JP2000313964A - Surface treated steel sheet excellent in working adhesion after coating and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated steel sheet excellent in working adhesion after coating and to provide a method for producing it. SOLUTION: The upper layer of a plated steel sheet having a chromate layer of 5 to 100 mg/m2 expressed in terms of Cr is provided with an organic composite film of 0.3 to 3 g/m2 in which, to 100 pts.wt. of hydrophilic resin solid contents, colloidal silica is contained by 5 to 50 pts.wt. as the solid contents, and, as the colloidal silica contained in the organic composite film, aspherical colloidal silica as a beady combined body in which the ratio of the length/the average particle size of spherical silica is >=4 and having branching of one or more places is used. In this way, the surface treated steel sheet excellent in working adhesion after coating can be obtd.

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 used for automobiles, home appliances, building materials and the like, has excellent workability after coating and is excellent in various performance balances, and a method for producing the same.

[0002]

2. Description of the Related Art Surface-treated steel sheets, such as electro-galvanized steel sheets and hot-dip galvanized steel sheets, have been developed so far.
It is widely used in applications such as building materials and automotive parts.

[0003] Most of these steel sheets are usually subjected to a chromate treatment or a phosphate treatment for the purpose of improving corrosion resistance and paint adhesion. Recently, however, chromate treatment has been carried out to meet various demands from customers. An organic composite steel sheet in which an organic composite film based on a special resin is formed on a plated steel sheet that has been applied has been developed. For example, tokuho 4-14
No. 191 discloses a method for producing a surface-treated steel sheet in which an aqueous composite is added to a chromate-coated plated steel sheet to form an organic composite film in which a colloidal sol having a specific fine particle size is additionally adjusted to improve corrosion resistance and fingerprint resistance. It has been disclosed. Further, Japanese Patent Application Laid-Open No. Sho 62-170340 and Japanese Patent Application Laid-Open
No. 10140 discloses a technique of adding silica sol to an organic resin film for the purpose of improving the corrosion resistance of the organic film itself.

[0004] The organic composite steel sheet obtained by these conventional techniques satisfies basic properties such as corrosion resistance, adhesion, and scratch resistance in a well-balanced manner, and is particularly used as a material for home appliances.

On the other hand, the upper layer of the organic composite film may be further coated for the purpose of corrosion resistance and design. However, when subjected to severe bending work to which compressive stress is applied, cohesive failure of the underlying organic composite film may occur and the coating film may be peeled off, and further improvement in performance has been desired.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface-treated steel sheet which can be used for automobiles, home appliances, building materials and the like, has excellent work adhesion after painting, and is excellent in various performance balances, and a method for producing the same. To provide.

[0007]

Means for Solving the Problems The inventors of the present invention have made various studies to solve the above-mentioned problems, and as a result, found that a plurality of spherical colloidal silica beads are formed on a plated steel sheet subjected to a chromate treatment. The balance of various performances is maintained by forming an organic composite film containing non-spherical colloidal silica, which is a body having a ratio of length / average particle diameter of 4 or more and having at least one branch. It has been found that a surface-treated steel sheet having excellent processing adhesion after painting can be obtained as it is.

[0008] The first of the present invention is based on the above-mentioned findings, and a hydrophilic resin solid content of 10% is formed on a plated steel sheet having a chromate layer of 5 to 100 mg / m ^{2 in} terms of Cr.
5 parts by weight of colloidal silica as solids
It has an organic composite coating of 0.3 to 3 g / m ² containing 50 parts by weight, and the colloidal silica contained in the organic composite coating is a conjugate of a plurality of spherical colloidal silica bonded in a bead shape. The ratio of the length of the conjugate to the average particle size of the spherical colloidal silica is 4 or more, and the conjugate is a sphere colloidal silica having one or more branches. Excellent surface treated steel sheet.

A second aspect of the present invention is a conjugate of a plurality of spherical colloidal silica particles bound in a bead shape, wherein the ratio of the length of the conjugate to the average particle diameter of the spherical colloidal silica is 4 or more and at least one portion. An organic composite paint in which a conjugate of spherical colloidal silica having a branch of 5 to 50 parts by weight as a solid content with respect to 100 parts by weight of a solid content of a hydrophilic resin is dried on a plated steel sheet having a chromate film. This is a method for producing a surface-treated steel sheet having excellent workability after coating, characterized by applying a weight of 0.3 to 3 g / m ² and baking.

The third aspect of the present invention is that the Cr equivalent is 5 to 100 m.
g / m ² on the upper layer of the plated steel sheet having a chromate layer,
0.3 to 5 parts by weight of colloidal silica as a solid content relative to 100 parts by weight of a hydrophilic resin solid content
-3 g / m ² , wherein the colloidal silica contained in the organic composite film is a combination of a plurality of spherical colloidal silicas bound in a rosary, the spherical colloid having a length of the combination. The ratio of silica to the average particle size is 4
A mixture of non-spherical colloidal silica, which is a combination of spherical colloidal silica having one or more branches and spherical colloidal silica, and non-spherical colloidal silica / all-colloidal silica (that is, non-spherical colloidal silica bond) The ratio of (body + spherical colloidal silica) is 0.1 or more.

A fourth aspect of the present invention is a conjugate of a plurality of spherical colloidal silica particles bonded in a bead shape, wherein the ratio of the length of the conjugate to the average particle diameter of the spherical colloidal silica is 4 or more and at least one portion. The blending ratio of non-spherical colloidal silica, which is a conjugate of spherical colloidal silica having a branch, and spherical colloidal silica is determined by the ratio of non-spherical colloidal silica / total colloidal silica (that is, non-spherical colloidal silica + spherical colloidal silica). 0.1 or more, and all colloidal silica has a hydrophilic resin solid content of 10
An organic composite coating compounded in a proportion of 5 to 50 parts by weight as a solid content with respect to 0 parts by weight is applied to a plated steel sheet having a chromate film at a dry weight of 0.3 to 3 g / m ² and then baked. This is a method for producing a surface-treated steel sheet having excellent processing adhesion after painting.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The present invention uses the conventional technology by using a silica having a shape different from that of silica conventionally added to an organic composite film, as a means for improving the work adhesion after coating without reducing corrosion resistance and weldability. It has succeeded in obtaining the performance exceeding.

Conventionally, the silica used for this purpose is spherical or an aggregate of spherical silica, whereas the silica used in the present invention is non-spherical colloidal silica, that is, a plurality of beads bonded in a bead shape. Wherein the ratio of the length of the conjugate to the average particle diameter of the spherical colloidal silica is 4 or more and 1
It is a combination of spherical colloidal silica having more than one branch, and the use of silica having such a shape significantly improves processing adhesion after coating.

It is known that the organic composite steel sheet containing spherical silica found in the prior art forms a denser film and improves the corrosion resistance particularly as the silica having a finer particle size is used.
However, such spherical silica has a problem that the cohesive strength at the time of agglomeration is weak, and when subjected to severe press working, cohesive failure of the coating occurs to lower the adhesion.

On the other hand, the colloidal silica conjugate used in the present invention is a conjugate of spherical silica in which the ratio of the length of the conjugate to the average particle size of the spherical colloidal silica is 4 or more, and has one or more branches. It has a unique shape. Non-spherical colloidal silica having such a branched shape has a strong binding force due to entanglement when agglomerated, and can be formed into an organic composite film as a whole by being contained in an organic resin. Furthermore, the aggregation form of the silica present in the surface layer of the organic film is different, and the non-spherical silica has a higher degree of surface irregularity than the spherical silica, so that the anchoring effect with the coating film is also improved. As described above, by improving both the toughness and the anchoring effect of the film, it is possible to achieve an improvement in the processing adhesion after coating.

Hereinafter, the surface-treated steel sheet having excellent work adhesion after coating and the method for producing the same according to the present invention will be described in detail.

The metal products applicable in the present invention include a galvanized steel sheet, a zinc-nickel plated steel sheet, a zinc-iron plated steel sheet, a zinc-chrome plated steel sheet, a zinc-aluminum plated steel sheet, a zinc-titanium plated steel sheet, and a zinc-coated steel sheet.
Zinc-based electroplating such as magnesium-plated steel sheet, zinc-manganese-plated steel sheet, hot-dip coating, vapor-deposited steel sheet,
Aluminum or aluminum alloy-plated steel sheet, lead or lead alloy-plated steel sheet, tin or tin alloy-plated steel sheet, and even a small amount of dissimilar metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese,
Examples include those containing iron, magnesium, lead, antimony, tin, copper, cadmium, arsenic, and the like, and / or those in which inorganic substances such as silica, alumina, and titania are dispersed. Further, the present invention is also applicable to multi-layer plating in which the above plating is combined with other types of plating, for example, iron plating, iron-phosphorus plating, and the like.

The coating weight of each plated steel sheet is preferably 1 g / m ² or more on one side, and if it is less than this, the corrosion resistance decreases.

In the present invention, a chromate film is formed as a first layer and an organic composite film is formed as a second layer from the lower layer on the plated surface of such a steel sheet. Means for forming the first layer chromate film include, for example, immersion chromate treatment in an aqueous solution mainly containing chromic anhydride, chromate, and dichromic acid, electrolytic chromate treatment, and further, colloidal silica or the like is added to the aqueous solution. A coating-type chromate treatment method in which the mixed treatment liquid is applied and dried without washing with water can be used.

The adhesion amount of the chromate film is 5 to 5 in terms of Cr.
It is preferred to be about 100 mg / m ² . Adhesion amount is C
If it is less than 5 mg / m ^{2 in} terms of r, sufficient corrosion resistance cannot be obtained, and if it exceeds 100 mg / m ² , cohesive failure of the chromate film itself occurs, and the adhesion of the film decreases.

The hydrophilic resin used as the organic composite film includes acrylic ester / acrylic acid copolymer, epoxy / acrylic acid, olefin / acrylic acid copolymer, olefin ionomer, styrene / acrylic acid copolymer,
A urethane / acrylic acid copolymer, urethane epoxy resin, ethyleneimine acrylic resin, or the like can be used, and it is preferable to use an emulsion dispersed in an aqueous solvent as a coating material. If necessary, a crosslinking agent such as various melamine resins and amino resins may be added. Among these, it is preferable to use an olefin / acrylic acid copolymer especially when both performance and cost are considered.

The hydrophilic resin contains non-spherical colloidal silica (colloidal silica binder). The non-spherical colloidal silica used in the present invention can be obtained by various methods. As an example, in the process of removing cations from an aqueous solution of sodium silicate and potassium silicate with a cation exchange resin to produce colloidal silica, alkaline earth is used. There is a method of adjusting the temperature and pH by adding a class of metal ions. Commercially available ones may be used. For example, PM-M, available from Nissan Chemical Industries,
PM-L or the like can be used.

The shape of the non-spherical colloidal silica thus obtained may be a conjugate having a ratio of conjugate length / spherical colloidal silica average particle diameter of 4 or more and having one or more branches. It is better to use The length / average particle diameter ratio is preferably in the range of 4 to 100. 4
If it is less than the value, there is no difference from the conventional spherical colloidal silica, and the processing adhesion after coating is not improved. On the other hand, if it exceeds 100, the non-spherical colloidal silica itself becomes unstable in the coating material, causing problems such as sedimentation. The average particle diameter is not particularly limited, but is preferably in the range of 10 to 50 nm in consideration of aggregation or sedimentation in a bath. Further, non-spherical colloidal silica having one or more branches is preferable, and the range of 1 to 50 is more preferable in consideration of coagulation or sedimentation in a bath.

As described above, the shape of the colloidal silica is based on the assumption that non-spherical colloidal silica having a length / average particle diameter ratio of at least 4 and having a spherical silica binder and having at least one branch is used. In some cases, it is also possible to use a mixture of conventional spherical silica.

However, the mixing ratio of the non-spherical colloidal silica to the total colloidal silica (ie, non-spherical colloidal silica + spherical colloidal silica) needs to be 0.1 (solid content weight ratio) or more, and less than 0.1 Does not improve the working adhesion after painting.

These silicas are converted to a hydrophilic resin solid content of 100
It is blended at a ratio of 5 to 50 parts by weight with respect to parts by weight. 5
If it is less than 50, sufficient corrosion resistance cannot be obtained, and if it exceeds 50, flexibility of the film cannot be obtained and the film becomes brittle, thereby deteriorating the adhesion.

These resins contained colloidal silica.
Chromate the organic composite paint beforehand.
The target surface-treated steel sheet is applied and baked
It can be obtained, but its adhesion amount is 0.3-3 g / m^TwoIn the range
is there. 0.3 g / m ^TwoIf less than, unevenness of the steel sheet surface
Corrosion resistance is inferior because it cannot be filled, and 3g / m^TwoTo
If it exceeds, the corrosion resistance is improved, but the weldability becomes difficult.
Not preferred.

As a coating method for forming these organic composite films, any method such as spraying, curtain, flow coater, roll coater, bar coater, brush coating, dipping, and air knife drawing may be used.

The baking temperature is desirably set at 80 to 250 ° C. If the temperature is lower than 80 ° C., the water in the coating is difficult to completely volatilize, so that the corrosion resistance is lowered.

Although there is no particular limitation on the drying equipment, a method using hot air blowing, a method using indirect heating with a heater, a method using infrared rays, a method using induction heating, and a method using these in combination can be adopted.

[0031]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(1) Kind of Metal Plate A plated steel plate shown in Table 1 was used.

[0033]

[Table 1]

(2) Chromate treatment EG and ZN shown in Table 1 were subjected to electrolytic chromatography by applying a predetermined amount of electricity at a current density of 10 A / dm ² in a bath of chromic acid 50 g / L and sulfuric acid 0.3 g / L. After the treatment, the substrate was washed with water and dried in a hot-air drying oven at an ultimate plate temperature of 80 ° C.

(3) Organic Composite Coating Treatment The chromate-treated plated steel sheet is made of an olefin / acrylic copolymer (Hitec S-7024, manufactured by Toho Chemical Industry Co., Ltd.) as a hydrophilic resin, and has the composition shown in Table 3. A predetermined amount of an organic composite coating material in which a hydrophilic resin and colloidal silica were blended in a ratio was applied with a bar coater, and baked and dried at a reaching plate temperature of 150 ° C. in a hot air drying furnace to prepare a sample for evaluation. The average particle diameter, the ratio of length / average particle diameter, and the number of branches of the colloidal silica used in this experiment were determined by applying a predetermined amount of colloidal silica diluted with water, drying the mixture, and using an electron microscope. Measured.

(4) Performance Evaluation Items The following evaluations were performed on evaluation samples prepared under the conditions (1) to (3).

A) Adhesiveness after coating The melamine alkyd resin paint (Kansai Paint Co., Ltd.) was applied to the evaluation sample prepared in (3) using a bar coater.
Amilac # 1000) was applied to a dry film thickness of 3 μm and baked at a furnace temperature of 130 ° C. for 20 minutes. next,
After leaving overnight, it was immersed in boiling water for 30 minutes. Thereafter, the evaluation sample was cut into a size of 300 (length) × 30 (width) mm, stretched by 20% with a tensile tester, and further bent 90 ° with the painted surface inside (R = 0 inside).
Was given. Lastly, a tape peeling test was performed on the processed inner painted surface using an adhesive tape (Nichiban Co., Ltd .: Scotch tape), and the peeling state of the coating film after the test was observed. The evaluation was performed by determining the peeling rate of the coating film in the width direction of the bent portion, and ◎ and ○ were judged to be good. ◎: No peeling ○: Peeling rate less than 10% △: Peeling rate 10% or more, less than 50% ×: Peeling rate 50% or more

B) Flat plate corrosion resistance The sample for evaluation prepared in (3) was subjected to an ambient temperature of 35 according to the salt spray test method described in JIS Z 2371.
At 5 ° C., a 5% aqueous NaCl solution is sprayed on the sample for evaluation,
The white rust occurrence rate after 72 hours was measured. In the following evaluation, ◎
And ○ were judged to be good. ◎: No white rust occurred ○: White rust occurrence rate less than 10% △: White rust occurrence rate 10% or more, less than 50% ×: White rust occurrence rate 50% or more

C) Continuous Weldability A continuous spot welding test was performed under the conditions shown in Table 2, and the number of hit points at which a nugget diameter of 3 mmφ or more could be formed stably was determined.

[0040]

[Table 2]

In the following evaluations, ◎ and ○ were judged to be good. ◎: Number of spots 5,000 or more ○: Number of spots 2500 to less than 5000 △: Number of spots 1000 to less than 2500 ×: Number of spots less than 1,000

Table 3 shows the above evaluation results. From Table 3,
It is clear that the surface-treated steel sheet of the present invention has excellent workability after coating in any case, and has good corrosion resistance and weldability.

[0043]

[Table 3]

[0044]

Since the surface-treated steel sheet of the present invention has excellent processing adhesion after painting, it is suitable as a material for home appliances, building materials and automobiles. Further, by the method for producing a surface-treated steel sheet according to the present invention, it is possible to provide a surface-treated steel sheet having excellent work adhesion after coating to the market while maintaining various performance balances.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B32B 27/18 B32B 27/18 Z C09D 7/12 C09D 7/12 Z C23C 22/24 C23C 22/24 C25D 11/38 301 C25D 11/38 301Z // C09D 201/00 C09D 201/00 (72) Inventor Yujiro Miyauchi 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Corporation Kimitsu Works (72) Inventor Akira Takahashi 1 Kimitsu, Kimitsu-shi, Chiba F-term in Kimitsu Works, Nippon Steel Corporation (reference) GB07 GB32 GB43 JA13B JA13C JA20H JB05B JK06 YY00B YY00C YY00H 4J038 CB061 CB161 CC021 CG141 CJ131 CJ141 DB371 DB481 DG321 D J011 GA06 HA446 KA20 NA12 PA19 PC02 4K026 AA02 AA07 BA01 BA06 BA11 BA12 BB02 BB06 BB08 BB10 CA16 CA39 CA41 DA15 DA16

Claims (4)

[Claims] 1. An upper layer of a plated steel sheet having a chromate layer of 5 to 100 mg / m ^{2 in} terms of Cr, containing 5 to 50 parts by weight of colloidal silica as a solid content relative to 100 parts by weight of a hydrophilic resin solid content. An organic composite coating of 0.3 to 3 g / m ² , wherein the colloidal silica contained in the organic composite coating is a conjugate of a plurality of spherical colloidal silica bonded in a bead shape, The ratio of the length of the spherical colloidal silica to the average particle diameter is 4 or more and 1
A surface-treated steel sheet having excellent workability after coating, characterized by being a combination of spherical colloidal silica having branches at more than one place. 2. A sphere-shaped conjugate comprising a plurality of spherical colloidal silica particles, wherein the ratio of the length of the conjugate to the average particle diameter of the spherical colloidal silica is 4 or more, and the spherical particles have one or more branches. An organic composite paint in which a binder of colloidal silica is blended at a ratio of 5 to 50 parts by weight as a solid content with respect to 100 parts by weight of a hydrophilic resin solid content is coated on a plated steel sheet having a chromate film in a dry weight of 0.3. A method for producing a surface-treated steel sheet having excellent workability after coating, characterized by baking after applying 3 g / m ² . 3. An upper layer of a plated steel sheet having a chromate layer of 5 to 100 mg / m ^{2 in} terms of Cr containing 5 to 50 parts by weight of colloidal silica as a solid content relative to 100 parts by weight of a hydrophilic resin solid content. The organic composite coating of 0.3 to 3 g / m ² , wherein the colloidal silica contained in the organic composite coating is a conjugate of a plurality of spherical colloidal silicas bonded in a bead shape, A mixture of non-spherical colloidal silica, which is a combination of spherical colloidal silica having a spherical particle colloidal silica having an average particle diameter of 4 or more and having one or more branches, and spherical colloidal silica; After painting, wherein the ratio of silica / total colloidal silica (ie non-spherical colloidal silica + spherical colloidal silica) is 0.1 or more Excellent surface treated steel sheet processability adhesion. 4. A sphere-shaped conjugate comprising a plurality of spherical colloidal silica particles, wherein the ratio of the length of the conjugate to the average particle diameter of the spherical colloidal silica is 4 or more and the spherical particles have one or more branches. The compounding ratio of non-spherical colloidal silica, which is a combination of colloidal silica, and spherical colloidal silica is 0.1 or more in the ratio of non-spherical colloidal silica / total colloidal silica (that is, non-spherical colloidal silica + spherical colloidal silica). An organic composite paint in which all colloidal silica is blended at a ratio of 5 to 50 parts by weight as a solid content with respect to 100 parts by weight of a hydrophilic resin solid content is coated on a plated steel sheet having a chromate film in a dry weight of 0%. after .3~3g / m ² coating, a method for producing a surface-treated steel sheet excellent in processability adhesion after coating, characterized in that burning