WO2020255438A1 - Chemical-conversion-treated steel sheet and method for manufacturing same - Google Patents

Abstract

The purpose of the present invention is to provide a chemical-conversion-treated steel sheet having excellent coating adhesion properties. A chemical-conversion-treated steel sheet (1A) includes: a Zn-based-material-plated steel sheet (10) comprising a Zn-based plating layer (12) formed on a surface of a base steel sheet (11); and a chemical-conversion-treated coating film (20A) formed on a surface of the Zn-based plating layer (12). The chemical-conversion-treated coating film (20A) contains an oxo acid salt of a Group-4 metal, an ammonium compound, a phosphoric acid salt of a Group-4 metal and a phosphoric acid salt containing no Group-4 metal, wherein if X represents the atomic ratio of nitrogen and Y represents the atomic ratio of a Group-4 metal in the chemical-conversion-treated coating film (20A), the value of X/(X+Y) is 0.15 to 0.35.

Description

Chemical conversion steel sheet and its manufacturing method

The present invention relates to a chemical conversion-treated steel sheet in which a chemical conversion-treated film is formed on the surface of a Zn-based plated steel sheet, and a method for producing the same.

Zn-based galvanized steel sheets are used in a wide range of applications such as automobiles, building materials, and home appliances. Normally, the surface of a plated steel sheet is subjected to a chrome-free chemical conversion treatment in order to impart corrosion resistance without oiling. Conventionally, titanium-based, zirconium-based, molybdenum-based, and composite systems of these have been developed as chemical conversion treatment liquids depending on the difference in rust preventive. Further, in order to enhance corrosion resistance, a system chemical conversion treatment liquid to which a silane coupling agent, silane, or the like is further added has also been developed (for example, Patent Document 1).

Japanese Patent Publication "Japanese Patent Laid-Open No. 2003-55777"

However, when the chemical conversion-treated film is mainly composed of an oxoacid salt of a Group 4 metal such as Zr as in the technique described in Patent Document 1, the chemical conversion-treated film becomes vitreous with a high barrier property against acids and alkalis. Therefore, when the chemical conversion-treated steel sheet is coated, the phosphate film is not formed because the plating layer is not dissolved in the phosphate treatment, which is a pretreatment for coating. As a result, there is a problem that the adhesion between the coating film and the chemical conversion-treated steel sheet after coating is inferior.

One aspect of the present invention is to realize a chemical conversion-treated steel sheet having excellent coating adhesion and a method for producing the same.

In order to solve the above problems, the chemical conversion-treated steel sheet according to one aspect of the present invention is formed on the surface of the base steel sheet, a Zn-based plated steel sheet having a Zn-based plating layer, and the surface of the Zn-based plating layer. The chemical conversion-treated film comprises a group 4 metal oxolate, an ammonium compound, a group 4 metal phosphate, and a group 4 metal-free phosphate. When the atomic ratio of nitrogen in the chemical conversion coating is X and the atomic ratio of group 4 metal is Y, X / (X + Y) is 0.15 to 0.35.

Further, in the method for producing a chemical conversion-treated steel sheet according to one aspect of the present invention, a Group 4 metal oxoate, an ammonium compound, and a Group 4 metal are used for a Zn-based plated steel sheet having a Zn-based plating layer on the surface of the base steel plate. A coating step of applying a chemical conversion treatment liquid containing phosphoric acid and a phosphoric acid containing no Group 4 metal, and heat-drying the chemical conversion treatment liquid to form a chemical conversion treatment film on the surface of the Zn-based plated steel plate. In the heat-drying step, the heat-drying of the chemical conversion treatment liquid is started immediately after the completion of coating of the chemical conversion treatment liquid in the coating step in a standing time of 35 seconds or less, and the Zn system is used. The temperature conversion time until the temperature of the plated steel sheet reaches 80 ° C. is set to 1 second or more and 10 seconds or less, the maximum reaching temperature of the Zn-based plated steel sheet is set to 70 ° C. or higher and 170 ° C. or lower, and the chemical conversion treatment liquid is heat-dried.

According to one aspect of the present invention, it is possible to provide a chemical conversion-treated steel sheet having excellent coating adhesion and a method for producing the same.

It is sectional drawing which shows typically the chemical conversion treatment steel sheet which concerns on Embodiment 1 of this invention. It is a flowchart which shows typically an example of the manufacturing method of the chemical conversion-treated steel sheet in one Embodiment of this invention. It is sectional drawing which shows typically the chemical conversion treatment steel sheet which concerns on Embodiment 2 of this invention.

[Embodiment 1]
Hereinafter, one embodiment of the present invention will be described in detail. The following description is intended to better understand the gist of the invention, and does not limit the present invention unless otherwise specified. Further, in the present specification, "AB" indicates that it is A or more and B or less.

<Summary explanation of findings of the invention>
First, the outline of the findings found by the present inventors is as follows.

Since the oxyacid salt of the Group 4 metal is easily converted into an inorganic polymer, a chemical conversion treatment film containing a compound of the Group 4 metal is formed by using a chemical conversion treatment solution containing the oxo acid salt of the Group 4 metal. be able to. Therefore, in general, oxoacid salts of Group 4 metals are often used as raw materials for chemical conversion treatment.

However, since the film formed from the oxoacid salt of the Group 4 metal is glassy, it has a high barrier property against acids and alkalis. Therefore, when the chemical conversion-treated steel sheet is coated, the phosphate film is not formed because the plating layer is not dissolved in the phosphate treatment, which is a pretreatment for coating. As a result, the adhesion between the coating film and the steel sheet after coating is inferior. The present inventors have diligently studied to realize a chemical conversion-treated steel sheet having excellent adhesion between the coating film and the steel sheet, and obtained the following new findings.

That is, the present inventors impose an oxoacid salt of a Group 4 metal and an ammonium compound in the chemical conversion treatment film, and (atomic ratio of nitrogen) / {(Group 4 metal) in the chemical conversion treatment film. It was found that by setting (atomic ratio) + (atomic ratio of nitrogen)} in a predetermined range, it is possible to suppress the polymerization of the oxoacid salt of the Group 4 metal in the chemical conversion treatment film. As a result, the chemical conversion coating is dissolved in the alkaline solution, so that the plating layer is easily dissolved in the phosphate treatment, which is a pretreatment for painting, so that the phosphate coating can be easily formed. As a result, it is possible to realize a chemical conversion-treated steel sheet having high adhesion between the coating film and the steel sheet.

Further, the present inventors further include an organic phosphate and an inorganic phosphate in the chemical conversion treatment film, whereby the chemical conversion treatment film is dissolved in the alkaline solution while ensuring the corrosion resistance of the chemical conversion treatment film. I found it easier to do. Since the phosphate existing as a chemical conversion treatment film is easily dissolved in the alkaline solution, the film that inhibits the reaction between the treatment solution and the plating layer disappears during the phosphate treatment, so that the phosphate film is formed. It becomes easy to precipitate. As a result, it is possible to realize a chemical conversion-treated steel sheet having a higher adhesion between the coating film and the steel sheet.

The chemical conversion-treated steel sheet and the manufacturing method thereof according to one aspect of the present invention will be described in detail below.

<Chemical conversion steel sheet>
FIG. 1 is a cross-sectional view schematically showing a chemical conversion-treated steel sheet 1 according to an aspect of the present invention. As shown in FIG. 1, the chemical conversion-treated steel sheet 1 in the present embodiment includes a Zn-based plated steel sheet 10 having a Zn-based plated layer 12 on the surface of the base steel sheet 11 and the surface of the Zn-based plated layer (the Zn-based plating). It has a chemical conversion treatment film 20 formed on the surface of a steel plate).

(Zn-based galvanized steel sheet)
As the original plate to be subjected to the chemical conversion treatment (chemical conversion original plate), a Zn-based plated steel sheet 10 having excellent corrosion resistance and designability is used. The “Zn-based plated steel sheet” in the present embodiment means a plated steel sheet having a Zn-based plated layer 12 on the surface of the base steel sheet 11. The Zn-based plating layer 10 may contain at least one selected from the group consisting of Al, Mg, Si, Ti, and B.

The Zn-based plating layer 12 of the present invention preferably contains 40% by mass or more of Zn in order to improve the adhesion between the Zn-based plating layer 12 and the chemical conversion treatment film 20. This is because the Zn-based plating layer 12 contains 40% by mass or more of Zn, so that the proportion of the Zn-containing phase on the surface of the Zn-based plating layer 12 on which the chemical conversion coating 20 is formed increases, and the Zn-based plating This is because sufficient adhesion can be obtained between the layer 12 and the chemical conversion coating film 20.

The Zn-based plating layer 12 of the Zn-based plated steel sheet 10 in the present embodiment may have an Al content of 0.1% by mass or more and 55.0% by mass or less, and a Mg content of 1.5% by mass or more and 10. It may be 0% by mass or less. Further, the Zn-based plating layer 12 may contain Si in the range of 0.005% by mass or more and 2.0% by mass in order to improve the adhesion between the base steel plate 11 and the Zn-based plating layer 12. .. Further, the Zn-based plated layer 12 contains 0.001% by mass or more and 0.1% by mass of Ti in order to suppress the formation and growth of the Zn ₁₁ Mg _2- phase, which adversely affects the appearance and corrosion resistance of the Zn-based plated steel sheet 10. It is preferable that B is contained in the following range and in the range of 0.0005% by mass or more and 0.045% by mass or less.

The Zn-based plated steel sheet 10 is manufactured by a conventional plating method such as a hot-dip galvanizing method or an electroplating method. The type of the base steel sheet 11 of the Zn-based plated steel sheet 10 is not particularly limited, and for example, ordinary steel, low alloy steel, stainless steel, and the like can be used.

(Chemical conversion coating)
The chemical conversion treatment film 20 is a film for improving the corrosion resistance of the Zn-based plated steel sheet 10. As used herein, the term "corrosion resistance" is used to mean either processed portion corrosion resistance or flat portion corrosion resistance. "Processed portion corrosion resistance" is the corrosion resistance of a portion (processed portion) of the chemical conversion-treated steel sheet 1 that has been subjected to processing (for example, bending) to deform the chemical conversion-treated steel sheet 1, and is particularly such as 180 ° bending. Corrosion resistance of the processed part when severe bending is applied. “Flat portion corrosion resistance” is the corrosion resistance of a portion of the chemical conversion-treated steel sheet 1 other than the processed portion.

The chemical conversion treatment film 20 of the present embodiment has a reaction layer 21 (first chemical conversion treatment layer) located on the surface of the Zn-based plated steel sheet 10 formed by the reaction between the chemical conversion treatment liquid and the surface of the Zn-based plated steel sheet 10. , A second chemical conversion treatment layer 22 mainly composed of a polymer of a group 4 metal oxolatetate formed on the upper layer of the reaction layer 21.

The chemical conversion treatment film 20 of the present embodiment will be described below together with the chemical conversion treatment liquid used for forming the chemical conversion treatment film 20. In the following, for the sake of clarity of the explanation, the chemical conversion treatment film 20 will be described without distinguishing between the reaction layer 21 and the second chemical conversion treatment layer 22, but the following description mainly describes the second chemical conversion treatment. Related to layer 22.

The chemical conversion treatment film 20 in the present embodiment is Zn-based plated with a chemical conversion treatment liquid containing a Group 4 metal oxoacid salt, an ammonium compound, organic phosphorus (organic phosphate), and inorganic phosphorus (inorganic phosphate). It is formed on the surface of the Zn-based plated steel plate 10 by applying it to the steel plate 10 and drying the chemical conversion treatment liquid. The chemical conversion-treated film 20 thus formed contains at least a group 4 metal oxoacidate, an ammonium compound, an organic phosphate, and an inorganic phosphate. By setting the pH of the chemical conversion treatment solution to 7 to 9, the polymerization of the oxoacid salt of the Group 4 metal proceeds suitably.

(Group 4 metal oxoacid salt)
The group 4 metal oxoacid salt is a component for forming a dense chemical conversion-treated film 20, and improves the corrosion resistance of the chemical conversion-treated steel sheet 1. The Group 4 metal is not particularly limited, and Ti, Zr, or Hf can be used. As used herein, oxoacid is used in the sense defined by IUPAC NIC 1990. The group 4 metal oxoacid is a group 4 metal oxoacid having a structure in which a plurality of (typically 4, 5, or 6) oxygen atoms are coordinated around the nucleus, which is a group 4 metal element. A salt consisting of an ion and some cation species.

The Group 4 metal is preferably Zr. That is, the oxo acid salt of the Group 4 metal is preferably Zr oxo acid salt. This is because when Ti is used as the Group 4 metal, the water-soluble compound of Ti is a fluoride salt, and the storage stability tends to decrease. Further, since Hf is expensive, the production cost of the chemical conversion treatment film is high.

The group 4 metal oxoacid salt is, for example, a hydride, an ammonium salt, an alkali metal salt, an alkaline earth metal salt, or the like, and is particularly preferably an ammonium salt of the group 4 metal oxoacid from the viewpoint of corrosion resistance. , Ammonium zirconium carbonate is particularly preferred. In order to form a film of a Group 4 metal oxoacid in the chemical conversion coating film 20, the chemical conversion treatment liquid may contain a Group 4 metal carbonate, a peroxoate, or the like as a Group 4 metal compound. ..

In the chemical conversion treatment liquid of the present embodiment, the concentration of the Group 4 metal is preferably 35 g / L or less. When the concentration of the Group 4 metal in the chemical conversion treatment liquid is higher than 35 g / L, the Group 4 metals are bonded to each other during storage of the chemical conversion treatment liquid, and the chemical conversion treatment liquid gels. Therefore, the chemical conversion treatment film 20 cannot be formed satisfactorily. That is, the chemical conversion treatment liquid of the present embodiment has high long-term storage stability because the concentration of the Group 4 metal is 35 g / L or less. The composition of the chemical conversion treatment liquid and the composition of the chemical conversion treatment film 20 formed by applying the chemical conversion treatment liquid and drying it are substantially the same.

(Ammonium compound)
Ammonium complexes the oxoacid salt of the Group 4 metal in the film forming process of the chemical conversion treatment film 20 and suppresses the polymerization of the oxo acid salt of the Group 4 metal. Therefore, in the present embodiment, the chemical conversion treatment liquid contains ammonia or an ammonium salt. As a result, the chemical conversion treatment film 20 in the present embodiment contains an ammonium compound. In order to prevent the oxoacid salt of the Group 4 metal from being polymerized, it is preferable to include the ammonium salt of the Group 4 metal compound in the chemical conversion treatment liquid.

In the chemical conversion-treated steel sheet 1 of the present embodiment, X / (X + Y) is 0.15 to 0.35 when the atomic ratio of nitrogen in the chemical conversion coating 20 is X and the atomic ratio of group 4 metal is Y. is there. When X / (X + Y) is 0.15 to 0.35, it is possible to suppress the polymerization of the oxoacid salt of the Group 4 metal in the chemical conversion treatment film 20. For this reason, the plating layer is likely to be dissolved in the phosphate treatment, which is a pretreatment for coating, and a phosphate film is easily formed. As a result, the adhesion between the coating film and the chemical conversion-treated steel sheet 1 can be improved.

When X / (X + Y) is smaller than 0.15, the effect of suppressing polymerization by ammonium becomes small. Therefore, the oxoacid salt of the Group 4 metal is polymerized, and the solubility of the chemical conversion treatment film 20 in the alkaline solution is lowered. As a result, the phosphate crystals do not precipitate in the phosphate treatment step. On the other hand, when X / (X + Y) is larger than 0.35, the barrier property of the chemical conversion coating film 20 is lowered, and the corrosion resistance of the flat portion is lowered.

The molar ratio of ammonium to the Group 4 metal in the chemical conversion treatment liquid is preferably 1 or more and 3 or less. When the molar ratio of ammonium to the Group 4 metal is less than 1, detailed control of the drying conditions for adjusting X / (X + Y) in the chemical conversion coating 20 to 0.15 to 0.35 is required. , Productivity is reduced. Further, when the molar ratio of ammonium to the Group 4 metal is larger than 3, the amount of nitrogen exhausted in the film forming process of the chemical conversion coating film 20 increases, which is not preferable in terms of the environment.

(Inorganic phosphate)
Since the inorganic phosphate has high reactivity, the chemical conversion coating 20 contains the inorganic phosphate to strengthen the chemical conversion coating 20 and improve the corrosion resistance of the chemical conversion coating 20. Inorganic phosphates include, for example, alkali metal phosphates (eg, sodium diphosphate, potassium diphosphate, sodium tripolyphosphate), alkaline earth metal phosphates (eg, calcium diphosphate), ammonium phosphate (eg, calcium diphosphate). For example, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, triammonium phosphate, etc.) can be used. In order to include the inorganic phosphate in the chemical conversion treatment film 20, inorganic phosphorus may be added to the chemical conversion treatment liquid. The inorganic phosphorus added to the chemical conversion treatment liquid is not limited as long as it is a water-soluble compound containing phosphorus.

(Organic phosphate)
The organic phosphate promotes the dissolution of the phosphate present as the chemical conversion coating 20 in the alkaline solution. As a result, the film that inhibits the reaction between the phosphate treatment solution and the Zn-based plating layer 12 disappears, so that the phosphate film is likely to precipitate. As the organic phosphate, for example, 1-hydroxyethane-1,1-diphosphonic acid, nitrilotris (methylene-phosphonic acid) and the like can be used. In order to include the organic phosphate in the chemical conversion treatment film 20, organic phosphorus may be added to the chemical conversion treatment liquid. The organic phosphorus added to the chemical conversion treatment liquid is not limited as long as it is a water-soluble compound containing phosphorus.

The chemical conversion-treated steel plate 1 in the present embodiment contains an organic phosphate and an inorganic phosphate in the chemical conversion-treated film, thereby ensuring the corrosion resistance of the chemical conversion-treated film 20 and forming the chemical conversion-treated film 20 in an alkaline solution. The existing phosphate is more easily dissolved (in other words, the paint adhesion is higher).

In the chemical conversion-treated steel plate 1 of the present embodiment, A / (A + B) is 0 when the molar ratio of the organic phosphate in the chemical conversion coating 20 is A and the molar ratio of the inorganic phosphate is B. It is preferably .5 to 0.9.

When A / (A + B) is less than 0.5 (that is, when the ratio of the organic phosphate to the total phosphate in the chemical conversion coating 20 is small), the organic phosphate promotes the dissolution of the phosphate. The effect will be small. On the other hand, when A / (A + B) is larger than 0.9 (that is, when the ratio of the inorganic phosphate to the total phosphate in the chemical conversion coating 20 is small), the corrosion resistance of the chemical conversion coating 20 is lowered. It ends up.

(Other components in the chemical conversion coating)
In the chemical conversion-treated steel plate 1 of one aspect of the present invention, in addition to the oxoacid salt of the Group 4 metal, the oxoacidate of the Group 5 metal and / or the Group 6 metal (excluding Cr) is contained in the chemical conversion-treated film 20. It may be included. By containing the oxoacids of the Group 5 metal and / or the Group 6 metal in the chemical conversion treatment film 20, it is possible to suppress the generation of cracks in the chemical conversion treatment film 20 during processing (in other words, the chemical conversion treatment film 20. Corrosion resistance can be improved). However, if the amount of the oxoate of the group 5 metal and / or the group 6 metal is large, the chemical conversion coating 20 becomes too strong, and the chemical conversion coating 20 is difficult to dissolve in the alkaline degreasing treatment or the phosphate treatment. turn into. Therefore, the oxoacid salt of the Group 5 metal and / or the Group 6 metal contained in the chemical conversion treatment film 20 is preferably 50% by mass or less.

In the chemical conversion-treated steel sheet 1 of one aspect of the present invention, it is preferable that the chemical conversion-treated film 20 further contains a compound containing a Group 1 metal. By containing the Group 1 metal in the chemical conversion treatment film 20, the number of hydroxyl groups in the chemical conversion treatment film 20 increases. As a result, a bond is likely to occur between the chemical conversion coating 20 and the Zn-based plated steel sheet 10. As a result, the adhesion between the chemical conversion coating 20 and the Zn-based plated steel sheet 10 can be improved. Further, when the number of hydroxyl groups in the chemical conversion treatment film 20 increases, it is suppressed that water is removed from the chemical conversion treatment film 20 when the chemical conversion treatment liquid is dried. As a result, it is possible to prevent cracks from being generated in the chemical conversion coating film 20 when the chemical conversion coating film 20 is formed. As a result, the corrosion resistance of the manufactured chemical conversion-treated steel sheet 1 can be improved.

Group 1 metals also have the function of improving the long-term storage stability (treatment liquid stability) of the chemical conversion treatment liquid. This is because the inclusion of the Group 1 metal in the chemical conversion treatment liquid increases the amount of hydroxyl groups in the chemical conversion treatment liquid, so that the binding of the Group 4 metal and phosphorus can be suppressed. That is, by including the Group 1 metal in the chemical conversion treatment liquid, it is possible to suppress the chemical conversion treatment liquid from becoming a gel, that is, to improve the long-term storage property of the chemical conversion treatment liquid.

In order to include the compound of the group 1 metal in the chemical conversion treatment film 20, for example, the phosphoric acid compound of the group 1 metal or the compound of other group 1 metal (for example, hydroxide) is contained in the chemical conversion treatment liquid. Just do it.

Further, the chemical conversion-treated steel sheet 1 of one aspect of the present invention may contain an organic resin as long as the amount does not reduce the adhesion between the coating film and the steel sheet.

When the chemical conversion treatment liquid used in the present embodiment contains a phosphate as a salt containing a specific oxoacid and also contains a group 1 metal, the molar ratio of phosphorus to the group 4 metal is 0.5 to 4, and the group 4 metal. It is preferable that the molar ratio of the Group 1 metal to the metal is 0.02 to 0.8, and the molar ratio of the Group 1 metal to phosphorus is 0.01 or more.

When the molar ratio of phosphorus to the Group 4 metal in the chemical conversion treatment liquid is smaller than 0.5, and when the molar ratio of phosphorus to the Group 4 metal is larger than 4, the chemical conversion coating film 20 has a chloride ion or the like. Since the film is easily permeable to corrosion factors, the corrosion resistance of the chemical conversion-treated steel plate 1 is lowered.

When the molar ratio of the Group 1 metal to the Group 4 metal or phosphorus in the chemical conversion treatment liquid is smaller than the above value, the number of hydroxyl groups derived from the Group 1 metal in the formed chemical conversion treatment film 20 becomes insufficient. Therefore, the number of bonds between the chemical conversion-treated film 20 containing Group 4 metal and phosphorus as main components and the Zn-based plated steel sheet 10 is reduced. As a result, the adhesion between the chemical conversion coating 20 and the Zn-based plated steel sheet 10 becomes insufficient.

When the molar ratio of the Group 1 metal to the Group 4 metal in the chemical conversion treatment liquid is larger than 0.8, the chemical conversion treatment film 20 is easily decomposed by the corrosion factor, so that the corrosion resistance of the chemical conversion treatment steel sheet 1 is lowered. ..

From the viewpoint of long-term storage of the chemical conversion treatment liquid, the molar ratio of the Group 1 metal to the Group 4 metal is 0.5 or more, and the molar ratio of the Group 1 metal to phosphorus is 0.18 or more. Is preferable.

The chemical conversion treatment liquid of the present embodiment has, for example, a group 4 metal concentration of 5 to 35 g / L, a phosphorus concentration of 0.8 to 60 g / L, and a group 1 metal concentration of 0.2 g / L or more. Further, the chemical conversion treatment liquid of the present embodiment may contain an amine, a silane coupling agent, or the like in addition to the above-mentioned substances. The amine dissolves a salt containing vanadium in a chemical conversion treatment solution while maintaining the valence of V at a pentavalent value, and forms a pentavalent or hexavalent Mo composite oxoacidate from the molybdate. The amine is preferably a low boiling point amine having a molecular weight of 80 or less. As the amine, for example, ethanolamine, 1-amino-2-propanol, ethylenediamine and the like can be used.

(Production method)
Hereinafter, a method for producing the chemical conversion-treated steel sheet 1 according to one aspect of the present invention (hereinafter, may be simply referred to as “the present production method”) will be described with reference to FIG.

As shown in FIG. 2, in the present manufacturing method, roughly, first, a Zn-based plated steel sheet 10 as a chemical conversion treatment original plate is prepared (S1: original plate preparation step). Next, a pretreatment for appropriately applying the chemical conversion treatment to the Zn-based plated steel sheet 10 is performed (S2: pretreatment step). In the pretreatment step S2, the pretreatment generally performed in the chemical conversion treatment may be performed, and roughly, a treatment for cleaning the surface of the Zn-based plated steel sheet 10 is performed.

Next, in the stage immediately before the chemical conversion treatment liquid is applied (S3: the step immediately before the treatment liquid is applied), the plate temperature of the Zn-based plated steel sheet 10 after the pretreatment is 60 ° C. or lower, preferably 50 ° C. or lower, more preferably normal temperature. To. This is because if the surface temperature of the Zn-based plated steel sheet 10 immediately before applying the chemical conversion treatment liquid is too high, the drying of the chemical conversion treatment liquid (that is, the reaction in the chemical conversion treatment liquid) is promoted, and the oxoacid of the Group 4 metal is promoted. This is because is polymerized.

Next, a chemical conversion treatment solution containing at least a Group 4 metal oxoacid salt, an ammonium compound, organic phosphorus, and inorganic phosphorus is applied to the surface of the pretreated Zn-based galvanized steel sheet 10 (S4: coating step). In the coating step S4, the liquid temperature of the chemical conversion treatment liquid is set to 55 ° C. or lower. The temperature of the chemical conversion treatment liquid is preferably 50 ° C. or lower, and more preferably normal temperature. This is because if the temperature of the chemical conversion treatment liquid is too high, the drying of the chemical conversion treatment liquid (that is, the reaction in the chemical conversion treatment liquid) is promoted, and the oxoacid salt of the Group 4 metal is polymerized.

In the coating step S4, a method such as a roll coating method, a spin coating method, or a spray method can be used. The amount of the chemical conversion treatment liquid adhering to the surface of the Zn-based plated steel sheet 10 is preferably in the range of 50 to 1000 mg / m ² . If the amount of adhesion is less than 50 mg / m ^2, the thickness of the chemical conversion coating film 20 becomes thin, so that sufficient corrosion resistance cannot be obtained. On the other hand, if the amount of adhesion is more than 1000 mg / m ² , the thickness of the chemical conversion coating film 20 becomes too thick, and the corrosion resistance becomes excessive. Considering the spot weldability, the amount of the chemical conversion treatment liquid adhering to the surface of the Zn-based plated steel sheet 10 is more preferably in the range of 50 to 500 mg / m ² .

Next, the Zn-based plated steel sheet 10 coated with the chemical conversion treatment liquid on the surface is the time from immediately after the completion of coating of the chemical conversion treatment liquid to the start of drying in the coating step (referred to as setting time or standing time in the present specification). , It will be left to stand for a short time (S5: Short-time standing step). The longer the settling time, the more the reaction in the chemical conversion treatment liquid progresses, and the oxoacid salt of the Group 4 metal becomes polymerized. Therefore, the setting time is preferably 35 seconds or less, and more preferably 30 seconds or less. The settling time is preferably 2 seconds or more in order to secure the reaction time between the chemical conversion treatment liquid and the Zn-based plated steel sheet 10.

Next, the Zn-based plated steel sheet 10 coated with the chemical conversion treatment liquid on the surface is heated to dry the chemical conversion treatment liquid (S6: heat drying step). In the heat-drying step S6, the temperature of the Zn-based galvanized steel sheet is raised until the surface temperature reaches 80 ° C. in order to allow the reaction in the chemical conversion treatment liquid to proceed at an appropriate speed so that the desired chemical conversion treatment film 20 can be obtained. The time is 1 second or more and 10 seconds or less, preferably 2 seconds or more and 7 seconds or less.

When the temperature rise time until the surface temperature of the Zn-based plated steel sheet reaches 80 ° C. is less than 1 second, the reaction time between the chemical conversion treatment liquid and the Zn-based plated steel sheet is short, and the corrosion resistance of the chemical conversion-treated steel sheet 1 is lowered. Not preferable. Further, if the temperature rising time until the surface temperature of the Zn-based plated steel sheet reaches 80 ° C. is longer than 10 seconds, the productivity of the chemical conversion-treated steel sheet 1 is lowered, which is not preferable.

Further, in the heat-drying step S6, when the maximum temperature reached by the Zn-based plated steel sheet 10 is high, dehydration of the chemical conversion-treated film 20 proceeds, the chemical conversion-treated film 20 becomes hard, and the corrosion resistance of the processed portion may deteriorate. Therefore, the maximum temperature reached by the Zn-based plated steel sheet 10 is set to 170 ° C. or lower, preferably 160 ° C. or lower. In the heat-drying step S6, heat-drying is performed in an air atmosphere using, for example, an electric furnace. Further, when the maximum temperature reached by the Zn-based plated steel sheet 10 is low, the corrosion resistance of the flat portion is lowered due to the residual nitrogen of the chemical conversion coating film 20. Therefore, the maximum temperature reached by the Zn-based plated steel sheet 10 is set to 70 ° C. or higher.

Next, the chemical conversion-treated steel sheet 1 having the chemical conversion-treated film 20 formed on the surface of the Zn-based plated steel sheet 10 is cooled (S7: cooling step). As a result, the chemical conversion-treated steel sheet 1 of the present embodiment is obtained.

[Embodiment 2]
Other embodiments of the chemical conversion-treated steel sheet of the present invention will be described below. Since the matters other than the matters described in the present embodiment are the same as the matters described in the first embodiment, the description thereof will be omitted.

The present inventors impose a phosphate of a Group 4 metal and a phosphate containing no Group 4 metal in the chemical conversion-treated film, thereby ensuring the corrosion resistance of the chemical conversion-treated film and in an alkaline solution. It was found that the chemical conversion coating film is easily dissolved. Since the phosphate existing as a chemical conversion treatment film is easily dissolved in the alkaline solution, the film that inhibits the reaction between the treatment solution and the plating layer disappears during the phosphate treatment, so that the phosphate film is formed. It becomes easy to precipitate. As a result, it is possible to realize a chemical conversion-treated steel sheet having a higher adhesion between the coating film and the steel sheet.

FIG. 3 is a cross-sectional view schematically showing the chemical conversion-treated steel sheet 1A according to the embodiment of the present invention. As shown in FIG. 1, the chemical conversion-treated steel sheet 1A has a chemical conversion-treated film 20A instead of the chemical conversion-treated film 20 in the first embodiment.

The chemical conversion coating 20A in the present embodiment contains a group 4 metal oxolate, an ammonium compound, a group 4 metal phosphate (group 4 metal phosphate), and a group 4 metal-free phosphate (group 4). A chemical conversion treatment liquid containing a metal-free phosphate) is applied to the Zn-based plated steel plate 10, and the chemical conversion treatment liquid is dried to form the surface of the Zn-based plated steel plate 10. The chemical conversion-treated film 20A thus formed contains at least a group 4 metal oxoacid salt, an ammonium compound, a group 4 metal phosphate, and a group 4 metal-free phosphate.

Group 4 metal phosphate is highly reactive. Therefore, when the chemical conversion coating 20A contains the phosphate of the Group 4 metal, the chemical conversion coating 20A becomes stronger and the corrosion resistance of the chemical conversion coating 20A is improved. Further, the phosphate containing no Group 4 metal promotes the dissolution of the phosphate present as the chemical conversion coating film 20A in the alkaline solution. Therefore, when the chemical conversion coating 20A contains a phosphate that does not contain a Group 4 metal, the coating that inhibits the reaction between the phosphate treatment liquid and the Zn-based plating layer 12 disappears, and the phosphate coating is precipitated. It will be easier. From the above, it is possible to realize a chemical conversion-treated steel sheet having excellent corrosion resistance and coating adhesion by incorporating a group 4 metal phosphate and a group 4 metal-free phosphate in the chemical conversion-treated film 20A. it can.

In the chemical conversion-treated steel plate 1A of the present embodiment, when the molar ratio of the phosphate containing no Group 4 metal in the chemical conversion coating 20A is D and the molar ratio of the phosphate of the Group 4 metal is E. , D / (D + E) is preferably 0.2 to 0.7.

When D / (D + E) is less than 0.2 (that is, when the ratio of Group 4 metal-free phosphate to the total phosphate in the chemical conversion coating 20A is small), Group 4 metal-free phosphorus The effect of the phosphate on promoting the dissolution of phosphate is reduced. On the other hand, when D / (D + E) is larger than 0.7 (that is, when the ratio of the phosphate of the Group 4 metal to the total phosphate in the chemical conversion coating 20A is small), the corrosion resistance of the chemical conversion coating 20A is high. It will drop.

Also in the chemical conversion-treated steel sheet 1A of the present embodiment, X / (X + Y) is 0.15 to 0.35 when the atomic ratio of nitrogen in the chemical conversion coating 20A is X and the atomic ratio of group 4 metal is Y. Is. When X / (X + Y) is 0.15 to 0.35, it is possible to suppress the polymerization of the oxoacid salt of the Group 4 metal in the chemical conversion treatment film 20A. For this reason, the plating layer is likely to be dissolved in the phosphate treatment, which is a pretreatment for coating, and a phosphate film is easily formed. As a result, the adhesion between the coating film and the chemical conversion-treated steel sheet 1A can be improved.

(Summary)
As described above, the chemical conversion-treated steel plate according to one aspect of the present invention is a Zn-based plated steel plate having a Zn-based plating layer on the surface of the base steel plate and a chemical conversion-treated coating film formed on the surface of the Zn-based plating layer. The chemical conversion-treated film contains an organic phosphate, an inorganic phosphate, an oxolate of a Group 4 metal, and an ammonium compound, and (atomic ratio of nitrogen) in the chemical conversion-treated film. / {(Atomic ratio of Group 4 metal) + (Atomic ratio of nitrogen)} is 0.15 to 0.35.

Further, in the method for producing a chemical conversion-treated steel sheet according to one aspect of the present invention, a Group 4 metal oxoate, an ammonium compound, an organic phosphorus, etc. The heating includes a coating step of applying a chemical conversion treatment liquid containing inorganic phosphorus and a heat-drying step of heating and drying the chemical conversion treatment liquid to form a chemical conversion treatment film on the surface of the Zn-based plated steel plate. In the drying step, the heat drying of the chemical conversion treatment liquid is started within 35 seconds immediately after the completion of the coating of the chemical conversion treatment liquid in the coating step, and the temperature of the Zn-based plated steel sheet reaches 80 ° C. The temperature rise time is 1 second or more and 10 seconds or less, the maximum temperature reached of the Zn-based plated steel sheet is 170 ° C. or less, and the chemical conversion treatment liquid is heat-dried.

Further, the chemical conversion-treated steel plate in another aspect of the present invention includes a Zn-based plated steel plate having a Zn-based plating layer on the surface of the base steel plate and a chemical conversion-treated coating formed on the surface of the Zn-based plating layer. The chemical conversion-treated film contains a group 4 metal oxolate, an ammonium compound, a group 4 metal phosphate, and a group 4 metal-free phosphate, and is contained in the chemical conversion-treated film. When the atomic ratio of nitrogen is X and the atomic ratio of group 4 metal is Y, X / (X + Y) is 0.15 to 0.35.

Further, in the method for producing a chemical conversion-treated steel sheet in another aspect of the present invention, a Group 4 metal oxoate, an ammonium compound, and 4 are used for a Zn-based plated steel sheet having a Zn-based plating layer on the surface of the base steel sheet. A coating step of applying a chemical conversion treatment liquid containing a group metal phosphoric acid and a group 4 metal-free phosphoric acid, and a heat-drying of the chemical conversion treatment liquid to form a chemical conversion treatment film on the surface of the Zn-based plated steel plate. In the heat-drying step including the heat-drying step of forming, the heat-drying of the chemical conversion treatment liquid is started immediately after the completion of coating of the chemical conversion treatment liquid in the coating step within a standing time of 35 seconds or less. The temperature conversion time until the temperature of the Zn-based plated steel sheet reaches 80 ° C. is set to 1 second or more and 10 seconds or less, the maximum reaching temperature of the Zn-based plated steel sheet is set to 70 ° C. or higher and 170 ° C. or lower, and the chemical conversion treatment liquid is heat-dried. To do.

[Appendix]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

Hereinafter, examples of the chemical conversion-treated steel sheet according to one aspect of the present invention will be described, but the present invention is not limited to these examples.

In this embodiment, using a steel strip of ultra-low carbon Ti-added steel having a plate thickness of 0.5 mm as a base material, Zn is contained in an amount of 40% by mass or more using a continuous hot-dip galvanizing production line under the conditions shown in Table 1. A Zn-based galvanized steel sheet is produced, and the original plate No. It was set to 1 to 14. Further, using the same steel strip as a base material, a pure galvanized steel strip was produced by an electrogalvanizing method, and the original plate No. It was set to 15. This No. The Zn-based plating layer of the Zn-based plated steel sheet of No. 15 is pure zinc except for unavoidable impurities.

In this example and comparative example, water-soluble zirconium ammonium carbonate as an oxolatet of a Group 4 metal, zirconium ammonium carbonate and diammonium hydrogen phosphate as an ammonium compound, and diammonium hydrogen phosphate as an inorganic phosphoric acid And 1-hydroxyethane-1,1-diphosphonic acid as organic phosphoric acid are appropriately adjusted and dissolved in water to prepare a chemical conversion solution having a Zr concentration of 10 g / L and a phosphorus concentration of 1.7 g / L. Was prepared, and No. The chemical conversion treatment liquid was applied to the original plates 1 to 15 and dried to prepare a chemical conversion treatment steel sheet. In addition, No. The chemical conversion-treated steel sheet of No. 19 used ammonium titanium fluoride as the oxoacid salt of the Group 4 metal.

Table 2 is a table showing various manufacturing conditions used for manufacturing the chemical conversion-treated steel sheets of Examples and Comparative Examples of the present invention. In addition, No. 12 and No. Under the production conditions of 21, heating was performed under drying conditions that required 5 seconds and 3 seconds, respectively, until the plate temperature reached 80 ° C., and heating was stopped when the plate temperatures reached 70 ° C. and 50 ° C., respectively.

Table 3 is a table showing the composition and physical properties of the chemical conversion coating film in the chemical conversion-treated steel sheets of Examples and Comparative Examples of the present invention, and the test results of the corrosion resistance of the chemical conversion-treated steel sheet.

In the examples and comparative examples shown in Table 3, the plating No. of Table 1 was used as the original plate of the chemical conversion-treated steel sheet. Using the Zn-based plated steel sheet shown in No. 1, the chemical conversion-treated steel sheet No. 1 to 28 were prepared. First, the surface of the original plate of the chemical conversion-treated steel sheet was degreased and dried. Next, the above chemical conversion treatment liquid was applied to the surface of the original plate, and immediately after that, the temperature of the original plate was raised to a predetermined temperature using an automatic discharge type electric hot air oven and dried by heating. As a result, a chemical conversion-treated film is formed on the surface of the original plate, and the chemical conversion-treated steel sheet No. 1 to 28 were prepared. In the above series of steps, various conditions were set based on the method for producing a chemical conversion-treated steel sheet according to one aspect of the present invention described in the above-described embodiment. The specific temperature of the chemical conversion treatment liquid, the temperature of the steel sheet at the time of coating, the setting time (time from application to the start of drying), and the drying conditions are as shown in Table 2.

(Identification of metal in chemical conversion coating)
For the produced chemical conversion-treated steel sheet, a metal element present in the chemical conversion-treated film was identified by a glow discharge emission spectrophotometer (GDS) (SPECTRUMA ANALYTIK GmbH; GDA750).

(Composition of chemical conversion coating)
The prepared chemical conversion-treated steel sheet was analyzed with an X-ray source MgKα using a photoelectron spectroscopic analyzer (Shimadzu Seisakusho Co., Ltd./KRATOS Co., Ltd .; ESCA-3400). Specifically, XPS spectra due to the binding energies of Group 4 metals (eg, Zr), phosphorus, and nitrogen were measured. Then, from the measured XPS spectrum, the phosphorus compound and the salt of the group 4 metal contained in the chemical conversion treatment film were identified. In addition, the molar ratio of organic phosphate, the molar ratio of inorganic phosphate, the atomic ratio of Group 4 metal, and the atomic ratio of nitrogen were calculated from the measured peak area due to the bond energy of each element of XPS. .. Then, the above-mentioned A / (A + B) and X / (X + Y) were calculated from the calculated molar ratio and atomic ratio.

(Evaluation of corrosion resistance)
The prepared chemical conversion-treated steel sheet was subjected to a corrosion resistance test as follows. First, a chemical conversion-treated steel sheet was cut into a size of 70 mm × 150 mm and used as a test piece. Next, the end face of the test piece was sealed, and a salt spray test was carried out for 120 hours in accordance with JIS Z2371, and white rust generated on the surface of the test piece was observed. Table 3 shows the results of the corrosion resistance test. In this corrosion resistance test, when the area ratio of white rust is 5% or less, it is "◎", when it is larger than 5% and 10% or less, it is "○", and when it is larger than 10% and 30% or less, it is "△". , The case where it is larger than 30% was regarded as "x", the corrosion resistance was evaluated, and the case where "Δ" or more was passed.

(Evaluation of phosphate treatment)
The prepared chemical conversion-treated steel sheet was subjected to a phosphate treatment test as follows. First, an alkaline degreasing agent (Surf Cleaner 53NF, manufactured by Nippon Paint) was dissolved in water at 20 g / L to prepare a degreasing solution, and the prepared chemical conversion-treated steel sheet was immersed in the degreasing solution for 4 minutes. Next, the test piece immersed in the degreasing solution was brushed with Palbond L15C (250 g / L of A agent + 250 g / L of B agent, 25 ° C.), a chemical chemical agent for phosphate treatment manufactured by Nihon Parkerizing Co., Ltd. Then it was left for 5 minutes.

Next, the surface condition of the brushed part was observed, the gray discoloration area ratio of the brushed part was determined, and evaluated according to the following criteria. Gray discoloration area ratio of 95% or more is "◎", 90% or more and less than 95% is "○", 85% or more and less than 90% is "△", 70% or more and less than 85% is "black paint △", 70% Phosphate treatment was evaluated with less than "x" as "x", and "black-painted Δ" or more was regarded as acceptable. The higher the gray discoloration area ratio, the more a phosphate film is formed and the gray color tone is exhibited.

(Evaluation of paint adhesion)
The prepared chemical conversion-treated steel sheet was subjected to a phosphorus coating adhesion test as follows. First, a melamine alkyd resin paint is applied on the film of the test piece subjected to the above phosphate treatment using a bar coater so that the dry film thickness is 25 μm, and baked at a furnace temperature of 130 ° C. for 20 minutes. , Manufactured a coating film. Next, the test piece on which the coating film was formed was left in water at 95 ° C. for 2 hours. Then, a notch of 100 squares having a width of 1 mm was made on the coating film using a cutter, a tape peeling test was carried out, and the coating adhesion was evaluated according to the following criteria. No peeling of the coating film is "◎", the number of peeled pieces is 1 or more and less than 6 is "○", the number of peeled pieces is 6 or more and less than 10 is "△", and the number of peeled pieces is 11 or more and less than 20 is "black coating △". , 20 or more peeled pieces were regarded as "x", and "black-painted Δ" or more were regarded as acceptable.

As shown in Table 3, the chemical conversion coating contains Group 4 metal oxoacids, ammonium compounds, organic phosphates, and inorganic phosphates, and X / (X + Y) is 0.15 to 0. The chemical conversion-treated steel sheet of No. 35 was excellent in corrosion resistance, phosphate treatment property, and coating adhesion.

On the other hand, No. Since diammonium hydrogen phosphate was not used in the chemical conversion-treated steel sheet of 20, no inorganic phosphate was formed on the chemical conversion-treated film. Therefore, the phosphate treatment property and the coating adhesion were low.

Also, No. Since 1-hydroxyethane-1,1-diphosphonic acid was not used in the chemical conversion-treated steel sheet of No. 21, no organic phosphate was formed in the chemical conversion-treated film. Therefore, the phosphate treatment property and the coating adhesion were low.

Also, No. 23 and No. In the chemical conversion-treated steel sheet No. 24, since the Group 4 metal was not added to the chemical conversion treatment liquid, the chemical conversion-treated film did not become dense and the corrosion resistance was low.

In addition, the temperature reached by the chemical conversion-treated steel sheet during drying was 180 ° C. In the chemical conversion-treated steel sheet of 24, the atomic ratio of nitrogen contained in the chemical conversion-treated film was small. Therefore, the phosphate treatment property and the coating adhesion were low.

Also, No. In the chemical conversion-treated steel sheet of 25, the temperature reached by the steel sheet in the drying step was low, so that the atomic ratio of nitrogen contained in the chemical conversion-treated film was large. Therefore, the corrosion resistance, the phosphate treatment property, and the coating adhesion were low. In addition, No. 26-No. The chemical conversion-treated steel sheet of No. 28 had low phosphate treatment property and coating adhesion.

Also, the plating No. in Table 1 Using Zn-based plated steel sheets prepared using 1 to 14, zirconium sulfate or zirconium nitrate is used as the group 4 metal compound used in the chemical conversion treatment liquid, ammonium molybdate is used as the oxo acid salt of the group 5 metal, and oxo of the group 6 metal is used. Chemically treated steel plate No. 1 in the same manner as above, except that vanadium pentoxide was used as the acid salt and sodium sulfate, potassium nitrate, or sodium pyrophosphate was used as the group 1 metal-containing compound. 31 to 51 were prepared. Table 4 shows No. It is a table concerning the film composition, the physical property and the corrosion resistance of the chemical conversion treatment steel sheet of 31-51.

As shown in Table 4, the conversion of the type of the original plate of the chemical conversion-treated steel plate, and the chemical conversion-treated coating regardless of the presence or absence of the oxoacid of Group 5 metal, the oxoacid of Group 6 metal, and the Group 1 metal compound. A chemical conversion-treated steel sheet containing a Group 4 metal oxoacid, an ammonium compound, an organic phosphate, and an inorganic phosphate and having an X / (X + Y) of 0.15 to 0.35 has corrosion resistance. It was excellent in phosphate treatment and coating adhesion.

In this example, No. 1 used in Example 1. The original plates of 1 to 15 were used. Further, in this example, water-soluble zirconium ammonium carbonate as an oxo acid salt of a Group 4 metal, zirconium ammonium carbonate and diammonium hydrogen phosphate as an ammonium compound, and zirconium phosphate as a phosphate of a Group 4 metal. And diammonium hydrogenphosphate as a phosphoric acid containing no Group 4 metal were appropriately adjusted and dissolved in water to prepare a chemical conversion treatment solution having a Zr concentration of 10 g / L and a phosphorus concentration of 1.7 g / L. Prepared. The chemical conversion treatment solution prepared in this manner was designated as No. A chemical conversion-treated steel sheet was prepared by applying it to the original plates 1 to 15 and drying it. In addition, No. The chemical conversion-treated steel sheet of 79 used ammonium titanium fluoride as the oxoacid salt of the Group 4 metal.

Table 5 is a table showing various manufacturing conditions used for manufacturing the chemical conversion-treated steel sheets of Examples and Comparative Examples of the present invention. In addition, No. 42 and No. Under the production conditions of 50, heating was performed under drying conditions that required 5 seconds and 3 seconds, respectively, until the plate temperature reached 80 ° C., and heating was stopped when the plate temperature reached 70 ° C. and 50 ° C., respectively.

Table 6 is a table showing the composition and physical properties of the chemical conversion coating film in the chemical conversion-treated steel sheets of Examples and Comparative Examples of the present invention, and the test results of the corrosion resistance of the chemical conversion-treated steel sheet.

In the examples and comparative examples shown in Table 3, the plating No. of Table 1 was used as the original plate of the chemical conversion-treated steel sheet. Using the Zn-based plated steel sheet shown in No. 1, the chemical conversion-treated steel sheet No. 61 to 91 were prepared. First, the surface of the original plate of the chemical conversion-treated steel sheet was degreased and dried. Next, the above chemical conversion treatment liquid was applied to the surface of the original plate, and immediately after that, the temperature of the original plate was raised to a predetermined temperature using an automatic discharge type electric hot air oven and dried by heating. As a result, a chemical conversion-treated film is formed on the surface of the original plate, and the chemical conversion-treated steel sheet No. 61 to 91 were prepared. In the above series of steps, various conditions were set based on the method for producing a chemical conversion-treated steel sheet according to one aspect of the present invention described in the above-described embodiment. The specific temperature of the chemical conversion treatment liquid, the temperature of the steel sheet at the time of coating, the setting time (time from application to the start of drying), and the drying conditions are as shown in Table 5.

(Identification of metal in chemical conversion coating)
For the produced chemical conversion-treated steel sheet, a metal element present in the chemical conversion-treated film was identified by a glow discharge emission spectrophotometer (GDS) (SPECTRUMA ANALYTIK GmbH; GDA750).

(Composition of chemical conversion coating)
The prepared chemical conversion-treated steel sheet was analyzed with an X-ray source MgKα using a photoelectron spectroscopic analyzer (Shimadzu Seisakusho Co., Ltd./KRATOS Co., Ltd .; ESCA-3400). Specifically, XPS spectra due to the binding energies of Group 4 metals (eg, Zr), phosphorus, and nitrogen were measured. Then, from the measured XPS spectrum, the phosphorus compound and the salt of the group 4 metal contained in the chemical conversion treatment film were identified. In addition, from the measured peak area due to the binding energy of each element of XPS, the molar ratio of phosphate of Group 4 metal, the molar ratio of phosphate not containing Group 4 metal, and the atomic ratio of Group 4 metal, and , The atomic ratio of nitrogen was calculated. Then, the above D / (D + E) and X / (X + Y) were calculated from the calculated molar ratio and atomic ratio.

(Evaluation of corrosion resistance)
The prepared chemical conversion-treated steel sheet was subjected to a corrosion resistance test as follows. First, a chemical conversion-treated steel sheet was cut into a size of 70 mm × 150 mm and used as a test piece. Next, the end face of the test piece was sealed, and a salt spray test was carried out for 120 hours in accordance with JIS Z2371, and white rust generated on the surface of the test piece was observed. Table 3 shows the results of the corrosion resistance test. In this corrosion resistance test, when the area ratio of white rust is 5% or less, it is "◎", when it is larger than 5% and 10% or less, it is "○", and when it is larger than 10% and 30% or less, it is "△". , The case where it is larger than 30% was regarded as "x", the corrosion resistance was evaluated, and the case where "Δ" or more was passed.

(Evaluation of phosphate treatment)
The prepared chemical conversion-treated steel sheet was subjected to a phosphate treatment test as follows. First, an alkaline degreasing agent (Surf Cleaner 53NF, manufactured by Nippon Paint) was dissolved in water at 20 g / L to prepare a degreasing solution, and the chemical conversion-treated steel sheet prepared in the degreasing solution was immersed in the degreasing solution at 50 ° C. for 4 minutes. Next, the test piece immersed in the degreasing solution was brushed with Palbond L15C (250 g / L of A agent + 250 g / L of B agent, 25 ° C.), a chemical chemical agent for phosphate treatment manufactured by Nihon Parkerizing Co., Ltd. Then it was left for 5 minutes.

Next, the surface condition of the brushed part was observed, the gray discoloration area ratio of the brushed part was determined, and evaluated according to the following criteria. Gray discoloration area ratio of 95% or more is "◎", 90% or more and less than 95% is "○", 85% or more and less than 90% is "△", 70% or more and less than 85% is "black paint △", 70% Phosphate treatment was evaluated with less than "x" as "x", and "black-painted Δ" or more was regarded as acceptable. The higher the gray discoloration area ratio, the more a phosphate film is formed and the gray color tone is exhibited.

(Evaluation of paint adhesion)
The prepared chemical conversion-treated steel sheet was subjected to a phosphorus coating adhesion test as follows. First, a melamine alkyd resin paint is applied on the film of the test piece subjected to the above phosphate treatment using a bar coater so that the dry film thickness is 25 μm, and baked at a furnace temperature of 130 ° C. for 20 minutes. , Manufactured a coating film. Next, the test piece on which the coating film was formed was left in water at 95 ° C. for 2 hours. Then, a notch of 100 squares having a width of 1 mm was made on the coating film using a cutter, a tape peeling test was carried out, and the coating adhesion was evaluated according to the following criteria. "◎" for no peeling of the coating film, "○" for 1 or more and less than 6 peeling, "△" for 6 or more and less than 10 peeling, "black coating △" for 11 or more and less than 20 peeling , 20 or more peeled pieces were regarded as "x", and "black-painted Δ" or more were regarded as acceptable.

As shown in Table 6, the chemical conversion coating contains a Group 4 metal oxoacid salt, an ammonium compound, a Group 4 metal phosphate, and a Group 4 metal-free phosphate, and is X / (X + Y. ) Is 0.15 to 0.35. The chemical conversion-treated steel sheets 61 to 79 were excellent in corrosion resistance, phosphate treatment property, and coating adhesion.

On the other hand, No. In the chemical conversion-treated steel sheets of 80, 86 and 87, since none of the phosphoric acids was contained in the chemical conversion treatment liquid, phosphate was not formed in the chemical conversion treatment film. Therefore, the phosphate treatment property and the coating adhesion were low.

No. In the chemical conversion-treated steel sheets of 81 and 83, since the chemical conversion treatment liquid did not contain phosphoric acid containing no Group 4 metal, the phosphate treatment property and the coating adhesion were low. No. In the chemical conversion-treated steel sheet of No. 82, since the chemical conversion treatment liquid did not contain phosphoric acid of the Group 4 metal, the chemical conversion-treated film did not become dense and the corrosion resistance was low.

No. In the chemical conversion-treated steel sheets of 84 and 91, the ultimate temperature of the steel sheet in the drying step was high, so that the atomic ratio of nitrogen contained in the chemical conversion-treated film was small. Therefore, the phosphate treatment property and the coating adhesion were low.

No. In the chemical conversion-treated steel sheet of 85, the temperature reached by the steel sheet in the drying step was low, so that the atomic ratio of nitrogen contained in the chemical conversion-treated film was large. Therefore, the barrier property of the chemical conversion treatment film was lowered, and the corrosion resistance was low.

No. In the chemical conversion-treated steel sheet of 88, since the chemical conversion treatment liquid did not contain the Group 4 metal, the corrosion resistance, the phosphate treatment property and the coating adhesion were low. No. In the chemical conversion-treated steel sheet of 89, the settling time was as long as 40 seconds, so that the oxoacid salt of the Group 4 metal was polymerized, and the phosphate treatment property and the coating adhesion were low.

No. In the 90 chemical conversion-treated steel sheet, the time required for the plate temperature to reach 80 ° C. in the drying step was as long as 13 seconds, so that the oxoacid salt of the Group 4 metal was polymerized, resulting in phosphate treatment and coating adhesion. Was low.

Also, the plating No. in Table 1 Using Zn-based plated steel sheets prepared using 1 to 14, zirconium sulfate or zirconium nitrate is used as the group 4 metal compound used in the chemical conversion treatment liquid, ammonium molybdate is used as the oxo acid salt of the group 5 metal, and oxo of the group 6 metal. No. 1 as described above, except that vanadium pentoxide was used as the acid salt and sodium sulfate, potassium nitrate, or sodium pyrophosphate was used as the group 1 metal-containing compound. Chemical conversion-treated steel sheets of 101 to 118 were produced. In addition, No. Using 15 original plates, No. 119 chemical conversion-treated steel sheets were prepared. Table 7 shows No. It is a table concerning the film composition, the physical property and the corrosion resistance of the chemical conversion treatment steel sheet of 71-89.

As shown in Table 7, the conversion of the type of the original plate of the chemical conversion-treated steel plate, and the chemical conversion-treated film regardless of the presence or absence of the oxoacid of the Group 5 metal, the oxoacid of the Group 6 metal, and the Group 1 metal compound Contains a Group 4 metal oxoacid, an ammonium compound, a Group 4 metal phosphate, and a Group 4 metal-free phosphate, with an X / (X + Y) of 0.15 to 0.35. Some chemical conversion-treated steel sheets were excellent in corrosion resistance, phosphate treatment, and coating adhesion.

1A Chemical conversion treated steel sheet 10 Zn-based plated steel sheet 11 Base steel sheet 12 Zn-based plated layer 20A Chemical conversion-treated film

Claims (7)

1. On the surface of the base steel plate,
   A Zn-based plated steel sheet having a Zn-based plating layer and
   It has a chemical conversion treatment film formed on the surface of the Zn-based plating layer.
   The chemical conversion coating contains a Group 4 metal oxoacid salt, an ammonium compound, a Group 4 metal phosphate, and a Group 4 metal-free phosphate.
   The chemical conversion-treated steel sheet is characterized in that X / (X + Y) is 0.15 to 0.35 when the atomic ratio of nitrogen in the chemical conversion-treated film is X and the atomic ratio of group 4 metal is Y. ..
2. The chemical conversion-treated steel sheet according to claim 1, wherein the group 4 metal oxo acid salt is a Zr oxo acid salt.
3. The chemical conversion coating according to claim 1 or 2, further comprising at least one compound selected from a group 5 metal oxoacid salt and a group 6 metal oxoacid salt excluding Cr. Chemical conversion treated steel plate.
4. The chemical conversion-treated steel sheet according to any one of claims 1 to 3, wherein the chemical conversion-treated film further contains a compound containing a Group 1 metal.
5. The chemical conversion-treated steel sheet according to any one of claims 1 to 4, wherein the Zn-based plating layer contains 40% by mass or more of Zn.
6. A Zn-based plated steel plate having a Zn-based plating layer on the surface of the base steel plate contains a Group 4 metal oxoate, an ammonium compound, a Group 4 metal phosphoric acid, and a Group 4 metal-free phosphoric acid. The coating step of applying the chemical conversion treatment liquid and
   A heat-drying step of heating and drying the chemical conversion treatment liquid to form a chemical conversion treatment film on the surface of the Zn-based plated steel sheet is included.
   In the heating and drying step,
   Immediately after the completion of coating of the chemical conversion treatment liquid in the coating step, heat drying of the chemical conversion treatment liquid was started within a standing time of 35 seconds or less.
   The temperature rise time until the temperature of the Zn-based plated steel sheet reaches 80 ° C. is set to 1 second or more and 10 seconds or less.
   A method for producing a chemical conversion-treated steel sheet, which comprises heating and drying the chemical conversion treatment liquid with the maximum temperature reached of the Zn-based plated steel sheet being 70 ° C. or higher and 170 ° C. or lower.
7. The method for producing a chemical conversion-treated steel sheet according to claim 6, wherein the Zn-based plating layer contains 40% by mass or more of Zn.

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