Manufacturing method of zinc phosphate treated steel sheet

Abstract

To provide a method for manufacturing a zinc phosphate treated steel sheet that can properly suppress unevenness of chemical conversion at the time of zinc phosphate film formation on a zinc phosphate treated steel sheet using a galvanized steel sheet having a sheet thickness of 0.3 mm or more and 3.3 mm or less as the base material.SOLUTION: A method for manufacturing a zinc phosphate treated steel sheet includes: a surface control treatment step (step S1); a film thickness uniform treatment step (step S2) of pressing a ringer roll 21 to a surface of a galvanized steel sheet SM that has been subjected to the surface control treatment to make a film thickness of surface control liquid uniform; and a zinc phosphate treatment step (step S4). In the film thickness uniform treatment step, when a sheet thickness of a galvanized steel sheet SM represents t[mm], a pressing pressure P [kgf / cm2] of the ringer roll 21 to the galvanized steel sheet SM is controlled within a range of the following formula: 0.27t3-0.90t2+1.60t+2.60≤P≤0.27t3-0.90t2+1.60t+3.60.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a zinc phosphate-treated steel sheet for use in automobiles, home appliances, building materials, etc. [Background technology]

[0002] Steel sheets with a zinc phosphate coating (hereinafter referred to as zinc phosphate-treated steel sheets) are primarily used for automobile bodies because they have low sliding resistance during press forming and allow the steel sheets to easily flow into press dies. A zinc phosphate-treated steel sheet is produced, for example, by plating a cold-rolled steel sheet with zinc, spraying a surface conditioner onto the surface of the steel sheet, and scattering a substance that will become the nuclei of zinc phosphate crystals onto the surface of the steel sheet, followed by zinc phosphate treatment to form a zinc phosphate coating. Examples of zinc phosphate treatment methods include a spray method and a coater method.

[0003] However, there is a problem of chemical conversion unevenness (uneven drawing) occurring on the steel sheet surface. In particular, since zinc phosphate treatment methods for steel sheet, such as spraying and coating, form a reactive chemical conversion coating (zinc phosphate coating), chemical conversion unevenness is likely to occur on the steel sheet surface. To solve this problem, a method for manufacturing a zinc phosphate-treated steel sheet has been proposed in the past, for example, as shown in Patent Document 1.

[0004] The method for producing a zinc phosphate-treated steel sheet shown in Patent Document 1 involves applying a surface conditioning liquid to the surface of a zinc-plated steel sheet to perform a surface conditioning treatment, then spraying gas onto the steel sheet surface at a spray pressure of 0.20 MPa or more, and then applying a zinc phosphate-based treatment liquid to the steel sheet surface to form a zinc phosphate coating.

[0005] According to the method for producing a zinc phosphate-treated steel sheet shown in Patent Document 1, a gas is blown onto the surface of the steel sheet immediately after the surface conditioning treatment, thereby uniformly leveling (smoothing) the surface of the steel sheet with the surface conditioning liquid, thereby suppressing unevenness in the subsequent formation of a zinc phosphate coating. As a result, a zinc phosphate-treated steel sheet with excellent surface quality can be produced. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-16835 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the conventional manufacturing method of zinc phosphate-treated steel sheet shown in Patent Document 1, for steel sheets having a thickness of 0.3 mm to 3.3 mm, scattering of the surface conditioning liquid causes unevenness in the chemical conversion during the formation of the zinc phosphate coating, and the method was not sufficient as a measure to suppress such unevenness. In particular, for thick steel sheets having a thickness of 2.3 mm or more, unevenness in the chemical conversion during the formation of the zinc phosphate coating became apparent.

[0008] Therefore, the present invention has been made to solve the conventional problems, and an object of the present invention is to provide a method for manufacturing a zinc phosphate-treated steel sheet that can appropriately suppress chemical conversion unevenness during zinc phosphate coating formation and produce a zinc phosphate-treated steel sheet with excellent surface appearance quality, for a zinc phosphate-treated steel sheet having a substrate of a zinc-based plated steel sheet having a sheet thickness of 0.3 mm or more and 3.3 mm or less. [Means for solving the problem]

[0009] The present inventors have focused on the surface condition of steel sheets immediately after surface conditioning and investigated the causes of and countermeasures for chemical conversion unevenness. As a result, they have found that in zinc phosphate treatment methods for steel sheets, such as spraying and coating, slight variations in the film thickness of the surface conditioning solution occur mainly due to wavy shapes formed on the steel sheet during the rolling process, which causes chemical conversion unevenness due to poor drawing during zinc phosphate coating formation. They have also found that the effects of such wavy shapes formed on the steel sheet are evident in steel sheets with a thickness of 0.3 mm to 3.3 mm, particularly in thick steel sheets with a thickness of 2.3 mm or more.

[0010] Therefore, the inventors attempted to eliminate the unevenness of the chemical conversion by pressing the steel sheet with a wringer roll after the surface conditioning treatment and before the zinc phosphate treatment to make the film thickness of the surface conditioning solution uniform. Initially, the pressing pressure of the wringer roll was set to 2.0 kgf / cm. 2 About 3.0kgf / cm 2 This was based on the idea of ​​making the film thickness of the surface conditioner liquid uniform, and was sufficient when making the film thickness of the surface conditioner liquid uniform on a flat steel plate, but if the pressing pressure of the wringer roll was higher than this, the effect of making the film thickness uniform was saturated, and it simply resulted in an unnecessary increase in power due to the increased load.

[0011] However, the unevenness of the chemical conversion occurs when the pressing pressure of the wringer roll is 2.0 kgf / cm 2 About 3.0kgf / cm 2 When the thickness is less than 1 / 2 mm, this occurs chronically. As a result of extensive investigation by the present inventors, it was found that the shape of the steel sheet is not completely flat, and that non-flat portions are prone to cause non-uniform chemical conversion, and that the optimum pressing pressure of the wringer roll to suppress non-uniform chemical conversion is determined by the thickness of the steel sheet.

[0012] Therefore, in order to solve the above-mentioned problems, a manufacturing method of a zinc phosphate-treated steel sheet according to one aspect of the present invention is a manufacturing method of a zinc phosphate-treated steel sheet using a zinc-based plated steel sheet having a thickness of 0.3 mm or more and 3.3 mm or less as a substrate, and includes: a surface conditioning treatment step of applying a surface conditioning liquid onto the surface of the zinc-based plated steel sheet to perform a surface conditioning treatment; a film thickness uniforming treatment step of, after the surface conditioning treatment step, pressing a wringer roll against the surface of the zinc-based plated steel sheet that has been subjected to the surface conditioning treatment to uniformize the film thickness of the surface conditioning liquid; and a zinc phosphate treatment step of, after the film thickness uniforming treatment step, applying a zinc phosphate-based treatment liquid to the surface of the zinc-based plated steel sheet that has been subjected to the film thickness uniforming treatment with the surface conditioning liquid to form a zinc phosphate coating, wherein in the film thickness uniforming treatment step, the pressing pressure of the wringer roll against the zinc-based plated steel sheet is set to P [kgf / cm 2] and the thickness of the zinc-based plated steel sheet is t [mm], the gist is to control it within the range of the following formula.

[0013] 0.27t 3 -0.90t 2 +1.60t+2.60≦P≦0.27t 3 -0.90t 2 +1.60t+3.60 [Effects of the Invention]

[0014] According to the manufacturing method of the zinc phosphate-treated steel sheet of the present invention, it is possible to appropriately suppress chemical conversion unevenness during the formation of a zinc phosphate coating on steel sheets having a thickness of 0.3 mm to 3.3 mm, and to produce zinc phosphate-treated steel sheets with excellent surface appearance quality. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic configuration diagram of a chemical conversion treatment facility to which a method for producing a zinc phosphate-treated steel sheet according to an embodiment of the present invention is applied. [Figure 2] 2 is a flowchart for explaining the flow of treatment in the chemical conversion treatment facility shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components. In addition, the drawings are schematic, and therefore it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship, and the drawings may also contain parts where the relationship and ratio of dimensions differ from each other.

[0017] FIG. 1 shows a schematic configuration of a chemical conversion treatment facility to which a method for producing a zinc phosphate-treated steel sheet according to one embodiment of the present invention is applied. The chemical conversion treatment equipment 1 shown in FIG. 1 is installed in an electrogalvanizing line, and produces a zinc-based plated steel sheet S in which a steel sheet S that has been cold-rolled and then annealed is plated with zinc in an electroplating equipment 50. M A chemical conversion coating (zinc phosphate coating) is formed on the surface of the steel sheet, resulting in the production of zinc phosphate-treated steel sheet.

[0018] Here, the zinc-based coated steel sheet S as the base steel sheet to be subjected to chemical conversion treatment is M Examples of such steel sheets include electrogalvanized steel sheets and electrogalvanized zinc-nickel alloy plated steel sheets. M may be a hot-dip galvanized steel sheet that has been hot-dip coated without going through the electroplating equipment 50. Furthermore, the steel sheet is a cold-rolled steel sheet, but may also be a hot-rolled steel sheet.

[0019] In addition, zinc-based coated steel sheet S M The thickness of the steel sheet S (thickness of the steel sheet S) is 0.3 mm or more. If the thickness is less than 0.3 mm, the sheet shape is unlikely to become wavy, and uneven chemical conversion during the formation of the zinc phosphate coating targeted by the present invention is unlikely to occur. On the other hand, if the thickness is 0.3 mm or more, a wavy sheet shape defect occurs, and in the case of the spray method or coater method used as the zinc phosphate treatment method, unevenness in the amount of zinc phosphate treatment chemical applied causes uneven chemical conversion during the formation of the zinc phosphate coating, resulting in poor surface appearance. If the thickness exceeds 3.3 mm, the method of the present invention (the zinc-based plated steel sheet S of the wringer roll 21 described later) is not performed. M Even if the pressing pressure against the surface is set, the sheet shape is not corrected sufficiently, and the surface appearance is not improved sufficiently. M The thickness of the steel plate S (thickness of the steel plate S) was set to 0.3 mm or more and 3.3 mm or less.

[0020] The chemical conversion treatment equipment 1 includes a surface conditioning treatment device 10, a film thickness uniforming treatment device 20, a gas blowing device 30, and a zinc phosphate treatment device 40. The surface conditioning treatment device 10 is a zinc-based coated steel sheet S MA surface conditioning solution is applied to the surfaces (upper and lower surfaces) of the plate to perform surface conditioning treatment. By performing the surface conditioning treatment before zinc phosphate treatment with the zinc phosphate treatment device 40, the reactivity between the zinc phosphate treatment solution and the plating can be increased during the zinc phosphate treatment.

[0021] The surface conditioning treatment device 10 uses a method of spraying a surface conditioning liquid, and is provided with a plurality of pairs of upper and lower surface conditioning liquid spray nozzles 12. The surface conditioning liquid spray nozzles 12 of each pair spray the zinc-based plated steel sheet S. M A surface conditioning liquid is sprayed on the top and bottom surfaces of the zinc-based coated steel sheet S. M The surface conditioning liquid is applied to the upper and lower surfaces of the zinc-plated steel sheet S. M The method may be a method of immersing the substrate in a surface conditioning liquid.

[0022] Here, it is preferable that the surface conditioning liquid contains Ti colloid, which has high dispersibility and can serve as reaction nuclei during the subsequent zinc phosphate treatment to form a zinc phosphate coating. In the surface conditioning treatment device 10, a transport roll 11 is installed upstream of the surface conditioning liquid spray nozzle 12.

[0023] The film thickness uniforming treatment device 20 is installed downstream of the surface conditioning treatment device 10, and is used to treat the zinc-based plated steel sheet S that has been subjected to surface conditioning treatment. M A wringer roll 21 is pressed against the surface (upper and lower surfaces) of the film to uniformize the film thickness of the surface conditioning liquid. The film thickness uniformization treatment device 20 is a device for uniformizing the thickness of the zinc-based plated steel sheet S from above and below. M The wringer roll 21 presses the zinc-based plated steel sheet S from above and below with a predetermined pressing pressure. M The surface is then pressed with a predetermined pressure to form a zinc-based coated steel sheet S. M The film thickness of the surface conditioning liquid present on the surface (upper and lower surfaces) is made uniform.

[0024] Here, the zinc-based coated steel sheet S of the ringer roll 21 M The pressure applied to the 2 ], Zinc-plated steel sheet S M When the plate thickness is t [mm], it is controlled within the range of the following formula.

[0025] 0.27t 3 -0.90t 2 +1.60t+2.60≦P≦0.27t 3 -0.90t 2 +1.60t+3.60

[0026] Here, the pressing pressure P [kgf / cm 2 ] to "0.27t 3 -0.90t 2 If the ratio is less than +1.60t+2.60, the surface conditioning solution is not sufficiently squeezed out. As a result, when the zinc phosphate treatment solution is applied by the zinc phosphate treatment device 40, the amount of the zinc phosphate treatment solution applied becomes non-uniform, and this non-uniformity causes uneven chemical conversion during the formation of the zinc phosphate coating, resulting in poor surface appearance. This is particularly true for zinc-based plated steel sheets S M For thick materials with a thickness of 2.3 mm or more, the plate shape becomes wavy, which causes irregularities in the chemical conversion during the formation of the zinc phosphate coating due to the non-uniformity of the amount of zinc phosphate treatment solution applied. For this reason, the pressing pressure P [kgf / cm] of the wringer roll 21 2 ] to "0.27t 3 -0.90t 2 +1.60t+2.60" or more, the surface conditioning liquid is sufficiently squeezed out, the amount of zinc phosphate treatment liquid adhered is uniform when the zinc phosphate treatment liquid is applied, and unevenness in the chemical conversion during the formation of the zinc phosphate coating due to non-uniformity in the amount of zinc phosphate treatment liquid adhered is prevented. On the other hand, the pressing pressure P [kgf / cm 2 ] to "0.27t 3 -0.90t 2If the pressure is greater than +1.60t+3.60", the wringer roll 21 will become rough due to excessive load, and the surface conditioning liquid will be locally evened out to an uneven state due to the roughness of the wringer roll 21, resulting in unevenness known as pear skin unevenness on the steel sheet surface. In addition, the excessive load will squeeze out the surface conditioning liquid excessively, causing the surface conditioning liquid to be locally evened out to an uneven state, resulting in uneven chemical conversion. Pressing pressure P [kgf / cm of the wringer roll 21 2 ] to 0.27t 3 -0.90t 2 +1.60t+2.60≦P≦0.27t 3 -0.90t 2 +1.60t+3.60, zinc-based coated steel sheet S M According to the thickness t of the zinc-plated steel sheet S M The wavy shape of the surface conditioning liquid is corrected, the surface conditioning liquid is appropriately squeezed out, and the amount of the surface conditioning liquid adhering to the steel sheet surface is leveled. As a result, when the zinc phosphate-based treatment liquid is applied, the amount of the zinc phosphate-based treatment liquid adhered becomes uniform, and unevenness in chemical conversion during the formation of the zinc phosphate coating can be improved. For this reason, in this embodiment, the pressing pressure P [kgf / cm] of the wringer roll 21 is set to 2 ] to 0.27t 3 -0.90t 2 +1.60t+2.60≦P≦0.27t 3 -0.90t 2 +1.60t+3.60.

[0027] The gas blowing device 30 is installed downstream of the film thickness uniformization treatment device 20, and is used to spray the zinc-based plated steel sheet S that has been subjected to the film thickness uniformization treatment of the surface conditioning liquid. M The gas is sprayed onto the surface (top and bottom) of the zinc-based coated steel sheet S, which has been treated with a surface conditioning liquid to make the film thickness uniform. M The surface conditioning liquid on the surfaces (upper and lower surfaces) is leveled (smoothed) more uniformly, which makes it possible to further suppress uneven chemical conversion during the formation of the zinc phosphate coating, which is caused by unevenness in the amount of zinc phosphate-based treatment liquid applied.

[0028] The gas blowing device 30 is provided with a pair of upper and lower gas blowing nozzles 31. The pair of gas blowing nozzles 31 blows the galvanized steel sheet S M Gas is blown onto both the top and bottom surfaces of the device. Galvanized steel sheet S from gas spray nozzle 31 M The pressure of the gas blown onto the upper and rear surfaces is preferably 0.20 MPa or more, and particularly preferably 0.30 MPa or more and 0.40 MPa or less.

[0029] In addition, the gas blowing nozzle 31 blows the zinc-based coated steel sheet S M The gas to be sprayed onto the upper and rear surfaces of the surface conditioning liquid may be any gas that does not practically affect the surface conditioning function of the surface conditioning liquid, and examples of such gases include air, nitrogen, helium, and argon. The zinc phosphate treatment device 40 is installed downstream of the gas blowing device 30, and is used to apply a zinc phosphate treatment solution to the zinc-plated steel sheet S which has been subjected to a film thickness uniformization treatment of the surface conditioning solution. M A zinc phosphate coating is formed by applying it to the surface (top and bottom).

[0030] The zinc phosphate treatment device 40 uses a method of spraying a zinc phosphate treatment solution, and is provided with a plurality of pairs of upper and lower zinc phosphate treatment solution spray nozzles 42. The zinc phosphate treatment solution spray nozzles 42 spray the zinc-based coated steel sheet S M A zinc phosphate treatment solution is sprayed onto the top and bottom surfaces of the zinc-plated steel sheet S. M The zinc phosphate treatment liquid is applied to the upper and lower surfaces of the substrate 1. The zinc phosphate treatment may be carried out by a coater method in addition to the spray method described above.

[0031] The zinc phosphate-based treatment solution is not particularly limited. Any commonly used zinc phosphate-based treatment solution can be used. It is possible to use a solution containing nitrate ions, F compounds, etc. in addition to Zn ions and phosphate ions. It is also possible to use a solution containing Ni, Mn, Mg, Co, Cu, etc.

[0032] The amount of zinc phosphate treatment solution applied was 1.0 g / m 2 More than 3.0g / m 2 The coating amount of the zinc phosphate treatment solution is preferably 1.0 g / m or less. 2 If the coating amount of the zinc phosphate treatment solution is less than 3.0 g / m, the zinc phosphate crystals may become coarse, which may result in a decrease in corrosion resistance and a poor appearance. 2 If the applied amount of the zinc phosphate-based treatment solution exceeds 1.0 g / m, the formability of the zinc phosphate-treated steel sheet and the adhesion of the zinc phosphate coating are reduced. 2 More than 3.0g / m 2 The following is the result.

[0033] In the zinc phosphate treatment device 40, a transport roll 41 is installed upstream of the zinc phosphate treatment liquid spray nozzle 42, and a transport roll 43 is installed downstream of the zinc phosphate treatment liquid spray nozzle 42. Zinc-based plated steel sheet S on which a zinc phosphate coating has been formed by the zinc phosphate treatment device 40 M The steel sheet is then subjected to a post-process to produce a zinc phosphate-treated steel sheet.

[0034] Next, the process flow in the chemical conversion treatment facility, which represents a method for producing a zinc phosphate-treated steel sheet according to one embodiment of the present invention, will be described with reference to the flowchart shown in Fig. 2. Fig. 2 is a flowchart for explaining the process flow in the chemical conversion treatment facility shown in Fig. 1.

[0035] First, before chemical conversion treatment is performed by the chemical conversion treatment equipment 1, the steel sheet S that has been cold rolled and then annealed is subjected to zinc plating or the like in the electroplating equipment 50. Then, the zinc-based plated steel sheet S that has been subjected to zinc plating or the like is M The substrate is subjected to chemical conversion treatment in a chemical conversion treatment facility 1.

[0036] Zinc-plated steel sheet S MThe thickness of the zinc-based plated steel sheet S is 0.3 mm or more and 3.3 mm or less. If the thickness is less than 0.3 mm, the sheet shape is unlikely to become wavy, and uneven chemical conversion during the formation of the zinc phosphate coating targeted by the present invention is unlikely to occur. On the other hand, if the thickness is 0.3 mm or more, a wavy sheet shape defect occurs, and in the case of the spray method or coater method used as the zinc phosphate treatment method, unevenness in the amount of zinc phosphate treatment chemical applied causes uneven chemical conversion during the formation of the zinc phosphate coating, resulting in poor surface appearance. If the thickness exceeds 3.3 mm, the method of the present invention (the zinc-based plated steel sheet S of the wringer roll 21 described later) is not performed. M Even if the pressing pressure against the surface is set, the sheet shape is not corrected sufficiently, and the surface appearance is not improved sufficiently. M The thickness of the steel plate S (thickness of the steel plate S) was set to 0.3 mm or more and 3.3 mm or less.

[0037] In the chemical treatment at chemical treatment facility 1, zinc-based plated steel sheet S M is transported to the surface conditioning treatment device 10, and first, in step S1, the surface conditioning treatment device 10 M A surface conditioning liquid is applied to the surfaces (upper and lower surfaces) of the substrate to perform a surface conditioning treatment (surface conditioning treatment step).

[0038] Next, in step S2, after step S1, the film thickness uniformization treatment device 20 treats the zinc-based plated steel sheet S that has been subjected to the surface conditioning treatment. M The wringer roll 21 is pressed against the surface (upper and lower surfaces) of the liquid, and a process for equalizing the film thickness of the surface conditioning liquid is carried out (film thickness equalization process).

[0039] In this film thickness uniforming treatment step, the zinc-based plated steel sheet S of the wringer roll 21 M The pressure applied to the 2 ], Zinc-plated steel sheet S M When the plate thickness is t [mm], it is controlled within the range of the above formula.

[0040] This makes it possible to manufacture zinc-based coated steel sheets. M According to the thickness t of the zinc-plated steel sheet S MThe wavy shape of the surface is corrected, the surface conditioning liquid is appropriately squeezed out, and the amount of the surface conditioning liquid adhering to the steel sheet surface is leveled. As a result, when the zinc phosphate treatment liquid is applied, the amount of the zinc phosphate treatment liquid adhered becomes uniform, and unevenness in chemical conversion during the formation of the zinc phosphate coating can be improved. For this reason, the zinc-based coated steel sheet S having a thickness of 0.3 mm or more and 3.3 mm or less can be applied. M In the case of a zinc phosphate-treated steel sheet having a base made of the above-mentioned material, it is possible to appropriately suppress unevenness in chemical conversion during the formation of a zinc phosphate coating, thereby producing a zinc phosphate-treated steel sheet with excellent surface appearance quality.

[0041] Next, in step S3, after step S2, the gas blowing device 30 blows the zinc-based plated steel sheet S which has been subjected to the film thickness uniformization treatment of the surface conditioning liquid. M A gas is blown onto the surface (upper and lower surfaces) of the substrate (gas blowing step).

[0042] This resulted in the zinc-based coated steel sheet S, which had been treated with a surface conditioning solution to make the film thickness uniform. M The surface conditioning liquid on the surfaces (upper and lower surfaces) is leveled (smoothed) more uniformly, which makes it possible to further suppress uneven chemical conversion during the formation of the zinc phosphate coating, which is caused by unevenness in the amount of zinc phosphate-based treatment liquid applied.

[0043] Next, in step S4, after step S3, the zinc phosphate treatment device 40 applies the zinc phosphate treatment solution to the zinc-based plated steel sheet S that has been subjected to the film thickness uniformization treatment of the surface conditioning solution. M A zinc phosphate coating is formed by applying it to the surface (upper and lower surfaces) of the material (zinc phosphate treatment process).

[0044] Here, the amount of zinc phosphate-based treatment solution applied was 1.0 g / m 2 More than 3.0g / m 2 The coating amount of the zinc phosphate treatment solution is preferably 1.0 g / m or less. 2 If the coating amount of the zinc phosphate treatment solution is less than 3.0 g / m, the zinc phosphate crystals may become coarse, which may result in a decrease in corrosion resistance and a poor appearance. 2If the applied amount of the zinc phosphate-based treatment solution exceeds 1.0 g / m, the formability of the zinc phosphate-treated steel sheet and the adhesion of the zinc phosphate coating are reduced. 2 More than 3.0g / m 2 The following is the result.

[0045] This completes the treatment in the chemical treatment equipment 1, and the zinc-based plated steel sheet S on which the zinc phosphate coating has been formed is obtained. M The steel sheet is then subjected to a post-process to produce a zinc phosphate-treated steel sheet. Although the embodiment of the present invention has been described above, the present invention is not limited to this and various modifications and improvements can be made.

[0046] For example, the gas blowing device 30 and the gas blowing step (step S3) may be omitted, and the zinc phosphate treatment (step S4) may be performed in the zinc phosphate treatment device 40 immediately after the film thickness uniforming treatment (step S2) in the film thickness uniforming treatment device 20. M Depending on the thickness t of the steel plate S M The wavy shape of the surface is corrected, the surface conditioner is appropriately squeezed out, and the amount of the surface conditioner adhering to the steel sheet surface is leveled. As a result, when the zinc phosphate-based treatment solution is applied, the amount of the zinc phosphate-based treatment solution adhered becomes uniform, and chemical conversion unevenness during zinc phosphate coating formation can be improved. As a result, chemical conversion unevenness during zinc phosphate coating formation can be appropriately suppressed for zinc phosphate-treated steel sheets with a thickness of 0.3 mm to 3.3 mm, and zinc phosphate-treated steel sheets with excellent surface appearance quality can be obtained. [Example]

[0047] Steel sheets S with thicknesses of 0.8 mm, 2.3 mm, and 3.0 mm that had been annealed after cold rolling were electroplated with a coating weight of 18 g / m per side using electroplating equipment 50. 2 , that is, the total amount of adhesion on both sides is 36 g / m 2 Electrogalvanization was carried out so that Next, the surface conditioning treatment device 10 is used to treat the electrogalvanized zinc-based plated steel sheet S MThe surfaces (upper and lower surfaces) of the plate were coated with a surface conditioning liquid (titanium colloid treatment liquid, PL-ZN 3.0 g / l, manufactured by Nihon Parkerizing Co., Ltd.) to perform surface conditioning treatment.

[0048] Next, the zinc-based plated steel sheet S that has been subjected to surface conditioning treatment is treated by a film thickness uniforming treatment device 20. M The film thickness of the surface conditioning solution was made uniform by pressing a wringer roll 21 against the surface (upper and lower surfaces) with the pressing pressure shown in Table 2. In Table 2, the "pressing pressure range" is the numerical range calculated using the above formula for each plate thickness. Next, the gas blowing device 30 is used to blow the zinc-based plated steel sheet S on which the film thickness of the surface conditioning liquid has been uniformized. M The gas was blown onto the surfaces (upper and lower surfaces) of the sample. A slit-shaped nozzle was used as the gas blowing nozzle 31 of the gas blowing device 30.

[0049] Next, a zinc phosphate treatment solution having the bath composition shown in Table 1 was applied to the zinc-plated steel sheet S M The zinc phosphate coating was formed by applying a coating of zinc phosphate-based treatment solution to the surfaces (upper and lower surfaces) of the zinc-based coated steel sheet S, thereby producing a zinc phosphate-treated steel sheet. The amount of zinc phosphate-based treatment solution applied is as shown in Table 2. In the zinc phosphate treatment device 40, a spray method was used, and the zinc phosphate-based treatment solution was sprayed onto the zinc-based coated steel sheet S using a zinc phosphate-based treatment solution spray nozzle 42. M The coating was sprayed onto the surface (top and bottom).

[0050] [Table 1]

[0051] The zinc phosphate-treated steel sheets obtained as described above were visually inspected for surface irregularities, and the presence or absence of pear-skin irregularities and incomplete drawing irregularities was confirmed. Here, pear-skin irregularities refer to irregularities that occur when the surface conditioner solution is locally leveled unevenly due to roughness of the wringer roll 21. This pear-skin irregularity is likely to occur when the pressing pressure P of the wringer roll 21 exceeds the upper limit of the pressing pressure determined by the above-mentioned formula (i.e., the value on the right side of the formula). Incomplete drawing irregularities refer to chemical conversion irregularities that occur during the formation of a zinc phosphate coating, when the wringer roll 21 is unable to completely squeeze out the surface conditioner solution, resulting in some of the surface conditioner solution slipping through the steel sheet, resulting in uneven adhesion of the zinc phosphate-based treatment solution. This incomplete drawing irregularity is likely to occur when the pressing pressure P of the wringer roll 21 is below the lower limit of the pressing pressure in the above-mentioned formula (i.e., the value on the left side of the formula).

[0052] The results obtained from the above are shown in Table 2 along with the conditions.

[0053] [Table 2]

[0054] In Table 2, for the evaluation of each type of unevenness, ○ means uniform and no unevenness, and × means there is unevenness. When all evaluation results were ○, the product was deemed to have passed. From Table 2, the thickness of the zinc-based coated steel sheet S is 0.8 mm. M The pressing pressure P of the wringer roll 21 is 2.8 kgf / cm 2 In the case of (Test No. 1), the pressing pressure P of the wringer roll 21 is the lower limit value of the pressing pressure in the above formula (3.4 kgf / cm 2 ) or less, which constitutes a comparative example, and poor squeezing unevenness occurred.

[0055] In addition, zinc-plated steel sheet S with a thickness of 0.8 mm M The pressing pressure P of the wringer roll 21 is 3.2 kgf / cm 2In the case of (Test No. 2), the pressing pressure P of the wringer roll 21 is the lower limit value of the pressing pressure in the above formula (3.4 kgf / cm 2 ) or less, which constitutes a comparative example, and poor squeezing unevenness occurred. In addition, zinc-plated steel sheet S with a thickness of 0.8 mm M The pressing pressure P of the wringer roll 21 is 5.0 kgf / cm 2 In the case of (Test No. 4), the pressing pressure P of the wringer roll 21 is the upper limit value of the pressing pressure in the above formula (4.4 kgf / cm 2 ), which constitutes a comparative example, and pear-skin-like unevenness occurred.

[0056] On the other hand, zinc-based coated steel sheet S with a thickness of 0.8 mm M The pressing pressure P of the wringer roll 21 is 4.0 kgf / cm 2 In the case of (Test No. 3), the pressing pressure P of the wringer roll 21 is within the pressing pressure range (3.4 to 4.4 kgf / cm 2 ) and constitutes an example of the present invention, and no pear-skin-like unevenness or poor drawing unevenness occurred, so it was passed. In addition, zinc-plated steel sheet S with a thickness of 2.3 mm M The pressing pressure P of the wringer roll 21 is 4.5 kgf / cm 2 In the case of (Test No. 5), the pressing pressure P of the wringer roll 21 is the lower limit value of the pressing pressure in the above formula (4.8 kgf / cm 2 ) or less, which constitutes a comparative example, and poor squeezing unevenness occurred.

[0057] In addition, zinc-plated steel sheet S with a thickness of 2.3 mm M The pressing pressure P of the wringer roll 21 is 6.5 kgf / cm 2 In the case of (Test No. 7), the pressing pressure P of the wringer roll 21 is the upper limit value of the pressing pressure in the above formula (5.8 kgf / cm 2 ), which constitutes a comparative example, and pear-skin-like unevenness occurred. On the other hand, zinc-plated steel sheet S with a thickness of 2.3 mm MThe pressing pressure P of the wringer roll 21 is 5.5 kgf / cm 2 In the case of (Test No. 6), the pressing pressure P of the wringer roll 21 is within the pressing pressure range (4.8 to 5.8 kgf / cm 2 ) and constitutes an example of the present invention, and no pear-skin-like unevenness or poor drawing unevenness occurred, so it was passed.

[0058] In addition, zinc-plated steel sheet S with a thickness of 3.0 mm M The pressing pressure P of the wringer roll 21 is 4.5 kgf / cm 2 In the case of (Test No. 8), the pressing pressure P of the wringer roll 21 is the lower limit value of the pressing pressure in the above formula (6.6 kgf / cm 2 ) or less, which constitutes a comparative example, and poor squeezing unevenness occurred. In addition, zinc-plated steel sheet S with a thickness of 3.0 mm M The pressing pressure P of the wringer roll 21 is 6.0 kgf / cm 2 In the case of (Test No. 9), the pressing pressure P of the wringer roll 21 is the lower limit value of the pressing pressure in the above formula (6.6 kgf / cm 2 ) or less, which constitutes a comparative example, and poor squeezing unevenness occurred.

[0059] On the other hand, zinc-based coated steel sheet S with a thickness of 3.0 mm M The pressing pressure P of the wringer roll 21 is 7.0 kgf / cm 2 In the case of (Test No. 10), the pressing pressure P of the wringer roll 21 is within the pressing pressure range (6.6 to 7.5 kgf / cm 2 ) and constitutes an example of the present invention, and no pear-skin-like unevenness or poor drawing unevenness occurred, so it was passed.

[0060] In these tests Nos. 1 to 10, the zinc-based coated steel sheet S M The thickness of the zinc-plated steel sheet is limited to 0.8 mm, 2.3 mm, and 3.0 mm. M It has been confirmed that good results can be obtained regardless of the plate thickness within the range of 0.3 mm to 3.3 mm. In addition, the pressing pressure P of the wringer roll 21 is within the range of the pressing pressure in the above formula (0.27t 3 -0.90t 2 +1.60t+2.60≦P≦0.27t 3 -0.90t 2 It has been confirmed that when the difference is within +1.60t+3.60), the yield rate for all unevenness including pear-skin unevenness and poor drawing unevenness is improved by 0.03%. [Explanation of symbols]

[0061] 1. Chemical treatment equipment 10. Surface conditioning treatment device 11 Transport roll 12 Surface conditioning liquid spray nozzle 20 Film thickness uniformization treatment device 21 Ringer Roll 30 Gas spraying device 31 Gas spray nozzle 40 Zinc phosphate treatment equipment 41 Transport roll 42 Zinc phosphate treatment solution spray nozzle 43 Transport roll 50 Electroplating Equipment S steel plate S M Zinc-plated steel sheet

Claims

1. A method for manufacturing a zinc phosphate-treated steel sheet using a zinc-based plated steel sheet having a thickness of 0.3 mm or more and 3.3 mm or less as a base, a surface conditioning treatment step of applying a surface conditioning liquid to the surface of the zinc-based plated steel sheet and performing a surface conditioning treatment; a film thickness uniforming step in which, after the surface conditioning step, a wringer roll is pressed against the surface of the zinc-based plated steel sheet that has been subjected to the surface conditioning step to uniformize the film thickness of the surface conditioning solution; a zinc phosphate treatment step of forming a zinc phosphate coating by applying a zinc phosphate treatment solution to the surface of the zinc-based plated steel sheet that has been subjected to the film thickness uniforming treatment with the surface conditioning solution after the film thickness uniforming treatment step, In the film thickness uniforming treatment step, the pressing pressure of the wringer roll against the zinc-based plated steel sheet is defined as P [kgf / cm ２ ] and the sheet thickness of the zinc-based plated steel sheet is t [mm], the method for producing a zinc phosphate-treated steel sheet is characterized by controlling the sheet thickness to be within the range of the following formula: 0.27t ３ -0.90t ２ +1.60t+2.60≦P≦0.27t ３ -0.90t ２ +1.60t+3.60

2. The coating amount of the zinc phosphate-based treatment solution was 1.0 g / m ２ 3.0g / m or more ２ 2. The method for producing a zinc phosphate-treated steel sheet according to claim 1, wherein the method comprises the following steps:

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