JP2007138191A - Coated steel sheet, member and panel for thin television - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel sheet provided with corrosion resistance and workability, and having excellent electromagnetic wave shielding properties even if a coated layer is thickened. <P>SOLUTION: The coated steel sheet is characterized in that both the sides of a steel sheet comprising, by mass, ≤30 ppm C, 0.06 to 0.15% Mn, ≤0.015% P and 0.025 to 0.06% Ti, and the balance Fe with inevitable impurities are each provided with an alloyed hot dip galvanizing layer, and both the sides of the plated steel sheet are provided with at least two layers of chromium-free films, wherein the total film thickness in one side is 5 to 18 μm, and the total film thickness in the other side is 0.3 to 1.0 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coated steel plate excellent in corrosion resistance, workability and electromagnetic wave shielding properties, a member using the same, and a thin TV panel.

  In recent years, the development of electronics has rapidly developed, and electromagnetic noise can cause malfunctions of other electronic devices, and can cause electromagnetic interference on television receivers due to the spread of personal computers and the like in general households. Has increased. Furthermore, it has been suggested that electromagnetic waves adversely affect the human body, and regulations on electromagnetic wave shielding are becoming more and more stringent. In addition, noise shielding has become more difficult than ever due to the increase in size of home appliances, and it is necessary to improve electromagnetic shielding technology.

  Conventionally, as an electromagnetic shielding technique, a pre-coated steel sheet (Patent Document 1) having a surface roughness and a coating thickness of a predetermined base steel sheet, a conductive surface-treated steel sheet (Patent Document 2) in which a resin is dispersed on a chromate film, and A surface-treated metal plate (Patent Document 3) having a coating film having a predetermined thermal emissivity on one surface and a coating film having a total film thickness of 3 μm or less on the other surface is disclosed.

  Further, thin TVs such as plasma display panels and liquid crystal televisions, for which demand has been increasing in recent years, require more advanced electromagnetic shielding technology for panels used on the back. This is because it is easy to create a gap in which electromagnetic waves leak due to an increase in screw spacing due to an increase in size, which is a disadvantageous direction for electromagnetic wave shielding, and these disclosed techniques have become insufficient. Yes.

  Originally, electromagnetic wave noise does not cause a problem because it does not leak as noise to the outside if the casing including the source is surrounded by a conductive material such as Fe and is grounded. That is, there is no problem as long as the inner surface of the housing is an unpainted steel plate or galvanized steel plate and has conductivity. However, many steel plates having a non-conductive film are used not only on the outer surface of the housing but also on the inner surface in order to impart corrosion resistance and design properties. Therefore, the steel plate surface used for the inner surface of the casing that requires electrical conductivity is subjected to chemical conversion treatment such as thin film chromate, and the resin composition (coating material) subjected to the chemical conversion treatment or containing a post-conductive substance. ) Has been used.

  However, in recent years, chromate-free steel plates that do not use Cr have become mainstream from the viewpoint of the environment. At the same film thickness, the corrosion resistance of the chromate-free chemical conversion treatment film is lower than that of chromate, so it is necessary to make the film thicker than conventional chromate treatment, both with chemical treatment only and with resin coating after chemical treatment. Electromagnetic shielding properties are becoming insufficient.

Further, a thin TV needs to be processed into a large panel, and a high degree of workability is required.
JP 63-7878 JP 63-114635 A JP 2004-243310 A

  An object of the present invention is to provide a coated steel sheet that has corrosion resistance and workability and is excellent in electromagnetic wave shielding properties even when the film thickness is increased.

  Another object of the present invention is to provide a member having a corrosion resistance and workability, and having excellent electromagnetic wave shielding properties even when the film thickness is increased, and a thin TV panel.

Means of the present invention for solving the above problems are as follows.
(1) C: 30 mass ppm or less, Mn: 0.06 to 0.15 mass%, P: 0.015 mass% or less, Ti: 0.025 to 0.06 mass%, alloyed on both surfaces of the steel sheet consisting of the remainder Fe and inevitable impurities There are at least two layers of chrome-free coating on both sides of a galvanized steel sheet with a hot dip galvanized layer, the total coating thickness on one side is 5 to 18 μm, and the total coating thickness on the other side is 0.3 to 1.0 μm A coated steel sheet characterized by

  (2) C: 30 mass ppm or less, Mn: 0.06 to 0.15 mass%, P: 0.015 mass% or less, Ti: 0.025 to 0.06 mass%, Nb: 0.005 to 0.02 mass%, balance Fe and inevitable impurities A steel plate comprising at least two layers of coatings not containing chromium on both sides of a plated steel plate having an alloyed hot-dip galvanized layer on both sides of the steel plate, the total thickness of one side being 5 to 18 μm, A coated steel sheet having a total film thickness of 0.3 to 1.0 μm.

  (3) C: 30 mass ppm or less, Mn: 0.06 to 0.15 mass%, P: 0.015 mass% or less, Ti: 0.025 to 0.06 mass%, B: 1 to 15 mass ppm, balance Fe and inevitable impurities The coated steel sheet having the alloyed hot dip galvanized layer on both surfaces of the steel sheet has at least two layers of films not containing chromium, the total film thickness on one surface is 5 to 18 μm, A coated steel sheet having a total film thickness of 0.3 to 1.0 μm.

  (4) C: 30 mass ppm or less, Mn: 0.06 to 0.15 mass%, P: 0.015 mass% or less, Ti: 0.025 to 0.06 mass%, Nb: 0.005 to 0.02 mass%, B: 1 to 15 mass ppm And having at least two layers of coatings not containing chromium on both sides of the plated steel plate having the alloyed hot-dip galvanized layer on both sides of the steel plate composed of the remaining Fe and inevitable impurities, and the total thickness of one side is 5 to A coated steel sheet having a thickness of 18 μm and a total film thickness on the other side of 0.3 to 1.0 μm.

  (5) The coated steel sheet according to any one of (1) to (4), wherein the surface roughness of the plated steel sheet is an arithmetic average roughness Ra defined by JIS B 0601-1994 of 0.6 to 1.3 μm. .

  (6) The coated steel sheet according to any one of (1) to (5), wherein the film on the one surface is composed of a chemical conversion film, an undercoat film, and an overcoat film in order from the plating layer side.

  (7) The coated steel sheet according to (6), wherein the top coat film contains a wax having a melting point of 70 to 140 ° C.

  (8) The lower layer film containing silica particles and phosphoric acid and / or a phosphoric acid compound on the plating layer side, and the upper layer containing Ca ion-exchanged silica and phosphoric acid compound on the lower layer film. The coated steel sheet according to any one of (1) to (7), comprising a film.

  (9) The coated steel sheet according to (8), wherein the film thickness of the lower layer film is 0.01 to 0.3 μm, and the film thickness of the upper layer film is 0.2 to 0.8 μm.

  (10) A member using the coated steel sheet of any one of (1) to (9) in whole or in part.

  (11) A thin panel for a television set using the coated steel sheet of any one of (1) to (9).

  ADVANTAGE OF THE INVENTION According to this invention, the coated steel plate excellent in corrosion resistance, workability, and electromagnetic wave shielding property can be obtained. Moreover, according to this invention, by using the said coated steel plate for the whole or one part, members, such as household appliances which need electromagnetic wave shielding property in addition to corrosion resistance and workability, can be provided. Furthermore, according to the present invention, by using the above-described coated steel plate, it is possible to provide a thin TV panel used on the back surface of a thin TV such as a plasma display panel or a liquid crystal TV that has recently been enlarged.

  The present invention will be described in detail below. First, the reason for limiting the component composition of the steel sheet will be described.

  As TV is increased in size, high workability is required for the rear panel of TV, and the composition of steel components must be optimized from the viewpoint of workability. Moreover, it is necessary to optimize the composition of steel components from the viewpoint of alloying after galvanizing.

C:
In order to improve elongation and r value, which are important in terms of workability, it is better that the amount of C is small. When the amount of C increases, a large amount of carbide forming elements such as Ti is required to fix this as a carbide, and not only the steel strength increases due to the generated carbide (precipitate) and the workability deteriorates, When the plating layer is alloyed by adding a large amount of Ti or the like, there is a problem that the Fe content is increased, the adhesion is deteriorated and the streaky appearance is uneven, and the surface appearance is deteriorated. Therefore, the amount of C is limited to 30 mass ppm or less.

  Mn: When the amount of Mn increases, the elongation and the r value are slightly lowered, and the workability is lowered. Therefore, Mn is limited to 0.15% by mass or less. Moreover, in order to prevent hot brittleness of steel, it is necessary to contain Mn 0.06 mass% or more. It is preferable to set it to 0.005 mass% or more.

  P: When the amount of P increases, it segregates at the grain boundary and lowers the elongation characteristic, so it is limited to 0.015% by mass or less.

Ti:
Ti forms TiC and TiN, detoxifies C and N, and has a function of improving elongation and r value. For that purpose, Ti needs to contain 0.025 mass% or more. If Ti is added in an amount exceeding 0.06% by mass, the Fe content tends to increase when the plating layer is alloyed, making it difficult to control the desired Fe content, and streaky appearance unevenness occurs due to Ti. There are problems such as easy to do. Therefore, Ti is 0.025 to 0.06 mass%.

  Furthermore, in addition to the above chemical components, one or more of the following chemical components may be added as necessary.

Nb:
Nb is a carbide-forming element, and may be added to precipitate solid solution C as NbC and render it harmless. The addition amount is suitably 0.005 to 0.02% by mass in view of the effect and cost.

B:
B segregates at the grain boundary and strengthens it, so that 1 mass ppm or more may be added. If the amount of B exceeds 15 mass ppm, the wettability at the time of hot dip galvanization is lowered, so 15 mass ppm or less is preferable.

  In the present invention, hot dip galvanizing is applied to a steel plate composed of the above-described chemical components, the remaining Fe and unavoidable impurities, and then heated to alloy the plated layer to form an alloyed hot dip galvanized layer on both surfaces of the steel plate. The alloyed hot-dip galvanized layer has a large number of fine irregularities generated on the surface during the alloying process. When a film not containing chromium is formed on the alloyed hot-dip galvanized layer and pressed from the upper surface of the film, a good electromagnetic wave shielding property is manifested by the large number of fine irregularities becoming conduction points.

Conventionally, it is known that when an alloyed hot-dip galvanized film has a film thickness of 5 μm or more, chips called enamel hair are easily generated during shearing. Since enamel hair causes push creases during processing, it is desirable that enamel hair is less generated. There is a correlation that enamel hair tends to occur when the amount of Γ layer formed at the steel plate / plating interface increases. In addition, when the coating amount is large, or when the iron content of the plating layer is high, the amount of Γ layer is likely to increase. Therefore, when a film of 5 μm or more is formed, the coating amount is 45 g / m ² or less (per side) And the iron content of the plating layer is preferably 11% by mass or less. Furthermore, the plating adhesion amount is preferably 40 g / m ² or less, and the iron content is preferably 10% by mass or less.

The lower limit of the plating adhesion amount is not particularly limited, but about 25 g / m ² or more is advantageous from the viewpoint that the adhesion amount can be controlled stably. If the iron content is low, uneven alloying is likely to occur, and a large number of fine irregularities are not stably formed, so 7.5% by mass or more is preferable.

  Al in the plating layer has an effect of suppressing alloying, suppresses a rapid increase in iron content, and further suppresses the formation of a Γ layer. If it is less than that, even if the iron content is 11% by mass or less, a large number of Γ layers are formed, and the possibility of enamel hair generation increases. When Al increases, it takes time for alloying, so 0.60% by mass or less is preferable.

For alloyed hot dip galvanized coatings with a film thickness of less than 5 μm, the plating coverage is 25-60 g / m ² (per side), the iron content is 8-13% by mass, and the Al content is 0.1-0.6% by mass. It is preferable that

  If the surface roughness of the above-mentioned alloyed hot-dip galvanized steel sheet is large, the corrosion resistance tends to deteriorate, and if it is small, the electromagnetic shielding properties are disadvantageous. From such a viewpoint, the surface roughness of the galvannealed steel sheet is preferably such that the arithmetic average roughness Ra defined in JIS B 0601-1994 is 0.6 to 1.3 μm. After alloying the plating layer, when the temper rolling is performed, the above-mentioned roughness can be easily adjusted by appropriately adjusting the temper rolling conditions such as the surface roughness of the rolling roll.

  In the present invention, the plated steel sheet having the alloyed hot-dip galvanized layer described above has at least two layers of films not containing chromium, the total thickness of one surface is 5 to 18 μm, and the other surface It is essential that the total film thickness is 0.3 to 1.0 μm.

  The reason why the film does not contain chromium is to cope with the environment. In addition, the coated steel sheet of the present invention is often used as an external member that touches the human hand or eye on one side, such as the back panel of a plasma display panel. The characteristics are required. Therefore, it has two or more coating films and requires a total coating thickness of 5 μm or more. Since enamel hair tends to be generated when the coating film thickness is increased, the upper limit is 18 μm. More preferably, it is 15 μm or less.

  Further, this one surface is preferably formed by three layers of a chemical conversion treatment film from the viewpoint of coating film adhesion, and an undercoat film and an upper coating film provided thereon from the viewpoint of corrosion resistance.

  The chemical conversion coating is formed mainly to improve the adhesion between the plated steel sheet and the coating film, and any substance that improves the adhesion is not a problem. It is preferable to contain fine particles, particularly dry silica. As other components, a metal salt compound, a resin, a silane coupling agent, or the like may be added.

  The undercoat coating film mainly contributes to the improvement of corrosion resistance, and is preferably formed by applying a known undercoat coating composition mainly composed of polyester and baking it. Although not particularly restricted, in order to obtain good corrosion resistance, it is preferable to contain a rust preventive pigment such as Ca ion-exchanged silica. The coating thickness is preferably 1 to 6 μm from the viewpoint of corrosion resistance.

  The top coating film is preferably formed by applying a known top coating composition containing a polyester resin as a main component and baking it. In order to improve the workability of the overhang portion and not cause wrinkles due to sliding during processing, it is preferable to add wax. As the wax species, polyethylene or microwax may be used, and those having a softening point of 70 to 140 ° C. are preferably contained. If the softening point of the wax is less than 70 ° C., the wax may be softened during coil storage or when used as a back panel. On the other hand, if the temperature exceeds 140 ° C., the effect of improving the slidability during pressing is reduced. In addition, if the amount of wax added in the coating film is less than 0.4% by mass, the effect of improving the slidability is not sufficient, and if it exceeds 2.0% by mass, the effect approaches a saturated state and is disadvantageous in terms of cost. -2.0 mass% is preferable. Further, as the top coat film on this surface, titanium oxide or carbon black for coloring, resin beads or aluminum pieces for appearance (design), etc. may be used as appropriate. The coating thickness is preferably 3 to 15 μm in view of uniformity of appearance and resistance to wrinkles.

  Further, from the viewpoint of electromagnetic shielding, it is essential that the film thickness on the other surface be 0.3 to 1.0 μm. Conventionally, the electromagnetic wave shielding property has been evaluated by the resistance value of the steel sheet surface, that is, the conductivity. In this application, as described later, the electromagnetic wave shielding property is directly measured by measuring the intensity of electromagnetic waves leaking from the housing. Evaluated. As a result, it was found that the evaluation of conductivity is insufficient for the evaluation of electromagnetic shielding properties. That is, it was found that the electromagnetic wave shielding property changed even below the measurement limit of conductivity. As a result, the film thickness on the other surface is essential to be 0.3 to 1.0 μm, and more preferably 0.8 μm or less.

  The coating film on the other side is preferably a two-layer coating film so that it is a thin film and has good corrosion resistance. The lower layer preferably contains fine silica particles for adhesion and corrosion resistance and phosphoric acid and / or a phosphoric acid compound for corrosion resistance. The phosphoric acid and phosphoric acid compound contained in the lower layer may contain one or more selected from these metal salts and compounds such as orthophosphoric acid, pyrophosphoric acid, and polyphosphoric acid. As the lower layer silica fine particles, either wet silica or dry silica may be used. The upper layer preferably has an organic resin film such as an epoxy resin containing Ca ion exchange silica for corrosion resistance.

  The film thickness of the lower layer film is preferably 0.01 to 0.3 μm in order to ensure adhesion and corrosion resistance. The thickness of the upper film is preferably 0.2 to 0.8 μm from the viewpoint of corrosion resistance.

  The formation method of each said membrane | film | coat is not specifically limited. It can be formed by applying a chemical conversion treatment solution, paint or chemical solution having the above film component to a plated steel sheet by a method such as roll coater coating or curtain flow coating, followed by heating.

(Preparation of painted plate)
The base steel sheet shown in Table 1 is a 0.5mm thick alloyed hot dip galvanized steel sheet, and electrogalvanized steel sheet and hot dip galvanized steel sheet as comparative materials. Manufactured. Hereinafter, all mass% is described as%.

Front side treatment:
If necessary, a chemical conversion treatment solution was applied, heated and dried so that the maximum plate temperature reached 100 ° C., and a chemical conversion treatment film shown in Table 2 was formed. On top of that, after applying an undercoat made of polyester resin to which the anticorrosive pigment shown in Table 3 was added to a predetermined dry film thickness, heat treatment was performed so that the maximum plate temperature reached 200 ° C after 30 seconds. It was. Furthermore, a top coating composed of a polyester resin to which carbon black, titanium oxide and the wax shown in Table 6 are added (partially no wax added) is applied to the upper layer so that the maximum plate temperature reaches 230 ° C. after 60 seconds. Heat treatment was performed.

Back side treatment:
Following the application of the undercoat paint on the front side, apply a predetermined amount of chemical solution for the lower layer to the back side and heat-treat so that the maximum plate temperature reaches 200 ° C after 30 seconds. Thus, a lower layer coating on the back surface having the composition shown in Table 4 was obtained. Following the application of the top coat on the front side, the upper layer paint is applied to the upper layer on the lower side, and heat treatment is performed so that the maximum plate temperature reaches 230 ° C after 60 seconds. Along with the formation, an upper layer film made of an epoxy resin to which a rust preventive pigment shown in Table 5 was added was obtained.

  The workability of the coated steel plate produced above was evaluated. Moreover, each evaluation of the generation | occurrence | production degree (enamel hair resistance), corrosion resistance, wrinkle resistance, and the conductivity of a back surface, electromagnetic wave shielding property, and corrosion resistance was performed. The evaluation method is described below.

(1) Workability A test piece was punched into 100 mmφ, and a truncated cone was formed with a punch diameter of 50 mmφ, a punch shoulder R: 4 mm, a die diameter: 70 mmφ, a die shoulder R: 4 mm, and a wrinkle holding pressure of 5 tons. The molding height at break was evaluated.
(Molding height at break)
16mm or more: ○
Over 14mm and less than 16mm: △
14mm or less: ×

(2) Front surface performance evaluation (2-1) Enamel hair A 100 mm wide test piece cooled to 0 ° C. with a hydraulic shearing machine at room temperature (20 ° C.) so that the front side coating film becomes the bottom burr. Was sheared. Shearing was performed 5 times under the same conditions, and each end of the lower burr was peeled off with tape. The total of the five peel lengths was evaluated as the enamel hair generation length as follows.
(Enamel hair generation length)
10mm or less: ○
Over 10mm and less than 30mm: △
30mm or more: ×

(2-2) Corrosion resistance
After cross-cutting a 50 x 80 mm test piece and conducting a salt spray test in accordance with the neutral salt spray test (JIS Z 2371-2000) for 24 hours, measure the maximum value of the rust outflow width as follows: Evaluated.
(Maximum rust outflow width)
0.3mm or less: ○
More than 0.3mm and 0.5mm or less: △
0.5mm or more: ×

(2-3) Scratch resistance
Using a rubbing tester made by Taihei Rika Kogyo Co., Ltd. on a 50 x 150 mm test piece, applying a load of 500 g to an area of about 10 mmφ through gauze, measuring the number of sliding times until the plating layer is exposed, the following It was evaluated as follows.
(Number of sliding)
More than 500 round trips: ○
More than 300 round trips and less than 500 round trips:
300 round trips or less: ×

(3) Performance evaluation of back surface (3-1) Conductivity The surface resistance was measured using a low resistance measuring device (Loresta GP: manufactured by Mitsubishi Chemical Corporation: ESP probe). At that time, the load applied to the tip of the probe was increased at 20 g / s, and the evaluation was made based on the load when the surface resistance was 1 × 10 ⁻⁴ Ω or less.
○: Average load for 10-point measurement is 350 g or less △: Average load for 10-point measurement is over 350 g and 700 g or less ×: Average load for 10-point measurement exceeds 700 g

(3-2) Electromagnetic wave shielding property As shown in FIG. 1, in an Al housing 3 having an Al plate 2 on one side, a flange 5 having a width of 20 mm on one side, and an opening of 100 × 100 × 100 mm. A 20MHz digital transmitter 4 is built in, and various coated steel plates (140 × 140mm) 1 are put on the opening so that the back surface 1b is the bottom surface and the gasket 6 installed on the flange 5 is brought into contact with the opening. 4 Kgf), 20 MHz to 1 GHz electromagnetic wave noise leaking to the outside from the mating surface of the gasket 6 and the coated steel plate 1 was amplified by the preamplifier 8 and then measured using the spectrum analyzer 9. The receiving antenna 7 is 50 mm from the housing flange, and a gasket 6 having a thickness of 1 mm is used between the flange 5 and the coated steel plate 1. The gasket 6 is a urethane sponge wound with conductive cloth (fiber plated with copper and nickel). Moreover, as evaluation of electromagnetic wave shielding property, it evaluated using the maximum noise intensity | strength. The maximum noise intensity with an original plate as plated is 40 dB, and 50 dB when a non-conductive coating film is applied to 5 μm, and the evaluation of electromagnetic shielding properties is as follows.
(Maximum noise intensity)
43 dB or less: ◎
43dB over 45dB: ○
More than 45dB and less than 47dB: △
Over 47 dB: ×

(3-3) Corrosion resistance
Four sides of a 50 × 80 mm test piece were sealed, and the flat plate portion was evaluated by the salt spray test described above. The white rust generation area ratio after performing the salt spray test for 96 hours was determined and evaluated as follows.
(White rust occurrence rate)
5% or less: ○
5% to 20% or less: △
Over 20%: ×

  Tables 6 and 7 show the configurations and evaluation results of the test coated steel sheets.

  All the coated steel sheets of the present invention have good workability, corrosion resistance, and electromagnetic shielding properties. On the other hand, the coated steel sheet outside the scope of the present invention is inferior in at least one of workability, corrosion resistance, and electromagnetic shielding properties.

Among the coated steel sheets of the present invention, the coating amount of the plating film on the front surface is 45 g / m ² or less, the iron content of the plating layer is 11% or less, and the Al content of the plating layer is 0.20% or more. Less generated and excellent in enamel hair resistance.

  The coated steel sheet of the present invention can be used for members such as home appliances that require electromagnetic shielding properties in addition to corrosion resistance and workability.

  Furthermore, the coated steel sheet of the present invention can be used for a thin TV panel used on the back of a thin TV such as a plasma display panel or a liquid crystal TV, which has been increasing in size in recent years.

It is a schematic diagram of the leakage noise measuring device for evaluating electromagnetic shielding properties.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coated steel plate 1b Back surface 2 Al plate 3 Al housing 4 Digital transmitter 5 Flange 6 Gasket 7 Antenna 8 Preamplifier 9 Spectrum analyzer

Claims (11)

C: 30 mass ppm or less, Mn: 0.06 to 0.15 mass%, P: 0.015 mass% or less, Ti: 0.025 to 0.06 mass%, alloyed hot dip galvanized on both surfaces of steel plate consisting of the remainder Fe and inevitable impurities It has at least two layers of coatings not containing chromium on both sides of a plated steel sheet having a layer, the total coating thickness on one side is 5 to 18 μm, and the total coating thickness on the other side is 0.3 to 1.0 μm Painted steel sheet characterized by Steel sheet containing C: 30 mass ppm or less, Mn: 0.06-0.15 mass%, P: 0.015 mass% or less, Ti: 0.025-0.06 mass%, Nb: 0.005-0.02 mass%, and remaining Fe and inevitable impurities The coated steel sheet having the alloyed hot-dip galvanized layer on both sides has at least two layers of films not containing chromium, the total film thickness on one side is 5 to 18 μm, and the total film thickness on the other side Is a coated steel sheet characterized by being 0.3 to 1.0 μm. Steel sheet containing C: 30 mass ppm or less, Mn: 0.06-0.15 mass%, P: 0.015 mass% or less, Ti: 0.025-0.06 mass%, B: 1-15 mass ppm, the balance being Fe and inevitable impurities The coated steel sheet having the alloyed hot-dip galvanized layer on both sides has at least two layers of films not containing chromium, the total film thickness on one side is 5 to 18 μm, and the total film thickness on the other side Is a coated steel sheet characterized by being 0.3 to 1.0 μm. C: 30 mass ppm or less, Mn: 0.06-0.15 mass%, P: 0.015 mass% or less, Ti: 0.025-0.06 mass%, Nb: 0.005-0.02 mass%, B: 1-15 mass ppm, the balance Featuring at least two layers of coatings not containing chromium on both sides of a plated steel plate having an alloyed hot-dip galvanized layer on both sides of a steel plate made of Fe and inevitable impurities, the total thickness of one side being 5-18 μm The coated steel sheet is characterized in that the total film thickness on the other surface is 0.3 to 1.0 μm. The coated steel sheet according to any one of claims 1 to 4, wherein the surface roughness of the plated steel sheet has an arithmetic average roughness Ra defined by JIS B 0601-1994 of 0.6 to 1.3 µm. The coated steel sheet according to any one of claims 1 to 5, wherein the film on the one surface comprises a chemical conversion film, an undercoat film, and an overcoat film in order from the plating layer side. The coated steel sheet according to claim 6, wherein the top coat film contains a wax having a melting point of 70 to 140 ° C. The film on the other surface comprises a lower layer film containing silica particles and phosphoric acid and / or a phosphoric acid compound on the plating layer side, and an upper layer film containing Ca ion-exchanged silica and a phosphoric acid compound on the lower layer film. The coated steel sheet according to any one of claims 1 to 7, characterized in that 9. The coated steel sheet according to claim 8, wherein the lower layer film has a thickness of 0.01 to 0.3 [mu] m, and the upper layer film has a thickness of 0.2 to 0.8 [mu] m. A member using the coated steel sheet according to any one of claims 1 to 9 in whole or in part. A panel for a thin-screen television, wherein the coated steel plate according to any one of claims 1 to 9 is used.

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