JP6540279B2 - Method of manufacturing black painted steel sheet - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a black-painted steel sheet generally used for members requiring decoration such as office supplies, electrical products or automobile parts in which galvanized steel sheets are used.

  Pre-coated steel sheets coated with a colored organic film have come to be used in place of post-painted products which have been coated after conventional forming and processing for home appliances, building materials, automobiles and the like. This precoated steel plate is a steel plate which has been subjected to a rustproofing treatment or a plated steel plate coated with a colored organic film, and has such characteristics that it has machinability, good workability and good corrosion resistance. . For example, Patent Document 1 discloses a technique for obtaining a precoated steel sheet excellent in workability, stain resistance, and hardness by defining the structure of a film.

  The coatings used for these precoated steel sheets are those with a coating thickness of greater than 10 μm. In addition, since a large amount of solvent-based paint is used, a dedicated coating facility such as an injector and an odor control facility is required, and it is generally manufactured on a dedicated coating line. That is, in addition to the manufacturing process of the steel plate used as the original material of a coating, since it passes an extra coating process, much cost besides the material cost which coating requires is needed. Therefore, the precoated steel sheet obtained is expensive.

  However, due to the diversification of user needs, there is also a demand for colored steel sheets in fields where the purpose is sufficiently achieved with durability in daily use conditions such as home appliances and interior building materials, and lower priced products are required. There is. That is, conventional expensive precoated steel sheets alone are not sufficient to meet diversified demands.

  For such needs, in Patent Document 2, a black coating film comprising a polyester resin containing a sulfonic acid group cured with a curing agent and carbon black on at least one surface of a zinc-based plated steel plate is 2 to 10 μm A chromate-free black painted metal sheet is disclosed, characterized in that it is formed with a thickness of Although this steel plate is excellent in various characteristics including the designability, it is not enough to be able to be resistant to scratching under severe conditions. That is, since the coating thickness is thin compared to the conventional pre-coated steel sheet, depending on the conditions, it is easy for the coating to be penetrated and wrinkled to reach the plating surface, and in this case the metal appearance of the plating surface looks like black coating It will be inferior in terms of design.

  In order to solve the above-mentioned problems, there is also known a technique in which the plating layer itself is blackened and combined with a black coating (Patent Documents 3, 4 and 5). The plating layer of this technology is a blackened Zn-Ni alloy plating layer, which is very hard and brittle, so cracking or peeling occurs in the plating layer during severe bending or overhanging, which propagates to the upper black coating film, and processing It will damage the design of the department. This phenomenon is particularly likely to occur when the thickness of the black coating is large. Therefore, if the thickness of the black coating is reduced, there is a slight improvement effect, but in such a case, the designability of the unprocessed flat plate portion is sufficient. As a result, it is difficult to simultaneously achieve the design of the unprocessed flat plate portion and the design of the processed portion.

JP-A-8-168723 WO 2010/137726 JP, 2009-160768, A JP, 2009-161796, A JP, 2014-000799, A

The present invention provides a black-painted steel sheet which is thin as compared with the conventional pre-coated steel sheet in view of the above-mentioned state of the art and which is excellent in wrinkling resistance and is compatible with the designability of an unprocessed flat plate portion and the designability of a processed portion. The purpose is to
Furthermore, it is another object to obtain a black-coated steel sheet having corrosion resistance.

As a result of intensive studies, the present inventors have found that the problem can be solved by optimizing the state of cracks in the Zn—Ni alloy plated layer, the blackening treatment, and the black coating film. That is to say, the subject matter of the present invention is as follows.
(1) It has a Zn-Ni alloy plating layer formed on at least one side of a steel plate and a blackening treatment layer covering the surface of the plating layer, and has a black organic coating layer on the upper layer thereof via a chemical conversion treatment layer It is a coated steel plate, and the Zn-Ni alloy plating layer has a crack that extends from the surface layer of the plating layer to the ground iron, and a blackening treatment layer exists to the plating surface layer inside the crack,
The cross-section of the Zn-Ni alloy plating layer is observed, and from the surface layer of the plating layer to the ground iron among the cracks intersecting with a straight line of any 10 μm length drawn in the direction parallel to the interface A method for producing a black-painted steel sheet , wherein one or more cracks reach the surface,
Forming a Zn—Ni alloy plated layer with a plating adhesion amount of 5 to 40 g / m ^{2 on} at least one side of the steel plate ;
By etching the surface of the Zn-Ni alloy plated layer with an acid, a crack reaching from the surface layer of the plated layer to the base iron is formed;
The blackened layer is formed by blackening the surface of the etched Zn-Ni alloy plated layer using an acidic aqueous solution containing phosphate ions and nitrate ions,
The chemical conversion treatment layer is provided on the blackening treatment layer covering the surface of the Zn-Ni alloy plating layer,
A method for producing a black-painted steel plate, characterized in that the black organic coating layer is further provided on the upper layer of the chemical conversion treatment layer.
(2) The method for producing a black-painted steel sheet according to the above (1), wherein the blackening treatment is performed by immersing the surface of the Zn—Ni alloy plated layer in an acidic aqueous solution containing phosphate ions and nitrate ions.
(3) The black-coated steel sheet according to the above (1), wherein the blackening treatment is performed by immersing the surface of the Zn-Ni alloy plating layer in an acidic aqueous solution containing phosphate ions and nitrate ions and then anodizing. Production method.
(4) The manufacturing method of the black-painted steel plate as described in any one of said (1)-(3) whose said acid etching is a sulfuric acid etching.
(5) In the organic film layer thickness Y ([mu] m) in the range of 0.3~10μm of the black, based on said number of cracks reaching the plating layer from the surface to the base steel X (number), the Y and the X is the following The manufacturing method of the black-painted steel plate as described in any one of said (1)-(4) which forms an organic membrane layer so that the relationship of (I) Formula may be satisfy | filled.
−0.6 × + 3.7 ≦ Y ≦ 2.7 × + 1.6 (I)
( 6 ) The black color according to any one of the above (1) to (5), wherein the black organic coating layer contains a fluorine resin compound having a particle diameter not more than twice the organic coating layer thickness Y (μm) Manufacturing method of painted steel sheet.
( 7 ) The manufacturing method of the black coated steel plate as described in said (6) whose said fluorine resin type compound is 0.1 mass% or more and 5 mass% or less of organic membrane | film | coat solid content.

  According to the present invention, it is possible to obtain a black-painted steel plate which is thin as compared with the conventional pre-coated steel plate, is excellent in the wrinkling resistance, and is compatible with the designability of the unprocessed flat plate portion and the designability of the processed portion.

  Hereinafter, the present invention will be described in detail. Unless otherwise stated,% means% by mass.

  The black-coated steel sheet of the present invention has a Zn-Ni alloy plated layer formed on at least one surface of a steel sheet and a blackening treatment layer covering the surface of the plating layer, and a black organic layer on the upper layer thereof via a chemical conversion treatment layer. A black-coated steel sheet having a coating layer, characterized in that the Zn-Ni alloy plated layer has a crack which extends from the surface layer of the plating layer to the ground iron and a blackening treatment layer exists in the plating surface layer inside the crack. It is.

  By the presence of the cracks, the stress of the plating layer at the time of processing deformation is alleviated, and there is an effect of making the coating film less likely to be cracked or peeled off. It becomes possible to express a deep and high-grade black design with the processed part.

  Although a blackening treatment layer is provided on the surface of the Zn—Ni alloy plating layer, it is necessary that the blackening treatment layer is present not only on the surface layer of the plating layer but also on the plating surface layer inside the crack. By this, it becomes possible to express the high-quality black design with the depth as described above. Here, the surface layer of the plating layer means an interface parallel to the surface of the steel plate among the interfaces of the plating layer. Moreover, the plating surface layer inside a crack means the interface of the plating layer located inside a crack.

A well-known thing can apply and a Zn-Ni alloy plating layer is not specifically limited, However, What is about 6 to 15% of Ni content rate of a plating layer, More preferably, about 9 to 13% is used. The amount of plating deposition is about 5 to 40 g / m ² .

  About the crack which reaches from a plating layer surface layer of a Zn-Ni alloy plating layer to ground iron, it is possible to form by acid etching processing after plating. It is also possible to simultaneously perform the formation of the crack and the blackening when the blackening treatment is performed.

  A known method can be applied to the blackening treatment, and the method is not particularly limited. However, when performing the crack formation simultaneously in the blackening treatment without performing the crack formation treatment in advance, the etching conditions of the blackening treatment, etc. Need to adjust. Specifically, a method of spray showering an acidic aqueous solution containing phosphate ion, nitrate ion or the like at an appropriate liquid flow rate on the steel sheet surface can be employed. Further, in order to form the blackening treatment layer even inside the crack, although depending on the bath conditions, treatment by immersion or spray is preferable, and in the electrolytic treatment, the inside of the crack may be difficult to be treated, which is not preferable.

  In the upper layer of the blackening treatment layer, a chemical conversion treatment layer for improving adhesion and corrosion resistance is provided. The chemical conversion treatment layer may or may not cover the inside of the plating layer crack. As a chemical conversion treatment layer, a thing free of chromate is desirable, and a publicly known thing can be applied. As an example, those containing at least one selected from silane coupling agents, organic resins, and polyphenol compounds are used.

  The silane coupling agent is not particularly limited. For example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylethoxysilane, N- [2- (vinylbenzylamino) ethyl ] 3-Aminopropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-gly Cidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyl Trimethoxysilane, γ-mercaptopropyltrimethoxysilane and the like can be mentioned. The silane coupling agents may be used alone or in combination of two or more.

  The organic resin is not particularly limited, and for example, known organic resins such as polyester resin, polyurethane resin, epoxy resin, phenol resin, acrylic resin, polyolefin resin and the like can be used. In order to further enhance the adhesion, it is preferable to use at least one of a polyester resin, a polyurethane resin, an epoxy resin, and a phenol resin.

  The polyphenol compound refers to a compound having two or more phenolic hydroxyl groups bonded to a benzene ring, or a condensate thereof. Examples of the compound having two or more phenolic hydroxyl groups bonded to the benzene ring include gallic acid, pyrogallol, catechol and the like. The condensate of the compound having two or more phenolic hydroxyl groups bonded to the benzene ring is not particularly limited, and examples thereof include polyphenol compounds widely distributed in the plant kingdom generally called tannic acid.

  In addition to the above, the chemical conversion treatment layer can also contain various rust inhibitors, inorganic compounds, and organic compounds.

  Although it is desirable that the black organic coating layer of the present invention is filled up into the plating layer cracks, it does not exclude the presence of unfilled portions. The black organic film layer is preferably made of a single layer, and the details thereof are not particularly limited. For example, those containing a resin, a curing agent and carbon black are used.

  As the resin, polyester resin, acrylic resin, polyurethane resin or the like is used. The polyester resin can be obtained, for example, by dissolving or dispersing, in water, one obtained by condensation polymerization of a polyester raw material comprising a polycarboxylic acid component and a polyol component. The polycarboxylic acid component is not particularly limited. For example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, azelaic acid And 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, dimer acid, trimellitic anhydride, pyromellitic anhydride and the like. These may be used alone or in combination of two or more. The polyol component is not particularly limited. For example, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,2-propanediol, triethylene glycol, 2-methyl-1,3-propanediol, 2,2 -Dimethyl-1,3-propanediol, 2-butyl-2-ethyl 1,3-propanediol, 1,4-butanediol, 2-methyl-1,4-butanediol, 2-methyl-3-methyl- 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1, 2-Cyclohexanedimethanol, hydrogenated bisphenol-A, dimer diol, trimethylolethane , Trimethylolpropane, glycerol, pentaerythritol, and the like. These may be used alone or in combination of two or more.

  As an acrylic resin, for example, unsaturated monomers such as styrene, alkyl (meth) acrylates, (meth) acrylic acid, hydroxyalkyl (meth) acrylates, alkoxysilane (meth) acrylates are polymerized in an aqueous solution Those obtained by radical polymerization using an initiator can be mentioned. The polymerization initiator is not particularly limited, and for example, persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobiscyanovaleric acid and azobisisobutyronitrile can be used.

  As a polyurethane resin, for example, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bisphenol hydroxypropyl ether, glycerin, trimethylolethane, trimethylolpropane and the like And those obtained by reacting a diisocyanate compound such as hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, etc., further chain-extending with a diamine or the like, and dispersing in water.

  The curing agent is not particularly limited as long as it hardens the resin, and examples thereof include melamine resin and polyisocyanate compound. The melamine resin is a resin obtained by condensing some or all of the methylol groups of a product obtained by condensing melamine and formaldehyde with a lower alcohol such as methanol, ethanol, butanol or the like. The polyisocyanate compound is not particularly limited, and examples thereof include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, and tolylene diisocyanate. Examples of the blocked products include blocked products of hexamethylene diisocyanate which is blocked products of the polyisocyanate compound, blocked products of isophorone diisocyanate, blocked products of xylylene diisocyanate, blocked products of tolylene diisocyanate, and the like. These curing agents may be used alone or in combination of two or more.

  As a black pigment of a coating film, carbon black is preferred, but other color pigments may be used in combination. The carbon black is not particularly limited. For example, known carbon blacks such as furnace black, ketjen black, acetylene black and channel black can be used. Also, known ozone treated, plasma treated, liquid phase oxidized carbon black can be used. The particle size of the carbon black to be used is not particularly limited as long as there is no problem in the dispersibility in the paint, the quality of the coating film, and the paintability. Specifically, the primary particle size of 10 to 120 nm can be used It is. It is preferable to use fine particle carbon black having a primary particle diameter of 10 to 50 nm, in consideration of the design (coloring property, hiding property) and corrosion resistance of a thin film. It is generally difficult to disperse the carbon black as it is the primary particle size, since these carbon blacks agglomerate during the process of dispersing in a paint. That is, in fact, they exist in the form of secondary particles having a particle size larger than the primary particle size in the paint, and also exist in the same form in the black coating film formed from the paint. The carbon black concentration in the coating film is preferably 1% to 20%, more preferably 3% to 12%. When the concentration of carbon black is high, the designability is improved, but the appearance, scratch resistance and chemical resistance of the processed portion tend to be lowered.

  In the black organic film, various rust inhibitors, lubricants, hard fine particles, conductive pigments and the like can be blended. As an antirust agent, various inorganic compounds such as colloidal silica and an organic antirust agent can also be used. As the lubricant, waxes such as fluorine resin compounds and polyethylene can be used. Resin beads etc. can be used as hard particulates. As the conductive pigment, fine particles of metal, inorganic or organic can be used. However, it is not limited to these.

  In order to improve the corrosion resistance of the black-coated steel sheet, it is preferable to add a fluorine resin-based compound. Examples of fluorine resin-based compounds include compounds containing a resin having a C-F bond, such as polytetrafluoroethylene resin (polytetrafluoroethylene resin etc.), polyvinyl fluoride resin, polyvinylidene fluoride resin, etc. .

  The fluorine resin compound is usually blended as a lubricant for the purpose of improving processability, but when such a fluorine resin compound is added to the black organic film of the present invention, only substances which are not fluorine resin compounds such as polyethylene can be obtained. The effect of improving the corrosion resistance can also be obtained as compared with the case of adding it. The reason is not clear, but when it is dried by heating to form a black organic film, the shape of a fluorine resin-based compound having a relatively high melting point (eg, polytetrafluoroethylene resin: 321 ° C.) does not substantially change its shape It is considered that a black organic film having a high barrier property is formed with a small gap with other film forming components. Alternatively, it is considered that the black organic film is also water repellent because of the water repellent action of the fluorine resin-based compound, and the water repellency is also exhibited to the salt water used in the corrosion resistance evaluation. Therefore, even when polyethylene and polytetrafluoroethylene are simultaneously added, for example, the effect is not impaired.

  In order to obtain the effects as described above, the particle diameter of the fluorocarbon resin-based compound needs to be at most twice the thickness Y (μm) of the organic coating layer. If the particle size is more than twice the thickness of the organic coating layer, the above effect can not be obtained. Further, the lower limit value of the particle diameter is not particularly limited, but a fluorine resin based compound generally used as a lubricant has a particle diameter of 1 μm or more.

  With respect to the content of the lubricant, 0.1 to 5% by mass is appropriate as a ratio to the film-forming component in the black organic film. If the content is 0.1% by mass or more, the effect is exhibited, and if the content is more than 5% by mass, the coating appearance tends to be poor and the stability of the coating is impaired.

  The thickness of the black organic coating layer is preferably 0.3 μm or more from the viewpoint of design. The upper limit is not particularly limited in view of characteristics, but it is preferable to be 10 μm or less in consideration of the cost. The definition of the thickness here is an average thickness, and the weight measured by the gravimetric method is converted into the thickness by dividing it by the specific gravity separately measured from the isolated coating film.

  The more preferable form of the crack which reaches from the plating layer surface layer of the Zn-Ni alloy plating layer of this invention to a ground iron is demonstrated below. The state of the crack can be confirmed by SEM observation at a magnification of about 5000 times from the cross section, and it is desirable that a large number exist in any visual field. Specifically, a straight line of 10 μm in length is drawn in the direction parallel to the ground iron interface in the vicinity of the center of the plating layer in the thickness direction in cross-sectional observation, and among the cracks intersecting this straight line It is desirable that one or more be measured.

Moreover, the more preferable form of the said crack is deeply related also with the thickness of a black organic membrane. When there are few cracks and the film thickness is low, the designability tends to decrease in both the flat portion and the processed portion, and when the film thickness is too thin with the cracks being small, the designability of the processed portion tends to decrease. As a result, as the number of cracks increases, the optimum film thickness area widens. About this, as a result of repeating experiments, if the number X (pieces) of the cracks and the black organic film layer thickness Y (μm) satisfy the relationship of the following formula (I), particularly good characteristics can be obtained. I know.
−0.6 × + 3.7 ≦ Y ≦ 2.7 × + 1.6 (I)

  About the adjustment of the number of the said crack, it can adjust with the density | concentration of the acid etching process after plating, temperature, and time. In addition, when performing the blackening treatment, even when the crack formation and the blackening are simultaneously performed, it is possible to adjust by the concentration, temperature, and time of the blackening treatment liquid. In either case, the optimum conditions differ depending on the coating weight of the plating, the Ni content, and the surface condition of the oxide film, etc. Therefore, preliminary tests are performed on the plated steel plates used in advance and the number of cracks is confirmed by SEM observation. It is desirable to keep it.

  Next, the present invention will be more specifically described by way of examples and comparative examples.

(First embodiment)
Examples 1 to 10, Comparative Examples 1 to 6
Using an alkaline degreasing aqueous solution (FC-E 6406 (manufactured by Nihon Parkerizing Co., Ltd.), 20 g / l, 60 ° C.) with an electric Zn-Ni alloy-plated steel sheet (plating adhesion amount: 10 g / m ² , Ni content 9.9%) It was treated by spray shower for 2 minutes, degreased and rinsed. After that, adjust the crack of the plating layer by etching treatment with sulfuric acid (20 g / l, 60 ° C, 4 seconds immersion), and further blackening treatment (NaNO ₃ : 80 g / l + H ₃ PO ₄ : 5 g / l, pH with NaOH Adjusted to 1.5, 50 ° C., 4 seconds immersion).

After that, a mixture of aqueous epoxy resin, 3 aminopropyltriethoxysilane and tannic acid in a ratio (mass ratio) of 40:30:30 is applied and dried at 80 ° C. to form a 100 mg / m ² chemical conversion film. did. Thereafter, an aqueous black paint was applied and dried at 200 ° C. to form films of various film thicknesses. The black paint contains various concentrations of carbon black (primary particle diameter: 20 nm) in paint containing polyester resin, polyurethane resin, melamine curing agent, and colloidal silica in a ratio (mass ratio) of 40: 30: 15: 15. Was added.

In addition, in the comparative example 1, it implemented to the chemical conversion treatment and black coating film application was not performed. In Comparative Examples 2, 3 and 4, the sulfuric acid etching process before the blackening process was not performed. In Comparative Example 5, a clear coating film containing no carbon black was applied. In Comparative Example 6, the conditions for the blackening treatment were anodic oxidation (NaNO ₃ : 80 g / l + H ₃ PO ₄ : 5 g / l, pH adjusted to 3 with NaOH, 50 ° C., 50 A / dm ² , 3 seconds). Other than that was processed similarly to the said Example.

  The contents of each level are shown in Table 1. Cracks in the plating layer of each sample were observed by SEM at a magnification of 5000 times from the cross section, and a straight line of 10 μm in length was drawn near the center of the plating layer in the thickness direction and a crack crossing this straight line Among them, the number of cracks reaching from the surface of the plating layer to the ground iron was measured. Five places were randomly selected, and the average was evaluated. The presence or absence of the blackening treatment layer of the plating surface layer inside the crack was confirmed by SEM and EDS observation of the cross section. The film thickness of the organic coating film calculated the adhesion amount by the gravimetric method, and was converted into film thickness from specific gravity.

  Performance evaluation was performed by the following methods and criteria. In all cases, a score of 3 or more was an acceptable level.

Flat plate appearance: The appearance was evaluated by the following evaluation criteria.
5: Both black and surface gloss are uniform. I can not see the ground through at all.
4: The black color is uniform, but the surface gloss is somewhat nonuniform (a level at which the eyes can be confirmed by looking carefully). The ground is not visible at all.
3: Black, surface glossiness is somewhat uneven (a level at which it can be confirmed by looking carefully with eyes). The ground is not visible at all.
2: Black color, uneven surface gloss (levels easily confirmed). The ground is not visible at all.
1: Black, uneven surface glossiness (levels that can be easily confirmed). The foundation looks slightly transparent.

Appearance after 0 T bending: 0 T bending (180 ° bending) was applied, the outside of the bent portion was peeled off, and the appearance was evaluated according to the following evaluation criteria.
5: The coating film is free from defects such as cracks and has a uniform black appearance. No color change is observed.
4: A slight discoloration was observed in the coating film, so slight discoloration was observed, but it had a nearly uniform black appearance. (The test board before the test is arranged side by side and the level understood somehow).
3: A slight crack was observed in the coating film, so slight discoloration was observed, but it has a substantially uniform black appearance. (A level that can be easily seen by arranging the test plate before the test sideways).
2: A crack was recognized in the coating film, and discoloration was observed (a level which can be seen only by the test plate).
1: A crack was recognized in the coating film, and the color loss was remarkable (a level that can be easily seen only by the test plate).

Eriksen (Ex) Appearance: Erichsen 7 mm extrusion was performed, the processed portion was peeled off from the tape, and the appearance was evaluated according to the following evaluation criteria.
5: The coating film is free from defects such as cracks and has a uniform black appearance. No color change is observed.
4: A slight discoloration was observed in the coating film, so slight discoloration was observed, but it had a nearly uniform black appearance. (The test board before the test is arranged side by side and the level understood somehow).
3: A slight crack was observed in the coating film, so slight discoloration was observed, but it has a substantially uniform black appearance. (A level that can be easily seen by arranging the test plate before the test sideways).
2: A crack was recognized in the coating film, and discoloration was observed (a level which can be seen only by the test plate).
1: A crack was recognized in the coating film, and the color loss was remarkable (a level that can be easily seen only by the test plate).

Scratchability: A cold-rolled steel plate (0.8 mm thick) is punched into a 40 mm diameter disk, and the disk is inclined at an elevation angle of 45 ° to the test plate, while applying a 1 kg load in the direction perpendicular to the disk surface, 10 mm / sec Scratch 50 mm with speed. The black appearance of the scratched buttocks was visually observed and evaluated according to the following criteria.
5: There is no difference in the black appearance of the normal part and the scratched buttocks. It looks like a uniform black appearance including the buttocks.
4: There is no difference in the black appearance of the scratched part, but it looks as if the glossiness changes a little.
3: A slight change is seen in the black appearance of the scratched part, but there is no exposure of the substrate at all.
2: A change was observed in the black appearance of the scratched part, and there was exposure of the substrate.
1: A noticeable change was observed in the black appearance of the scratched part, and there was a marked substrate exposure.

Ethanol resistance: After installing the test plate on the rubbing tester, the film condition after rubbing the ethanol-impregnated absorbent cotton for 10 cycles with a load of 49.03 kPa (0.5 kgf / cm ² ) was evaluated by the following evaluation criteria .
5: There is no mark on the rubbing surface at all.
4: There is a very slight mark on the rubbing surface (a level at which you can distinguish the rubbing trace by focusing your eyes).
3: A slight mark is formed on the rubbed surface (a level at which rubbing marks can be easily identified if the eyes are tightened).
2: A clear mark is formed on the rubbing surface (a level at which rubbing marks can be instantly determined).
1: The coating film is dissolved on the rubbing surface, and the substrate is exposed.

Alkali resistance: The film state after being immersed in a 2% aqueous solution of a test plate at 55 ° C. in an alkaline degreaser (Surf Cleaner 53, manufactured by Nippon Paint) for 30 minutes while being stirred was evaluated according to the following evaluation criteria.
5: There is no mark before and after treatment.
4: A slight trace is seen after treatment but there is no change in blackness.
3: A slight change in blackness is observed after treatment, but there is no abnormality such as film peeling.
2: A change in blackness was observed after treatment, and slight film peeling was observed.
1: A noticeable change in blackness is observed after the treatment, and there is film peeling.

  Table 1 shows the evaluation results. The values outside the scope of the present invention are underlined. In all the examples of the present invention, good characteristics above acceptable levels were obtained.

Second Embodiment
Examples 11 to 41
After the same original plate as in the first embodiment and the same alkaline degreasing, the cracked state of the plating layer was changed by changing the treatment time by the same sulfuric acid etching treatment. Then, blackening treatment (NaNO ₃ : 80 g / l + H ₃ PO ₄ : 5 g / l, pH adjusted to 1.5 with NaOH, 50 ° C., 3 seconds immersion, 2 seconds anodic oxidation at 40 A / dm ² ) went. Thereafter, a chemical conversion treatment was performed in the same manner as in the first example, and a coating film in which carbon black was adjusted to 10.5% with the same coating film as in the first example was applied with various film thicknesses.

  The contents of each level are shown in Table 2. The plating layer crack of each sample was evaluated in the same manner as in the first example. The presence or absence of the blackening treatment layer of the plating surface layer inside the crack was confirmed by SEM and EDS observation of the cross section, and it was confirmed that any level was also present. The film thickness of the organic coating was determined in the same manner as in the first example.

Examples 42 to 46
After the same original plate as in the first embodiment and the same alkaline degreasing, etching and blackening treatment were simultaneously performed by the following method. An acidic aqueous solution containing 0.5 mol / L of phosphate ion and 1.4 mol / L of nitrate ion, which is a mixture of sodium nitrate, phosphoric acid and sodium diphosphate, at a pH of 0.6 and a liquid temperature of 30 ° C, onto a steel plate Liquid flux of 200 L / m ² / min. The blackening treatment (treatment time: 2 to 10 seconds) was performed so as to obtain a predetermined crack amount by the spray shower treatment of Thereafter, a chemical conversion treatment was performed in the same manner as in the first example, and a coating film in which carbon black was adjusted to 10.5% with the same coating film as in the first example was applied with various film thicknesses. The contents of each level are shown in Table 2. The plating layer crack of each sample was evaluated in the same manner as in the first example. The presence or absence of the blackening treatment layer of the plating surface layer inside the crack was confirmed by SEM and EDS observation of the cross section, and it was confirmed that any level was also present. The film thickness of the organic coating was determined in the same manner as in the first example.

Table 2 also shows the evaluation results. In addition to the evaluation of the first embodiment, the evaluation here also added the evaluation by the following method and criteria with respect to the designability in a shape close to the actual processed product. The sample was subjected to 100 mm × 200 mm square tube reduction so that the black-painted surface was on the outside (punch, die shoulder R 5 mm, throttle depth 30 mm). After degreasing and cleaning the sample, it was divided into a flat plate portion with a small degree of processing and a R portion with a large degree of processing, and the designability was evaluated according to the following criteria.
5: A level that is uniform and beautiful compared to after-painted products.
4: Uniform beautiful, but slightly less deep compared to after-painted products.
3: Very slight nonuniformity of a level which can be confirmed by looking closely at eyes is recognized.
2: There is a level of unevenness that can be easily confirmed, and the design is inferior.
1: Unevenness of the level which can be checked easily is remarkable, and it is very inferior in the designability.

  As shown in Table 2, in all of the examples of the present invention, good characteristics above acceptable levels were obtained. Further, in Table 2, those satisfying the formula (I) are shown by ○, but those satisfying the formula (I) have a rating of 5 in any of the evaluation indexes and showed extremely good characteristics. .

Third Embodiment
Examples 15-1 to 15-16
The same original plate as Example 15 of the first embodiment, the same alkaline degreasing, the same sulfuric acid etching treatment, the same blackening treatment (NaNO ₃ : 80 g / l + H ₃ PO ₄ : 5 g / l, pH value with NaOH The same chemical conversion treatment was carried out after adjustment to 1.5, immersion at 50 ° C. for 3 seconds, and anodic oxidation at 40 A / dm ² for 2 seconds.

  After that, various lubricants were added to the coating film in which carbon black was adjusted to 10.5% in the same manner as in the first embodiment under the conditions shown in the "lubricant" column of Table 3, and coated with a film thickness of 4 μm.

Corrosion resistance A black painted plate sample on which a black organic paint film (black paint film) was formed was cut into a size of 70 mm × 150 mm, four sides were sealed, and a salt spray test was conducted under the conditions specified in JIS Z2371. The corrosion area ratio of the flat portion of the surface was determined and evaluated. The judgment criteria are as follows, and 3 to 5 points were accepted:
5: No white rusting after 120 hours,
4: White rusting occurred after 120 hours, area ratio less than 3%,
3: White rusting occurred after 120 hours, area ratio less than 5%,
2: White rusting occurred after 120 hours, area ratio 5% or more,
1: After 120 hours there is red rusting, whole surface white rusting.

  The performance evaluations other than the corrosion resistance were the same as in the first and second examples.

  From the results of the examples in Table 3, the corrosion resistance was good when polytetrafluoroethylene with a particle diameter of 4 μm was added, particularly when it was added at a concentration of 0.1% by mass or more and 5% by mass or less. The corrosion resistance was also good when polyvinyl fluoride or polyvinylidene fluoride having a particle diameter of 4 μm was added. The corrosion resistance was also good when polytetrafluoroethylene with a particle diameter of 6 μm and 8 μm was added. Both polytetrafluoroethylene and polytetrafluoroethylene are fluorine resin-based compounds, and the particle size thereof is not more than twice the thickness Y (μm) of the organic coating layer and is within the preferable range.

  On the other hand, when polytetrafluoroethylene having a particle diameter of 10 μm and 12 μm was added, no remarkable improvement in the corrosion resistance was observed, and the score was 3. This is because the particle diameter of the fluorine resin-based compound is more than twice the thickness Y (μm) of the organic coating layer.

  Further, in Examples 15-14 to 15-16 in which polyethylene wax, carbana wax and paraffin wax were added, the material added was not a fluorine resin compound, and therefore the score is 3, and all of them have remarkable corrosion resistance improvement effects Was not seen.

  The black-painted steel plate of the present invention can be suitably used for members that require decoration, such as office supplies, appliances, or automobile parts.

Claims (7)

A black painted steel plate having a Zn-Ni alloy plating layer formed on at least one surface of a steel plate and a blackening treatment layer covering the surface of the plating layer, and having a black organic coating layer on the upper layer thereof via a chemical conversion treatment layer. There is a crack in which the Zn-Ni alloy plating layer reaches from the surface layer of the plating layer to the ground iron, and a blackening treatment layer exists in the plating surface layer inside the crack,
The cross-section of the Zn-Ni alloy plating layer is observed, and from the surface layer of the plating layer to the ground iron among the cracks intersecting with a straight line of any 10 μm length drawn in the direction parallel to the interface A method for producing a black-painted steel sheet , wherein one or more cracks reach the surface,
Forming a Zn—Ni alloy plated layer with a plating adhesion amount of 5 to 40 g / m ^{2 on} at least one side of the steel plate ;
By etching the surface of the Zn-Ni alloy plated layer with an acid, a crack reaching from the surface layer of the plated layer to the base iron is formed;
The blackened layer is formed by blackening the surface of the etched Zn-Ni alloy plated layer using an acidic aqueous solution containing phosphate ions and nitrate ions,
The chemical conversion treatment layer is provided on the blackening treatment layer covering the surface of the Zn-Ni alloy plating layer,
A method for producing a black-painted steel plate, characterized in that the black organic coating layer is further provided on the upper layer of the chemical conversion treatment layer. The method for producing a black-painted steel sheet according to claim 1, wherein the blackening treatment is performed by immersing the surface of the Zn-Ni alloy plated layer in an acidic aqueous solution containing phosphate ions and nitrate ions. The method for producing a black-painted steel sheet according to claim 1, wherein the blackening treatment is performed by immersing the surface of the Zn-Ni alloy plated layer in an acidic aqueous solution containing phosphate ions and nitrate ions and then anodizing. The said acid etching is a sulfuric acid etching, The manufacturing method of the black coated steel plate as described in any one of Claims 1-3. In the black organic film layer thickness Y (μm) is in the range of 0.3 to 10 μm , based on the number X (pieces) of cracks reaching from the surface layer of the plating layer to the ground iron , the Y and the X below (I) The manufacturing method of the black-painted steel plate as described in any one of Claims 1-4 which forms an organic coating layer so that the relationship of Formula may be satisfy | filled.
−0.6 × + 3.7 ≦ Y ≦ 2.7 × + 1.6 (I) The said black organic coating layer contains the fluorine resin type compound of the particle size of 2 times or less of twice the organic coating layer thickness Y (micrometer) , manufacture of the black coated steel plate as described in any one of Claims 1-5. How . The method for producing a black-coated steel sheet according to claim 6, wherein the fluorine resin-based compound is 0.1% by mass or more and 5% by mass or less of the organic coating solid content.