JP2003221681A - Surface treated steel sheet superior in formability and corrosion resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent corrosion resistance, blackening resistance, dew condensation resistance, chromium elution resistance, adhesiveness to an adhesive tape, and roll formability. <P>SOLUTION: This surface treated steel sheet has a coating containing (A) a copolymer resin obtained from (i) styrene, (ii) (meth) acrylic acid, (iii) (meth) acrylate having a 3-6C alkyl chain, and (iv) a vinyl monomer capable of copolymerizing with them, (B) a chromium compound, as a main component, formed on the surface of an Al-Zn alloy plated steel sheet, wherein the above (A) copolymer resin comprises 30-60 mass% of styrene, 0.5-5 mass% of (meth) acrylic acid, and 20-60 mass% of (meth) acrylate having a 3-6C alkyl chain, with respect to 100 mass% of the solid content of the above (A). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet which is provided with excellent workability and corrosion resistance on an Al-Zn alloy plated steel sheet which is mainly used unpainted for applications such as building materials and home appliances.

[0002]

2. Description of the Related Art 55% Al-Zn alloy plated steel sheet is
Building material products such as building roofing materials and outer wall materials, guardrails,
It is used in soundproof walls, civil engineering products such as drains, home appliances, and industrial equipment. In these applications, since it is used without coating, it is necessary that the surface of the plated steel sheet is not discolored and a clean surface appearance is maintained for a long period of time. Further, in the case of building material use, since the plated steel sheet is formed by roll forming, roll forming property (plating does not build up on the roll) is required. Further, the appearance after roll forming is also important, and it is preferable that there is no film damage and excellent corrosiveness.

As prior arts for improving the above problems, Japanese Patent Nos. 2048167, 2097278 and 25 are available.
There is a method described in No. 54401.

Japanese Patent No. 2048167 discloses that 0.1 to 2 parts by weight of hexavalent chromium and 0.5 to 5 parts by weight of wax solids are added to 100 parts by weight of an acrylic resin emulsion.
5 to 50 parts by mass of a hydrophilic solvent is mixed to adjust the pH to 6 to 8
A coating film is formed using a coating composition prepared as described above.
The acrylic resin emulsion contains an anionic and / or nonionic reactive emulsifier capable of undergoing radical polymerization with α, β-ethylenically unsaturated monomers in an amount of 0.
5 to 5% by mass, and obtained by emulsion polymerization,
It has an acid value of 0-9. The film obtained by this technique has good workability, but has a problem of long-term corrosion resistance because of the large amount of chromium eluted.

Japanese Patent No. 2097278 discloses that a specific water-soluble or water-dispersible resin is mixed with hexavalent chromium in a specific ratio for the purpose of improving roll forming property and corrosion resistance.
Further, it is a technique relating to a treatment method of applying a treatment liquid having a pH adjusted to 3 to 10 onto the surface of an Al-Zn alloy plated steel sheet. Since the chromium of the film obtained by this technique is hexavalent chromium and the pH of the treatment liquid is 3 or more, the reactivity between the resin film and the hexavalent chromium has not progressed sufficiently or the reaction has not occurred. Since the speed is very slow, chromium is likely to be eluted from the resin film. For example, when dew condensation occurs, chromium is significantly eluted and uneven appearance is likely to occur. To reduce the occurrence of this uneven appearance, it is effective to reduce the amount of chromium deposited and reduce the amount of chromium eluted.
Since the corrosion resistance depends on the chromium deposition amount, sufficient corrosion resistance cannot be obtained even if the chromium deposition amount is reduced. Further, even if the amount of deposited chromium is increased, chromium is eluted from the resin film, so that a significant improvement in corrosion resistance cannot be expected.

Japanese Patent No. 2554401 discloses (a) (a) β
-1 to 20 parts by mass of an α, β-ethylenically unsaturated monomer having a ketoester group, and (b) a processable α, β-ethylenically unsaturated monomer having two or more radically polymerizable groups of 0.05 to 5 parts by mass, and (c) α, β- other than the above
0 to 10 parts by mass of a radically polymerizable reactive emulsifier (b) of 0.2 to 10 parts by mass was added to 100 parts by mass of a monomer mixture containing the rest of the ethylenically unsaturated monomer, and emulsion polymerization was performed. An aqueous resin dispersion having an acid value of 15 and 1/1000 to 1 in this aqueous resin dispersion
The present invention relates to a resin composition for coating a zinc-aluminum alloy-plated steel sheet, which is obtained by mixing chromium (VI) ions in a mass ratio of / 10. However, although this coating resin composition has good stability in the coexistence with chromium, it has a problem in long-term corrosion resistance due to the large elution of chromium.

As described above, according to the conventional technique, a surface-treated material of an Al--Zn alloy-plated steel sheet which can satisfy various properties such as workability, corrosion resistance, roll forming property and blackening resistance has not been obtained. The current situation.

[0008]

SUMMARY OF THE INVENTION The present invention is intended to solve the problems of the prior art and is excellent in workability, corrosion resistance, and roll forming properties, and in addition, blackening and dew condensation cause uneven appearance. An object of the present invention is to provide a surface-treated steel sheet of an Al—Zn alloy-plated steel sheet that is difficult and can maintain a beautiful plating appearance for a long period of time.

[0009]

Means for Solving the Problems The inventors of the present invention have made extensive studies as to the means for solving the problems of the above-mentioned prior art, and as a result, have found that the specific co-existence on the surface of the Al--Zn system plated steel sheet It has been found that the above problems can be solved by forming a film containing a polymer resin and a chromium compound.

That is, according to the present invention, (A) (i) styrene, (ii) (meth) acrylic acid, and (iii) an alkyl chain having 3 to 6 carbon atoms are formed on the surface of an Al-Zn alloy plated steel sheet. A surface-treated steel sheet having a film mainly composed of a (meth) acrylic acid ester having (b), a copolymer resin obtained from (iv) a vinyl monomer copolymerizable therewith, and (B) a chromium compound. In (a), the mass ratio of (i) styrene to the solid content of 100% by mass of the copolymer resin is 30 to 60 mass%, (ii) the mass ratio of (meth) acrylic acid is 0.5 to 5 mass%, (Iii) The present invention relates to a surface-treated steel sheet excellent in corrosion resistance and workability, characterized in that a (meth) acrylic acid ester having an alkyl chain having 3 to 6 carbon atoms has a mass ratio of 20 to 60 mass%. .

The Al-Zn alloy plated steel sheet is A
It is preferable to contain 1 to 25 to 75 mass%. Also,
It is preferable that the chromium compound contains hexavalent chromium and trivalent chromium. Further, the ratio of hexavalent chromium contained in the (B) chromium compound [hexavalent chromium / (trivalent chromium + 6
[Valent chrome)] is preferably in the range of 0.3 to 0.9 in terms of metallic chromium. Further, it is preferable that the solid content mass of the (A) copolymer resin and the mass ratio [resin / Cr] of the (B) chromium compound in terms of metal chromium are in the range of 10 to 200. Further, the amount of Cr in the film is 1 to 10
It is preferably characterized in that it is 0 mg / m ² .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The constitution of the present invention will be described in detail below.

According to the invention of claim 1, (A) (i) styrene, (ii) (meth) acrylic acid, and (iii) an alkyl group having 3 to 6 carbon atoms are formed on the surface of the Al-Zn alloy plated steel sheet. A surface treatment for forming a film containing (meth) acrylic acid ester having a chain, (iv) a copolymer resin obtained from a vinyl monomer copolymerizable therewith and (B) a chromium compound as main components. In the steel sheet, the mass ratio of (i) styrene is 30 to 60 mass% and the mass ratio of (ii) (meth) acrylic acid is 0.5 to 5 mass% with respect to 100 mass% of the solid content of the (A) copolymer resin. , (Iii) the mass ratio of the (meth) acrylic acid ester having an alkyl chain having 3 to 6 carbon atoms is 20 to 60 mass%.

The component (A) of the present invention comprises (i) styrene, (ii) (meth) acrylic acid, and (iii) a carbon number of 3 to.
A (meth) acrylic acid ester having an alkyl chain of 6,
(Iv) A copolymer resin obtained from these and a vinyl monomer copolymerizable therewith. The mass ratio of (i) styrene to the solid content of the copolymer resin is in the range of 30 to 60% by mass, preferably 35 to 60% by mass, and more preferably 40 to 60% by mass. (I) Styrene is a hydrophobic monomer, and improvement in corrosion resistance can be expected by increasing the amount of styrene. When the amount of styrene in the copolymer resin is less than 30% by mass, the effect of improving the corrosion resistance is insufficient, while when it exceeds 60% by mass, the film forming property of the resin itself is extremely deteriorated, which is not preferable.

The component (A) copolymer resin contains (ii) (meth) acrylic acid as an essential component, and (ii) (meth) acrylic acid has the effect of imparting dispersion stability of the emulsion and adhesion to the metal surface. There is. The polymerization ratio of (ii) (meth) acrylic acid in the copolymer resin is in the range of 0.5 to 5% by mass, preferably 0.5 to 4% by mass, and more preferably 1 to 4% by mass. If the mass ratio of (meth) acrylic acid in the copolymer resin is less than 0.5% by mass, the stability of the emulsion and the adhesion to the metal surface are deteriorated, which is not preferable, while if it exceeds 5% by mass. Is not preferred because the hydrophilicity of the resulting coating becomes strong and the water resistance decreases.

Used in the component (A) copolymer resin (ii)
i) Examples of the (meth) acrylic acid ester having an alkyl chain having 3 to 6 carbon atoms include (meth) acrylic acid-n-propyl and its isomers, (meth) acrylic acid-n-butyl and its isomers, Examples thereof include (meth) acrylic acid-n-pentyl and isomers thereof, and (meth) acrylic acid-n-hexyl and isomers thereof. The (meth) acrylic acid ester contributes to the improvement of the processability of the film, but when the alkyl chain of the (meth) acrylic acid ester is 2 or less, the film itself has a strong hydrophilic property, so that the processability and water resistance are low. It is not preferable because it decreases. On the other hand, when the alkyl chain of the (meth) acrylic acid ester is 7 or more, the glass transition temperature of the obtained film becomes low and the blocking property is lowered, which is not preferable. The polymerization ratio of (iii) (meth) acrylic acid ester having an alkyl chain having 3 to 6 carbon atoms in the copolymer resin is 20 to 60% by mass, preferably 20 to 55.
It is mass%, more preferably 25 to 55 mass%. When the polymerization ratio of (iii) the (meth) acrylic acid ester having an alkyl chain of 3 to 6 carbon atoms in the copolymer resin is less than 20% by mass, the effect of improving the workability of the film is poor, while 6
If it exceeds 0% by mass, the absolute amount of styrene, which is effective in improving the corrosion resistance of the coating, decreases, which is not preferable. still,
The ratio of methacrylic acid ester to acrylic acid ester is not particularly limited and is included in the copolymer resin (meth).
All acrylic acid esters may be methacrylic acid esters or acrylic acid esters.

The vinyl monomer used as the component (A) (iv) copolymerizable therewith is not particularly limited, but examples thereof include 2-hydroxyethyl (meth) acrylate and (meth). Hydroxypropyl acrylate, acrylamide, N-methylol acrylamide,
Diacetone acrylamide, glycidyl methacrylate, vinyl toluene, vinyl acetate, aryllonitrile,
Examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylate having an alkyl chain having 7 or more carbon atoms. In addition, (i
v) The polymerization ratio of the vinyl monomer copolymerizable therewith is not particularly limited, but it has a role of adjusting the glass transition temperature of the copolymer resin, and the glass transition temperature is 10 to 70 ° C, preferably 15 to 60 ° C. It is preferable to adjust the range.

The method for polymerizing the (A) copolymer resin of the present invention is not particularly limited, and examples thereof include emulsion polymerization method, suspension polymerization method, bulk polymerization method and solution polymerization method. A preferred emulsion polymerization method is preferable. The surfactant used in this emulsion polymerization method is not particularly limited, but nonionic surfactants, anionic surfactants, nonion-anionic surfactants, nonionic interfaces having unsaturated double bonds. Examples thereof include an activator, an anionic surfactant having an unsaturated double bond, and a nonionic-anionic surfactant having an unsaturated double bond. The amount of the surfactant used in the emulsion polymerization is not particularly limited, but is preferably 1 to 10% by mass with respect to 100% by mass of all the monomers of the acrylic-styrene resin. 100% by weight of all monomers of acrylic-styrene resin
When the amount of the surfactant is less than 1% by mass, it is not preferable because the mixing stability of chromium is deteriorated. On the other hand, when the amount exceeds 10% by mass, the surfactant bleeds on the surface of the film at the time of forming the film, so that the adhesive tape is It is not preferable because the adhesiveness of the material to be bonded to the surface of the steel sheet is reduced when it is used by consumers.

Furthermore, in the invention of claim 1, the component (B) chromium compound is an essential component.

According to the second aspect of the invention, the effect of improving the characteristics of the present invention is manifested when the content of Al in the galvanized coating of the plated steel sheet which is the base of the Al—Zn alloy plated steel sheet is 25 to 75 mass%. It has become. Particularly preferably 50
About 60% by mass, especially 55% Al-Zn alloy plated steel sheet is preferable. In the Al-Zn alloy plated steel sheet of the present invention, Si in the plating film is 0.5% by mass or more of the Al amount,
In particular, those containing about 1 to 3% by mass are also included.

[0021] In the invention of claim 3, the chromium compound (B) contains a chromium compound containing hexavalent chromium and trivalent chromium. Hexavalent chromium has excellent anticorrosion properties, but its high solubility in water makes it suitable for applications requiring long-term anticorrosion properties.
Valuate chromium alone is not sufficient. Therefore, trivalent chromium is used together in the present invention. The ratio of hexavalent chromium to trivalent chromium in the component (B) [hexavalent chromium / (trivalent chromium + hexavalent chromium)] is not particularly limited,
In the invention, it is specified that the range is 0.3 to 0.9 in terms of metallic chromium. This value is more preferably 0.5
~ 0.8. Ratio of hexavalent chromium and trivalent chromium in component (B) [hexavalent chromium / (trivalent chromium + hexavalent chromium)]
Is less than 0.3 in terms of metal chromium, the long-term corrosion resistance may be poor because the absolute amount of hexavalent chromium, which has an effect on anticorrosion, is small. If it exceeds 0.9, chromium is eluted. It is not preferable because it becomes easy and the long-term corrosion resistance decreases.

In the fifth aspect of the invention, the mass ratio [resin / Cr] of the (A) copolymer resin to the solid content of the (B) chromium compound and the (B) chromium compound in terms of metallic chromium is 10 to 200. The range is preferably 20 to 150, more preferably 50 to 150. When the solid content mass of the (A) copolymer resin and the mass ratio [resin / Cr] of the (B) chromium compound in terms of metal chromium are less than 10, the absolute amount of chromium increases, so the amount of eluted chromium is relatively large. It is not preferable because it increases On the other hand, (A)
When the solid content mass of the copolymer resin and the mass ratio [resin / Cr] of the chromium compound (B) in terms of metal chromium are more than 200, the corrosion resistance is lowered because there are few chromium compounds having an anticorrosion effect, which is not preferable.

In the invention of claim 6, the amount of Cr in the film is 1
˜100 mg / m ² . 1 mg
If it is less than / m ^2, it is not preferable because the corrosion resistance is greatly reduced, and if it ^exceeds 100 mg / m ² , the Cr fixing ratio is lowered and Cr is easily eluted, which is not preferable.

The amount of the film formed on the surface of the Al—Zn alloy plated steel sheet of the present invention is 1 to 3 g / m ²
The range is preferably, and more preferably 1.2 to
It is 2.0 g / m ² . If the amount of the coating formed on the surface of the Al—Zn alloy plated coating is less than 1 g / m ^2, it is not preferable because the workability and corrosion resistance that are the features of the present invention are insufficient, while 3 g / m ² not economical because the effect is saturated if it exceeds m ^2.

The method of treating the coating formed on the surface of the Al—Zn alloy plated steel sheet of the present invention is not particularly limited, and it is applied by using any method such as a roll coater. Is possible, electric furnace,
Using a hot blast stove, induction heating furnace, etc.
It is preferable to dry at 150 ° C. for 60 seconds or less.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. It should be noted that these examples are provided for the purpose of explaining the present invention, and do not limit the present invention in any way.

[Preparation of test plate] (1) Test material 5% Al-Zn alloy plated steel sheet (GF) 55% Al-Zn alloy plated steel sheet (GL) (2) Degreasing treatment Silicate alkaline degreasing agent Fine cleaner 43
After degreasing treatment with 36 (registered trademark: manufactured by Nippon Parkerizing Co., Ltd.) (concentration 20 g / L, temperature 60 ° C., spraying for 20 seconds), it was washed with tap water. (3) Method of adjusting surface treatment agent At room temperature, the copolymer resin of Table 1 and the chromium compound of Table 2 are put in this order into distilled water and mixed with stirring using a propeller stirrer, and the surface treatment agent of Table 3 is obtained. Was adjusted. (4) Method for producing surface-treated steel sheet The surface-treatment chemicals prepared as described above were applied to the surface of the test material with a bar coater and dried at an ambient temperature of 240 ° C.
The coating amount (g / m ² ) was adjusted by appropriately adjusting the solid content concentration of the surface treatment agent. [Evaluation of coating performance] (1) Corrosion resistance of processed part Bending (5T) sample JIS-Z
The salt spray test according to −2371 was carried out for 240 hours, the occurrence of white rust in the bent portion was observed, and the evaluation was performed according to the following criteria. <Evaluation criteria> ◎: White rust occurrence area ratio is less than 10% of the total area ○: White rust occurrence area ratio is 10% or more and less than 25% of the total area △: White rust occurrence area ratio is 25% or more of the entire area 50 Less than%: White rust occurrence area ratio is 50% or more of the total area (2) 150 cm in a wet tester with black denaturation resistance of 50 ° C. and humidity of 98% or more
A test plate of × 150 cm was left in a stacked state for 6 days so that the surface of the steel plate was wet, and the degree of discoloration due to black discoloration was evaluated according to the following criteria. <Evaluation Criteria> ◎: No change in appearance ○: Discolored area is less than 10% of the total area △: Discolored area is 10% or more and less than 30% of the total area ×: Discolored area is 30% or more of the total area (3) Condensation resistance 150cm in a humidity tester with a temperature of 50 ℃ and humidity of 98% or more
A test plate having a size of 150 cm was left in a stacked state for 6 days so that the surface of the steel plate was wet, and evaluated according to the following criteria. <Evaluation Criteria> ◎: No yellow coloration in dew condensation water on test plate surface Δ: Some yellow coloration in dew condensation water on test plate surface (almost uniform when dried) ×: Yellow coloration in dew condensation water on test plate surface (dry) And (4) Chromium elution test plate was immersed in boiling water for 2 minutes, the amount of chromium adhesion before and after immersion was measured, and evaluated according to the following criteria. <Evaluation Criteria> ◎: No change in chromium adhesion amount ○: Chromium adhesion amount decreases before and after immersion. Reduction rate less than 5% △: Chromium adhesion amount decreased before and after immersion. Reduction rate 5% or more 1
Less than 0% x: Chromium adhesion amount decreases before and after immersion. Reduction rate 10% or more (6) Roll forming property A bead pull-out test is performed with a bead having a tip diameter of 5 mmR pressed against a test plate having a width of 30 mm with a load of 100 kgf, and the appearance is visually evaluated according to the following criteria. It was ◎: No film damage ○: Very slight film damage (no problem in practical use) △: Little film damage (problem in practical use) ×: Large film damage (problem in practical use) of Examples and Comparative Examples of the present invention The test results are shown in Tables 4 and 5. In Examples 1 to 10 using the surface-treated plate of the AlZn alloy plated steel sheet of the present invention, corrosion resistance, blackening resistance,
The dew condensation resistance, chromium elution resistance, adhesive tape adhesion, and roll forming properties were all good. On the other hand, in Comparative Examples 1 to 5 of the surface-treated steel sheets that are outside the scope of the present invention, two or more performances among corrosion resistance, blackening resistance, dew condensation resistance, chromium elution resistance, adhesive tape adhesion, and roll forming property are provided. Was inferior, or some properties were significantly inferior.

[0028]

As described above, by using the surface-treated steel sheet obtained by subjecting the surface of the Al-Zn alloy plated steel sheet to the treatment of the present invention, excellent corrosion resistance, blackening resistance, dew condensation resistance, and chromium elution resistance are obtained. It can be seen that the industrial utility value is extremely high since it is possible to obtain the adhesiveness, adhesive tape adhesiveness and roll forming property.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 28/00 C23C 28/00 A (72) Inventor Keiji Yoshida 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Inventor Masaaki Yamashita 1-2 No. 1-2 Marunouchi, Chiyoda-ku, Tokyo F Term in Nihon Steel Pipe Co., Ltd. (reference) 4F100 AA22C AA22H AB03A AB10B AB18B AB31B AK12C AK25C AK80C AL01C BA03 BA07 BA10A BA10C CC00C EH71B GB07 GB48 JB02 JL00 JL01 JM02B YY00B YY00C 4K026 AA02 AA13 AA22 BA06 BA12 BB01 BB08 BB09 CA37 CA38 CA39 DA02 DA15 DA16 EA08 4K027 A21 0502 A02

Claims (6)

[Claims] 1. A surface of an Al—Zn alloy plated steel sheet,
(A) (i) Styrene, (ii) (meth) acrylic acid, and (iii) having an alkyl chain having 3 to 6 carbon atoms (meth)
A surface-treated steel sheet having a film mainly composed of an acrylate ester, (iv) a copolymer resin obtained from a vinyl monomer copolymerizable therewith, and (B) a chromium compound, wherein (A) The mass ratio of (i) styrene is 30 to 60 mass% and the mass ratio of (ii) (meth) acrylic acid is 0.5 to 5 relative to 100 mass% of the solid content of the copolymer resin.
A surface-treated steel sheet excellent in corrosion resistance and workability, characterized in that the mass ratio of (iii) (meth) acrylic acid ester having an alkyl chain having 3 to 6 carbon atoms is 20 to 60 mass%. 2. The surface-treated steel sheet according to claim 1, wherein the Al—Zn alloy plated steel sheet contains 25 to 75 mass% of Al. 3. The surface-treated steel sheet according to claim 1, wherein the chromium compound contains hexavalent chromium and trivalent chromium. 4. The ratio of hexavalent chromium contained in the (B) chromium compound [hexavalent chromium / (trivalent chromium + hexavalent chromium)] is in the range of 0.3 to 0.9 in terms of metallic chromium. The surface-treated steel sheet according to any one of claims 1 to 3, characterized in that. 5. The mass ratio [resin / Cr] in terms of metal chromium of the (A) copolymer resin and the (B) chromium compound is in the range of 10 to 200. The surface-treated steel sheet according to item 1. 6. The amount of Cr in the film is 1 to 100 mg /
surface treated steel sheet according to any one of claims 1 to 5, characterized in that the m ^2.