JP2009160768A - Black coated steel sheet, worked article and steel sheet for thin type television - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a black coated steel sheet having both of bending workability and press mark resistance even if its film thickness is as thin as 0.5-5 μm by properly forming a single organic coating film, and also to provide a worked article and a panel for a thin type TV set. <P>SOLUTION: The black coated steel sheet is equipped with: a blacked Zn-Ni alloy plated layer formed on at least one surface of the steel sheet; a chemical conversion coating film formed on the plated layer and containing no chromium; and the single organic coating film having 0.5-5 μm film thickness which is formed of polyester resin having hydroxide value of ≥10 and ≥40°C glass transition temperature (Tg) and an imino type melamine. <P>COPYRIGHT: (C)2009,JPO&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 (painted steel sheets), mainly modified polyester resin or epoxy resin is used for the undercoat on the outer surface side to ensure 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 achieve the conventional two-coat coating with a total film thickness of about 20 μm even when the film thickness of the organic film is as thin as 0.5 to 5 μm by optimizing a single organic film. The object is to provide a black coated steel plate, a processed product, and a flat panel panel for televisions, which have good bending workability and press resistance at the same level as a steel plate.

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 10 or more on the conversion coating And a black coating characterized by comprising a polyester resin having a glass transition temperature (Tg) of 40 ° C. or higher and a single organic film having a thickness of 0.5 to 5 μm formed of imino melamine steel sheet.

  (2) The variation width ΔL of the L value after the ethanol rubbing test is performed 20 times with a load of 1 kg on the surface of the organic film is 1.5 or less, as described in (1) above Black painted steel plate.

  (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 5 μm, it is the same level as a conventional 2-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 panel for TV having excellent bending workability and press resistance.

The present invention will be specifically described below.
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, and a chemical conversion film 4 containing no chromium formed on the plating layer. A single film having a thickness of 0.5 to 5 μm formed on the chemical conversion film by a polyester resin having a hydroxyl value of 10 or more and a glass transition temperature (Tg) of 40 ° C. or more and an imino melamine. Organic film 5 is provided.

(Blackened Zn-Ni alloy plating layer)
The blackened Zn—Ni alloy plating layer 3 serving as the base steel plate of the coated steel sheet 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 include a chemical film made of a Zn compound, phosphate, silica, and urethane resin.

(Single organic film)
The single organic film 5 on the chemical film is formed of a polyester resin having a hydroxyl value of 10 or more and a glass transition temperature (Tg) of 40 ° C. or more and an imino melamine, that is, the polyester resin The organic film is crosslinked with imino melamine.

When the glass transition temperature Tg of the polyester resin is less than 40 ° C., the toughness of the film is lowered, sufficient press workability cannot be obtained, and the characteristics such as the film hardness and the resistance to press wrinkles are also lowered. It is.
Further, when the hydroxyl value of the polyester resin is less than 10 KOHmg / g, the crosslinking reaction becomes insufficient, so that a sufficient film hardness cannot be obtained, and the press resistance is inferior.

  The single organic film 5 formed on the chemical conversion film is formed of imino melamine as a cross-linking agent so that the polyester resin is sufficiently cross-linked for the purpose of reducing dissolution and discoloration by an organic solvent. A coated film is used. The imino melamine is preferably a trifunctional imino 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 amount of carbon black added is determined from the viewpoint of securing the base hiding property, and the hiding property varies depending on the degree of dispersion and the film thickness in the coating film, but it is added in an amount of 1 to 12% by mass in the coating film. preferable.

  The film thickness of the single organic film 5 is 0.5 to 5 μm. 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. Further, when the film thickness of the organic film 5 exceeds 5 μm, peeling occurs in the film on the top of the bent portion due to the stress caused by the deformation of the bent 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.

  The variation width ΔL of the L value after the ethanol rubbing test is performed 20 times with a load of 1 kg on the surface of the organic film 5 is 1.5 or less. The ethanol rubbing test is a test in which the solvent resistance of the film is measured by sliding back and forth while applying a constant load in a state where 5 ml of ethanol is soaked in the gauze. L value is lightness.

  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 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, A chemical conversion film having a composition shown in Table 2 that does not contain chromium, formed by heating so that the ultimate plate temperature becomes 100 ° C. after 9 seconds of heating, and a number average molecular weight 30000 shown in Table 3 on the chemical conversion film, glass It was formed by applying an organic film paint containing a polyester resin having a transition temperature of 60 ° C. and a hydroxyl value of 15 KOHmg / g and trifunctional imino melamine and heating to reach a plate temperature of 190 ° C. after 40 seconds of heating. A black coated steel sheet having a single organic film having a film thickness of 4 μm.

(Example 2)
Example 2 is the same black coated steel sheet as Example 1 except that the hydroxyl value of the polyester resin was 10.

(Example 3)
Example 3 is the same black coated steel sheet as Example 1 except that the hydroxyl value of the polyester resin was 20.

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.

(Example 5)
Example 5 is the same black coated steel sheet as Example 1 except that the film thickness of the single organic film was 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-coated steel sheet as Example 1 except that the hydroxyl value of the polyester resin is 8.

(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 0.3 μm.

(Comparative Example 3)
Comparative Example 3 is the same black coated steel plate as Example 1 except that the film thickness of the single organic film was 8 μm.

(Comparative Example 4)
Comparative Example 4 is the same black-coated steel sheet as Example 1 except that the glass transition temperature Tg of the polyester resin was 30 ° C.

(Comparative Example 5)
Comparative Example 5 is the same black coated steel plate as Example 1 except that bifunctional imino benzoguanamine was used instead of trifunctional imino melamine.

(Comparative Example 6)
Comparative Example 6 is the same black coated steel sheet as Example 1 except that hexafunctional melamine-based full alkyl was used instead of trifunctional imino melamine.

(Conventional example 1)
In Conventional Example 1, as shown in FIG. 2, an electrogalvanized layer 13 having an adhesion amount of 20 g / m ² formed on one surface of a steel plate 12, and a chemical conversion treatment solution is applied on the plated layer and heated for 9 seconds. The chemical conversion film 14 shown in Table 2 that does not contain chromium formed by heating so that the ultimate plate temperature is 100 ° C. later, and the number average molecular weight 15000, the glass transition temperature 50 ° C., and the hydroxyl value are on this chemical conversion film. Apply an undercoat containing 15 KOH mg / g and hexafunctional hexamethoxymethylated melamine, rust preventive pigment, etc., and undercoat with a film thickness of 5 μm formed so that the plate temperature reached 170 ° C. after 30 seconds of heating On this film and this undercoat coating film, a top coating composition containing 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 melamine is applied. Was formed by heating so as to be 190 ° C. After heating 40 seconds thickness comprises a top coating film of 15 [mu] m, the total thickness is a conventional coated steel plate of 20 [mu] m.

(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>
The bendability is obtained by subjecting the coated steel sheet 1 to a test piece cut into a size of 60 mm in length and 30 mm in width, and bending the coated steel sheet at room temperature (0T bending according to JIS Z2248-1996). The degree of coating of the film at the top of the bent portion is evaluated by the ERV method. Here, the measurement of ERV (enamel rating value) obtained by the ERV method, as shown in FIG. 3, seals the end face with a frame sealing tape that exposes 10 mm × 10 mm at the top of the bent portion, and makes contact with the electrolyte. This is a value measured with an enamelator, with the area kept constant, at a temperature of 20 to 25 ° C., and 1% by mass of saline solution 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 the anode and the cathode as the C electrode. According to this ERV measurement, the larger the current flows, the more defects exist in the organic film that is an insulator, and the metal of the plating layer is exposed.

Here, when the ERV is 5 mA or more, cracking of the organic film is visually confirmed, and when the contact bending is performed, it is determined that the appearance is impaired and the bending workability is inferior. Evaluation of bending workability 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

<Abrasion resistance>
The variation range ΔL of the L value after the ethanol rubbing test was performed 20 times with a load of 1 kg on the surface of the organic film of each coated steel sheet was evaluated. Evaluation was performed according to the following criteria.
◎: ΔL is 1.5 or less ○: ΔL is more than 1.5 and less than 2.5 ×: ΔL is more than 2.5

<Corrosion resistance>
Each coated steel sheet was sprayed with 5% salt water at 35 ° C. for 8 hours, and then the process of resting for 16 hours was defined as one cycle, and changes in the coating film surface appearance after 3 cycles were evaluated. Evaluation was performed according to the following criteria.
◎: No change on coating film surface ○: White rust generation of less than 10% in area on coating film surface ×: Many white rust generations exceeding 10% on coating film surface

Table 4 shows the evaluation results.

  From Table 4, Examples 1 to 7 have good bending work at the same level as the 2-coated steel sheet 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 5 μm. It can be seen that it has excellent press resistance 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. Nos. 1 to 7 have good bending workability at the same level as the two-coated steel sheet of Conventional Example 2, even though the baking temperature is lower than that of the top coat film of Conventional Example 2 despite the single organic film. It can also be seen that it has press-resistance.

  Furthermore, Comparative Examples 1 to 6, which are outside the scope of the present invention, were inferior in bending workability and press wrinkle resistance.

  According to the present invention, by optimizing a single organic film, a black coated steel sheet that achieves both bending workability and press resistance even when the film thickness is as thin as 0.5 to 5 μm. It is now possible to provide processed products and flat panel panels.

The black coated steel plate of this invention is shown. A conventional 2-coated steel sheet is shown. The schematic diagram for demonstrating ERV method 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;
A single organic film having a film thickness of 0.5 to 5 μm formed on the chemical conversion film by a polyester resin having a hydroxyl value of 10 or more and a glass transition temperature (Tg) of 40 ° C. or more and an imino melamine. A black coated steel sheet characterized by comprising a film.   The black coated steel sheet according to claim 1, wherein a fluctuation range ΔL of L value after an ethanol rubbing test is performed 20 times with a load of 1 kg on the surface of the organic film is 1.5 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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