JPH07228978A - Production of galvannealed steel sheet composite material having excellent bare corrosion resistance and coatability - Google Patents

Abstract

PURPOSE:To develop the galvannealed steel sheet having excellent bare corrosion resistance without impairing coatability and corrosion resistance after coating by subjecting the galvannealed steel sheet to a phytin acid treatment, coating type chromate treatment and org. resin coating treatment. CONSTITUTION:An aq. soln. contg. the phytin acid of a concn. of 0.1 to 5.0% is applied on the surfaces of the galvannealed steel sheet and is so adjusted that the adhesion of the phytin acid attains 10 to 500mg/m<2>. This steel sheet is dried without washing and a chromate treating liquid consisting of an aq. acidic soln. contg. bichromic acid and tervalent Cr ions is applied thereon to form chromate films of 30 to 100mg/m<2> in terms of Cr. Finally, a water-soluble or water-dispersible org. acid emulsion consisting of an acrylic polymer, etc., as a base or a soln. of an org. solvent-soluble resin with a thinner, etc., as a solvent is applied on the chromate films and is dried.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alloyed hot-dip galvanized alloy which has further excellent bare corrosion resistance without impairing the excellent coating film adhesion and the corrosion resistance after coating which the alloyed hot-dip galvanized steel sheet itself has. The present invention relates to a method for manufacturing a plated steel sheet composite material.

[0002]

2. Description of the Related Art Generally, zinc plating, which utilizes the principle of sacrificial corrosion, is the most effective and economical method for preventing corrosion of steel. Therefore, in the midst of strong demand for high added value of steel sheets, nearly 90% of thin steel sheets, especially surface-treated steel sheets, are composed of galvanized steel sheets, and are used in a wide range of fields such as building materials, automobiles, and home appliances. Has been done. The mechanism of sacrificial anticorrosion by zinc is that a battery is formed under the condition that zinc and a different metal of iron are in contact with each other. This is to prevent the dissolution of the anode due to the formation of a battery and consequently prevent the corrosion of steel. Therefore, since the anticorrosive action ends when the zinc in contact with the steel disappears, it is necessary to suppress the corrosion of the zinc layer in order to maintain the action effect in the long term. As a result, chromate treatment is usually performed on the galvanized layer. Thus, by combining galvanizing and chromate treatment, the corrosion resistance of steel is significantly improved, but from the aspect of its anticorrosion mechanism, when used after coating after chromate treatment, there is a problem with coating adhesion etc. There is. Therefore, there is provided an alloyed hot dip galvanized steel sheet in which iron as a raw material is diffused in a galvanized layer by performing an alloying annealing treatment after hot dip galvanizing in order to improve coating film adhesion.

As described above, the galvannealed steel sheet is a galvanized steel sheet having excellent coatability. However, in terms of bare corrosion resistance (temporary rust resistance) during the period from the steel sheet manufacturer to the user, the chromate treatment is not necessary. Even if it is applied, iron is alloyed and contained in the galvanized layer, so it is hard to say that it is sufficiently satisfactory as compared with a normal galvanized steel sheet. Therefore, in automotive applications, which account for most of the applications of alloyed hot-dip galvanized steel sheets, the phosphate pretreatment of the user is relatively early after the production.
It is often applied in the form of pre-coated metal (PCM), which has been painted and applied by a steel plate manufacturer to home appliances. As outlined above, alloyed hot-dip galvanized steel sheets have excellent coatability, but there is no known method for imparting sufficient bare corrosion resistance to them,
Its use is limited.

[0004]

DISCLOSURE OF THE INVENTION The present invention has a further excellent bare corrosion resistance without impairing the original good coating properties of the material of the galvannealed steel sheet, that is, excellent coating film adhesion and corrosion resistance. It is intended to provide a method for producing a novel surface-treated alloyed hot-dip galvanized steel sheet composite material capable of imparting

[0005]

[Means for Solving the Problems] The inventors of the present invention have proposed an alloyed hot-dip galvanized steel sheet composite material capable of simultaneously satisfying the corrosion resistance in the raw material state without impairing the excellent coatability of the alloyed hot-dip galvanized steel sheet. As a result of intensive studies to provide a manufacturing method, the method of the present invention has been completed. That is, the method of the present invention comprises contacting the surface of an alloyed hot-dip galvanized steel sheet with an aqueous solution containing phytic acid, then drying it without washing with water, and then subjecting the surface to dichromate ions and trivalent chromium ions. An alloyed hot dip galvanized steel sheet composite material excellent in bare corrosion resistance and coatability, characterized by being dried without being washed with water after being brought into contact with the contained chromate treatment liquid, and further being coated with an organic resin on the surface. Is a manufacturing method.

[0006]

The method of the present invention comprises three steps of phytic acid treatment, galvanizing chromate treatment, and organic resin coating treatment on a galvannealed steel sheet. Each step will be described below.

In the treatment with the aqueous solution of phytic acid, phytic acid reacts with the surface of the galvannealed steel sheet to form a metal salt of phytic acid, which stabilizes the coating type chromate film formed in the next step. To improve the corrosion resistance of the steel sheet. The treatment liquid for phytic acid treatment is an aqueous solution containing phytic acid as an essential component, the phytic acid concentration is 0.1 to 5.0%, and the pH of the aqueous solution is preferably 2 to 11. Sources of phytic acid include phytic acid, ammonium salts of phytic acid, and metal salts. However, it is not preferable to use an alkali metal salt as the metal salt of phytic acid, and it is preferable to use a salt of magnesium, calcium, zinc, or the like. Further, a fluoride, a complex fluoride, an organic acid, and / or a mineral acid may be added to the treatment liquid, if necessary.

The phytic acid treatment method may be any of known methods such as spraying, dipping, pouring and roll coating, as long as the surface of the alloyed hot-dip galvanized steel sheet is sufficiently contacted with the treatment liquid and coated. May be However, in some cases, for the purpose of uniformly treating the surface, after contact with the liquid,
By squeezing roll or air knife or the like, to control the wet coating amount of about 1 to 10 ml / m ^2, and the amount of phytic acid deposition is preferably controlled so as to be 10 to 500 mg / m ^2. Further, there is no particular limitation on the treatment liquid temperature and the liquid contact time during the treatment. After the treatment, it is dried without washing with water, but the drying temperature at this time is not particularly limited.

Next, a coating type chromate treatment step is performed. The chromate film formed in this step improves the corrosion resistance of the alloyed hot-dip galvanized steel sheet and the adhesion between the resin and metal, and is the core step of the method of the present invention. The chromate treatment liquid is an acidic aqueous solution containing dichromate ions and trivalent chromium ions as essential components. The dichromate ion is usually supplied in the form of an aqueous solution of chromic anhydride, but it can also be supplied in the form of an ammonium salt, a strontium salt, a barium salt, a zinc salt of chromate or dichromic acid. Further, trivalent chromium ions are produced by adding a reducing agent such as methanol, ethanol, oxalic acid, starch, dextrin, starch and pyrogallol to an aqueous solution containing dichromate ions to partially reduce the dichromate ions, Alternatively, it can be supplied by dissolving chromium carbonate, chromium hydroxide, or chromium oxide in an aqueous chromic acid solution. The composition ratio of dichromate ion to trivalent chromium ion is preferably such that the weight ratio of trivalent chromium to total chromium is 10 to 60%.

It is also possible to add anions such as phosphate ions, fluorine ions and complex fluorine ions to the chromate treatment liquid. Addition of these anions stabilizes the trivalent chromium ions in the treatment liquid state, contributes to the promotion of reduction of dichromate ions during the film formation, and the trivalent chromium ions react with the anions during the film formation. By forming a sparingly soluble salt, the adhesion and corrosion resistance after coating are improved. Phosphate ions added to the chromate treatment solution include acids such as orthophosphoric acid, ammonium salts such as ammonium phosphate, zinc phosphate, manganese phosphate, nickel phosphate, cobalt phosphate, aluminum phosphate, and phosphoric acid. It can be supplied in the form of a metal phosphate such as barium or chromium phosphate. A desirable addition amount of phosphate ions is phosphate ion / total chromium = 2/1 or less in a weight ratio with respect to total chromium. Fluorine ions and complex fluoride ions added to the chromate treatment liquid are in the form of hydrofluoric acid, hydrofluoric acid, borohydrofluoric acid, zircon hydrofluoric acid, titanium hydrofluoric acid or their metal salts. It is preferable that the weight ratio of total fluorine to total chromium is 0.1 or less.

There is no particular limitation on the method for treating the surface of the galvanized steel sheet with the alloying solution using the above chromate treatment solution, and if uniform coating is possible, spraying, dipping, pouring, roll coating, etc. , Various methods can be used. After the chromate treatment, the treated material is dried without washing. This drying is preferably performed by hot air or induction heating so that the maximum temperature of the alloyed hot-dip galvanized steel sheet reaches 90 ° C or higher. The amount of chromate film formed by this method is preferably 30 to 100 mg / m ² in terms of chromium. Therefore, since the wet coating amount of the chromate treatment liquid changes depending on the coating method and the coating conditions, it is preferable to appropriately control the concentration of the treatment liquid.

After the above steps, an organic resin coating film is formed on the chromate treated surface. The organic resin coating film keeps the corrosion resistance of the chromate film for a long period of time by blocking the underlying chromate film from the corrosive environment, and also removes chromium in the bare state (contaminates the environment as hexavalent chromium). It has a preventive action. In addition, unpainted galvannealed steel sheets tend to have fingerprints and the like that tend to deteriorate the appearance when they are handled (that is, they have low fingerprint resistance), but by applying an organic resin coating, fingerprint resistance can be improved. The sex can be improved. The organic resin used for the organic resin coating is not particularly limited, but metal (in this case, zinc-iron alloy)
It is preferable to use a resin based on an acrylic polymer, a urethane polymer, and / or an epoxy polymer in consideration of the adhesiveness with and chemical stability. Also,
As a form of the organic resin coating agent, a water-soluble or water-dispersible resin emulsion and an organic solvent-soluble resin can be used.

A resin of a type that uses water as a solvent, such as a water-soluble or water-dispersible resin, has been in increasing demand due to recent environmental problems (solvent regulation). When applied, a trace amount of dichromate ions will be dissolved and mixed in the resin coating solution, and therefore the stability of the resin coating solution at that time must be taken into consideration. Therefore, for example, when an emulsion of a water-dispersible resin is used, it is preferable that the surfactant used for emulsion-polymerizing the resin monomer at the time of its production is nonionic. At this time, if a significant amount of the cationic surfactant is contained in the surfactant, the emulsion may become unstable during coating and resin agglomeration may occur.
On the other hand, in the case of an organic solvent-soluble resin, such a problem does not occur, and the resin raw material may be diluted with a thinner or the like so that the conditions are convenient for coating equipment.

These organic resin coating methods include
There is no particular limitation, and brush coating, spray coating, flow coating
Known methods such as cloth and roll coating can be used.
Drying after applying the organic resin liquid is done by hot air or induction heating.
The maximum plate temperature of galvannealed steel sheet is 100
The temperature may be set to ~ 250 ° C., and especially for the heating time.
There is no limit. The amount of coating is the dry coating weight.
0.5-3.0 g / m ²Is preferred.

[0015]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

[0016] Examples 1-2 were subjected to the following operations in each of Comparative Examples 1-5 Examples 1-2 and Comparative Examples 1-5. 1. Preparation of surface treatment liquid 1.1 Preparation of phytic acid treatment liquid Add ammonia water to a 3% aqueous solution of phytic acid to obtain pH =
A phytic acid treatment liquid was prepared by adjusting the pH to 6.5.

1.2 Preparation of Chromate Treatment Liquid 500 ml of an aqueous solution containing 50 g of chromic anhydride, 8 g of phosphoric acid and 1 g of zircon hydrofluoric acid was added with methanol to reduce a part of the dichromate ion. Deionized water was added to bring the total volume to 1000 ml. 35 g / l
As a result, a chromate-treated solution containing the dichromate ion and the trivalent chromium ion of 9 g / l was obtained.

1.3 Preparation of Organic Resin Coating Agent 1 (Acrylic Resin Aqueous Emulsion) Aqueous emulsifier solution (A) was added as a 70% aqueous solution of polyoxyethylene octyl phenyl ether (nonionic surfactant): 4 parts by weight, and Oxyethylene-polyoxypropylene block polymer (nonionic surfactant): 4
Parts by weight and 150 parts by weight of deionized water were dissolved by heating to maintain the mixture at 40 ° C. Next, for the preparation of the monomer emulsion (B), methacrylic acid: 4 parts by weight, n
-Butyl acrylate: 82 parts by weight, N-methylol acrylamide: 2 parts by weight, methacrylic acid: 4 parts by weight, 70% aqueous solution of polyoxyethylene octyl phenyl ether: 16 parts by weight, polyoxyethylene-polyoxypropylene block polymer: 2 Parts by weight, and deionized water: 150 parts by weight are mixed with the emulsifier aqueous solution (A) in a container separate from the above, and 5% animonium persulfate for preparing the polymerization initiator (C) in a separate container. Aqueous solution: 10 parts by weight and a 5% aqueous solution of sodium acid sulfite were mixed. 1 part of the monomer emulsion (B) in the emulsifier aqueous solution (A)
0% and about 25% of the polymerization initiating liquid (C) are added, respectively, and the mixed liquid is heated to 40 to 50 ° C. to perform polymerization for 20 minutes, and the monomer emulsion (B) is further added to the polymerization system.
Remaining 90% and the remaining 75% of the polymerization initiator (C) were added dropwise over 3 hours. After completion of dropping, the polymerization system was kept at the above temperature for 1 hour to complete the polymerization. The acrylic resin aqueous emulsion obtained by the above operation is diluted with deionized water,
A resin coating liquid having a resin solid content of 30% by weight was prepared.

1.4 Preparation of resin coating agent 2 (solvent-based epoxy resin) A block urethane-modified epoxy resin raw material having a resin solid content of 40% by weight was diluted with methyl ethyl ketone to obtain a resin solid content of 30% by weight. A resin coating solution was prepared.

2. Preparation of test piece Using the above surface treatment solution, an alloyed hot-dip galvanized steel sheet (300 mm x 200 mm x plate thickness: 0.8 mm) was treated by the steps shown below, and the obtained treated test pieces were subjected to various performance tests. I went to

3. Treatment Process The actual treatment process used in each of Examples 1-2 and Comparative Examples 1-5 is shown below. In addition, Examples 1 and 2 and Comparative Example 1
Table 1 shows the combinations of the surface treatment steps in each of Nos. 5 to 5, but as can be seen, in Comparative Examples 1 to 5, any of the phytic acid treatment, the chromate treatment, and the resin coating treatment was omitted. (1) Alkali degreasing: Palclean-342 (trademark, Note 1) was bathed at a concentration of 20 g / l, and spray degreasing was performed at 60 ° C for 20 seconds. ↓ (2) Washing with water: tap water, spraying for 20 seconds ↓ (3) Draining: squeezing rolls ↓ (4) Phytic acid treatment: The phytic acid treatment liquid described in 1.1 above was applied with a roll coater. At this time, the coating conditions of the roll coater were set so that the wet coating amount was 2 ml / m ² . ↓ (5) Drying: Set the furnace temperature of the hot-air heating furnace to 150 ° C, 1
Heated for 0 seconds to dry. The maximum ultimate plate temperature at this time was 90 ° C. ↓ (6) Chromate treatment: The chromate treatment liquid described in 1.2 above was applied by a roll coater. At this time, the coating conditions of the roll coater were set so that the wet coating amount was 2 ml / m ² . ↓ (7) Drying: Set the furnace temperature of the hot-air heating furnace to 150 ° C, 1
Heated for 0 seconds to dry. The maximum ultimate plate temperature at this time was 90 ° C. ↓ (8) Resin coating: The resin coating liquid 1 or 2 shown in the above 1.3 or 1.4 was applied using a bar coater for coating. The amount of film is 2 g / dry film
The type of coating bar was chosen to be m ² . ↓ (9) Drying: Set the furnace temperature of the hot air heating furnace to 350 ° C, 1
Heated for 0 seconds to dry. The maximum ultimate plate temperature at this time was 170 ° C. ↓ (10) Coating: Amilak 1000 (trademark, Note 2) was coated with a coating bar coater to a film thickness of 5 μm. ↓ (11) Baking: After setting for 10 minutes or more, baking was performed at 120 ° C. for 30 minutes. Note 1: Weak alkaline degreasing agent manufactured by Nihon Parkerizing Co., Ltd. Note 2: Melamine alkyd paint, manufactured by Kansai Paint Co., Ltd.

4. Performance test Bare plate of alloyed hot-dip galvanized steel sheet composite material produced by the above method (steps up to 9 in the test plate production process)
The corrosion resistance, fingerprint resistance, and alkali resistance are tested by the following methods, and after coating (the test plate preparation step 1
As the performance of the steps (up to 1), coating film adhesion and corrosion resistance are
Each was tested and evaluated by the methods shown below.

(1) Bare corrosion resistance A salt spray test was conducted in accordance with JIS-Z2371, and the longest salt spray time at which the rusting area was less than 5% by visual judgment was measured and evaluated.

(2) Fingerprint resistance A test plate was pressed with a thumb and the state of traces of fingerprints was visually judged based on the following judgment criteria. ◎: No trace ○: Slight traces are observed △: Traces are recognized ×: Very traces are noticeable

(3) Alkali resistance The test plate was washed with an alkaline cleaner (Palclean-3) having a concentration of 2%.
64S: trademark, manufactured by Nippon Parkerizing Co., Ltd.), spray cleaning is performed at 60 ° C. for 2 minutes, and the amount of chromium deposited on the test plate before and after alkaline cleaning is measured by fluorescent X-ray analysis. Was calculated, and the alkali resistance of the test test plate was displayed from the chromium fixation rate according to the following criteria. Fixing rate = [Amount of chromium deposited after alkali cleaning (mg /
m ² )] / [Amount of chromium deposited before alkali cleaning (mg /
m ² )] × 100 (%) ◎: Fixing rate 90% or more ○: Fixing rate less than 90% 80% or more △: Fixing rate less than 80% 70% or more ×: Fixing rate less than 70%

(4) Adhesion after coating Adhesion after coating was evaluated for its primary adhesion and secondary adhesion by the following three types of methods: a goose stitch test, an Erichsen test, and a DuPont impact test. Regarding the secondary adhesion, it was left for 240 hours in a humid atmosphere of 50 ° C. and 98% RH and then subjected to a test. Since each test result is evaluated on a scale of 10 points, their average points are classified as shown below and comprehensively evaluated. ◎: Average 9 points or more ○: Average 7 points or more and less than 9 points △: Average 5 points or more and less than 7 points ×: Less than 5 points When the alloyed hot-dip galvanized steel sheet according to the present invention is used for coating at the user's destination , A test in which spray cleaning was performed at 60 ° C. for 2 minutes using a 2% -concentration alkaline cleaner (Palclean-364S: trademark, manufactured by Nippon Parkerizing Co., Ltd.) on the assumption that degreasing is performed prior to that. One piece was evaluated in the same manner.

・ Gourd-eye test: 100 pieces of 1 mm square 1 piece of goggles are cut on the coated surface with an NT cutter, and the state of the coating film remaining after peeling the cellophane tape is 11 according to the following criteria.
Graded. 10: No peeling of 100 pieces 9 to 6: No peeling of 100 pieces, but the edges of each gobang are slightly peeled 5-3: Number of peeling gobangs 1 to 30 2-1: Number of peeling gobangs 31 to 990: Peeling off the entire surface Erichsen test: 3 mm on the coated surface with an Erichsen tester
The appearance after extruding and peeling the cellophane tape was evaluated in 10 levels according to the following criteria. 10: No peeling 9-8: Peeling slightly in a dot 7-4: Peeling in a circle 3-2: Peeling badly in a circle 1: Almost all peeling DuPont impact test: DuPont impact tester on coated surface , 1/2 inch, 500 g, and 30 cm were used to perform a surface-lining backing impact test, and the appearance after peeling of the cellophane tape was evaluated on a scale of 10 according to the following criteria (in the case of the lining, parenthesized). 10: No peeling 9-7: Slightly peeled in spots 6-4: Slightly peeled 3-2: Peeled in a circle (peeled in a plane) 1: Large peeled in a circle (large peeled in a plane) )

(5) Corrosion resistance after coating After cross cutting with an NT cutter on the coated surface, J
According to IS-Z-2371, a salt spray test was performed, and the longest salt spray time at which the maximum rust swell width on one side from the cut portion was less than 2 mm was measured and evaluated. Further, a test piece subjected to spray cleaning at 60 ° C. for 2 minutes using a 2% concentration alkaline cleaner (Palclean-364S: trademark, manufactured by Nippon Parkerizing Co., Ltd.) was similarly measured and evaluated.

5. Test results Table 1 shows the performance test results.

[Table 1]

In the embodiment of the present invention, phytic acid treatment,
It can be seen that when the chromate treatment and the resin coating treatment are combined, the bare corrosion resistance and the coating performance (corrosion resistance, adhesion) are simultaneously improved. Moreover, it can be seen that incidental performances such as fingerprint resistance and alkali resistance before coating are excellent. On the other hand, when the resin sealing step is omitted as in Comparative Example 1, the corrosion resistance deteriorates, and the fingerprint resistance, alkali resistance, etc. also deteriorate. If the chromate treatment step is omitted as in Comparative Example 2, the corrosion resistance is further deteriorated. Further, when the phytic acid treatment step is omitted as in Comparative Example 3, the corrosion resistance equivalent to that of the Examples is not obtained, although not as much as Comparative Examples 1 and 2. Further, as in Comparative Examples 4 and 5, when the chromate treatment alone and the resin sealing alone are used, the bare corrosion resistance is particularly deteriorated.

[0031]

Industrial Applicability By using the production method of the present invention, it becomes possible to produce a composite material in which excellent coating film adhesion, post-coating corrosion resistance and bare corrosion resistance are simultaneously imparted to a galvannealed steel sheet. .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B05D 7/24 F 7717-4D B32B 15/08 G C23C 22/53 22/78 28/00 C ( 72) Inventor Kazuyuki Oyama 1-15-1 Nihonbashi, Chuo-ku, Tokyo Within Japan Parkerizing Co., Ltd. (72) Inventor Nagaharu Ueno 20-1 Shintomi, Futtsu City, Chiba Pref. Inventor Hiroshi Kanai 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd.

Claims (3)

[Claims] 1. A surface of an alloyed hot-dip galvanized steel sheet is brought into contact with an aqueous solution containing phytic acid, then heat-dried without washing with water, and then the surface contains dichromate ions and trivalent chromium ions. After being brought into contact with the chromate treatment liquid, it is heated and dried without being washed with water, and further, an organic resin coating is applied to the surface, bare corrosion resistance,
A method for producing an alloyed hot-dip galvanized steel sheet composite material having excellent paintability. 2. The method for producing an alloyed hot-dip galvanized steel sheet composite material according to claim 1, wherein the organic resin coating is applied with a water-soluble or water-dispersible resin. 3. The method for producing an alloyed hot-dip galvanized steel sheet composite material according to claim 1, wherein the organic resin coating is applied by an organic solvent-soluble resin.