JP5292962B2 - Surface-treated steel sheet and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet with good corrosion resistance without forming zinc-based plated layer even in the case where film thickness of an organic resin layer is thin, and a method for manufacturing the same. <P>SOLUTION: The surface-treated steel sheet is obtained by forming a layer comprising an organic inhibitor on at least one surface of a substrate steel sheet pickled with aqueous nitric acid solution until a prescribed Fe intensity is reached, and forming an organic resin layer of &le;5 &mu;m film thickness on the organic inhibitor layer. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention is a surface-treated steel sheet mainly used for electrical products, and particularly relates to a surface-treated steel sheet that can have good corrosion resistance without applying zinc-containing plating and a method for producing the same.

  As a pre-coated steel plate (painted steel plate) used for an electrical product such as a flat panel television, for example, as disclosed in Patent Document 1, a plated layer is formed on the surface of the steel plate, and directly or on the plated layer. A coated steel plate formed by forming a film containing a predetermined resin through a chemical conversion film is exemplified. The coated steel sheet of Patent Document 1 can achieve good corrosion resistance by the action of the plating layer and the resin film.

Here, the type of the plating layer varies depending on the application, but from the viewpoint of having good corrosion resistance and cost, a steel plate provided with a zinc-based plating layer, such as a hot dip galvanized steel plate, electric In general, a galvanized steel sheet, a galvannealed steel sheet, an aluminum-zinc alloy plated steel sheet, or the like is used. However, such a zinc-based plating layer is galvanized on the surface of the steel sheet from the viewpoint of increasing the product cost and eliminating elements other than steel plate components as much as possible when recycling the steel sheet due to the recent rise in the price of zinc raw materials. A surface-treated steel sheet that does not form a layer is desired.
As a steel material not provided with the zinc-based plating layer, for example, in Patent Document 2, a steel material manufactured by a degreasing treatment step of the steel material, a step of making the surface of the steel material uneven by an oxidation treatment, and a step of coating a modified polyolefin resin. Is mentioned.

However, as long as the resin layer (modified and modified polyolefin resin layer in Patent Document 2) can be formed thick on the surface of the steel material as in the steel material of Patent Document 2, it is possible to have a certain corrosion resistance, When used for household electrical appliances, it is difficult to form a sufficiently thick resin layer on the surface of the steel sheet, which is not preferable from the viewpoint of cost. It is believed that it cannot be obtained.
JP 2007-11985A Japanese Patent Laid-Open No. 3-80969

  An object of the present invention is to provide a surface-treated steel sheet having good corrosion resistance and a method for producing the same without forming a zinc-based plating layer even when the organic resin layer is thin.

As a result of repeated studies to solve the above-mentioned problems, the present inventors used a steel plate pickled with an aqueous nitric acid solution as a base steel plate, and applied and dried an organic inhibitor solution on the pickled surface of the steel plate. Forming a layer made of an organic inhibitor, and forming an organic resin layer having a film thickness of 5 μm or less on the organic inhibitor layer, the surface of the steel sheet by the action of the pickling treatment and the organic inhibitor layer A surface-treated steel sheet with good corrosion resistance is formed without forming a zinc-based plating layer on the steel sheet surface even when the thickness of the organic resin layer is as thin as 5 μm or less. It was found that it can be obtained.

The present invention has been made based on such findings, and the gist thereof is as follows.
(1) to at least one surface of the element areas steel sheet was subjected to pickling treatment of dipping for less than 30 seconds to ambient temperature the 5～40Mass% nitric acid aqueous solution, washed with water, dried, then, pickling surfaces of steel plates A surface-treated steel sheet, wherein an organic inhibitor solution is applied and dried to form a layer composed of an organic inhibitor, and an organic resin layer having a thickness of 5 μm or less is formed on the organic inhibitor layer.

( 2 ) The surface-treated steel sheet according to (1) , wherein the organic inhibitor is 1,5-diphenylcarbonohydrazide, N, N′-diphenylethylenediamine or dithiooxamide.

( 3 ) The surface-treated steel sheet according to (1) or (2) , wherein the organic resin is an epoxy resin.

( 4 ) The surface-treated steel sheet according to any one of (1) to ( 3 ), wherein the organic resin layer contains a rust preventive pigment.

( 5 ) At least one side of the steel sheet is subjected to pickling treatment in which it is immersed in a 5 to 40 mass% nitric acid aqueous solution at room temperature for less than 30 seconds, then washed with water and dried, and then on the pickled surface of the steel sheet. A method for producing a surface-treated steel sheet, comprising: forming an organic inhibitor layer by applying and drying an organic inhibitor solution; and applying and drying a paint containing an organic resin to form the organic resin layer.

( 6 ) The method for producing a surface-treated steel sheet according to ( 5 ), wherein the organic resin is an epoxy resin.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the film thickness of an organic resin layer is thin, it becomes possible to provide the surface treatment steel plate provided with favorable corrosion resistance, and its manufacturing method, without forming a zinc-type plating layer. It was.

Hereinafter, the configuration of the present invention and the reasons for limitation will be described.
In the surface-treated steel sheet according to the present invention, a layer made of an organic inhibitor was formed on at least one surface of a base steel sheet that had been pickled with an aqueous nitric acid solution, and an organic resin layer having a thickness of 5 μm or less was formed on the organic inhibitor layer. This is a surface-treated steel sheet.

  The surface-treated steel sheet of the present invention is characterized by using a base steel sheet that has been pickled with an aqueous nitric acid solution. By performing pickling treatment with an aqueous nitric acid solution, a dense protective film is formed on the surface of the base steel plate. Furthermore, by forming an organic inhibitor layer on the surface that has been subjected to pickling treatment, the organic inhibitor covers minute defects existing on the surface of the steel sheet, thereby providing good corrosion resistance without forming a zinc-based plating layer. Can be provided. Moreover, the steel plate used as a board | substrate will not be specifically limited if it is a steel plate which can perform the said pickling process, According to a use, it can select suitably.

  The pickled surface of the steel sheet can be formed by immersing the steel sheet in an aqueous nitric acid solution (5 to 40 mass%) at room temperature for less than 30 seconds, and then washing and drying. Here, the concentration of the nitric acid aqueous solution is limited to 5 to 40 mass%. When the concentration is less than 5 mass%, the dense protective film is not easily formed on the steel sheet surface, so that the corrosion resistance is reduced. If the content exceeds 40 mass%, the steel plate reacts violently, resulting in unevenness on the surface and a significant decrease in appearance. The reason why the immersion time is set to less than 30 seconds is that when the immersion time is 30 seconds or more, unevenness occurs on the surface of the steel sheet, and the appearance is remarkably deteriorated.

  Further, the surface-treated steel sheet of the present invention is obtained by forming a layer made of an organic inhibitor on the surface of the pickled base steel sheet. This layer made of an organic inhibitor is a layer provided to enhance the corrosion resistance effect. In order to obtain the above effect, the thickness of the layer made of an organic inhibitor is preferably 0.01 to 0.3 μm. The type of the organic inhibitor is not particularly limited as long as it acts as a corrosion inhibitor, but 1,5-diphenylcarbonohydrazide, N, N′-diphenylethylenediamine is particularly preferable because it can exhibit a particularly high corrosion resistance effect. Alternatively, dithiooxamide is more preferable.

  In addition, the layer which consists of the said organic inhibitor can be formed by apply | coating an organic inhibitor solution to the pickling process surface of the said base steel plate with a roll coater, a bar coater, etc., and making it dry. The organic inhibitor layer may be a continuous layer or a discontinuous island shape. However, in order to obtain better corrosion resistance, the organic inhibitor layer is preferably a continuous layer.

  The surface-treated steel sheet of the present invention is obtained by forming an organic resin layer on the organic inhibitor layer. This organic resin layer is a layer provided on the surface of the steel plate so as to be provided with corrosion resistance, scratch resistance, designability, and the like, and is not particularly limited as long as it is a layer made of an organic resin. However, it is preferable to use an epoxy resin from the viewpoint that high corrosion resistance can be obtained by a synergistic effect with the pickled surface of the steel sheet.

  Furthermore, the film thickness of the organic resin layer needs to be 5 μm or less. If the film thickness exceeds 5 μm, the electrical resistance on the surface of the steel sheet is increased, so that the grounding property is remarkably lowered and the manufacturing cost is increased. Further, in order to obtain the effect of the organic resin layer described above, the film thickness is preferably set to 0.3 μm or more.

  In addition, the said organic resin layer can be formed by apply | coating the coating material containing the said organic resin on the said organic inhibitor layer, and making it dry.

  Moreover, it is preferable that the said organic resin layer contains a rust preventive pigment. This is because the corrosion resistance can be further improved by containing a rust preventive pigment. The type of the anticorrosion pigment is not particularly limited, but it is more preferable to use aluminum phosphomolybdate, zinc phosphate or aluminum tripolyphosphate from the viewpoint of further improving the corrosion resistance.

The surface-treated steel sheet of the present invention is analyzed in the depth direction from the surface of the base steel sheet after the nitric acid pickling treatment using GDS, and the time required to obtain a predetermined Fe strength is subjected to the pickling treatment. It is preferable that it is in the range of 2 to 10 times with respect to the steel plate that is not.
Here, the GDS refers to a glow discharge optical emission spectrometer, and the concentration of each element at a predetermined depth from the surface is determined by the relationship between the measurement time (seconds) and the light intensity (V). It is something you can know. Therefore, when the analysis by GDS is performed, if the time required to obtain the predetermined Fe intensity is long, the energy required to reach Fe is required accordingly, so the corrosion resistance is also increased. . In addition, the time required to obtain the predetermined Fe strength is in the range of 2 to 10 times, because the protective film is hardly formed when less than 2 times, compared with a steel plate not subjected to pickling treatment This is because a great effect cannot be exerted on the corrosion resistance. On the other hand, if it exceeds 10 times, although the corrosion resistance is increased, unevenness is formed on the surface of the steel sheet, and the appearance is remarkably deteriorated.

  Fig. 1 shows the strength (V) and analysis time of each element (O, C and Fe) analyzed in the depth direction from the surface of the base steel sheet after the nitric acid pickling treatment using a GDS (glow discharge optical emission spectrometer). (A) is a graph showing the analysis results of a base steel sheet that has been pickled for 10 seconds using a 20 mass% nitric acid aqueous solution, (b) The analysis result about the cold-rolled steel plate which has not performed the pickling process is shown. As shown to Fig.1 (a), the base steel plate of this invention is required until it obtains predetermined Fe intensity | strength (for example, 5V) compared with the steel plate (FIG.1 (b)) which has not performed the predetermined pickling. It can be seen that the time is more than three times longer.

  The predetermined Fe intensity is 4.5 V, and the time until the intensity is obtained is preferably in the range of 5 to 30 seconds. The reason why the predetermined Fe intensity is set to 4.5 V is because it is easy to read the time until the target intensity is obtained, and the time until the intensity is obtained is set to 5 to 30 seconds. This is because the protective film is hardly formed, so there is a possibility that sufficient corrosion resistance cannot be provided, and when it exceeds 30 seconds, a uneven pattern is formed on the surface and the appearance is remarkably deteriorated.

  The above description is merely an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

  Examples of the present invention will be described.

(Examples 1-10 and Comparative Examples 3-5)
On one side of a cold rolled steel sheet with a thickness of 0.8mm, as a pretreatment, in an alkaline degreasing solution (liquid temperature: 70 ° C) with sodium orthosilicate (60g / L), the counter electrode is a stainless steel plate, and the current density is 5A / dm. After performing electrolytic degreasing for 30 seconds in ² , the sample was washed with water, immersed in a nitric acid solution under the conditions shown in Table 1 for a predetermined time (see Table 1), pickled, then washed with water and dried.
After the above pickling treatment, a predetermined organic inhibitor solution was applied to the surface of the base steel plate subjected to the nitric acid pickling treatment and dried to form an organic inhibitor layer having a structure shown in Table 1. Thereafter, a coating containing an organic resin and, if necessary, a rust preventive pigment is applied on the organic inhibitor layer and dried to form an organic resin layer having the structure shown in Table 1, and a surface treatment to be a sample A steel plate was produced.
In addition, about each manufactured sample, it analyzes by the depth direction from the surface after the said pickling process by GDS, measures time (second) until predetermined Fe intensity | strength (4.5V) is obtained, and pickling process Table 1 shows the ratio with respect to the steel sheet (Comparative Example 1) not subjected to.
In addition, the film thickness (μm) of the organic inhibitor layer and the organic resin layer was measured at three arbitrary film thicknesses per field using an optical microscope or an electron microscope, and a total of 15 in at least 5 fields. It is set as the average value of the film thickness measured at the location or more.

(Comparative Example 1)
In Comparative Example 1, a surface-treated steel sheet as a sample was manufactured under the same conditions as in Example 1 except that the predetermined pickling treatment was not performed.

(Comparative Example 2)
In Comparative Example 2, the same steel sheet as in Example 1 was subjected to the same pretreatment as in Example 1, then washed with water, and immersed in an aqueous hydrochloric acid solution having a concentration of 10 mass% and a temperature of room temperature for 60 seconds. A surface-treated steel sheet as a sample was manufactured under the same conditions as in Example 1 except that the sample was pickled.

  Various tests were performed on samples of the respective surface-treated steel sheets obtained as described above. The evaluation method of the test conducted in this example is shown below.

  Various tests were performed on samples of the respective surface-treated steel sheets obtained as described above. The evaluation method of the test conducted in this example is shown below.

(Evaluation method)
(1) Corrosion resistance The following corrosion resistance evaluation was performed about each sample of the Example and the comparative example. Specifically, for each sample, artificial sea salt is attached at a frequency of twice a week (attachment amount: 10 mg / m ² ), and the dry environment (60 ° C, 35% RH) and wet environment (40 ° C, 95% RH) with a transition time of 1 hour, hold for 3 hours, leave it for 2 weeks, observe the surface condition of each sample, and Evaluated according to. The evaluation results are shown in Table 2.
○: Red rust generation area ratio less than 10% ×: Red rust generation area ratio 10% or more Further, photographs of the appearance of the samples of Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. 2A is a photograph of the sample of Example 1, (b) is the sample of Comparative Example 1, and (c) is a photograph of the sample of Comparative Example 2. FIG.

Ｌ_１、ａ_１、ｂ_１：試験前の値、Ｌ_２、ａ_２、ｂ_２：試験後の値
○：ΔＥ≦２
×：２＜ΔＥ (2) Fingerprint resistance Each sample of the examples and comparative examples was immersed in an artificial fingerprint liquid defined in JIS K 2246: 2007 for 1 minute at 20 ° C, and the color difference (ΔE) before and after immersion was determined. The fingerprint property was evaluated. Evaluation was performed according to the following evaluation criteria, and the evaluation results are shown in Table 2.
ΔE is calculated according to the following calculation formula using L value, a value, and b value measured by a color computer manufactured by NEC Corporation.

L ₁ , a ₁ , b ₁ : value before test, L ₂ , a ₂ , b ₂ : value after test ○: ΔE ≦ 2
×: 2 <ΔE

(3) Heat dissipation About each sample of an Example and a comparative example, the aluminum foil was affixed on the inner surface (side surface and bottom face) of the housing | casing assembled with the acrylic resin board (plate thickness 2mm), and was coat | covered completely. A silicon rubber heater was set on an aluminum frame installed at the center of the inner bottom surface of the housing so as to be positioned at a height of 10 mm from the bottom surface. Each sample was cut into a size of 300 mm in length and 300 mm in width, used as a top plate of the housing, and placed and sealed so as to be in contact with the packing installed at the upper surface opening (side upper end) of the housing. In the space between the sheath type platinum resistance thermometer and the heater below, an aluminum foil (200 mm long, 200 mm wide) for preventing direct radiation from the heater to the sheath type platinum resistance thermometer is directly above the silicon rubber heater. And it installed in parallel with the bottom face at a fixed position of 35 mm from the bottom face, and supported the four corners of the aluminum foil with a wire so that the position could be maintained.
Then, a sheath type platinum resistance thermometer (diameter: 1.6 mmφ, length: 150 mm) is placed on the side surface of the casing inside the casing, which is 35 mm away from the top plate vertically downward and 40 mm away from the aluminum foil vertically upward. It is inserted so as to maintain the horizontal position, and the temperature in the vicinity of 35 mm can be measured from the center in the horizontal direction inside the case and vertically downward from the top plate, and then a voltage is supplied from the DC stabilized power supply to generate heat. (Input 65 V × 705 mA = 45.8 W).
The change in the internal temperature of the case was recorded in a data logger, and the heat absorption / release performance of the top plate was determined from the temperature when the internal temperature of the case reached a steady state. The evaluation criteria are shown below, and the evaluation results are shown in Table 2.
○: Temperature drop is 5 ° C or higher compared to electrogalvanized plate ×: Temperature drop is less than 5 ° C compared to electrogalvanized plate

(4) Appearance The appearance of each sample of Examples and Comparative Examples was visually evaluated. The evaluation criteria are shown below, and the evaluation results are shown in Table 2.
○: Uneven appearance ×: Uneven appearance

  From the results in Table 2, the surface-treated steel sheets of Examples 1 to 10 have better corrosion resistance, fingerprint resistance, heat dissipation and appearance than the surface-treated steel sheets of Comparative Examples 1 to 5. Recognize. 2A to 2C also show that the surface-treated steel sheet of Example 1 is superior to the surfaces of Comparative Examples 1 and 2 in corrosion resistance.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where the film thickness of an organic resin layer is thin, it is possible to provide the surface treatment steel plate provided with favorable corrosion resistance, and its manufacturing method, without forming a zinc plating layer. .

The strength (V) and analysis time (seconds) of each element (O, C and Fe) analyzed in the depth direction from the surface of the base steel sheet after the nitric acid pickling treatment using GDS (Glow Discharge Optical Emission Spectrometer) (A) shows the analysis result of the base steel sheet subjected to pickling treatment for 10 seconds using 20 mass% nitric acid aqueous solution, and (b) shows pickling treatment. The analysis result about the cold-rolled steel plate which has not been given is shown. It is the photograph which image | photographed the external appearance about the sample of Example 1, Comparative Example 1, and Comparative Example 2, (a) is the sample of Example 1, (b) is the sample of Comparative Example 1, (c) is Comparative Example 2. A sample of is shown.

Claims (6)

For at least one surface of the element areas steel sheet was subjected to pickling treatment of dipping for less than 30 seconds to ambient temperature the 5～40Mass% nitric acid aqueous solution, washed with water, dried, then the pickling surfaces of steel, organic A surface-treated steel sheet, wherein a layer composed of an organic inhibitor is formed by applying and drying an inhibitor solution, and an organic resin layer having a thickness of 5 μm or less is formed on the organic inhibitor layer. The organic inhibitors are 1,5-diphenyl-carbonitrile Bruno hydrazide, N, surface-treated steel sheet according to claim 1, wherein the N'- diphenyl diamine or dithiooxamide. The surface-treated steel sheet according to claim 1 or 2 , wherein the organic resin is an epoxy resin. The surface-treated steel sheet according to any one of claims 1 to 3 , wherein the organic resin layer contains a rust preventive pigment.   At least one side of the steel sheet is subjected to a pickling treatment in which it is immersed in a 5 to 40 mass% nitric acid aqueous solution at room temperature for less than 30 seconds, then washed with water and dried. A method for producing a surface-treated steel sheet, comprising forming an organic inhibitor layer by applying and drying an organic resin layer, and then applying and drying a coating containing an organic resin to form the organic resin layer. The method for producing a surface-treated steel sheet according to claim 5 , wherein the organic resin is an epoxy resin.

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