JPS6012432B2 - Bright galvanizing bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of brightly galvanizing metal and its galvanizing grade.

Currently, most galvanizing is carried out with alkaline solutions containing soluble zinc compounds and sodium cyanide.

However, this sodium cyanide solution produces semi-bright galvanizing, so various brighteners are added to the plating grade to obtain bright galvanizing. This brightening agent is well known and includes, for example, aldehydes, ketones, thioureas, organic acid salts, and various other agents. This cyanide-containing rating is because cyanide is toxic, making it difficult to treat wastewater, and this has become an important issue, especially as waste treatment has been raised as a social issue recently. There is.

Since cyanide-containing baths have problems in waste disposal, much research has been carried out to develop cyanide-free baths that do not have these drawbacks. Galvanized grades that contain little or no cyanide already exist, but most of these galvanized grades are made with solutions of sodium sulfite and excess sodium hydroxide. be.

When galvanizing is carried out using a high-strength zincate alkali without using additives such as brighteners, a dull, spongy, and poor-appearing lick is produced. In order to eliminate this drawback, attempts were made to improve the smoothness of the plating by adding glycolate, but it was not possible to obtain a bright zinc plating that could be used industrially. Also, alkanolamines, alone or together with aldehydes, as described in U.S. Pat. No. 3,317,412,
It has been proposed to add a high pH zincate plating bath. However, this type of plating bath is not stable, does not produce a practically lustrous plating, and does not produce a ~bright zinc plating compared to the cyanide plating grades currently in use. There are disadvantages such as narrow space. Furthermore, German Patent No. 1253003 discloses the addition of alkylene amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenebentamine, alone or together with aldehydes, to high pH zincate plating baths. There is. This plating grade produces glossy zinc plating and is relatively stable compared to the above-mentioned plating grades, but the range in which bright zinc plating is produced is narrow and uniform electrodeposition (throwing property) ) is defective. For these reasons, the above-mentioned plating methods have not yet been adopted industrially. Practical experience shows that it is necessary to add small amounts of sodium cyanide even to so-called cyanide-free coating baths in order to provide a gloss that meets current demands.

It has been previously published that the reaction product of epichlorohydrin and an amine is effective in zinc cyanide plating.

For example, U.S. Patent No. 2 of Winters (Win rs)
No. 791554 contains a reaction product of epichlorohydrin and ammonia or a primary amine and is applied to a conventional zinc cyanide plating grade for 75 to 90 t/so (10 to 1 z/ga).
It is described that 1> is added.

In this case, an epichlorohydrin-primary amine reaction product is used for zinc cyanide, but when this reaction product is added to a plating grade that does not contain cyanide, uniform electrodeposition and None can be obtained that meet current standards in terms of current density, gloss, etc. Bumso
U.S. Pat. No. 3,227,638 (n) gives an example of the addition of a reaction product of a cyclic amine, namely epichlorohydrin, and hexamethylenetetramine to a cyanide-containing plate.

However, when this reaction product, which is commonly used in ordinary zinc cyanide, is added to a low cyanide grade (approximately 15 evenings/night) or a cyanide-free grade, the stability of the bath solution may be affected. becomes defective and is not practical. Additionally, large amounts of secondary brighteners are added to the low cyanide plating grades to produce good gloss. U.S. Patent No. 268,920 (filed July 3, 1972) by the same assignee as the present application describes a soluble zinc compound that can be plated electrolytically and a water-soluble reaction product of an amine and epihalohydrin. An alkaline galvanized grade containing substantially no cyanide was described.

The water-soluble reaction product has repeating units of tertiary amine groups and quaternary amine groups, and has a molecular weight of about 250 or more. To the bath described in US Pat. However, you cannot get good results. The head lead plating method described in the above-mentioned US Pat.

A wide range of current densities is, of course, highly desirable, especially for rack plating operations requiring high current densities. When using the plating bath described in the above-mentioned US patent application, it is not possible to produce a bright plating at current densities above 11 A/d (10 melon sf).

At high current densities, the deposit becomes matte or dark gray, for example. On the other hand, when the plating of the present invention is used, glossy plating can be produced at a current density of 27 A/d〆 (25th SF) or less. That is, the present invention provides a galvanizing bath that provides uniform electrodeposition and gloss comparable to or superior to conventional cyanide-containing galvanizing grades, and that is substantially cyanide-free.

The plating structure of the present invention includes at least one electroplatable soluble zinc compound and a suitable amount of a pyridine compound having at least one amine-containing substituent. The soluble zinc salt commonly used in plating of the present invention is
Any zinc compound may be used as long as it is soluble in an alkaline solvent and can be hazy-plated.

Such zinc compounds are well known and include, for example, zinc sulfate, zinc acetate and zinc oxide. Other alkaline soluble zinc compounds can also be used, as is well known to those skilled in the art. As with conventional galvanizing baths, the amount of zinc in the bath can be varied.

However, the zinc concentration in the plating bath of the present invention is preferably in the range of about 7 to 30 oz/gal. In order to supply zinc to the plating grid, a normal soluble zinc anode may be used, or if a non-falling anode is used, an appropriate alkali-soluble zinc compound may be added to the plating grid. Good too.

To make the plating bath alkaline, any alkaline substance that dissolves the desired amount of zinc compound can be used.

For example, sodium hydroxide, potassium hydroxide, etc. can be used to provide alkalinity. in this case,
Since sodium hydroxide has a high solubility in alkali zincate, sodium hydroxide is more suitable. The amount of alkaline compounds such as sodium hydroxide should be in excess of the amount needed to produce sodium zincate.

There is no particular limit to the amount of excess, ie, free, sodium hydroxide, as long as all the zinc is dissolved in the solution and no zinc precipitation occurs. pH of plating bath of the present invention
The values can be varied as is well known to obtain the best results.

However, it is better to keep the pH of the electrolyte above 1 s.
The pyridine compounds used in the metallurgy of the present invention have at least one amine-containing substituent. Examples of pyridine compounds that can be used in the dew gas rating of the present invention include compounds shown in the following general formula.

In the formula, each R,, R2, R3, R4 and R5 is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkyl group, a lower alkyl group, a lower alkyl group, a lower alkyl group, a lower alkyl group, a lower alkyl group. Nyl group, hydroxyl group, carboxyl group, amine residue, lower alkylol group, lower alkylcarboxyl group, lower alkylamine residue; or hydroxyl group, carboxyl group, amine residue, lower alkylol group, lower alkylcarboxyl group, or lower alkylamine A group formed by the reaction of a residue with an alkyl sultone, an alkyl lactone, or an epoxide, and Z is absent or 0-, or the above formula (1)
This is a group that produces a quaternary amine compound by reacting the compound (1) in which at least one of the groups R, , R2, R3, R4 and R5 contains an amine nitrogen atom with a quaternizing agent.

The pyridine compound used in the Kamekimetsukaku of the present invention is preferably a pyridine derivative having at least one amine substituent, and representative examples thereof include 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2, 3-diaminopyridine, 2,4-diaminopyridine, 2,5
-diaminopyridine, 3,4-diaminopyridine and 3,5-diaminopyridine.

In the present invention, the alkyl sultone that can be reacted with pyridine with good results is propane sultone.

Other alkyl sultones can also be used. An example of the alkyl lactone that can be reacted with compound (1) is 8-propiolactone, but other lactones can be used as well. Epoxides that can be reacted with pyridine (1) include ethylene oxide, propylene oxide, epichloropidrine, allyl glycidyl ether, 2,3-epoxyptane, di(1,2-dimethyl-1,2-epoxypropyl) ether and Examples include Q,8-epoxypropionic acid.

Pyridine (1) can be quaternized using well-known quaternizing agents such as pendyl chloride, methyl chloride, dimethyl sulfate and allyl chloride.

As the general formula (1), aminopyridine, for example 2
Good results can be obtained by using -aminopyridine, 3-aminopyridine, 3-aminopyridine, and the like.

At present, even better results can be obtained when using aminopyridines of the formula (1), especially reaction products of 2- and 3-aminopyridines and epichlorohydrin. Also, U.S. Patent No. 2791554 of Winters (Winte Ore) and Nobel (NoGI)
As described in U.S. Patent Application No. 26,892, each of the pyridines of formula (1) and their epihalohydrin reaction products are combined with ammonia or aminoepihalohydrin reaction products having a molecular weight of about 250 or more. Best results can be obtained when used with According to this particular combination, the current density is 27 A/d (2
It is possible to produce very high-gloss galvanizing within the range of 5 sf). When using pyridine and the epichlorohydrin reaction product of pyridine, the range of current densities that produce bright galvanizing described in the specification of the aforementioned U.S. patent application can be expanded. , pyridine and aminepihalohydrin reaction products, alkylene amines, alkanolamines, etc., are not in the same range of current densities. As already apparent to those skilled in the art, the amount of the pyridine compounds of the invention, or their epihalohydrin reaction products, can vary within a wide range.

Usually, the effect of increasing the current density while retaining the galvanizing gloss can be seen by adding as little as 0.01 μl of the pyridine compounds and their reaction products. Usually about 0.1 to 1 log/log concentration is useful, although higher concentrations can be used. In general, bright galvanizing can be produced over the entire range of current densities up to a concentration of 1 night/day, but the addition of higher amounts of pyridine compound does not provide any particular additional benefit. As can be seen, the amount of pyridine compounds used depends not only on the type of these compounds used, but also on the range of current density required to produce bright galvanizing. Therefore, if the current density does not need to be very high, the amount of pyridine compound can be reduced. The aminopyridine-epihalohydrin reaction product can be produced by simply heating aminopyridine with epichlorohydrin.

The particular 3-aminopyridine (Formula 1) used in the examples below was prepared by dissolving 28 moles of 2-aminopyridine in 19 liters (5 gallons) of water and gradually adding 49.1 moles of epichlorohydrin. The temperature was prepared by adding the following ingredients to prevent the temperature from rising suddenly. In this reaction, it is desirable that the temperature does not exceed 90 oo. The reaction product is then held at about 75-8000 for about 45 minutes and then cooled. . The final product has a volume of approximately 7 gallons. The 27% solution used in the examples described later was obtained by diluting this reaction product to adjust the solid content to 27%. Raw materials other than epichlorohydrin such as other epoxides, alkyl sultones and their homologs and isomers,
It can be used when reacted with pyridine to produce a soluble product.

The amounts of raw materials used can also be varied, but the exact composition of the reaction products is unknown. In the present invention, the polyelectrolyte used to produce bright zinc plating from a substantially cyanide-free electrolyte, i.e., the aminoepyhalohydrin reaction product, is an aqueous solution of ammonia or an alkyleneamine and an epihalohydrin. It is a product of sexual military condensation.

This polycondensation product has approximately 250 amine groups as repeating units.
It is a polymer with a molecular weight of . Water-soluble epihalohydrin-alkylene amine military condensates can be prepared by directly reacting epihalohydrin with a linear or branched alkylamine or ammonia. With respect to alkylene amine polycondensates, reference to "amine" or "alkyl amine" also includes ammonia.

The epihalohydrin-alkylene amine polycondensate used in the present invention has amine groups such as primary amine, secondary amine, tertiary amine, and quaternary amine as repeating units.

The epihalohydrin-alkylene amine car condensate mainly has primary amine groups and secondary amine groups as repeating units,
U.S. Patent No. 27915 to Winters (Win s)
No. 54, it can be prepared by reacting epichlorohydrin with a primary amine or ammonia.

The ammonia-epichlorohydrin reaction product can be prepared by methods such as those described in Winters, column 2, Group 6 et seq. Halohydrin reaction products can be similarly prepared by using an amount of ethylenediamine corresponding to the amount of ammonia stated in that patent, column 3, lines 49-53. Epihalohydrin Lower alkyl amines are advantageous for the reaction.

Examples of these amines are ethylenediamine, trimethylamine, triethanolamine, dimethylaminopropylamine, diethylaminop. Pyramine, N,
Examples include N'-dimethylamine ethylamine and N,N'-dimethyl-N'-methylpropylene diamine. For example, the methyl, ethyl, and propyl groups of these amines can be interchanged. As mentioned above, the first
Polycondensates containing repeating units of amines, secondary amines, or tertiary amines are effective for galvanized grades that are substantially free of cyanide, but polycondensates containing quaternary amines are particularly effective. It is valid.

Amines can be prepared by quaternizing agents in a well-known manner using well-known quaternizing agents such as methyl chloride, methyl sulfate, allyl chloride, penzyl chloride, butene chloride, hexyl chloride, and propargyl chloride.
It can be graded.

If the resulting polymer already contains a tertiary or quaternary amine as a repeating unit, epiha. It is advantageous to quaternize the amine after the reaction with the hydrin in the following step. However, this is not necessarily necessary. The military condensate of the present invention having a repeating unit of tertiary amine or quaternary amine can be prepared by first reacting epihalohydrin with a primary amine or monoamine, and then carrying out the quaternization reaction in step 0 described below. The repeating units constituting the polymer can be tertiary or quaternary amines. In this way, the products described in the aforementioned Winters patent can be converted into tertiary and quaternary amines by the action of methyl chloride in the steps described below. In the present invention, the shrimp halohydrin to be reacted with the amine is not only well-known, but also includes various saturated and unsaturated homologues and isomers, which react with alkylamines to produce water-reducing products. Either is fine.

This water-soluble polymer can also be prepared by polymerizing epichlorohydrin by a well-known method and reacting this polymer with an alkylamine. If it is desired that a tertiary amine and a quaternary amine be present as repeating units constituting the polymer, the product may be prepared, for example, by a method similar to Step 0 below, depending on the type of amine used and other reaction conditions. Therefore, it is sufficient to make it quaternary. Step 1 Pour 102 ml of dimethylaminopropylamine into a three-neck round bottom flask containing 612 ml of water.

Place the flask in a water bath and attach the rope strainer, thermometer, and funnel. After cooling the solution to 2,500 ℃, 161 ml of epichlorohydrin is gradually added over 1 hour. The molar ratio of epichlorohydrin to dimethylaminopropylamine was 1.75:1. Epic.
After all the ruhydrin was added to the aqueous solution, the reaction was continued for 30 minutes, and then the wind strength of the reaction product was adjusted to about 6 with sulfuric acid.
Step 0 Using a round bottom flask similar to the flask used in Step 1,
Dissolve 452 ml of dimethylaminopropylamine on 820 ml of water and react this solution with 368 ml of epichlorohydrin (epichlorohydrin and dimethylaminopropylamine).

The molar ratio with lopylamine is 0.9:1). After the reaction is complete, the reaction product is placed in an autoclave with 110℃ of sodium hydroxide, and heated to 5,000℃ while stirring.Methyl chloride is pressurized to 2.8-3.5k9/300℃ in an autoclave. After blowing, the autoclave is cooled and the contents are removed. The product has a solid content of 50%,
and adjust to pH 6. The amount of polyelectrolyte used in the present invention varies depending on its type and the brightness of the galvanizing.

When using a solution containing sodium zincate and free sodium hydroxide, the plating is gray with no shine. When a small amount of polyelectrolyte is added to this, the plating becomes semi-gloss, and when further polyelectrolyte is added, the gloss increases, and a plating with the best gloss can be formed. Of course, more polymer electrolytes can be added. Generally, a platter containing sodium zincate and free sodium hydroxide is added to a 0.000.
After one night/adding the epichlorohydrin-dimethylaminopropylamine condensation product, the matte gray zinc plating becomes a semi-gloss plating. Furthermore, when the amount of this polymer electrolyte is increased, the gloss of the plating becomes even better. In the case of the above-mentioned polyelectrolytes, the best results were obtained at one night/concentration. It is also possible to further improve the gloss by adding conventional brighteners, such as aldehyde brighteners, such as vanillin, hydroquine benzaldehyde, anisaldehyde, bisulfite adducts of aldehydes.

This secondary brightener may be optionally added if it is desired to further increase the gloss. Therefore, the amount of this secondary brightener can vary within a wide range. For example, anisaldehyde can be used in combination with polyelectrolytes in amounts ranging from as little as 0.1/day to as much as 1/day or more. Also,
If it is desired to use cyanide, small amounts of cyanide, such as sodium cyanide, can also be added to the plating baths of the invention.

However, adding more than 15 g/gal of cyanide does not particularly improve the results. Furthermore, in the present invention, adding cyanide is not an essential requirement for forming glossy plating.
The plating bath of the present invention can be treated with the same current as in ordinary plating.

For example, according to the Hull cell test method, 27 A/d (25 sf)
) can be carried out at a current density of: However, within this range, a range of about 2.7 to 5.4 A/d (25 to 5 beats sf) is suitable, and 2.7 A/d is usually optimal. It is possible to apply plating to the following articles.

Galvanizing occurs at the cathode, and most galvanizing is performed by immersing the steel product as the cathode in a plating bath. Comparative Example 1 A galvanized sheet having the following composition was prepared.

Metallic zinc 12 min/gal (1. loss z/gal) Caustic soda 120 t/s (1 loss z/gal) Condensation reaction product (formed by reacting epichlorohydrin and dimethylaminopropylamine from step 01) substance, molecular weight 4000-5000) 1-6 cC/ga (6 CC/ga
l) Anisuarte'hydrobizalphite 0.01 t/gal (0.04 t/gal) After electrolyzing the solution for a short time, a plating test was conducted using a Hull cell tester.

The steel plate was plated for 2 minutes using a current axis without damage at room temperature. Plating is 0.1 to 9.7 A/d (1 to 9 sf
) was quite glossy. However, above this current density range, the color was matte gray and there was no adhesion. Further, in the range of 7.5 to 9.7 A/d (70 to 9 melon sf), the luster of the steel plate was not sufficient. Example 1
0.4 ton of 3-aminopyridine was added to the temperature gauge used in Comparative Example 1.

The steel plate was plated using a Hiroshi tester for 2 minutes using a Hull cell tester. The plating was glossy and uniform over the entire surface, with no adhesion defects or gray spots. The additive used in this example prevented the formation of gray areas and expanded the current density range, and also exhibited properties as a brightener for high current densities. Example 2 To the test solution used in Comparative Example 1, 1.5 minutes/3-picolylamine was added.

There were no gray, dull areas or areas with poor adhesion over the entire surface of the steel plate, but at any current density,
The gloss was poorer than when 3-aminopyridine was used. Example 3 0.8/day of 2-aminopyridine was added to the soaking bath used in Comparative Example 1, and the same treatment was performed.

In this case, similar to Example 1, good results could be obtained. Example 4 0.50 cc/night (approximately 2
A reaction product of 2-aminopyridine and epichlorohydrin (7% solution) was added, and the steel plate was plated in the same manner as in Example 1.

A plating was formed on the steel plate with no gray or adhesion defects, and this plating was glossier than that obtained in Example 1. Comparative example: 303 yen (80 ga
1) A rating scale was prepared.

Zinc 18 pm/evening (2.4 oz/gal
) Caustic soda 180 oz/gal (24 oz/gal
) Condensation reaction product (product obtained by reacting epichlorohydrin and dimethylaminopropylamine from step 0', molecular weight 4000-5000) 3-2 cC/night (12C
C/gal) Vanillin 0.026 t/t (0.
A deep box with sharp green areas was plated in the above plating bath at a current density of about 6.2 A/dW (6 SF).

As a result of plating, a gray area appeared on the outer green area. Example 5 In the case used in Comparative Example 2, 0.6 evening/evening (27
% solution) of the reaction product of 2-aminopyridine and epichlorohydrin.

6. The parts used in Comparative Example 2. When the plate was plated again with Mushi/d〆 (sf of 6), no gray areas appeared.
Example 6 A reaction product obtained by reacting 1 mole of 2-aminopyridine with 1.3 moles of ethylene oxide by the above method was added for 0.5 min/day.
A 27% solution was added to the tsusaki kaku prepared in Comparative Example 1.

When plating a steel plate for 2 minutes using a Hull cell tester, it reached a range of 27 A/d or more (25 peaks SF).
Produced a glossy finish. Example 7 A galvanized grate having the following composition was prepared.

Metallic zinc 11.2 evenings/so (1. $z/gal
) Caustic soda 112 evenings/so (1 mother z/gal
) epichlorohydrin-ethylenediamine reaction product (
Using the aforementioned solution (prepared according to U.S. Pat. No. 2,791,554 to Winters) at 4 cc/gal (15 cc/gal), the specimens were plated at 2A for 5 minutes using a Hull cell tester. Metsuki is uA/d〆 (1 melon sf)
It is dull white in the following range, 1.1 to 4. The color was semi-gloss at 10-4 sf. 4.3A/d
When the coating was over 400 sf, it was matte and had no adhesion.

When a 27% solution of the reaction product of 0.60 [/] was added to the above solution, the resulting lump was 10. There was luster within the range of ship/d (10 melons SF) or less.

Example 812 evening/evening (1. z/gal) of metallic zinc, 120 tano (1 loss/saddle) of caustic soda, 20c
c/ When a plating test was conducted using the plating grade containing tetraethylenebentamine, spongy matte plating was produced. 1.2cc/2 of the reaction product of 2-aminopyridine and epichlorohydrin
When a 7% solution was added, the current density was 5.4 A/d (
A semi-gloss finish was produced in the following range (5 sf).

Example 9 A plate having the following composition was prepared.

Metallic zinc 10.5 oz/t (1.4 oz/g
al) Caustic soda 1502/so (2 melons/g
al) Epichlorohydrin-amine reaction product (according to Nobel U.S. Pat. No. 26,892) 3-2CC
Anisaldehyde bisulfite 0.16 CC/gal) Reaction product of 2-picolylamine and methyl chloride for quaternization 0.08 CC/gal (Event/gal) Using the above plating bath, a plating test was conducted with a Hull cell tester, and a glossy plating was produced within a current density range of 27 A/d and (25 melon sf) or less.

Claims (1)

[Claims] 1. In an alkaline galvanizing bath capable of bright galvanizing, (1) the alkaline aqueous solution does not contain cyanide compounds or has a cyanide content substantially less than 15 g/l; (2) Contains an amount of soluble zinc compound capable of electroplating zinc, and (3) as a galvanizing brightener, pyridine derivatives such as 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,3- Contains at least one pyridine derivative selected from the group of diaminopyridine, 2,4-diaminopyridine, 2,5-diaminopyridine, 3,4-diaminopyridine and 3,5-diaminopyridine, and further
(4) As a galvanizing photoselector, amine and epihalohydrin, or amine and polyepihalohydrin having a repeating unit of amino group and having a molecular weight of 200 or more are reacted to form a repeating unit of soluble amino groups in a galvanizing bath. A bright galvanizing bath characterized by containing a polycondensate having a molecular weight of 200 or more.