JPH09165686A - Resin chromate bath and surface treated steel sheet - Google Patents

Abstract

(57) Abstract: To provide a resin chromate bath having an excellent bath life, and a surface-treated steel sheet having a film excellent in bare corrosion resistance, paint adhesion and Cr elution resistance. SOLUTION: Reduction rate of chromium [trivalent Cr / (trivalent Cr
+6 valent Cr) × 100] contains 40 to 65% by weight of chromic acid, phosphoric acid and a resin, and is composed of an aqueous liquid having a phosphoric acid / resin (weight) ratio of 0.3 to 1.0. Resin chromate bath and cold rolled steel plate, Zn or Zn
A surface-treated steel sheet having a resin chromate film formed from the bath on a base alloy-plated steel sheet.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a metal such as a cold-rolled steel sheet, a Zn-plated steel sheet, a Zn-based alloy-plated steel sheet, Ni,
A resin chromate treatment bath for forming a resin chromate film by coating and drying the surface of a metal plated steel sheet of Cu, Pd, Sn, Cd, Al, Ti or the like, or a plated steel sheet of an alloy of these metals, and a resin chromate film The present invention relates to a surface-treated steel sheet having

[0002]

2. Description of the Related Art Cold rolled steel sheets, Zn plated steel sheets, Zn-Ni
System, Zn-Ni-Co system, Zn-Ni-Cr system, Zn-
Fe-based, Zn-Co-based, Zn-Cr-based, Zn-Mn-based, etc. Zn-based alloy plated steel sheets, Ni, Cu, Pb, Sn, C
In order to improve the corrosion resistance of a metal-plated steel sheet of d, Al, Ti or the like, or an alloy-plated steel sheet of these metals, a chromate treatment is generally performed to form a chromate film. This chromate treatment can be roughly divided into electrolytic chromate treatment and coating chromate treatment. Electrolytic chromate treatment is performed, for example, by using chromic acid as a main component and adding sulfuric acid in addition to this (Japanese Patent Publication No. 39-7461) and phosphoric acid (Japanese Patent Publication No. 30-3514, Japanese Patent Publication No. 30-3514). Publication No. 35-8917, Japanese Patent Publication No. 36
-9559, JP-B-36-9560), those to which boric acid has been added (US Pat. Nos. 2733199 and 2780592), and those to which halogens (Cl ⁻ , F ⁻ ) have been added (JP-B-39-143).
No. 63), etc., a steel sheet has been subjected to cathodic electrolytic treatment using a bath containing various anions.

As the coating-type chromate treatment, a method of coating an acidic aqueous solution containing a water-soluble chromium compound containing trivalent chromium as a main component, an inorganic colloid compound and an inorganic anion (JP-A-63-218279), Cr ⁶⁺ part of 3
A method in which colloidal silica is mixed with chromic acid reduced to a valence and treated (JP-A-63-243279), which contains a water-soluble chromium compound containing trivalent chromium as a main component, an inorganic colloid compound and an inorganic anion. Those treated with a liquid (JP-A-63-218279), those treated with a liquid in which a chromic acid of a specific element is mixed with a colloidal compound in a specific ratio and an inorganic anion (JP-A-63-178873), Cr ⁶⁺ / (C
Chromic acid having a specified ratio of r ⁶⁺ + Cr ³⁺ ), treated with a liquid containing an inorganic colloid and an inorganic anion, Si
Treatment with an aqueous chromic acid solution containing O ₂ and PO ₄ ^{3− and} having a molar ratio of trivalent Cr / total Cr defined (Japanese Patent Laid-Open No. 1-6527).
No. 2), which is treated with a solution containing a specific amount of hexavalent and trivalent chromium ions containing a specific amount of trivalent chromium ions and a specific amount of each sodium salt of fluorofluoride (Japanese Patent Application Laid-Open No. HEI-1). -56879), which is treated with an aqueous solution containing a specific amount of trivalent chromium ions containing a specific amount of trivalent chromium ions and a specific amount of SiO ₂ (JP-A-1-
No. 56877), a method of treating a hexavalent and trivalent chromium ion containing a specific amount of trivalent chromium ion with a liquid containing a specific amount of ammonium silicofluoride and a silane coupling agent (JP-A-1- 56878), which contains a specific proportion of chromium and silica sol, and treats a liquid having a specified Cr ⁶⁺ amount and silica sol particle size (JP-A-2-104672), specific proportions of chromium ion, phosphoric acid, and silicic acid. What contains a sol and is treated with a liquid in which hexavalent chromium ions in all chromium ions are specified (Japanese Patent Laid-Open No. 2-85372), chromic acid, an anhydrous colloid compound, and a silane coupling agent are compounded in a specific ratio. What treats liquid (JP-A-3-146676), 3
Specified Cr / 6 Specified Cr, silica gel, phosphoric acid, Zn
Examples thereof include those treated with a liquid containing (JP-A-3-68783).

Among the chromate coatings, the chromate coating formed by electrolytic treatment has a small amount of Cr elution but is not sufficient in corrosion resistance, and the coating has poor scratch resistance at the time of processing, so that after processing Corrosion resistance is extremely reduced. If the chromate film formed by the coating process is used as it is after the treatment, the chromate film is likely to elute, which causes pollution problems, which is not preferable. In addition, the corrosion resistance and the adhesiveness of the coating are not always sufficient, and the coating is likely to be flawed during processing, and the corrosion resistance after processing is considerably low.

On the other hand, as a recent tendency, a chromate having a higher corrosion resistance is being developed. Among them, so-called resin-type chromate, in which a resin coexists in a chromic acid bath, is being studied. In the treatment with resin type chromate, various resins are added to the chromic acid bath. At that time, the strong oxidizing action of chromic acid (Cr ⁶⁺ → Cr ³⁺ ) causes the resin to gradually react and stabilize the bath. Difficult to maintain. Many resins, when added to a chromic acid bath, oxidize, coarsen, settle or gel within a few seconds at the shortest and at most hours at the longest. Therefore, the bath cannot be used, and the formed resin chromate film does not easily become a constant component. Since there has been no resin stable in a chromic acid bath up to now, it has been said that a resin chromate that can be stably operated for a long time is industrially impossible. Further, even if a known resin chromate is treated on a steel plate within a short time after the bath is constructed, the formed chromate film is likely to be partly eluted in a degreasing bath or a chemical bath, which causes pollution problems, which is not preferable. In addition, the corrosion resistance and paint adhesion are not always sufficient. In order to succeed in the treatment method using resin chromate, firstly the resin is extremely stable in the chromic acid bath, and the film obtained by applying it to the steel sheet has excellent Cr elution resistance, corrosion resistance and paint adhesion. It is necessary to develop a resin chromate film with excellent properties.

Recently, several treatment methods using resin chromates have been proposed. For example, a treatment method in which chromic acid is composed of amorphous silica, a phosphoric acid compound and polyacrylic acid, and the C / Si ratio of the outermost layer of the film is specified (Japanese Patent Laid-Open No. 2-163385), chromate solution A method in which an acrylic emulsion of a copolymer such as methyl methacrylate is added under certain conditions and treated (JP-A-2-
179883), chromic acid, a chromic acid reduction product, an acrylic emulsion, a method of applying a liquid containing silica sol under specific conditions (JP-A-3-215683), chromic acid,
Chromic acid reduction product, acrylic emulsion, wet type silica sol treated with a liquid containing specific conditions (JP-A-3-215681), ethylenically unsaturated carboxylic acid component, hydroxyl group-containing monomer component, other ethylene-based Treatment using a metal surface treatment composition obtained by mixing an aqueous emulsion composed of an unsaturated compound, a water-soluble chromium compound, an aqueous colloid of an inorganic compound and an inorganic substance which reacts with an amphoteric metal to form a sparingly water-soluble salt ( JP-A-5-230666) and the like. However, any of the treatments disclosed in these known documents are insufficient, especially in terms of bath life in a resin chromate bath and chromium elution resistance of the formed film.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and significantly improves the bath life in a resin chromate bath, and at the same time, cold-rolled steel sheet, Zn-plated steel sheet, Zn-based alloy-plated steel sheet. , Ni, Cu, Pb, Sn,
Provided with a metal plated steel sheet of Cd, Al, Ti, etc., and a resin chromate bath capable of forming a coating film excellent in Cr elution resistance, corrosion resistance and paint adhesion on an alloy plated steel sheet of these metals The first purpose is to do so.

A second object of the present invention is to provide a cold rolled steel sheet, a Zn plated steel sheet, a Zn alloy plated steel sheet, Ni, Cu, Pb,
Chromate coating on Sn-, Cd-, Al-, Ti-plated metal sheets and alloy-plated steel sheets of these metals, which have excellent Cr elution resistance by the above treatment bath, bare corrosion resistance after processing, and excellent paint adhesion. Cr formed with a specific amount
It is intended to provide a surface-treated steel sheet excellent in elution property, bare corrosion resistance after processing, and coating adhesion.

A third object of the present invention is to provide cold rolled steel sheet, Zn plated steel sheet, Zn alloy plated steel sheet, Ni, Cu, Pb,
On the metal-plated steel sheet of Sn, Cd, Al, Ti, etc. and the alloy-plated steel sheet of these metals, a specified amount of a chromate film excellent in Cr elution resistance and paint adhesion is formed by the above treatment bath, and specified on it. The present invention provides a surface-treated steel sheet which is coated with a specific amount of the above resin and has excellent Cr elution resistance, corrosion resistance after processing, and coating adhesion.

A fourth object of the present invention is to provide cold rolled steel sheet, Zn plated steel sheet, Zn alloy plated steel sheet, Ni, Cu, Pb,
Form a specified amount of chromate film with excellent scratch resistance, paint adhesion and Cr elution resistance on the metal plated steel sheets of Sn, Cd, Al, Ti, etc. and alloy plated steel sheets of these metals by the above treatment bath. , On top of which SiO ₂ , Sn
O ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO,
To provide a surface-treated steel sheet which is coated with a specific amount of a resin mixed with a colloid (sol) such as Al ₂ O ₃ or powder, and which has excellent corrosion resistance after processing, coating adhesion and Cr elution resistance. Is.

[0011]

SUMMARY OF THE INVENTION The present invention provides a resin chromate film containing special chromic acid, phosphoric acid and resin as components and a phosphoric acid / resin ratio in a specific region, or a special inorganic substance. A special resin chromate film as a component is formed on various metals such as cold rolled steel plate or Zn or Zn alloy plated steel plate, and there is almost no elution of chromate, and it has excellent bare corrosion resistance and paint adhesion after processing. At the same time, it is possible to form a resin chromate film excellent in adhesion to various organic resins, and an extremely stable resin chromate treatment bath, that is, the present invention is a reduction ratio of chromium [trivalent Cr / (trivalent Cr + hexavalent Cr ) × 100] comprises 40 to 65% by weight of chromic acid, phosphoric acid and a resin, and the phosphoric acid / resin (weight ratio) is 0.3 to 1.0. Resin chromate bath and symptoms, and to a surface treated steel sheet characterized by having a chromate film formed from the bath. This extremely stable treatment bath, in other words, the extremely long life of the treatment bath, can be achieved by coexistence of special chromic acid and phosphoric acid and a specific ratio of phosphoric acid / organic matter.
The present inventors have found that the use of special chromic acid significantly improves the Cr elution resistance of the formed chromate film, and Cr hardly elutes even under considerably severe conditions. The inventors have found that when the ratio of phosphoric acid / organic substances coexisting with is set to a specific value, these synergistic effects exhibit extremely excellent paint adhesion and bare corrosion resistance after processing, and completed the above-described present invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The resin chromate bath of the present invention is an aqueous liquid containing a special chromic acid, phosphoric acid and a resin. The chromic acid used in the present invention is chromic acid in which hexavalent Cr in chromic acid is reduced to trivalent Cr in a specific ratio. Chromic acid is a reduction ratio of chromium, that is, the ratio of the weight of trivalent Cr to the total weight of hexavalent Cr and trivalent Cr, the value of trivalent Cr / (trivalent Cr + hexavalent Cr) × 100 is 40 to 65 weight. Must be in the range of%. Here, the chromium reduction rate is obtained as follows. Obtain the total amount of chromium by atomic absorption spectrometry (weight), determine the amount of hexavalent chromium in the chromic acid solution by diphenylcarbazide absorptiometry (weight), subtract the amount of hexavalent chromium from the total amount of chromium, and determine the amount of trivalent chromium. (Weight) is calculated (in accordance with JIS-K-0102).

The bath contains trivalent Cr in an amount of 40 to 65% by weight.
Is extremely stable in the range of, and stability is reduced when it is less than 40% by weight or exceeds 65% by weight. The Cr elution resistance is extremely good when the ratio of trivalent Cr is 40 to 65% by weight, and Cr is easily eluted when it is less than 40% by weight or more than 65% by weight. When the proportion of trivalent Cr is 65% by weight or less, excellent paint adhesion is exhibited, and when it exceeds 65% by weight, the paint adhesion is lowered. When the proportion of trivalent Cr is 65% by weight or less, excellent bare corrosion resistance after working is exhibited, and when it exceeds 65% by weight, bare corrosion resistance after working is lowered.

Preferred trivalent Cr / (trivalent Cr + hexavalent C
The range of r) × 100 is 40 to 65% by weight, and more preferably 45 to 60% by weight.

The amount of the special chromic acid used is 2 to 50 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the resin.
Parts by weight. If it is less than 2 parts by weight, it is difficult to secure the corrosion resistance, and if it exceeds 50 parts by weight, the Cr elution resistance is lowered.

Examples of phosphoric acid include phosphoric acid (orthophosphoric acid), polyphosphoric acid, phosphoric anhydride, and hypophosphorous acid. Also, phosphates can be used. As the phosphate, various sodium phosphate-based, potassium phosphate-based, ammonium phosphate-based,
There are compounds such as calcium phosphate salts. Among them, it is preferable to use orthophosphoric acid, polyphosphoric acid and phosphoric anhydride. When polyphosphoric acid and phosphoric anhydride are used, it is necessary to convert them into orthophosphoric acid in order to determine the weight ratio with the resin. The ratio of orthophosphoric acid or orthophosphoric acid is shown below.

Weight ratio of phosphoric acid and resin in the bath (phosphoric acid /
Resin) is 0.3 to 1.0, preferably 0.5 to
0.9, and more preferably 0.6 to 0.8. When the phosphoric acid / resin ratio is 0.3 or more, the bath becomes extremely stable,
If it is less than 0.3, the stability of the bath decreases. When the phosphoric acid / resin ratio is 1.0 or less, it shows extremely excellent Cr elution resistance,
If it exceeds 1.0, Cr is likely to be eluted. Further, when the phosphoric acid / resin ratio is 1.0 or less, excellent paint adhesion is exhibited,
If it exceeds 1.0, the adhesiveness of the paint is significantly reduced. Further, when the ratio of phosphoric acid / resin is 1.0 or less, excellent bare corrosion resistance after working is exhibited, and when it exceeds 1.0, bare corrosion resistance after working is significantly reduced.

The absolute amounts of phosphoric acid and organic resin added are not important, but the weight ratio phosphoric acid / resin is important. The reason for this is not clear at this point in time, but phosphate radicals are coordinated on the surface of the emulsion resin, and it becomes a kind of barrier layer, which greatly improves the stability of the resin, in other words, the stability of the bath. Seem.

Regarding the ratio of trivalent Cr to the total of hexavalent Cr and trivalent Cr in the above chromic acid, trivalent Cr
The stable region of the bath exists in the region of 40 to 65% by weight because the decrease of hexavalent Cr reduces the oxidation function of chromic acid and the barrier layer formed on the surface of the resin by phosphoric acid. It is believed that the formation significantly improves the stability of the bath. This is also because the amount of hexavalent Cr, which is the main cause of the elution of Cr, is relatively decreased by increasing the amount of trivalent Cr. Trivalent Cr does not elute because it easily becomes an oxide or hydroxide during film formation. It is considered that the reason why the trivalent Cr is easily eluted in the region where the ratio of trivalent Cr exceeds 65% by weight is that since the chromic acid itself is gelated and a stable chromate film is not formed, the film itself is easily eluted. When the proportion of trivalent Cr exceeds 65% by weight, the bath becomes unstable because the chromic acid itself becomes unstable and gels due to the increase of trivalent Cr.

The resin used in the present invention may be any resin as long as it is stable to some extent even in the presence of chromic acid.
As a preferable example of such a resin, methyl methacrylate-butyl acrylate-styrene-methacrylic acid-
Acrylic acid-organic phosphorus monomer copolymer resin, methyl methacrylate-butyl acrylate-glycidyl methacrylate-methacrylic acid-organic phosphorus monomer copolymer resin, methyl methacrylate-butyl acrylate-
Glycidyl methacrylate-methacrylic acid-hydroxyethyl acrylate copolymer resin, methyl methacrylate-butyl acrylate-styrene-glycidyl methacrylate-methacrylic acid-acrylic acid-organic phosphorus monomer copolymer resin, methacrylic Methyl acrylate-butyl acrylate-styrene-glycidyl methacrylate-methacrylic acid-organic phosphorus monomer copolymer resin, methyl methacrylate-butyl acrylate-glycidyl methacrylate-methacrylic acid-acrylic acid copolymer resin , Methyl methacrylate-butyl acrylate-glycidyl methacrylate-methacrylic acid-acrylic acid-hydroxyethyl acrylate copolymer resin, methyl methacrylate-butyl acrylate-methacrylic acid-acrylic -Hydroxyethyl acrylate copolymer resin, methyl methacrylate-butyl acrylate-methacrylic acid-hydroxyethyl acrylate copolymer resin, styrene-butyl acrylate-hydroxyethyl acrylate-methacrylic acid-hydroxyethyl acrylate Copolymer resin, butyl acrylate-methacrylic acid-hydroxyethyl acrylate-based copolymer resin, (meth) acrylic acid-based copolymer of methyl methacrylate-butyl acrylate-methacrylic acid-hydroxyethyl acrylate Polymer resins may be mentioned. Further, an acrylic amide resin, an acrylamide resin, an acrylic resin, a styrene resin, a urethane resin, or an epoxy resin can be used.

In addition to the above-mentioned essential components, a colloid (sol) or powder of an inorganic substance may be added to the resin chromate bath of the present invention. The addition of these further extends the life of the bath and further improves the bare corrosion resistance of the resulting coating after processing. As the inorganic substance, SiO ₂ ,
SnO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , Mg
O, Al ₂ O ₃ , ZrO _{2 and the} like can be mentioned, and these can be used alone or as a mixture. When powder is used, its particle size is preferably 2 to 12 μm. The amount used is not particularly limited, but is preferably 3 to 30 parts by weight with respect to 100 parts by weight of the resin present in the resin chromate bath,
More preferably 10 to 25 parts by weight.

The concentrations of chromic acid, phosphoric acid and resin in the bath are 0.2-5% by weight, 1-10% by weight and 1% by weight, respectively.
-20% by weight, more preferably 0.5-3% by weight, 2
˜5% by weight, 4 to 10% by weight.

The coating method of the resin chromate bath of the present invention is not particularly limited, and any coating method such as roll coating, spray coating, brush coating, dip coating and curtain flow can be used.

The amount of the chromate film deposited on the steel sheet (coating amount) is preferably 10 to 300 mg / m ^{2 in} terms of Cr, and more preferably 40 to 100 mg / m ² .
When the amount of the chromate film deposited is 10 mg / m ² or more in terms of Cr, the obtained film exhibits excellent bare corrosion resistance after processing and coating adhesion. On the other hand, even if the coating amount is changed, Cr elution hardly changes. Further, even when colloidal silica is added to the above-mentioned bath, the relationship between the adhesion amount and bare corrosion resistance after processing and paint adhesion is almost unchanged, and the Cr elution resistance is not affected by the adhesion amount. From the economical point of view, the upper limit of the amount of the chromate film deposited is 300 mg / Cr in terms of Cr.
and m ^2.

The resin chromate treatment bath of the present invention is applied to a cold-rolled steel sheet, a Zn-plated steel sheet or a Zn-based alloy-plated steel sheet, and exhibits excellent corrosion resistance, paint adhesion and Cr elution resistance. Form a film. As the Zn-based alloy, Zn-Ni-based, Zn-Ni
-Co type, Zn-Ni-Cr type, Zn-Fe type, Zn-
Co-based, Zn-Cr-based, Zn-Mn-based, Zn-Al-based,
Examples thereof include Zn-Mg based alloys. The resin chromate treatment bath of the present invention can be used not only for Zn or Zn-based alloy plated steel sheets, but also for metals such as Ni, Cu, Pd, Cd, Sn, Al and Ti, or plated steel sheets of these alloys. it can. Plating methods include electroplating, hot dip plating,
Any other plating method may be used.

Since the obtained resin chromate film has extremely excellent adhesion with other organic resins, various resins can be further applied thereon to produce an organic composite steel sheet. Examples of such resins include methyl methacrylate, which is mixed in the resin chromate bath of the present invention, butyl acrylate, resins obtained by copolymerizing methacrylic acid and hydroxyethyl acrylate, and methyl methacrylate, Resin obtained by polymerizing or copolymerizing at least one selected from butyl acrylate, styrene, glycidyl methacrylate, methacrylic acid, acrylic acid and organic phosphorus monomer hydroxyethyl methacrylate, olefin-acrylic acid copolymer resin , Polyacrylic acid and its copolymer resin, polyacrylic acid ester and its copolymer resin, polymethacrylic acid ester and its copolymer resin, epoxy resin, acrylic modified epoxy resin, ester modified epoxy resin, urethane modified epoxy Fat, urethane-modified epoxy ester resin, vinyl-modified epoxy resins, vinyl-modified epoxy ester resin and the like, which are used alone or as a mixture.

These resins further include SiO ₂ and Sn.
O ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO,
Colloid (sol) of inorganic substances such as Al ₂ O ₃ and ZrO ₂
Alternatively, one or more powders may be added.
The particle size of these sols or powders is more effective when fine particles having a particle size of about 2 to 15 nm are used. The addition amount is preferably 10 to 60 parts by weight with respect to 100 parts by weight of the resin. Within this range, the corrosion resistance of the coating film is very good. It is more preferably 15 to 45 parts by weight. It is desirable that the resin or the mixture of the resin and the inorganic substance is applied in a dry film amount of 0.2 to 3.0 g / m ² .

[0028]

EXAMPLES The present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples. (Determination of range of trivalent Cr / (trivalent Cr + hexavalent Cr) × 100 (wt%)) trivalent Cr / (trivalent Cr + hexavalent Cr)
A value of x100 (wt%) shows how the stability of the resin chromate bath, that is, the service life, and how the properties of the formed chromate film are affected. Chromic acid is 20 g / l (constant) in terms of CrO ₃ and the total of trivalent Cr + hexavalent Cr is constant and trivalent Cr
I made the thing which changed the ratio of. The resin is copolymerized with 35 parts by weight of methyl methacrylate-40 parts by weight of butyl acrylate-20 parts by weight of methacrylic acid-15 parts by weight of hydroxyethyl acrylate as a main component and 30% by weight.
60 g / l of water-based resin emulsion (solid content concentration)
(Solid content) (constant). Chromic acid is trivalent Cr / (3
What changed the value Cr + hexavalent Cr) x100 (weight%) was used. A resin chromate bath composed of these aqueous liquids was prepared, and the stability (lifetime) of the bath was investigated. In addition, the above aqueous solution was applied to an electric Zn-plated steel sheet (Zn deposition amount: 30 g / m ² ) so that the Cr deposition amount (Cr conversion) was 55 mg / m ^2, and dried to form a film having a Cr resistance. It was investigated how elution, paint adhesion and bare corrosion resistance after processing change. Table 1 shows the results.

[0029]

[Table 1]

The bath stability depends on the proportion of trivalent Cr in the bath being 40.
The bath is extremely stable at ˜65 wt%, and less than 40 wt% or more than 65 wt% reduces the stability of the bath. When the ratio of trivalent Cr is 40% by weight or more, the Cr elution resistance of the film is extremely good. When the proportion of trivalent Cr is 40% by weight or more, the coating adhesion of the coating is very good. Further, when the ratio of trivalent Cr is 65% by weight or less, it shows excellent bare corrosion resistance after processing,
If it exceeds 65% by weight, the bare corrosion resistance after processing is lowered.

Stability of bath The bath is allowed to stand at 50 ° C., and gelation of the bath or sedimentation of the resin is observed. ◎: stable for 50 days or more ○: stable for 30 days to less than 50 days Δ: stable for 10 days to less than 30 days ×: stable for 1 day to less than 10 days × ×: stable for less than 1 day

Cr elution resistance Chromate film is immersed in boiling water for 2 hours to elute Cr
The amount was determined. ◎: less than ^{1mg / m 2 ○: 1mg /} m 2 or more to 3 mg / m less than ² △: 3mg / m ² or more ~7mg / m ² less ×: 7mg / m ² or more to 15 mg / m ² less than ××: 15 mg / M ² or more

Coating Adhesion A melamine-based low-temperature baking coating (baking temperature: 100 ° C.) was spray-coated on the obtained chromate film so that the thickness would be 30 μm after baking, followed by immersion in boiling water for 30 minutes and then 2 mm Goban. The coating film was cut on the eye and peeled off with a tape to evaluate the peeled area of the coating film. ◎: Coating peeling area 0% ○: 〃 more than 0% to 1% △: 〃 more than 1% to 10% ×: 〃 more than 10% to 50% XX: more than 50%

The bare corrosion resistance after processing was evaluated by performing a cylindrical drawing process with a drawing depth of 50 mm and then performing a corrosion test, and checking the occurrence of red rust on the side surface subjected to the ironing process. The corrosion test is a salt spray test according to the JIS-Z-2371 standard (salt water concentration 5% by weight, tank temperature 35 ° C., spray pressure 20).
PSI) shows the rusting condition after 1000 hours. ◎: Red rust occurrence rate 0% ○: 〃 more than 0% to 1% △: 〃 more than 1% to 10% ×: 〃 more than 10% to 50% XX: more than 50%

(Weight ratio of phosphoric acid and resin in the bath (phosphoric acid
/ Resin)) The total concentration of hexavalent Cr and trivalent Cr is C
rO_Three Converted to 20g / l (constant), 50 weights of trivalent Cr
% Special chromic acid and methacrylic acid resin as the resin.
Chill 35 parts by weight-Butyl acrylate 40 parts by weight-Metaa
20 parts by weight of acrylic acid-hydroxyethyl acrylate 1
30% by weight (solid content) obtained by copolymerizing 5 parts by weight as a main component
Form) Water-based organic resin emulsion 60 g / l (solid
Min) (constant), and phosphoric acid is distributed in various proportions.
Make a resin chromate composed of the combined aqueous liquid to
The qualitative, that is, how life changes is investigated.
In addition, the above aqueous solution was applied to an electric Zn plated steel sheet (Zn adhesion amount:
30g / m^Two) Has a Cr deposit of 55 mg / m ^TwoWill be
The film when applied by coating and dried to form C resistance
What is the elution property, paint adhesion and bare corrosion resistance after processing?
The results are shown in Table 2.

[0036]

[Table 2]

When the ratio of phosphoric acid / resin is 0.3 or more, the bath becomes extremely stable, and when it is less than 0.3, the stability of the bath decreases.
Excellent resistance to Cr with phosphoric acid / resin ratio of 1.0 or less
It shows an elution property, and when it exceeds 1.0, Cr is easily eluted. When the phosphoric acid / resin ratio is 1.0 or less, the paint adhesion is extremely excellent, and when it exceeds 1.0, the paint adhesion is significantly reduced. Further, when the phosphoric acid / resin ratio is 1.0 or less, it shows extremely excellent bare corrosion resistance after processing, and when it exceeds 1.0, the bare corrosion resistance after processing is significantly reduced.

The total concentration of hexavalent Cr and trivalent Cr is CrO.
20 g / l (constant) in terms of ₃ and using special chromic acid containing 50% by weight of trivalent Cr, phosphoric acid was fixed at 40 g / l, and 35 parts by weight of methyl methacrylate as a resin-40 parts by weight of butyl acrylate. -A resin chromate bath consisting of an aqueous liquid containing 20 parts by weight of methacrylic acid-30 parts by weight (solid content) of an aqueous organic resin emulsion obtained by copolymerizing 15 parts by weight of hydroxyethyl acrylate as a main component in various proportions. It was made and examined how the stability of the bath, ie, the service life, changed. Further, the above aqueous liquid was applied to an electric Zn-plated steel sheet (Zn adhesion amount: 30 g / m ² ) so that the Cr adhesion amount was 55 mg / m ^2, and the film formed by drying was Cr elution resistance, paint adhesion It was investigated how the corrosion resistance and the bare corrosion resistance change after processing. The results are shown in Table 3.
Shown in

[0039]

[Table 3]

When the ratio of phosphoric acid / resin is 0.3 or more, the bath becomes extremely stable, and when it is less than 0.3, the stability of the bath decreases.
Excellent resistance to Cr with phosphoric acid / resin ratio of 1.0 or less
It shows an elution property, and when it exceeds 1.0, Cr is easily eluted. When the phosphoric acid / resin ratio is 1.0 or less, the paint adhesion is extremely excellent, and when it exceeds 1.0, the paint adhesion is significantly reduced. Further, when the phosphoric acid / resin ratio is 1.0 or less, it shows extremely excellent bare corrosion resistance after processing, and when it exceeds 1.0, the bare corrosion resistance after processing is significantly reduced.

(Effect of Colloidal Silica) 100 parts by weight (60 g / l) of copolymer resin of methyl methacrylate-butyl acrylate-methacrylic acid-hydroxyethyl acrylate, 67 parts by weight of phosphoric acid (40 g / l) ( Phosphoric acid / resin (weight ratio) = 0.67), 50 wt% reduced chromic acid (50 wt% hexavalent Cr, 50 wt% trivalent Cr) 3
3 parts by weight (20 g / l) (20 g / l in terms of chromic acid)
The stability of a bath prepared by mixing colloidal silica in various proportions in the mixed aqueous liquid was examined, and the unit weight was 30 g / m 2.
^The amount of Cr deposited on the electro-galvanized steel sheet of No. ² is 50 mg / m ²
A film was formed so as to have the following properties, and the Cr elution resistance, the bare corrosion resistance after processing, and the paint adhesion were examined. Here, the evaluation method of Cr elution resistance and paint adhesion was the same as the above, but the bare corrosion resistance after processing was evaluated in the salt spray test in JIS-Z-2371 in the rusting condition after 2000 hours. Table 4 shows the results.

[0042]

[Table 4]

The stability of the bath depends on the amount of colloidal silica added.
Therefore, there was no particular impact. That is, colloidal
May gel especially by adding silica
No tendency to settle out.
For example, even if left at 50 ° C for at least 20 days,
It didn't change. This is a conventionally known resin chromate bath
However, the resin may not settle or gel within a few hours at the longest.
Therefore, if the resin used in the present invention is in a chromic acid bath,
It means that it is stable. 30 parts by weight of colloidal silica
If it exceeds, the Cr elution resistance tends to decrease. Colloid
After processing with 3 to 30 parts by weight of dull silica, the bare corrosion resistance is further improved.
improves. In addition, colloidal silica exceeds 30 parts by weight
Then, the paint adhesion tends to decrease. This tendency is
SiO instead of idal silica_TwoPowder or Sn
O_Two, Cr _TwoO_Three, Fe_TwoO_Three, Fe_ThreeO_Four, MgO,
Al_TwoO_Three, ZrO_TwoColloid (sol) or powder
Almost the same result was obtained even when the above composition was added. Also these
Almost the same results can be obtained by blending two or more of these
Was.

(Amount of coating film) Next, methacrylic acid methyl ester
-Butyl acrylate-methacrylic acid-hydroxye
100 parts by weight of copolymer resin of chill acrylate (60 g
/ L) (solid content), 67 parts by weight of phosphoric acid (40 g / l)
(Phosphoric acid / resin (weight ratio) = 0.67), 50% by weight reduction
Original chromic acid (50 weight% of hexavalent Cr, 50 weight of trivalent Cr
%) 33 parts by weight (20 g / l) (20 g in terms of chromic acid)
/ L) The blended aqueous liquid has a basis weight of 30 g / m ^Two Electric Z
Films are formed on n-plated steel sheets by varying the amount of Cr deposited.
, Cr elution resistance, bare corrosion resistance after processing and paint adhesion
I investigated about it. Evaluation of Cr elution resistance and paint adhesion
The method is the same as above. The bare corrosion resistance after processing is salt water.
The rusting state after 1500 hours was evaluated in the spray test. Evaluation
The criteria are the same as above. Table 5 shows the results.

[0045]

[Table 5]

Even when the coating amount was changed, the Cr elution hardly changed. Further, excellent corrosion resistance after processing and paint adhesion were secured at 10 mg / m ² or less in terms of Cr. The following results: Adhesion amount of resin chromate is 10mg / m in terms of Cr
² or more, and the upper limit is 300 in terms of Cr from the economical point of view.
It is mg / m ² .

Example 1 50 wt% reduced chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) ×) was applied to a Zn-plated steel sheet (weight per unit area: 20 g / m ² ).
100 = 50% by weight) 20 g / l, phosphoric acid 40 g / l,
Methyl methacrylate 5 parts by weight-butyl acrylate 35
Parts by weight-styrene 20 parts by weight-methacrylic acid 40 parts by weight-acrylic acid 3 parts by weight-organic phosphorus monomer 1 part by weight An aqueous liquid containing 60 g / l of a copolymer is coated on a roll and dried at 150 ° C. A coating film was obtained. 20% by weight of all the components of the coating film converted to chromic acid 20 parts by weight of phosphoric acid 40 parts by weight of the above copolymer 60 parts by weight of phosphoric acid / copolymer (weight ratio) 0.67 The adhesion amount of the obtained chromate film is calculated as Cr. At 51m
g / m ² .

Example 2 Zn-Ni alloy-plated steel sheet (weight per unit area: 20 g / m ² ,
Ni = 11.5 wt%), 45 wt% reduced chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) × 100 = 45 wt%) 25 g / l, phosphoric acid 45 g / l, methyl methacrylate 30 Parts by weight-butyl acrylate 37 parts by weight-glycidyl methacrylate 10 parts by weight-methacrylic acid 40
Parts by weight-acrylic acid 3 parts by weight-organic phosphorus monomer 1 part by weight Copolymer resin 80 g / l, 20 parts by weight of colloidal silica are mixed with an aqueous solution, which is applied by a roll and dried at 150 ° C. to form a coating film. Got 25 relative to the weight component total Cr 45 parts by weight of chromic acid conversion 25 parts by weight of phosphoric acid the copolymer 80 parts by weight of phosphoric acid / copolymer 0.56 SiO ₂ 20 parts by weight (100 parts by weight of the copolymer of the coating Part) The amount of the obtained chromate film deposited is 48 m in terms of Cr
g / m ² .

Example 3 Zn-Ni alloy plated steel sheet (Basis weight: 20 g / m ² ,
Ni = 12.3 wt%), 40 wt% reduced chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) × 100 = 40 wt%) 15 g / l, phosphoric acid 45 g / l, methyl methacrylate 30 Parts by weight-butyl acrylate 37 parts by weight-glycidyl methacrylate 10 parts by weight-methacrylic acid 4
0 parts by weight-acrylic acid 3 parts by weight-organic phosphorus monomer 1 part by weight copolymer resin 80 g / l, colloidal silica 15
Aqueous liquid containing 1 part by weight is coated with a roll, and the temperature is 150 ° C.
And dried to obtain a coating film. 15 parts by weight of all Cr components of the coating film in terms of chromic acid 45 parts by weight of phosphoric acid 80 parts by weight of the above copolymer 15 parts by weight of phosphoric acid / copolymer 0.56 SiO ₂ (19 parts by weight of 100 parts of the copolymer) (Part by weight) The amount of the obtained chromate film deposited is 55 m in terms of Cr.
g / m ² . Furthermore, 30 parts by weight of methyl methacrylate-37 parts by weight of butyl acrylate-10 parts by weight of glycidyl methacrylate-40 parts of methacrylic acid.
Parts by weight-acrylic acid 3 parts by weight-organic phosphorus monomer 1 part by weight An aqueous solution of a resin obtained by copolymerization is coated with a roll and dried at 150 ° C, and a coating amount of 1.3 g / m ² is applied. Got

Example 4 Zn-Fe alloy plated steel sheet (Basis weight: 20 g / m ² ,
Fe = 12.8 wt%), 55 wt% reduced chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) × 100 = 55 wt%) 30 g / l, phosphoric acid 60 g / l, methyl methacrylate 20 Parts by weight-butyl acrylate 37 parts by weight-styrene 5 parts by weight-glycidyl methacrylate 15 parts by weight-methacrylic acid 20 parts by weight-acrylic acid 5 parts by weight-organic phosphorus monomer 1 part by weight copolymer resin 70 g / l, An aqueous liquid containing 15 g / l of colloidal silica was coated with a roll and dried at 150 ° C. to obtain a coating film. Ingredients of coating film Total Cr in terms of chromic acid 30 parts by weight Phosphoric acid 60 parts by weight The above copolymer 70 parts by weight Phosphoric acid / copolymer 0.86 SiO ₂ 15 parts by weight (21 parts based on 100 parts by weight of the copolymer) (Part by weight) The amount of the obtained chromate film deposited is 43 m in terms of Cr.
g / m ² . Further, on the obtained chromate film, 5 parts by weight of methyl methacrylate-33 parts by weight of butyl acrylate-20 parts by weight of styrene-3 parts by weight of glycidyl methacrylate-38 parts by weight of methacrylic acid-1 part by weight of organic phosphorus monomer An aqueous liquid containing 15 parts by weight of colloidal silica is coated on 100 parts by weight of the copolymer resin of 1. by a roll and dried at 150 ° C., and an adhesion amount of 1.1 g /
A film of m ² was obtained.

Example 5 Zn-Mg alloy plated steel sheet (Basis weight: 30 g / m ² ,
Mg = 1.2% by weight) and 52% by weight reduced chromic acid (3
Cr / (trivalent Cr + hexavalent Cr) × 100 = 52% by weight) 10 g / l, phosphoric acid 20 g / l, methyl methacrylate 15 parts by weight-butyl acrylate 33 parts by weight-styrene 5 parts by weight-glycidyl methacrylate 10 parts by weight
An aqueous liquid containing 60 g / l of a copolymer resin of 39 parts by weight of methacrylic acid and 3 parts by weight of acrylic acid was coated with a roll and dried at 150 ° C. to obtain a coating film. Ingredients of coating film 30 parts by weight of total Cr in terms of chromic acid 20 parts by weight of phosphoric acid 60 parts by weight of the above copolymer 60 parts by weight of phosphoric acid / copolymer 0.33 SiO ₂ 15 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 21 parts by weight) The amount of the obtained chromate film deposited is 52 m in terms of Cr.
g / m ² . Further, an aqueous liquid prepared by blending 30 parts by weight of colloidal silica with 100 parts by weight of the olefin / acrylic acid copolymer resin was coated on a roll by using 145
Dry at ℃, olefin / acrylic acid copolymer resin 1
An organic composite plated steel sheet having a coating film composed of 00 parts by weight and colloidal silica 30 parts by weight of 1.5 g / m ² was produced.

Example 6 Zn-Ni alloy plated steel sheet (Basis weight: 20 g / m ² :
Ni = 12.4 wt%) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 42% by weight), 40 g / l,
70 g / l phosphoric acid, 5 parts by weight of methyl methacrylate, 33 parts by weight of butyl acrylate, 15 parts by weight of glycidyl methacrylate, 30 parts by weight of methacrylic acid, 3 parts by weight of acrylic acid, 14 parts by weight of hydroxyethyl acrylate. An aqueous liquid containing 80 g / l of the united resin was applied on a roll and dried at 150 ° C. to obtain a coating film. Components of coating film Total Cr is 40 parts by weight in terms of chromic acid 70 parts by weight of phosphoric acid 80 parts by weight of the above copolymer 80 parts by weight of phosphoric acid / copolymer 0.88 The adhesion amount of the obtained chromate film is 61 m in terms of Cr.
g / m ² . Further thereon, an aqueous liquid prepared by mixing 20 parts by weight of colloidal silica with 100 parts by weight of the olefin / acrylic acid copolymer resin was coated with a roll, and 145
Dry at ℃, olefin / acrylic acid copolymer resin 1
An organic composite plated steel sheet having a coating film composed of 00 parts by weight and 20 parts by weight of colloidal silica was 1.5 g / m ² was produced.

Example 7 Zn-Mg alloy plated steel sheet (Basis weight: 30 g / m ² ,
Reduced chromic acid (trivalent Cr / (3
(Valent Cr + hexavalent Cr) = 45% by weight), 25 g / l, phosphoric acid 50 g / l, methyl methacrylate 5 parts by weight-butyl acrylate 33 parts by weight-glycidyl methacrylate 1
5 parts by weight-30 parts by weight of methacrylic acid-3 parts by weight of acrylic acid-14 parts by weight of hydroxyethyl acrylate Copolymer resin 60 g / l, colloidal silica 15 g / l, M
Aqueous liquid containing 3 g / l of gO was coated on a roll,
It dried at 0 degreeC and the coating film was obtained. Ingredients of coating film Cr is 25 parts by weight in terms of chromic acid Phosphoric acid 50 parts by weight Copolymer 60 parts by weight Phosphoric acid / copolymer 0.83 SiO ₂ 15 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 25 parts by weight) Mg 3 parts by weight The amount of the obtained chromate film deposited is 61 m in terms of Cr.
g / m ² . Further, 5 parts by weight of methyl methacrylate, 33 parts by weight of butyl acrylate, 15 parts by weight of glycidyl methacrylate, 30 parts by weight of methacrylic acid, 5 parts by weight of acrylic acid and 14 parts by weight of hydroxyethyl acrylate were copolymerized. An aqueous liquid composed of the obtained resin was applied by a roll and dried at 160 ° C. to produce an organic composite plated steel sheet having a coating film of the resin of 1.4 g / m ² .

Example 8 Zn-Ni alloy plated steel sheet (Basis weight: 30 g / m ² ,
Ni = 13.9% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 50% by weight) 40 g / l, phosphoric acid 80 g / l, methyl methacrylate 15 parts by weight-butyl acrylate 33 parts by weight-glycidyl methacrylate 10 parts by weight-methacrylic acid 38 parts by weight An aqueous liquid containing 60 g / l of a resin obtained by copolymerizing 3 parts by weight of acrylic acid, 10 g / l of colloidal silica, and 3 g / l of MgO was coated with a roll and dried at 150 ° C. to obtain a coating film. . Ingredients of coating film 40 parts by weight of total Cr in terms of chromic acid 80 parts by weight phosphoric acid 80 parts by weight The above copolymer 80 parts by weight Phosphoric acid / copolymer 1.0 SiO ₂ 10 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 12.5 parts by weight) The amount of the obtained chromate film deposited is 61 m in terms of Cr.
g / m ² . Furthermore, an organic resin 100 obtained by copolymerizing 15 parts by weight of methyl methacrylate, 33 parts by weight of butyl acrylate, 10 parts by weight of glycidyl methacrylate, 38 parts by weight of methacrylic acid, and 3 parts by weight of acrylic acid. An aqueous solution containing 28 parts by weight of Aerosil is applied to a part by weight with a roll and dried at 155 ° C. to form a coating film comprising 28 parts by weight of the above-mentioned organic resin Aerosil at 1.0 g /
An organic composite plated steel sheet having m ² was produced.

Example 9 Zn-Cr type alloy plated steel sheet (Basis weight: 20 g / m ² ,
Cr = 10.8% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 50% by weight) 40 g / l, phosphoric acid 20 g / l, methyl methacrylate 15 parts by weight-butyl acrylate 33 parts by weight-glycidyl methacrylate 10 parts by weight-acrylic acid 41 parts by weight Resin 30 g / l obtained by copolymerization, colloidal silica 3 g / l, Mg
Apply an aqueous solution containing 0.5 g / l of O on a roll and
A coating film was obtained by drying at 0 ° C. Components of coating film 40 parts by weight of total Cr in terms of chromic acid 20 parts by weight phosphoric acid 20 parts by weight The above copolymer 30 parts by weight Phosphoric acid / copolymer 0.67 SiO ₂ 3 parts by weight MgO 0.5 parts by weight Chromate obtained The coating amount is 52m in terms of Cr
g / m ² . Furthermore, an aqueous liquid of vinyl-modified epoxy resin was applied onto the roll by coating, and dried at 145 ° C. to form a film of vinyl-modified epoxy resin at 1.3 g /
An organic composite plated steel sheet having m ² was produced.

Example 10 Zn-Ni alloy-plated steel sheet (weight per unit area: 20 g / m ² ,
Ni = 12.1% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 53 wt%) 20 g / l, phosphoric acid 40 g / l, methyl methacrylate 5 parts by weight-butyl acrylate 33 parts by weight-methacrylic acid 38 parts by weight-
Acrylic acid 3 parts by weight-hydroxyethyl acrylate 2
An aqueous liquid containing 100 g / l of a resin obtained by copolymerizing 0 part by weight of the resin and 15 g / l of colloidal silica was coated with a roll and dried at 150 ° C. to obtain a coating film. Ingredients of coating film 20 parts by weight of total Cr in terms of chromic acid 40 parts by weight phosphoric acid 40 parts by weight The above copolymer 100 parts by weight Phosphoric acid / copolymer 0.4 SiO ₂ 15 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 15 parts by weight) MgO 0.5 parts by weight The amount of the obtained chromate film deposited is 38 m in terms of Cr.
g / m ² . Further thereon, an aqueous liquid prepared by mixing 30 parts by weight of Aerosil with 100 parts by weight of urethane modified epoxy ester resin is applied by a roll and dried at 145 ° C. to obtain 100 parts by weight of urethane modified epoxy ester resin and 30 parts by weight of Aerosil. An organic composite plated steel sheet having a coating film of 1.4 g / m ² was produced.

Example 11 Zn-Ni alloy plated steel sheet (Basis weight: 20 g / m ² ,
Ni = 12.1% by weight) and 40% by weight reduced chromic acid (3
Valence Cr / (trivalent Cr + hexavalent Cr) = 40 wt%) 20 g
/ L, phosphoric acid 40 g / l, methyl methacrylate 30 parts by weight-butyl acrylate 40 parts by weight-methacrylic acid 1
An aqueous liquid containing 80 g / l of a resin obtained by copolymerizing 0 part by weight of 15 parts by weight of hydroxyethyl acrylate and 15 g / l of colloidal silica was coated with a roll, and
A coating film was obtained by drying at ℃. Ingredients of coating film 20 parts by weight of total Cr in terms of chromic acid 40 parts by weight phosphoric acid 40 parts by weight The above copolymer 80 parts by weight Phosphoric acid / copolymer 0.5 SiO ₂ 15 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 19 parts by weight) coating weight of the resulting chromate film, 45 m in Cr terms
g / m ² . Furthermore, 100 parts by weight of the urethane-modified epoxy ester resin and 25 parts by weight of Aerosil were applied on a roll and dried at 145 ° C. to obtain 100 parts by weight of the urethane-modified epoxy ester resin and 30 parts by weight of Aerosil. 1.4 g / m ²
The organic composite plated steel sheet having the above was manufactured.

Example 12 Zn-Ni alloy plated steel sheet (Basis weight: 20 g / m ² ,
Ni = 12.1% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 42% by weight) 20 g / l, phosphoric acid 35 g / l, styrene 50 parts by weight-butyl acrylate 40 parts by weight-hydroxyethyl acrylate 15 parts by weight-methacrylic acid 10 parts by weight are copolymerized. An aqueous liquid containing 90 g / l of the resin thus obtained and 15 g / l of colloidal silica was coated with a roll and dried at 150 ° C. to obtain a coating film. Ingredients of coating film 20 parts by weight of total Cr in terms of chromic acid 35 parts by weight phosphoric acid 35 parts by weight 90 parts by weight of the above phosphoric acid / copolymer 0.39 SiO ₂ 15 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 17 parts by weight) The amount of the obtained chromate film deposited is 53 m in terms of Cr.
g / m ² . Further, an aqueous liquid prepared by mixing 100 parts by weight of vinyl-modified epoxy ester resin with 25 parts by weight of colloidal silica was applied on a roll and dried at 145 ° C. to obtain 100 parts by weight of vinyl-modified epoxy ester resin and 25 parts by weight of colloidal silica. 1.1 g of a film consisting of
An organic composite-plated steel sheet having / m ² was produced.

Example 13 Zn-Ni alloy-plated steel sheet (weight per unit area: 20 g / m ² ,
Ni = 12.8% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 45% by weight), phosphoric acid 40 g
/ L, 30 parts by weight of methyl methacrylate-40 parts by weight of butyl acrylate-30 parts by weight of styrene-10 parts by weight of methacrylic acid-15 parts by weight of hydroxyethyl acrylate 60 g / l, colloidal Aqueous liquid containing 6 g / l of silica was coated with a roll,
A coating film was obtained by drying at ℃. Ingredients of coating film 15 parts by weight of total Cr in terms of chromic acid 40 parts by weight of phosphoric acid 60 parts by weight of the above copolymer 60 parts by weight of phosphoric acid / copolymer 0.67 SiO ₂ 6 parts by weight of SiO (based on 100 parts by weight of the copolymer) ₂ 10 parts by weight) The adhesion amount of the obtained chromate film is 48 m in terms of Cr.
g / m ² . Furthermore, 100 parts by weight of an olefin / acrylic acid copolymer resin is added to the above and colloidal silica 2 is added.
Aqueous liquid containing 5 parts by weight was applied on a roll, and the temperature was 145 ° C.
Dried with olefin / acrylic acid copolymer resin 100
An organic composite plated steel sheet having a film composed of 1 part by weight and 25 parts by weight of colloidal silica was 1.1 g / m ² .

Example 14 Zn-Ni alloy-plated steel sheet (weight per unit area: 20 g / m ² ,
Ni = 13.2% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 50% by weight) 15 g / l, phosphoric acid 40 g / l, butyl acrylate 40 parts by weight-methacrylic acid 30 parts by weight-hydroxyethyl acrylate 1
An aqueous liquid containing 60 g / l of an organic resin obtained by copolymerizing 5 parts by weight and 6 g / l of colloidal silica was coated with a roll and dried at 150 ° C. to obtain a coating film. Ingredients of coating film 15 parts by weight of total Cr in terms of chromic acid 40 parts by weight of phosphoric acid 60 parts by weight of the above copolymer 60 parts by weight of phosphoric acid / copolymer 0.67 SiO ₂ 6 parts by weight of SiO (based on 100 parts by weight of the copolymer) ₂ 10 parts by weight) The amount of the obtained chromate film deposited is 61 m in terms of Cr.
g / m ² . Furthermore, 100 parts by weight of an olefin / acrylic acid copolymer resin is added to the above and colloidal silica 2 is added.
Aqueous solution containing 0 parts by weight is coated with a roll, and the temperature is 165 ° C.
Dried with olefin / acrylic acid copolymer resin 100
An organic composite plated steel sheet having a coating film composed of 16 parts by weight and 20 parts by weight of colloidal silica was produced at 1.6 g / m ² .

Example 15 Zn-Ni alloy plated steel sheet (Basis weight: 20 g / m ² ,
Ni = 13.2% by weight) and reduced chromic acid (trivalent Cr /
(Trivalent Cr + hexavalent Cr) = 50% by weight) 20 g / l, phosphoric acid 45 g / l, acrylic amide resin 60 g / l,
An aqueous liquid containing 6 g / l of colloidal silica was coated with a roll and dried at 150 ° C. to obtain a coating film. Ingredients of coating film 20 parts by weight of total Cr in terms of chromic acid 45 parts by weight Phosphoric acid 60 parts by weight The above copolymer 60 parts by weight Phosphoric acid / copolymer 0.75 SiO ₂ 6 parts by weight (based on 100 parts by weight of the copolymer SiO ₂ 10 parts by weight) The amount of the obtained chromate film deposited is 57 m in terms of Cr.
g / m ² . Furthermore, 100 parts by weight of an olefin / acrylic acid copolymer resin is further added onto the colloidal silica 3
Aqueous liquid containing 0 parts by weight was applied on a roll and then applied at 155 ° C.
Dried with olefin / acrylic acid copolymer resin 100
An organic composite plated steel sheet having a coating film composed of 1 part by weight and 30 parts by weight of colloidal silica was 1.0 g / m ² .

Comparative Example 1 A Zn-plated steel sheet was coated with an aqueous liquid containing 15 g / l of chromic acid (100% by weight of hexavalent Cr) and 25 g / l of phosphoric acid on a roll and dried at 150 ° C. A chromate film of 48 mg / m ^{2 in} terms of Cr was formed.

Comparative Example 2 Zn-NI alloy plated steel sheet (Basis weight: 20 g / m ² ,
Ni = 12.8% by weight), an aqueous liquid of chromic acid (hexavalent Cr 100% by weight chromic acid) 15 g / l, phosphoric acid 25 g / l, colloidal silica 15 g / l was applied by a roll, and 17
It was dried at 0 ° C. to form a chromate film having an adhesion amount of 62 mg / m ^{2 in} terms of Cr.

Comparative Example 3 Zn-Ni alloy plated steel sheet (adhesion amount: 20 g / m ² ,
Ni = 12.9% by weight), chromic acid (hexavalent Cr 100% by weight chromic acid) 20 g / l, phosphoric acid 25 g / l, acrylic emulsion 100 g / l were mixed with an aqueous solution, and dried at 150 ° C. To obtain a coating film. Components of coating film Total Cr is 20 parts by weight in terms of chromic acid Phosphoric acid 25 parts by weight Acrylic resin 100 parts by weight Phosphoric acid / acrylic resin 0.25 SiO ₂ 6 parts by weight The amount of the obtained chromate film is calculated in terms of Cr. 52 m
g / m ² .

Comparative Example 4 Zn-Ni alloy plated steel sheet (adhesion amount: 20 g / m ² ,
Ni = 12.5 wt%) with chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) = 30 wt%) 15 g / l, phosphoric acid 8
An aqueous solution containing 0 g / l, 70 g / l of acrylamide resin, 10 g / l of Aerosil and 10 parts by weight of Aerosil was coated with a roll and dried at 165 ° C. to obtain a coating film. Components of coating film Total Cr in terms of chromic acid 15 parts by weight Phosphoric acid 80 parts by weight Acrylamide resin 70 parts by weight Phosphoric acid / acrylamide resin 1.14 SiO ₂ 10 parts by weight The amount of the resulting chromate film deposited is in terms of Cr. 58m
g / m ² .

Comparative Example 5 Zn-Ni alloy plated steel sheet (adhesion amount: 20 g / m ² ,
Ni = 12.3 wt%) with chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) = 10 wt%) 25 g / l, phosphoric acid 1
An aqueous solution containing 0 g / l and 100 g / l of an acrylic amide resin was coated with a roll and dried at 120 ° C. to obtain a coating film. Components of coating film Total Cr is 25 parts by weight in terms of chromic acid Phosphoric acid 10 parts by weight Acrylic amide resin 100 parts by weight Phosphoric acid / acrylic amide resin 0.1 Adhesion amount of the obtained chromate film is 51 m in terms of Cr.
g / m ² . Further, an aqueous solution of an epoxy resin was coated on it with a roll and dried at 155 ° C. to produce an organic composite plated steel sheet having a coating of the epoxy resin of 1.2 g / m ² .

Comparative Example 6 Zn-Ni alloy plated steel sheet (adhesion amount: 20 g / m ² ,
Ni = 12.9 wt%) with chromic acid (trivalent Cr / (trivalent Cr + hexavalent Cr) = 10 wt%) 25 g / l, phosphoric acid 1
An aqueous liquid containing 0 g / l, 100 g / l of acrylic emulsion, and 10 g / l of colloidal silica was applied by a roll and dried at 150 ° C. to obtain a coating film. Components of coating film Total Cr in terms of chromic acid 25 parts by weight Phosphoric acid 10 parts by weight Acrylic resin 100 parts by weight Phosphoric acid / acrylic resin 0.1 SiO ₂ 10 parts by weight The amount of the obtained chromate film is calculated in terms of Cr. 45m
g / m ² . On top of that, epoxy resin 10
Epoxy resin 1 was prepared by coating an aqueous solution prepared by mixing 25 parts by weight of Aerosil with 0 part by weight with a roll and drying at 155 ° C.
1. A coating consisting of 00 parts by weight and 25 parts by weight of Aerosil is 1.
An organic composite plated steel sheet having 1 g / m ² was produced.

Bare corrosion resistance after processing by the salt spray test of Examples 1 to 15 and Comparative Examples 1 to 6 when treated on Zn or Zn-based alloy plated steel sheets, melamine-based low temperature baking type (baking temperature: 110 ° C.) The coating adhesion, the Cr elution resistance and the bath stability when 30 μm was applied are shown in Tables 6, 7 and 8.

[0069]

[Table 6]

[0070]

[Table 7]

[0071]

[Table 8]

As is clear from Tables 6, 7 and 8, Z
When the n-plated steel sheet is treated with the chromate bath of the present invention, bare corrosion resistance after processing hardly changes after 1000 hours, and a little red rust occurs at 1500 hours. When the Zn-based alloy-plated steel sheet is treated with the chromate bath of the present invention, the bare corrosion resistance after processing is 2
There is almost no change after 000 hours, and only a little red rust occurs after 3000 hours. Further, the organic compound-plated steel sheet of the present invention in which the layer of the above-mentioned resin is further formed on the obtained chromate layer by performing the treatment with the chromate bath of the present invention, the bare corrosion resistance after processing is 4000 hours. There is only a small amount of red rust. On the other hand, a film formed from a known chromate bath (Comparative Examples 1 and 2)
Shows a considerable amount of red rust after 100 hours of SST. In addition, resin chromates other than the present invention with various resins added (
In Comparative Examples 3 and 4), red rust was considerably generated in 400 hours. The adhesion of the coating film is similar, and the treated steel sheet of the present invention shows extremely excellent adhesion even in a low temperature baking type (110 ° C. baking) where it is difficult to obtain paint adhesion, but the known chromate film (Comparative Examples 1, 2 ) Is a resin chromate other than the present invention (
In the case of Comparative Examples 3 and 4), the paint adhesion is extremely poor. Cr
Regarding the elution property, when the treatment with the bath of the present invention is carried out, almost no Cr elution occurs. On the other hand, a large amount of Cr was found to be eluted from the known chromate film (Comparative Examples 1 and 2) and the resin chromate other than the present invention (Comparative Examples 3 and 4). Further, the bath life of the resin chromate baths (Examples 1 to 15) according to the present invention is extremely long and does not change for a long time. On the other hand, the resin chromate baths other than the present invention (Comparative Examples 3, 4, 5, and 6) have extremely short bath lives, and the resin gels and becomes unusable in an extremely short time.

[0073]

As described above, the reduction rate of chromium (trivalent Cr / (trivalent Cr + hexavalent Cr) × 100) is 40 to 65.
Phosphoric acid / organic resin (weight ratio) using wt% chromic acid
The aqueous liquid in which phosphoric acid and a resin coexist so that the water content becomes 0.3 to 1.0 has an extremely long bath life, and cold-rolled steel sheet or Z
Chromium elution resistance on n or Zn alloy plated steel sheet,
The surface-treated steel sheet and organic composite plated steel sheet that can form a chromate film with excellent bare corrosion resistance and paint adhesion after processing and have a specified amount of chromate film formed from the above chromate bath have extremely excellent bare corrosion resistance. Show. Moreover, since it has excellent adhesion to paints and excellent resistance to chromium elution, it can be used as it is after processing or after painting, so it is most suitable as a base for coated steel sheets. From such characteristics, the treated steel sheet of the present invention is
It can be used in a wide range of fields such as building materials and the automobile industry.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Keitaro Shibata 2-3-6 Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Corporation (72) Inventor Ikuo Kikuchi Fuji-cho, Himeji-shi, Hyogo Prefecture No. 1 Nippon Steel Works Hirohata Works (72) Inventor Kiyoshi Omori No. 1 Fuji-machi, Hirohata-ku, Himeji City, Hyogo Prefecture Shin Nippon Steel Works Hirohata Works

Claims (8)

[Claims] 1. A reduction ratio of chromium [trivalent Cr / (trivalent Cr
+6 valent Cr) × 100] contains 40 to 65% by weight of chromic acid, phosphoric acid and resin, and phosphoric acid / resin (weight ratio)
A resin chromate bath, wherein the resin chromate bath is composed of an aqueous liquid of 0.3 to 1.0. 2. The resin chromate bath further comprises sol or powder of SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃
At least one selected from the group consisting of O ₄ , MgO, ZrO ₂ , SnO ₂ and Al ₂ O ₃ is added to resin 100
A resin chromate bath comprising an aqueous liquid containing 3 to 30 parts by weight with respect to parts by weight. 3. A cold rolling steel sheet, a Zn-plated steel sheet or a Zn-based alloy-plated steel sheet on which a reduction ratio of chromium [trivalent Cr /
(Trivalent Cr + hexavalent Cr) × 100] is 40 to 65% by weight.
A chromate film formed from a resin chromate bath comprising an aqueous liquid containing chromic acid, phosphoric acid and a resin, and having a phosphoric acid / resin (weight ratio) of 0.3 to 1.0. Treated steel plate. 4. The surface-treated steel sheet according to claim 3, wherein the amount of the chromate film deposited is 10 to 300 mg / m ² in terms of Cr. 5. A cold rolled steel sheet, a Zn plated steel sheet or a Zn-based steel sheet.
Chromium reduction rate [Trivalent Cr /
(Trivalent Cr + hexavalent Cr) × 100] is 40 to 65% by weight.
Chromic acid, phosphoric acid, resin and sol or powder
SiO_Two, Cr _TwoO_Three, Fe_TwoO_Three, Fe_ThreeO_Four, Mg
O, ZrO_Two, SnO_TwoAnd Al_TwoO _ThreeFlock of
Containing at least one selected from
(Amount ratio) is 0.3 to 1.0
Having a chromate film formed from a mate bath
Characterized surface-treated steel sheet. 6. The surface-treated steel sheet according to claim 5, wherein the amount of the chromate film deposited is 10 to 300 mg / m ² in terms of Cr. 7. At least one selected from methyl methacrylate, butyl acrylate, styrene, glycidyl methacrylate, methacrylic acid, acrylic acid, an organic phosphorus monomer and hydroxyethyl methacrylate on the chromate film. A resin obtained by polymerization or copolymerization of olefin, olefin-acrylic acid copolymer resin, epoxy resin, acrylic modified epoxy resin, ester modified epoxy resin, urethane modified epoxy resin, urethane modified epoxy ester resin, vinyl modified epoxy resin and vinyl modified resin. The surface-treated steel sheet according to claim 3 or 5, wherein a resin film made of at least one resin selected from the group consisting of epoxy ester resins has an adhesion amount of 0.2 to 3.0 g / m ^2. . 8. The resin film on the chromate film, in addition to the resin, is in the form of sol or powder, such as SiO ₂ , Cr ₂ O ₃ , and F.
at least one selected from the group consisting of e ₂ O ₃ , Fe ₃ O ₄ , MgO, ZrO ₂ , SnO ₂ and Al ₂ O _3.
The seed is formed from a mixture containing 10 to 60 parts by weight with respect to 100 parts by weight of the resin, and the coating amount of the seed is 0.2 to 3.
It is 0 g / m < ² >, The surface-treated steel plate of Claim 3 or 5 characterized by the above-mentioned.