion is defined as a thickness of the zinc alloy plating film.
With such definitions, when a partial region having a specifically higher nickel concentration (this is a case where the alloying element of the alloying element concentration is nickel) than that in a region on the surface side of an initial region, that partial region is called a nickel-enriched region (this is a case where the alloying element in the alloying element-enriched region is nickel). The initial region is represented by a range between the member-side end portion of the zinc alloy plating film and a position moved from the member-side end portion to the surface side by 30% of the thickness of the zinc alloy plating film.
The existence of the nickel-enriched region should be determined from the overall shape of the depth profile, but the following evaluation method also helps confirm the existence of the nickel-enriched region. That is, provided that the range of 40% to 60% of the thickness of the zinc alloy plating from the surface-side end portion is defined as an intermediate region, in the zinc nickel alloy plating film having a nickel-enriched region, when an average value of the nickel concentration in the intermediate region (this average value is also referred to as an “intermediate region average value”) [Ni1] and a maximum value of the nickel concentration in the above initial region (this maximum value is also referred to as an “initial region maximum value”) [Ni2] satisfy Expression (1) below, there is a high possibility that the nickel-enriched region occurs in the initial region.
When such a nickel-enriched region exists on the side of the zinc-nickel alloy plating film proximal to the member to be plated, poor appearance is likely to occur, and this tendency will be noticeable if the current density is high.
On the other hand, the zinc alloy plating film (zinc-nickel alloy plating film) according to the present embodiment is formed from the plating bath containing the glycine-containing water-soluble substance and the polyamine (A); therefore, the nickel-enriched region is less likely to occur, and Expression (1) below is likely to be satisfied.
Thus, the zinc alloy plating film (zinc-nickel alloy plating film) according to the present embodiment is less likely to cause poor appearance even in a portion formed under conditions of a high current density, specifically, exceeding 10 A/dm2.
The embodiments heretofore explained are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, the elements disclosed in the above embodiments also include all design modifications and equivalents belonging to the technical scope of the present invention.
For example, the zinc alloy plating film included in zinc alloy plated member may be subjected to a chemical conversion treatment or the like.
The effects of the present invention will be described below based on examples, but the present invention is not limited to these examples.
Zinc alloy plating baths having the following compositions and a pH of 5.3 were prepared:
For each of the prepared plating baths, electrolysis was performed using a Hull cell tester (“B-55” available from YAMAMOTO-MS Co., Ltd.) under the following conditions:
The appearance observation was performed for a portion with a current density of 11 A/dm2 in the silver-white zinc-nickel alloy plating film formed on the cathode plate. The results are listed in Table 1. The abbreviation “Gly/PA” in Table 1 means the glycine/polyamine ratio (here and hereinafter).
As listed in Table 1, no particular poor appearance was observed in the portion with a current density of 11 A/dm2 in each of the zinc-nickel alloy plating films formed from the zinc-nickel plating baths according to the present examples containing glycine as the glycine-containing water-soluble substance and diethylenetriamine as the polyamine (A).
The depth profile was measured by glow discharge optical emission spectroscopy (GD-OES) for the portion with a current density of 11 A/dm2 in each of the obtained zinc-nickel alloy plating films. The depth profile of the zinc-nickel alloy plating film of Example 2 is illustrated in
The member-side end portion of the zinc alloy plating film is represented by the depth, indicated by the solid arrow in
The depth profile was obtained for the nickel concentration of the portion with a current density of 11 A/dm2 in each of the zinc-nickel alloy plating films produced in Examples and Comparative Examples. The results are illustrated in
As illustrated in
For confirmation, from each of the depth profiles illustrated in
As listed in Table 2, the zinc-nickel alloy plating films of Comparative Examples are recognized to have a tendency that the maximum value [Ni2] in the initial region is larger than the average value [Ni1] in the intermediate region ([Ni1]<[Ni2]), and the presence of a nickel-enriched region has been confirmed. On the other hand, the zinc alloy nickel platings of Examples are recognized to have a tendency that the average value [Ni1] in the intermediate region is larger than or equal to the maximum value [Ni2] in the initial region ([Ni1]≥[Ni2]), and no nickel-enriched region has been confirmed.
Based on the composition of the plating solution of Example 1, as listed in Table 3, a plurality of types of plating solutions having different nickel-equivalent molar concentrations of bath-soluble nickel-containing substances and molar concentrations of glycine were prepared. In Table 4, the numbers in the columns of “Ni,” “Gly,” and “DETA” are the molar concentrations of nickel (unit: mol/L), the molar concentrations of glycine (unit: mol/L), and the molar concentrations of diethylenetriamine (unit: mmol/L), respectively. The numbers in the column of “Gly/Ni” are the calculation results (glycine/nickel ratio) of (molar concentration of glycine)/(molar concentration of nickel), and the numbers in the column of “Gly/PA” are the calculation results (glycine/polyamine ratio) of (molar concentration of glycine)/(molar concentration of diethylenetriamine).
For each of the prepared plating solutions, electrolysis was performed under the same conditions as in Example 1, and the appearance of the portion with a current density of 11 A/dm2 in the zinc-nickel alloy plating film formed on the cathode plate was observed. The results have been such that, as listed in Table 3, the films according to all of Examples are bright (silver-white appearance, the observer's eyes can be clearly confirmed when facing the cathode plate to look into it).
The depth profiles were measured by glow discharge optical emission spectroscopy (GD-OES) for the portions with a current density of 11 A/dm2 in the obtained zinc-nickel alloy plating films. The results are illustrated in
Plating baths listed in Table 4 were prepared. The plating bath of Comparative Example 4 is included in the scope of the electrolytic composition disclosed as Example 1 of Patent Document 3.
In the plating bath of Example 14, diethylenetriamine, which is one type of the polyamine according to the present invention, was added to the plating bath of Comparative Example 4 so that the glycine/polyamine ratio would be the same as in Example 1 (6.0).
The plating bath of Example 15 has almost the same composition as the plating bath of Example 1. The plating bath of Comparative Example 5 was obtained by removing the diethylenetriamine from the plating bath of Example 15 and containing the same amount of boric acid as in the plating bath of Comparative Example 4. In other words, the plating bath of Comparative Example 5 was obtained by modifying the plating bath of Comparative Example 4 so that the nickel concentration and the chlorine concentration were the same as those in Example 15.
The plating bath of Comparative Example 6 was obtained by removing the boric acid from the plating bath of Comparative Example 4. This composition differs in the nickel concentration and chlorine concentration from the plating bath of Comparative Example 1 illustrated for reference.
Plating baths listed in Table 5 were prepared. The plating bath of Comparative Example 7 was obtained by removing the glycine from the plating bath of Comparative Example 4 included in the scope of the electrolytic composition disclosed as Example 1 of Patent Document 3 and containing the same amount of diethylenetriamine as in Example 14.
The plating bath of Comparative Example 8 was obtained by containing the same amount of boric acid as in Comparative Example 4 in the plating bath of Comparative Example 1.
The plating bath of Example 16 has the same composition as that of the plating bath of Example 15.
The plating bath of Example 17 was obtained by containing the same amount of boric acid as in Comparative Example 4 (15 g/L=0.24 mol/L) in the plating bath of Example 16.
The plating bath of Example 18 was obtained by containing 100 g/L (1.9 mol/L) of ammonium chloride in the plating bath of Example 16 and lowering the concentration of potassium chloride to 120 g/L (1.6 mol/L) to adjust the chlorine concentration to 180 g/L (5.1 mol/L). The chlorine concentration (152 g/L) of Example 16 is 4.3 mol/L.
The plating bath of Example 19 was obtained by containing 220 g/L (4.1 mol/L) of ammonium chloride in the plating bath of Example 16 and also containing the same amount of boric acid as in Comparative Example 4 (15 g/L=0.24 mol/L).
For each of the plating baths prepared in Examples 14 to 20 and Comparative Examples 4 to 8, electrolysis was performed using a Hull cell tester (“B-55L” available from YAMAMOTO-MS Co., Ltd.) under the following conditions:
The appearance observation was performed for each of the obtained zinc-nickel alloy plating films. The results are listed in Table 6.
Each cathode plate formed with the zinc-nickel alloy plating film was equally divided into 20 regions in a direction with different current densities, and the arithmetic average value of the current density in the end portion on the higher current density side and the current density in the end portion on the lower current density side was obtained for each of 19 regions excluding the region with the highest current density. The obtained arithmetic average value was taken as the average current density in that region. The numerical values (unit: A/dm2) in the second row of Table 6 indicate the average current densities.
The numbers in bold in each row of Examples and Comparative Examples are the results of classifying the appearance evaluation results of respective regions as follows:
As listed in Table 6, all of the zinc-nickel alloy plating films according to Examples 15 to 20 had a bright appearance from the region with an average current density of 0.01 A/dm2 to the region with an average current density of 11 A/dm2. On the other hand, the zinc-nickel alloy plating films according to Comparative Examples were not able to obtain a bright appearance over a wide area as in Examples. In particular, in the zinc-nickel alloy plating film according to Comparative Example 4, which is included in the scope of the electrolytic composition disclosed as Example 1 of Patent Document 3, a black appearance due to an unduly high nickel concentration in the plating film was confirmed in the region on the low current density side while a burnt appearance due to an excessive current density was observed in the region with an average current density of 11 A/dm2, and a bright appearance was not able to be obtained even at a moderate current density.
The depth profile of nickel was measured by glow discharge optical emission spectroscopy (GD-OES) for the portion with a current density of 11 A/dm2 of the zinc-nickel alloy plating film according to each of Comparative Examples 4 and 6 to 8 and Examples 16 to 20 (
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-035404 | Mar 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/008540 | 3/1/2022 | WO |
