JPH09176866A - Chromated plated steel sheet excellent in coating material adhesion and corrosion resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a chromated plated steel sheet with the adhesion to an overcoat and corrosion resistance remarkably improved. SOLUTION: This chromated plated steel sheet has a chromated coating film with the coating weight per side controlled to 10-50mg/m<2> , expressed in terms of metallic chromium, on at least one side of a galvanized steel sheet, the atomic ratio of the colloidal silica content Si/(Si+Cr+Zn+P) in the outermost layer is controlled to >=0.5, further the atomic ratio of the phosphorus content P/(Si+Cr+Zn+P) in the outermost surface is preferably controlled to 0.05-0.10, and this chromated plated steel sheet is excellent in coating material adhesion and corrosion resistance.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a chromate-treated plated steel sheet excellent in paint adhesion and corrosion resistance and a method for producing the same, and in particular, a surface treatment layer effective for further improving the adhesion and corrosion resistance with a topcoat paint. It is an improvement proposal regarding the structure of the chromate-treated coating as the above.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets are used for home electric appliances and the like as they are without being resin-coated, or they are used for home electric appliances and the like after resin coating. Therefore, in order to adapt to various uses, the zinc-based plated steel sheet needs a surface treatment that has corrosion resistance as the final rust preventive and adhesion to the topcoat paint (hereinafter referred to as "paint adhesion"). Become.

On the other hand, coating type chromate treatment has been widely used as a simple surface treatment technique for improving the corrosion resistance and coating adhesion of zinc-based plated steel sheets. In this coating type chromate treatment, a chromate treatment liquid consisting of an aqueous solution containing hexavalent chromium and trivalent chromium is applied to the surface of a galvanized steel sheet, and the obtained coating film is dried in a furnace to form a chromate treatment film. Surface treatment.

As a technique for improving such a coating type chromate treatment, a technique for adding various chemicals to a chromate treatment liquid has been proposed so far in order to improve the corrosion resistance and the adhesion of paint or control the color tone. For example,. JP-A-64-56878 discloses a chromate-treated steel sheet containing a silane coupling agent in the presence of a silicofluoride in order to obtain a chromate-treated steel sheet having excellent primary and secondary adhesion with a paint. A technique of applying the liquid to the surface of the steel sheet has been proposed. However, since the chromate treatment liquid according to the above proposal contains a fluoride, there is a problem that the stability of the treatment liquid is poor.

[0005] In JP-A-63-307281, the particle size is
Aqueous colloidal silica with a relatively large diameter of 40 to 100 μm,
A technique has been proposed in which the chromate film is preferably compounded in an amount of 0.2 to 5 in terms of SiO ₂ / CrO ₃ weight ratio. According to this technique, the hydroxyl groups of the aqueous colloidal silica are exposed on the surface of the coating film, and it is possible to improve the primary and secondary adhesion with the coating material in a wide range of the chromium adhesion amount of 20 to 150 mg / m ^2. . It also discloses that the corrosion resistance is improved by adding H ₃ PO ₄ or the like. However, the above proposal must limit the particle size of colloidal silica to a large size.

[0006] In JP-A-2-163385, a chromate treatment liquid consisting of chromic acid, silica sol (SiO ₂ / CrO ₃ weight ratio of 1/2 to 2), phosphoric acid and polyacrylic acid is applied to the surface of a zinc-based plated steel sheet. Then, the C / Si atomic% ratio of the outermost surface layer of the chromate film is adjusted to 8 to 8 by drying.
Chromated steel sheets controlled to 40 have been proposed. According to this technique, it is possible to stabilize the primary adhesion to the coating material and the corrosion resistance within the range of the chromium deposition amount of 20 to 60 mg / m ² . However, the chromate treatment liquid according to the above proposal has a problem that the liquid life is short because it contains polyacrylic acid having a high molecular weight. Moreover, the above proposal does not consider secondary adhesion.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, the particle size of colloidal silica is not limited to a large diameter, and the addition of a fluoride or polyacrylic acid which adversely affects the stability of the chromate treatment liquid. No, it improves the corrosion resistance and paint adhesion of the chromate treated film. To propose a chromate-treated plated steel sheet excellent in primary adhesion to a coating material and corrosion resistance, and a method for producing the same. To propose a chromate-treated plated steel sheet excellent not only in primary adhesion and corrosion resistance with paint but also in secondary adhesion with paint and a method for producing the same. It is an object of the present invention to propose a method for advantageously producing the chromate-treated plated steel sheet described in and above.

[0008]

[Means for Solving the Problems] In order to achieve the above-mentioned objects, the inventors have conducted earnest research on the relationship between the structure of a coating type chromate-treated coating containing colloidal silica and the adhesiveness of a coating. as a result, . Increasing the content of colloidal silica in the chromate treatment liquid, and reducing the amount of adhesion of the treated coating, the chromate-treated coating obtained, regardless of the particle size of the colloidal silica, colloidal silica in the coating segregated to the surface side, Shows excellent paint adhesion (primary adhesion) and corrosion resistance. Furthermore, in addition to the colloidal silica content in the outermost layer of the coating, the chromate-treated coating has a corrosion resistance and a primary adhesion to the coating as well as a secondary adhesion to the coating if the phosphorus content is limited to a predetermined range. It was found that it is also excellent in, and came to complete the present invention.

That is, the present invention has (1) a chromate-treated coating having an adhesion amount of 10 to 50 mg / m ² in terms of metal chromium on one surface of at least one surface of a zinc-based plated steel sheet. The colloidal silica content in the outermost layer of the treated film is the atomic ratio Si / (Si + Cr + Zn + P)
A chromate-treated plated steel sheet excellent in paint adhesion and corrosion resistance, which is characterized by being 0.5 or more (first invention).
(2) On at least one surface of the zinc-based plated steel sheet, a chromate-treated coating having an adhesion amount in terms of metallic chromium of 10 to 50 mg / m ² per one surface is provided, and colloidal silica in the outermost layer portion of the chromate-treated coating. Content is Si / (Si + Cr +
The atomic ratio of (Zn + P) is 0.5 or more, and the phosphorus content in the outermost layer is P / (Si + Cr + Zn + P) in the atomic ratio of 0.
It is a chromate-treated plated steel sheet excellent in paint adhesion and corrosion resistance, characterized by having a value of 05 to 0.10. (2nd invention).

Then, as a method for producing the chromate-treated plated steel sheet according to (1) above, (3) at least one surface of the zinc-based plated steel sheet, colloidal silica having a SiO ₂ / Cr ratio of 3 to 5 and H 2 are used. Chromium reduction rate [Cr ³⁺ / (Cr ³⁺ + Cr ⁶⁺ ) × 100%] containing 0.1 to 0.5 phosphoric acid in ₃ PO ₄ / Cr ratio
Chromate treatment liquid, which is an aqueous solution of partially reduced chromic acid of 60% or less, has an adhesion amount in terms of metallic chromium of 10 to 10 per side.
It is applied at 50 mg / m ² and the resulting chromate film is dried within the reach plate temperature range of 80 to 200 ° C.
A method for manufacturing a chromate-treated plated steel sheet is proposed.
Further, as a method for producing the chromate-treated plated steel sheet according to (2), (4) colloidal silica having a SiO ₂ / Cr ratio of 3 to 5 on at least one surface of the zinc-based plated steel sheet.
A partially reduced chromic acid aqueous solution containing 30 to 60% of chromium reduction rate [Cr ³⁺ / (Cr ³⁺ + Cr ⁶⁺ ) × 100%] containing phosphoric acid with H ₃ PO ₄ / Cr ratio of 0.3 to 0.5 , The chromate treatment liquid was applied so that the amount of adhesion in terms of metallic chromium was 30 to 50 mg / m ² per side, and the obtained chromate treatment film was reached
We propose a method for producing chromate-treated plated steel sheets by drying in the range of 80-150 ° C.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The chromate-treated plated steel sheet of the first invention according to the present invention is characterized in that it has a chromate-treated coating film having a high colloidal silica content in the coating surface layer portion on at least one surface of the zinc-based plated steel sheet. The steel sheet is obtained by increasing the content of colloidal silica in the chromate-treating liquid when chromate-treating the zinc-based plated steel sheet, and particularly by limiting the amount of the treated coating adhered to a predetermined range. With this,
The amount of hexavalent chromium in the coating and in the outermost layer of the coating is also controlled at the same time. That is, the chromate-treated coating constituting the chromate-treated plated steel sheet of the first invention is a poorly soluble coating in which hexavalent chromium reacts with the base zinc and incorporates a part of colloidal silica at the interface with the plated steel substrate. On the surface side, a film is formed in which most of the colloidal silica is uniformly concentrated. As a result, according to the first aspect of the present invention, it is possible to provide a chromate-treated plated steel sheet that is excellent in both primary adhesion to a coating material and corrosion resistance.

[0012] The chromate-treated plated steel sheet of the second invention according to the present invention is characterized in that at least one surface of the zinc-based plated steel sheet has a chromate-treated coating in which both the colloidal silica content and the phosphorus content in the surface layer of the coating are limited. Yes, these chromate-treated plated steel sheets are used for chromating zinc-based plated steel sheets.
It can be obtained by limiting the chromate treatment condition in the first invention to a narrower range. That is, in the chromate-treated coating film that constitutes the chromate-treated plated steel sheet of the second invention, hexavalent chromium reacts with the zinc base material at a part of the colloidal coating at the interface with the plated steel sheet base material, as in the first invention. Form a poorly soluble film incorporating silica,
On the surface side, most of the colloidal silica is uniformly thickened to form a film. Particularly, in the chromate-treated coating according to the second aspect of the invention, part of phosphorus is segregated on the surface side of the coating. As a result, according to the second aspect of the present invention, it is possible to provide a chromate-treated plated steel sheet which is excellent in both primary and secondary adhesion with a coating material and corrosion resistance.

Each structure of the present invention will be described in detail below. (1) Chromium reduction rate of chromate treatment liquid. Chromium reduction rate of chromate treatment liquid in the first invention
Cr3 ⁺ / ( ^Cr3 ++ ^Cr6 +) x 100% is 60% or less. The reason for this is that when the chromium reduction rate exceeds 60%, hexavalent chromium, which plays an important role in corrosion resistance, is insufficient and the corrosion resistance of the chromate-treated coating deteriorates. Further, the chromate treatment liquid thickens to deteriorate the coatability (control of the coating amount, etc.), and the quality deterioration easily occurs due to the poor appearance of the chromate treatment film. . Chromium reduction rate of chromate treatment liquid in the second invention
Cr3 ⁺ / ( ^Cr3 ++ ^Cr6 +) x 100% is within the range of 30 to 60%. The reason for this is that if the chromium reduction rate is less than 30%, the ratio of hexavalent chromium in the outermost surface layer of the chromate-treated coating becomes high, and the secondary adhesion with the paint deteriorates. On the other hand, when the chromium reduction rate exceeds 60%, for the same reason as above,
This is because the corrosion resistance is deteriorated and the quality is apt to be deteriorated due to the poor appearance.

(2) Concentration of Colloidal Silica in Chromate Treatment Solution By causing the colloidal silica to be segregated on the surface layer of the chromate treatment film, the colloidal silica in the chromate treatment solution can be exhibited in order to exhibit excellent adhesion with the coating material. Controlling the concentration is important. The colloidal silica concentration in the present invention is 3 to 5 in terms of SiO ₂ / Cr ratio in both the first invention and the second invention. The reason for this is that if the colloidal silica concentration is less than 3 in terms of SiO ₂ / Cr ratio, the content of colloidal silica in the surface layer of the coating after drying will be small, and excellent adhesion with the coating cannot be obtained. On the other hand, if the colloidal silica concentration is greater than 5 in SiO ₂ / Cr, the viscosity of the chromate treatment liquid increases and it becomes difficult to control the coating amount.
This is because the deterioration of the quality of the film due to the poor appearance of the film is likely to occur.

(3) Concentration of phosphoric acid in the chromate treatment liquid. The phosphoric acid concentration in the chromate treatment liquid in the first invention is in the range of 0.1 to 0.5 in terms of H ₃ PO ₄ / Cr ratio. The reason for this is that if the phosphoric acid concentration is less than 0.1 in the H ₃ PO ₄ / Cr ratio, the wettability of the chromate treatment liquid with the plated steel sheet is insufficient and it is difficult to obtain a uniform treated film, especially when the chromium deposition amount is small. Corrosion resistance deteriorates. On the other hand, if the phosphoric acid concentration is H ₃ P
This is because if the O ₄ / Cr ratio exceeds 0.5, the amount of phosphorus segregated in the outermost layer of the treated film increases, the ratio of colloidal silica decreases, and the adhesion to the coating decreases. This tendency is particularly remarkable when the chromium reduction rate is low and the chromium deposition amount (coating deposition amount) is large. . In the second invention, by segregating phosphorus on the surface layer of the chromate-treated film, in order to exhibit excellent secondary adhesion with the coating material, the phosphoric acid concentration in the chromate-treated liquid is set to be higher than that in the first invention. Needs to be further restricted. That is, the phosphoric acid concentration in the chromate treatment liquid in the second aspect of the invention is in the range of 0.3 to 0.5 in terms of H ₃ PO ₄ / Cr ratio. The reason for this is that the phosphoric acid concentration is 0.3 in the H ₃ PO ₄ / Cr ratio.
When it is less than the above, the phosphorus content in the surface layer portion of the chromate-treated coating after drying becomes small, and although the corrosion resistance and the primary adhesion to the coating are excellent, the secondary adhesion to the coating becomes insufficient. On the other hand, when the concentration of phosphoric acid exceeds 0.5 in H ₃ PO ₄ / Cr ratio, the amount of phosphorus segregated in the outermost layer of the treated film increases and the ratio of colloidal silica decreases, resulting in a decrease in the primary adhesion to the coating. This is because the secondary adhesiveness is also lowered.

(4) Coating amount of chromate treatment liquid (amount of chromate treatment coating adhered). The coating amount of the chromate treatment liquid in the first invention is such that the amount of adhesion of the chromate treatment coating in terms of metallic chromium is 10 to 50.
mg / m ^2, preferably adjusted to be 20-40 mg / m ^2. The reason for this is that the amount of colloidal silica and chrome required to maintain the primary adhesion and corrosion resistance with the paint is such that the amount of chromium chromate coating deposited in terms of metallic chromium is less than 10 mg / m ^2. Therefore, a treated coating film containing Pd cannot be obtained, and both the primary adhesion with the coating material and the corrosion resistance deteriorate. On the other hand, the amount of adhesion of the chromate-treated film in terms of metallic chromium is
With a coating amount of more than 50 mg / m ² , excellent corrosion resistance is obtained, but hexavalent chromium appears in large amounts on the surface layer of the coating, resulting in insufficient coating adhesion. Moreover, in order to obtain a chromium deposition amount of more than 50 mg / m ² , it is necessary to increase the viscosity of the treatment liquid, which easily causes quality deterioration due to non-uniform appearance. . The coating amount of the chromate treatment liquid in the second invention is such that the amount of adhesion of the chromate treatment coating in terms of metallic chromium is 30 to 50.
Adjust to be mg / m ² . The reason for this is that when the coating amount of the chromate-treated coating in terms of metallic chromium is less than 30 mg / m ^2, the phosphorus content in the surface layer portion of the chromate-treated coating after drying is small, and it is The next adhesion is poor. On the other hand, when the coating amount of the chromate-treated coating in terms of metal chromium exceeds 50 mg / m ² , excellent corrosion resistance is obtained, but the ratio of chromium and phosphorus in the coating surface layer becomes high and the ratio of colloidal silica Deteriorates, the primary adhesiveness with the coating material decreases, and the secondary adhesiveness also decreases. Moreover, as in the first aspect of the invention, deterioration in quality is likely to occur due to non-uniformity in appearance.

(5) Drying temperature of chromate-treated coating. In the first invention, the drying temperature of the chromate-treated coating is an important control item for influencing the redox reaction between hexavalent chromium and the base zinc and the dehydration condensation reaction of the treated coating, and obtaining the above-mentioned coating characteristics. , The ultimate plate temperature is 80 to 200 ℃
Adjust within the range of. The reason for this is that when the drying temperature is less than 80 ° C. as the ultimate plate temperature, the redox reaction between the hexavalent chromium in the applied treatment liquid and the zinc base does not proceed sufficiently, so the 6 The ratio of valent chromium becomes high, and especially when the coating amount is increased, the primary adhesion is deteriorated. On the other hand, when the drying temperature is higher than 200 ° C, the redox reaction between hexavalent chromium and the base zinc and the dehydration condensation reaction of the treated coating proceed together, especially when the coating adhesion is reduced, the corrosion resistance deteriorates. Is. When a chromate-treated coating with a small amount of coating film and a high chromium reduction rate is dried, it is more desirable that the drying temperature is within the range of 80 to 150 ° C in the ultimate plate temperature, and the amount of coating film deposition is large. When the chromate-treated coating having a low chromium reduction rate is dried, the drying temperature is more preferably within the range of 120 to 200 ° C. as the ultimate plate temperature. . In the second aspect of the invention, the drying temperature of the chromate-treated coating affects the reaction between phosphoric acid and the base zinc and the degree of concentration of phosphorus in the coating surface layer. Therefore, it is an important control item for obtaining the coating structure described above. Adjust the ultimate plate temperature within the range of 80 to 150 ° C. The reason is that the drying temperature depends on the plate temperature
If the temperature is less than 80 ° C, the redox reaction between the hexavalent chromium in the applied treatment liquid and the base zinc does not proceed sufficiently, so the ratio of hexavalent chromium in the outermost layer of the treated film becomes high and the secondary adhesion Becomes worse. On the other hand, the drying temperature is 150
This is because if the temperature exceeds ℃, the phosphorus content in the outermost layer of the treated film becomes low and the secondary adhesiveness deteriorates.

(6) Colloidal Silica Content in the Outermost Layer of Chromate-treated Coating The colloidal silica content in the present invention is the atomic ratio of Si / (Si + Cr + Zn + P) in both the first invention and the second invention. Set to 0.5 or more. The reason is that the content of colloidal silica in the outermost layer of the chromate-treated coating is Si /
When the atomic ratio of (Si + Cr + Zn + P) is less than 0.5, the amount of hydroxyl groups on the outermost surface of colloidal silica that contributes to the adhesion is insufficient,
This is because the primary adhesion is poor.

(7) Phosphorus content in the outermost layer of the chromate-treated coating The phosphorus content in the second invention is P / (Si + Cr + Zn +
The atomic ratio of P) is 0.05 to 0.10. The reason for this is that the phosphorus content in the outermost layer of the chromate-treated coating is P / (Si
This is because if the atomic ratio of + Cr + Zn + P) is less than 0.05, the amount of phosphorus compound that contributes to the secondary adhesion will be insufficient and the secondary adhesion will deteriorate. On the other hand, the phosphorus content in the outermost layer of the chromate-treated coating is 0.10 in terms of the atomic ratio P / (Si + Cr + Zn + P).
This is because when the content exceeds the above value, the amount of the phosphorus compound, which becomes another compound of phosphoric acid and contributes to the secondary adhesion, becomes insufficient and the secondary adhesion is deteriorated.

[0020]

EXAMPLES The present invention will be specifically described below based on examples. (1) Both sides of 0.8mm thick low carbon steel plate are galvanized in a high productivity continuous plating line according to the known electrogalvanizing method, and the zinc adhesion amount is about 20g / m ² per side.
A galvanized steel sheet was obtained. Then, the obtained galvanized steel sheet is immediately immersed in a chromate treatment liquid, and then the chromate treatment liquid is applied while controlling the coating amount by a roll squeeze, and then the applied chromate treatment film is dried in an oven. By doing so, the chromate-treated steel sheets according to the first invention, the second invention and the respective comparative examples were obtained. Table 1 to Table 6 show the component composition of the chromate treatment liquid and the chromate treatment conditions at this time. The coating method is not particularly limited, such as spraying or coating with a roll coater, in addition to dipping. Further, the coating amount control method is not particularly limited, and a method using an air knife other than a method using a roll squeeze. In this embodiment, ST-O manufactured by Nissan Chemical Industries (particle size 10 to 20 nm) was used as the colloidal silica, but the particle size and shape are not particularly limited. (2) From the chromate treated steel plate thus obtained,
A 00 mm x 200 mm test plate was cut out and the primary adhesion, secondary adhesion, corrosion resistance and appearance were evaluated.

The results of performance evaluation of the chromate-treated steel sheet according to the first aspect of the present invention are shown in Tables 1 and 2 as comparative examples.
Table 3 shows the performance evaluation of the chromate-treated steel plate that deviates from the applicable range of the present invention. Tables 4 and 5 show the performance evaluation results of the chromate-treated steel sheet according to the second invention of the present invention, and Table 6 shows the performance evaluation of the chromate-treated steel sheet that deviates from the scope of the present invention as a comparative example. The ratio of constituent atoms in the outermost layer of the chromate-treated coating was measured by XPS.
(X-ray photoelectron spectroscopy).

[Paint Adhesion] An alkyd melamine resin manufactured by Nippon Paint Co., Ltd. was used, and this resin was applied to the surface of the test plate.
It was applied to a thickness of 20 to 25 μm and dried at 130 ° C. for 15 minutes to obtain a test material. The primary adhesion with the paint is a 1 mm square cross cut that reaches the base zinc on the surface of the coating film of the sample material.
After 100 pieces were put in and extruded by 7 mm with Erichsen, a tape peeling test was performed and evaluated, and the residual rate of the coating film at this time was used as an index of primary adhesion. The secondary adhesion with the coating material was evaluated by immersing the above-mentioned test material in boiling water for 2 hours, and immediately after inserting the above-mentioned cross-cut, the same test as the above-mentioned primary adhesion. The evaluation points are 5 when the coating film residual rate is 95% or more,
Less than 95% to 80% or more 4, 4, less than 80% to 60% or more 3, 60
Less than 40% to 40% or more 2, less than 40% to 20% or more 1, 20%
The value less than 0 was set as 0, and the evaluation points of 4 or more were defined as the coating adhesion level in the present invention.

[Corrosion resistance] The corrosion resistance in Table 1, Table 2 and Table 3 was 5 after a salt spray test according to JIS Z2371.
% Of white rust was evaluated, and 168 hours or more was defined as the level of corrosion resistance in the present invention (first invention).
The corrosion resistance in Table 4, Table 5 and Table 6 was evaluated by the white rust generation rate after continuing the salt spray test according to JIS Z2371 for 168 hours. In the evaluation, ⊚ indicates that white rust did not occur, ∘ indicates that the white rust occurrence area was 5 to 15%, x indicates that white rust occurred on the entire surface, and Δ indicates the others.

[Appearance] The uniformity of the coating film was visually evaluated on a scale of 5 to 4, and 4 or more was defined as the appearance level in the present invention.

From the results shown in Table 1, Table 2 and Table 3, it becomes clear that the above-mentioned embodiment according to the first invention will be described below. (1) Chromium Reduction Ratio of Chromate Treatment Liquid It was found that the chromate treatment steel plate exhibits excellent primary adhesion with a coating material and good corrosion resistance when the chromium reduction ratio of the chromate treatment liquid is within the range of application of the present invention. . On the contrary,
It has been found that when the chromium reduction rate is higher than the applicable range of the present invention, the primary adhesion to the coating is excellent, but the corrosion resistance and the uniformity (appearance) of the coating film are deteriorated (see Comparative Example 1).

(2) Concentration of Colloidal Silica in Chromate Treatment Solution When the concentration of colloidal silica in the chromate treatment solution is within the scope of the present invention, the chromate-treated steel sheet has good primary adhesion to coating material and good corrosion resistance. It was On the other hand, if the colloidal silica concentration is less than the applicable range of the present invention, the primary adhesion with the coating is insufficient, while if the colloidal silica concentration exceeds the applicable range of the present invention, the appearance becomes poor ( See Comparative Example 2).

(3) Concentration of Phosphoric Acid in Chromate Treatment Solution When the concentration of phosphoric acid in the chromate treatment solution is within the range of application of the present invention, the chromate-treated steel sheet has excellent primary adhesion with coating material and good corrosion resistance. It turned out to show. On the contrary,
If the phosphoric acid concentration is less than the applicable range of the present invention, the primary adhesion with the coating is excellent, but the corrosion resistance is deteriorated, while if the phosphoric acid concentration exceeds the applicable range of the present invention, on the contrary, it is a coating with excellent corrosion resistance. It was found that the primary adhesion of No. 1 was deteriorated (see Comparative Example 3).

(4) Amount of Chromate Treatment Liquid (Amount of Chromate Treatment Film Adhesion) When the amount of chromate treatment liquid is within the applicable range of the present invention in terms of the amount of chromium chromate treatment film adhered in terms of metallic chromium. It has been found that the chromate-treated steel sheet exhibits excellent primary adhesion with a coating material and good corrosion resistance. On the other hand, if the application range of the present invention is not satisfied, both the primary adhesion and the corrosion resistance with the coating material deteriorate, while if the application range of the present invention is exceeded,
It was found that although the corrosion resistance was excellent, the primary adhesion with the paint and the uniformity (appearance) of the coating film were deteriorated (see Comparative Example 4).

(5) Drying Temperature of Chromate-treated Film When the drying temperature of the chromate-treated film is the ultimate plate temperature within the applicable range of the present invention, the chromate-treated steel sheet has excellent primary adhesion with coating material and good corrosion resistance. It turned out to show. On the other hand, if the drying temperature is the ultimate plate temperature and does not fall within the applicable range of the present invention, the primary adhesiveness with the coating becomes poor, while if the drying temperature exceeds the applicable range of the present invention, the primary adhesiveness with the coating becomes poor. Was excellent, but the corrosion resistance was found to deteriorate (see Comparative Example 5).

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

From the results shown in Table 4, Table 5 and Table 6, it became clear that the above-mentioned embodiment according to the second invention is described below. (1) Chromium reduction rate of chromate treatment liquid Chromium reduction rate of chromate treatment liquid is within the range of application of the present invention, chromate treated steel sheet shows excellent primary and secondary adhesion with coating material and good corrosion resistance. I understood. On the other hand, when the chromium reduction rate is lower than the application range of the present invention, the secondary adhesion with the coating is poor, while when it is higher than the application range of the present invention, the corrosion resistance and the uniformity of the coating film (appearance) Was found to be poor (see Comparative Example 1).

(2) Concentration of Colloidal Silica in Chromate Treatment Solution If the concentration of colloidal silica in the chromate treatment solution is within the range of application of the present invention, the chromate treated steel sheet has primary and secondary adhesion with the coating and corrosion resistance. Was also good. On the other hand, if the colloidal silica concentration is less than the applicable range of the present invention, both primary and secondary adhesion with the coating is poor, while if the colloidal silica concentration exceeds the applicable range of the present invention, the appearance becomes poor. (See Comparative Example 2).

(3) Concentration of Phosphoric Acid in Chromate Treatment Solution When the concentration of phosphoric acid in the chromate treatment solution is within the range of application of the present invention, the chromate-treated steel sheet has excellent primary and secondary adhesion with the coating material. It was found that it exhibited excellent corrosion resistance. On the other hand, if the phosphoric acid concentration is less than the applicable range of the present invention, the primary adhesiveness and corrosion resistance with the paint are excellent, but the secondary adhesiveness with the paint is poor, while the phosphoric acid concentration is within the applicable range of the present invention. It was found that when the value exceeds 1.0, the primary and secondary adhesion with the paint is deteriorated although the corrosion resistance is excellent (see Comparative Example 3).

(4) Amount of Chromate Treatment Liquid (Amount of Chromate Treatment Film Adhesion) When the amount of the chromate treatment liquid is within the applicable range of the present invention as the amount of chromium chromate treatment film attached in terms of metallic chromium. It has been found that the chromate-treated steel sheet exhibits excellent primary and secondary adhesion with a coating material and good corrosion resistance. On the other hand, if the application range of the present invention is not satisfied, the secondary adhesion with the coating is poor, while if it exceeds the application range of the present invention, the corrosion resistance is excellent but the primary and secondary adhesion and the coating with the coating are excellent. It was found that the uniformity (appearance) of the film deteriorates (see Comparative Example 4).

(5) Drying Temperature of Chromate-treated Film The drying temperature of the chromate-treated film is the ultimate plate temperature, and within the scope of the present invention, the chromate-treated steel sheet has both primary and secondary adhesion with the coating and corrosion resistance. Was also good. On the other hand, it has been found that when the drying temperature is the ultimate plate temperature and deviates from the applicable range of the present invention, the secondary adhesiveness with the paint is deteriorated (see Comparative Example 5).

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

As described above, according to the first aspect of the present invention, it is possible to provide a chromate-treated steel sheet which is excellent in primary adhesion to a coating material and corrosion resistance. Further, the second aspect of the present invention
According to the invention, it is possible to provide a chromate-treated steel sheet which is excellent not only in the primary adhesion and the corrosion resistance with the paint but also with the secondary adhesion with the paint. Regarding these points, ESCA
The following can be considered from the analysis results such as (electron spectroscopy for chemical analysis) and GDS (glow discharge emission spectroscopy).

That is, when the chromate treatment is carried out under the constitution and treatment conditions of the chromate treatment liquid according to the present invention, most of the colloidal silica in the chromate-treated coating segregates on the surface layer side of the coating, and hexavalent chromium and the base zinc are added. And the trivalent chromium ratio in the outermost layer of the coating increases. As a result, in the obtained chromate-treated steel sheet, the hydroxyl groups on the outermost surface that contribute to the adhesion are increased and the primary adhesion is improved, while hexavalent chromium required for corrosion resistance remains moderately in the film. Shows excellent corrosion resistance. However, when the drying temperature of the chromate-treated coating is too low, a soft coating having a high hexavalent chromium ratio in the coating and in the outermost surface layer portion is formed, and when the chromium deposition amount is too large, in the coating and in the outermost surface portion. Since the chromium ratio, especially the hexavalent chromium ratio becomes high, the corrosion resistance is excellent in any case, but the primary adhesion with the coating is deteriorated. On the other hand, if the drying temperature of the chromate-treated coating is too high, the oxidation-reduction reaction between hexavalent chromium and the base zinc or the dehydration condensation reaction of trivalent chromium or silica proceeds too much, and the corrosion resistance deteriorates.

Further, when the phosphorus content and the silica content in the outermost layer of the coating are limited to specific ranges in the constitution and processing conditions of the chromate treatment liquid according to the present invention, not only the primary adhesion to the paint but also the secondary adhesion Adhesion is improved. Although the reason for this improvement in secondary adhesion is not clear, phosphoric acid exists in two forms: reaction with the base zinc and segregation on the surface of the coating, and the abundance ratio of these greatly changes depending on the treatment conditions. Therefore, it is considered that the characteristics of the coating change greatly accordingly. Therefore, if the treatment conditions of the present invention are limited, the phosphorus content and the silica content in the outermost layer of the coating can be controlled within a specific range, and the secondary adhesion is improved. For example, if the addition amount of phosphoric acid is too large, it is considered that the coating adhesion is deteriorated because the colloidal silica on the coating surface that contributes to the adhesion is covered with phosphorus.

Regarding the relationship between the addition of phosphoric acid and the corrosion resistance in the present invention, it is considered that excellent corrosion resistance can be obtained by improving the wettability of the chromate treatment solution with phosphoric acid and by uniformly etching the base zinc.

The reason why the chromate-treated coating of the present invention containing colloidal silica has improved corrosion resistance in the salt spray test is considered to be that corrosion products having low conductivity are formed in the initial stage of the test.

[0046]

As described above, according to the present invention, the particle size of colloidal silica is not limited to a large diameter, and the addition of fluoride or polyacrylic acid which adversely affects the stability of the chromate treatment liquid. It is possible to provide a chromate-treated steel sheet in which the corrosion resistance of the chromate-treated coating and the paint adhesion are further improved without performing

Front Page Continuation (72) Inventor Hideo Ohgishi, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Pref., Technical Research Laboratory, Kawasaki Steel Co., Ltd. (72) Yoshihiro Naruse 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Kawasaki Steel Technical Research Institute Co., Ltd.

Claims (4)

[Claims] 1. The amount of adhered metal chromium on at least one side of a zinc-based plated steel sheet is 10 to 50 mg / side.
m ² having a chromate-treated coating, and the content of colloidal silica in the outermost layer of the chromate-treated coating is Si /
A chromate-treated plated steel sheet with excellent paint adhesion and corrosion resistance, characterized by an atomic ratio of (Si + Cr + Zn + P) of 0.5 or more. 2. The amount of adhered metal chromium on at least one side of the zinc-based plated steel sheet is 10 to 50 mg / side.
m ² having a chromate-treated coating, and the content of colloidal silica in the outermost layer of the chromate-treated coating is Si /
Chromate treatment with excellent paint adhesion and corrosion resistance, characterized in that the atomic ratio of (Si + Cr + Zn + P) is 0.5 or more and the phosphorus content in the outermost layer is P / (Si + Cr + Zn + P) atomic ratio of 0.05-0.10. Plated steel sheet. 3. A chromium reduction rate containing colloidal silica having an SiO ₂ / Cr ratio of 3 to 5 and phosphoric acid having an H ₃ PO ₄ / Cr ratio of 0.1 to 0.5 on at least one surface of a zinc-based plated steel sheet. Cr ³⁺ /
(Cr ³⁺ + Cr ⁶⁺ ) × 100%] is a partially reduced chromic acid aqueous solution of 60% or less, so that the amount of adhesion in terms of metallic chromium is 10 to 50 mg / m ² The chromate-treated plated steel sheet according to claim 1 is produced by applying and drying the obtained chromate-treated film within a range of an ultimate plate temperature of 80 to 200 ° C. An excellent method for producing chromate-treated plated steel sheets. 4. A chromium reduction rate containing colloidal silica having an SiO ₂ / Cr ratio of 3 to 5 and phosphoric acid having an H ₃ PO ₄ / Cr ratio of 0.3 to 0.5 on at least one surface of a zinc-based plated steel sheet. Cr ³⁺ /
(Cr ³⁺ + Cr ⁶⁺ ) × 100%] is a partially reduced chromic acid aqueous solution of 30 to 60%, so that the chromate treatment liquid has an adhesion amount in terms of metallic chromium of 30 to 50 mg / m ² per side. The chromate-treated plated steel sheet according to claim 2 is manufactured by drying the obtained chromate-treated coating film in an ultimate temperature range of 80 to 150 ° C. to obtain coating adhesion and corrosion resistance. An excellent method for producing chromate-treated plated steel sheets.