JPH11310749A - Water-based surface treating agent, surface-treated steel sheet, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a chromium (VI)-free surface-treating agent which can give a treated sheet equivalent in performance to a chromate-treated one and to obtain a surface-treated steel sheet on which a coating film of the surface treating agent has been formed. SOLUTION: There are provided a water-based surface-treating agent containing 50-85.9 wt.% (in terms of the solid matter) acrylic emulsion having a glass transition temperature of 20-70 deg.C, 4-10 wt.% (in terms of the solid matter) imino-containing methylated melamine resin, 10-40 wt.% (in terms of the solid matter) at least either of colloidal silica containing adsorbed ammonium ions or colloidal silica coated with aluminum oxide, and 0.1-10 wt.% (in terms of the solid matter) ammonium vanadate and having a pH of 8-10 and a surface- treated steel sheet prepared by forming a coating film of the water-based surface-treating agent on a steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to home appliances, construction materials,
The present invention relates to a water-based surface treatment agent and a surface-treated steel sheet which are used for automobiles and do not contain hexavalent chromium and have excellent corrosion resistance.

[0002]

2. Description of the Related Art In the field of surface treatment of steel sheets, a chromate treatment containing hexavalent chromium is frequently used to improve the corrosion resistance of the steel sheets. However, hexavalent chromium is known to be a harmful element, and there is an increasing demand for surface treatment agents and surface-treated steel sheets that do not contain this hexavalent chromium. In addition, electrolytic chromate mainly composed of trivalent chromium may contain a small amount of hexavalent chromium, and may be difficult to use in the future. Chromate treatment is used as a primary rust preventive treatment for steel sheets and plated steel sheets, and as a base treatment for painting and coating. However, development of a chromium-free treatment technology to replace this chromate treatment is desired. As a surface treatment technique not containing chromium, there is a phosphate treatment such as a zinc phosphate treatment. However, phosphate treatment is slightly inferior to chromate as a primary rust preventive treatment, and chromium sealing is necessary to ensure corrosion resistance even as a coating base treatment, and is not a sufficient substitute for chromate. It is.

JP-A-5-195244 discloses a “method of treating a metal surface with a chromium-free coating type acidic composition”.
a) each of the anionic components is 1) at least 4 fluorine atoms and 2) at least one selected from the group consisting of titanium, zirconium, hafnium, silicon and boron;
B) cobalt, magnesium, manganese, zinc, nickel, tin, zirconium, and b) cobalt, magnesium, manganese, zinc, nickel, tin, zirconium,
A cation component of an element selected from the group consisting of iron, aluminum and copper, wherein the total number of cations is at least 1/3 of the total number of anions of component a); c)
Aqueous acid comprising a free acid in an amount sufficient to maintain the pH of the composition in the range of about 0.5 to 5.0, and optionally, d) a composition that forms an organic resin film by direct drying. There has been proposed a metal surface treatment method for forming a chromium-free conversion coating on a metal surface with a liquid composition.

Japanese Patent Application Laid-Open No. 145486/1995 entitled "Composition for metal surface treatment and treatment method" includes: a) a fluorine atom and at least one atom of titanium, zirconium, hafnium, silicon and boron. , An ionizable hydrogen atom,
And / or a component comprising an anion containing at least one oxygen atom, provided that the ratio of the number of cations of component b) to the number of anions of component a) is 1/5 or more, and c) a phosphorus-containing organic oxyanion and / or phosphone. A component comprising an acid anion; d) a component comprising one or more of a water-soluble and water-dispersible polymer and a polymer-forming resin; and e) an amount sufficient to maintain the pH of the composition at 0.5 to 5.0. There has been proposed a treatment method for forming a coating layer containing no chromium on a metal surface by using an aqueous composition containing the above acid component.

[0005]

However, any of the chromium-free metal surface treatment methods proposed in the above publications have the same performance as conventional chromate-treated ones, that is, the same corrosion resistance as the chromate-treated one. The film adhesion has not yet been satisfied. The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a surface treatment agent and a surface-treated steel sheet for post-treatment having the same performance as conventional chromate treatment, and for pre-coating. It is.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the gist of the invention is as follows.
(1) 50 to 85.9% by weight of an acrylic emulsion having a glass transition point of 20 to 70 ° C in terms of solids, 4 to 10% by weight of a methylated melamine resin containing an imino group in terms of solids, and ammonium ion At least one of the adsorbed colloidal silica or the colloidal silica coated with aluminum oxide is 10 to 40% by weight in terms of solid content, and ammonium vanadate is 0.1 to 0.1% in terms of solid content.
An aqueous surface treatment agent, wherein the aqueous surface treatment agent contains 10 to 10% by weight and has a pH of 8 to 10.

(2) The aqueous surface treating agent described in the above (1) is used as a solid film, and the amount of the solid film attached is 0.3 to 10 g /
surface-treated steel sheet, characterized in that m ^2, and a baking drying (3) wherein (1) in applying the aqueous surface-treating agent according to the steel plate, a peak metal temperature of 50 to 250 ° C. Conditions A method for producing a surface-treated steel sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The surface treating agent and the surface treated steel sheet of the present invention will be described below. The acrylic emulsion and imino group-containing methylated melamine resin in the present invention will be described. The basic skeleton of the acrylic emulsion is basically a linear type, but may have a crosslinked structure.
Number average molecular weight (hereinafter referred to as Mn) is 100000-2
00000, and Mn is 100,000.
Below this, the film strength is insufficient, and above 200,000, the reflow properties are reduced and the uniform applicability is poor. With internal cross-linking type,
Glass transition temperature (Tg) of 20 to 70 ° C, preferably 5
0 to 70 ° C. If the Tg is less than 20 ° C., the film strength is insufficient, and if it is 70 ° C. or more, the film elongation is insufficient, and the adhesion and corrosion resistance of the processed portion are reduced.

The particle size of the acrylic emulsion is 300 nm
It is desirable that: If it exceeds 300 nm, the film-forming properties will deteriorate and the corrosion resistance will decrease. The acrylic emulsion is blended at 50 to 85.9% by weight in terms of solid content. 5
If the amount is less than 0%, the film-forming property is deteriorated, and the adhesion and the corrosion resistance are reduced. If the amount exceeds 85.9%, the amount of ammonium vanadate or silica having a rust-preventing effect decreases, and the corrosion resistance decreases. Further, a methylated melamine resin containing an imino group (hereinafter, referred to as a melamine resin)
Is used as a crosslinking agent for the acrylic emulsion, thereby increasing the film strength. The melamine resin is blended in an amount of 4 to 10% by weight in terms of solid content. If it is less than 4%, there is no effect of improving the strength, and if it exceeds 10%, on the contrary, it becomes too hard, and the coating of the processed portion is easily cracked and the corrosion resistance of the processed portion is reduced.

As the colloidal silica, at least one of an ammonium ion adsorption type and an aluminum oxide coating type is used. Colloidal silica having ammonium ions adsorbed thereon has a particularly high affinity for zinc-based plated steel sheets, and has a remarkable effect of improving corrosion resistance. For example,
"Snow-Tex N", "Snow-Tex NS", "Snow-Tex NXS" (all manufactured by Nissan Chemical Industries, Ltd.),
"Adelite AT-20N" (manufactured by Asahi Denka Kogyo KK) and the like. Colloidal silica coated with aluminum oxide has a similar effect. For example, "Adelite AT-
20A "(manufactured by Asahi Denka Kogyo KK) and the like. The amount of colloidal silica added is 10 to 40% by weight in terms of solid content.
And preferably 25 to 35% by weight. If it is less than 10%, the corrosion resistance is poor, and if it exceeds 40%, the corrosion resistance is reduced. In addition, it becomes difficult to paint.

[0011] Ammonium vanadate has a high rust prevention effect. 0.1 to 10% in terms of solid content in the treatment bath. If it is less than 0.1%, the corrosion resistance is insufficient, and if it exceeds 10%, the liquid stability is poor. The feature of the present surface treatment agent is that ammonium vandate and colloidal silica are used in combination. It is considered that ammonium vandate is adsorbed on the surface of colloidal silica and synergistically improves the rust prevention effect. In particular, when the colloidal silica is an ammonium-in adsorption type or an aluminum oxide coating type, the colloidal silica is easily adsorbed and the corrosion resistance is improved.

The pH of the treatment bath is preferably from 8 to 10. If the pH is less than 8, the bath life becomes short. pH 10
If it exceeds, the base material is dissolved by the alkali content,
The base metal is eluted in the treatment bath, which may cause a decrease in adhesion and corrosion resistance. In addition, bath stability may decrease. Drugs can be added to adjust the pH of the bath. To the surface treatment agent of the present invention, a known solvent, a film-forming aid, or the like may be added to improve the film-forming property and form a uniform and smooth coating film. For example, alcohol-based, ketone-based, ester-based, and ether-based ones can be used. The addition of the solvent is also useful for preventing water from volatilizing at 100 ° C. at once at the time of baking, thereby preventing the occurrence of fire.

The surface treating agent of the present invention may contain other components. For example, pigments, surfactants, additives, silane coupling agents and the like. Examples of the pigment include inorganic pigments such as titanium oxide, zinc oxide, zirconium oxide, calcium carbonate, barium sulfate, aluminum oxide, kaolin gray, carbon black, and iron oxide, and organic pigments such as cyanine blue. As the silane coupling agent, for example, γ-aminopropyltrimethoxysilane,
γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, N- (2- (vinylbenzylamino) ethyl) -3-aminopropyltrimethoxysilane, etc. Can be

The above-mentioned surface treatment agent is applied on a steel plate by a known method, and dried and baked to form a surface treatment film. The method of application is not particularly limited, and known methods can be used. Examples thereof include methods such as roll coating, spraying, air knife, spin coating, curtain coating, and dip coating. If necessary, the surface treatment agent of the present invention can be applied after performing a pretreatment on the surface of the steel sheet by a known method. For example, washing with water, washing with hot water, alkali degreasing, pickling, grinding, brushing, solvent degreasing, and the like.

Examples of the steel sheet to be treated include a cold-rolled steel sheet, a hot-rolled steel sheet, a galvanized steel sheet, a zinc alloy-plated steel sheet in which the alloy element is at least one of Ni, Cr and Fe, and the above-mentioned galvanized or zinc alloy. S based on plated steel
Zinc-based dispersion-coated steel sheets, hot-dip galvanized steel sheets, galvannealed steel sheets, zinc-aluminum alloy-coated steel sheets, zinc-aluminum alloy-coated steel sheets, stainless steel sheets, and the like, in which metal oxides such as iO ₂ , TiO ₂ , ZrO ₂ , and BaCrO ₄ are dispersed and deposited. .

The amount of the surface treatment agent deposited after drying is not particularly limited, but is preferably 0.3 to 10 g / m ² , more preferably 0.5 to 5 g / m ² . If it is less than 0.3 g / m ² , the corrosion resistance cannot be ensured, and if it exceeds 10 g / m ² , the drying property decreases. In addition, the film adhesion of the Erichsen processed part,
The coating film adhesion of the Erichsen-treated portion after the application of the overcoat film is reduced. Further, the corrosion resistance of the Erichsen processed part may be reduced.

The conditions for drying and baking the surface treating agent are not particularly limited, but it is desirable that the ultimate plate temperature is 50 to 250 ° C, particularly preferably 80 to 220 ° C. If it is lower than 50 ° C., the drying property is insufficient. On the other hand, when the temperature exceeds 250 ° C., the curing proceeds too much, and a slight tendency to decrease in adhesion is observed.
The method of drying is not limited, but known methods such as hot air heating, induction heating, near infrared heating, far infrared heating, and indirect heating can be applied. A method may be used in which the steel sheet is preheated, applied while hot, and dried with residual heat.

The same surface can be treated a number of times with the surface treating agent according to the invention. That is, it is also possible to form a multi-layered film by forming the first layer on a steel sheet by the above-described method and then forming the second layer by the same method. In this case, the adhesion amount after drying may exceed 10 g / m ² . The formation of each layer need not necessarily be performed under the same conditions.

[0019]

The present invention will be described in more detail with reference to examples. Plate thickness of 20 g / m ² per one side of plating.
An 8 mm electrogalvanized steel sheet is treated with an alkaline degreasing agent “Surf Cleaner 155” (manufactured by Nippon Paint Co., Ltd.) at 60 ° C. 10
It was degreased for 2 seconds, washed with water and dried. Next, a surface treatment agent having a composition shown in Tables 1 and 2 was applied by a roll coater,
It was dried in a hot air drying oven. Table 1 shows the coating weight and drying conditions.
And in Table 2. In addition, amino alcohol 2M-ABS (DMEA) (manufactured by Kokusan Chemical Co., Ltd.) was used as needed to adjust the pH of the treating agent. The stability of the treatment liquid was good, and after leaving it at room temperature for three months, the quality was almost the same as the initial one. Further, a hot-dip galvanized steel sheet having a coating thickness of 0.8 mm with a coating weight of 60 g / m ² per side,
Thickness 0.8m amount plating adhesion of one surface per 40 g / m ²
The same applies to a surface treated steel sheet made from an alloyed hot-dip galvanized steel sheet having a thickness of 0.8 mm and a zinc-nickel alloy-coated steel sheet (nickel content: 11% by weight) having a coating weight of 20 g / m ² per side having a thickness of 0.8 mm. The method was evaluated. The plating types are shown in Tables 1 and 2. EG is an electrogalvanized steel sheet, GI is a hot-dip galvanized steel sheet, GA is an alloyed hot-dip galvanized steel sheet, and ZN is a zinc-nickel alloy-plated steel sheet. The production example of the acrylic emulsion is as follows.

[0020]

[Table 1]

[0021]

[Table 2]

In a 3 liter flask equipped with a stirrer, a condenser, a nitrogen inlet tube, two dropping funnels and a thermometer, 2 g of a radical polymerization type anionic reactive emulsifier "AQUALON HS-10" (Daiichi Kogyo Seiyaku Co., Ltd.) , A radical polymerization type anionic reactive emulsifier “AQUALON RN-5”
0 "(Daiichi Kogyo Seiyaku Co., Ltd., active ingredient 65%) 6.2 g,
And 300 g of ion-exchanged water. Further, styrene / methyl methacrylate / acrylic acid 2 was added to an emulsifier aqueous solution obtained by dissolving 8 g of “AQUALON HS-10” and 24.8 g of “AQUALON RN-50” in 600 g of ion-exchanged water.
-Ethylhexyl / acrylic acid / 4-hydroxybutyl acrylate / ethylene glycol dimethacrylate = 3
A monomer mixture of 00/290/295/10/100 (weight ratio) was added with stirring to emulsify, and the obtained pre-emulsion was charged into one dropping funnel. The other dropping funnel was charged with an aqueous initiator solution obtained by dissolving 3 g of ammonium persulfate in 300 g of ion-exchanged water.

Under a nitrogen atmosphere, 1/1 of the total amount of the pre-emulsion is
After charging 0 into the flask and heating to 80 ° C., 1/4 of the total amount of the aqueous initiator solution was charged to start the reaction. Ten minutes after the addition of the initiator, the remaining pre-emulsion and the remaining initiator aqueous solution were uniformly dropped over 120 minutes and 140 minutes, respectively. Thereafter, the mixture was stirred at 80 ° C. for 120 minutes to complete the reaction. After cooling, the reaction was neutralized with aqueous ammonia to obtain an acrylic emulsion having a solid content of 45% by weight. The surface treating agent was mixed and dissolved by adding pure water in an amount of 20% solid content by weight, colloidal silica, and ammonium vanadate. Add the resin solution to this solution,
It was obtained by stirring while adjusting the pH as needed. As the colloidal silica, "Adelite AT-20N" (manufactured by Asahi Denka Kogyo KK) as an ammonium ion adsorption type, and "Adelite AT-20" as an aluminum oxide coating type.
A "(made by Asahi Denka Kogyo KK). In Tables 1 and 2,
In the column of silica, "N" indicates the former and "A" indicates the latter. Cymel 327 (manufactured by Mitsui Cytec) was used as the melamine resin. About the created surface-treated steel sheet,
The following evaluation was performed.

1. Finished Appearance The appearance of the treated film was visually judged and scored. The score was 5: uniform, 4: extremely slight unevenness, 3: partially uneven, 2: entirely uneven, and 1: extremely uneven throughout.

2. Adhesion of the surface-treated film The adhesion was determined by the cross-cut tape method (clearance interval: 1 mm) described in JIS K 5400, 8.5.2. Also, J
The adhesiveness of the coating at a portion extruded by 7 mm with an Erichsen tester specified in 8.2 of IS K 5400 was examined by a tape peeling method, and a score was given. The rating was 10: no peeling, 8: a peeling area of 5% or less, 6: a peeling area of more than 5% to 10% or less, a peeling area of more than 10% to 30% or less, 2: 3
The peeled area was more than 0%. When it was difficult to visually determine the adhesion, the coating was dyed with a 3% acetone solution of methyl violet, and the coating was present in the dyed portion, and the coating was not present in the unstained portion, and the adhesion was determined. The same applies to the evaluation of the appearance of the treated film.

3. Olga Select 100 which is a melamine alkyd paint
(Nippon Paint Co., Ltd.) was applied by spraying to a dry film thickness of 25 μm, dried and baked in a hot-air oven at 150 ° C. for 20 minutes, and the adhesion was confirmed in the same manner as in 2. In addition, after the grids are formed on the coating film, the part with the grids is JIS K
7mm with Erichsen tester specified in 8.2 of 5400
After extrusion, the cross-cut part was peeled off with a tape in the same manner as in 2, and the adhesion of the coating film was examined. Further, after the surface-treated steel sheet was immersed in boiling water for 30 minutes and allowed to stand for 24 hours, the adhesion of the coating film after the application of the amylac coating film by the above-described method was examined.

4. Fingerprint resistance Fingerprints were attached to the film of the surface-treated steel sheet, and the visibility of the fingerprints was visually judged and scored. The rating was 5: no fingerprint mark was visible, 4: very slight fingerprint mark was visible, 3: fingerprint mark was visible, 2: fingerprint mark was noticeable, 1: fingerprint mark was very noticeable.

5. Condensation resistance Water droplets of distilled water were dropped on the film surface of the surface-treated steel sheet, and left for one day to dry the water. After that, traces were visually judged and scored. The score is 5: no trace, 4: very slight trace, 3: trace remains, 2: trace trace is outstanding,
1: It was determined that traces were very noticeable.

6. Corrosion resistance (SST) Flat plate (seal end and back of steel plate as cut)
Salt water spray test (specified in JIS Z 2371) for a 7 mm Erichsen machined part (the end face and the back face of a steel sheet extruded by 7 mm with an Erichsen test machine are sealed)
And the area ratio (%) of the generated white rust was visually determined.

[7] Solvent resistance Press oil was impregnated into the case and applied on the film of the surface-treated steel sheet. The oil was wiped off with gauze impregnated with ethanol or kerosene, and the marks on the film were visually judged and scored. In order to clean oil stains and the like, an operation of wiping with a solvent such as kerosene or ethanol is sometimes performed. At this time, the test is performed to evaluate whether or not the film is damaged by these solvents. The rating was 5: no trace, 4: extremely slight trace, 3: trace trace, 2: trace trace was noticeable, 1: trace trace was very noticeable.

The evaluation results are shown in Tables 1 and 2. In the comparative inorganic chromate treatment, silica (Snowtex O, manufactured by Nissan Chemical Industries, Ltd.) was added to chromic acid having a reduction ratio of 40% so that chromic acid / silica = 1/3 (weight ratio of solid content). Using an agent, the amount of adhesion was adjusted to 50 mg / m ² as Cr using an air knife, and dried at a drying plate temperature of 60 ° C. (Comparative Example No. 48). Further, a treatment agent obtained by adding 5% of strontium chromate and 28% of Snowtex N as a rust preventive agent to 67% by weight of olefin resin in terms of solid content and having an adhesion amount after drying of 1.0 g / m ² was obtained. A surface-treated steel sheet coated with a roll coater and dried at an ultimate sheet temperature of 150 ° C. was also used for comparison (Comparative Example No. 4).
7).

In the examples, compared to the inorganic chromate treatment and the treatment in which strontium chromate was added in place of ammonium vanadate, which was tested for comparison, Example No. 1 having better dew condensation resistance and a smaller film adhesion amount was used. 2,
No. 7 with a slightly lower drying plate temperature of 50 ° C., No. 10 and 2 with a small amount of ammonium vanadate or silica
It can be seen that the corrosion resistance is equal to or higher than 6 and 27. Nos. 1, 2, 10, 26 and 27 also have top coat adhesion,
The condensation resistance is superior to the treatment containing hexavalent chromium.
In addition, the corrosion resistance level is inferior to that of the comparative example containing the chromium-based rust inhibitor at 240 hours of salt water spray, but has the same performance up to 72 hours and is practical.

On the other hand, as an example out of the scope of the present invention, Comparative Example No. 36 having a small amount of resin has poor adhesion and corrosion resistance and Comparative Example No. 37 having a small amount of melamine resin.
Comparative Example N with poor corrosion resistance and solvent resistance and high silica content
In Comparative Example Nos. 39 and 40, where o38 was poor in adhesion and corrosion resistance, and in Comparative Examples Nos. 39 and 40 where the amount of silica was small, the corrosion resistance was poor.
In Comparative Example No. 41 having a large amount of ammonium a, the workability and corrosion resistance of the processed portion were poor. In Comparative Example No. 42 having a small amount of ammonium Va, the adhesion and corrosion resistance were poor, and in Comparative Example No. 43 having a low resin Tg, the corrosion resistance and solvent resistance were low. Comparative Example No. 44, in which the properties were poor and the resin Tg was high, the corrosion resistance of the processed portion was poor, and Comparative Example No. 45, in which the pH of the treating agent was low, was poor in bath stability and the pH of the treating agent was high, in Comparative Example No. 46
Is poor in corrosion resistance and adhesion. Comparative Examples Nos. 47 and 48 contain hexavalent chromium as described above. According to the present invention, a surface-treated steel sheet excellent in corrosion resistance, dew condensation resistance, and adhesion of a top coating film can be obtained even at a level where the plating type of the original sheet is changed.

[0034]

As described above, the surface treatment agent and the surface-treated steel sheet according to the present invention can be prepared by combining a conventional acrylic resin with ammonium vanadate not containing hexavalent chromium and silica by the conventional chromate treatment or chromium-based treatment. Compared to rust-proofing pigment-containing treatment agents and films, it has excellent resistance to dew condensation and almost the same corrosion resistance. That is, the present invention provides a surface treatment agent and a surface-treated steel sheet having low pollution and excellent rust prevention ability.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Motoo Kabeya 4-1-1-15 Minamishinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd., Tokyo Office (72) Inventor Satoshi Kobori 4-chome, Minamishinagawa, Shinagawa-ku, Tokyo 1-115 Nippon Paint Co., Ltd. Tokyo Office (72) Inventor Masateru Takimoto 2-1-2 Oyodo Kita, Kita-ku, Osaka-shi, Osaka Nippon Paint Co., Ltd. Osaka Office

Claims (3)

[Claims] 1. An acrylic emulsion having a glass transition point of 20 to 70 ° C. is converted to a solid content of 50 to 85.9% by weight, and an imino group-containing methylated melamine resin is converted to a solid content of 4 to 8% by weight.
10% by weight and at least one of colloidal silica to which ammonium ions are adsorbed or colloidal silica coated with aluminum oxide,
A water-based surface treatment agent containing -40% by weight and 0.1-10% by weight of ammonium vanadate in terms of solid content, and having a pH of 8-10. 2. A surface-treated steel sheet, wherein the aqueous surface treating agent according to claim 1 is used as a solid film, and the solid film has an adhesion amount of 0.3 to 10 g / m ² . 3. A method for producing a surface-treated steel sheet, comprising applying the aqueous surface treating agent according to claim 1 onto a steel sheet, and drying and baking under conditions where the reached sheet temperature is 50 to 250 ° C.