JPH11189898A - Electrolytic chromate treated steel sheet excellent in film adhesion and color tone and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic chromate treated steel sheet excellent in film working adhesion and simultaneously satisfying a surface color tone sufficiently good as the one for a thinning-worked 2 piece can and to provide a method for producing it. SOLUTION: In an electrolytic chromate treated steel sheet in which a metallic chromium layer of 70 to 200 mg/m<2> coating weight is formed on the surface of a steel sheet, and a chromium hydrated oxide layer of 7 to 25 mg/m<2> coating weight expressed in terms of metallic chromium is formed on the upper layer, granular projections of <=50 nm maximum grain size are formed on the chromium layer, and the total of the occupancy area of the granular projections is regulated to 5 to 80% the surface area of the steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic chromate treated steel sheet having excellent film adhesion and color tone, and a method for producing the same, which is used for a laminated steel sheet for a thinned two-piece can.

[0002]

2. Description of the Related Art Conventionally, when making food or beverage cans, a two-piece can manufacturing method is known in which a metal plate is subjected to a process such as drawing, ironing, tensioning, bending, and the like, and a can bottom and a can body are integrally formed. Is being done. There are two-piece cans in which, after forming a metal plate and then applying a coating, a laminated steel plate in which an organic resin film is thermally fused to a metal plate in advance is subjected to a forming process. Has been put to practical use by the method disclosed in Japanese Patent Application Laid-Open Publication No. H10-209,878. When manufacturing a two-piece can body by forming a laminated steel plate, the base metal plate is an electrolytic chromate-treated steel plate (tin-free steel,
(Hereinafter referred to as TFS). A chromium metal layer is formed on the surface of TFS and a hydrated oxide layer of chromium is formed on the surface of the metal layer. In can processing, peeling at the interface between the metal plate and the organic resin film is prevented.

On the other hand, in recent years, can manufacturers have been reducing the thickness of can bodies from the viewpoint of material saving, and in the case of two-piece cans, measures have been taken to increase the working ratio during molding.
As the degree of processing increases, the deformation during molding increases, so that the risk of film peeling increases. Further, in the case of performing the retort treatment, the adhesion deteriorates due to the attack of the adhesion interface by the high-temperature steam, so that the adhesion after processing must be kept higher. Therefore, even for contents that require retort treatment, greater adhesion is required at the time of lamination than before.

Izumi et al. (CAMP-ISIJ) investigated the relationship between the density of granular protrusions of metallic chromium on the TFS surface and the adhesive strength based on a T-peel test of a PET film as a way to improve the adhesion of the laminate film.
vol. 8 (1995) -718). Where T
It has been found that the presence of the granular protrusions on the FS surface increases the surface area of the contact surface between the TFS and the film and contributes to the improvement of the adhesion.

[0005]

However, in the above-mentioned report by Izumi et al., A PET film was sandwiched by TFS as an evaluation means, the film was completely melted and pressed, and then its tensile strength was examined by a T-peel test. However, no study has been made on the processing adhesion which is a problem when a two-piece can is manufactured. JP-B-63-26200 and JP-A-63-63200 disclose methods for producing chromium-plated steel sheets for welding cans having granular projections of metallic chromium.
JP-A-186894 discloses that a metal chromium layer in which granular projections having a particle diameter of 5 to 1000 nm are mixed can be formed by performing anodic electrolysis after performing cathodic electrolysis in a chromic acid solution and then performing cathodic treatment again. ing. There, a chromium-plated steel sheet having a mixture of granular projections having a particle size of 5 to 1000 nm has been obtained, and the causal relationship between the density of the granular projections, the weldability, and the improvement in corrosion resistance after painting has been discussed. No suitability was discussed.
On the other hand, when manufacturing a two-piece can body by molding a laminated steel sheet, it is necessary to control the color tone of the laminated steel sheet in order to secure designability when printing on the outer surface of the molded can body. Specifically, when the brightness of the underlying steel sheet is insufficient or the hue is inappropriate, the printed color does not look good when a white film is laminated.

In Japanese Patent Application Laid-Open No. 7-197295, T
Studies have been made to control the color tone of FS, and as the TFS conditions for improving the color tone, the adhesion amount of chromium hydrated oxide was kept at 25 mg / m ² and the granularity of metallic chromium on the TFS surface was reduced. It has been found that the number of projections needs to be 20 / μm ² or less. However, no detailed study of the density taking into account the particle size of the granular projections affecting the color tone has been made so far. In view of such circumstances, an object of the present invention is to provide an electrolytic chromate-treated steel sheet which has excellent film processing adhesion and, at the same time, satisfies a sufficiently good surface color for a thinned two-piece can, and a method for producing the same.

[0007]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The steel sheet of the present invention has an adhesion amount of 70 to
And 200 mg / m ² of metallic chromium layer, coating weight reckoned as metal chromium thereon: In the electrolytic chromate treated steel sheet to form a 7~25mg / m ² of hydrated chromium oxide layer formed by, on the chromium layer, Electrolytic chromate treatment excellent in film adhesion and color tone, characterized in that granular projections having a maximum particle size of 50 nm or less are formed, and the total area occupied by the granular projections is 5 to 80% of the surface area of the steel sheet. It is a steel plate.

(2) The production method of the present invention is the method for producing an electrolytic chromate-treated steel sheet according to the above (1), wherein a compound containing hexavalent chromium is used as a main component, and F ^- and SO ₄ ^{2 in a} weight ratio. ^A step of subjecting the steel sheet to at least one pass of anodic electrolysis and at least one pass of cathodic electrolysis in an aqueous solution containing an amount of SO ₄ ²⁻ that satisfies ⁻ / F ⁻ ≦ 0.05; Is the cathodic electrolytic treatment, and the amount of electricity passed in the anodic electrolytic treatment is 0.05 to 2
A method for producing an electrolytic chromate-treated steel sheet having excellent film adhesion and color tone, characterized by performing an intermittent electrolytic treatment of C / dm ² .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above-mentioned problems, the present inventors have studied the effects of TF on film processing adhesion and color tone.
As a result of a detailed investigation of the influence of the particle size and density of the metallic chromium granular projections on the S surface, the following findings were obtained.

[0010] When granular projections of chromium metal are present on the surface of TFS, the area of the contact interface between the chromium hydrated oxide on the outermost layer of TFS and the laminate film is increased, so that the adhesion is improved. However, at the same time, the color tone of the TFS deteriorates in both brightness and hue.

FIG. 1 shows the effect of a laminated steel sheet obtained by laminating a transparent polyester film having a thickness of 25 μm on TFS having granular projections having various particle diameters and densities on the spectral reflectance curve in the visible region.

The wavelength integrated value of the spectral reflectance reflects the intensity of the reflected light and has a close correlation with the brightness. That is, the higher the curve is located in FIG. 1, the brighter the color tone is. In addition, 10 in the curve between 480 nm and 700 nm.
The average value of the reflectance-wavelength gradient measured at nm intervals is 10
The value corrected to the reflectance difference per 00 nm is described in
K value (% / 1
000 nm). The K value is an effective means for evaluating the TFS surface hue. The smaller this value is, that is, the steeper the slope of the curve in FIG. Is good as a hue. Conversely, when the K value is large, redness is strongly felt, which is not preferable as the hue of the laminated steel sheet.

FIG. 1 shows that the flat metallic chromium (sample E) having no granular projections has the brightest, strong blue color and good color tone. On the other hand, if there are granular projections,
A decrease in reflectance is seen. The difference from the best curve E increases in the order of A → B → C → D. A in which protrusions having a particle diameter of 50 nm exist at high density shows a spectrum almost similar to that of the curve E, except that the reflectance slightly decreases on the short wavelength side. On the other hand, when protrusions with a particle diameter of 150 nm B to D are present, it can be seen that the reflectance is reduced and the brightness is reduced in all wavelength regions from short wavelength to long wavelength. Further, as the density of the granular projections increases, the reflectance on the short wavelength side greatly decreases, and the tendency of relatively increasing redness is recognized, which is not preferable in terms of hue.

The effect of the granular projections on the change in the spectral reflection curve of the TFS after lamination is explained by the scattering of light by the granular projections. If visible light is reflected on a flat surface, and if there is unevenness much smaller than the wavelength on the flat surface, the light will be totally reflected without being affected by the unevenness. As it gets closer, the incident light is scattered by the irregularities, and the reflectivity decreases. Therefore, the surface scattering of visible light is firstly scattered from short-wavelength light as the unevenness increases, and as long as the unevenness size is small, the scattering of long-wavelength light is small. Scattering will occur. T
In the case of FS, when the particle diameter of the granular projections is 50 nm, the reflectance decreases only in the short wavelength region, and at 150 nm, the reflectance decreases in the entire visible light region. In addition, as the density of the granular projections increases, the surface scattering increases, so that the reflectance decreases and the brightness decreases remarkably. However, in the case of A having a particle diameter of 50 nm, the decrease in lightness is extremely small and the color tone is good despite the presence of granular protrusions one digit larger than those of B to D having a diameter of 150 nm. For the above reasons, it can be seen that there is a range of the particle size and density of the granular projections that have a very small adverse effect on the laminate color tone of TFS. The present inventors have conducted a thorough investigation of the particle size and density that do not adversely affect the laminate color tone, and found that the range is such that the particle size of the metallic chromium granular projections is all 50 nm or less, and the area occupied by the granular projections. The total was determined to be 5 to 80% of the steel sheet surface area.

However, in forming the metal chromium layer having the granular projections having the above-described particle diameter and density, the total area occupied by the granular projections is controlled to 5 to 80% of the surface area of the steel sheet while controlling the particle diameter to 50 nm or less. It is very difficult to do this, and in previous studies, for example, 5-1000 nm
However, it was not possible to control the particle size to 50 nm or less, although it was possible to generate granular protrusions having the particle size distribution described above.

The inventors of the present invention have studied the composition of a chromic acid solution for performing anodic electrolysis in detail. As a result, when the anodic electrolysis treatment is performed in a F ^- added chromic acid solution containing no SO ₄ ^2- at all, As shown in FIG.
It has been found that it is possible to form a metal chromium layer in the range of 0 to 500 mg / m ² , in which granular protrusions exceeding 50 nm are not mixed.

As shown in FIG. 3, SO ₄ ^2- / F ⁻
When the weight ratio is less than 0.05, the granular projections having a size exceeding 50 nm are not formed, but when the weight ratio of SO ₄ ²⁻ / F ⁻ exceeds 0.05, those exceeding 50 nm begin to mix. Was.

Based on the above findings, the present inventors adjusted the concentration of SO ₄ ^2- in the electrolytic chromate treatment solution and the amount of electricity supplied in the anodic electrolysis treatment to adjust the metal chromium layer applied to the steel sheet surface and the upper layer thereof. An electrolytic chromate treated steel sheet excellent in both film processing adhesion and color tone by controlling the attached amount of each chromium hydrated oxide layer and the maximum particle size and density of the granular projections of the chromium layer within a certain range. The present inventors have found a manufacturing method and completed the present invention.

That is, the present invention, by limiting the film of the electrolytic chromate treated steel sheet and the electrolytic treatment conditions to the following ranges, is excellent in film processing adhesion, and at the same time, has a sufficiently good surface tone for a two-piece thinned can. And a method for producing the same.

The reasons for limiting the coating of the electrolytic chromate treated steel sheet of the present invention and the reasons for limiting the electrolytic treatment conditions will be described below. (1) Coating of electrolytic chromate-treated steel sheet The electrolytic chromate-treated steel sheet of the present invention has a metal chromium layer having an adhesion amount of 70 to 200 mg / m ^{2 on} the surface of the steel sheet, and an adhesion amount in terms of metal chromium of 7 to 200 mg / m ^2. A chromium hydrated oxide layer of 25 mg / m ² , wherein the chromium layer has granular projections having a maximum particle size of 50 nm or less;
And the sum of the occupied areas of the granular projections is 5 to 8 of the steel sheet surface area.
0%.

The amount of metal chromium layer adhered is 70 to 200 mg.
/ M is ² reasons, first is less than 70 mg / m ² is for a sufficient film processing adhesiveness is not obtained, the upper limit is 200 mg / m ^2, even film processing is increased any more adhesion amount This is because there is no improvement in adhesion and there is no need to increase the amount of adhesion.

[0022] The hydrated chromium oxide coating weight is 7~25mg / m ² reckoned as metal chromium in the case of less than 7 mg / m ^2, the adhesion area by arranging how granular projections of the metallic chromium on the surface layer This is because, even if it is increased, the absolute amount of the hydrated chromium oxide is insufficient, so that the coatability is lowered and the adhesion to the laminate film becomes insufficient. On the other hand, if the hydrated oxide exceeds 25 mg / m ² , even if the base material is flat metallic chromium having no granular protrusions, the hydrated oxide itself is colored brown and the color tone deteriorates. It is.

The reason why the particle diameter of the metallic chromium granular projections present on the surface of the metallic chromium layer is all limited to 50 nm or less is that when the granular projections exceeding 50 nm exist or are mixed, the color tone is determined by the surface scattering of the maximum particle diameter. Ruled,
This is because reflected light is reduced in all wavelength regions. In order for the color tone to be as good as that of flat metal chromium, it is necessary that all the particle diameters of the granular projections do not exceed 50 nm. In addition, the total area occupied by the granular projections is calculated as 5% of the surface area of the steel sheet.
The reason for limiting the content to ~ 80% is that if the content is less than 5%, the increase in the adhesion area due to the presence of the granular projections is small, so that no improvement in the film adhesion is observed. Therefore, in order to improve the film adhesion, the total area occupied by the granular projections needs to be 5% or more of the surface area of the steel sheet. If it exceeds 80%, it can be said that the particle size is 50 nm or less and the surface scattering is limited to only the short wavelength region of visible light, but the amount of reflected light is insufficient and the brightness is reduced, and at the same time, the bluish is insufficient. This is because the deterioration of the hue due to this cannot be ignored. Therefore, in order to obtain a good color tone, the total area occupied by the granular projections must be 80% or less of the surface area of the steel sheet.

The method of measuring the particle size and the occupied area ratio of the granular projections (total occupied area of the granular projections / surface area of the steel sheet) is not particularly limited. Scanning transmission electron microscope (TEM) of 10,000 times the surface of the sample coated with the hydrated oxide
It is desirable to take a photograph and measure the particle size and the occupied area ratio of the granular projections from the photograph (because the particle size measurement is easy and the observation area can be secured). When actually calculating the particle diameter and the occupied area ratio of the granular projections of the sample, the maximum particle diameter (maximum outer diameter) of the granular projections in the range (viewing area) photographed is taken. The ratio between the total area of the grains and the area of the visual field obtained by the analysis. In addition, as shown in FIG. 4, the measurement of the maximum particle size and the occupied area ratio of the granular projections requires that the number of measured granular projections be at least 300 μm ² or more, so that an appropriate maximum particle size and occupied area ratio cannot be obtained. .

The form of the granular projections is not particularly defined because it is not constant. However, since single crystal grains mainly formed in the same direction as the base crystal orientation are formed, (10
The four-fold symmetry (quadrangle) depending on the (0) plane and the six-fold symmetry (hexagon) depending on the (111) plane are often observed (projections other than grains related to the plating form are not taken into account). By adjusting the coating of the above-mentioned electrolytic chromate-treated steel sheet, it becomes possible to obtain an electrolytic chromate-treated steel sheet which is excellent in film processing adhesion and at the same time satisfies a sufficiently good surface tone for a thin-walled two-piece can.

The steel sheet having such characteristics can be manufactured by the following manufacturing method. (2) as a main agent a compound electrolytic chromate treatment steel sheet manufacturing process including (manufacturing method) hexavalent chromium, F ^-
And an amount of S satisfying SO ₄ ²⁻ / F ⁻ ≦ 0.05 by weight ratio.
A step of subjecting the steel sheet to one or more passes of anodic electrolysis and one or more passes of cathodic electrolysis in an aqueous solution containing O ₄ ^2- ; And the amount of electricity passed in the anodic electrolysis treatment is 0.0
An intermittent electrolytic treatment of 5 to ² C / dm ² is performed.

First, a compound containing hexavalent chromium (chromic anhydride) is used as a main component, F ⁻ is used as an auxiliary, and SO ₄ ^{2− is} used in a weight ratio.
The use of an aqueous solution containing an amount of SO ₄ ²⁻ that satisfies / F ⁻ ≦ 0.05 is necessary for suppressing the growth of granular projections, as described above. That is, SO ₄ ^2- / F
^When- exceeds 0.05, the maximum particle size of the granular projections is 50 nm.
Beyond. The reason why the electrolytic treatment is performed intermittently two or more times in such a solution, and at least one anodization is performed in any of the electrolysis except the final electrolysis, and the cathodic treatment is performed in the remaining electrolysis. This is because anodic electrolysis is a process necessary for forming sites that generate preferential precipitation and granular projections in the next cathodic electrolysis,
It goes without saying that performing anodizing at the final stage of electrolysis is meaningless.

The amount of electricity passed in the anodic electrolytic treatment is 0.05 to 2
Reason for performing intermittent electrolytic treatment is a C / dm ^2, the current amount of electricity is less than 0.05 C / dm ^2, formed is insufficient filling ratio of the particulate protrusions is less than 5%. On the other hand, 2C
If the ratio exceeds / dm ² , the occupied area ratio of the granular projections exceeds 80%, and the color tone deteriorates. In addition, oxidative dissolution of metallic Cr by anodic electrolytic treatment significantly reduces the electrolytic efficiency, which is uneconomical.

The reason why the intermittent electrolytic treatment is performed in the present invention is that a desired surface-treated steel sheet cannot be obtained by the continuous electrolytic treatment. That is, when plating with a plating facility having a finite electrode length, the electrode length becomes too long in continuous electrolysis (synonymous with performing electrolysis in one pass), and the plating tank becomes large in general, in order to obtain a desired plating adhesion amount. Since it is indispensable, electrolysis is performed with a plurality of electrodes. At that time, as shown in FIG. 5, a current-carrying part and an electroless part are formed,
Electrolysis is necessarily intermittent. Although the formation mechanism of the granular protrusions by anodic electrolysis is unknown in many respects, it is generally considered that the protrusions are formed by the following mechanism. In other words, the surface oxide layer of iron or chromium formed in advance by cathodic electrolysis or immersion in a chromic acid solution causes non-uniform dissolution at the micro level by anodic electrolysis, thereby exposing the metal base or diluting the oxide layer. A large number of locations are generated, which become sites that preferentially precipitate in the next cathodic electrolysis and generate granular projections. The action of SO ₄ ^2- in the anodic electrolysis is related to the etching ability when dissolving the surface oxide layer of iron or chromium inhomogeneously, and is considered to have a stronger etching ability than F ^−. . That is, when heterogeneous dissolution occurs, the etching rate of the oxide is higher at the site where SO ₄ ^2- is adsorbed than at the site where F ⁻ is adsorbed, and the site where granular projections are generated is relatively wide. As a result of the area being secured, large granular projections are generated in the cathode treatment.

Since adsorption capacity compared with the high, ^- [0030] SO ₄ ^2-F-
Competitive adsorption causes the generation of large granular projections even with relatively small additions. In competitive adsorption weight ratio of 0.05 near the border of F ^{- -} Results SO ₄ ^2- / F studies have considered the SO ₄ ^2-a dominant state transition to the dominant state.

From the above description, it can be seen that the particle size control is F ^- and S
By O ₄ ^2-of competitive adsorption, since Yes No is determined, SO ₄ ^2- / F ^- if 0.05 or less of chromic acid solution at a weight ratio, the anodic electrolysis and metallic chromium chromium The first half and the second half of the one-liquid method for simultaneously depositing hydrated oxides and the two-liquid method for depositing chromium hydrated oxide after forming a metal chromium layer may be used. An effect can be obtained by performing the processing of the invention. Hereinafter, the effects of the present invention will be proved by giving examples of the present invention.

[0032]

EXAMPLES (Test Materials) All test materials (Examples 1 to 6 of the present invention)
And Comparative Examples 1 to 7) are made of low carbon Al-killed steel and have a thickness of 0.1 mm.
20mm T4CA material is used as the original steel strip, and the vertical T
The FS line includes various projections having various adhesion amounts, particle diameters, and occupied area ratios (total occupied area of granular projections / surface area of steel sheet) shown in Table 1 under various electrolytic chromate treatment conditions as shown below. TFS on which a chromium metal layer and chromium hydrated oxide having various adhesion amounts were deposited was manufactured, and then film lamination was performed under the following conditions.

(1) Electrolytic chromate treatment conditions (Example 1 of the present invention): one-component method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 4 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis) b. Electrolytic treatment In the first pass, anodic electrolytic treatment (current density 5 A / dm ² , treatment time 0.08 seconds) was performed, and subsequently, cathodic electrolytic treatment (current density 50 A / dm ² ) in ² to 6 passes. The amount of electricity passed in the anodic electrolysis is 0.4 C / dm ² . (Invention Example 2): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis) b. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis) c. Electrolytic treatment In the above plating bath, after the first pass anodic electrolytic treatment (current density 10 A / dm ² , treatment time 0.12 seconds),
On the fifth pass, a cathodic electrolytic treatment (current density 40 A / dm ² ) was performed. In the above chemical conversion bath, cathodic electrolysis (current density: 30 A / dm ² ) was performed in the first to fourth passes. The amount of electricity passed in the anodic electrolytic treatment is 1.2 C / dm ² .

(Example 3 of the present invention): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis) b. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis) c. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 2 A / dm ² , treatment time 0.3 seconds) is performed in the second pass following cathodic electrolytic treatment (current density 40 A / dm ² ) in the first pass.
Then, in the third to fifth passes, the cathodic electrolytic treatment (current density 40 A)
/ Dm ² ). In the above-mentioned chemical conversion bath, the cathodic electrolytic treatment (current density 30 A / dm ² ) was performed in the first to fourth passes. The amount of electricity passed in the anodic electrolysis is 0.6 C / dm ² .

(Example 4 of the present invention): Two-liquid method a. Plating bath composition CrO ₃ : 175 g / l, Na ₂ SiF ₆ : 5 g / l,
SO ₄ ^2- : 0.6 g / l.

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, cathodic electrolytic treatment (current density 40 A / dm ² ) was performed in the first to fourth passes. In the chemical conversion bath, anodic electrolysis (current density 2 A / dm ² , processing time 0.3 seconds) is performed in the first pass, and then cathodic electrolysis (current density 30 A / dm ² ) is performed in the second to fifth passes. went. The amount of electricity passed in the anodic electrolysis is 0.6 C / dm ² .

(Example 5 of the present invention): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO
₄ ^2- : 0.13 g / l.

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 10 A / dm ² , treatment time 0.12 seconds) is performed in the first pass, and then cathodic electrolytic treatment (current density 40 A / dm) is performed in the second to fifth passes.
² ) did. In the above-mentioned chemical conversion bath, the cathodic electrolytic treatment (current density 30 A / dm ² ) was performed in the first to fourth passes. The amount of electricity passed in the anodic electrolytic treatment is 1.2 C / dm ² .

(Invention Example 6): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 1 A / dm ² , treatment time 0.3 seconds) is performed in the second and third passes following the first pass cathodic electrolytic treatment (current density 40 A / dm ² ). Then, in the fourth pass, the cathodic electrolytic treatment (current density 40 A
/ Dm ² ). In the above chemical conversion bath, cathodic electrolysis (current density: 20 A / dm ² ) was performed in the first to third passes. The amount of electricity passed in the anodic electrolysis is 0.6 C / dm ² . (Comparative Example 1): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO
₄ ^2-: 0.65g / l. b. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 10 A / dm ² , treatment time 0.12 seconds) is performed in the first pass, and then cathodic electrolytic treatment (current density 40 A / dm) is performed in the second to fifth passes.
² ) did. In the above-mentioned chemical conversion bath, the cathodic electrolytic treatment (current density 30 A / dm ² ) was performed in the first to fourth passes. The amount of electricity passed in the anodic electrolytic treatment is 1.2 C / dm ² . (Comparative Example 2): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Chemical bath composition CrO ₃ : 35 g / l, NH ₄ F: 1.2 g / l, SO
₄ ^2- <0.01 g / l (concentration of inevitable contamination from plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, cathodic electrolytic treatment (current density: 60 A / dm ² ) was performed in the first to third passes. In the above chemical bath,
In the fourth pass, a cathodic electrolytic treatment (current density 30 A / dm ² ) was performed.

(Comparative Example 3): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 10 A / dm ² , treatment time 0.12 seconds) is performed in the first pass, and then cathodic electrolytic treatment (current density 30 A / dm ² ) in the second pass.
Was done. In the above chemical conversion bath, cathodic electrolysis (current density: 30 A / dm ² ) was performed in the first to third passes. The amount of electricity passed in the anodic electrolytic treatment is 1.2 C / dm ² . (Comparative Example 4): One-part method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 8 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Electrolytic treatment In the above plating bath, anodic electrolysis (current density 10
A / dm ² , processing time 0.1 second)
At the sixth pass, a cathodic electrolytic treatment (current density: 50 A / dm ² ) was performed. The amount of electricity passed in the anodic electrolysis is 1 C / dm ² .

(Comparative Example 5): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 1 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 10 A / dm ² , treatment time 0.1 second) is performed in the first pass, and then cathodic electrolytic treatment (current density 40 A / dm) in the second to fifth passes.
² ) did. In the above chemical conversion bath, cathodic electrolytic treatment (current density 30 A / dm ² ) was performed in the first to fifth passes. The amount of electricity passed in the anodic electrolysis is 1 C / dm ² .

(Comparative Example 6): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, anodic electrolytic treatment (current density 2 A / dm ² , treatment time 0.6 seconds) is performed in the second pass, following the first pass cathodic electrolytic treatment (current density 40 A / dm ² ). ,
Cathode electrolysis (current density 40 A / dm ² ) is performed in the third pass, and anodic electrolysis (current density 2 A / dm ² ) is performed in the fourth pass.
² , a processing time of 0.6 seconds), and a cathodic electrolytic treatment (current density 40 A / dm ² ) was performed on the fifth and sixth passes. In the above-mentioned chemical conversion bath, cathodic electrolytic treatment (current density 30A) in the first to fourth passes
/ Dm ² ). The amount of electricity passed in the anodic electrolysis is 2.
4 C / dm ² .

(Comparative Example 7): Two-liquid method a. Plating bath composition CrO ₃ : 100 g / l, NaF: 6 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

B. Chemical bath composition CrO ₃ : 50 g / l, NH ₄ F: 2 g / l, SO ₄ ^2-
<0.01 g / l (concentration unavoidably mixed due to plating chemicals, from ICP analysis).

C. Electrolytic treatment In the above plating bath, following the first pass anodic electrolytic treatment (current density 0.2 A / dm ² , treatment time 0.1 second),
Cathode electrolytic treatment on the 5th to 5th pass (current density 40A / dm ² )
Was done. In the above-mentioned chemical conversion bath, the cathodic electrolytic treatment (current density 30 A / dm ² ) was performed in the first to fourth passes. The amount of electricity passed in the anodic electrolysis is 0.02 C / dm ² .

(2) Film Lamination Conditions The film lamination was performed under the following single conditions using a transparent film on one side of the steel sheet and a white film on the other side.

A. Transparent film surface Film material: Transparent biaxially oriented polyester film (copolymer of polyethylene glycol and terephthalic acid / isophthalic acid), film thickness: 25 μm, film melting point: 229 ° C, steel sheet temperature immediately before lamination: 230 ° C, after lamination Remaining biaxial orientation degree: 17 to 19%.

B. White film surface Film material: White biaxially oriented polyester film (polyethylene glycol and terephthalic acid / isophthalic acid copolymer, average particle size 0.3 μm titanium oxide 12% by weight
Added), film thickness: 10 μm, melting point of the film: 229 ° C., steel sheet temperature immediately before lamination: 230 ° C.,
Remaining biaxial orientation degree after lamination: 20 to 24%.

The laminating speed was 40 m / min for both the transparent film surface and the white film surface. (Evaluation of processing adhesion) A disc having a blank diameter of 80 mm was punched out of a laminated steel sheet, subjected to redrawing, and then subjected to retort treatment. 5. The total peeling was set to 1, and the evaluation was made in five steps. In addition, two-stage test conditions of the following conditions 1 and 2 were provided by a combination of the drawing process and the subsequent retort conditions, and a more severe workability and adhesion under retort conditions were examined.

A. Processing adhesion test conditions (drawing and retort conditions) Condition 1: drawing ratio = 1.6, retort conditions = 110 ° C
× 30 minutes, condition 2: drawing ratio = 2.0, retort condition = 125 ° C. × 30 minutes.

A score of 4 was obtained under the condition 2 with a higher degree of processing.
The above was judged to be good in processing adhesion. (Color) JI to measure the brightness of the white film surface of the laminated steel sheet
The evaluation was made in five steps based on the brightness index L ^* value of a 10-degree visual field defined in SZ8729 (the higher the score, the better).

Rating 5: L ^* ≧ 83, Rating 4:83> L ^*
≧ 77, rating 3: 77> L ^* ≧ 70, rating 2: 70> L
^* ≧ 60, rating 1:60> L ^* . Further, when evaluating the hue using the K value, it is difficult to quantify the difference in hue on the white film laminated surface, and it is easier to compare the hue on the transparent film laminated surface. Hue quality was evaluated on a scale of 5 using the K value of TFS after lamination as an index (the higher the grade, the better).

Rating 5: -20 ≧ K, Rating 4: -15 ≧ K
> -20, score 3: -10 ≧ K> -15, score 2: -5
≧ K> −10, rating 1: K> −5 Table 1 also shows the evaluation results of the processing adhesion and the color tone.

From Table 1, it can be seen that Examples 1 to 6 of the present invention, which were produced under the production conditions of the present invention, showed that the deposition amount of metal chromium and chromium hydrated oxide, the particle size of the metal chromium granular protrusion, and the occupied area ratio (granular protrusion Is the laminated steel sheet whose total area occupied by the steel sheet / surface area of the steel sheet is within the range of the present invention, and is capable of peeling the film under any of the low working degree (condition 1) and the high working degree (condition 2). On the other hand, the results are at a satisfactory level and no problem is caused in the color tone.

On the other hand, in Comparative Example 1, SO ₄ in the electrolytic treatment solution was used.
^{2- The} concentration is out of the range of the present invention, and although the adhesion to the processing of the laminate film is excellent, the grain size of the granular projections is larger than the range of the present invention, so that the color tone is deteriorated.
Comparative Example 2 is a flat metal chromium having no granular protrusions.
It is a laminated steel sheet to which a chromium hydrate oxide having an upper limit of the amount of adhesion in the present invention is adhered. Although there is no problem with the color tone, the film processing adhesion is insufficient under the condition 2 of high processing degree because of peeling. In Comparative Example 3, since the number of passes of the cathodic electrolysis treatment in the plating bath was small, the amount of deposited metal chromium was insufficient, and the processing adhesion was poor. Comparative Example 4 is F the electrolysis solution ^- for high density, the adhesion amount of dissolved chromium hydrous oxide becomes conspicuous of hydrated chromium oxide in the electrolyte is insufficient, it has poor processability adhesion. In Comparative Example 5, the particle diameter and the occupied area ratio were within the range of the present invention. However, since the number of passes of the cathodic electrolysis treatment in the chemical conversion bath was large, the adhesion amount of hydrated chromium oxide was too large, Is good but has poor color tone. In Comparative Example 6, since the amount of electricity supplied in the anodic electrolysis exceeds the range of the present invention, the occupied area ratio of the granular projections is large, and the color tone is not excellent. On the contrary, in Comparative Example 7, since the amount of electricity passed in the anodic electrolysis treatment was below the range of the present invention, the occupied area ratio of the granular projections was small, and the improvement in working adhesion was poor.

As described above, according to the production conditions of the present invention, the adhesion amount of metallic chromium and hydrated oxide is limited within the scope of the present invention, and the range of the particle diameter and the occupied area ratio of the predetermined metallic chromium granular projections is limited. It has been confirmed that by setting the inside, it is possible to manufacture an electrolytic chromate-treated steel sheet having excellent film processing adhesion and color tone.

[0071]

[Table 1]

[0072]

As described above, according to the present invention, it is possible to provide a method for producing an electrolytic chromate-treated steel sheet having excellent film adhesion and color tone by specifying the film and electrolytic treatment conditions of the electrolytic chromate-treated steel sheet.

By using the manufacturing method of the present invention, it is possible to cope with an increase in the working ratio of a thinned two-piece can.
The economic value is extremely high because it can be adapted to contents that require retort processing as the adhesion is improved.

[Brief description of the drawings]

FIG. 1 is a view showing the influence of metallic chromium granular projections on the spectral reflection curve of a transparent film-laminated steel sheet.

FIG. 2 is a graph showing the relationship between the amount of deposited chromium metal and the particle size of granular projections.

FIG. 3 shows the effect of SO ₄ on the particle size change of metallic chromium granular protrusions.
^2-/ F ^- micrographs showing the effect of.

FIG. 4 is a diagram showing a relationship between a visual field area and a grain occupation area ratio according to the embodiment of the present invention.

FIG. 5 is a diagram showing an outline of an intermittent electrolytic treatment plating facility according to an embodiment of the present invention.

Claims (2)

[Claims] 1. The amount of adhesion on the surface of a steel sheet: 70 to 200 m
g / m ² of a metal chromium layer, and an upper layer of the chromium hydrated oxide layer having a coating weight of 7 to 25 mg / m ^{2 in} terms of metal chromium. Characterized in that granular projections having a maximum particle diameter of 50 nm or less are formed and the total area occupied by the granular projections is 5 to 80% of the surface area of the steel sheet, and is excellent in film adhesion and color tone. Treated steel sheet. 2. The method for producing an electrolytic chromate-treated steel sheet according to claim 1, wherein a compound containing hexavalent chromium is used as a main component, and F ⁻ and SO ₄ ²⁻ / F ⁻ ≦ 0.05 in weight ratio. A step of subjecting the steel sheet to one or more passes of anodic electrolysis and one or more passes of cathodic electrolysis in an aqueous solution containing a satisfying amount of SO ₄ ^2- ; Electrolytic treatment,
And the amount of electricity passed in the anodic electrolysis treatment is 0.05 to 2 C /
dm ² intermittent electrolytic treatment,
A method for producing an electrolytic chromate treated steel sheet having excellent film adhesion and color tone.