JP5949656B2 - Black painted steel plate, processed product, and thin TV panel - Google Patents

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 is excellent in appearance and appearance after processing even when the coating film is thin.

  When coated steel sheets are used for applications such as television panels, they are generally subjected to pressing and bending, and are required to have good bending workability and good appearance after pressing. ing. Usually, pre-coated steel sheets (painted steel sheets) use mainly modified polyester resin or epoxy resin for the undercoat on the outer surface side to ensure adhesion to the base steel sheet, corrosion resistance, etc. 2 coats that mainly provide stain resistance, design properties, scratch resistance, ethanol resistance, and hydrochloric acid resistance or alkali resistance barrier properties by using a polyester or acrylic coating on the film. It is common to use a steel plate. Further, a three-coated steel sheet in which an intermediate coating film is formed between the undercoat film and the topcoat film has been developed.

  From the viewpoint of ensuring concealability and corrosion resistance, the conventional two-coated steel sheet has a film thickness of about 5 μm for the undercoat film and a minimum film thickness of 12 μm for the top coat film as disclosed in Patent Document 1, for example. In general, the total film thickness of these coating films is 20 μm or more. However, in order to form a coating film of 20 μm or more, it takes a long time for painting and baking, and the thicker the coating film, the more disadvantageous in terms of manufacturing costs. From the viewpoint of resource recycling, it has been desired to make the coating film thinner.

In order to meet the demand, for example, in Patent Document 2, by adding resin particles in the coating film, even with a film thickness of 10 μm or less, it is excellent in bending workability and appearance after press working and sufficiently A coated steel sheet having a high coating hardness has been proposed.
Patent Document 3 discloses a black coated steel sheet having an excellent appearance after press working even under severer processing conditions than before by increasing the hardness of the organic film, and having a film thickness of the formed organic film of 10 μm or less. Proposed.
Further, in Patent Document 4 and Patent Document 5, by optimizing the organic film, even if the film thickness of the organic film is as thin as 0.5 to 5 μm, the total film thickness is about 20 μm. A black coated steel sheet having good bending workability and press resistance, which is equivalent to that of a coated steel sheet, has been proposed.

JP-A-4-215873 JP 2007-269010 A JP 2010-0665254 A JP 2009-160768 A JP 2009-161796 A

  However, the black coated steel sheets described in Patent Documents 3 to 5 have been desired to be further improved in appearance (in the present invention, the whiteness (L value) is kept low). Further, these black coated steel sheets had no room for improvement because they did not consider the appearance deterioration accompanying the stretching of the film by processing, that is, the fluctuation range of the whiteness (L value).

  The object of the present invention is to solve the above-mentioned problems, and even when the formed coating film is very thin, the black coated steel sheet excellent in appearance and appearance after processing, and the black coating The object is to provide a processed product using a steel plate and a panel for a thin TV.

  As a result of repeated studies to solve the above problems, the present inventors formed a very thin single organic coating film with a film thickness of 0.3 to 2 μm, and contained carbon black in the single organic coating film. By optimizing the amount, it was found that the obtained black coated steel sheet has a high appearance and can secure an excellent appearance even during stretching.

The present invention has been made based on such findings, and the gist thereof is as follows.
(1) A zinc-based plating layer formed on at least one surface of a steel sheet, a chemical conversion film not containing chromium formed on the zinc-based plating layer, and a single organic coating film formed on the chemical conversion film Prepared,
The single organic coating is greater than the carbon black 12 wt%, contains 50% by weight or less, the film thickness is 0.3~2μm der is, the organic resin constituting the said single organic coating film, a hydroxyl value of 2 ~ 20KOHmg / g, a polyester resin having a number average molecular weight of 20000 or more and less than 50000, Tg of 20 to 70 ° C, and the zinc-based plating layer is a blackened Zn-Ni alloy plating layer Painted steel sheet.

(2) The whiteness (L value) of the surface on which the single organic coating film is formed is 25 or less, and the fluctuation range (ΔL) of whiteness during uniaxial stretching of 40% is 2 or less. The black coated steel sheet according to (1) above, which is characterized.

(3) The black coated steel sheet according to (1) or (2), wherein the single organic coating film contains 15% by mass to 50% by mass of carbon black.

( 4 ) A processed product obtained by pressing the black-coated steel sheet according to any one of (1) to ( 3 ) above.

( 5 ) Among the processed products according to ( 4 ), the surface on which the single organic coating film is formed is a convex surface exposed to the outside, and the panel for a thin-screen television.

  According to the present invention, even when the formed coating film is very thin, the appearance of the black coated steel sheet and the appearance after processing can be secured at a high level.

Hereinafter, the configuration of the present invention and the reasons for limitation will be described.
A black-coated steel sheet according to the present invention includes a zinc-based plating layer formed on at least one surface of a steel sheet, a conversion film not containing chromium formed on the zinc-based plating layer, and a single coating formed on the conversion film. With organic coating. Details of each component of the coated steel sheet will be described below.

(Zinc-based plating layer)
The zinc-based plating layer of the present invention is not particularly limited. For example, hot dip galvanizing, electrogalvanizing, alloying hot dip galvanizing, aluminum-zinc alloy plating (for example, hot dip zinc-55 mass% aluminum alloy plating, hot dip zinc-5 mass% aluminum alloy plating), iron-zinc alloy plating And a layer formed by various zinc-based plating such as nickel-zinc alloy plating.
Among these, it is preferable to use a blackened Zn—Ni alloy plating layer from the viewpoint of securing the appearance of the black coated steel sheet. The blackened Zn—Ni alloy plating layer may be formed by a conventional method. For example, black color such as anodic electrolytic treatment, cathodic electrolytic treatment, alternating electrolytic treatment, and anodic oxidation treatment is applied to the Zn—Ni alloy plated layer. It is possible to form it by performing a chemical treatment.

Further, the amount of deposition of the zinc-based plated layer (g / m ²⁾ of, in particular but not limited, it is preferably in the range of per side 5 to 100 g / m ^2. This is because excellent corrosion resistance can be obtained without incurring economic deterioration in the range of 5 to 100 g / m ² . A range of 10 to 70 g / m ² is more preferable.

(Chemical conversion film)
The chemical conversion film of the present invention is formed mainly for improving the adhesion between the zinc-based plating layer and a single organic coating film described later. Although it will not specifically limit if high adhesiveness can be ensured, it shall not contain chromium from a viewpoint of environmental protection.
In addition, the chemical conversion film of this invention is formed by apply | coating the conventionally well-known chemical conversion liquid which does not contain chromium to the plating layer surface, and heat-drying.

Further, the chemical conversion film is not particularly limited as long as it does not contain chromium and can improve the adhesion, but it is more preferable that it can improve not only the adhesion but also the corrosion resistance.
Specifically, silica fine particles are preferably contained from the viewpoint of adhesion and corrosion resistance, and phosphoric acid and / or a phosphoric acid compound are preferably contained 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. About the said phosphoric acid and a phosphoric acid compound, what is necessary is just to contain 1 or more types chosen from orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, these metal salts, a compound, etc., for example.
Furthermore, you may add suitably 1 or more types of additives, 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.

The adhesion amount of the chemical conversion film is not particularly limited, but is preferably in the range of 10 to 500 mg / m ² per side. Adhesion and corrosion resistance can be sufficiently obtained when the amount of chemical conversion film is 10 mg / m ² or more, while the above effect can be obtained without causing economic deterioration if the amount of adhesion is 500 mg / m ² or less. Because it is.

  As for the formation method of the chemical conversion film, for example, the chemical conversion treatment liquid is applied to the surface of the zinc-based plating layer by a roll coater, a curtain flow coater, a dipping pull-up method, etc. It can form by drying so that steel plate temperature may be 80-140 degreeC.

(Single organic coating)
The single organic coating film of the present invention contains carbon black in an amount of more than 12% by mass and 50% by mass or less, and has a film thickness of 0.3-2 μm.
By containing carbon black in an amount in the above range, the amount of carbon black is increased compared to the conventional case, and the whiteness (L value) of the coating film can be sufficiently reduced, resulting in a very thin film thickness of 0.3 to 2 μm. Even if it is a case, it is possible to ensure excellent appearance, and even when the coating film is stretched along with press processing, etc., it is possible to ensure excellent appearance as when there is no processing (after processing) Excellent appearance.

The content of carbon black in the single organic coating film exceeds 12% by mass and is 50% by mass or less because when the content is 12% by mass or less, the amount of carbon black is too small and after sufficient processing On the other hand, if the content exceeds 50% by mass, the coating film becomes brittle.
In addition, the carbon black content is preferably 15% by mass to 50% by mass, and 16% by mass to 50% by mass from the viewpoint of securing the coating film strength while ensuring better appearance after processing. It is more preferable that it is mass%, and it is further more preferable that it is 20 mass%-40 mass%.

-Carbon black The carbon black may be a known one. For example, those having a particle diameter of 10 nm to 800 nm, a pH of 3 to 10, a DBP oil absorption of 50 to 150 (ml / 100 g), and an ash content of less than 1% by mass can be used.
Further, as the surface treatment of carbon black, it is preferable to perform silicon treatment, alkylsilane treatment, titanate treatment, POE-modified silane treatment, silane coupling agent treatment, and the like.

  Commercially available carbon blacks include “color for talker black” (registered trademark, manufactured by Tokai Carbon Co., Ltd.), “SUNBLACK (for color)” (registered trademark, manufactured by Asahi Carbon Co., Ltd.), "Show Black" (registered trademark, manufactured by Showa Cabot Co., Ltd.), "Niteron" "HTC" (registered trademark, manufactured by Nisshin Carbon Co., Ltd.), "Dia Black" (registered trademark, manufactured by Mitsubishi Chemical Corporation) ) And the like can be suitably used.

-Organic resin It does not specifically limit as organic resin used for the said single organic coating film, For example, an acrylic type, a polyester type, an epoxy type, a fluorine type, a polyurethane type etc. are mentioned. From the point which can ensure favorable bending workability, it contains polyester resin .

The polyester resin is a copolymer obtained by heating and 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, neopinthyl glycol, triethylene glycol, glycerin. Pentaerythritol, trimethylolpropane, trimethylolethane and the like can be used.

  Commercially available polyester resins include “Almatex” (registered trademark, manufactured by Mitsui Toatsu Chemical Co., Ltd.), “Alkinol” (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), “Desmophen” (registered) Trademarks, manufactured by Sumitomo Bayer Urethane Co., Ltd.) and “Byron” (registered trademark, manufactured by Toyobo Co., Ltd.) can be suitably used.

  More preferable polyester resins include urethane-modified polyester resins obtained by reacting polyester resins with aliphatic diisocyanate compounds. Specific examples of the aliphatic diisocyanate compound include hexamethylene diisocyanate, trimethylhexamethyl diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, and methylcyclohexane diisocyanate.

Organic resin The polyester resin has a hydroxyl value of 2 to 20 KOHmg / g . If the hydroxyl value is 2 KOHmg / g or more, the crosslinking reaction is sufficient to obtain a sufficient coating film hardness. On the other hand, if the hydroxyl value is 20 KOHmg / g or less, sufficient bending workability is obtained. is there.
Furthermore, the number average molecular weight of the polyester resin is 20000 or more and less than 50000 . If the number average molecular weight is 20000 or more, the molecular weight between crosslinks of the coating film is not too short, and the crosslink density does not become too high. Therefore, elongation does not decrease and bending workability does not deteriorate. This is because the film strength does not become too high and the coating film of the deformed part does not peel off.Furthermore, if the number average molecular weight is 50000 or less, sufficient crosslinking density can be obtained, resulting in sufficient barrier properties. This is because the coating film does not swell.
Furthermore, the glass transition temperature Tg of the said polyester resin is 20-70 degreeC . If the Tg is 20 ° C. or higher, the toughness of the coating will not be reduced, sufficient press workability will be obtained, and the properties such as coating hardness and coating adhesion after processing will not be reduced. On the other hand, if Tg is 70 ° C. or less, sufficient bending workability can be obtained.

-Other fillers In addition, the said single organic coating film can contain a rust preventive pigment and a rust preventive agent according to the objective and use.
Examples of the rust preventive pigment and rust preventive agent include zinc phosphate, aluminum phosphate, aluminum phosphite, molybdate, phosphate molybdate, vanadic acid / phosphoric acid mixed pigment, silica, and calcium silicate. Generally known materials such as adsorbed silica can be used.
Further, it is possible to use color pigments such as zinc white, titanium dioxide, barium sulfate, and zinc together.

  The single organic coating film may further contain a gloss adjusting agent, resin particles, a lubricant, and the like.

Curing agent The single organic coating film may contain a curing agent component for the purpose of imparting stain resistance, abrasion resistance, and the like, and may be a baked cured coating film.
As the curing agent component, an isocyanate compound and / or an amino resin can be used. Moreover, you may use these 2 types or more in mixture.
As the isocyanate compound, an isocyanate compound obtained by a general production method can be used, and among them, it can be used as a one-component paint. Polyisocyanate compounds blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam, oxime are preferred.

  More preferred polyisocyanate compounds include non-yellowing hexamethylene diisocyanate (hereinafter referred to as HDI) and derivatives thereof, tolylene diisocyanate (hereinafter referred to as TDI) and derivatives thereof, 4,4′-diphenylmethane diisocyanate (hereinafter referred to as XDI). , Isophorone diisocyanate (hereinafter IPDI) and its derivatives, trimethylhexamethylene diisocyanate (hereinafter TMDI) and its derivatives, hydrogenated TDI and its derivatives, hydrogenated MDI and its derivatives, hydrogenated XDI and its derivatives, etc. Can do. Furthermore, “Sumijoule” (registered trademark) (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), “Death Module” (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 reaction of urea, benzoguanamine, melamine, and the like with formaldehyde, and those obtained by alkyl etherification with alcohols such as methanol and butanol are used.
Specifically, methylated urea resin, n-butylated benzoguanamine resin, iso-butylated melamine resin and the like can be mentioned. Furthermore, “Cymel” (trade name, manufactured by Mitsui Cyamide Co., Ltd.), “Uban” (registered trademark) (trade name, manufactured by Mitsui Toatsu Chemicals), “Sumimar” (registered trademark) (trade name, Sumitomo) Commercially available amino resins such as “Chemical Industry Co., Ltd.” and “Melan” (registered trademark) (trade name, manufactured by Hitachi Chemical Co., Ltd.) can also be used.

  When the single organic coating film is cured using the curing agent, the blending ratio (weight ratio of solid content) of the organic resin and the curing agent in the single organic coating film is: organic resin / curing agent: 99 / 1 to 60/40, desirably 95/5 to 75/25. It is preferable that the compounding quantity of a hardening | curing agent shall be 0.75-20 mass% in the ratio in a coating-film solid content. If the blending amount of the curing agent is 0.75% by mass or more, the coating film hardness is sufficient, while if it is 20% by mass or less, coating film cracking does not occur during bending.

-Film thickness The film thickness of the said single organic coating film is 0.3-2 micrometers, Preferably, it is 1-2 micrometers. When the film thickness is less than 0.3 μm, not only is the background concealing property insufficient, but the appearance deterioration accompanying the stretching of the coating film by press processing, that is, the fluctuation range of whiteness (L value) becomes large. is there. On the other hand, if the film thickness exceeds 2 μm, not only will it take a long time to form the coating film, but peeling will occur in the coating film at the top of the bending section due to the stress caused by the deformation of the coating film in the bending section. Therefore, it is not preferable.

  In addition, the measurement of the film thickness of the said single organic coating film measured the film thickness of three arbitrary places per visual field using the optical microscope or the electron microscope about the cross section of the steel plate which formed the coating film, and at least 5 visual fields. Thus, the average value of the film thickness measured at a total of 15 or more points is calculated and obtained.

-Formation of a single organic coating film Although the coating method of the coating material for forming the said single organic coating film is not specifically limited, Preferably it is good to apply by roll coater coating.
After the coating is applied, a heat treatment is performed by heating means such as hot air drying, infrared heating, induction heating, etc. to obtain a colored coating film obtained by crosslinking and curing the resin. The heating conditions are 15 to 150 seconds and 200 ° C. (final plate temperature) or lower, and preferably the ultimate plate temperature is 180 ° C. or higher.

・ Whiteness (L value), fluctuation range of whiteness during stretching (ΔL)
The black coated steel sheet of the present invention has a whiteness (L value) of 25 or less on the surface on which the single organic coating film is formed, and a whiteness fluctuation range (ΔL) of 2% at 40% uniaxial stretching is 2. The following is preferable.
This is because if the L value is 25 or less, a sufficient black color can be obtained and the appearance quality is not deteriorated.
Further, if the variation range (ΔL) of whiteness during uniaxial stretching of 40% is 2 or less, a sufficient appearance after processing can be obtained. Here, the variation (ΔL) in whiteness at 40% uniaxial stretching can be calculated by taking the difference in whiteness between before stretching and 40% uniaxial stretching.

(Processed products, flat panel TVs)
The processed product of the present invention is formed by pressing the above-described black-coated steel sheet of the present invention. In the thin TV panel of the present invention, the surface on which the single organic coating film is formed of the processed product is a convex surface that is exposed to the outside.
Since the processed product and the thin TV panel of the present invention use the above-described black-coated steel sheet, the appearance and the appearance after processing are excellent.

Examples of the present invention will be described.
(Samples 1-24)
The zinc-based plating layer shown in Table 1 is provided on both sides of the steel plate, and the chemical conversion treatment solution is applied on the plating layer on one side, and heated so that the ultimate plate temperature becomes 100 ° C. after 10 seconds of heating. A chemical conversion film having the composition shown in Table 2 and containing no formed chromium was formed. Then, after applying a paint for a colored single organic coating film containing a polyester resin, a curing agent (imino group-containing melamine resin), and carbon black as a colored single organic coating film on the chemical conversion film, 20 hours from the start of heating. A colored single organic coating film was formed by performing a heat treatment so that the ultimate plate temperature was 190 ° C. after 2 seconds.
The Tg, number average molecular weight, and hydroxyl value of the polyester resin are shown in Table 3. As the imino group-containing melamine resin, Cymel 327 manufactured by Mitsui Cyamide Co., Ltd. was used. Further, as the carbon black, Niteron # 10 manufactured by Nisshin Carbon Co., Ltd. having a particle size of 41 nm, pH of 7.6, DBP oil absorption of 126 (ml / 100 g), and ash content of 0.12% by mass was used. Table 3 shows the composition, baking temperature (final plate temperature), and film thickness of the colored single organic coating film.
Various performance was investigated about the samples 1-24 of each black coating steel plate obtained by the above-mentioned procedure.

(Evaluation)
Various evaluation was performed about the sample of the black coated steel plate obtained as mentioned above. The evaluation method is shown below.

(1) Appearance: Whiteness (L value)
About each sample, L value was measured using the test piece cut out to the size of 50 mm in length and 50 mm in width based on JIS Z 8729.
Evaluation was performed according to the following criteria, and the results are shown in Table 4.
○: L value ≦ 25
×: L value> 25

(2) Appearance after processing: variation range of whiteness (ΔL) during uniaxial stretching of 40%
For each sample, use a test piece cut into a size of 300 mm in length and 25 mm in width, draw a 5 mm scribed circle on the test piece, and then apply uniaxial tension in the long-side direction with a tensile tester. The whiteness at a site with an elongation of 40% determined by a scribed circle was measured. Thereafter, the fluctuation range (ΔL) of whiteness was calculated according to the following formula.
ΔL = (L value at 40% elongation) − (L value before processing)
The calculated fluctuation range (ΔL) of whiteness is evaluated according to the following criteria, and the results are shown in Table 4.
A: ΔL ≦ 1.0
○: 1 <ΔL ≦ 1.5
Δ: 1.5 <ΔL ≦ 2.0
×: ΔL> 2.0

(3) Bending workability For each sample, in accordance with JIS Z2248-1996, the coated steel plate is a test piece cut into a size of 60 mm in length and 30 mm in width, and the coated steel plate is bent at 180 ° at room temperature. The so-called so-called 0T bend was observed visually at the top of the bent portion.
Evaluation was performed according to the following criteria, and the results are shown in Table 4.
○: No cracking of the organic coating film is observed ×: Cracking of the organic coating film is observed

(4) Substrate hiding property For each sample, the surface of the zinc-based plating layer before the formation of the conversion coating was scratched with a metal pen at the tip, and then the conversion coating and the colored single organic coating were formed. Was observed.
Evaluation was performed according to the following criteria, and the results are shown in Table 4.
○: No flaws are observed ×: Flaws are observed (5) Solvent resistance For each sample, L after performing an ethanol rubbing test on the surface of the organic coating film 20 times with a load of 9.8 N (1 kgf) The value was measured, and the fluctuation range (ΔL) from the L value before the test was calculated. Here, the ethanol rubbing test is a reciprocal sliding while applying a constant load in a state where 5 g of ethanol is soaked in gauze.
Evaluation was performed according to the following criteria, and the results are shown in Table 4.
A: ΔL ≦ 1.5
○: 1.5 <ΔL ≦ 2.5
×: 2.5 ≦ ΔL

The results in Table 4, each sample of the real施例and Reference Examples (1～12,15,16,19～24) are appearance after processing, bending workability, evaluation results of the green body concealing properties and solvent resistance Was well balanced. On the other hand, it was found that each sample (13, 14, 17, 18) of the comparative example showed a result that at least one of the evaluation items was defective.

ADVANTAGE OF THE INVENTION According to this invention, even if the formed coating film is very thin, the black coated steel plate excellent in the external appearance and the external appearance after a process can be provided. As a result, the processed product using the black coated steel plate and the panel for a thin TV are also excellent in appearance and appearance after processing as compared with the conventional product.

Claims (5)

A zinc-based plating layer formed on at least one surface of a steel sheet, a chemical conversion film not containing chromium formed on the zinc-based plating layer, and a single organic coating film formed on the chemical conversion film,
The single organic coating is greater than the carbon black 12 wt%, contains 50% by weight or less, the film thickness is 0.3~2μm der is, the organic resin constituting the said single organic coating film, a hydroxyl value of 2 ~ 20KOHmg / g, a polyester resin having a number average molecular weight of 20000 or more and less than 50000, Tg of 20 to 70 ° C, and the zinc-based plating layer is a blackened Zn-Ni alloy plating layer Painted steel sheet.   The surface on which the single organic coating film is formed has a whiteness (L value) of 25 or less, and a variation range (ΔL) of whiteness at 40% uniaxial stretching is 2 or less. The black coated steel plate according to claim 1.   3. The black coated steel sheet according to claim 1, wherein the single organic coating film contains 15% by mass to 50% by mass of carbon black. A processed product obtained by pressing the black-coated steel sheet according to any one of claims 1 to 3 . The thin TV panel according to claim 4 , wherein the surface on which the single organic coating film is formed is a convex surface exposed to the outside.