JPS5937749B2 - Bright chromate treatment agent and its treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved bright chromate treatment agent that produces a bright chromate film with excellent corrosion resistance on zinc or galvanized materials, and a chromate treatment method using the same.

Unlike colored chromate-treated films, conventional glossy chromate-treated films do not contain hexavalent chromate, so they have poor corrosion resistance and are susceptible to white rust.

Furthermore, as processing solutions with lower concentrations have become popular in recent years, the concentration of chromate drops below the level required for film formation shortly after the start of use. The current situation is that most bright chromate treated products have virtually no corrosion resistance.

Techniques for improving the corrosion resistance of glossy chromate films have existed for a long time, such as adding a titanium compound to the chromate treatment solution (see Japanese Patent Publication No. 37-5711), As
A method of adding compounds such as , W, Mo, V etc.
41088), a method of adding an alkyl silicate to the treatment (see Japanese Patent Publication No. 45-24845), or a method of secondary treatment with silicate sol or silicate aqueous solution after chromate treatment (Japanese Unexamined Patent Publication No. 53-1988). 10883
4 and 53-108835) have been proposed, but each has its own merits and demerits, and has not yet achieved a satisfactory effect. On the other hand, it is known that a water-soluble resin such as polymethacrylic acid or its derivatives is added to the chromate treatment solution, but this method is for the purpose of baking treatment, and is used for bright chromate treatment. It is technically different from the chemical conversion treatment method. In view of the above facts, the present inventors continued intensive research into improving the corrosion resistance of bright chromate films on zinc or galvanized materials, and found that they added a specific polyacrylamide-based water-soluble resin to the conventional chromate solution. The present invention was completed based on the finding that the treated material significantly suppresses the occurrence of white rust. It has also been found that corrosion resistance can be further improved by post-treating with a polyvalent metal salt aqueous solution after treatment with this treatment solution. That is, the first aspect of the present invention is a chemical conversion treatment agent for bright chromate that is composed of an acidic aqueous solution containing a hexavalent chromium compound as a main ingredient, and has a degree of hydrolysis of 20 to 20.
This is a bright chromate treatment agent for zinc or galvanized materials, which is characterized by adding 80% polyacrylamide water-soluble polymer.

Bright chromate treatment agents consist of hexavalent chromium compounds such as chromic anhydride and sodium dichromate, mineral acids such as sulfuric acid and nitric acid,
It is an aqueous solution composed of a fluorine compound such as acidic sodium fluoride, and conventional processing agents can be used as they are in the present invention.

In other words, although the liquid composition varies depending on the processing purpose, processing conditions, and the object to be processed, hexavalent chromium compounds contain C.
0.1-10g/1 as rO3, H2S040.1-
109/1, HN03:5-509/1, fluoride:0.
A dilute acidic aqueous solution containing a hexavalent chromium compound as a main ingredient is 1 to 209/l and the remainder is water. In addition to hydrolyzed polyacrylamide added to such treatment agents, corresponding acrylic acid and acrylamide copolymers equivalent thereto can also be applied. Regarding the degree of polymerization, if the degree of polymerization is low, there will be no effect when adding it, while if it is too high, it will cause stickiness and the processing operation will be inconvenient, but the effect will not increase according to the degree of polymerization, so it should be approximately 1000 or more. In most cases, around 10,000 is suitable. In addition, the degree of hydrolysis refers to the rate at which a part of the amide group is hydrolyzed with an alkali to form a carboxylic acid salt, and in the present invention, the degree of hydrolysis is 20 to 80.
% is suitable, and in many cases a range of 30 to 70% is preferred. The degree of hydrolysis of polyacrylamide is 20% to 80
%, the polyacrylamide hydrolyzate has no chelating effect on chromium, and a strong chromate coating cannot be formed. The ratio of adding such a water-soluble resin to the chromate treatment agent varies depending on various conditions, but is suitably 0.1 to 59/l, particularly 0.5 to 59/l.
2f! A concentration of /j is preferred. Note that sulfuric acid or nitric acid can be used to adjust the properties of the liquid when adding the resin. The chromate treatment agent according to the present invention can be used for treatment without any change from conventional methods, thereby improving the corrosion resistance of the bright chromate film. Although this was unexpected, the solution life is extended and an excellent corrosion-resistant coating can be obtained from a solution that has a low chromic acid concentration and does not form a chemical conversion coating in a typical chromate treatment solution. Furthermore, when the conventional chromate treatment solution becomes aged, replenishing it with new solution will have an adverse effect on the aging process, so either prepare a new bath and discard the aged solution, or use an ion exchange resin to remove harmful ions before use. However, the processing agent according to the present invention can be used effectively even if a new solution is added to the aged solution to replenish the effect of the chemical conversion film without any substantial difference.

The chemical conversion film produced by the chromate treatment according to the present invention has a uniform bluish luster from start to finish.In contrast, with conventional chromate treatment solutions, as the concentration of chromic acid decreases, the film becomes thinner and its appearance becomes uneven. A significant difference is observed compared to film effects such as the tendency to In this way, by adding the above-mentioned water-soluble resin to a conventional general gloss chromate treatment agent, without any operational changes from the conventional method, benefits can be obtained by itself, including a marked improvement in the corrosion resistance of the film. However, if the material is further subjected to chromate coating treatment using the chromate treatment agent and then immersed in a polyvalent metal aqueous solution, stable corrosion resistance can be obtained, the amount of the water-soluble resin added can be reduced, and the applicable value of the degree of hydrolysis can be expanded. A more stable effect can be obtained. Here, the polyvalent metal salt refers to alkaline earth metals such as calcium, magnesium, barium, or strontium, sulfates, nitrates, or phosphates of manganese, chromium, molybdenum, titanium, and the like. The concentration when using is 0.01-0.1 mol/l
The pH of the liquid may be between 4.5 and 8. The treatment operation is almost the same as that of chromate treatment, and after the chromate treatment described above, the product is washed with water if necessary, immersed for 1 to 30 seconds, preferably 2 to 20 seconds, and then washed with water, hot water, and dried. end. The present invention will be further explained below with reference to Examples.

Example 1 Commercially available bright chromate treatment agent 1CP-33 (Japan M.
Anshita Teichi Co., Ltd. product) 15d/11 degree of polymerization 10,000
Various gloss chromate treatment agents were prepared consisting of 2 g/l of hydrolyzed polyacrylamide.

Bright chromate treatment method> A test piece of a galvanized mild steel plate (50m1 x 10011) was immersed in a bright chromate treatment solution for 10 seconds at room temperature.
Leave in air for 5 seconds, rinse with water for 5 seconds, then dry.

Post-treatment method using polyvalent metal salt aqueous solution> After gloss chromate treatment, the test piece was washed with water and immersed in polyvalent metal salt aqueous solution for 5 seconds at room temperature, left in air for 5 seconds, washed with water for 5 seconds, and immersed in boiling water at 80 to 90°C for 5 seconds. Dip for 15 seconds at 70°C.
Let dry for a minute.

<Corrosion Resistance Test> Corrosion resistance is evaluated by a salt spray test based on JIS-Z-2371.

The results are shown as rating ▲, but this is the first one below.
According to the criteria in the table, the results of the evaluation of the criteria are shown in Table 2. Note that ▲1 (processing agent with zero degree of hydrolysis of polyacrylamide) is a comparative example. Example 2 Same as Example 1 except that a polyacrylamide hydrolyzate with a different degree of polymerization with a degree of hydrolysis of 60% was used: A chromate film was formed using the same treatment agent and treatment method, and its corrosion resistance was investigated. Example 3 in which the results shown in the table were obtained The chromate treatment agent and treatment method were the same as in Example 1, except that a polyacrylamide hydrolyzate with a degree of hydrolysis of 60% and a degree of polymerization of 5000 was used and the amount added was changed. When a chromate film was formed and its corrosion resistance was investigated, the results shown in Table 4 were obtained.

Example 4 Polymerization degree 10000) Using a copolymer of acrylic acid and acrylamide corresponding to a hydrolysis degree of 60%: K
A chromate film was formed using the same treatment agent and treatment method as in Example 1, except for the above, and its corrosion resistance was examined.
The results shown in Table 5 were obtained.

Example 5 ICP-33,15g/l) Polyacrylamide hydrolyzate 2g/l with degree of polymerization 5000 and degree of hydrolysis 60%
After treatment in the same manner as in Example 1 with a chromate treatment agent consisting of The results in the table were obtained.

In addition, the concentration of manganese sulfate is 0.086 mol to 0.34 mol.
A similar post-treatment was carried out using an aqueous solution with different mol/l concentration, but there was no particular influence of the concentration during this time, and good results were obtained.

Example 6 and Comparative Examples Bath preparation composition: ICP-33, 157nIV1, and a bright chromate treatment agent composed of 29/l of polyacrylamide hydrolyzate with a degree of hydrolysis of 60% and a degree of polymerization of 10,000 (for comparison, the above-mentioned polyacrylamide Hydrolyzate (P
An aging test was conducted in the same manner as in Example 1 for the additive-free gloss chromate treatment agent of AM).

That is, with the conventional additive-free gloss chromate treatment agent having the above composition, the treatment amount is 67 dw? It was confirmed that the corrosion resistance of the chromate film decreased rapidly from 67d/l.
After the I/L treatment, the first new solution replenishment is performed at the Z amount (I
CP-33.5m1) The water-soluble resin Zy) was then refilled with the new solution for the second time at 100 drrI-/l, and then the same amount of Z was applied at the time of bath preparation, and the corrosion resistance of the formed film was investigated, as shown in Table 7. The results were obtained. As is clear from the above results, the corrosion resistance of the film does not recover even if the conventional type of chromate treatment agent is replenished with a new chemical after aging, and a new bath must be prepared. By replenishing it, you can obtain the same stable treatment effect as when preparing a bath.

Claims (1)

[Claims] 1. A chemical conversion treatment agent for bright chromate composed of an acidic aqueous solution containing a hexavalent chromium compound as a main ingredient, which is obtained by adding a water-soluble polyacrylamide polymer having a degree of hydrolysis of 20 to 80%. A bright chromate treatment agent for zinc or galvanized materials. 2 After chromate treatment by immersing zinc or galvanized material in a chromate treatment agent made by adding a polyacrylamide water-soluble polymer with a degree of hydrolysis of 20 to 80% to an acidic aqueous solution containing a hexavalent chromium compound as the main ingredient, A bright chromate treatment method for zinc or galvanized materials, which is then subjected to immersion treatment in a polyvalent metal salt aqueous solution.