JP2009052088A - Non-chromate conversion coated electrogalvanized steel sheet superior in white-rust resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-chromate conversion coated electrogalvanized steel sheet superior in white-rust resistance. <P>SOLUTION: The non-chromate conversion coated electrogalvanized steel sheet 10 superior in white-rust resistance has a non-chromate conversion coated film 3 on an electrogalvanized layer 2, and contains Ni in a range from the interface between the electrogalvanized layer 2 and the non-chromate conversion coated film 3 to 0.04 μm deep in a depth direction of the electrogalvanized layer 2 so that the content is controlled to 500 mass ppm or less in atom terms. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-chromate chemical conversion electro-zinc plated steel sheet excellent in white rust resistance. The electric Zn-plated steel sheet of the present invention is used, for example, in the fields of home appliances, automobile parts, building materials, and the like, particularly indoors such as chassis and case parts, steel furniture, etc. of home appliances and OA equipment. It is suitably used for the intended use.

  Electric Zn-plated steel sheets are often used without painting due to user requests for omission of painting, so the occurrence of white rust, which is a rust of Zn itself that exhibits sacrificial anticorrosive action on steel sheets, has become a problem. . Therefore, conventionally, for the purpose of improving the white rust resistance, a chromate conversion treated electro-Zn plated steel sheet in which chromate conversion treatment is performed on the electro-Zn plating layer has been widely used. However, in recent years, from the viewpoints of global environmental problems and regulations on the use of hazardous substances, non-chromate conversion treated Zn-plated steel sheets that have been subjected to non-chromate conversion treatment that does not substantially contain hexavalent chromium (Cr) have been actively developed. Therefore, studies for preventing the occurrence of white rust in the non-chromate chemical conversion electroplated Zn-plated steel sheet are underway.

  Incidentally, the electrical Zn plating layer usually contains a small amount of nickel (Ni). This is because, in actual production, Ni is an inevitable impurity element that can inevitably be mixed into the plating layer in the manufacturing process of the electroplated Zn-plated steel sheet. Specifically, Ni is caused by, for example, melting of a conductor roll using a Ni alloy such as Hastelloy or mixing of a Zn-Ni plating solution at the time of production switching from an electric Zn-plated steel sheet to a Zn-Ni alloy-plated steel sheet. In addition, it is included in the electric Zn plating layer.

  Patent Documents 1 to 3 propose a technique for increasing the white rust resistance of a non-chromate chemical conversion treated Zn-plated steel sheet by controlling the amount of Ni added.

Among these, Patent Document 1 mainly describes a method of controlling the Ni content of the entire electro-Zn plating layer within a range of 50 to 700 ppm in order to suppress the blackening phenomenon. Blackening is a corrosion phenomenon observed in the early stage of a moist environment where chlorine ions exist before white rust occurs, and occurs in a relatively mild corrosive environment. The causative substance of black rust is an amorphous oxide deviating from the stoichiometric composition of “Zn _x O _1-x ” produced during the oxidation reaction (corrosion reaction) of Zn. It is said that the reaction occurs because it ends halfway. Therefore, in Patent Document 1, a predetermined amount of Ni, which is an element slightly more noble than Zn, is added for the purpose of moderately promoting the oxidation reaction of Zn as long as white rust is not generated.

Patent Document 2 focuses on a reaction layer formed at the interface between the non-chromate chemical conversion coating and the electroplated Zn layer, and if the alkali resistance of the reaction layer is increased, corrosion resistance after alkali degreasing (white rust resistance) is also achieved. It was made based on the knowledge of improvement. Specifically, the white rust resistance is improved by controlling the total amount of Ni and the like contained in the plating surface layer within 1 μm in the depth direction from the plating surface in the range of 50 to 3000 mg / m ² . .

Patent Document 3 was proposed by the same applicant as Patent Document 2 after the application of Patent Document 2. In Patent Document 3, “If the layer containing Ni or the like is too thick as in Patent Document 2, the adhesion between the non-chromate chemical conversion coating film and the electric Zn plating layer is reduced, and chemical conversion treatment is performed when subjected to press working. Based on the knowledge that “a part of the film is missing and good white rust resistance cannot be obtained”, a predetermined amount of an oxide such as Ni instead of metallic Ni coexists in a range within 50 nm from the plating surface. The white rust is improved.
JP 2000-355790 A JP 2004-263252 A JP 2006-265578 A

  An object of the present invention is to provide a non-chromate chemical conversion treated Zn-plated steel sheet excellent in white rust resistance.

  The electric Zn-plated steel sheet of the present invention that has solved the above-mentioned problem is a non-chromate chemical conversion-treated electric Zn-plated steel sheet having a non-chromate chemical conversion treatment film on the electric Zn-plated layer. Ni contained in the range of 0.04 μm in the depth direction of the electric Zn plating layer from the interface with the non-chromate chemical conversion coating is suppressed to 500 ppm or less (ppm means mass ppm, hereinafter the same) in terms of atoms. It has a gist.

  In a preferred embodiment, Ni in the electric Zn plating layer is suppressed to 1000 ppm or less in terms of atoms.

  Since the electric Zn plated steel sheet of the present invention is configured as described above, the white rust resistance of the non-chromated steel sheet is greatly improved.

In order to improve the white rust resistance of the non-chromate conversion treated electro-zinc-plated steel sheet, the present inventor has been focusing on Ni among elements that can be inevitably contained in the electro-zinc plating layer. It was. as a result,
(A) The generation of white rust cannot be sufficiently suppressed only by controlling the amount of Ni in the entire electroplated Zn layer as taught in the above-mentioned Patent Document 1, and as taught in Patent Document 2, a non- It is necessary to control the amount of Ni present at the interface between the chromate conversion coating and the electroplated Zn layer,
(B) Particularly, it is the outermost surface portion of the electroplated Zn layer (specifically, the region within the range of about 0.04 μm from the interface toward the plating layer) that greatly affects the white rust resistance improvement. Yes, as in Patent Document 2, it is not enough to control the amount of Ni in the surface portion of the plating layer (in the range of about 1 μm from the interface toward the plating layer), and there is variation in the white rust resistance improvement effect. Being
(C) In order to appropriately control the amount of Ni in the outermost surface portion of the plating layer as in (a) above, the temperature of the plating solution is particularly in the normal range (generally performed at 50 to 60 ° C.). The present inventors have found that it is necessary to set a lower value than the above, and have completed the present invention.

  The above will be explained in a little more detail.

  As described above, the electrical Zn plating layer inevitably contains Ni in the production process of the non-chromate chemical conversion treated electrical Zn-plated steel sheet. Here, Ni in the electric Zn plating layer is not uniformly distributed over the entire plating layer, but is present in a large amount on the plating layer surface side (side of the interface in contact with the non-chromate chemical conversion coating film). In the “outermost surface region” defined by the present invention (region in the range of about 0.04 μm from the interface toward the plating layer side), the “Ni concentrated layer” in which most Ni exists in a metallic state is observed. (See FIG. 4 below). This is because Zn is selectively dissolved by a substitution reaction between Zn in the electrical Zn plating layer and a small amount of Ni in the plating layer or the plating solution, and Ni is substituted with Zn to precipitate as metal Ni ( This is thought to be due to substitution precipitation. The “Ni-enriched layer” generated by substitutional precipitation of Ni is seen in the “outermost surface region” described above, and is not seen in the “surface region” around 1 μm from the surfactant defined in Patent Document 2. Therefore, in order to ensure excellent white rust resistance, the present invention has been reached based on the idea that it is important to control the amount of metallic Ni in the “outermost surface region” where the Ni concentrated layer is observed. It depends on you.

  That is, according to the results of the study by the present inventor, a high correlation between the amount of metallic Ni in the “surface region” and white rust resistance specified in Patent Document 2 is not necessarily recognized, and Ni in the above “surface region” is not recognized. Variations in properties were observed, such as white rust resistance being reduced even when the amount was controlled. On the other hand, the amount of metallic Ni existing in the “outermost surface region” on the interface side more than that of Patent Document 2 has a high correlation with white rust resistance, and can be an extremely good evaluation index. I found it.

  On the other hand, Patent Document 3 also attempts to improve the white rust resistance by paying attention to the “outermost surface region” (the region within 0.05 μm from the interface in Patent Document 3) that is almost the same as the present invention. However, in Patent Document 3, Ni oxide, which hardly exists originally, is deposited on the “outermost surface region” by a special plating process (using a plating solution containing nitrate ions and sulfate ions in a predetermined ratio). With the aim of improving white rust resistance, this special plating treatment is not performed, and the amount of metallic Ni present in the “outermost surface area” is controlled to improve white rust resistance. The means is different from the present invention. In Patent Document 3, attention is paid only to oxides of Ni, and attention is not paid to metal Ni as in the present invention. The amount of metal Ni present in the “outermost surface region” is related to white rust resistance. We have not conducted any experiments on the effects.

  In this specification, for convenience of explanation, the “electrical Zn plating layer” may be abbreviated as “Zn plating layer” or “plating layer” in some cases. In addition, non-chromate chemical treatment Zn-plated steel sheet is abbreviated as “non-chromate electro-Zn-plated steel sheet” or “non-chromo-electric Zn-plated steel sheet”, and non-chromate chemical conversion coating film is abbreviated as “non-chromate film” or “non-chromium film”. There is a case. Further, in order to distinguish from “surface layer having a depth of about 1 μm from the interface” described in Patent Document 2, “region in the range of about 0.04 μm in the depth direction of the plating layer from the interface” is particularly referred to as “outermost surface layer. Or “outermost surface area”.

  Hereinafter, with reference to FIG. 1 and FIG. 2, an embodiment of a non-chromate chemical conversion treated Zn-plated steel sheet according to the present invention will be described in detail.

  As shown in the overall cross-sectional view of FIG. 1, the non-chromate conversion treated electro-Zn plated steel sheet 10 of the present invention has an electro-Zn plating layer 2 and a non-chromate conversion-treated film 3 sequentially applied on the steel sheet 1. As shown in the partial sectional view of FIG. 2 in which the interface 4 between the electric Zn plating layer 2 and the non-chromate chemical conversion coating 3 is enlarged, it is included in the range of 0.04 μm from the interface 4 in the depth direction of the electric Zn plating layer 2. Metal Ni contained in the region (A in FIG. 2) is suppressed to 500 ppm or less.

  3 and 4 show No. 1 in Table 1 of Examples described later. 10 (invention example) and No. 1 It is a graph which shows distribution (depth direction profile) of Ni amount of an electric Zn plating layer about 24 (comparative example). FIG. 3 shows the Ni amount profile up to a depth of 1 μm, and FIG. 4 shows the Ni amount profile up to a depth of 0.1 μm in FIG. 3 and FIG. 10 and no. The numerical values of 24 “Ni amount up to 1 μm depth (average value)” (FIG. 3) and “Ni amount up to 0.04 μm depth (average value)” (FIG. 4) are also shown.

  From these figures, No. 10 (invention example) and No. 1 It can be seen that the outermost surface area of 24 (Comparative Example) has a “Ni concentrated layer” having a Ni concentration peak in the vicinity of about 0.01 μm from the interface. No. 10 and no. The results of the Ni content and corrosion resistance of the 24 outermost surface layers are as shown in Table 1. The Ni content of the outermost surface layer from the interface to the depth of 0.04 μm is 1598 ppm, which is much higher than the upper limit (500 ppm) of the present invention. No. exceeding 24, while white rust resistance was lowered, the Ni content of the outermost surface layer was 386 ppm, which was controlled within the range of the present invention. No. 10 is excellent in white rust resistance.

  Thus, the present invention is characterized in that the amount of metallic Ni in the outermost surface layer existing within about 0.04 μm from the interface is suppressed to 500 ppm or less. In the present invention, Ni in the outermost surface layer is mostly present as metallic Ni and may exist in the form of an oxide or the like, but the amount of metallic Ni in the outermost surface layer was controlled regardless of the form of Ni. It depends on you. In Patent Document 3 described above, an acidic plating solution containing nitrate ions and sulfate ions in a predetermined ratio in order to precipitate Ni oxide useful for improving white rust resistance in the “outermost surface layer”. However, in the present invention, such a special treatment is unnecessary, and the amount of metallic Ni that is extremely useful for white rust resistance can be controlled only by appropriately adjusting the plating temperature. In this respect, it is positioned as a simpler white rust resistance improving technique than Patent Document 3.

  In the present invention, the amount of Ni contained in the outermost surface layer of about 0.04 μm from the interface is preferably as small as possible, thereby enhancing the effect of improving white rust resistance. The amount of Ni in the outermost surface layer is particularly affected greatly by the composition of the plating solution, the production line, and the like. Therefore, these may be appropriately controlled so that the desired effect is obtained. It is preferable to make it. However, as shown in Patent Document 1 described above, since Ni is an element useful for improving prevention of blackening, in order to improve blackening resistance, the amount of Ni contained in the outermost surface layer is approximately It is preferable to be 50 ppm or more.

In the present invention, the amount of Ni contained in the outermost surface layer of about 0.04 μm from the interface was measured using a high-frequency glow discharge optical emission spectroscopy (GD-OES) device (GD-OES: Glow Discharge Optical Emission Spectroscopy). The GD-OES analysis is a method of analyzing elements in the depth direction from the surface (upper layer) of the sample while scraping the sample by high-frequency sputtering. Specifically, as will be described in detail in the Examples section below, an analytical sample prepared by cutting an electric Zn-plated steel sheet before non-chromate chemical conversion treatment into a size of 50 mm × 50 mm is prepared, and the Zn-plated surface of the sample is prepared. The Ni content distribution in the depth direction of the Zn plating layer from the interface was measured by performing high-frequency sputtering in the Ar glow discharge region and continuously dispersing the emission lines in the Ar plasma of the Ni element to be sputtered. A value (average value) obtained by dividing the total amount of Ni up to a depth of 0.04 μm by 0.04 μm was defined as “amount of metallic Ni in the outermost surface layer”. In the examples, analysis was performed under the following conditions using a Rigaku glow discharge luminescence surface analyzer (GDA750, JY-5000 RF).
Ar gas pressure: 2.5 hPa, power 30 W, frequency 50 Hz,
Duty cycle 0.2

  In the present invention, it is preferable that Ni in the electric Zn plating layer is suppressed to 1000 ppm or less in terms of atoms. In Patent Document 1 described above, the amount of Ni in the electroplated Zn layer is kept low for the purpose of improving white rust resistance. However, in the present invention, the amount of Ni in the outermost surface layer is mainly within the scope of the present invention. As a means for controlling the thickness, the amount of Ni in the Zn plating layer is adjusted. If the amount of Ni in the Zn plating layer is too large, it will be difficult to control the content of Ni in the outermost layer, and the hardness of the plating layer will increase and the adhesion between the plating layer and the non-chromate chemical conversion coating will decrease. And other problems will occur. Moreover, as shown in the column of Examples described later, even if the amount of Ni in the electric Zn plating layer is kept low, if the amount of Ni in the outermost surface layer is large, the desired white rust resistance can be ensured. It turned out that it was not possible. Based on the above viewpoint, in the present invention, the preferable amount of Ni in the plating layer is controlled.

  In addition, the form of Ni in the electric Zn plating layer is not particularly limited, and may exist as a metal like Ni of the outermost surface layer described above, or may exist in the form of an oxide or the like. In the present invention, it is sufficient that Ni in the plating layer is suppressed to 1000 ppm or less in terms of atoms regardless of the form of Ni.

  Ni in the electroplated Zn layer should be as small as possible, and as a result, the amount of Ni in the outermost surface layer can generally be easily kept low. In detail, although it changes also with plating conditions, such as plating solution temperature, generally it is preferable that it is 500 ppm or less, and it is more preferable that it is 200 ppm or less.

  The amount of Ni contained in the electroplated Zn layer can be analyzed using a method such as inductively coupled plasma optical emission spectrometry (ICP) or inductively coupled plasma mass spectrometry (ICP-MS). In the analysis, it is preferable to dilute the plating layer with hydrochloric acid or the like in order to eliminate measurement errors caused by matrix elements such as Zn, Na, and S contained in the plating solution. The dilution rate may be appropriately controlled within an appropriate range according to the concentration of the matrix element, the amount of Ni to be measured, and the like.

  In the examples described later, after the plating layer is diluted with hydrochloric acid diluted twice, the amount of Ni in the plating layer is analyzed. Specifically, an analytical sample prepared by cutting a non-chromate chemical conversion electro-plated steel sheet to a size of 50 mm × 50 mm is prepared, placed in a hydrochloric acid solution diluted twice, and immersed until the dissolution reaction of Zn is completed. And an immersion liquid (1) was obtained. In this example, in order to eliminate measurement errors due to substitutional precipitation of Ni once dissolved on the steel plate surface as a base material, the above sample is pulled up quickly (approximately within 10 seconds) immediately after the dissolution reaction of Zn, Again, it was immersed in a newly prepared hydrochloric acid solution (2-fold diluted solution) for 30 seconds to obtain an immersion solution (2). Thereafter, the immersion liquids (1) and (2) obtained as described above were combined and the volume was adjusted, and then an ICP-MS analyzer (PLASMAQUAD type manufactured by VGI) or an ICP analyzer (ICPV-1000 manufactured by Shimadzu Corporation). ) Was used to analyze the amount of Ni. In this example, the latter ICP analyzer was used for analysis.

In the electro-Zn plating layer 2, the amount of plating adhesion is preferably approximately 3 g / m ² or more, and thereby, good corrosion resistance (particularly white rust resistance) can be obtained even in the state of plating. From the viewpoint of corrosion resistance, the larger the amount of plating adhesion, the better. However, if it exceeds 100 g / m ² , the effect of improving corrosion resistance is saturated and economically useless, so the upper limit is generally 100 g / m ^2. Is preferred. A preferable lower limit of the amount of plating is 5 g / m ² . Moreover, a preferable upper limit is 60 g / m < ² > and a more preferable upper limit is 40 g / m < ² >.

  The electric Zn plating layer 2 only needs to be provided on at least a predetermined surface of the steel plate 1 as a base material, and may be provided on only one surface of the steel plate 1 or may be provided on both surfaces.

  The non-chromate chemical conversion coating coated on the plating layer 2 does not substantially contain Cr. Here, “substantially does not contain” means that an amount of Cr inevitably mixed in the process of producing the non-chromate film is acceptable. For example, in the present invention, when a small amount of Cr compound is eluted from a manufacturing container, a coating apparatus, etc. in the process of preparation and application of a treatment liquid used for a non-chrome film, there is a possibility that Cr is mixed into the film. is there. Even in such a case, it is preferable that the amount of Cr contained in the non-chrome film is generally within the range of 0.01% by mass or less.

  As the non-chromate chemical conversion coating 3, a coating usually used for a non-chromate chemical conversion electroplated zinc plated steel sheet can be used, (1) an organic coating mainly composed of an organic resin, and (2) mainly composed of an inorganic substance. Any inorganic coating can be used. This is because the structure of the non-chromate chemical conversion coating is not a feature of the present invention.

  Hereinafter, these films will be described in detail.

(1) Organic non-chromic film mainly composed of organic resin As the above-mentioned organic film, typically, epoxy resin, polyester resin, polyurethane resin, acrylic resin, polyethylene, polypropylene, ethylene- In addition to olefin resins such as acrylic acid copolymers, styrene resins such as polystyrene, ethylene copolymer resins containing ethylenically unsaturated carboxylic acids as polymerization components, polyvinyl resins, polyamide resins, fluorine resins, etc. Can be mentioned. In addition to the organic resin, an organic film containing a polyphenol compound such as tannic acid can also be used. These organic coatings are suitable for satisfying the characteristics particularly required in uncoated electric Zn-plated steel sheets, for example, required characteristics such as corrosion resistance, anti-fingerprint resistance, scratch resistance, and conductivity. .

  The above-mentioned organic coatings are used to improve the quality of corrosion resistance, lubricity, scratch resistance, workability, weldability, electrodeposition coating properties, adhesion to the plating layer, etc. Inorganic pigments such as physical particles and various phosphates, solid lubricants, crosslinking agents and the like may be contained. Further, it may contain wax particles, an organic silane compound, a naphthenate, and the like.

  Among the above organic non-chromic films, (a) a resin component of a carboxyl group-containing resin and (b) a film containing a Si-based inorganic compound (typically colloidal silica) (hereinafter referred to as “resin” in particular) It may be referred to as “film”). By using the above resin film, the effect of the steel sheet of the present invention (the effect of improving the white rust resistance by controlling the amount of Ni in the outermost surface layer) is more effectively exhibited, the white rust resistance is remarkably improved, and the alkali resistance Degreasing properties and paintability are also improved (see Example 2 described later). The resin film is described in detail in, for example, Japanese Patent Application Laid-Open No. 2006-43914, and the outline thereof will be described.

(A) Resin component of carboxyl group-containing resin First, the carboxyl group-containing resin is not particularly limited as long as it has a carboxyl group. For example, a monomer having a carboxyl group such as an unsaturated carboxylic acid is used as a raw material. Examples thereof include a polymer synthesized by polymerization as a part or the whole, or a resin modified with a carboxylic acid using a functional group reaction.

  A commercially available product may be used as the carboxyl group-containing resin, and examples thereof include Hitech S3141 (manufactured by Toho Chemical). The resin component may contain an organic resin other than the carboxyl group-containing resin.

(B) Si-based inorganic compound Examples of the Si-based inorganic compound include silicate and / or silica. These may be used alone or in combination of two or more.

  Among these, examples of the silicate include potassium silicate and lithium silicate.

  Typical examples of silica include colloidal silica and scaly silica. In addition, dry silica such as pulverized silica, gas phase method silica, silica sol, and fumed silica may be used.

  Of these, the use of colloidal silica is particularly preferred. As a result, the strength of the resin film is increased, and in a corrosive environment, silica is concentrated in the heel portion of the film, and the corrosion of Zn is suppressed and the corrosion resistance is further enhanced. As the colloidal silica, commercially available products may be used. For example, Snowtex series “ST-40”, “ST-XS”, “ST-N”, “ST-20L”, “ST-20L” manufactured by Nissan Chemical Industries, Ltd., “ ST-UP "," ST-ZL "," ST-SS "," ST-O "," ST-AK ", and the like.

  The mass ratio of (a) resin component and (b) Si-based inorganic compound (typically colloidal silica) constituting the resin film is approximately (a) resin component: (b) Si-based inorganic compound = 5 parts. ~ 45 parts: preferably in the range of 55 parts to 95 parts. If the content of the resin component is small, the corrosion resistance, alkali degreasing resistance, paintability, etc. tend to decrease. On the other hand, if the content of the resin component is large, the abrasion resistance, conductivity, etc. will decrease. . In addition, when the content of the Si-based inorganic compound is small, abrasion resistance, conductivity, etc. tend to decrease, and when the content of the Si-based inorganic compound is large, the resin component is decreased, so that the resin film is formed. As a result, the corrosion resistance decreases.

  The resin film may further contain a silane coupling agent. By adding the silane coupling agent, the bond between the above-described carboxyl group-containing resin and the Si-based inorganic compound is strengthened, so that the white rust resistance is further improved.

  The silane coupling agent preferably has a lower alkoxy group such as an alkyl group having 1 to 5 carbon atoms, an allyl group, or an aryl group. Specifically, for example, glycidoxy group-containing γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxymethyldimethoxysilane, etc. Silane coupling agent; γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-amino Amino group-containing silane coupling agents such as propylmethyldimethoxysilane; Vinyl group-containing silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris (β-methoxyethoxy) silane; γ-methacryloxypropyltrimethoxysilane Meta Riloxy group-containing silane coupling agents; mercapto group-containing silane coupling agents such as γ-mercaptopropyltrimethoxysilane and γ-mercaptopropylmethyldimethoxysilane; halogens such as γ-chloropropylmethoxysilane and γ-chloropropyltrimethoxysilane Examples thereof include a group-containing silane coupling agent. These silane coupling agents may be used alone or in combination of two or more.

  Among the above, the glycidoxy group-containing silane coupling agent is preferably used because it has particularly high reactivity and is excellent in corrosion resistance and alkali resistance.

  A commercially available product may be used as the silane coupling agent, and examples thereof include γ-glycidoxypropyltrimethoxysilane “KBM403” (manufactured by Shin-Etsu Chemical Co., Ltd.).

  The content of the silane coupling agent is preferably in the range of approximately 5 parts by mass to 25 parts by mass with respect to 100 parts by mass in total of the resin component and the Si-based inorganic compound. If the content of the silane coupling agent is small, the white rust resistance improving effect is not exhibited effectively, and the reactivity between the carboxyl group-containing resin and the Si-based inorganic compound is reduced, resulting in abrasion resistance, paintability, etc. Decreases. On the other hand, when there is much content of a silane coupling agent, stability of the film preparation liquid used for preparation of a resin film will fall, and there exists a possibility of gelatinizing. Moreover, since the quantity of the silane coupling agent which does not contribute to reaction increases, there exists a possibility that the adhesiveness of a Zn plating layer and a non-chrome film may fall.

  Hereinafter, the constitution and the preparation method of the urethane resin improved film, which is a typical example of the above-mentioned tree film, are described in JP-A-2006-43913 disclosed by the applicant of the present application (see, for example, paragraphs [0020] to [0071]). ) And briefly explain. However, the resin film used in the present invention is not limited to this.

  The resin film is obtained from the following aqueous resin liquid. The aqueous resin liquid is a silica particle having 5 to 45 parts by mass of an aqueous carboxylate-containing polyurethane resin liquid and an aqueous ethylene-unsaturated carboxylic acid copolymer dispersion as a nonvolatile resin component, and an average particle diameter of 4 to 20 nm. It contains 100 parts by mass in a total of 55 to 95 parts by mass, and further contains a silane coupling agent in a ratio of 5 to 25 parts by mass with respect to a total of 100 parts by mass. The blending ratio of PU) to the nonvolatile resin component (EC) of the ethylene-unsaturated carboxylic acid copolymer aqueous dispersion is PU: EC = 9: 1 to 2: 1 in terms of mass ratio.

  First, the carboxyl group-containing polyurethane resin aqueous solution will be described.

  As the aqueous carboxyl group-containing polyurethane resin liquid, either an aqueous dispersion in which a carboxyl group-containing polyurethane resin is dispersed in an aqueous medium or an aqueous solution in which the carboxyl group-containing polyurethane resin is dissolved in an aqueous medium can be used. The aqueous medium may contain a trace amount of a hydrophilic solvent such as alcohol, N-methylpyrrolidone and acetone in addition to water.

  The carboxyl group-containing polyurethane resin is preferably obtained by subjecting a urethane prepolymer to a chain extension reaction with a chain extender, and the urethane prepolymer reacts, for example, a polyisocyanate component and a polyol component described later. Obtained.

  As the polyisocyanate component constituting the urethane prepolymer, at least one polyisocyanate selected from the group consisting of tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and dicyclohexylmethane diisocyanate (hydrogenated MDI) is used. It is preferable. Here, as the polyol component constituting the urethane prepolymer, 1,4-cyclohexanedimethanol, polyether polyol, and all three types of polyols having a carboxyl group are used, preferably all three types are used. Is a diol. The polyether polyol is not particularly limited as long as it has at least two hydroxyl groups in the molecular chain and the main skeleton is composed of alkylene oxide units. For example, polyoxyethylene glycol, polyoxypropylene glycol And polyoxytetramethylene glycol.

  The chain extender for chain extending reaction of the urethane prepolymer described above is not particularly limited, and examples thereof include polyamines, low molecular weight polyols, and alkanolamines.

  A known method can be used to prepare the aqueous solution of the carboxyl group-containing polyurethane resin. For example, the carboxyl group of the carboxyl group-containing urethane prepolymer is neutralized with a base, and emulsified and dispersed in an aqueous medium. There are a method of extending the reaction, a method of emulsifying and dispersing the carboxyl group-containing polyurethane resin in the presence of an emulsifier with a high shearing force, and the like.

  Next, the ethylene-unsaturated carboxylic acid copolymer aqueous dispersion will be described.

  The ethylene-unsaturated carboxylic acid copolymer aqueous dispersion is not particularly limited as long as the ethylene-unsaturated carboxylic acid copolymer is a liquid in which the ethylene-unsaturated carboxylic acid copolymer is dispersed in an aqueous medium. Is a copolymer of ethylene and an ethylenically unsaturated carboxylic acid. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. A copolymer can be obtained by polymerization using a legal method or the like.

  The ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, and the carboxyl group is neutralized with an organic base (for example, an amine having a boiling point of 100 ° C. or less) or a monovalent metal ion such as Na. Thus, an aqueous dispersion can be obtained.

  Here, monovalent metal ions are used for neutralization as described above, but are effective in improving solvent resistance and film hardness. The monovalent metal compound preferably contains one or more metals selected from sodium, potassium, and lithium, and a hydroxide, carbonate, or oxide of these metals is preferable. Among these, NaOH, KOH, LiOH and the like are preferable, and NaOH has the best performance and is preferable. The present invention improves the blot stain phenomenon derived from NaOH.

  The amount of the monovalent metal compound may be in the range of 0.02 to 0.4 mol (2 to 40 mol%) with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. preferable. When the amount of the metal compound is less than 0.02 mol, the emulsion stability becomes insufficient. However, when the amount exceeds 0.4 mol, the hygroscopicity (particularly with respect to the alkaline solution) of the resulting resin film increases, and degreasing Since corrosion resistance after a process deteriorates, it is not preferable. A more preferable lower limit of the amount of the metal compound is 0.03 mol, a still more preferable lower limit is 0.1 mol, and a more preferable upper limit of the amount of the metal compound is 0.2 mol.

  If the total amount (neutralization amount) of the organic base (preferably an amine having a boiling point of 100 ° C. or less) and a monovalent metal compound is too large, the viscosity of the aqueous dispersion may rapidly increase and solidify. In addition, since excessive alkali content causes deterioration of corrosion resistance, a large amount of energy is required for volatilization, which is not preferable. However, if the neutralization amount is too small, the emulsifiability is inferior, which is not preferable. Therefore, the total amount of the organic base and the monovalent metal compound is preferably in the range of 0.3 to 1.0 mol with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer.

  The ethylene-unsaturated carboxylic acid copolymer aqueous dispersion described above is an extremely small fine particle (oil droplet) state having an average particle size of 5 to 50 nm by emulsifying an organic base and a monovalent metal ion in combination. To obtain a dispersion in an aqueous medium. For this reason, it is presumed that the film forming property of the obtained resin film, the adhesion to the metal plate, the densification of the film are achieved, and the corrosion resistance is improved. The aqueous medium may contain a hydrophilic solvent such as alcohol or ether in addition to water. The particle diameter of the resin particles in the aqueous dispersion can be measured by a laser diffraction method using, for example, a light scattering photometer (manufactured by Otsuka Electronics Co., Ltd.).

  As a method for preparing the ethylene-unsaturated carboxylic acid copolymer aqueous dispersion, the ethylene-unsaturated carboxylic acid copolymer is put together with an aqueous medium into, for example, a homogenizer device or the like, and heated at 70 to 250 ° C. as necessary. And an organic base such as an amine having a boiling point of 100 ° C. or lower and a monovalent metal compound is appropriately added in the form of an aqueous solution or the like (an amine having a boiling point of 100 ° C. or lower is added first, or an amine having a boiling point of 100 ° C. or lower is added. The monovalent metal compound is added almost simultaneously) and stirred with high shearing force.

  Next, the carboxyl group-containing polyurethane resin aqueous liquid and the ethylene-unsaturated carboxylic acid copolymer aqueous dispersion obtained by the above-described method are blended with silica particles and a silane coupling agent in a predetermined amount, and if necessary, a wax is added. A desired aqueous resin solution is obtained by blending a crosslinking agent and the like. Silica particles, silane coupling agent, wax, cross-linking agent, etc. may be added at any stage, but after adding the cross-linking agent and silane coupling agent, heat is applied so that the cross-linking reaction will not proceed and gel. It is desirable not to multiply.

  The organic non-chromic film (resin film) suitably used in the present invention has been described above.

(2) Inorganic non-chromic film mainly composed of inorganic substances As the inorganic film used in the present invention, typically, zinc phosphate, iron phosphate, manganese phosphate, calcium phosphate, magnesium phosphate, etc. Examples of such a film mainly composed of phosphate include a film mainly composed of silicate such as sodium silicate, potassium silicate, lithium silicate and the like. Alternatively, a commonly used inorganic film such as molybdic acid or vanadic acid can also be used. Of these, inorganic coatings mainly composed of silicates are particularly suitable for applications that undergo strong sliding during press working.

  The above-mentioned inorganic coatings are used to improve the quality of corrosion resistance, lubricity, scratch resistance, workability, weldability, electrodeposition coatability, adhesion to the plating layer, etc. Inorganic pigments such as physical particles and various phosphates may be contained. Further, it may contain wax particles, an organic silane compound, a naphthenate, and the like.

  The non-chromate chemical conversion coating film used in the present invention may be composed of the above-mentioned (1) organic film or (2) single-layer type consisting only of an inorganic film, or a laminated type combining these. It may be configured. In the case of the latter laminated type, the combination order is not particularly limited, and the lower layer may be an inorganic film, the upper layer may be an organic film, and vice versa. The number of stacked layers is not limited to two, and may be three or more.

  In addition to the above components, the non-chromate chemical conversion coating film 3 used in the present invention usually includes components (for example, anti-skinning agents, leveling agents, antifoaming agents, penetrants) as long as the effects of the present invention are not impaired. , Emulsifiers, film-forming aids, color pigments, lubricants, surfactants, conductive additives for imparting conductivity, thickeners, dispersants, drying agents, stabilizers, antifungal agents, preservatives, An antifreezing agent and the like may be contained.

  The thickness of the non-chromate chemical conversion coating 3 is generally preferably in the range of 0.05 to 20 μm, and more preferably in the range of 0.2 to 2.0 μm. When the thickness of the resin film is less than 0.05 μm, the white rust resistance is lowered. On the other hand, when the thickness exceeds 20 μm, the white rust resistance improving effect is saturated and is economically wasteful, and the conductivity and workability are also reduced. Will fall.

  In addition, in FIG. 1 mentioned above, although the example of the electrical Zn plating steel plate which coat | covered the electrical Zn plating layer 2 and the non-chromate chemical conversion treatment film 3 on the steel plate 1 is shown, this invention steel plate is limited to this. In addition, on the non-chromate chemical conversion coating 3, an organic resin film, an organic / inorganic composite film, an inorganic film, and an electrodeposition coating film are provided for the purpose of improving corrosion resistance (particularly white rust resistance) and paintability. A film such as may be provided.

  Here, as said organic resin membrane | film | coat, the substantially same thing as the organic type membrane | film | coat which comprises the nonchromate chemical conversion treatment film 3 mentioned above is mentioned. Specifically, for example, urethane resins, epoxy resins, acrylic resins, polyethylene, polypropylene, olefin resins such as ethylene-acrylic acid copolymers, styrene resins such as polystyrene, polyesters or copolymers thereof, Examples thereof include a film formed by combining a known resin for coating materials such as a modified product with colloidal silica, a solid lubricant, a crosslinking agent, or the like as necessary.

  Moreover, as said organic-inorganic composite membrane | film | coat, the membrane | film | coat formed by combining the said organic resin and water glass forming components, such as sodium silicate, is mentioned typically.

  Moreover, as said inorganic type film | membrane, the water glass film | membrane and the film | membrane formed from a lithium silicate are mentioned typically.

  Next, the manufacturing method of the non-chromate electric Zn plating steel plate concerning the present invention is explained.

  First, a base steel plate (plating original plate) serving as a base material is prepared. The base steel plate is not particularly limited as long as it is usually used for an electric Zn-plated steel plate. For example, various steel plates such as a normal steel plate, an Al killed steel plate, and a high-tensile steel plate can be used. The plating original plate is preferably subjected to pretreatment such as degreasing and pickling before performing electro-Zn plating.

  Next, an electric Zn plating layer is formed on the base steel plate by an electric Zn plating method to produce an electric Zn plating steel plate.

  In the present invention, in particular, the greatest feature is that the plating temperature is controlled to be lower than usual (approximately 20 to 45 ° C.) and the amount of Ni in the outermost surface layer is appropriately adjusted. As described above, Ni is deposited as a metal by substitution deposition reaction of Zn and Ni in the outermost surface layer, but such a chemical reaction is sensitive to the surrounding environment, and is a metal that precipitates against changes in plating temperature. The amount of Ni also changes significantly (see the examples described later). The plating temperature is usually about 50 ° C. at the lowest in actual production because of the relationship with the production line and productivity of the steel sheet used, and a temperature lower than that, especially room temperature (generally around 30 ° C.) or less. However, in the present invention, in order to control the amount of Ni in the outermost surface region, it is set to be lower than the conventional plating temperature. As shown in the examples described later, when the plating temperature reaches about 50 ° C. or higher, even if the Ni content in the plating solution is appropriately controlled, for example, by appropriately controlling the Ni concentration in the plating solution, the most Since the amount of Ni in the surface layer cannot be kept low within a predetermined range, the desired white rust resistance cannot be obtained. Considering the white rust resistance improving effect and productivity, the plating temperature should be low, and is generally preferably 30 ° C. or lower.

  In this invention, conditions other than the plating temperature mentioned above are not limited, Other plating conditions other than the above can be suitably set suitably in the range which does not impair the effect | action of this invention. Specifically, it is preferable to perform plating as follows.

  In the present invention, an acidic Zn plating solution that is usually used, for example, an acidic plating solution such as a plating solution containing zinc sulfate and sulfuric acid, or a plating solution containing zinc sulfate, sodium sulfate and ammonium sulfate can be used. In the present invention, a plating solution containing a blending amount of nitric acid described in Patent Document 3 is not used.

  In the acidic plating solution, Ni is preferably suppressed to approximately 400 ppm or less. Thereby, the Ni amount of the outermost surface layer can be controlled relatively easily within the range of the present invention, and the Ni amount of the entire plating layer can be easily controlled within the preferable range. The smaller the amount of Ni added to the plating solution, the better. In general, it is more preferably 200 ppm or less, and further preferably 100 ppm or less.

  Here, “the amount of Ni in the plating solution is preferably suppressed to 400 ppm or less” means that Ni is introduced as an active element even though it is mixed as an inevitable impurity element in the plating solution. In any case, it means that the amount of Ni in the plating solution is preferably within the above range. As described above, Ni is an impurity that can be inevitably mixed in the manufacturing process, and may be positively added to the plating solution to prevent blackening (for example, the above-mentioned patent document). However, the present invention is intended to include any aspect, and that means that the present invention is not intended to be limited to any aspect.

  In addition, in order to suppress the Ni amount in the outermost surface layer and the Ni amount in the electric Zn plating layer within the range defined in the present invention, in addition to controlling the Ni addition amount in the acidic solution as described above. It is also preferable to pay attention to Zn as a raw material, an anode material used for electric Zn plating, and the like. Specifically, it is preferable to control Ni in Zn as a raw material to about 10 ppm or less. Further, when a Hastelloy alloy or the like is used as an anode material, the amount of Ni in the electric Zn plating layer may increase due to elution of the anode material. Therefore, an anode material that does not substantially contain Ni (for example, a Ti electrode) is used. It is preferable to use it.

  When Ni is added to the plating bath, the addition form of Ni is not particularly limited, and any form can be adopted as long as the Ni addition amount in terms of atoms satisfies the above range. For example, it may be added to the plating solution in a metal state such as metal powder or metal foil, or added in the form of a metal salt such as sulfate, chloride, phosphate, carbonate, oxide salt. Also good. When adding in the form of a metal salt, the valence of the element is not particularly limited, and a value that can be normally taken can be adopted.

In addition to the above elements, other components that are usually added may be added to the plating solution. For example, a conductive auxiliary agent such as Na ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ , KCl, or NaCl may be added for the purpose of increasing conductivity and reducing power consumption.

  The pH of the plating solution is preferably within the range of 0.5 to 4.0, preferably within the range of 1.0 to 2.0, in consideration of the relationship with current efficiency and plating burn phenomenon. Is more preferable.

  It is preferable that the relative flow rate of the plating solution is generally in the range of 0.3 to 5 m / sec. Here, the relative flow velocity means the difference between the flow direction velocity of the plating solution and the plate passage direction velocity of the steel plate that is the plating original plate.

  The type of electrode (anode) used for electroplating is not particularly limited as long as it is normally used. For example, Pb—Sn electrode, Pb—In electrode, Pb—Ag electrode, Pb—In—Ag electrode, etc. In addition to lead-based electrodes, examples include iridium oxide electrodes and zinc electrodes.

  As the plating cell, either a vertical cell or a horizontal cell can be used. The method of electro Zn plating is not particularly limited, and examples thereof include constant current plating and pulse plating.

  After the plating layer is formed as described above, a non-chromate chemical conversion treatment film is formed based on a conventional method. Prior to the formation of the non-chromate conversion treatment film, for example, amines such as Co, Ni, Mo, V, phosphate, nitrate, etc., for the purpose of improving film adhesion, corrosion resistance, and appearance control on the surface of the plating layer You may perform the well-known pretreatment using.

  Hereinafter, although the formation method of the resin film used preferably among the (1) organic type films mentioned above is explained in detail, the present invention is not limited to this.

  First, a chromate-free chemical conversion treatment liquid (hereinafter sometimes simply referred to as “treatment liquid”) containing a predetermined amount of a resin component of a carboxyl group-containing resin and a Si-based inorganic compound, preferably containing a predetermined amount of a silane coupling agent. Prepare). The treatment liquid is obtained by dissolving and dispersing in an aqueous solvent (for example, hydrochloric acid or nitric acid solution) that can completely dissolve the following components.

  The mass ratio of the resin component and the Si-based inorganic compound contained in the treatment liquid is preferably generally within the range of resin component: Si-based inorganic compound = 5 parts to 45 parts: 55 parts to 95 parts. If the amount of the resin component such as carboxyl group-containing resin is small, the corrosion resistance, alkali degreasing resistance, paintability, etc. tend to decrease. On the other hand, if the amount of the resin component is large, the abrasion resistance, conductivity, etc. decrease. Will come to do. Also, if the amount of colloidal silica is small, the abrasion resistance, conductivity, etc. tend to decrease, and if the amount of colloidal silica is large, the resin component is reduced and the film-forming property of the resin film is reduced, resulting in corrosion resistance. Will fall.

  The treatment liquid may further contain a silane coupling agent. The content of the silane coupling agent contained in the treatment liquid is generally in the range of 5 to 25 parts by mass with respect to a total of 100 parts by mass of the resin component and the Si-based inorganic compound, as shown in the examples described later. It is preferable. If the content of the silane coupling agent is low, the stain resistance improving effect is not exhibited effectively, and the reactivity between the carboxyl group-containing resin and the Si-based inorganic compound is reduced, resulting in abrasion resistance, paintability, corrosion resistance, etc. Decreases. On the other hand, when there is much content of a silane coupling agent, stability of the film preparation liquid used for preparation of a resin film will fall, and there exists a possibility of gelatinizing. Moreover, since the quantity of the silane coupling agent which does not contribute to reaction increases, there exists a possibility that the adhesiveness of a Zn plating layer and a resin film may fall.

  In addition to the above components, a wax or a crosslinking agent may be added to the treatment liquid as necessary. Further, the treatment liquid usually contains components (for example, anti-skinning agents, leveling agents, antifoaming agents, penetrating agents, emulsifying agents, film-forming aids, color pigments, lubricants) as long as the effects of the present invention are not impaired. Agents, surfactants, conductive additives for imparting conductivity, thickeners, dispersants, drying agents, stabilizers, antifungal agents, preservatives, antifreeze agents, etc.).

  The treatment liquid containing the above components can be obtained by using a known method such as a roll coating method, a spray coating method, a curtain flow coater method, a knife coater method, a bar coating method, a dip coating method, or a brush coating method. When applied to one or both sides of the plate, and then heated and dried, an electric Zn-plated steel plate provided with a desired resin film is obtained.

  The heating / drying temperature is preferably a temperature at which the crosslinking reaction between the carboxyl group-containing resin to be used and the Si-based inorganic compound proceeds sufficiently (for example, approximately a plate temperature of 90 to 100 ° C.). In addition, when spherical polyethylene wax is used as the lubricant, it is possible to perform drying in the range of about 70 to 130 ° C. because maintaining the spherical shape improves the workability in the subsequent processing step. desirable.

  The non-chromate electric Zn-plated steel sheet obtained in this way is extremely excellent in white rust resistance, so that it is used in fields such as home appliances, automobile parts, and building materials, and particularly home appliances mainly used indoors. It is suitably used for applications such as chassis, case parts, steel furniture, and the like of OA equipment.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. It is possible and such an aspect is also included in the technical scope of the present invention. Hereinafter, unless otherwise specified, “%” means mass%.

Example 1
In this example, the influence of the amount of Ni contained in the range of 0.04 μm in the depth direction of the plating layer from the interface between the plating layer and the non-chrome coating on the white rust resistance was examined. In Example 1, an organic non-chromic film based on a polyolefin resin was produced and tested.

(1) Production of electric Zn-plated steel sheet An Al-killed cold-rolled steel sheet produced by a conventional method was used as a plating original sheet. This was degreased and pickled, and then electroplated using a plating solution having the following composition in a circulating plating apparatus having a plating area of 180 mm × 300 mm to obtain an electrical Zn-plated steel sheet.

(Plating solution composition)
A plating solution containing the following components and added with Ni in the range shown in Table 1 in the form of sulfate was used.
ZnSO ₄ · 7H ₂ O 350 g / L
Na ₂ SO ₄ 70 g / L
H ₂ SO ₄ 20 g / L
_{FeSO 4 · 7H 2 O 9g /} L
Fe ₂ (SO ₄ ) ₃ · nH ₂ O (n = 9.5) 1.8 g / L
Na ₂ MoO ₄ · 2H ₂ O 0.03 g / L
40% Cr ₂ (SO ₄ ) ₃ solution 0.9 g / L
Sn standard solution 0.1mg / L

Other plating conditions are as follows.
Current density: 50 A / dm ²
・ Plating temperature: 20-60 ° C
・ Plating solution flow rate: 1.5m / sec
-Electrode (anode): IrOx electrode-Amount of plating: 20 g / m ²

(2) Preparation of electro-Zn-plated steel sheet provided with non-chromate chemical conversion coating film Separately, an epoxy-based crosslinking agent (“Rikabond AP355B” manufactured by Chuo Rika Kogyo Co., Ltd.) was added to a polyolefin-based dispersion (“Chemical S100” manufactured by Mitsui Chemicals, Inc.). 5% by solid content (value when the solid content of the overcoat resin film forming composition is 100%: the same applies hereinafter), silica particles having a particle diameter of 10 to 20 nm (“Snowtex 40” manufactured by Nissan Chemical Industries, Ltd.) A composition for forming a non-chromate chemical conversion film was prepared by blending and stirring 30% of the solid content and spherical polyethylene wax (“CHEMIPARL W700” manufactured by Mitsui Chemicals) to a solid content of 5%.

The above composition is applied by bar coating on an electro-Zn-plated steel sheet, dried by heating at a plate temperature of 90 ° C. for 1 minute, and a non-chromate chemical conversion electro-Zn film with an overcoat resin film of 1 g / m ² of deposit is formed. A plated steel sheet was obtained.

(3) Analysis of Ni content in electric Zn plating layer and outermost surface layer An analytical sample prepared by cutting the non-chromate conversion treated electric Zn-plated steel sheet thus obtained into a size of 50 mm × 50 mm was prepared and described above. Based on the method, the amount of Ni in the plating layer and in the outermost surface layer was analyzed. According to the measurement method of this example, the detection limit of the Ni amount in the plating layer is 0.02 ppm, and the detection limit of the Ni amount in the outermost layer is 10 ppm.

  Furthermore, for reference, “Ni content from interface to 1 μm depth” (Ni content in the surface layer) defined in Patent Document 2 was measured by the same method as Ni content in the outermost surface layer. Thereby, it is possible to compare which of the “Ni amount in the outermost surface layer” defined in the present invention and “Ni amount in the surface layer” defined in Patent Document 2 is useful as an index of white rust resistance. it can.

(4) Evaluation of white rust resistance About each electric Zn plating steel plate obtained as mentioned above, the salt spray test prescribed | regulated to JISZ2371 is implemented, and the white rust generation | occurence | production area ratio after 96-hour progress is based on the following reference | standard. Judgment was made and white rust resistance was evaluated. In this example, the evaluation standard “◎” or “◯” was determined to be acceptable (example of the present invention).
A: Less than 5% B: 5% or more and less than 10% B: 10% or more and less than 50% X: 50% or more These results are also shown in Table 1.

  From Table 1, it can be considered as follows.

  No. Nos. 1 to 15 are examples in which plating is performed while controlling the temperature of the plating solution to 40 ° C. or lower and the low temperature range recommended in the present invention, and the amount of metallic Ni in the outermost surface layer is suppressed within the scope of the present invention. In addition, since the amount of Ni in the entire plating layer is controlled within a preferable range, the white rust resistance is excellent. In particular, no. When the temperature of the plating solution was controlled to be lower than about 28 ° C. as in 1 to 10, white rust resistance was further improved.

  In contrast, no. Nos. 16 to 25 are examples in which the temperature of the plating solution is plated at a high temperature of about 50 to 60 ° C., and since the Ni amount of the outermost surface layer exceeds the range of the present invention, all have white rust resistance. It is falling.

  Here, No. 1 in which the plating solution temperature was controlled to be lower. 1-15 and No. 1 in which the plating solution temperature was set high as in the prior art. Comparing 16 to 26, when the Ni concentration in the plating solution is approximately the same, generally, when the temperature of the plating solution is lowered, the Ni amount of the entire plating layer is also lowered, and accordingly, the Ni in the outermost layer is reduced. There was a general tendency to reduce the amount.

  When attention is paid to the “Ni amount up to a depth of 1.0 μm” (Ni amount of the surface layer) defined in Patent Document 2, the Ni amount of the surface layer and the white rust resistance are not necessarily highly correlated. I was not able to admit. The amount of Ni in the surface layer was set to No. As shown in FIG. Even if it was as low as 12 ppm as in 6, they all exhibited good white rust resistance. On the other hand, in the comparative examples, No. Although there was an example in which the amount of Ni in the surface layer was as low as 89 ppm as in No. 18, it was inferior in white rust resistance, and it was found that the amount of Ni in the surface layer was not a good index for evaluating white rust resistance. .

Also, from Table 1, No. It can be read that the inventive examples 1 to 15 are different from the steel sheet of Patent Document 2. That is, when “conversion of ppm is performed by setting the Ni amount within 1 μm from the surface: 50 to 3000 mmg / m ² ” defined in claim 3 of Patent Document 2 described above, the specific gravity of Zn is 7.14 g / cm ³ , The amount of Ni in the surface layer of Patent Document 3 is much higher than that of any steel plate of the present invention example (at the maximum, 424 ppm of No. 11).

  Furthermore, it has been found that the amount of Ni in the entire plating layer is not a useful index for evaluating white rust resistance. That is, No. 1 in Table 1. 16-25, no. 16 to 24 are examples in which the amount of Ni in the plating solution is appropriately controlled and the amount of Ni in the entire plating layer is also controlled to 1000 ppm or less, which is within the preferable range of the present invention. Since it exceeded the scope of the invention, the desired white rust resistance could not be obtained.

  It was also found that even when the Ni concentration in the plating solution was controlled to the same level, the Ni amount in the outermost surface layer and the Ni amount in the entire plating layer varied greatly depending on the temperature of the plating solution. In Table 1, No. 11 (example of the present invention) and No. No. 25 (Comparative Example) is an example in which the amount of Ni in the plating solution is as high as 400 ppm. 11, since the temperature of the plating solution was controlled to be low as specified in the present invention, not only the Ni amount of the entire plating layer but also the Ni amount of the outermost surface layer was kept low within the scope of the present invention, and white rust resistance Is also good. In contrast, no. In No. 25, since the temperature of the plating solution was set to 60 ° C., which was high to the conventional level, both the outermost surface layer and the entire Ni amount of the plating layer were high, and the white rust resistance was lowered. Thus, even if the Ni concentration in the plating solution is controlled to the same level, the rate of substitutional precipitation reaction between Zn and Ni greatly varies depending on the temperature of the plating solution. The amount of Ni changed remarkably, and it was confirmed that the white rust resistance was greatly influenced by this.

  From the above results, in order to ensure good white rust resistance, it is not sufficient to control the Ni content of the entire plating layer and the Ni content of the surface layer within 1 μm from the interface, and 0.04 μm from the interface. It was confirmed that it is extremely important to control the amount of metallic Ni in the outermost surface layer within the range, and for that purpose, it is good to control the temperature of the plating solution to about 40 or less.

Example 2
In this example, the amount of Ni in the outermost surface layer affects white rust resistance in the same manner as in Example 1 except that a non-chromate chemical conversion treated Zn-coated steel sheet provided with a non-chromic film different from that in Example 1 was used. The effect was investigated. Specifically, in this example, an organic non-chromic film (resin film) was prepared based on the method described in Example 1 of Japanese Patent Application Laid-Open No. 2006-43913, and the experiment was performed by changing the temperature of the plating solution. I did it.

(1) Preparation of Resin Aqueous Solution Here, a resin film was prepared from a carboxyl group-containing polyurethane resin aqueous solution, an ethylene-unsaturated carboxylic acid copolymer aqueous dispersion, silica particles, and a resin aqueous solution containing wax. A specific manufacturing method is as follows.

(1-1) Preparation of Carboxyl Group-Containing Polyurethane Resin Aqueous Liquid Polytetramethylene ether glycol manufactured by Hodogaya Chemical Co., Ltd. (Polytetramethylene Ether Glycol) as a polyol component in a 0.8 L internal synthesizer equipped with a stirrer, thermometer and temperature controller 60 g of an average molecular weight of 1000), 14 g of 1,4-cyclohexanedimethanol and 20 g of dimethylolpropionic acid were charged, and 30.0 g of N-methylpyrrolidone was further added as a reaction solvent. 104 g of tolylene diisocyanate (hereinafter sometimes simply referred to as “TDI”) was added as an isocyanate component, and the temperature was raised from 80 to 85 ° C. and reacted for 5 hours. The obtained prepolymer had an NCO content of 8.9%. Further, 16 g of triethylamine was added for neutralization, a mixed aqueous solution of 16 g of ethylenediamine and 480 g of water was added, emulsified at 50 ° C. for 4 hours, and subjected to chain extension reaction to obtain an aqueous polyurethane resin dispersion (nonvolatile resin component 29 0.1%, acid value 41.4).

(1-2) Preparation of Ethylene-Unsaturated Carboxylic Acid Copolymer Aqueous Dispersion Into an autoclave having an internal capacity of 0.8 L equipped with a stirrer, thermometer and temperature controller, 626 parts by mass of water, ethylene- 160 parts by mass of an acrylic acid copolymer (acrylic acid 20% by mass, melt index (MI) 300) is added, and 40% by mol of triethylamine, sodium hydroxide with respect to 1 mol of the carboxyl group of the ethylene-acrylic acid copolymer. Was added at a high speed under an atmosphere of 150 ° C. and 5 Pa, and cooled to 40 ° C. to obtain an aqueous dispersion of an ethylene-acrylic acid copolymer. Subsequently, 4,4′-bis (ethyleneiminocarbonylamino) diphenylmethane (manufactured by Nippon Shokubai, Chemite DZ-22E, “Chemite” is a registered trademark), ethylene-acrylic acid copolymer as a crosslinking agent in the aqueous dispersion. It added so that it might become a ratio of 5 mass parts with respect to 100 mass parts of united non-volatile resin components.

(1-3) Preparation of Resin Aqueous Liquid Carboxyl group-containing polyurethane resin aqueous liquid obtained above, ethylene-acrylic acid copolymer aqueous dispersion, colloidal silica (“ST-XS” manufactured by Nissan Chemical Industries, Ltd., A total of 100 parts by mass in terms of non-volatile components is blended so that the blending ratio of the average particle diameter of 4 to 6 nm is 5 parts by mass: 25 parts by mass: 70 parts by mass. An aqueous resin liquid was prepared by adding 10 parts by mass of γ-glycidoxypropyltrimethoxysilane (“KBM403” manufactured by Shin-Etsu Chemical) as a ring agent.

  The resin film thus obtained contains a resin component, colloidal silica, and a silane coupling agent in a mass ratio, and generally contains resin component: colloidal silica: silane coupling agent = 30 parts: 70 parts: 10 parts. ing.

(2) Production of electro-Zn-plated steel sheet provided with resin film The aqueous resin solution obtained in (1) above was applied on the electro-Zn-plated steel sheet obtained in (1) of Example 1 by a roll drawing method ( Single-side coating), and heat-dried in an experimental furnace at a furnace temperature of 220 ° C. and a plate temperature of 95 ° C. to obtain a non-chromate chemical conversion treated Zn-plated steel sheet having a resin film (non-chromate film) with a thickness of 0.5 μm. It was.

  The white rust resistance and the amount of Ni of the thus obtained non-chromate electric Zn-plated steel sheet were measured in the same manner as in Example 1.

  These results are shown in Table 2.

  No. Nos. 26 to 40 are examples in which plating is performed while controlling the temperature of the plating solution to about 20 to 40 ° C., the temperature specified in the present invention. Since it is suppressed within the scope of the invention and the amount of Ni in the entire plating layer is also controlled within a preferable range, the white rust resistance is excellent.

  In contrast, no. 41-50 is the example which plated the temperature of the plating solution at about 50-60 ° C. and a temperature higher than that of the present invention, and since the Ni amount of the outermost surface layer exceeds the range of the present invention, The white rust resistance is reduced.

  As described above, the same effect as in Example 1 could be confirmed even when the structure of the non-colored film was changed to a resin film instead of the inorganic film shown in Example 1.

Example 3
In this example, the amount of Ni in the outermost surface layer affects white rust resistance in the same manner as in Example 1 except that a non-chromate chemical conversion treated Zn-coated steel sheet provided with a non-chromic film different from that in Example 1 was used. The effect was investigated. Specifically, in this example, a phosphate film was prepared by the method shown below, and the experiment was performed by changing the temperature of the plating solution.

As the phosphate treatment solution, an immersion type zinc phosphate treatment solution “PB-3312” manufactured by Nippon Parkerizing Co., Ltd. was used. The treatment solution had a free acidity (FA) of 2.4 points and a total acidity (TA) of 16.9 points. Here, FA and TA have the following meanings.
(A) When 10 ml of FA: phosphate treatment solution is titrated with bromophenol blue as an indicator and 0.1 N sodium hydroxide solution as a titrant, the color of the treatment solution changes from yellow to blue yellow. The number of mL of titrant required up to this point is taken as the FA point.
(B) TA: When titrated with 10 mL of phosphate treatment solution using phenolphthalein as an indicator and 0.1 N sodium hydroxide solution as a titration solution, the color of the treatment solution turns pink. TA point is the number of mL of titrant required.

Next, using the above-mentioned phosphate treatment solution, phosphate treatment was performed according to the following procedures (1) to (6).
(1) Pickling: immersed in 0.2% sulfuric acid solution for 5 seconds (2) Washing in water: 30 seconds (3) Surface adjustment: immersed at room temperature (4) Chemical conversion treatment: The above phosphoric acid treatment solution at 60 ° C. for 5 seconds Immersion in (5) Washing with water: 15 seconds (6) Drying: Performed at 70 ° C. until the surface was dried.

The electro-zinc plated steel sheet provided with the phosphate film thus obtained was subjected to a salt spray test in the same manner as in Example 1, and the white rust occurrence area ratio after 24 hours was determined according to the following criteria. The white rust resistance was evaluated. In this example, the evaluation standard “◎” or “◯” was determined to be acceptable (example of the present invention).
A: Less than 5% B: 5% or more and less than 10% Δ: 10% or more and less than 50% ×: 50% or more These results are shown in Table 3.

  No. Nos. 51 to 59 are examples in which plating is performed while controlling the temperature of the plating solution to about 20 to 40 ° C., the temperature specified in the present invention. Since it is suppressed within the scope of the invention and the amount of Ni in the entire plating layer is also controlled within a preferable range, the white rust resistance is excellent.

  In contrast, no. 60 to 67 is an example in which the temperature of the plating solution is plated at about 50 to 60 ° C., which is higher than the present invention, and since the Ni amount of the outermost surface layer exceeds the range of the present invention, The white rust resistance is reduced.

  As described above, the same effect as in Example 1 could be confirmed even when the structure of the non-coated film was changed to the phosphate film instead of the inorganic film shown in Example 1.

FIG. 1 is a schematic cross-sectional view showing the entire electro-zinc plated steel sheet of the present invention. FIG. 2 is an enlarged partial cross-sectional view of the interface 4 between the electric Zn plating layer 2 and the non-chromate chemical conversion coating 3 in FIG. 3 shows No. 1 in Table 1 of the example. 10 (invention example) and No. 1 It is a graph which shows distribution (up to 1 micrometer depth) of Ni amount of an electric Zn plating layer about 24 (comparative example). 4 shows No. 1 in Table 1 of the examples. 10 (invention example) and No. 1 It is a graph which shows distribution (up to 0.1 micrometer depth) of Ni amount of an electric Zn plating layer about 24 (comparative example).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Electrical Zn plating layer 3 Non-chromate chemical conversion treatment film 4 Interface between electrical Zn plating layer and non-chromate chemical conversion treatment coating 10 Non-chromate electrical Zn plating steel plate

Claims (2)

A non-chromate conversion treated electro-Zn plated steel sheet having a non-chromate conversion treatment film on the electro-Zn plating layer,
Ni contained in the range of 0.04 μm in the depth direction of the electric Zn plating layer from the interface between the electric Zn plating layer and the non-chromate chemical conversion treatment film is 500 ppm or less in terms of atoms (ppm means mass ppm, hereinafter , The same)), a non-chromate chemical conversion electroplated steel sheet excellent in white rust resistance.   The non-chromate chemical conversion treated electro-zinc plated steel sheet according to claim 1, wherein Ni in the electro-zinc plated layer is suppressed to 1000 ppm or less in terms of atoms.