JP3279209B2 - Manufacturing method of surface treated steel sheet with excellent paint adhesion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a zinc phosphate treatment.
Surface-treated steel sheets based on galvanized steel sheets that can form a coating film with excellent coating adhesion even when painted without performing (bonding treatment), and at the same time have good corrosion resistance and can be used even when unpainted. It relates to a method of manufacturing.

[0002]

2. Description of the Related Art From the viewpoint of cost reduction by rationalizing the manufacturing process, there has been demand for coating adhesion and corrosion resistance without zinc phosphate treatment for surface-treated steel sheets using zinc-based plated steel sheets as a base material. And so on. There is also an increasing need to consider naked (unpainted) use as well as painting applications. This is because, when the coating material and the bare material are used separately, at least two types of surface-treated steel sheets must be kept in stock, which tends to increase the stock, which is disadvantageous in terms of cost.

Accordingly, it is desirable that one type of surface-treated steel sheet can be used for both painted and unpainted applications. For that purpose, the surface-treated steel sheet is required to have excellent coating adhesion even when coated without performing the zinc phosphate treatment, and to have sufficiently high corrosion resistance without coating. As a surface-treated steel sheet that can satisfy such demands, a chromate-treated plated steel sheet obtained by chromating a zinc-based plated steel sheet is considered, and various chromate-treated plated steel sheets have been proposed so far.

For example, JP-A-2-163385 and JP-A-4-9477
And JP-A-4-9478 relate to a chromate-plated steel material having excellent paint adhesion and corrosion resistance. However, the surface-treated steel sheets described in each of these publications do not contain a fluorine compound, have insufficient corrosion resistance, and have poor paint adhesion in a wet environment.

[0005] In the case of home appliances,
(E.g., outdoor units for air conditioners) or those used near humid bathrooms (e.g., washing machines) .Coating adhesion in a humid environment is essential due to the high temperature and high humidity in Japan in the summer. It is the characteristic of. Without this property, rust is likely to occur due to swelling and peeling of the coating film during use in a humid environment.

JP-A-64-56878 discloses Cr ³⁺ / all Cr
It is disclosed that a chromate-treated plated steel sheet having excellent coatability is manufactured using a chromate-treatment solution partially reduced to satisfy ≧ 0.3. However, when the obtained surface-treated steel sheet is left in a humid environment after coating, Cr ⁶⁺ is strongly eluted, and it may be difficult to secure coating adhesion. This publication also describes that the coating adhesion is ensured by the addition of a silane coupling agent, but the silane coupling agent is simply added to the silane coupling agent when left in a wet environment after coating. Water molecules are adsorbed to the polar functional groups of the coupling agent, and inhibit the hydrogen bond between the silane coupling agent and the paint, which contribute to the paint adhesion of the chromate film, so that the paint adhesion is reduced.

[0007] JP-A-63-171685 discloses that Cr ³⁺ / total Cr
A corrosion-resistant white chromate treatment method using a chromate treatment solution of 0.1 to 0.7 is disclosed. However, this method does not always provide sufficiently high coating adhesion in a wet environment. In addition, the chromate treatment solution used is Mg ²⁺ , C
a ²⁺ , Sr ²⁺ , Ba ²⁺ , Al ³⁺ , Zn ²⁺ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Sn
^Although containing one or more of ²⁺ , these metal ions are substituted for Zn by local cell reaction with Zn when applied to a zinc-based plated steel sheet and preferentially precipitate on the steel sheet. for that reason,
The consumption rate of the metal ions is higher than the consumption rate of the chromate solution, so that it is difficult to control the bath to keep the composition of the treatment solution constant, and the composition of the chromate film (therefore, its characteristics) tends to fluctuate. In addition, alkaline earth metal ions such as Ca ²⁺ , Ba ²⁺ , and Sr ²⁺ hinder the etching of zinc, which hinders the adhesion of the chromate film to the plating surface, and as a result, the corrosion resistance and the water-resistant secondary coating adhesion. The consequences are disturbing.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for producing a surface-treated steel sheet in which the drawbacks of the conventional chromate-coated steel sheet have been eliminated. Specifically, it can be painted without zinc phosphate treatment, has excellent paint adhesion that can maintain paint adhesion for a long time even if left in a wet environment after painting, An object of the present invention is to provide a method for producing a surface-treated steel sheet made of a chromate-treated galvanized steel sheet, which exhibits good corrosion resistance that can withstand use in (painting).

[0009]

Means for Solving the Problems The present inventors have repeated studies focusing on the fact that the unreacted reducing agent remaining in the chromate treatment liquid has the ability to reduce Cr ⁶⁺ even after the formation of a chromate film. . As a result, if ethylene glycol is used as the reducing agent and unreacted ethylene glycol remains in the chromate film to some extent, the Cr ⁶⁺ content in the film is reduced by reduction after the formation of the chromate film, Therefore, it has been found that a chromate film having excellent paint adhesion and corrosion resistance can be obtained, and the above-mentioned problems can be solved.

According to the present invention, an aqueous solution of chromic acid of 10 to 100 g / l in terms of CrO ₃ is prepared by adding an ethylene glycol / Cr weight ratio of 0.22 to 0.2.
Cr ³⁺ / total Cr = 0.4 ~
In an aqueous solution of 0.65, the weight ratio of H ₃ PO ₄ /Cr=0.45 to 1.5
Phosphoric acid and SiO ₂ / Cr weight ratio = 2-5 particle size 10-100 nm
A wet-process silica and a hexafluorosilicic acid having a H ₂ SiF ₆ / Cr weight ratio of 0.1 to 0.3,
A surface with excellent paint adhesion, characterized in that it is applied to a galvanized steel sheet and dried by heating at 40-140 ° C to form a chromate film with a Cr weight of 5-60 mg / m ² on the plating. This is a method for producing a treated steel sheet.

In a preferred embodiment, the chromate treatment liquid further comprises at least one resin selected from an acrylic aqueous emulsion resin and an acrylic styrene aqueous emulsion resin in a ratio of resin solids / Cr weight ratio of 0.5 to 5. Contained in.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A surface-treated steel sheet manufactured according to the present invention is a zinc-plated steel sheet as a base material, which is subjected to a coating type chromate treatment. When the plated steel sheet is plated on both sides, it is preferable to perform the chromate treatment on both sides, but depending on the application, only one side may be used.

The base material zinc-coated steel sheet is a general term for a zinc-coated steel sheet and a zinc alloy-coated steel sheet. The plating technique may be either electroplating or hot-dip plating. Galvanized steel sheets include electro-galvanized steel sheets, electro-zinc alloy-coated steel sheets (eg, Zn-Ni, Zn-Fe, Zn-Co, Zn-Cr, etc.), hot-dip galvanized steel sheets, hot-dip galvanized steel sheets (e.g., , Zn-Al
Etc.), as well as galvannealed steel sheets.
A multi-layer plated steel sheet having two or more plating layers can also be used as a base material, in which case the top layer may be a zinc-based plating layer. The coating weight of the galvanized steel sheet is not particularly limited, and may be the same as the conventional one.

The features of the present invention reside in the composition of the chromate treatment solution applied to the zinc-coated steel base material and the drying conditions after application. The first feature of the chromate treatment liquid used in the present invention is that a chromic acid aqueous solution having a concentration of 10 to 100 g / l in terms of CrO _{3 is} reduced with ethylene glycol in an amount of ethylene glycol / Cr weight ratio of 0.22 to 0.35. Then, Cr ³⁺ / total Cr (Cr reduction ratio) = 0.4 to 0.65.

The amount of ethylene glycol required to reduce the total amount of Cr ⁶⁺ to Cr ³⁺ is, according to the theoretical formula of the oxidation-reduction reaction,
The ethylene glycol / Cr weight ratio is 0.35. It is said that the reduction reaction of Cr ⁶⁺ with ethylene glycol is relatively slow, but immediately after the addition of Cr ⁶⁺ , the reaction progresses rapidly due to the heat generated by the reduction reaction. Thereafter, the reduction reaction becomes progressively slower, consuming up to about 65% of ethylene glycol, stopping the reaction in solution. If the ethylene glycol / Cr weight ratio is constant, the higher the chromic acid concentration in the aqueous chromic acid solution,
The reduction rate increases. This is because the higher the chromic acid concentration, the larger the amount of heat generated during the reaction and the higher the reaction temperature.

In order to ensure coating adhesion in a wet environment, it is better that the Cr ⁶⁺ content in the chromate film is small.
This is because Cr ⁶⁺ is water-soluble, and finally Cr ⁶⁺ / total Cr (Cr unreduced ratio) ≦ 0.39 (that is, Cr ³⁺ / total Cr) in the chromate film after drying. ≧ 0.61), it was found that coating adhesion in a wet environment was ensured.
Therefore, it is conceivable that the chromate treatment liquid is reduced in advance so that Cr ³⁺ / total Cr ≧ 0.61 in the solution. For example, when the above reduction reaction is carried out under heating, Cr ³⁺
/ Total Cr ≧ 0.61. However, Cr ³⁺ / all Cr
When ≧ 0.65, the stability of the chromic acid aqueous solution is rapidly deteriorated, and the gelation of the chromate treatment liquid is promoted. Therefore,
The reduction reaction is preferably performed without heating using only reaction heat.

In order to avoid the gelation and secure the coating adhesion, the Cr reduction ratio of the chromate treatment liquid must be controlled within a very narrow range of Cr ³⁺ / total Cr = 0.61 to 0.65. In view of the fact that the reduction ratio fluctuates due to slight fluctuations in the reaction conditions, it is practically impossible to control the Cr reduction ratio within such a narrow range. Therefore, in the present invention by utilizing the reduction of Cr ⁶⁺ by unreacted reducing agent remaining in the film during the after chromate film formation, finally the Cr ³⁺ content in the chromate coating Cr ³⁺ / total Cr ≧ 0.61 To ensure coating adhesion in a humid environment. In this case, the Cr reduction ratio in the chromate treatment liquid may be Cr ³⁺ / total Cr <0.61, and the control of the Cr reduction ratio becomes easy.

As described above, ethylene glycol is a relatively mild reducing agent, and the reaction stops before it is completely consumed in an aqueous chromic acid solution, so that the unreacted reducing agent remains in the film even after the film is formed. Has been captured. Therefore, the reduction reaction proceeds slowly during heating and drying after the formation of the film.
If the Cr reduction rate in the applied treatment liquid is Cr ³⁺ / total Cr ≧ 0.4, the reduction reaction after the film formation by the unreacted ethylene glycol is used to finally obtain Cr ³⁺ / total Cr. ≧ 0.61
It turns out that you can. Therefore, if the Cr reduction ratio is in the range of Cr ³⁺ / total Cr = 0.4 to 0.65, a chromate film having excellent coating adhesion in a wet environment can be formed without gelation of the chromate treatment solution. .

When the amount of ethylene glycol added is as large as ethylene glycol / Cr> 0.35, Cr decreases during reduction in a solution.
^{3 +} / total Cr> 0.65, resulting in gelation of the chromate treatment solution. On the other hand, if the amount of ethylene glycol added is as small as ethylene glycol / Cr <0.22, Cr ³⁺
/ The total Cr ≧ 0.61 cannot be achieved, and the desired coating adhesion cannot be ensured. Preferably, the ethylene glycol / Cr weight ratio is 0.24 to 0.32.

If the reducing agent is as strong as hypophosphorous acid, the reduction reaction is too fast and the reducing agent is completely consumed in the solution, so that the unreacted reducing agent is not taken into the film. No reduction reaction after film formation can be expected. On the other hand, when the reducing agent is glycerin, the reduction reaction is too slow, and it is difficult to obtain a predetermined Cr reduction rate in a chromic acid aqueous solution, and furthermore, the reduction reaction after film formation does not easily proceed.

The concentration of the aqueous chromic acid solution is 10 to 10 in terms of CrO _3.
0 g / l. If CrO ₃ <10 g / l, the calorific value at the time of reduction in an aqueous solution is too small, and reduction is difficult to occur,
It becomes difficult to reach the required minimum Cr reduction ratio of Cr ³⁺ / total Cr = 0.4. Conversely, if CrO ₃ > 100 g / l, this calorific value is too large, and the reduction reaction may proceed too much, possibly exceeding Cr ³⁺ / total Cr = 0.65. The concentration of the chromic acid aqueous solution is
Preferably, CrO ₃ is in the range of 13 to 80 g / l.

A second feature of the chromate treatment solution used in the present invention is that phosphoric acid is added within a range of H ₃ PO ₄ / Cr weight ratio = 0.45 to 1.5. Phosphoric acid has the following effects: it promotes the reduction reaction, improves the water adhesion and corrosion resistance of the coating by suppressing the elution of chromium after film formation, and forms a complex with Cr ³⁺ to form a colorless chromate treatment. For example, and the like. In order to improve paint adhesion and corrosion resistance, the addition of phosphoric acid to the chromate treatment solution is indispensable. In addition, steel sheets with noticeable coloring tend to be avoided because of poor design when used naked in home appliances, etc.
From this point, the addition of phosphoric acid is also advantageous. H ₃ PO ₄ / Cr <
When the ratio is 0.45, the coloring (yellow) of the steel sheet becomes remarkable, and the corrosion resistance and the paint adhesion cannot obtain predetermined performance. When H ₃ PO ₄ /Cr>1.5, the phosphoric acid reacts with SiO ₂ coexisting in the solution to promote gelation of the chromate treatment solution. The preferred amount of phosphoric acid is H ₃ PO ₄
/Cr=0.48-1.3.

The third feature of the chromate treatment solution used in the present invention is that the SiO ₂ / Cr weight ratio is 2 to 5 and the particle size is 10 to 10.
This is to add 0 nm wet silica (silica sol). The effects of the addition of silica include improvement in corrosion resistance, improvement in coating adhesion, colorless color tone, improvement in fingerprint resistance, and the like.
Colorlessness of color tone and improvement of fingerprint resistance are properties required when considering naked use in home appliances, and in addition to the improvement of corrosion resistance, the surface-treated steel sheet of the present invention is not only used for painting, Even naked can be used sufficiently.

If SiO ₂ / Cr <2, the above-mentioned effect of adding silica cannot be sufficiently obtained. On the other hand, SiO ₂ / Cr
When it is> 5, the gelation of the chromate treatment solution is promoted by the reaction with phosphoric acid, and when held in a wet environment after coating, water molecules are adsorbed on the silica having polarity,
Hydrogen bonding between the silica and the paint, which contributes to the coating adhesion, is inhibited, resulting in a decrease in coating adhesion. Preferred SiO ₂
The addition amount is SiO2 / Cr = _{2.5 to} 4.0.

When the fumed silica is used, the coating adhesion is improved, but the fingerprint resistance is very poor. On the other hand, when the particle size of the silica is less than 10 nm, the adsorption between the silicas becomes severe, and the gelation of the chromate treatment solution is induced. On the other hand, SiO ₂
If the particle size exceeds 100 nm, the stability of the silica in the chromate treatment solution will be degraded, causing sedimentation, and even if applied to a steel plate, a predetermined amount of SiO ₂ cannot be incorporated into the coating. The preferred silica particle size is between 10 and 80 nm.

A fourth feature of the chromate treatment liquid used in the present invention is that it contains hexafluorosilicic acid (H ₂ SiF ₆ ) in such an amount that the H ₂ SiF ₆ / Cr weight ratio becomes 0.1 to 0.3. H ₂
When SiF ₆ is added, the surface of the plating film is lightly etched, the adhesion between the chromate film and the plating film is improved, and even if the wet environment is maintained for a long time, the coating adhesion can be secured. Corrosion resistance is also improved.

If H ₂ SiF ₆ /Cr<0.1, the above effect can hardly be expected. When H ₂ SiF ₆ /Cr>0.3, etching becomes excessive and the surface of the plating film becomes rough,
It becomes a dark color tone and is inferior in design. further,
Excessive addition of H ₂ SiF ₆ destroys the sol state of the coexisting wet silica, not only does not provide the effect of the addition of silica, but also promotes the gelation of the chromate treatment solution. The preferable addition amount of this fluorine compound is H ₂ SiF ₆ /Cr=0.15 to 0.25.

The above is an essential component of the chromate treatment solution used in the present invention. In addition, at least one type of acrylic or acrylstyrene-based aqueous emulsion resin is prepared by adding a resin solid content / Cr weight ratio of 0.5 to It is preferable to include the amount of 5 in the chromate treatment liquid.

In the acrylic aqueous emulsion resin, since the ester group of the acrylate ester is easily adsorbed on SiO ₂ ,
Since the acrylic styrene aqueous emulsion resin has an unsaturated bond of styrene unit easily adsorbed on SiO _2, both can be easily dispersed in chromating solution containing wet silica, uniformly incorporated into the chromate coating It is. When an aqueous emulsion resin is present in the chromate film, the components in the paint are hydrogen-bonded to the polar groups in the resin, improving the coating adhesion and corrosion resistance, making the color tone colorless and fingerprint resistance similar to wet silica. The effect of improvement can be obtained. In addition, since the aqueous emulsion resin suppresses the reaction between silica and phosphoric acid by the above-mentioned adsorption, the aqueous emulsion resin has an effect of suppressing gelation of the chromate treatment liquid, and prolongs the liquid life.

As the acrylic or acrylstyrene-based aqueous emulsion resin, those used in emulsion paints can be used. The resin used has a glass transition point
Those having a (Tg) of 50 ° C. or less are preferred. If the Tg of the resin is higher than 50 ° C., the resin does not soften by drying in a short time, the distribution of the resin in the film becomes uneven, and as a result, the corrosion resistance deteriorates.
When the amount of the aqueous emulsion resin added is resin solid content / Cr <
At 0.5, the above effect is hardly observed. When the resin solid content / Cr> 5, since the resin component is an insulating material, it is necessary for the electromagnetic wave shielding which is one of the performances required recently in home electric appliances. Conductivity is impaired. The preferable addition amount is resin solid content / Cr = 0.75-4.

The chromate treatment solution used in the present invention may contain one or more other components (eg, (Surfactant).

After the chromate treatment solution is applied to a zinc-based plated steel sheet as a base material, it is heated and dried to form a chromate film on the plating. The coating may be performed by a conventional means such as roll coating, dipping, spraying and the like. The amount of coating is such that the amount of the chromate film after drying is 5 to 60 mg / m ^{2 in} terms of Cr. If the amount of Cr attached is less than 5 mg / m ² , sufficient corrosion resistance cannot be obtained. When Cr deposition amount is more than 60 mg / m ^2, when painted, because the stress on the chromate film a strong stress is applied to the coating film is concentrated, coating adhesion even cohesive failure of the chromate film to a sufficient , And the coating film is peeled off in appearance. The preferable Cr adhesion amount is 10 to 50 mg / m ² .

Drying after coating is performed at a relatively low temperature of 40 to 140 ° C. If the drying temperature is less than 40 ° C., the above-described reduction of Cr ⁶⁺ by unreacted ethylene glycol after film formation does not proceed sufficiently during the short-time drying, and the amount of Cr ^{3+ in} the film is reduced in a humid environment. Cannot be reliably increased to Cr ³⁺ / total Cr ≧ 0.61, which is necessary for ensuring coating adhesion. On the other hand, when the drying temperature is 14
If the temperature exceeds 0 ° C, the ethylene glycol incorporated in the film volatilizes before exerting the reducing action, so that the Cr ³⁺ content cannot be reliably increased to Cr ³⁺ / total Cr ≧ 0.61 . The drying temperature is preferably between 70 and 120 ° C. The drying time depends on the temperature, but is usually preferably about 0.1 to 10 minutes.

As described above, the surface-treated steel sheet manufactured as described above has sufficient corrosion resistance, has little coloring (yellow) or is colorless, and has excellent fingerprint resistance. ) Can be used satisfactorily. In addition, it can be applied directly without zinc phosphate treatment, and it shows excellent coating adhesion that the coating does not peel even if left in a wet environment for a long time after coating, so it is also suitable for coating, There is an advantage that the zinc phosphate treatment step can be omitted. The type of paint is not particularly limited, but alkyd paint, acrylic paint, melamine alkyd paint, and the like are suitable.

[0035]

EXAMPLE A chromate treatment solution having the composition shown in Table 1 was roll-coated on one surface of a double-sided hot-dip galvanized steel sheet. The chromate treatment solution is prepared by adding a predetermined amount of a reducing agent ethylene glycol to a predetermined concentration of a chromic acid aqueous solution, stirring the mixture at room temperature for 24 hours to perform a reduction reaction, and then adding a predetermined amount of phosphoric acid and wet silica (manufactured by Nissan Chemical Snowtex), H ₂ SiF _6, and optionally adding an aqueous emulsion resin, was prepared by mixing. The concentration of Cr ^{6+ in} the aqueous solution after reduction with ethylene glycol was measured by the atomic absorption method, and the reduction ratio (Cr ³⁺ / total Cr ratio) calculated from the measured value is also shown in Table 1.

The water-soluble emulsion resin used was acrylic resin Movinyl DM774 (Tg: 20 ° C., manufactured by Hoechst Synthesis).
, Acrylic styrene type is Polytron F2000 (Tg: 40 ° C,
Asahi Kasei). After applying the chromate treatment liquid,
The steel sheet was heated at a temperature shown in Table 1 for 5 minutes to dry the film, and a chromate film having a Cr adhesion amount shown in Table 1 was formed.
The obtained surface-treated steel sheet was tested for coating adhesion, corrosion resistance, color tone, fingerprint resistance and conductivity as follows.

Coating adhesion On a chromate film of a test piece, a melamine alkyd-based paint (Glymin # 500 manufactured by Shinto Paint) or an acrylic paint
(Shinto Paint Super Glymin # 1000) dried film thickness 20
μm, the former is 120 ° C and the latter is
The coating film was baked at 130 ° C. to produce a painted test piece. The primary and secondary adhesion of each painted test piece was evaluated as follows.

[0038] Primary adhesion: The painted test specimen is grid-cut (100 grids at 1 mm intervals) and peeled off with a transparent adhesive tape. Secondary adhesion: After immersing the painted test piece in hot water at 80 ° C for 2 hours, perform a cross-cut and tape peeling test in the same manner as above (Secondary adhesion is measured when left in a wet environment for a long time) Is an indicator of paint adhesion).

Corrosion resistance: Evaluated according to the following criteria by the white rust generation area ratio (%) when a salt spray test was conducted for 72 hours in accordance with JIS Z2371. 5: 0%, 4: 1 to 5%, 3: 5 to 10%, 2: 10 to 15
%, 1: 15% or more.

Color tone: Evaluated according to the following criteria based on the b value measured by a color difference meter (manufactured by Minolta). 5: b ≦ 14: 1 <b ≦ 2 3: 2 <b ≦ 3 2: 3 <b ≦ 4 1: 4 <b.

Fingerprint resistance: A fingerprint was actually imprinted and visually evaluated according to the following criteria. 5: not visible at all 4: faint depending on the angle of light 3: faint from any position 2: clearly visible from any position 1: discoloration.

Conductivity: Evaluated according to the following criteria based on the measured value of the surface resistance per 0.9 mmφ stylus measured with an SQ meter (manufactured by Yamazaki). 5: 10Ω or less 4: 10 to 20Ω 3: 20 to 30Ω 2: 30 to 50Ω 1: 50Ω or more. As described above, all of the items have passed the grades 4 and 5.

[0043]

[Table 1]

As can be seen from the above table, the base material zinc-coated steel sheet was treated with an appropriate amount of ethylene glycol to reduce the Cr reduction ratio to 0.40.
Appropriate amount of phosphoric acid in chromic acid aqueous solution partially reduced so as to be within the range of ~ 0.65, wet silica having an average particle size of 10 to 100 nm,
And chromate treatment solution with H ₂ SiF ₆
The surface-treated steel sheet of the present invention, in which a chromate film having an adhesion amount of 5 to 60 mg / m ² is formed by heating and drying at ~ 140 ° C, is excellent not only in primary adhesion but also in secondary adhesion, and is excellent in a wet environment. It was proved that the coating adhesion was maintained even when left unattended. It also has excellent corrosion resistance, fingerprint resistance, color tone, and conductivity,
It has been proved that it can be used not only for painting but also naked.

On the other hand, in liquid No. 7 having an ethylene glycol / Cr weight ratio of <0.22, the amount of the reducing agent was too small and the Cr reduction ratio was low.
Below 0.40, the amount of Cr ⁶⁺ in the chromate film was too large, so paint adhesion after leaving in a wet environment (secondary adhesion)
And the color tone and the corrosion resistance became insufficient. Even in liquid No. 1 in which the concentration of the chromic acid aqueous solution was CrO ₃ <10 g / l, the calorific value was insufficient and the reduction reaction did not proceed, and the Cr reduction ratio was less than 0.40, and the same result as above.

On the other hand, the ethylene glycol / Cr weight ratio> 0.
In Liquid No. 6 of 35, the amount of the reducing agent was too large, and the Cr reduction ratio exceeded 0.65, and the chromate-treated liquid gelled. CrO ₃ concentration> 100
Even with g / l liquid No. 5, the reduction reaction proceeded excessively due to heat generation, the Cr reduction ratio exceeded 0.65, and the chromate treatment liquid also gelled. Furthermore, gelation also occurred in Liquid No. 9 having too much phosphoric acid content and Liquid No. 18 having too small a particle diameter of wet silica. In Liquid No. 21 in which the particle diameter of the wet silica was too large, the silica precipitated.

In the liquid No. 8 in which the amount of phosphoric acid was too small, the color tone and the corrosion resistance deteriorated. In the liquid No. 10 in which the amount of wet silica was too small, all the properties except the conductivity were lowered, and the amount of H ₂ SiF ₆ was reduced. Too much liquid
In No. 12, the coating adhesion and corrosion resistance were reduced. On the other hand, in the liquid No. 11 containing too much wet silica, the secondary adhesion was significantly reduced, and in the liquid No. 13 containing too much H ₂ SiF ₆ , the color tone was deteriorated. Liquid No. 17 in which the amount of the aqueous emulsion resin added was too large.
Then, the conductivity decreased. Also, the drying temperature was too low N
In o.22 and No.23, which was too high, the secondary adhesion decreased, and the fingerprint resistance, color tone, and corrosion resistance also decreased. .

[0048]

According to the method of the present invention, coating can be performed directly without performing zinc phosphate treatment, excellent coating adhesion can be maintained even when used in a wet environment after coating, and corrosion resistance and surface color tone can be maintained. It is possible to obtain a surface-treated steel sheet which is excellent in fingerprint resistance and electrical conductivity and can be used for both painted and unpainted applications.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takao Nakahara 1850 Minato, Wakayama-shi Sumitomo Metal Industries Co., Ltd.Wakayama Steel Works (72) Inventor Yoji Kitayama 1850 Minato, Wakayama-shi Sumitomo Metal Industries Co., Ltd.Wakayama Works (72) Inventor Shunichi Maru 4-1-24 Shigino Nishi, Joto-ku, Osaka Asahi Chemical Industry Co., Ltd. (72) Inventor Toshio Kiya 4-1-24 Shigino-nishi, Joto-ku, Osaka Asahi Chemical Industry Co., Ltd. (56) References JP-A-63-103082 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86

Claims (2)

(57) [Claims] 1. An aqueous chromic acid solution of 10 to 100 g / l in terms of CrO ₃ is reduced with ethylene glycol in an amount of 0.22 to 0.35 by weight of ethylene glycol / Cr to obtain Cr ³⁺ / total Cr = 0.4 to 0.65.
Phosphoric acid having a H ₃ PO ₄ / Cr weight ratio of 0.45 to 1.5, wet silica having a particle size of 10 to 100 nm having a SiO ₂ / Cr weight ratio of 2 to 5, and H ₂ SiF ₆ / A chromate treatment solution containing hexafluorosilicic acid having a Cr weight ratio of 0.1 to 0.3 is applied to a zinc-based plated steel sheet, and dried by heating at 40 to 140 ° C.
A method for producing a surface-treated steel sheet having excellent paint adhesion, characterized in that a chromate film having a weight of 5 to 60 mg / m ² is formed on plating. 2. The chromate treatment liquid further contains at least one resin selected from an acrylic aqueous emulsion resin and an acrylic styrene aqueous emulsion resin at a resin solids / Cr weight ratio of 0.5 to 5; A method for producing the surface-treated steel sheet according to claim 1.