JP5018470B2 - Black-coated steel sheets, processed products, and flat-screen TV steel sheets - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a black coated steel sheet in which bending workability, and pressing flaw resistance are made compatible with each other even when a film thickness as thin as 0.5 to 5 &mu;m is used by optimizing a single organic film, and to provide a workpiece and a panel for a thin television. <P>SOLUTION: The steel sheet includes a blackened Zn-Ni alloy plating layer formed on at least one surface of the steel sheet, a chemical conversion film formed on the plating layer, not containing chromium, and a single organic film of 0.5 to 5 &mu;m in film thickness formed on the chemical conversion film, and further, the organic film is &ge;200 N/mm<SP>2</SP>in hardness, and &lt;5 mA in ERV of bending processed apex part when the film is subjected to 0T bending for bending 180&deg; pursuant to JIS (Japanese Industrial Standard) Z 2248-1996. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a black coated steel sheet, a processed product, and a thin TV panel, and more particularly to a black coated steel sheet that achieves both good bending workability and press resistance. The black coated steel sheet of the present invention is suitable for use as a material for AV equipment typified by a thin TV panel such as a liquid crystal television or a plasma television.

  For example, when a coated steel sheet is formed into, for example, a television panel or the like, press working or bending is generally performed, and bending workability and press resistance are required. Usually, in pre-coated steel sheets (coated steel sheets), mainly modified polyester resin or epoxy resin is used for the undercoat on the inner surface, ensuring adhesion to the underlying steel sheet, corrosion resistance, etc. 2-coated steel sheet that imparts stain resistance, design properties, scratch resistance, and ethanol, hydrochloric acid resistance, or alkali resistance barrier properties by using polyester or acrylic coatings for the film Further, a three-coated steel sheet in which an intermediate coating film is formed between the undercoat film and the topcoat film is common.

  Further, as disclosed in Patent Document 1, the conventional two-coated steel sheet has an undercoat film thickness of about 5 μm, an overcoat film thickness of about 15 μm, and the total film thickness of these coating films is 20 μm. Generally, it is a degree. However, if the total film thickness is such, it takes a long time for painting and baking, and the thicker the coating, the more disadvantageous it is in terms of manufacturing costs. Therefore, it is desired to reduce the thickness of the coating film.

JP-A-4-215873

  In Patent Document 2, the corrosion resistance of the blackening treatment layer is improved by applying heat treatment to the Zn-Ni alloy-plated steel sheet on which the blackening treatment layer is formed. A method of manufacturing a black steel sheet that combines both electromagnetic wave shielding properties and corrosion resistance by enabling thinning is disclosed.

JP 2006-291256 A

  However, the black steel sheet described in Patent Document 2 does not consider bending workability and press warpage resistance at all.

The object of the present invention is to optimize a single organic film, so that even if the film thickness of the organic film is as thin as 0.5 to 3 μm, the conventional two coats having a total film thickness of about 20 μm The object is to provide a black coated steel sheet, a processed product, and a panel for a flat-screen television, which have good bending workability and press-resistance to the same level as a coated steel sheet.

In order to achieve the above object, the gist of the present invention is as follows.
(1) A blackened Zn—Ni alloy plating layer formed on at least one surface of a steel plate, a conversion coating not containing chromium formed on the plating layer, and a hydroxyl value of 2 to 20 KOHmg on the conversion coating A single organic film having a glass transition temperature (Tg) of 40 to 70 ° C. and a film thickness of 0.5 to 3 μm formed of a polyester resin having a number average molecular weight of 5000 to 30000 , Further, the organic film has a hardness of 200 N / mm ² or more, and a black ERV of less than 5 mA when bent at 0T bent at 180 ° according to JIS Z2248-1996. Painted steel sheet.

  (2) The black coated steel sheet according to the above (1), wherein the fluctuation range ΔL of the L value after the ethanol rubbing test is performed 10 times with a load of 0.5 kg on the surface of the organic film is 1 or less.

  (3) A processed product formed by pressing the black-coated steel sheet according to (1) or (2) so that the surface of the black-coated steel sheet having the organic film is a convex surface. .

  (4) Using the black coated steel sheet according to the above (1) or (2), press forming so that the surface of the black coated steel sheet having the organic film is a convex surface exposed to the outside. A panel for a flat-screen TV.

According to the present invention, by optimizing a single organic film, even if the film thickness is as thin as 0.5 to 3 μm, it is equivalent to a conventional two-coated steel sheet having a total film thickness of about 20 μm. It is possible to provide a black coated steel plate, a processed product, and a thin TV panel having a good level of bending workability and press resistance.

Hereinafter, the present invention will be specifically described.
As shown in FIG. 1, a black coated steel sheet 1 of the present invention includes a blackened Zn—Ni alloy plating layer 3 formed on at least one surface of a steel plate 2 and a chemical composition containing no chromium formed on the plating layer. A film 4 and a single organic film 5 having a film thickness of 0.5 to 3 μm formed on the chemical conversion film are provided. This organic film 5 has a hardness of 200 N / mm 2 or more, and an ERV of the top of the bent portion when bent by 0T according to JIS Z2248-1996 is less than 5 mA.

  The hardness is the indentation depth (μm) when a test load of 3.0 mN is applied to the organic film 5 of the coated steel plate 1 using a regular square pyramidal indenter. Fischer scope (registered trademark) HM2000) means the hardness calculated from the indentation depth. FIG. 2 and FIG. 3 show a graph representing the relationship between the load and the indentation depth, and a graph representing the relationship between the indentation depth and the hardness.

Here, the hardness of 200 N / mm ² or more can protect the plated surface even when subjected to sliding in a state where pressure is applied from the mold during pressing, and can maintain a good coating appearance (that is, withstand resistance). This is because it is excellent in press durability, and is difficult to handle during transport and handling.

The ERV is obtained by subjecting a test piece obtained by cutting the coated steel sheet to a size of 60 mm in length and 30 mm in width, and subjecting the coated steel sheet to close contact bending (0T bending in accordance with JIS Z2248-1996) at room temperature. The degree of coating of the film at the top of the processed part is evaluated by the ERV method. Here, as shown in FIG. 4, the measurement of ERV (enamel rating value) obtained by the ERV method is performed by sealing the end face of the bent portion top with a frame seal tape exposing 10 mm × 10 mm. This is a value measured with an enamelator in which the contact area is kept constant and the temperature is 20 to 25 ° C. and 1% by mass of saline is used as an electrolyte. In the present invention, the current value is obtained after applying a DC voltage of 6 V for 4 seconds in an electrolytic solution in which a metal exposed portion is formed on the flat portion of the bent portion to serve as an anode and a cathode as a C electrode. According to the ERV measurement, the larger the current flows, the more the organic film that is an insulator has a defect, and the metal of the plating layer is exposed. Here, it was less than 5 m A in ERV, confirmed cracking of the organic film visually that more than 5 mA, because bending to impair the appearance when, that bending workability is inferior.

(Blackened Zn-Ni alloy plating layer)
The blackened Zn—Ni alloy plating layer 3 serving as the base steel plate of the coated steel plate 1 of the present invention can be a blackened Zn—Ni alloy plating layer formed by a conventional method. Further, the plating layer 3 is formed by blackening a Zn—Ni alloy plating layer on the surface portion of the plating layer 3 by, for example, anodic electrolytic treatment, cathodic electrolytic treatment, alternating electrolytic treatment, anodizing treatment, or the like. A chemical layer is formed.

(Chemical conversion film)
The conversion coating 4 formed on the blackened plating layer does not contain chromium from the viewpoint of environmental protection. The chemical conversion film 4 is formed mainly for improving the adhesion between the plating layer and the organic film. Any material can be used as long as it improves adhesion, but not only adhesion but also corrosion resistance is preferable. Examples of the chemical film 4 include a chemical film made of a mixture of Zn compound, phosphate, silica, and urethane resin.

(Single organic film)
The single organic film 5 formed on the chemical conversion film has a hardness of 200 N / mm ² or more, and an ERV of a bent portion top when bent at 180 ° according to JIS Z2248-1996 is less than 5 mA. It is.
From the viewpoint of imparting the above properties, the single organic film 5 preferably contains a polyester resin. Moreover, it is preferable that the number average molecular weight of this polyester-type resin is 5000-30000, the glass transition temperature Tg is 40-70 degreeC, and a hydroxyl value is 2-20 KOHmg / g.

If the number average molecular weight of the polyester resin is less than 5,000, the molecular weight between crosslinks of the film is too short and the crosslink density becomes too high, so the elongation is lowered and bending workability is deteriorated, or the film strength is too high. This is because the film of the deformed portion is easily peeled off. On the other hand, when the number average molecular weight exceeds 30000, sufficient crosslinking density cannot be obtained. For this reason, there exists a possibility that a membrane | film | coat may become easy to swell with an organic solvent.
In addition, when the glass transition temperature Tg is less than 40 ° C., the toughness of the film is lowered, sufficient press workability cannot be obtained, and characteristics such as film hardness and chemical hardness film adhesion tend to be lowered. On the other hand, when the glass transition temperature Tg exceeds 70 ° C., sufficient bending workability may not be obtained.
Furthermore, when the hydroxyl value of the polyester-based resin is less than 2 KOHmg / g, the crosslinking reaction becomes insufficient, so that sufficient film hardness cannot be obtained. On the other hand, when the hydroxyl value exceeds 20 KOHmg / g, the crosslinking density is high. It becomes too much, and the elongation is lowered, and there is a possibility that sufficient bending workability cannot be obtained.

  The single organic film 5 formed on the chemical conversion film is a trifunctional imino type as a curing agent so as not to be dissolved or swelled by an organic solvent or to be excessively softened at a high temperature. It is preferable to further contain melamine. The trifunctional imino melamine is obtained by etherifying three methylol groups of trimethylolmelamine obtained by condensation polymerization of melamine and formaldehyde with a lower alcohol such as methanol, ethanol, or butanol. You may use what condensed this several molecules as needed.

The single organic film 5 may further contain carbon black as a color pigment, a gloss modifier, resin particles, a lubricant, and the like.
The addition amount of the carbon black is determined from the viewpoint of securing the base concealing property. Although the base hiding property varies depending on the degree of dispersion and the film thickness in the coating film, it is preferably 1 to 12% by mass in the coating film.

Thickness of the single organic film 5 may be Re be between 0.5 to 5 [mu] m, in the present invention Ru can be 0.5 to 3 [mu] m. This is because if the thickness of the single organic film is less than 0.5 μm, the concealing property of the base color and the base surface becomes insufficient, and in addition, it is not preferable in terms of corrosion resistance. Moreover, when the film thickness of the organic film exceeds 5 μm, film peeling at the bending top portion occurs due to stress due to film deformation at the bending portion. In addition, the film thickness of the organic film 5 is a film thickness measured at a total of 15 or more positions in at least 5 fields of view by measuring the film thickness at any 3 positions per field using an optical microscope or an electron microscope. Average value.

  It is preferable that the fluctuation range ΔL of the L value after the ethanol rubbing test is performed 10 times with a load of 0.5 kg on the surface of the organic film 5 is 1 or less. The ethanol rubbing test is a test in which ethanol (5 ml) is impregnated in a gauze of a certain area, a constant load is applied, and the film is slid back and forth, and the solvent resistance of the film is measured. is there.

  The above-described black-coated steel sheet 1 is suitable for members used in applications such as television panels that are pressed or bent so that the film surface becomes a convex surface. For example, when used for a television panel, excellent bending workability and press-resistance are exhibited.

Next, a black-coated steel sheet according to the present invention was prototyped and its performance was evaluated, and will be described below.
Example 1
In Example 1, a blackened Zn—Ni alloy plating layer having a composition shown in A of Table 1 formed by performing anodization formed on one surface of a steel sheet, and a chemical conversion treatment liquid were applied on the plating layer. The chemical conversion film shown in Table 2a, which does not contain chromium, was formed by heating so that the ultimate plate temperature was 100 ° C. after 9 seconds of heating, and the number average molecular weight 25000 shown in Table 3 on this chemical conversion film. Apply an organic film paint containing a polyester resin having a glass transition temperature of 80 ° C., a hydroxyl value of 10 KOHmg / g and a trifunctional imino melamine, and heated to reach a plate temperature of 190 ° C. after 40 seconds of heating. A black coated steel sheet comprising a single organic film having a thickness of 3 μm.

(Example 2)
Example 2 is the same black-coated steel sheet as Example 1 except that the number average molecular weight of the polyester resin is 5000.

(Example 3)
Example 3 is the same black coated steel plate as Example 1 except that the number average molecular weight of the polyester resin is 30000.

Example 4
Example 4 is the same black coated steel plate as Example 1 except that the film thickness of the single organic film is 0.5 μm.

(Reference example)
The reference example is the same black coated steel plate as in Example 1 except that the film thickness of the single organic film is 5 μm.

(Example 6)
Example 6 is the same black-coated steel sheet as Example 1 except that the glass transition temperature Tg of the polyester resin was 40 ° C.

(Example 7)
Example 7 is the same black-coated steel sheet as Example 1 except that the glass transition temperature Tg of the polyester resin is 70 ° C.

(Comparative Example 1)
Comparative Example 1 is the same black painted steel plate as Example 1 except that the film thickness of the single organic film was 0.3 μm.

(Comparative Example 2)
Comparative Example 2 is the same black coated steel plate as Example 1 except that the film thickness of the single organic film was 7 μm.

(Conventional example 1)
As shown in FIG. 5, the conventional example 1 has an electrogalvanized layer 13 shown on B in Table 1 formed on one surface of a steel plate 12, and a chemical conversion treatment liquid is applied on the plated layer and heated for 9 seconds. The chemical conversion film 14 shown in a in Table 2 that does not contain chromium, which is formed by heating so that the ultimate plate temperature is 100 ° C. later, has a number average molecular weight of 15000, a glass transition temperature of 50 ° C., a hydroxyl group on this chemical conversion film Formed by applying an undercoat paint containing a 15 KOH mg / g polyester resin, hexafunctional hexamethoxymethylated melamine, rust preventive pigment, etc., and heating to reach a plate temperature of 170 ° C. 30 seconds after heating An undercoat film 15 having a thickness of 5 μm, a polyester resin having a number average molecular weight of 15000, a glass transition temperature of 35 ° C., and a hydroxyl value of 8 KOHmg / g, and a trifunctional imino-type film on the undercoat film. A conventional coating having a total film thickness of 20 μm, comprising a top coating film 16 having a thickness of 15 μm formed by applying a top coating containing min and heating to 190 ° C. after 40 seconds of heating. This is a steel plate 10.

(Conventional example 2)
In Conventional Example 2, the undercoat was heated to 210 ° C. after 30 seconds to form an undercoat film, and the topcoat was heated to 230 ° C. after 40 seconds to form an overcoat film. Except this, it is the same coated steel plate as in Conventional Example 1.

<Bending workability>
In accordance with JIS Z2248-1996, the coated steel plate was cut into a test piece cut to a size of 60 mm in length and 30 mm in width, and the top of the bent portion was visually observed when the coated steel plate was bent at 180 ° at room temperature. Observed. Evaluation was performed according to the following criteria.
○: No cracking of the organic film was confirmed ×: Cracking of the organic film was confirmed

About the sample which performed said 0T bending, ERV was further measured by the method mentioned above further after that. Evaluation was performed according to the following criteria.
◎: ERV less than 2 mA ○: ERV 2 mA or more and less than 5 mA ×: ERV 5 mA or more

<Press resistance>
Each of the coated steel sheets was visually evaluated for damage to the coating film on the side wall after the cylindrical cup was molded at a blank diameter of 67 mmφ, a punch diameter of 33 mmφ, a molding speed of 300 mm / s, and a wall surface temperature of 80 ° C. Evaluation was performed according to the following criteria.
◎: No damage occurred ○: Some damage was observed ×: Many damage occurred

<Ethanol resistance>
The fluctuation range ΔL of the L value after the ethanol rubbing test was performed 10 times with a load of 0.5 kg was evaluated on the surface of the organic film of each coated steel sheet. Evaluation was performed according to the following criteria.
○: ΔL is 1 or less Δ: ΔL is more than 1 and less than 10 ×: ΔL is more than 10

<Corrosion resistance>
Each of the coated steel sheets was sprayed with 5% by weight of salt water at 35 ° C. for 8 hours, and then the process of resting for 16 hours was defined as 1 cycle, and the change in the coating film surface appearance after 3 cycles was evaluated. Evaluation was performed according to the following criteria.
○: No change on coating surface △: Slight rusting on coating surface ×: Many rusting on coating surface

Table 4 shows the evaluation results.

From Table 4, Examples 1 to 4 and Examples 6 and 7 are the two-coated steel sheets of Conventional Example 2 having a total film thickness of about 20 μm even when the film thickness is as thin as 0.5 to 3 μm. It can be seen that it has the same level of good bending workability and press resistance.

Further, in the case of the conventional two-coated steel sheet, the conventional example 1 in which the baking temperature of the top coat film is low is inferior to the conventional example 2 in which the baking temperature of the top coat film is high. 1-4 and Examples 6 and 7, even though the organic film is single, even if the baking temperature is lower than that of the top coat film of Conventional Example 2, it is the same level as the 2-coated steel sheet of Conventional Example 2 It can be seen that it has excellent bending workability and press resistance.

  Further, Comparative Examples 1 and 2 having a film thickness outside the proper range of the present invention were inferior in bending workability and resistance to press wrinkles.

According to the present invention, by optimizing a single organic film, even if the film thickness is as thin as 0.5 to 3 μm, a black coating that achieves both bending workability and press resistance It is now possible to provide steel plates, processed products, and thin TV panels.

The black coated steel plate of this invention is shown. The graph showing the relationship between a load and an indentation depth is shown. The graph showing the relationship between indentation depth and hardness is shown. The schematic diagram for demonstrating ERV method is shown. A conventional 2-coated steel sheet is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Black coating steel plate 2 Steel plate 3 Blackening Zn-Ni type plating layer 4 Chemical conversion film 5 Single organic coating 10 Conventional coating steel plate 12 Steel plate 13 Electrogalvanization layer 14 Chemical conversion coating 15 Undercoat coating 16 Top coating

Claims (4)

A blackened Zn-Ni alloy plating layer formed on at least one side of the steel plate;
A conversion film not containing chromium formed on the plating layer;
The film thickness formed on the chemical conversion film by a polyester resin having a hydroxyl value of 2 to 20, a glass transition temperature (Tg) of 40 to 70 ° C., and a number average molecular weight of 5000 to 30000 is 0.5 to 3. with a single organic film of μm,
Further, the organic film has a hardness of 200 N / mm ² or more, and a black ERV of a bent portion top when bent at 0T according to JIS Z2248-1996 is less than 5 mA. Painted steel sheet.   The black coated steel sheet according to claim 1, wherein the fluctuation range ΔL of the L value after the ethanol rubbing test is performed 10 times with a load of 0.5 kg on the surface of the organic film is 1 or less.   A processed product formed by pressing the black-coated steel sheet according to claim 1 or 2 so that the surface of the black-coated steel sheet having the organic film is a convex surface.   A thin-screen television panel formed by pressing the black-coated steel sheet according to claim 1 or 2 so that the surface of the black-coated steel sheet having the organic film is a convex surface exposed to the outside. .

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