JP2009173022A - Coated steel sheet, product, and panel for thin television - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel sheet, a product and a panel for a thin television that implement the same level of satisfactory ease of bending and pressing flaw resistance even with a reduced film thickness of ≤10 μm as existing double-coated steel sheets having a total film thickness of about 20 μm. <P>SOLUTION: A zinc-based plating layer is formed on each side of a steel sheet. A chromium-free chemical conversion coating is formed on each zinc-based plating layer of the steel sheet. A colored single organic coating having a hardness of ≥200 N/mm<SP>2</SP>, an ERV of a bent end subjected to 0T bending conforming to JIS Z 2248-1996 of less than 5 mA, a thickness of ≤10 μm, and a color pigment content of 5 to 15 mass% is formed on the chemical conversion coating on either side of the steel sheet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coated steel sheet, a processed product, and a thin TV panel, and more particularly, to a coated steel sheet that achieves both good bending workability and press resistance. The 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 a TV 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 side to ensure adhesion to the underlying steel sheet, corrosion resistance, etc. 2-coat steel sheet that imparts mainly 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.

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

  The object of the present invention is to optimize the organic film, so that even if the film thickness of the organic film is as thin as 10 μm or less, it is at the same level as a conventional two-coated steel sheet with a total film thickness of about 20 μm. An object of the present invention is to provide a coated steel plate, a processed product, and a thin TV panel having good bending workability and press resistance.

In order to achieve the above object, the gist of the present invention is as follows.
(1) A zinc-based plating layer is formed on both surfaces of a steel plate, a chemical conversion film not containing chromium is formed on the zinc-based plating layer of the steel plate, and the chemical conversion coating on one surface of the steel plate is When the hardness is 200N / mm ² or more and the 0V bending according to JIS Z 2248-1996 is 0T bending, the ERV of the bending top is less than 5mA, and the content of the color pigment with a film thickness of 10μm or less is 5 ～ A coated steel sheet characterized by forming a colored single organic film of 15% by mass.

(2) The coated steel sheet according to (1), wherein the conductive load on the other surface of the steel sheet on which the chemical conversion film is formed is 500 g or less.

(3) Further, the organic resin layer is formed on the chemical conversion film on the other surface of the steel sheet, and the conductive load on the other surface is 500 g or less, (1) or (2) above Painted steel sheet.

(4) The colored single organic film has a variation width (ΔL) of 1 or less when a xylene rubbing test is performed 10 times with a load of 0.5 kg on the surface thereof. The coated steel sheet according to any one of (1) to (3) above.

(5) Using the coated steel sheet according to any one of the above (1) to (4), press working so that the surface of the coated steel sheet having the colored single organic film becomes a convex surface. Processed product formed.

(6) Using the coated steel sheet according to any one of (1) to (4) above, press the coated steel sheet so that the surface having the colored single organic film is a convex surface exposed to the outside. Panel for thin TVs formed by processing.

  According to the present invention, even when the film thickness is as thin as 10 μm or less, the coating has good bending workability and press wrinkle resistance equivalent to the conventional two-coated steel sheet having a total film thickness of about 20 μm. It is now possible to provide steel plates, processed products, and thin TV panels.

The present invention will be specifically described below.
In the coated steel sheet of the present invention, a zinc-based plating layer and a chemical conversion film are sequentially formed on both surfaces of the steel sheet, and a colored single organic film is formed on the chemical conversion film on one surface of the steel sheet.
Details of each part of the coated steel sheet will be described below.

(Zinc-based plating layer)
Examples of the steel sheet on which a zinc-based plating layer serving as a base steel sheet of the coated steel sheet of the present invention is formed include a hot dip galvanized steel sheet, an electrogalvanized steel sheet, an alloyed hot dip galvanized steel sheet, and an aluminum-zinc alloy plated steel sheet (for example, molten steel). Various zinc-based plated steel sheets such as zinc-55% by mass aluminum alloy plated steel sheet, hot dip zinc-5% by mass aluminum alloy plated steel sheet, iron-zinc alloy plated steel sheet, nickel-zinc alloy plated steel sheet can be used.

(Chemical conversion film)
The chemical conversion film formed on the zinc plating layer does not contain chromium from the viewpoint of environmental protection. The chemical conversion film is formed mainly for improving the adhesion between the plating layer and the organic film. Any material that improves adhesion can be used, but it is more preferable to improve not only adhesion but also corrosion resistance. It is preferable to contain silica fine particles from the viewpoint of adhesion and corrosion resistance and to contain phosphoric acid and / or a phosphoric acid compound from the viewpoint of corrosion resistance. As the silica fine particles, either wet silica or dry silica may be used, but it is preferable that silica fine particles having a large effect of improving adhesion, particularly dry silica, be contained. Silica is preferably contained in the chemical conversion film in an amount of 1 to 20% by mass in terms of improving adhesion and corrosion resistance. The phosphoric acid or phosphoric acid compound may contain at least one selected from these metal salts and compounds such as orthophosphoric acid, pyrophosphoric acid, and polyphosphoric acid. Moreover, it is preferable that phosphoric acid or a phosphoric acid compound is contained in the chemical conversion film in an amount of 0.1 to 5% by mass in terms of improving the corrosion resistance. Furthermore, you may add 1 or more types, such as resin, such as an acrylic resin, an epoxy resin, an amine modified epoxy resin, and a polyester resin, and a silane coupling agent.

(Colored single organic film)
The colored single organic film formed on the chemical conversion film has a hardness of 200 N / mm ² or more and an ERV of the bending top when 0T bending according to JIS Z 2248-1996 is less than 5 mA. A colored single organic film having a film thickness of 10 μm or less.

The hardness is the indentation depth (μm) when a test load of 3.0 mN is applied to the colored single organic film on one surface of the coated steel plate using a square tetragonal Vickers indenter. It means a hardness calculated from the indentation depth measured by a testing machine (Fischerscope (registered trademark) HM2000). FIG. 1 and FIG. 2 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 is set to 200 N / mm ² or more to protect the plated surface and maintain a good film appearance even when the die is slid under pressure from the mold during pressing. In other words, it is excellent in press-resisting resistance, is difficult to handle when transporting or handling, and has the hardness required when used in applications such as TV panels.

  The ERV (enamel rating value) is a test piece obtained by cutting the coated steel sheet into a size of 60 mm in length and 30 mm in width, and the coated steel sheet is subjected to close bending at room temperature (0T bending according to JIS Z 2248-1996) ) And the degree of coverage of the colored single film at the top of the tightly bent portion is evaluated by the ERV method. Here, as shown in FIG. 3, the measurement of ERV obtained by the ERV method is such that the top surface of the bent portion is sealed with a frame seal tape exposing 10 mm × 10 mm, and the contact area with the electrolyte is kept constant. It is the value measured with the enamellator which uses 20 mass% and 1 mass% salt solution as electrolyte solution in the state made into. 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 the cathode as a C electrode. According to this ERV measurement, it can be seen that the more current flows, the more defects are present in the organic film, which is an insulator, and the plating metal is exposed. Further, the reason why the ERV is less than 5 mA is that when the current is 5 mA or more, the organic film is visually cracked, and when bent, the appearance is impaired, that is, the bending workability is poor.

In addition, the organic resin used for the colored single organic film is not particularly limited, and examples thereof include acrylic, polyester, epoxy, fluorine, polyurethane, and the like. It is preferable to contain a polyester-type resin from the point to have.
The polyester resin is a copolymer obtained by heat-reacting a polybasic acid component and a polyhydric alcohol by a known method. As the polybasic acid component, for example, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopintyl glycol, and triethylene glycol. Glycerin, pentaerythritol, trimethylolpropane, trimethylolethane and the like can be used. Commercially available polyester resins include “Almatex” (registered trademark) (trade name, manufactured by Mitsui Toatsu Chemical Co., Ltd.), “Alkinol” (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), “Desmophen” (Registered trademark) (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), “Byron” (registered trademark) (trade name, manufactured by Toyobo Co., Ltd.), and the like.
Further, as a more preferable polyester resin, a urethane-modified polyester resin obtained by reacting a polyester resin with an aliphatic diisocyanate compound can be used. Specific examples of the aliphatic diisocyanate compound include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, and methylcyclohexane diisocyanate.

Further, for the purpose of imparting stain resistance, wear resistance, etc., it is possible to add a curing agent component to form a baked cured film. As the curing agent component, an isocyanate compound and / or an amino resin can be used. Moreover, you may mix and use these 2 or more types. As the isocyanate compound, an isocyanate compound obtained by a general production method can be used. Among them, phenol, cresol, aromatic secondary amine, tertiary alcohol, which can be used as a one-component paint, can be used. Polyisocyanate compounds blocked with a blocking agent such as lactam or oxime are preferred.
More preferable polyisocyanate compounds include non-yellowing hexamethylene diisocyanate (hereinafter abbreviated as HDI) and derivatives thereof, tolylene diisocyanate (hereinafter abbreviated as TDI) and derivatives thereof, 4,4′-diphenylmethane diisocyanate (hereinafter referred to as “diisocyanate”). , XDI) and derivatives thereof, isophorone diisocyanate (hereinafter abbreviated as IPDI) and derivatives thereof, trimethylhexamethylene diisocyanate (hereinafter abbreviated as TMDI) and derivatives thereof, hydrogenated TDI and derivatives thereof, hydrogenated MDI and derivatives thereof And hydrogenated XDI and its derivatives. Furthermore, "Sumijoule" (registered trademark) (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), "Desmodule" (registered trademark) (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), "Coronate" (registered trademark) ) (Trade name, manufactured by Nippon Polyurethane Co., Ltd.) can also be used.

As the amino resin that is a curing agent, resins obtained by reacting urea, benzoguanamine, melamine and the like with formaldehyde, and those obtained by alkyl etherification with alcohols such as methanol and butanol can be used. Specific examples include methylated urea resins, n-butylated benzoguanamine resins, and iso-butylated melamine resins. In addition, “Cymel” (trade name, manufactured by Mitsui Ciamid Co., Ltd.), “Uban” (registered trademark) (trade name, manufactured by Mitsui Toatsu Chemicals), “Sumimar” (registered trademark) (trade name, Sumitomo) A commercially available amino resin such as “Chemical Industry Co., Ltd.” and “Melan” (registered trademark) (trade name, manufactured by Hitachi Chemical Co., Ltd.) can also be used.
In the case of curing using a curing agent, the blending ratio (weight ratio of solid content) of the organic resin and the curing agent is organic resin / curing agent: 99/1 to 80/20, desirably 97/3 to 90/10. It is preferable to do this. The blending amount of the curing agent is 0.75 to 15% by weight as a ratio in the solid content of the film. If the blending amount of this curing agent is less than 0.75% by weight, the film hardness becomes insufficient, while if it exceeds 15% by weight, film cracking occurs during bending.

In addition, an appropriate amount of wax can be blended in the colored single organic film depending on the purpose and application. As this wax, natural wax or synthetic wax can be used.
Further, the colored single organic film has a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin diurarate, lead 2-ethyl heisoate, etc. depending on the purpose and application; other antifoaming agent, pigment dispersion Various additives such as an agent and a flow preventive agent can be appropriately blended.
Furthermore, the colored single organic film may contain a particulate acrylic resin, a nylon resin, or the like depending on the purpose and application.

  Further, the colored single organic film can be blended with a rust preventive pigment and a rust preventive agent depending on the purpose and application. Anti-corrosive pigments include zinc phosphate, zinc phosphite, aluminum phosphate, aluminum phosphite, molybdate, phosphate molybdate, vanadic acid / phosphoric acid mixed pigment, silica, and calcium silicate. Generally known rust preventive pigments and rust preventives such as adsorbed type silica can be used.

The number average molecular weight of the organic resin used for the colored single organic film is preferably 20000 to 50000, the glass transition temperature Tg is 20 to 70 ° C., and the hydroxyl value is 2 to 20 KOHmg / g.
If the number average molecular weight is less than 20,000, the molecular weight between crosslinks of the film is too short, and the crosslink density becomes too high. On the other hand, if the number average molecular weight exceeds 50,000, sufficient crosslinking density cannot be obtained, resulting in insufficient barrier properties and swelling of the film.
If the glass transition temperature Tg is less than 20 ° C., the toughness of the film is lowered, sufficient press workability cannot be obtained, and characteristics such as film hardness and film adhesion after processing tend to be lowered. On the other hand, if the glass transition temperature Tg exceeds 70 ° C., sufficient bending workability may not be obtained.
Furthermore, if the hydroxyl value of the polyester resin is less than 2 KOHmg / g, the crosslinking reaction is insufficient, so that sufficient film hardness cannot be obtained. On the other hand, if the hydroxyl value exceeds 20 KOHmg / g, sufficient processability is obtained. This is because it may not be obtained.

  Moreover, the said colored single organic membrane | film | coat needs to contain 5-15 mass% of color pigments in a membrane | film | coat as the name. This is because the subsequent painting process can be omitted, and it is possible to have a background color and a background hiding property. This is because if the content is less than 5%, the amount of pigment is too small and the hiding property of the base color and the background becomes insufficient. On the other hand, if the content exceeds 15%, the amount of pigment becomes excessive and the coating becomes brittle.

  The color pigment is preferably carbon black. This is because if carbon black is used, it can be colored with a small amount of addition, and high concealability can be secured.

The film thickness of the colored single organic film needs to be 10 μm or less. This is because if the thickness exceeds 10 μm, the amount of the film detached from the cut end face at the time of press working increases and may adhere to the product. Furthermore, the film thickness is more preferably 3 to 5 μm. If it is less than 3 μm, the film thickness becomes uneven, and there are few colored pigments, so there is a portion where the color tone is not stable, and the concealment of the base color and base color tends to be insufficient, It is because it is not preferable also in terms of corrosion resistance.
In addition, the film thickness of the said organic film measured the film thickness of arbitrary three places per field using an optical microscope or an electron microscope, and averaged the film thickness measured in 15 or more places in total in at least 5 fields of view. Value.

  The colored single organic film preferably has a variation range (ΔL) of 1 or less when an ethanol rubbing test is performed 10 times with a load of 4.9 N (0.5 kgf) on the surface. The ethanol rubbing test is a test to measure the solvent resistance of the film by reciprocating the colored single organic film under a constant load with 5 g of ethanol soaked in gauze. The brightness (L value) is measured, and the difference becomes the fluctuation range (ΔL). The reason why the fluctuation range (ΔL) of the L value is 1 or less is that when it exceeds 1, the solvent resistance becomes insufficient.

(The other side of the steel plate)
In addition, when the coated steel sheet of the present invention is used as, for example, a panel for a thin TV, the back surface of the coated steel sheet that becomes the inner surface of the pressed panel may have conductivity due to the necessity for welding, electromagnetic shielding, and the like. preferable.
In such a case, by having the above-mentioned chemical conversion film not containing chromium on the other surface of the steel sheet, the steel sheet has corrosion resistance and adhesion similar to those of the conventional chromate film, and also has excellent conductivity. Specifically, the conductive load is preferably 500 g or less from the viewpoint of electromagnetic shielding properties. More preferably, it is 300 g or less. The conductive load is the minimum load with a surface resistance of 10 ⁻⁴ Ω or less.

  For applications where the degree of demand for corrosion resistance is not so high, the other surface can be formed only as a chemical conversion film containing no chromium, and can be provided as a coated steel sheet having particularly excellent electromagnetic shielding properties.

  Furthermore, in the case where only the chemical conversion film not containing chromium is formed on the other surface of the steel sheet, and the application has a high requirement for corrosion resistance, the chemical conversion film not containing chromium formed on the other surface of the steel sheet. However, it is preferable to contain 1 or more types chosen from an epoxy resin, an amine modified epoxy resin, and a polyester resin. Moreover, when these resins are contained, it is preferable to cure using a melamine resin or the like as a curing agent. The total content of the resin and the curing agent in the chemical film is preferably 30 to 50% by mass. When a curing agent is used, the content of the curing agent in the chemical film is preferably 1 to 20% by mass. . Moreover, when the resin is contained in the chemical film, the other components of the chemical film are 1 to 10% by mass of phosphoric acid and / or a phosphoric acid compound and 1 to 10% by mass to improve the corrosion resistance. It is preferable to use inorganic additives such as manganese carbonate, aluminum carbonate, and zinc carbonate.

  Moreover, an organic resin layer can be formed on the chemical conversion film as necessary for applications that require a particularly high degree of corrosion resistance. As an organic resin seed | species of an organic resin layer, an epoxy resin and a polyester resin are preferable. The organic resin layer preferably contains Ca ion-exchanged silica as a rust preventive pigment in order to obtain further excellent corrosion resistance. Moreover, it is preferable that content of the antirust pigment with respect to an organic resin layer shall be 0.1-50 mass%. This is because by making it within this range, the corrosion resistance can be improved without deteriorating the conductivity of the organic resin layer.

Furthermore, it is advantageous for the organic resin layer to contain a heat-absorbing pigment for applications that require a high degree of heat dissipation. Examples of the organic resin species for exhibiting heat dissipation include epoxy resin, acrylic resin, urethane resin, phenol resin, urea resin, and polyester resin. The heat-absorbing pigment is not particularly limited, and a known pigment may be used, but in order to increase the emissivity, carbon black, aniline black, polymethylene dye, trisazo dye amine salt, cyanine dye Or the metal complex, iron oxide, silicon oxide, and magnesium silicate are illustrated. These heat absorbing pigments may be added alone or in combination of two or more.
Furthermore, desired heat dissipation can be obtained by making the emissivity of the organic resin layer containing the said heat absorptive pigment into the range of 0.3-0.8. Here, the emissivity is a value obtained by integrating the spectral reflectance (R) of the surface relative to 1 (100%) of the black body radiation at the same temperature in the wavelength range of 4.5 to 25 μm and integrating it in the wavelength range. It is. The specific amount of the heat-absorbing pigment added to the organic resin layer is preferably 0.1% by mass or more and 20% by mass or less. This is because when the addition amount is 0.1% by mass or more, a sufficient heat absorption effect can be obtained, and when the addition amount is 20% by mass or less, the deterioration of the corrosion resistance of the organic resin layer is prevented.

  In addition, the coated steel sheet of the present invention is used in applications such as electronic devices and home appliances that are pressed so that the surface having the colored single organic film becomes a convex surface and further requires electromagnetic shielding properties. It is suitable for the member made. For example, it is suitable for use in a back panel of a thin TV such as a plasma display panel or a liquid crystal television.

  Moreover, the place mentioned above only showed an example of embodiment of this invention, and can change a various change in a claim.

Examples of the present invention will be described.
(Examples 1-15 and Comparative Examples 1-2)
Galvanized steel sheets with a thickness of 0.5 mm (plating type code: EG), alloyed hot-dip galvanized steel sheets (Fe content: 10 mass%, plating type code: GA), hot-dip galvanized steel sheets for coating Plated steel plate (plating type symbol: GI), hot-dip Zn-Al-plated steel plate (Al content: 4.5 mass%, plating type symbol: GF) and hot-dip Zn-Al-plated steel plate (Al content: 55 mass%, plating type symbol) : GL) was prepared. Table 1 shows the coating amount (g / m ² ) of the plated steel sheet. In addition, the plating adhesion amount and the plating composition of one surface (front surface) and the other surface (back surface) of the steel plate were the same. After degreasing the zinc-based plated steel sheet, the following processing steps (i) and (ii) were performed to prepare a coated steel sheet as a sample. Table 1 shows the coating amount (g / m ² ) and film thickness (μm) of the plated steel sheet.
(I) The chemical conversion treatment for forming the chemical conversion film shown in Table 2 on the back surface after applying and drying a chemical conversion treatment chemical for forming the chemical conversion film shown in Table 1 on the front side with a bar coater A chemical was applied, and then a heat treatment was performed so that the ultimate plate temperature reached 100 ° C. after 10 seconds of heating to form a chemical film on the front and back surfaces having a predetermined thickness. Tables 1 and 3 show the composition and film thickness for each chemical conversion film.
(Ii) Thereafter, as a colored single organic film on the front surface, a paint for a colored single organic film on the front surface (containing polyester resin (base resin), a curing agent shown in Table 1, and carbon black (color pigment)) (See Table 1 for the amount) so that the dry film thickness shown in Table 1 is applied, and then, if necessary, an organic resin paint having the composition shown in Table 2 is applied to the back surface. Heat treatment was performed so that the ultimate plate temperature was 190 ° C. after 2 seconds, and a colored single organic film on the front side or an organic resin layer on the back side was formed.

<Evaluation of the front side>
(1) Hardness As for the hardness, the indentation depth (μm) when a test load of 3.0 mN is applied using the above-mentioned regular square pyramidal indenter is used as an ultra-fine indentation hardness tester (Fischerscope (registered trademark)). ) HM2000), and obtained from the indentation depth.

(2) Bending workability (visual evaluation)
The bending workability is in accordance with JIS Z2248-1996, bending the coated steel sheet into a test piece cut into a size of 60 mm in length and 30 mm in width and bending the coated steel sheet to 180 ° at room temperature. The top of the processed part was visually observed. Evaluation was performed according to the following criteria.
○: No cracking of the organic film is confirmed ×: Cracking of the organic film is confirmed

(3) Bending workability (Evaluation by ERV)
Evaluation by ERV measured ERV by the ERV method mentioned above about the sample which performed 0T bending in said (2). Evaluation was performed according to the following criteria.
◎: Less than 2mA ○: 2mA or more, less than 5mA △: 5mA or more, less than 10mA ×: 10mA or more

(4) Substrate concealment The concealment concealment is the front surface of the plated steel sheet before film formation, after scratching the tip with a metal pen, and performing the above-described processing steps to produce each coated steel sheet, The front side was visually observed. Evaluation was performed according to the following criteria.
○: I do not know the scratch ×: I can clearly see the scratch

(5) Resistance to press wrinkling Damage to the film on the side wall after visual observation of each coated steel sheet after forming a cylindrical cup at a blank diameter of 67mmφ, a punch diameter of 33mmφ, a molding speed of 300mm / s, and a wall surface temperature of 80 ° C Evaluation was performed according to the criteria.
◎: No damage occurred ○: Some damage was observed ×: Many damage occurred

(6) Solvent resistance The ethanol rubbing test was performed 10 times with a load of 4.9 N (0.5 kgf) on the surface of the organic coating on each coated steel sheet, and the fluctuation range (ΔL) of the L value before and after the ethanol rubbing test was measured. And evaluated according to the following criteria.
◎: ΔL is 1 or less ○: ΔL is more than 1 and 2 or less ×: ΔL is more than 2

(7) Corrosion resistance After cutting a test piece (size: 100 × 50 mm) from each of the above samples and tape-sealing the end and back of the test piece, spraying 5% by weight of salt water at 35 ° C. for 8 hours, The process of resting for 16 hours was defined as 1 cycle, and the change in the coating surface appearance after 3 cycles was evaluated. Evaluation was performed according to the following criteria.
◎: No change on the film surface ○: Slight rusting on the film surface ×: Many rusting on the film surface

<Evaluation of the back surface>
(8) Conductivity The surface resistance value of the back surface of each sample 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 probe tip was increased at 20 g / s, and the load value when the surface resistance was 10 ⁻⁴ Ω or less was evaluated as follows.
Load value when surface resistance is 10 ^-4 Ω or less ◎: Average load of 10 point measurement is 300 g or less ○: Average load of 10 point measurement is more than 300 g to 500 g or less △: Average load of 10 point measurement is more than 500 g 700g or less x: Average load of 10 point measurement is over 700g and 960g or less

(9) Heat dissipation With respect to the samples of Examples 14 and 15 and Comparative Examples 1 and 2, the heat dissipation was measured under the following conditions.
Measuring equipment: Far-infrared spectroradiometer JIR-E500, manufactured by JEOL Ltd., measuring temperature: 100 ° C., measuring wavelength: 4.5 to 25 μm, resolution: 8 cm ⁻¹ , integration count: 100 times, other conditions: JIS R1801: Based on 2002, the emissivity was calculated from the measurement results and evaluated according to the following criteria.
◎: 0.5 or more, less than 0.8 ○: 0.3 or more, less than 0.5 △: 0.1 or more, less than 0.3 ×: less than 0.1

Table 5 shows the evaluation results of the above tests.
According to this, the coated steel plates of Examples 1 to 15 all have excellent hardness, base concealability, bending workability, press resistance, solvent resistance, corrosion resistance, and conductivity. In particular, it can be seen that both are superior in bending workability and press warpage resistance as compared with Comparative Examples 1 and 2. In addition, it can be seen that Examples 14 and 15 also have high emissivity and excellent heat dissipation.

  According to the present invention, even when the film thickness is as thin as 10 μm or less, the coating has good bending workability and press wrinkle resistance equivalent to the conventional two-coated steel sheet having a total film thickness of about 20 μm. It is now possible to provide steel plates, processed products, and thin TV panels.

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.

Claims (6)

A zinc-based plating layer is formed on both surfaces of the steel sheet, a conversion film not containing chromium is formed on the zinc-based plating layer of the steel sheet, and the hardness is 200 N on the conversion film on one side of the steel sheet. in / mm ² or more and, JIS Z 2248-1996 bending the top of the ERV when the bending 0T conforming to is less than 5 mA, the film thickness is the content of the following coloring pigment 10 [mu] m 5 to 15 wt% A coated steel sheet characterized by forming a colored single organic film.   The coated steel sheet according to claim 1, wherein the conductive load on the other surface of the steel sheet on which the chemical conversion film is formed is 500 g or less.   Furthermore, the organic resin layer is formed on the chemical conversion film of the other surface of the said steel plate, The electroconductive load of the said other surface is 500 g or less, The coated steel plate of Claim 1 or 2 characterized by the above-mentioned.   The colored single organic film has an L value fluctuation width (ΔL) of 1 or less when an ethanol rubbing test is performed 10 times with a load of 0.5 kg on the surface thereof. The coated steel plate of any one of -3.   A processed product formed by pressing the coated steel sheet according to any one of claims 1 to 4 so that a surface having the colored single organic film of the coated steel sheet becomes a convex surface. .   Using the coated steel sheet according to any one of claims 1 to 4, the surface having the colored single organic film of the coated steel sheet is formed by pressing so as to be a convex surface exposed to the outside. A panel for a flat-screen TV.

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