JP5087761B2 - Pre-coated steel sheet - Google Patents

Description

  The present invention relates to a pre-coated steel sheet that is excellent in workability, weather resistance, aesthetic durability, and the like, which is used as an exterior material for electrical equipment products, an interior / exterior material for construction, and the like.

  Pre-coated steel sheets do not need to be painted after forming, and can be omitted from processing manufacturers and work environments can be improved, so various materials for electrical equipment products and exterior materials such as roofs and walls of buildings, It is used in a wide range of interior materials such as partitions.

  Such pre-coated steel sheets are usually used after being subjected to various processing including 90 ° bending and 180 ° bending by press forming, roll forming or emboss forming, and therefore require excellent workability and coating film durability. Is done. For this reason, as the resin for the coating film used for the precoated steel sheet, a thermosetting polyester resin that forms a cured coating film by baking at 200 ° C. or higher, a fluorine resin that has excellent weather resistance, and the like are used. Yes.

  In recent years, the need for high performance and high functionality for pre-coated steel sheets has increased. In particular, aesthetic durability, that is, adhesion of fungi, algae, etc., floating smoke in the atmosphere, various oily mist, exhaust There is also a demand for measures against deteriorating the aesthetics of the precoated steel sheet due to adhesion of combustion products such as gas, carbon black, and other substances.

  Pre-coated steel sheets with individual functions such as antibacterial function and anti-contamination function have been developed so far, but pre-coated steel sheets that function in combination with other functions have not been developed yet. Is the actual situation.

  The precoated steel sheet with antibacterial function includes those in which a compound containing silver, copper, etc. is dispersed in the coating film. Molds, fungi, and algae on the coating film surface by the antibacterial action of these compounds It suppresses or kills the growth of the plant. On the other hand, the pre-coated steel sheet with anti-contamination function is to keep the coating surface as hydrophilic as possible so that the contaminated components attached to the surface can be washed away with rain water to suppress the deposition of deposits. It is.

  In particular, as a pre-coated steel sheet having antibacterial function and anti-contamination function, it utilizes a method of decomposing organic matter attached by a photocatalyst, and by dispersing a substance having photocatalytic activity in the coating film on the steel sheet surface, The organic substances adhering to the active oxygen produced are decomposed. However, the technology using this photocatalyst decomposes surface deposits such as organic substances adhering to the surface of the steel sheet and at the same time gradually decomposes the coating film itself as a matrix. In addition, there is a problem that wear of the coating film is promoted.

In this regard, conventionally, proposals have been made to use an inorganic material, a fluororesin, or an organic-inorganic composite that is not easily decomposed as a matrix coating film of a photocatalyst (Patent Documents 1 to 3). There is also a proposal for a method (Patent Document 4) in which a photocatalyst layer containing a photocatalyst and a fluororesin wax is formed on at least one surface of a metal plate via a protective film formed of an inorganic paint.
JP 2007-55207 A JP 2006-233073 A JP 2006-192716 A JP 2007-181951 A

  However, with respect to the technique disclosed in Patent Document 1, although a photocatalytically active substance is dispersed in an inorganic coating film, the coating film itself has poor flexibility although it has excellent weather resistance such as discoloration. Therefore, when the coating film is applied to the precoated steel sheet as it is, there is a problem that cracks are easily generated when bending or drawing is performed, and the coating film is peeled off.

  Further, the technology disclosed in Patent Document 2 relates to a steel plate in which a photocatalytically active substance is dispersed in a fluororesin coating film. However, there is a disadvantage that the coating film as a matrix is decomposed by the photocatalyst. This drawback can be solved by increasing the thickness of the coating film, but increasing the film thickness results in poor flexibility, resulting in new problems such as poor workability. End up.

  The technique disclosed in Patent Document 3 relates to a surface-treated metal obtained by dispersing a photocatalytically active substance in a coating film made of an organic-inorganic composite, but compared with the inorganic coating film of Patent Document 1. Although it is slightly excellent in workability, in order to satisfy the level of workability required for the precoated steel sheet, it is necessary to reduce the film thickness, resulting in a problem that the photocatalytic function is lowered.

  Furthermore, the coated metal plate of Patent Document 4 also has a problem that the coating film as a matrix is decomposed by the photocatalyst when this is applied to an exterior material.

  In general, since the photocatalyst film layer has a high refractive index, it tends to exhibit an interference color due to unevenness in the amount of the photocatalytically active substance attached. In particular, the surface of the base substrate to be treated is highly glossy or has a surface roughness. In the case of a small one, there is a problem that processing unevenness and interference color become conspicuous and the aesthetic appearance is impaired.

  As described above, all of the conventional techniques are difficult to apply to pre-coated steel sheets, and the processability and weather resistance required as the characteristics of the pre-coated steel sheets, aesthetic durability using photocatalytic functions, and a coating for a photocatalyst. The film did not satisfy the decomposition resistance of the film, and the countermeasure against interference color due to processing unevenness was not fully considered.

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and a precoated steel sheet having a chemical conversion treatment film and a resin film formed thereon on the surface of the zinc-based plated steel sheet. The pre-coated steel sheet can be obtained by adding a device to the structure of the resin film, that is, by forming a colored resin layer via a primer layer and laminating two predetermined clear film layers on the colored resin layer. An object of the present invention is to provide a precoated steel sheet excellent in various properties such as high weather resistance, aesthetic durability and anti-decomposition performance against a photocatalyst in addition to the required appearance uniformity and workability.

  The inventors can solve the above-mentioned problems of the prior art and propose a new technique according to the following summary configuration as an effective means for realizing the above-described object.

The present invention provides a precoated steel sheet having a chemical conversion film and a resin film formed thereon on at least one surface of a zinc-based plated steel sheet, wherein the resin film is made of a thermosetting resin containing a rust preventive pigment. Contains a primer layer (A), a colored resin layer (B), a clear coating layer (C) having a silicon compound as a main component and a film thickness of 0.2 μm or more, and titanium oxide particles having photocatalytic activity. deposition amount per one surface is clear coating layer is 10mg / m ² ~2000mg / m ² in terms of TiO ₂ and (D), Tona is, the colored resin layer (B), 60 ° specular gloss Is a pre-coated steel sheet characterized by having a surface roughness Ra (center line average roughness) of 0.8 μm or more .

In the present invention, the colored resin layer (B), the weight ratio of polyvinylidene fluoride and acrylic resin 85: 15 to 50: to the main component 50 organosol-based baking type fluororesin, before Symbol click rear coating layer (C) a silicon compound in, it is an acrylic silicone resin, titanium oxide particles of the clear coating layer (D) is a mixture of anatase type crystalline titanium oxide and amorphous titanium oxide This is a more preferable solution.

  According to the precoated steel sheet of the present invention configured as described above, the two types of clear layers (C) having a predetermined thickness on the resin film characteristic of the present invention; in particular, on the colored resin layer (B). ) And (D), the performance such as workability and weather resistance required for the precoated steel sheet is improved. In particular, the clear layer (D) which is the outermost layer exhibits a photocatalytic function, can decompose and clean various organic substances adhering to the surface, and can permanently maintain the aesthetics of the surface. In addition, since the clear layer (C) mainly composed of a silicon compound is provided between the clear layer (D) and the colored resin layer (B), the anti-decomposition performance of the clear layer (D) against the photocatalyst is effective. The pre-coated steel sheet having good processability, weather resistance and aesthetic durability can be obtained by suppressing degradation and degradation of the lower colored resin layer (B) by the photocatalyst. In particular, the appearance uniformity can be improved by using the colored resin layer (B) having a specific glossiness and surface roughness.

  The precoated steel sheet of the present invention has a chemical conversion film and a resin film formed thereon on at least one surface of a zinc-based plated steel sheet, and a primer layer (A), a colored resin layer ( B) and two types of clear layers (C) and (D) are sequentially laminated.

  The zinc-based plated steel sheet used in the present invention can be formed, for example, electrogalvanized steel sheet, hot-dip galvanized steel sheet, hot-dip zinc-5 mass% aluminum alloy-plated steel sheet, hot-dip zinc-55 mass% aluminum alloy-plated steel sheet, etc. Is the target. The thickness of the plated steel sheet is not particularly limited, but is preferably about 0.2 to 1.6 mm from the viewpoint of forming.

  In the present invention, a chemical conversion coating is first formed on one or both surfaces of the galvanized steel sheet prior to the formation of the resin coating (primer layer A) characteristic of the present invention. This chemical conversion film is formed to strengthen the adhesion between the zinc-based plated steel sheet and the primer layer (A) and to provide corrosion resistance.

  Examples of the chemical conversion coating suitably used in the present invention include, for example, a phosphate treatment coating, a chromate treatment coating, a silica-containing chromate treatment coating, a chromate-free rust inhibitor made of various metal oxides, or an organic resin alone or In order to improve the adhesion and corrosion resistance, it is preferable that the composite is composed of a thin film containing an organic resin and a metal oxide, a phosphoric acid compound and / or chromic acid. In this case, as the organic resin, it is desirable to use a water-dispersible resin, for example, an acrylic resin or a urethane resin dispersed with an emulsifier.

Of these chemical conversion coating components, chromic acid acts as a binder for obtaining adhesion between the chemical conversion coating and the zinc-based plating layer, while the organic resin is a chemical conversion coating and a primer layer described later. Acts to improve adhesion to (A). The chromium content in the chemical conversion film is preferably 20 mg / m ² or more in terms of metal chromium. This is because when the chromium content is less than 20 mg / m ² , sufficient corrosion resistance as a precoated steel sheet cannot be obtained.

Further, the chromate-free rust preventive agent used as the chemical conversion coating component is silicic acid and / or silicic acid compound, calcium or calcium compound, zirconic acid and / or zirconic acid compound, vanadic acid and / or vanadic acid compound, molybdic acid. It is preferable that it contains 1 or more types of a compound, phosphoric acid, and / or a phosphoric acid type compound, and content is 0.3-3.0 g / m < ² >. The reason for making the amount of this chromate-free rust inhibitor 0.3 to 3.0 g / m ² is 0.3
If it is less than g / m ² , the corrosion resistance and adhesion as a pre-coated steel sheet cannot be obtained, and if it exceeds 3.0 g / m ² , workability will be reduced. Further, as the binder, for example, a water dispersible acrylic resin or urethane resin may be used.

  In the precoated steel sheet of the present invention, the primer layer (A) is first formed as the first layer on the surface of the chemical conversion film formed on at least one surface of the zinc-based plated steel sheet as described above. This primer layer (A) is made of a thermosetting resin containing a rust preventive pigment, and includes a chemical conversion treatment film and an upper film (colored resin layer (B), clear film layer (C), (D)) described later. It is a layer formed to obtain adhesion and further corrosion resistance.

  The layer thickness of the primer layer (A) is preferably 2 μm or more and 10 μm or less. If the layer thickness is less than 2 μm, sufficient rust preventive properties cannot be obtained. This is not preferable because it causes a decrease.

  Although it does not specifically limit as a thermosetting resin which becomes the main body of a primer layer (A), It is preferable to use 1 type, or 2 or more types, such as a polyester-type resin and an epoxy-type resin, As a polyester-type resin, bisphenol is used. Examples include A-added polyester resins. In addition, some epoxy resins are partially replaced with urethane resins, phenol resins, amino resins, etc., and epoxy compounds comprising bisphenols such as bisphenol A, bisphenol F, bisphenol AD, and epihalohydrin or β-methyl epihalohydrin. Or a copolymer thereof. Furthermore, monocarboxylic acid or dicarboxylic acid modified products, mono, di or polyalcohol modified products, mono or diamine modified products, mono, di or polyphenol modified products of these epoxy compounds can also be used as epoxy resins.

  The reason for limiting the main component of the primer layer (A) to the thermosetting resin is that when a room temperature drying resin or a thermoplastic resin is used, an upper film (colored resin layer (B), clear film layer (C ), (D)), there is a problem that deformation or deterioration accompanying softening occurs depending on the baking temperature, and strong adhesion to the upper film cannot be obtained.

  A polyisocyanate compound and / or an amino resin can be used as the curing agent for the primer layer (A). As the polyisocyanate compound, hexamethylene diisocyanate (hereinafter referred to as HDI) and derivatives thereof obtained by a general production method, tolylene diisocyanate (hereinafter referred to as TDI) and derivatives thereof 4.4′-diphenylmethane diisocyanate (hereinafter referred to as MDI) and Its compounds, xylylene diisocyanate (hereinafter referred to as XDI) and derivatives thereof, isophorone diisocyanate (hereinafter referred to as IPDI) and derivatives thereof, trimethylhexamethylene diisocyanate (hereinafter referred to as TMDI) and derivatives thereof, hydrogenated TDI and derivatives thereof, hydrogenated MDI and Compounds such as derivatives thereof, hydrogenated XDI and derivatives thereof can be used. In particular, it is preferable to use a polyisocyanate compound blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam, or oxime, which can be used as a one-pack type paint. This blocked polyisocyanate compound can be stored in a single liquid and can be easily used as a paint.

  Examples of the amino resin used for the curing agent include 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. Specific examples include methylated urea resins, n-butylated benzoguanamine resins, methylated melamine resins, n-butylated melamine resins, and iso-butylated melamine resins.

  The blending ratio of the curing agent in the primer layer (A) is preferably 9 to 50% by mass in the resin solid content, and if it is less than 9% by mass, the coating film hardness is insufficient. This is because the processability is insufficient when the content exceeds mass%.

  Furthermore, a curing catalyst such as p-toluenesulfonic acid, tin octoate, or dibutyltin dilaurate may be used for the primer layer (A) depending on the purpose and application. Further, extender pigments such as calcium carbonate, kaolin, and clay, color pigments such as titanium oxide, dial, mica, carbon black, and aluminum powder, and various additives such as antifoaming agents and leveling agents may be added.

  And in this invention, in the primer layer (A), when performing a forming process as a pre-coated steel sheet, or when used outdoors for a long period of time, coating blistering or plating from a cut edge portion or a coating scratch portion In order to prevent corrosion, 5 mass% to 50 mass% of an antirust pigment is included. If the content of the rust preventive pigment is less than 5% by mass, there is no effect of improving the corrosion resistance, and if it exceeds 50% by mass, the workability deteriorates as the flexibility of the coating film decreases, which is not preferable. .

  As rust preventive pigments, chromate, silica pigment, phosphite pigment, calcium compound, aluminum oxide, zirconic acid or / and zirconic acid compound, vanadic acid or / and vanadic acid compound, molybdate compound, It is preferable to use one or a mixture of two or more of phosphoric acid and / or phosphoric acid compounds. Among them, it is preferable to use chromate from the viewpoint of further improving rust prevention.

  Next, the colored resin layer (B) will be described. The colored resin layer (B) is formed on the primer layer (A) described above. As the resin of this colored resin (B), a resin excellent in adhesion with the primer layer (A) and capable of continuous coating in a pre-coated steel sheet manufacturing facility, for example, a polyester resin, a fluorine resin, an acrylic resin, urethane A resin based on resin or a composite of these components is advantageously suitable.

  In particular, in the present invention, in order to improve the workability of the pre-coated steel sheet and the durability (resistance to weathering) outdoors, as a main resin of the colored resin layer (B), polyvinylidene fluoride and acrylic resin are in a mass ratio. It is preferable to use an organosol-type baking type fluororesin blended at a ratio of 85:15 to 50:50, more preferably 85:15 to 75:25. This is because, by using an organosol-type baking type fluororesin that is a mixture of polyvinylidene fluoride and an acrylic resin, it is possible to suppress crystallization of polyvinylidene fluoride, which is a crystalline resin, and durability (resistance to weathering). ) And processability can be improved, and the adhesion between the primer layer (A) as the lower layer of the colored resin layer (B) and the clear coating layer (C) as the upper layer can be improved. Because it can.

  When the amount of the polyvinylidene fluoride of the organosol-based baking type fluororesin exceeds 85% by mass, the coating property is lowered and the crystallization of the polyvinylidene fluoride is advanced, so that the workability is lowered. On the other hand, if this amount is less than 50% by mass, the durability, particularly weather resistance, of polyvinylidene fluoride is greatly reduced, which is not preferable.

  As the acrylic resin contained in the organosol-based baking type fluororesin, a thermoplastic acrylic resin and a thermosetting acrylic resin can be used alone or in combination. As thermoplastic acrylic resins, from the viewpoint of compatibility with polyvinylidene fluoride, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylic One or two or more monomer polymers such as acid amyl, or a copolymer of these monomers with acrylic acid, styrene, or the like can be used. On the other hand, the thermosetting acrylic resin is composed of an acrylic resin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a glycidyl group or an isocyanate group, and a curing agent such as an alkylated melamine, a polyol or a polyamide. Can be used.

  The colored resin layer (B) controls the color tone of the appearance of the pre-coated steel sheet, and titanium oxide, petal, mica, carbon black, fired black, titanium yellow, yellow iron oxide, phthalocyanine blue are included in the coating film. And various color pigments such as phthalocyanine green. This color pigment is contained in an amount of about 15% by mass to 60% by mass. The reason is that the target hue can be formed as a stable and concealed coating film within the range of this content. In addition, additives such as a gloss adjusting agent such as synthetic silica, an antifoaming agent for improving coating workability, a surface adjusting agent, and an anti-scratch agent for a coating film can be blended as necessary.

In the present invention, in order to more effectively reduce and suppress the generation of interference colors caused by unevenness in the amount of adhesion of the clear coating layer (D), which is a photocatalytic coating layer, 60 of the colored resin coating layer (B) is used. ° Specular gloss (JIS Z 8471) of 20% or less and surface roughness Ra (centerline average roughness: JIS B 0601)) of 0.8 μm or more , preferably glossiness of 2% or more, 16% or less, and the surface roughness Ra is 1.2 μm or more and 3.0 μm or less. This is because when the surface condition (glossiness and surface roughness Ra) of the resin coating layer (B) is out of the above range, the clear coating layer (D) has an interference color due to coating unevenness such as roping and chatter marks. This may be caused by streaks, which may reduce aesthetics.
The gloss of the colored resin coating layer (B) can be adjusted by adding a matting agent, and the surface roughness Ra is an inorganic substance such as a metal oxide and / or a polyamide resin in the coating film. It can be adjusted by adding resin fine particles such as acrylic resin.

  The colored resin layer (B) preferably has a layer thickness of 8 to 25 μm. If the layer thickness is less than 8 μm, the color tone becomes unstable as the concealing property decreases, and sufficient durability, workability and corrosion resistance of the processed part cannot be obtained. On the other hand, if the layer thickness exceeds 25 μm, film defects such as the occurrence of cracks (foaming) are likely to occur, and further, cracks occur due to an increase in internal strain during processing, which leads to a decrease in performance.

  The colored resin layer (B) is applied to the primer layer (A) surface of the galvanized steel sheet by a normal method for producing a precoated steel sheet, for example, a chemical solution diluted with an organic solvent by a roll coater or a curtain coater. It can be formed continuously by baking at a temperature of about 230 to 270 ° C.

  Next, the clear coating layer (C) will be described. The clear coating layer (C) is formed on the colored resin layer (B) and improves the adhesion between the clear coating layer (D) as the upper layer and the colored resin layer (B) as the lower layer. Has a function. Further, the clear coating layer (C) functions to suppress the colored resin layer (B) from being decomposed and deteriorated over time by the photocatalytic action of the titanium oxide fine particles blended in the clear coating layer (D). Also have.

  The main component of the clear coating layer (C) is a silicon compound such as acrylic silicon resin, trialkoxysilane and its condensate, acrylic silicate and its condensate, organohydroxysilane and its condensate, or a composition thereof and silica. It is composed of a composite composition, and it is particularly preferable to use an acrylic silicon resin. As the acrylic silicone resin, it is possible to use a composite, copolymerized or cross-linked with another cross-linking agent, or a cross-linked one using an acrylate or silicon-containing cross-linking agent. it can.

  The acrylate component of the acrylic silicone resin functions to improve the flexibility of the clear coating layer (C) and to improve the adhesion with the colored resin layer (B) as the lower layer. The acrylate component includes alkyl-containing acrylic monomers and oligomers or polymers such as methyl acrylate and methyl methacrylate, hydroxyl-containing acrylic monomers and oligomers or polymers such as 2-hydroxyethyl acrylate, and ethylenic unsaturated compounds such as acrylic acid. One or more of carboxylic acid monomers, oligomers or polymers, acrylic monomers, oligomers or polymers containing amide groups or glycidyl groups can be used.

  On the other hand, the silicon component of the acrylic silicone resin strengthens the adhesion with the clear coating layer (D) formed on the upper layer, and the clear coating layer (C) itself is caused by the photocatalyst contained in the clear coating layer (D). It has a function of suppressing decomposition and deterioration.

  Examples of the silicon component include alkoxysilane compounds such as methyltriethoxysilane, dimethyldiethoxysilane, phenylmethyldiethoxysilane, and γ-glycidoxypropyltrimethoxysilane, hydrolysates thereof, or one of condensates thereof. Two or more types can be used.

  The layer thickness of the clear coating layer (C) is preferably 0.2 μm or more, more preferably 0.5 μm or more. On the other hand, the upper limit thickness of the clear coating layer (C) is not particularly defined. However, when the composition itself is poor in flexibility, it is preferably a thinner film, particularly 1 μm or less, in order to suppress deterioration of workability. As a result, good processability can be obtained regardless of the type of the composition.

  Various additives such as silica fine particles, a dispersant, a coupling agent, or an ultraviolet absorber may be added to the clear coating layer (C) within a range that does not change the color tone. As a method for forming the clear coating layer (C) by a continuous coating line, there is a method in which a solution diluted in an organic solvent is applied by a curtain coater, roll coater or die coater and baked. In addition, when using an acrylic silicon resin as a main component of a clear membrane | film | coat layer (C), it is preferable to bake at the temperature of about 150-200 degreeC after application | coating.

  Next, the clear coating layer (D) will be described. The clear coating layer (D) is formed on the clear coating layer (C). This clear coating layer (D) has a new function for pre-coated steel sheets, that is, when the pre-coated steel sheets are used as interior / exterior materials, it decomposes and cleans various organic substances adhering to the surface, It has an effective function to maintain aesthetics permanently. This function is exhibited by the titanium oxide fine particles having photocatalytic activity contained in the coating layer (D).

  In the present invention, it is preferable to use anatase type crystalline titanium oxide as the titanium oxide fine particles having a high level of photocatalytic activity. As anatase type crystalline titanium oxide, those having a particle diameter of about 0.001 to 0.2 μm are optimal in terms of paintability and photocatalytic properties. As such anatase type crystalline titanium oxide, for example, Ishihara Sangyo ( ST-01, ST-21, ST-30L, etc. manufactured by Co., Ltd. are mentioned.

  In general, anatase type crystalline titanium oxide exhibits activity with respect to light having a short wavelength in the ultraviolet region, and therefore, when a precoated steel sheet is used as an exterior member, it can exhibit photocatalytic properties by ultraviolet rays contained in sunlight. it can. On the other hand, when a pre-coated steel sheet is used as an interior member, it is preferable to use a visible light responsive anatase type crystalline titanium oxide. As this visible light responsive titanium oxide, an oxide doped with nitrogen, sulfur or carbon is used. Titanium, oxygen-deficient titanium oxide, dye-sensitized titanium oxide, metal-supported titanium oxide, or the like can be used.

  Amorphous titanium oxide may be blended in the clear coating layer (D) together with the anatase type crystalline titanium oxide as described above. In this case, the mixing ratio of the anatase type crystalline titanium oxide and the amorphous titanium oxide is preferably 10:90 to 80:20 by mass ratio. Amorphous titanium oxide has the effect of improving the stability of the coating chemical and improving the action of the film as a binder, and the workability and durability of the film.

The clear coating layer (D) is titanium oxide particles deposited per galvanized steel sheet one side is 10mg / m ² ~2000mg / m ² in terms of TiO ₂ amount, and more preferably 50mg / m ² ~2000mg / a m ^2. When the adhesion amount is less than 10 mg / m ² , the photocatalytic properties are greatly deteriorated or a uniform film cannot be formed. On the other hand, when it exceeds 2000 mg / m ² , various forming processes are applied as a pre-coated steel sheet. When this occurs, cracks and peeling occur in the film, and in some cases, the cracks may propagate to the lower colored resin layer (B).

  The layer thickness of the clear coating layer (D) is determined according to the amount of the titanium oxide particles attached, and is preferably 0.05 to 5.0 μm, more preferably 0.1 to 2.0 μm. The reason for this range is that when the layer thickness is less than 0.05 μm, sufficient photocatalytic properties cannot be obtained. On the other hand, when the layer thickness exceeds 5.0 μm, defects such as voids and cracks occur in the film, resulting in a decrease in workability. This is to invite. The layer thickness of the clear coating layer (D) is more preferably 0.1 to 1.0 μm, and 0.1 to 0.5 μm in order to ensure suppression of interference colors due to uneven adhesion amount.

  In addition to the fine titanium oxide particles, the clear coating layer (D) includes one or more of metal oxides and compounds such as silicon, aluminum and zirconium, or phosphoric acid compounds as binders and additives for film formation. An inorganic compound may be included.

  To this clear film layer (D), an antibacterial agent, an adsorbent such as activated carbon or zeolite may be added as long as the color tone is not changed, and the addition of these can further enhance aesthetic durability such as antibacterial properties. .

  As a method of forming the clear coating layer (D) on the clear coating layer (C) which is the lower layer in the continuous coating line, water or an organic solvent is used on the clear coating layer (C) forming surface of the galvanized steel sheet. There is a method in which a diluted chemical solution is applied by a roll coater or a die coater and baked at a temperature of about 180 to 250 ° C.

  As described above, the precoated steel sheet of the present invention is formed by laminating the above-described resin films composed of the layers (A) to (D) via a chemical conversion film on one surface or both surfaces of a zinc-based plated steel sheet. Yes, by obtaining the above-mentioned various properties required as a pre-coated steel sheet by the interaction of each layer (A) to (D), and in particular by providing two types of clear coating layers (C) and (D) The aesthetic durability by the photocatalyst and the decomposition resistance against the photocatalyst can be obtained.

  Each layer (A) to (D) as the resin film is formed on at least one surface of the plated steel sheet, but the same film layer (A) to (D) is also formed on the other surface (back surface). In addition, a so-called service coat of 1 coat and 1 bake used in a normal pre-coated steel sheet may be formed on the back surface after the chemical conversion treatment.

The invention is illustrated by the following examples.
( Reference Example 1)
In this reference example 1, a zinc-plated steel sheet is subjected to a chemical conversion treatment with a silica-containing coating-type chromate treatment liquid so that the adhesion amount is 40 mg / m ² in terms of metal chromium, and a chemical conversion treatment film having a thickness of 0.35 mm A hot dip galvanized steel sheet (I) (plating adhesion amount: 130 g / m ² on one side) was used.
To this hot-dip galvanized steel sheet (I), a melamine curable polyester resin paint (a-1) containing about 20% by mass of strontium chromate as a rust preventive pigment (Precolor Primer FX-2 (BASF Coatings Japan Co., Ltd.) ))) Was applied with a bar coater so that the dry film thickness was 5 μm, and baked at about 230 ° C. for 60 seconds to form a primer layer (A).

  Next, on this primer layer (A), an organosol baking type fluororesin (pre-color No. 8800 (BASF Coatings Japan) (with a mixing ratio of polyvinylidene fluoride and acrylic resin of 80:20 by mass ratio) Co., Ltd.)) and paint (b-1) mixed with titanium oxide and calcined black as a color pigment were applied with a bar coater to a dry film thickness of 21 μm and then baked at about 240 ° C. for 60 seconds. Then, a colored resin layer (B) having a 60 ° specular glossiness of 25% and a surface roughness Ra of 0.3 μm was formed.

  Next, on this colored resin layer (B), an acrylic silicon resin having a weight average molecular weight of about 20000 comprising n-butyl acrylate as an acrylic component, methyl methacrylate, and γ-methacryloxypropyltriethoxysilane as a silicon component. The solution (c-1) was applied with a bar coater so that the dry film thickness was 2 μm, and dried at about 150 ° C. for 15 seconds to form a clear coating layer (C).

Further, on the clear coating layer (C), an anatase-type titanium oxide (ST-21 manufactured by Ishihara Sangyo Co., Ltd.) is added to an amorphous titanium oxide dispersion (Nippon Parkerizing Co., Ltd.) so that the solid content ratio is 20% by mass. the Ltd. PTI-5600) to the mixed chemical solution (d-1), the amount deposited was coated with a bar coater so 200 mg / ^{m 2} in terms of TiO _2, a dry film thickness of 0.2 [mu] m, about 220 A clear layer (D) was formed by drying at ° C for 15 seconds to produce a precoated steel sheet ( Reference Example 1) of the present invention.

(Inventive Examples 1-6, Reference Examples 2-9, Comparative Examples 1 to 10)
The precoat of Reference Example 1 except that the galvanized steel sheet, primer layer (A), colored resin layer (B), clear coating layer (C) and clear coating layer (D) were changed to various conditions shown in Table 1. In the same manner as the steel sheets, precoated steel sheets of the present invention examples (Inventive Examples 1 to 6 ) , precoated steel sheets of Reference Examples (Reference Examples 2 to 9), and precoated steel sheets of Comparative Examples (Comparative Examples 1 to 10) were produced.

In addition, the type (II) of the zinc-based plated steel sheet in Table 1 is a 0.35 mm thick 55% aluminum-zinc alloy-plated steel sheet (plating adhesion amount) that has been subjected to the same chemical conversion treatment as the type (I). Is one side 80 g / m ² ), and the type (a-2) of the primer layer (A) is a polyester resin paint obtained by removing the melamine resin as a curing agent from (a-1).
In addition, the type (b-2) of the colored resin layer (B) is an organosol-based baking type fluororesin (Rheoflow C (manufactured by Nippon Fine Coating Co., Ltd.) in which polyvinylidene fluoride and acrylic resin are in a mass ratio of 55:45. ), A fluorine resin paint in which titanium oxide and calcined black are mixed as a color pigment), and type (b-3) is a melamine curable polyester resin paint in which titanium oxide and carbon black are mixed as a color pigment, The types (b-4), (b-5), and (b-6) are fluororesin paints obtained by mixing the type (b-1) with various types of baked silica for surface adjustment. ) 60 ° specular gloss 6%, surface roughness Ra 2.4 μm, type (b-5) 60 ° specular gloss 22%, surface roughness Ra 2.3 μm, type (b -6) 60 ° specular gloss 16%, surface roughness It is 0.5μm in a.
Also, the type (c-2) of the clear coating layer (C) is an organosilica sol obtained by dissolving methyltriethoxysilane in a solvent, and the type (c-3) is an acrylic resin emulsion paint that does not contain a silicon compound. It is.
Further, the type (d-2) of the clear coating layer (D) is anatase type crystalline titanium oxide (ST-21 manufactured by Ishihara Sangyo Co., Ltd.) dispersed in the organosilica sol so that the solid content ratio is 40% by mass. Type (d-3) is an organosilica sol that does not contain titanium oxide particles having photocatalytic activity.

All the pre-coated steel plates manufactured according to the above (Invention Examples 1 to 6 , Reference Examples 2 to 9, and Comparative Examples 1 to 10) were subjected to the following various tests, and the results are shown in Table 1.
(Test and evaluation method)
(1) Appearance uniformity The appearance of the obtained precoated steel sheet was evaluated visually. The evaluation criteria were as follows.
◎: No interference color and good appearance ○: Interference color is slightly generated, but there is no occurrence of unevenness, discoloration, etc. Appearance is good △: Unevenness, discoloration (interference color, etc.) occurs slightly ×: Unevenness, Discoloration (interference color, etc.) clearly occurs

(2) Bending workability In the room (20 ° C), the same two steel plates are stacked, and the upper end portions of these steel plates are sandwiched between pre-coated steel plates that are bent at 180 °. The state of the film (presence of cracks) was evaluated visually. The evaluation criteria were as follows.
◎: Cracks are not recognized ○: Cracks are slightly observed △: Cracks are clearly generated ×: Cracks are severely generated

(3) Bending adhesion In the room (20 ° C), the same two steel plates are stacked, and the upper ends of these steel plates are sandwiched between pre-coated steel plates that are bent at 180 °. After applying the adhesive tape (manufactured by Nichiban), it was peeled off, and the area of the peeled film was evaluated (the smaller the peeled film area, the better the adhesion of the paint processing part). The evaluation criteria were as follows.
○: Peeling rate less than 5% △: Peeling rate 5% or more and less than 30% ×: Peeling rate 30% or more

(4) Weather resistance An accelerated weather resistance test was conducted for 1000 hours under the following conditions to evaluate the appearance. The evaluation criteria were as follows.
A: Almost no change in color tone or gloss.
○: Slight changes in color tone and gloss are recognized.
Δ: Color tone and gloss change are clearly recognized.
X: Significant changes in color tone and gloss such as severe chalking.
<Accelerated weather resistance test conditions>
Number of sunshine carbon arc lamps: 1 (no filter used)
Power supply voltage: Single-phase AC 180-230V
Off-Irradiation cycle: 60 minutes-60 minutes Irradiation conditions Temperature indicated by the black panel thermometer: 63 ± 3%
Relative humidity: 50 ± 5%
Light-off conditions Air temperature: 30 ° C
Relative humidity: 98% or more Cooling water temperature on the back of the test piece: Approx. 7 ° C
Injection of water onto the surface of the test piece: Not performed Irradiance received on the surface of the test piece: 285 ± 50 W / m ^{2 for} 300 to 700 mm

(5) Aesthetic durability
Pre-coated steel sheets of the present invention example and comparative example cut to 200 mm × 300 mm square,
(A) The wall of the building adjacent to the road (about 1m above the ground)
(B) Hut wall adjacent to paddy field (contacts the ground)
In addition, each was left standing for 6 months in a vertically standing state, and the subsequent appearance was evaluated. The evaluation criteria were as follows.
○: There is almost no deposit on the surface, and the aesthetics are maintained. △: The surface is slightly covered with deposits, and the initial aesthetic is almost lost. ×: Vigorous deposits that cannot be removed by washing (algae and other organisms, Carbon etc.), and the initial aesthetic disappears

From the results shown in Table 1, in Examples 1 to 6 of the present invention, excellent performance was obtained in all evaluation tests. On the other hand, in Comparative Example 1, since the clear film layer (C) was not formed, deterioration was observed in all of the bending adhesion, weather resistance and aesthetic durability.
Moreover, in Comparative Example 2, since the film thickness of the clear coating layer (C) is thinner than the range of the present invention, degradation and degradation by the photocatalyst cannot be suppressed, and degradation is observed in weather resistance and aesthetic durability. It was.
Furthermore, in Comparative Example 3, since the clear coating layer (D) was not formed, the effect of the photocatalyst was not obtained, and deterioration in aesthetic durability was recognized.
In Comparative Example 4, since the clear coating layer (D) does not contain titanium oxide, the aesthetic durability effect by the photocatalyst cannot be exhibited. In Comparative Example 5, the clear coating layer (C) contains a silicon compound. Therefore, decomposition and deterioration by the photocatalyst could not be suppressed.
In Comparative Example 6, since the primer layer (A) was not formed, the adhesion of the coating film was greatly reduced, and the peeling of the coating film or the occurrence of rust was observed in each item below workability. In Comparative Example 7, since the rust preventive pigment was not included in the primer layer (A), generation of rust was recognized in the aesthetic durability test. Further, in Comparative Example 8, since the primer layer (A) was not thermosetting, deterioration of workability, adhesion, and coating film peeling and rust generation in the aesthetic durability test were observed.
In Comparative Example 9, since the titanium oxide content of the clear coating layer (D) is small, the effect of the photocatalyst cannot be obtained, and deterioration in aesthetic durability is observed. On the other hand, in Comparative Example 10, the clear coating layer (D) Since the content of titanium oxide was too large, slight discoloration was observed and cracks occurred in the film when bent at 180 °.

  The pre-coated steel sheet of the present invention is excellent in workability, weather resistance, aesthetics and the like, and of course, it is suitable as an exterior material for electrical equipment products and an interior / exterior material for buildings. It can be used for required applications.

Claims (4)

In a pre-coated steel sheet having a chemical conversion treatment film and a resin film formed thereon on at least one surface of a zinc-based plated steel sheet,
The resin film is
A primer layer (A) made of a thermosetting resin containing a rust preventive pigment;
A colored resin layer (B);
A clear coating layer (C) containing a silicon compound as a main component and having a film thickness of 0.2 μm or more;
Containing titanium oxide particles having a photocatalytic activity, the amount of deposition per one side is clear coating layer is 10mg / m ² ~2000mg / m ² in terms of TiO ₂ and (D),
Tona is,
The pre-coated steel sheet, wherein the colored resin layer (B) has a 60 ° specular gloss of 20% or less and a surface roughness of Ra (center line average roughness) of 0.8 μm or more .   2. The colored resin layer (B) is mainly composed of an organosol-baked fluororesin having a mass ratio of polyvinylidene fluoride and acrylic resin of 85:15 to 50:50. Pre-coated steel sheet. The precoated steel sheet according to claim 1 or 2 , wherein the silicon compound in the clear coating layer (C) is an acrylic silicon resin. The precoat according to any one of claims 1 to 3 , wherein the titanium oxide particles in the clear coating layer (D) are made of a mixture of anatase type crystalline titanium oxide and amorphous titanium oxide. steel sheet.