JPH05112889A - Zincate-type zinc-iron alloy plating bath - Google Patents

Abstract

PURPOSE:To form a Zn-Fe alloy plating layer with the variation in the Fe coprecipitation rate reduced and to form a nice-looking black chromate film thereon without using Ag by adding an org. compd.-based brightener to the zincate-type Zn-Fe alloy plating bath. CONSTITUTION:A compd. formed by making a thiourea derivative shown by the general formula quaternary with a 1-4C alkylating agent and an alkylated polyalkylpolyamine obtained by partially alkylating the basic nitrogen atom of a polyalkylpolyamine with 1-3C alkyls are incorporated as a brightener into a Zn-Fe alloy plating bath consisting of an aq. soln. contg. a Zn source such as ZnO, an alkali metal hydroxide such as KOH and NaOH, a bior trivalent water-soluble Fe salt and the citrate, tartrate and ethanolamine as the complexing agent to solubilize the Fe salt. A Zn-Fe alloy plating film with the variation of Fe coprecipitation rate reduced and excellent in brightness is formed, and a black chromate film free of Ag is stably formed thereon.

Description

Detailed Description of the Invention

[0001]

This invention relates to Fe in the presence of complexing agents.
The present invention relates to a zincate-type zinc-iron alloy plating bath containing a salt of (II, III) and a brightener.

[0002]

2. Description of the Related Art It is well known that the corrosion resistance of a galvanized coating is improved by co-depositing iron (Fe) or nickel (Ni) in the galvanized coating. Therefore, F
Various zinc alloy plating baths capable of co-depositing e and Ni have been proposed.

Among many zinc alloy plating baths reported to date, a typical plating bath capable of precipitating Zn--Fe or Zn--Ni alloys uses a complexing agent Fe.
And a zincate type zinc alloy plating bath containing a salt of Ni or Ni. An example of this type of alloy plating bath is disclosed in JP-A-60-181293.

[0004] In zinc-based plating, chromate treatment is often performed after plating for the purpose of improving corrosion resistance. However, if the eutectoid ratio of Fe or Ni is too high, a good chromate film can be obtained. Absent. On the other hand, if the eutectoid ratio is too low, the function of improving corrosion resistance will not be exhibited. Therefore, Fe
The eutectoid rate of Ni and Ni needs to be controlled quite strictly.
The desirable eutectoid ratio range is 0.1-0.1% for Fe.
It is known as a result of research that 5% and Ni are 2 to 20%.

In terms of appearance, it is desirable that the plated surface has gloss. This is because the quality of the finish of the post-treatment represented by chromate treatment or the like is greatly affected by the glossiness of the plated surface before the treatment.

In the plating process, it is technically difficult to make the current density uniform over the entire surface of the object to be plated. For example, in an object to be plated having irregularities, the convex portion has a higher current density than the concave portion, but it is difficult to approximate the current densities of both portions. Therefore, the important condition required for a practical zinc alloy plating bath is that a good bright plating film can be obtained in a wide current density range and that a substantially constant alloy ratio can be secured in a wide current density range. is there.

As a result of studying various conventional alloy plating baths, it was found that the conditions required for the above alloy plating baths were not sufficiently satisfied. Therefore, the inventor of the present invention has developed the following zinc-iron alloy plating bath in order to improve the deficiency of the conventional alloy plating solution. This zinc-iron alloy plating bath is a zincate type plating bath containing a Zn compound, an alkali hydroxide, a salt of Fe (II, III), a complexing agent for solubilizing these metal salts, and a brightening agent. Thus, an alkylated polyalkylene polyamine in which a basic nitrogen atom of the polyalkylene polyamine is partially alkylated by a C1 to C3 alkyl group is used as a brightener. This zinc-
The iron alloy plating bath is disclosed in JP-A-62-23878. It was also found that this zinc-iron alloy plating bath provided a bright plating film in a fairly wide current density range, and that the variation in the eutectoid ratio of Fe due to the high and low current densities was small. The current density range in which a good plating film can be obtained in this zinc-iron alloy plating bath is 0.2 to 15 A / dm ² .

Further, the inventor of the present invention is disclosed in the above-mentioned Japanese Patent Laid-Open No. 62-62
The zinc-iron alloy plating bath disclosed in Japanese Patent No. 23878 is further improved. This zinc-iron alloy plating bath is
In a zincate-type zinc-iron alloy plating bath containing a Zn compound, an alkali hydroxide, a salt of Fe (II, III), a complexing agent for solubilizing these metal salts, and a brightening agent, poly as a brightening agent. Alkylated polyamines in which the basic nitrogen atom of an alkylene polyamine is partially alkylated by a C1-C3 alkyl group, a reaction product of imidazole or a derivative thereof with epihalohydrin, or imidazole or a derivative thereof and epihalohydrin with an aliphatic amine In combination with the reaction product obtained by reacting in the presence of. This improved alloy plating bath is disclosed in JP-A-2-141596. According to this zinc-iron alloy plating bath, the usable current density range is further widened (0.1-
It was found to be 20 A / dm ² ).

[0009]

The inventor of the present invention has improved the zinc-iron alloy plating bath to the extent that it can be put to practical use, but there is still room for improvement.
Therefore, the first object of the present invention is to provide the above-mentioned Japanese Patent Laid-Open No. 2-1.
Further improvement of the plating bath disclosed in No. 41596. Now, for the zinc alloy plating film,
Chromate treatment is usually applied to improve its corrosion resistance. In the conventional zinc-iron alloy plating bath, by improving the brightener composition, the high current density tolerance of the plating film itself has been expanded, and among the chromate treatments, for the black chromate treatment using the yellow chromate or silver compound,
It is possible to process up to a high current density range that is almost equal to the limiting current density of the plating film itself. By the way, as an advantage other than the zinc-iron alloy plating bath, a black chromate film (hereinafter referred to as a silver-free black chromate film) can be obtained even if the black chromate does not contain a silver compound. This silver-free chromate film is a zinc-iron alloy plating and is specifically obtained in the range of iron eutectoid ratio of 0.3-0.6%. Since it contains no silver compound, it is inexpensive and chromate-free. The corrosion resistance does not deteriorate because silver is not contained in the film, and because the chromate film has water repellent properties, it has approximately twice the corrosion resistance as the conventional yellow chromate film. In the zinc-iron alloy plating bath, although the appearance of the plating film itself is good in the high current density range, there is a drawback that a uniform silver-free black chromate film is not formed due to the inhibition of the eutectoid organic substances in the plating film. Typically,
There is a correlation between the appearance of the chromate film and the superiority or inferiority of the corrosion resistance.It is known that a good chromate film has excellent corrosion resistance.Therefore, zinc-iron alloy plating film can be applied over a wide current density range. Development of a plating bath capable of forming a good silver-free chromate film even when worn is desired. This wide current density range is specifically 20 A except for the plating film itself and silver-free black chromate in the conventional bath.
/ Dm ² until it had been possible treatment, only the silver without chromate is 10A / dm ² is limited, for use in normal rack barrel plating, especially in the case of rack processing, setting the average current density is 2 -4A / dm ² , depending on the shape (unevenness, etc.) of the object to be processed and the relative position to the electrode plate, a current density of 4 times the average current density or more flows at the tip of the object, resulting in black chromate without silver. Tolerance limit for 10A /
At about dm ² , the set average current density had to be lowered considerably. On the other hand, in the present invention, the silver-free black chromate film is formed so as to sufficiently cover the set average current density of 2-4 A / dm ² in the ordinary rack processing.
Good and uniform chromate finish should be obtained even in the high current density area of A / dm ² , and 30A for alloy plating itself and chromate treatment other than silver-free black chromate.
/ Dm ² can be supported. Therefore, a second object of the present invention is zinc-suitable for forming a good chromate film (in particular, a silver-free black chromate film).
It is to provide a plating bath capable of obtaining an iron alloy plating.

[0010]

The plating bath of the present invention comprises:
Zn compound, alkali hydroxide, Fe (II, II
A salt of I) and a complexing agent for solubilizing the Fe salt,
A zincate-type zinc-iron alloy plating bath containing a brightener, wherein the brightener comprises:

[Chemical 2] A compound obtained by quaternizing a thiourea derivative represented by the following general formula with an alkylating agent having a C1-C4 alkyl group and a basic nitrogen atom of a polyalkylenepolyamine
An alkylated polyalkylene polyamine partially alkylated with a -C3 alkyl group.

[0011]

According to the zinc-iron alloy plating bath of the present invention, the following effects are exhibited. 1) A good bright plating film can be obtained in a wide current density range of 0.1-30 A / dm ² . 2) Within a wide current density range of 0.1-30 A / dm ² , the variation in the eutectoid ratio of iron is extremely small. 3) With respect to the plating film obtained at a current density of 0.1-30 A / dm ² , a chromate film other than silver-free black chromate can be formed to have a uniform and excellent appearance. 4) A silver-free black chromate film having a good appearance can be formed on a plating film obtained at a current density of 0.1-20 A / dm ² .

[0012]

EXAMPLES Next, examples of the present invention will be described in detail. The plating bath of the present invention comprises a Zn compound, an alkali hydroxide,
A zincate type bath containing a salt of Fe (II, III) and a complexing agent for solubilizing these metal salts is used as a basic bath to which a brightening agent is added. The basic bath composition is as follows. Basic bath composition Zinc (as Zn ²⁺ ): 5-40 g /
l Alkali hydroxide (NaOH etc.): 30-200 g /
l Iron (as Fe ²⁺ or Fe ³⁺ ): 0.02-5 g /
l Complexing agent: 1-100 mol / Fe ion 1 mol

In the above basic bath, ZnO can be usually used as the Zn compound, and NaOH, KOH or the like can be used as the alkali hydroxide. Further, as the Fe salt, Fe ₂ (SO ₄ ) ₃・ 7 ₂ O, F
_{eSO 4 · 7H 2 O, Fe} (OH) 3, FeCI 3 · 6
H ₂ O, FeCI ₂ .4H ₂ O, etc. can be used.
Further, as the complexing agent (chelating agent) for solubilizing the Fe salt, oxycarboxylic acid salts such as citrate, tartrate and gluconate; monoethanolamine,
Amino alcohols such as diethanolamine and triethanolamine; Polyamines such as ethylenediamine (EDA), diethylenetriamine and triethylenetetramine; Aminocarboxylic acid salts such as ethylenediaminetetraacetic acid salt and nitroacetic acid salt; Polyhydric alcohols such as sorbit and pentaerythritol It is possible to use those selected from the group consisting of classes; and mixtures thereof, but triethanolamine is preferred.

The following three types of brighteners were used.

[Chemical 3] A compound obtained by quaternizing a thiourea derivative represented by the general formula (1) with an alkylating agent having a C1-C4 alkyl group (hereinafter referred to as a brightener 1) is used as the thiourea derivative represented by the above general formula. , Bisaminoethylthiourea, N-aminoethyl-N'-methylaminoethylthiourea, bismethylaminoethylthiourea, N-methylaminoethyl-
N'-Dimethylaminoethylthiourea, bisdimethylaminoethylthiourea, bisaminopropylthiourea, bismethylaminopropylthiourea, bisdimethylaminopropylthiourea, bisdimethylaminobutylthiourea and the like can be used. Further, as the alkylating agent, CH ₃ Cl, CH ₃ Br, CH ₃ I, C ₂ H ₅ Cl,
C ₂ H ₅ Br, C ₂ H ₅ I, (CH ₃ ) ₂ SO ₄ , (C
₂ H ₅ ) ₂ SO ₄ , C ₃ H ₇ Cl, C ₃ H ₇ Br, C ₃
H ₇ I etc. can be used. The amount of brightener 1 added is 0.1-50 g / l (preferably 0.5-30 g / l)
Is.

An alkylated polyalkylene polyamine obtained by partially alkylating a basic nitrogen atom of the polyalkylene polyamine with an alkylating agent having a C1 to C3 alkyl group (hereinafter referred to as brightener 2) Molecular weight 30
0 to 5000, for example, polyethyleneimine, polypropyleneimine, polybutyleneimine, etc. can be used, and the alkylating agent is a C1 to C3 compound,
For example, CH ₃ CI, CH ₃ Br, CH ₃ I, C ₂ H ₅ B
r, C ₂ H ₅ I, (CH ₃ ) ₂ SO ₄ , (C ₂ H ₅ ) ₂
SO ₄ , C ₃ H ₇ I, C ₃ H ₇ CI, C ₃ H ₇ Br, etc. can be used.

The reaction product of imidazole or its derivative with epihalohydrin or the reaction product obtained by reacting imidazole or its derivative with epihalohydrin in the presence of an aliphatic amine (hereinafter referred to as brightener 3) The brightening agent 3, which will be described in detail, is one of the brightening aid components that can be optionally used in the present invention to further improve the glossiness. Here, as a derivative of imidazole, 1-methylimidazole, 1-ethylimidazole, 2-methylimidazole, 1,2-dimethylimidazole, 1-ethyl-2-methylimidazole, 1-vinylimidazole,
2-Methyl-1-vinylimidazole, 1- (2′-hydroxyethyl) imidazole, 1- (2′-hydroxyethyl) 2-methylimidazole and the like can be used, and epichlorohydrin is used as the epihalohydrin,
Epibromohydrin or the like can be used. Further, as the aliphatic amine, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, tripropylamine, ethyleneamines (for example, ethylenediamine, diethylenetriamine) and the like can be used.

Similar to the brightener 3, in the plating bath of the present invention, in order to further improve the glossiness, other brightening aids may be added to the combination of the brightener 1 and the brightener 2 if necessary. May be used. The gloss aid is selected from the group consisting of polyvinyl alcohol (PVA), water-soluble polymers such as gelatin, sulfur compounds such as thiourea, aromatic aldehydes such as anisaldehyde, heliotropin and vanillin, and mixtures thereof. Things can be used.

Next, the present invention will be described with reference to specific examples. Preparation of Brightener 1 Three kinds of thiourea derivatives were dissolved in 100 g of water, cooled to 50 ° C. or lower by water cooling, and dimethylsulfate was added to the solution over 30 minutes while stirring. Then, the reaction product No. I-VI was obtained by heating to 80 ° C. while continuing stirring, maintaining the state for 2 hours, then stopping stirring and allowing to cool. The above reaction product No. I
Table 1 shows the types of thiourea derivatives used for the preparation of -VI and the amount of dimethylsulfate added.

[Table 1] Thiourea derivative dimethylsulfate reaction product Name Addition amount Addition amount No. (g) (g) I Thiocarbazide 22 150 II Bisaminoethylthiourea 33 50 III Bisdimethylaminopropyl thiourea 50 50 IV Bisaminoethyl Thiourea 33 100 V Bisdimethylamino propylthiourea 50 100 VI Bismethylaminoethylthiourea 41 75

Preparation of Brightening Agent 2 Three kinds of polyethyleneimine having different molecular weights were added to 100 parts of water.
g, and dimethylsulfate was added to the solution over 30 minutes while cooling with water and stirring. Then, the reaction products NO. VII to IX were obtained by heating to 80 ° C. while continuing stirring, maintaining the state for 2 hours, then stopping stirring and allowing to cool. Table 2 shows the molecular weight and the addition amount of polyethyleneimine and the addition amount of dimethylsulfate used for the preparation of the reaction product.

[Table 2] ──────────────────────────── polyethyleneimine dimethylsulfuric acid reaction product ──────────── ────── Average molecular weight addition amount addition amount NO. (G) (g) ──────────────────────────── VII 600 20 88 ──────────────────────────── VIII 1400 40 58 ───────────────── ──────────── IX 3000 40 58 ─────────────────────────────

Preparation of Brightening Agent 3 20 g of imidazole was dissolved in 100 g of water, and 27 g of epichlorohydrin was added to the solution over 30 minutes while cooling with water and stirring. Then, the reaction product was heated to 95 ° C. with continuous stirring, kept in that state for 2 hours, then stopped stirring and allowed to cool.
I got NO. X.

Preparation of Zn-Fe alloy plating bath ZnO as Zn compound, N as alkali hydroxide
aOH, Fe ₂ (SO ₄₎ as a salt of Fe ₃ · 7H ₂
21 kinds (NO. 1-21) of zincate type containing 0, triethanolamine as a complexing agent, brightening agent 1 as a brightening agent, brightening agent 2 and brightening agent 3 as a glossing auxiliary agent and other glossing auxiliary agents A Zn-Fe alloy plating bath was prepared. Further, as a control plating bath, a bath containing only the brightener 2 without the brightener 1, a bath containing only the brightener 3, and the brightener 2
A bath (NO. 1 ′ to 7 ′) containing both the brightener 3 and the brightener 3 was prepared. In addition, a gloss aid (vanillin, polyvinyl alcohol, thiourea) is appropriately added. The composition of each plating bath is shown in Tables 3-5. It should be noted that these tables are divided into three for convenience of space, and should be read as one table.

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

Zn-Fe Alloy Plating Using the plating baths shown in Table 3, plating was performed under the following plating conditions. Plating conditions Bath temperature (° C) 25 Energization time (min) 10 Cathode material Polished iron plate Cathode current density (A / dm ² ) 0.1, 0.5, 2, 5, 10, 2
0, 30 Anode material Iron plate Stirring method Cathode locker Tables 6 and 7 show the relationship between the current density and the appearance and the relationship between the current density and the Fe eutectoid ratio in the plating film obtained as a result.
Shown in. The appearance is by visual observation (the judgment criteria are shown in the table), and the eutectoid ratio is a value determined by atomic absorption spectrometry after removing the plated coating.

[0026]

[Table 6]

[0027]

[Table 7]

Chromate treatment The plating film obtained under the above conditions was subjected to chromate treatment in order to form a silver-free black chromate film. For the chromate bath, a chromate treatment liquid commercially available under the trade name of "Metas Ultramate Silverless 637" from Yuken Kogyo Co., Ltd., which is the applicant of the present application, is 100 m.
It was prepared by diluting to 1 / l. Bath temperature and treatment time are 20-25 ° C and 40-60 seconds, respectively. It is known that a silver-free black chromate film cannot be obtained unless the iron content in the zinc-iron alloy is 0.3-0.6%. (Products obtained by plating bath No. 1-8) were excluded. Table 8 shows the results of visual measurement of the appearance of the silver-free black chromate film thus obtained.

[0029]

[Table 8]

Results As can be seen from Table 6, a good bright plating film can be obtained in the entire current density range of 0.1-30 A / dm ² for all the baths No. 1-21. As can be seen from Table 7, in the bath of No. 9-21, the change in the Fe eutectoid rate with the change in the current density is extremely small. Further, as can be seen from Tables 6 and 8, among the plating films obtained from the conventional baths (especially those having a high current density side), those having glossiness but having no good silver-free black chromate film are not formed. However, with regard to the plating film obtained from the bath of No. 9-21 of the present invention, a silver-free black chromate film having a good appearance is formed.
Since it is generally known that a chromate film having a good appearance exhibits excellent corrosion resistance, it can be said that the zinc-iron alloy plating obtained from the bath of the present invention is also excellent in terms of corrosion resistance. Further, in Table 5 and Table 6, No.
As can be seen by paying attention to the baths 11, 14, 17, 20 and 21, the plating bath of the present invention is good even if no gloss auxiliary agent such as vanillin (aromatic carbonyl compound), polyvinyl alcohol or thiourea is used. A zinc-iron alloy plating film is obtained.

The above specific examples are for explaining the content of the invention in an easy-to-understand manner, and do not limit the scope of the invention. It

Claims (1)

[Claims] 1. A Zn compound, an alkali hydroxide, and Fe
A zincate-type zinc-iron alloy plating bath containing a salt of (II, III), a complexing agent for solubilizing the Fe salt, and a brightening agent, wherein the brightening agent is: A compound obtained by quaternizing a thiourea derivative represented by the following general formula with an alkylating agent having a C1-C4 alkyl group and a basic nitrogen atom of a polyalkylenepolyamine
A zincate-type zinc-iron alloy plating bath containing an alkylated polyalkylene polyamine partially alkylated with a C3 alkyl group.