JPH01225780A - Highly corrosion-resistant chromated steel sheet, its production, and chromating solution - Google Patents

Abstract

PURPOSE:To form a chromate film having excellent corrosion resistance and suitability for coating on the following steel sheets by treating the cold-rolled steel sheet or Zn plated steel sheet with a chromating soln. contg. specified amts. of CrO3, an amine, or an amino acid and further contg. one or >=2 kinds among a silicate compd., F ion, and phosphate ion. CONSTITUTION:The cold-rolled or Zn-plated steel sheet is treated with the chromating soln. having the following composition. Namely, the soln. contains 5-300g/l CrO3, an amine or an amino acid in the 1/120-2/3 molar ratio of the amino group to Cr, <=300g/l silicate compd. as silicate, <=300g/l F or F complex ion as F ion, <=300g/l of one or >=2 kinds among phosphate ions as P, the Cr<3+>/Cr<6+> is controlled to 0/10-90/10, and the soln. further contains a reducing agent such as alcohol and saccharides. The obtained chromate film contains specified amts. of one or >=2 kinds among org. cation, silica, F ion, and phosphate ion, contains 5-300mg/m<2> chromate expressed in terms of Cr, and has high corrosion resistance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides corrosion resistance for use in home appliances, building materials, automobile steel plates, etc.
The present invention relates to a chromate-treated cold-rolled steel sheet or a zinc-plated steel sheet with excellent paintability, a chromate treatment method, and a chromate treatment liquid used therein.

[Conventional technology]

Conventionally, a chromate film containing chromium as the main component has been formed on zinc-plated steel sheets in order to prevent the formation of white rust, and on cold-rolled steel sheets in order to prevent the formation of red rust. In recent years, more and more users are using zinc-plated steel sheets processed into electrical appliances, building materials, automobile parts, etc. without painting them, and the corrosion resistance of the chromate film treated by zinc-plated steel sheet manufacturers is simply called primary rust prevention. In addition, it is required to have a final rust prevention function, and a higher level of corrosion resistance than ever before is required. On the other hand, there are many uses in which zinc-based plated steel sheets or cold-rolled steel sheets are coated with paint, and there is an increasing demand for chromate-treated zinc-based plated steel sheets or cold-rolled steel sheets that have performance as a base treatment for painting.

Conventional techniques related to the surface treatment method of the present invention include the following.

(1) Chromate treatment method in which chromic anhydride is treated with a liquid containing sodium silicate or potassium silicate and phosphoric acid as main components (Japanese Patent Publication No. 52-14691).

(2) 1f of water glass or sodium silicate! ! Alternatively, surface treatment of steel materials is characterized by applying a treatment liquid containing 0.1% to 10% of an organic silane coupling agent to a solution containing 0.1% to 30% of the two types, and drying the solution. Act (Japanese Unexamined Patent Publication No. 52-50940).

(3) pH 3 containing trivalent chromium, sulfate ions and polycarboxylic acid resin as main components on the surface of zinc or zinc alloy
After applying a chromium-containing aqueous solution of . The aqueous solution has a dry film thickness of 0.
．． A method for surface treatment of zinc or zinc-lead alloy, characterized by applying the coating to a thickness of 2 to 1 μm and then drying it.
Special Publication No. 58-53069).

(4) A method of applying a treatment liquid mainly containing hydrated chromium oxide to various metal surfaces, and then applying a low concentration aqueous solution of a water-soluble resin (Japanese Patent Publication No. 52-35620).

(5) A method of treating zinc-based plated steel sheets with a chromate treatment solution with or without addition of fluorine ions, silicate compounds, silane coupling agents, and reducing agents
．． -135579).

[Problem to be solved by the invention]

Regarding (1) above, although the corrosion resistance in a flat plate is good, there is a drawback that the corrosion resistance after processing is poor.

Regarding (2), the purpose is to provide primary rust prevention and improve paint adhesion, but even a flat plate is insufficient in rust prevention.
It has the disadvantage of extremely poor rust prevention after processing.

Regarding (3), although it has excellent corrosion resistance, it has the disadvantage that sufficient adhesion and scratch resistance cannot be obtained for painting by the user. Furthermore, since the two-layer process is performed, the process is complicated.

As for (4), since a two-layer treatment is performed, the treatment process is complicated, and if the amount of resin deposited is small, sufficient corrosion resistance cannot be obtained. Furthermore, since the surface layer is coated with a resin film, the user is highly selective in choosing the paint, and some paints have no adhesion at all. Furthermore, weldability may deteriorate.

Regarding (5), the paintability was significantly improved by adding a silane coupling agent to the chromate solution, but the corrosion resistance in the bare state was still insufficient, and the white rust generation time in SST was The best time was 300 hours.

Therefore, the object of the present invention is to improve paintability as well as bare corrosion resistance on galvanized steel sheets, with white rust occurrence time of 400 hours or more in SST, and with reference to the above-mentioned prior art, and on cold-rolled steel sheets, red rust does not occur on cold-rolled steel sheets. It is an object of the present invention to provide a highly corrosion-resistant surface-treated steel sheet that lasts for 24 hours or more, a method for producing the same, and a chromate treatment solution used therein.

[Means for Solving the Problems] The present invention provides a chromate coating layer containing organic cations, silica, fluorine ions, and phosphate ions on a cold-rolled steel sheet or a zinc-plated steel sheet, with a chromate coating layer having a Cr1i of 5 to 300.
The present invention provides a highly corrosion-resistant chromate-treated steel sheet characterized by having a corrosion resistance of mg/m2. - Here, the chromate coating layer includes (a) an organic cation in a molar ratio of 2/3 to 1 to Cr;
/1000, (b) the weight ratio of silica to Cr is 5.0 or less, (c) the weight ratio of fluorine ions to Cr is 0.3 or less, and (d) the weight of phosphate ions to P and to Cr. 4 in ratio
．． It is preferable that the organic cation contains one or more of the following, and it is preferable that the organic cation is an amino group.

The present invention also provides the following (a) and (b) and (c)
), (d), and (e).

(a) Chromic anhydride 5-300g/Jl! , (b) amine and/or amino acid in amino group/Cr molar ratio of 1/120 to 2/3, (c) silicic acid compound as silicic acid of 300 g/l or less, (d) fluorine ion and/or fluorine (e) 3087 g/fl or less when the complex ion is a fluorine ion and (e) 300 g/fl or less when the phosphate ion is P.

Here, the ratio of Cr3+/Cr6+ in the chromate treatment liquid is preferably O/10 to 90/10, and the chromate treatment liquid preferably contains a reducing agent.

The present invention further provides a highly corrosion-resistant chromate-treated steel sheet, characterized in that a chromate coating layer is formed on a part or all of the surface of a cold-rolled steel sheet or a galvanized steel sheet using any of the above-mentioned chromate treatment solutions. A manufacturing method is provided.

Note that the method for manufacturing chromate-treated steel sheets herein is not limited to those that are sold as steel sheets themselves, but also broadly includes cases where chromate treatment is applied to finished products and semi-finished products such as automobiles and home appliances.

The present invention will be explained in more detail below.

The steel sheet targeted by the present invention may be a general cold-rolled steel sheet or a galvanized steel sheet such as a hot-dip galvanized steel sheet, an electrogalvanized copper sheet, or a zinc-based alloy plated steel sheet. That is, in the wood invention, improvement of corrosion resistance and paintability is achieved by forming a chromate film on a steel plate.

Although chromate treatment has been widely known as a passivation treatment, the present inventors have come to think that the addition of cations may have a large effect on passivation. Therefore, we decided to add components that can become organic cations, such as amines, to the chromate treatment solution. It has been found that this significantly improves the corrosion resistance and paintability of the steel plate.

The chromate treatment solution of the present invention has 5 to 30% chromate anhydride.
0 g/JQ, one of the following: fluorine or fluorine complex ions as fluorine ions not more than 30 g/JZ, silicic acid compounds as silicic acid not more than 300 g/It, phosphate ions as P not more than 300 g/A, or A reducing agent is added to an aqueous solution of chromic acid containing two or more types of C,! */c,
6 * After adding or not adding so that the ratio is 0/10 to 90/10, amine and/or amino acid is added at a molar ratio of amino group/Cr of 1/120 to 2/3.

The highly corrosion-resistant chromate-treated steel sheet of the present invention uses the above-mentioned chromate treatment solution to form a chromate coating layer on a cold-rolled steel sheet or a zinc-plated steel sheet in an amount of 5 to 300 mg/g in terms of Cr.
m' was formed.

The present invention is characterized by the addition and use of amines and/or amino acids in the chromate treatment.

Examples of amines include primary amines such as isopropylamine, isobutylamine, t-butylamine, and cyclohexylamine, secondary amines such as dicyclohexylamine and diethylamine, tertiary amines such as triethanolamine and triethylamine, and guanidine (HN = It is preferable to use unsaturated special H2 amines such as = c < N H2). Amino acids such as glycine and alanine, which are sometimes used as regulators, can also be used.Amino acids generally have the structure NH2R-COOH, and are bipolar ions.NH3-R-COOe)-tz Q,■
By establishing a rapid equilibrium with NH, -R-COOH or NH2-R-COOe, it is stable over a wide pH range, and can be added to chromic acid in large amounts compared to amines. Although it is not necessarily clear what kind of structure amine forms in chromic acid and contributes to passivation in chromate treatment,
The alkyl groups of tertiary amines exist stably compared to primary and secondary amines, and some of the amino groups are thought to be oxidized to become nitro groups. However, among these, it is thought that a component having the remaining nitrogen atom as a cation is effective for passivation in chromate treatment. In addition, amines alone can only be added in small amounts (amino group/Cr molar ratio ≦115) to the chromate solution, but they can be added by diluting them with pure water in advance or adding amino acids such as glycine and alanine. , it becomes possible to increase the amount added.

The chromate treatment used in the present invention may be a reactive chromate treatment, a coating type chromate treatment, or an electrolytic chromate treatment, but it is necessary to use an amine or amino acid suitable for each treatment condition.

In other words, reactive chromate is originally mostly Cr, which reacts with the zinc-based plating surface along with etching agents such as fluorine and nitric acid, but amines and amino acids are highly effective as reducing agents. It cannot be used in some cases because chromate does not react with the galvanized surface. Therefore, in such cases, use amines or amino acids with low reducing power, or add a small amount of chromate. It is better to

In addition, any chromate treatment requires hot air drying or baking, but care must be taken to determine the decomposition temperature and boiling point of the amine. For example, triethanolamine has a boiling point of 3
The temperature is as high as 60°C, and the general baking of chromate treatment has a problem in that it cannot be completely dried after the treatment. In order to produce a highly corrosion-resistant film that is difficult to peel off from the surface of a steel sheet, it is necessary to use additives such as amines and amino acids that have a decomposition temperature and boiling point that match the temperature for chromate baking.

Next, various reasons for limitations of the present invention will be explained.

In the composition of the treatment liquid used in the present invention, chromic anhydride is a basic substance that forms a chromate film, but if the concentration is less than 5 g/f1, the expected corrosion resistance cannot be obtained.

If it exceeds 300 g/fl, chromic acid stains due to unreacted chromic acid tend to appear on the treated sheet in the case of zinc-plated steel sheets, and a large amount of chromic acid from the treatment solution is carried out, which is not economical.

Fluorine ions or fluorine complex ions have the effect of improving the adhesion between the surface of the zinc-based plated steel sheet and the chromate film, thereby improving corrosion resistance.

Additives that supply fluorine ions or fluorine complex ions include hydrobutic acid, or their anguinium salts, metal salts such as ammonium fluoride, sodium hexafluoroaluminate, sodium silicofluoride,
Fluorine-containing compounds such as potassium titanium buttride can be used alone or in combination. As for the amount of fluorine, it is best to have a concentration of 3.0 g/fL or less as fluorine ions; if it exceeds 30 g/It, the amount of these fluorine compounds incorporated into the chromate film increases, resulting in a decrease in corrosion resistance.

The F- ion is an amino group and a chromate ion (cry, "-
or (:r20.'-) interaction, ie, passivation. Further, in some cases, impurities exceeding the solubility may impair the appearance of the treated surface.

The concentration content of the silicic acid compound is 30% as silicic acid.
A range of 0 g711 or less is most effective. 30
If it exceeds 0 g/l, the amount of silicic acid compound incorporated into the chromate film will increase, the adhesion between the chromate film and the cold-rolled steel sheet or zinc plating will be impaired, and the corrosion resistance after processing will be reduced. Furthermore, as the silicic acid compound that also reduces weldability, silicic acid sol, silicic acid fine powder, etc. can be suitably used.

Next, the reason why the chromic acid anhydride in the treatment liquid is reduced to Cr3+/Cr'' of O/10 to 90/10 using a reducing agent will be explained.

When chromic anhydride is reduced, trivalent chromium in the treatment solution increases. When this treatment solution containing trivalent chromium is applied to a steel plate, and after drying, the steel plate is immersed in hot water or an alkaline solution, the amount of chromium dissolved can be extremely reduced, and the corrosion resistance after degreasing is improved. When the ratio of Cr3"/Cr'+ is out of the range of 0/10 to 90/10, the corrosion resistance after degreasing improves as described above, but the liquid stability decreases and
This is because it gels within ~2 days.

Examples of the reducing agent include H2O2, alcohols, monosaccharides, trisaccharides, polysaccharides, and hydrazine.
Examples of alcohols that can be used include methanol, ethanol, propatool, ethylene glycol, polyethylene glycol, etc., and examples of sugars that can be used include glucose, sucrose, starch, etc., but are not limited thereto.

Further, phosphoric acid is added to suppress precipitation of Cr'+, and it is desirable to add 300 g/λ or less of phosphoric acid ions as P. If it exceeds 300 g/λ, PO4
Similar to the case where the 3- ion is an F- ion, it hinders the interaction between the amino group and chromic acid (cry, '- or Cry, ''), resulting in poor corrosion resistance.

Next, adjust the amount of amine or amino acid added to
The reason why the molar ratio of Cr is limited to 1/120 to 2/3 will be described. Addition of less than 17120 does not result in sufficient improvement in corrosion resistance.

・ Also, since amines generally react violently with chromic acid and tend to form a gel-like substance, it can be reduced to about 1/10 with pure water (
It is desirable to dilute and add to a concentration of 100 g/l or less as crO2, but even if this method is used, it is possible to add at most 1/10 of the Cr ratio with certain amines (e.g. isobutylamine). It is only that.

By using it in combination with glycine, it is possible to increase the amount added, but it is impossible to exceed 2/3 of the amount that can be added with glycine alone, and a gel-like substance will form, and if chromate treatment is performed, , unevenness occurs on the galvanized steel sheet. Furthermore, by adding amines or amino acids, adhesion with alkyd/melamine paints and the like is improved, and paintability is improved.

Chromate treatment is carried out using a chromate treatment solution containing the above-mentioned compounds, and the amount of chromate film deposited is preferably 5 to 300 mg/m 2 in terms of chromium amount. The amount of chromate film deposited is 5 mg
/ m'', the coating on the surface of the steel plate will be incomplete and the corrosion resistance, paintability, and corrosion resistance after painting will deteriorate.
When it exceeds mg/m2, processing adhesion deteriorates.

This chromate film contains organic cations such as chromic acid and amino groups as essential components, and also contains one or more components selected from silica, fluorine ions, and phosphate ions. . The actions of these components are as described above.

It should be noted that a chromate film having a content of these components in the following range is formed using a chromate treatment liquid having the above-mentioned preferred composition.

Organic cation: 2/3 to 1/10 in molar ratio to Cr
00 Silica: Weight ratio to Cr: 5.0 or less Fluorine ions: Weight ratio to Cr: 0.3 or less Phosphate ions: P to diCr weight ratio: 4.0 or less It achieves extremely high corrosion resistance and high paint adhesion.

The above-mentioned organic cation is preferably one having an amino group because it easily forms a cation in the chromate solution and is relatively stable.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. Table 1 shows the compositions and drying conditions of the steel sheets used, the treatment liquid, and the treatment liquid. In addition, E shown in the type of plating in the table
G stands for electrogalvanizing, GI stands for hot dip galvanizing, GA
"CR" refers to unplated cold-rolled steel sheet, and "Zn-Ni" refers to Zn-Ni electroplating. Processes cold rolled steel sheets and various galvanized steel sheets,
By drying with hot air or baking, chromate-treated steel plates (see Table 2) on which chromate films of various compositions were formed were obtained. In 8.9 of the comparative examples, the amount of chromium deposited was outside the range of the present invention.

A test piece was taken from the obtained chromate-treated steel plate, and a corrosion resistance test, a paintability test, a weldability test, and a chromium solubility test were conducted as performance evaluations (see Table 3).

As a corrosion resistance test, a salt spray test was conducted on the flat plate part and the Erichsen extrusion part. As a paintability test, a base tape peel test was conducted after painting.

The test method and evaluation method for each test are as follows.

(1) Salt spray test This was carried out in accordance with JIS-Z-2371.

Flat plate portion: After sealing the end face, the evaluation was based on the time required for the amount of white rust to reach 5% in the case of zinc-plated steel sheets and the amount of red rust to reach 5% in area ratio in the case of cold-rolled steel sheets.

Erichsen extrusion: Using an Erichsen extrusion tester, a 6 mm extrusion was subjected to the test, and in the case of a zinc-based plated steel sheet in the salt spray test, 2
Evaluation was made based on the degree of white rust generated after 40 hours, and in the case of cold rolled steel sheets, the degree of red rust generated after 10 hours.

5: No rust (0%) 4: Slight rust (less than 5% rust) 3: Slight rust (
6-10% rust) 2: Significant rust (11-20%)
Rust) 1: Excessive rust (21% or more) (2
) A test piece was prepared using a melamine alkyd paint (Nippon Paint Co., Ltd. Orga Select 100) as a paintability test paint. The test method and evaluation method for each test are as follows.

Substrate adhesion test: On the painted test piece, 100 squares of 1 mm square were cut with a cutter so as to reach the steel substrate, and cellophane tape was adhered to the test piece and then peeled off.

5...No peeling 4...Number of peeling lines 1 to 10 3...Number of peeling lines 11 to 30 2...Number of peeling lines 31 to 50 1...Number of peeling lines 50 or more ( 3) Weldability Test Using a 10100x300 test piece, the chromate-treated surfaces were aligned and the appropriate current range was determined under the following welding conditions.

Equipment name: Mitsubishi Electric Corporation WS-2X1000
Welding was carried out using an S-type spot welder with a welding current of 6 to 13 KA at intervals of 0.5 KA.

Welding pressure: 200 kg/cm 2 constant current application time: 10 cycles Holding time: 5 cycles Evaluation of weldability Under each welding condition, the occurrence of dust, nugget diameter, and weld strength were measured. The normal welding current range was determined based on the nugget diameter (J (major axis) (minor axis)) engraving current of 4.5 ft or more and the dust generation limit current value.

When a nugget diameter of 4.5 ft or more is formed, a sufficient welding strength of 300 kgf or more can be obtained.

Evaluation Appropriate current range 0 5KA or more △ 3-4. 5KAX
2.5KA or less (4) Chromium solubility test Hot water test: Cut the above chromate-treated steel plate into a 32 x 32 mm square, measure the amount of chromium adhesion on this test piece using a fluorescent X-ray analyzer, and immerse it in boiling water for 5 minutes. It was determined by the amount of chromium deposited before and after immersion after washing with water.

(5) Liquid stability When a cationic substance is added to a chromate liquid, the liquid tends to deteriorate. Amino acids have carboxyl groups in addition to amino groups, so they are stable over a relatively wide pH range, but amines are unstable in chromic acid and are prone to gelation.
Therefore, the stability of the chromate solution becomes a problem. The evaluation criteria are as follows.

O・・・・・・Room temperature=Stable for more than 5 days△・・・・
...Room temperature = gelling in 1 to 4 days...
...Room temperature: Gells within one day [Effect of the invention] When the chromate treatment solution of the present invention is used to chromate treat a cold-rolled steel sheet or a zinc-plated steel sheet, not only paintability but also bare corrosion resistance is improved. A chromate-treated steel sheet is obtained, which can be suitably used for home appliances, building materials, and automobile steel sheets.

Claims (7)

[Claims] (1) A chromate coating layer containing organic cations, silica, fluorine ions, and phosphate ions is applied on a cold-rolled steel sheet or a zinc-plated steel sheet in an amount of 5 to 300 mg/cm in terms of Cr.
A highly corrosion-resistant chromate-treated steel sheet characterized by having m^2. (2) The chromate coating layer includes (a) an organic cation in a molar ratio of 2/3 to 1 to Cr;
/1000, (b) the weight ratio of silica to Cr is 5.0 or less, (c) the weight ratio of fluorine ions to Cr is 0.3 or less, and (d) the weight of phosphate ions to P and to Cr. 4 in ratio
．． The highly corrosion-resistant chromate-treated steel sheet according to claim 1, containing one or more of the above-mentioned chromate-treated steel sheets in an amount of 0 or less. (3) The highly corrosion-resistant chromate-treated steel sheet according to claim 1 or 2, wherein the organic cation is an amino group. (4) Below (a) and (b), (c), (d)
), (e) A chromate treatment solution containing one or more components selected from (e). (a) Chromic anhydride 5-300 g/l, (b) amine and/or amino acid with amino group/Cr
(c) 300 g/l or less of silicic acid compound as silicic acid, (d) 30 g/l or less of fluorine ion and/or fluorine complex ion as fluorine ion, and ( e) Phosphate ion is 300g/l or less as P. (5) Cr^3^+/Cr^ in the chromate treatment solution
The chromate treatment liquid according to claim 4, wherein the ratio of 6^+ is 0/10 to 90/10. (6) The chromate treatment liquid according to claim 4 or 5, wherein the chromate treatment liquid contains a reducing agent. (7) A chromate coating layer is formed on part or all of the surface of a cold-rolled steel sheet or a galvanized steel sheet using the chromate treatment solution according to any one of claims 4, 5 and 6. A method for producing highly corrosion-resistant chromate-treated steel sheets.