JP2787365B2 - Organic thin film coated Cr-containing zinc-based multi-layer rust-proof steel sheet having excellent long-term adhesion of organic thin film and cationic electrodeposition coating property, and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an organic thin film-coated Cr-containing zinc-based material which is excellent in long-term adhesion of organic thin films used for automobiles, home appliances, building materials and the like and cationic electrodeposition coating properties. TECHNICAL FIELD The present invention relates to a multilayer rust-proof steel plate and a method for producing the same.

(Prior art) Electrogalvanized steel sheet as a surface-treated steel sheet that can improve corrosion resistance without impairing the workability, weldability, and paintability of cold-rolled steel sheets, especially phosphatability, and that can be mass-produced It is well known that is manufactured and widely used. However, in recent years, corrosion of automobile bodies has become severe due to the spraying of salt to prevent road freezing in winter in cold regions, and the use of galvanized steel sheets has been promoted as a measure to strengthen rust prevention. There is a high demand for good rust-proof steel plates. In order to improve the corrosion resistance of these galvanized steel sheets, it is known that the corrosion resistance is improved by increasing the amount of zinc plating. As a method, various alloy plating methods have been proposed in order to suppress the dissolution of zinc itself. Many of these contain iron group elements such as Fe, Ni, and Co as alloy components.

Electro-zinc alloy-plated steel sheets made of these zinc-iron group elements are disclosed in, for example, Japanese Patent Publication No. 50-29821 and Japanese Patent Publication No.
As described in JP-A-61831, it is characterized by excellent corrosion resistance after unpainting or after painting, and has been industrially produced and put to practical use, but further improvement in corrosion resistance is required.
On the other hand, various electroplated steel sheets have been proposed in which the corrosion resistance is improved by adding Cr to the zinc or zinc-based alloy plating. For example, Japanese Patent Publication No. 59-3831
59-40234, JP-A-61-130498, JP-A-61-61498
-270398 and JP-A-62-54099. All of these have a low Cr content of 5% or less from the viewpoint of workability and chemical conversion treatment, and the effect of Cr is insufficient for corrosion resistance. As a remedy, a composite eutectoid method of organic matter and Cr was developed to improve corrosion resistance by increasing the Cr content.
It greatly contributes to the improvement of corrosion resistance. More recently, an organic composite steel sheet with a chromate film coated on a Cr-containing zinc-based alloy plating layer or a Cr-containing zinc alloy-based organic dispersion plating layer and then provided with a composite organic thin film has been developed as a highly corrosion-resistant surface-treated steel sheet. However, there is a strong demand for improvement of the adhesion of the composite organic film to the plating surface for a long period of time and the reduction of the cationic electrodeposition coating property due to the electric resistance of the composite organic film.

(Problems to be Solved by the Invention) In general, in the case of an organic composite steel sheet in which a chromate film is applied on a Cr-containing zinc-based alloy plating layer or a Cr-containing zinc alloy-based organic dispersion plating layer and then a composite organic thin film is provided, a composite organic steel sheet is used. The life of the rust-prevention effect is determined by the period of time for maintaining good adhesion of the thin film to the plating surface. Therefore, it is necessary to extend this period, and to reduce the cationic electrodeposition coating property due to the electrical resistance of the composite organic thin film. SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic composite thin film with such a property that a path through which ions can pass through the organic thin film quickly when it is put into an electrodeposition paint tank.

(Means for Solving the Problems) The gist of the present invention is that a Cr-containing zinc-based alloy plating layer or a Cr-containing zinc alloy-based organic dispersion plating layer having a thickness of 1 μm or more and 100 μm or less is formed on a steel sheet, and A chromate containing 0.03 to 60% of hexavalent chromium in a weight ratio with respect to the amount of chromium is applied, and a water-imparting treatment is applied thereon to give a non-figure type diffusion property. An organic thin film coated Cr-containing zinc-based multi-layered rust-preventive steel sheet excellent in long-term adhesion of the organic thin film and cationic electrodeposition coating characteristic characterized by having a composite organic thin film, and long-term adhesion of the organic thin film and When manufacturing an organic thin film-coated Cr-containing zinc-based multi-layer rust-preventive steel sheet with excellent cationic electrodeposition coating properties, use an electroplating method to deposit a Cr-containing zinc-based alloy plating layer or a Cr-containing zinc alloy layer having a thickness of 1 to 100 microns. A gold-based organic dispersion plating layer is formed, and water containing hexavalent chromium in an amount of 0.03 to 60% by weight with respect to the total amount of chromium and capable of evaporating at the time of baking in a composite organic thin film coating step following this processing step. And / or chromate-dried to contain 0.1% or more and 40% or less of alcohol with respect to the organic thin film, and then use a solvent-type composite organic thin film paint to form a film.
Applying a wet coating of 0.3 to 3 microns and baking while evaporating the water and / or alcohol remaining in the chromate coating to impart a water permeability treatment to impart non-fixed diffusion characteristics. This is a process for producing a Cr-containing zinc-based multi-layer rust-proof steel sheet coated with an organic thin film, which is excellent in long-term adhesion of an organic thin film and excellent cationic electrodeposition coating properties.

(Action) In the present invention, the life of rust prevention is such that the Cr-containing zinc-based alloy plating layer or the Cr-containing zinc alloy-based organic dispersion plating layer under the organic coating generates corrosion products due to corrosion, Focusing on the large relationship with the decrease in the adhesion of the organic film that occurs due to accumulation on the surface, micro-defects are distributed so that water can easily diffuse into the organic film for the long life of the rust prevention effect. In addition, it enhances the ability of corrosion products to diffuse out and remove. In order to give these microscopic defects to the organic coating, there is a method in which, for example, water-soluble salts are previously charged and placed in the organic coating, but this salt adversely affects the electrodeposition coatability by the user. Or cause abnormal corrosion. Therefore, in the present invention, as an alternative method, a substance capable of generating a gas at the time of baking the paint, specifically water or alcohol, is placed in the chromate layer below the organic film, and gasified at the time of baking. Micro defects are given by passing through the organic film. It is important to provide the following chromate film prior to the coating of the organic film in order to provide the micro defects required for the organic film according to the gist of the present invention.

That is, hexavalent chromium is added in a weight ratio of 0.03 to the total chromium amount.
Chromate is dried to contain 0.1% to 40% of water and / or alcohol which can be evaporated at the time of baking in a composite organic thin film coating step following this treatment step. It is important to provide on the Cr-containing zinc alloy plating layer or the Cr-containing zinc alloy organic dispersion plating layer. If the amount of evaporable water or alcohol is less than 0.1%, the diffusibility of the corrosion product is insufficient, and if it exceeds 40%, repelling and aside of the coating film occur. In addition, under a coating film with micro defects as described above, the corrosion resistance and the Cr content in the degreasing process by the user
In order to suppress the solutes, those containing hexavalent chromium in an amount of 0.03 to 60% by weight with respect to the total amount of chromium give good results.
The organic resin used in the present invention is of a solvent type, and it is essential to use one that does not dissolve the evaporable substance charged in the chromate. Resins such as commonly used resins, such as acrylic resins and modified resins thereof, epoxy resins and modified resins thereof, olefin resins and modified resins thereof, urethane resins and modified resins thereof can be used in the method of the present invention. Its molecular weight is 1000-10000
Epoxy resin systems give particularly good results. This is considered to be due to the fact that optimum micro defects are formed by this treatment in the curing process of the epoxy resin.

As described above, when the organic film is given an abnormal diffusion property of water, the uniformity of the deposited film and the gas pin (the hydrogen gas taken into the film during the electrodeposition) But,
It is possible to prevent the generation of small holes which are generated because the holes do not come off smoothly in the baking process.

When the organic thin film coated Cr-containing zinc-based multi-layered rust-preventive steel sheet with excellent long-term adhesion and cationic electrodeposition coating property of the organic thin film made in this way is immersed in water, it becomes more susceptible to water absorption than the normal diffusion method. A much faster rate of water absorption occurs. When treated in accordance with the present method, the organic coating has a good result in the range of 0.3 to 3 μm, and has a low solubility of 1 to 100 μm in size of hardly soluble oxide particles, nitride particles and carbide particles of 40%. When it is contained within the range, the uniform dispersibility of the microscopic defect portion is improved.

In addition, the Cr-containing zinc alloy-based organic dispersion plating targeted by the present invention refers to the following plating.

1) Zn-Cr-cation polymer plating 2) Zn-Ni-Cr-cation polymer plating 3) Zn-Co-Cr-cation polymer plating 4) Zn-Fe-Cr-cation polymer plating 5) Zn-Mn-Cr- Cationic polymer plating 6) Zn-Sn-Cr-cationic polymer plating 7) Zn-Ni-Cr- sparingly soluble inorganic oxide-cationic polymer plating 8) Zn-Co-Cr- sparingly soluble inorganic oxide-cationic polymer plating 9) Zn-Fe-Cr-poorly soluble inorganic oxide-cationic polymer plating 10) Zn-Mn-Cr-poorly soluble inorganic oxide-cationic polymer plating 11) Zn-Sn-Cr-poorly soluble inorganic oxide-cationic polymer plating 12 ) Zn-Mn-Cr-Ni-poorly soluble inorganic oxide-cationic polymer plating 13) Zn-Sn-Cr-Ni-poorly soluble inorganic oxide-cationic polymer plating 14) Zn-Ni-Cr-poorly soluble metal powder- Cationic polymer plating 15) Zn-Co-Cr- Poorly soluble metal powder-cationic polymer plating 16) Zn-Fe-Cr-poorly soluble metal powder-cationic polymer plating 17) Zn-Mn-Cr-poorly soluble metal powder-cationic polymer plating 18) Zn-Sn-Cr-poorly soluble Metal powder-cationic polymer plating 19) Zn-Mn-Cr-Ni-sparingly soluble metal powder-cationic polymer plating 20) Zn-Sn-Cr-Ni-sparingly soluble metal powder-cationic polymer plating 21) Zn-Fe element Multiple species-Cr-cation polymer plating 22) Multiple species of Zn-Mn-Fe element-Cr-cation polymer plating 23) Multiple species of Zn-Sn-Fe element-Cr-cation polymer plating 24) Zn-Fe element Multiple types of elements-Cr-slightly soluble oxide-cationic polymer plating 25) Multiple types of Zn-Mn-Fe group elements-Cr-poorly soluble inorganic oxide-cationic polymer plating 26) Multiple types of Zn-Sn-Fe group elements Species-Cr-Insoluble inorganic oxide-Cationic polymer plating 27) Zn-Fe genus Plurality of elements-Cr-sparingly soluble metal powder-cationic polymer plating 28) Plurality of Zn-Mn-Fe element-Cr-sparingly soluble metal powder-cationic polymer plating 29) Zn-Sn-Fe element -Cr-poorly soluble metal powder-cationic polymer plating 30) Plating in which the sparingly soluble oxide is replaced by sparingly soluble nitride in the above plating compositions 7) to 13) 31) Plating composition of above 24) to 26) 32) Plating in which sparingly soluble oxides are replaced by sparingly soluble nitrides 32) Plating in which sparingly soluble oxides are replaced by sparingly soluble carbides in the plating compositions of 7) to 13) above 33) of 24) to 26) above Plating in which sparingly soluble oxide is replaced by sparingly soluble carbide in the plating composition The cationic polymer described here is insoluble in water when the molecular weight is 200 or more and -COOH group and -OH group are removed from its skeleton. An organic resin that has an amine group. Specifically, it refers to the following organic resins.

A) Cationized olefin resin B) Cationized acrylic resin C) Cationized vinyl resin D) Cationized epoxy resin E) Cationized polyester resin F) Cationized urethane resin G) Cationized natural resin H) Cationized amino resin I) Cationized imide resin J) Cationized amide resin K) Polyaminosulfonate In addition, the hardly soluble oxide referred to here is an oxide particle of the following element or a particle whose surface is covered with 70% or more of this oxide. Say

Ti, Si, Al, Nb, Zr, Ta, Pb, In, Hf, W, Os Furthermore, the insoluble nitride mentioned here is a nitride particle of the following element or the surface of this nitride. A particle covered by more than 70%.

Ti, Si, Al, Nb, Zr, Ta, Pb, In, Hf, W, Os, B, Co, Fe, NiFurthermore, the hardly soluble carbide mentioned here is carbide particles of the following elements or A particle whose surface is covered with more than 70% of carbide.

Ti, Si, Al, Nb, Zr, Ta, Pb, In, Hf, W, Os, B, Co, Fe, Ni In addition, the hardly soluble metal powder described here is a metal powder that is hardly soluble in the plating solution. The following is a specific example.

Ti, Si, Al, Nb, Zr, Ta, Pb, In, Hf, W, Os, Au, Ag, Co, Fe, Ni Example 1 As an electroplating solution, Zn ²⁺ was 40 g / l, Ni ²⁺ 20g / l, Cr
³⁺ 15.5g / l, molecular weight 3500 as cationic polymer
A plating solution containing 2 g / l of polyamine sulfone is prepared using sulfate and chromium sulfate. After adjusting the pH of the plating solution to 3.4 using sulfuric acid, the lead electrode was used as an anode at room temperature,
Perform electroplating at a current density of 80 A / dm ² with a pole ratio of 1: 1.
Zn: Cr: Ni: cationic polymer with a coating weight of 30 g / m ² having a ratio of 86.5:
A 9: 4: 0.5 Cr-containing zinc alloy-based organic dispersion plated steel sheet was obtained. Further, on the upper layer of this Cr-containing zinc alloy-based organic dispersion plated steel sheet, a chromate containing 50% of hexavalent chromium in a weight ratio to the total chromium amount was equivalent to 50 mg / m ^{2 in} terms of Cr, and heated to 200 ° C. The mixed sol of Si, Al, and Ti is adjusted in the range of 0.1% to 10% to the moisture equivalent to 0.01, 0.1, 1.0, 10, and 100% of the amount of organic film to be baked later, respectively. The soaked chromate is applied and dried. Next, an epoxy resin having a molecular weight of 5000 and SiO ₂ having a particle size of 8 mm were added to the chromate by 25% by weight based on the solid content.
A wet-coating film equivalent to 0.8 micron in thickness was prepared using a solvent-type composite organic thin-film coating material with a solid content of 22% by weight.
The upper solvent type organic coating film was baked at 50 ° C. for 15 seconds while evaporating water remaining in the chromate film. FIG. 1 shows the long-term adhesion of the coating film, and FIG. 2 shows the gas pin properties during electrodeposition coating. The long-term adhesion of the upper organic film was determined by a cyclic corrosion test (immersion in 1% salt water for 2 minutes, drying at 70 ° C for 20 minutes,
The value obtained was compared with the time until the organic thin film was peeled off by 50% or more with Cellotape (registered trademark) by drying.
The electrodeposition coatability was affected by the turnover of the paint, which was treated with 100 sheets of cold rolled steel sheet of 1 dm ² area per liter of U-600 paint, heated to 85 ° C and sealed and stored for 3 months. It was used as a paint to reproduce the electrodeposition paint of the actual machine. In the electrodeposition coating, the electric conductivity was adjusted with isopropyl alcohol and the bath temperature was adjusted so that a deposited film of 30 μm was obtained at 170 V in 2 minutes. Gas pins were expressed by the number generated in an area of 1 dm ² . The method of the present invention shows good results for both evaluations.

Example 2 As an electroplating solution, Zn ²⁺ was 40 g / l, Mn ²⁺ was 15 g / l, and Cr was
A plating solution containing 15.5 g / l of ³⁺ , 2 g / l of (NH ₄ ) SO _3, and 2 g / l of a polyamine sulfone having a molecular weight of 4500 as a cationic polymer is prepared using sulfate and chromium sulfate. Was adjusted to pH = 4.1 with this plating solution with sulfuric acid, and the lead electrode at room temperature as an anode, Kyokuhi 1: 1 subjected to electroplating at a current density of 80A / dm ^2, the deposition amount of 30 g / m ² A Cr-containing zinc alloy-based organic dispersion plated steel sheet having a ratio of Zn: Cr: Mn: cationic polymer of 85.5: 7: 7: 0.5 was obtained. Further, a chromate film containing 40% of hexavalent chromium in a weight ratio to the total chromium amount of 50 mg / m in terms of Cr is provided on the upper layer of the Cr-containing zinc alloy-based organic dispersion plated steel sheet.
² equivalent, and a chromate film containing a 1: 1 mixture of water and propyl alcohol by incorporating 15% of silica sol at 10 g / m ^{2 was} applied, and 30 ° C., 60 ° C., 80 ° C., 120 ° C., 150 ° C.
The solution was heated to 200 ° C. and 200 ° C., held for 10 seconds, and then cooled to room temperature. Next, an epoxy resin having a molecular weight of 5,000 and a paint for a solvent-type composite organic thin film having a solid content of 22% by weight, containing 25% by weight of a solid content of SiO ₂ having a particle size of 8 mm were used on the chromate. A wet coating film having a thickness of 0.8 μm was applied, and the upper solvent type organic coating film was baked at 150 ° C. for 15 seconds while evaporating water remaining in the chromate film. Table 1 shows the results. The method of the present invention shows good results for both evaluations. The extractability of the underlayer chromium by the degreasing solution was evaluated by the weight loss after immersion in a 1% caustic soda solution at 40 ° C. for 10 minutes. The evaluation method described above was used for the evaluation in the examples described below.

Example 3 As an electroplating solution, Zn ²⁺ was 40 g / l, Ni ²⁺ was 20 g / l, and Cr was
³⁺ 15.5 g / l, particle size 8 mm micron silica 10 g / l,
A plating solution containing 2 g / l of polyamine sulfone having a molecular weight of 4000 as a cationic polymer is prepared using sulfate and chromium sulfate. After adjusting the plating solution to pH = 2.0 using sulfuric acid, electroplating was performed at a current density of 80 A / dm ² with a lead electrode as an anode at a normal temperature and a pole ratio of 1: 1 to obtain a coating amount of 30 g / m ^2.
The ratio of Zn: Cr: Ni: silica: cationic polymer is 84.5: 9: 3:
A 3: 0.5 Cr-containing zinc alloy-based organic dispersion plated steel sheet was obtained.
Furthermore, on the upper layer of the Cr-containing zinc alloy-based organic dispersion plated steel sheet, hexavalent chromium in a weight ratio to the total chromium amount of 10, 20,
Chromate coating containing 30, 40, 50, 60, 70, 80, 90%
A chromate film equivalent to 50 mg / m ^{2 in} terms of Cr and containing water by containing 20% of silica sol was applied at 9 g / m ² , heated to 80 ° C., kept for 20 seconds, and then cooled to room temperature.
Next, a film is formed on the chromate using an epoxy resin having a molecular weight of 5,000 and a solvent type composite organic thin film paint having a solid content of 22% by weight and containing 25% by weight of a solid content of SiO ₂ having a particle size of 8 mm. A wet coating film having a thickness of 0.8 μm was applied, and the upper solvent type organic coating film was baked at 150 ° C. for 15 seconds while evaporating water remaining in the chromate film. Table 2 shows the results. The method of the present invention shows good results for both evaluations.

Example 4 As an electroplating solution, Zn ²⁺ was 40 g / l, Mn ²⁺ was 15 g / l, Cr
A plating solution containing 15.5 g / l of ³⁺ , 2 g / l of (NH ₄ ) SO _3, and 2 g / l of a polyamine sulfone having a molecular weight of 4500 as a cationic polymer is prepared using sulfate and chromium sulfate. Was adjusted to pH = 4.1 with this plating solution with sulfuric acid, and the lead electrode at room temperature as an anode, Kyokuhi 1: 1 subjected to electroplating at a current density of 80A / dm ^2, the deposition amount of 30 g / m ² A Cr-containing zinc alloy-based organic dispersion plated steel sheet having a ratio of Zn: Cr: Mn: cationic polymer of 85.5: 7: 7: 0.5 was obtained. Further, on the upper layer of this Cr-containing zinc alloy-based organic dispersion plated steel sheet, a chromate containing 40% of hexavalent chromium in a weight ratio to the total chromium amount is equivalent to 50 mg / m ^{2 in} terms of Cr, and a mixture of water and propyl alcohol. 5900m for 1: 1 mixture
subjected to g / m ² contained chromate film was, 30 ℃, 80 ℃, 110
Heated for 20 seconds at a temperature of 150C and 150C, respectively, was made. Then, after cooling to 30 ° C., an epoxy resin having a molecular weight of 8000 and a Si powder having a particle diameter of 8 millimicrons are placed on the chromate.
Using a solvent type composite organic thin film paint having a solid content of 22% by weight, containing 25% by weight of O ₂ with respect to the solid content, and a film thickness of 0.1, 0.2, 0.3, 0.
Apply a wet film equivalent to 4,0.5,0.6,0.7,0.8,0.9,1.0,2.2,3.2,4.5 microns, and evaporate the water remaining in the chromate film at 150 ° C while evaporating the water in the upper layer. Membrane
It was baked for 15 seconds to produce each level of treated steel sheet. Tables 3 and 4 show the evaluation results. The method of the present invention shows good results for both evaluations.

Example 5 As an electroplating solution, Zn ²⁺ was 36 g / l, Cr ³⁺ was 15.5 g / l,
2 g / l of (NH ₄ ) SO ₃ and a cationic polymer having a molecular weight of 45
2 g / l of polyamine sulfone with a molecular weight of 1200
A plating solution containing 10 g / l of an amine-modified epoxy resin is prepared using sulfate and chromium sulfate. Was adjusted to pH = 4.1 with this plating solution with sulfuric acid, and the lead electrode at room temperature as an anode, Kyokuhi 1: 1 subjected to electroplating at a current density of 80A / dm ^2, the deposition amount of 30 g / m ² The ratio of Zn: Cr: cationic polymer is 90.
A 3: 8.2: 1.5 Cr-containing zinc alloy-based organic dispersion plated steel sheet was obtained. Further, on the upper layer of the Cr-containing zinc alloy-based organic dispersion plated steel sheet, a chromate containing 55% of hexavalent chromium in a weight ratio to the total chromium content is equivalent to 50 mg / m ^{2 in} terms of Cr, and silica sol is a weight percentage. By adding 0.2 g / l of CMC (carboxy methyl cellulose) having 10% and molecular weight of 250,000, the mixture of water and propyl alcohol at a ratio of 1: 1 is 2250 m.
A chromate film containing g / m ² was applied and heated at 80 ° C. and 300 ° C. for 30 seconds. After cooling to 30 ° C., an epoxy resin having a molecular weight of 7700 and SiO ₂ having a particle size of 5 millimicrons were added to the chromate by 25% based on the solid content.
%, Containing 0.1%, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8,
A wet coating of 0.9, 1.0, 2.2, 3.2, and 4.5 microns is applied, and the upper solvent-type organic coating is baked at 200 ° C. for 15 seconds while evaporating water remaining in the chromate coating. A level treated steel sheet was produced. Table 5 shows the evaluation results. According to the method of the present invention, the number of gas pins generated during the cationic electrodeposition coating is significantly reduced, the number of cycles up to 50% organic film peeling by taping due to the decrease in adhesion in the cycle test is increased, and the base chromium degreaser It can be seen that the effect of preventing a decrease in the amount of adhesion due to the extraction into the solvent is obtained.

Example 6 As an electroplating solution, Zn ²⁺ was 36 g / l, Cr ³⁺ was 15.5 g / l,
2 g / l of (NH ₄ ) SO ₃ and a cationic polymer having a molecular weight of 45
A plating solution containing sulfate and chromium sulfate to which various plating components are added is prepared based on a plating solution containing 2 g / l of polyamine sulfone of No. 00 and 10 g / l of an amine-modified epoxy resin having a molecular weight of 12000 as required. Was adjusted to pH = 4.1 with this plating solution with sulfuric acid, and the lead electrode at room temperature as an anode, Kyokuhi 1: 1 subjected to electroplating at a current density of 80A / dm ^2, the deposition amount of 30 g / m ² Various types of Cr-containing zinc alloy-based organic dispersion plated steel sheets are manufactured. Further, on the upper layer of the Cr-containing zinc alloy-based organic dispersion plated steel sheet, a chromate containing 55% of hexavalent chromium in a weight ratio to the total chromium content of 50 mg / m ^{2 in} terms of Cr and silica sol in a weight percentage of 15% were added. % And molecular weight of 150,000
The ratio of water to methyl alcohol by the addition of CMC 0.2 g / l of 1: 1 mixture subjected to chromate film moistened 2250 mg / m ^2, and making those heated at each temperature of 80 ° C. and 270 ° C. 30 seconds Was. Then, after cooling to 30 ° C., a solvent type composite organic material having a solid content concentration of 20% by weight containing, on the chromate, an epoxy resin having a molecular weight of 7,700 and SiO ₂ having a particle diameter of 5 mm 25% by weight based on the solid content. Using a thin film paint, apply a wet film equivalent to a thickness of 0.9 micron, and bake the upper solvent type organic film over 15 seconds at 200 ° C while evaporating water remaining in the chromate film. A treated steel sheet was prepared using a Cr-containing zinc alloy-based organic dispersion plated steel sheet as a base. Tables 6 and 7 show the evaluation results. According to the method of the present invention, the number of gas pins generated during cationic electrodeposition coating is significantly reduced, the number of cycles up to 50% organic film peeling by taping due to a decrease in adhesion in a cycle test is increased, and the base chromium degreasing solution is used. It can be seen that the effect of preventing a decrease in the amount of adhesion due to the extraction into the solvent is obtained.

(Effects of the Invention) As described above, according to the present invention, it is possible to improve the adhesion of the composite organic film to the plated surface for a long period of time and the reduction of the electrodeposition coatability due to the electric resistance of the composite organic film. An organic thin film-coated zinc-containing multi-layered rust-preventive steel sheet excellent in long-term adhesion and cation electrodeposition coating property can be obtained economically.

[Brief description of the drawings]

Fig. 1 shows the relationship between the content of water temporarily left in the chromate film with respect to the organic skin (horizontal axis) and the number of cycles (vertical axis) until the organic film was peeled by 50% in the cellophane peel test by the cyclic corrosion test. Fig. 2 shows the chromate content in the organic thin film (horizontal axis)
FIG. 3 is a diagram showing the relationship between the number of gas pins generated on the electrodeposition coating surface of 1 dm ² (vertical axis).

Claims (2)

(57) [Claims] 1. A Cr-containing zinc-based alloy plating layer or a Cr-containing zinc alloy-based organic dispersion plating layer having a thickness of 1 μm or more and 100 μm or less on a steel sheet, A chromate containing 0.03 to 60% of chromium is applied, and a water-imparting treatment is applied on the chromate to produce a 0.3 to 3 micron thick composite organic thin film with non-fixed diffusion characteristics. Organic thin film coated Cr-containing zinc-based multi-layer rust-resistant steel sheet with excellent long-term adhesion of organic thin film and excellent cationic electrodeposition coating property. 2. A method for producing an organic thin film coated Cr-containing zinc-based multi-layer rust-preventive steel sheet which is excellent in long-term adhesion of the organic thin film and cationic electrodeposition coating property according to claim 1, and has a thickness of 1 μm by an electroplating method. A Cr-containing zinc-based alloy plating layer or a Cr-containing zinc alloy-based organic dispersion plating layer having a thickness of at least 100 μm or less is provided, and hexavalent chromium is contained in an amount of 0.03 to 60% by weight with respect to the total amount of chromium, and this treatment is performed. Chromate drying so that water and / or alcohol capable of evaporating at the time of baking in the composite organic thin film coating step following the step is contained in an amount of 0.1% or more and 40% or less with respect to the organic thin film. A wet coating film having a thickness of 0.3 to 3 microns is applied thereto, and baked while evaporating water and / or alcohol remaining in the chromate film to perform a water permeability imparting treatment. Method for producing a long-term adhesion as well as organic thin film-coated Cr-containing zinc-based multilayered rustproof steel sheet excellent in the cationic electrodeposition coating of the organic thin film characterized in that to have I click type diffusion properties.