Precoated steel plate excellent in workability, weatherability, and photocatalyst activity and its production

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a precoated steel sheet having excellent processability, weather resistance and photocatalytic activity, and a method for producing the same.

【0002】

[Conventional technology]

TiO₂ Photocatalysts such as are activated by light irradiation and are organic substances, NO._X , SO_XIt has the effect of decomposing such things. Utilizing this effect, anatase-type TiO₂ It has been studied to impart photocatalytic activity to a coated steel sheet by providing a coating film containing particles and silica on the surface of a base material. When organic substances are used in the base coating film of this type of coated steel sheet, active oxygen (O) generated by the photocatalytic reaction is used.₂^-, OH, etc.) decomposes the organic coating film, and there is a concern that the coating film may peel off due to chalking. Therefore, an inorganic material is generally used as the base resin (see JP-A-7-13272, JP-A-8-164334, WO96 / 29375, etc.). The organic coating film may be decomposed by a photocatalytic reaction, but the decomposition of the organic coating film is suppressed when a relatively stable fluororesin is used as a base. Therefore, anatase-type TiO based on fluororesin₂ A coating film to which particles are added has been proposed (Japanese Unexamined Patent Publication No. 7-171408). This coating film is relatively excellent in processability because the base resin is organic. Further, in Japanese Patent Application Laid-Open No. 10-225658, anatase-type TiO is mainly used for silica-organosilane-based paints.₂ A photocatalytic pre-coated steel sheet on which an organic / inorganic composite coating film to which particles are added is introduced.

【0003】

[Problems to be Solved by the Invention]

TiO₂ The inorganic coating film to which the photocatalytic activity is imparted by the addition of the above is inferior in processability, cracks are generated by bending or the like, and the coating film is easily peeled off from the surface of the steel sheet. Therefore, in applications such as building materials and home appliances that require bending, photocatalytic activity must be imparted by a post coat that forms a coating film after processing. However, since postcoats have low productivity, precoating that can reduce manufacturing costs is required, but inorganic precoated steel sheets that fully satisfy the workability required for applications such as building materials and home appliances have been developed. Not.

【0004】

On the other hand, the organic coated steel sheet using a fluorine-based resin in order to increase the resistance to decomposition by active oxygen generated by the photocatalytic reaction has not sufficiently satisfied the weather resistance required for building materials and the like. For example, TiO₂ TiO by coating other inorganic substances around the particles₂ How to prevent direct contact between particles and organic coating, TiO₂ Decomposition of the organic coating film is suppressed by a method such as reducing the amount of particles blended, but TiO is used by either method.₂ The photocatalytic activity of the particles decreases. A coated steel sheet on which an organic / inorganic composite coating film to which photocatalytic activity is imparted is inferior in processability as in the case of an inorganic coated steel sheet. For example, even when the coating film is thinned to a film thickness of about 1 μm, 10T cannot be cleared in the T-bending tape peeling test, and the characteristics required for photocatalytic pre-coated steel sheets (specifically, in the T-bending tape peeling test). 2T or less) is not obtained.

【0005】

[Means for solving problems]

The present invention has been devised to solve such a problem, and is made of acrylic silicate, colloidal silica and TiO.₂ It is an object of the present invention to provide a precoated steel sheet which exhibits excellent photocatalytic activity and has a balance between weather resistance and processability by forming a coating film in a form in which particles are involved. In order to achieve the object of the precoated steel sheet of the present invention, colloidal silica and TiO are formed on an acrylic silicate having a three-dimensional network structure produced by a polymerization reaction of an acrylic resin and an organoalkoxysilane.₂ It is characterized by having a coating film in which particles are dispersed.

【0006】

As the base resin for forming the coating film, colloidal silica: 10 to 60% by weight, partially hydrolyzed condensate of organoalkoxysilane: 10 to 60% by weight, polymer or copolymer of unsaturated ethylenic monomer. : A resin composition having a composition of 20 to 70% by weight is used. TiO₂ As the particles, anatase-type, rutile-type or the like titania powder having a particle size of 200 nm or less is used, and the particles are dispersed at a ratio of 10 to 150 parts by weight with respect to 100 parts by weight of the base resin. TiO₂ The dispersed coating film is preferably formed with a film thickness of 0.2 to 10 μm. In addition, in order to improve workability, steel sheets and TiO₂ An organic or organic / inorganic composite coating film having excellent adhesion to both of the dispersed coating films can be provided as an intermediate layer. The intermediate layer is preferably blended with a radical inhibitor such as benzotriazole or diphenylpicrylhydrazil.

【0007】

This precoated steel sheet is obtained by dissolving a partial hydrolysis condensate of colloidal silica and organoalkoxysilane in an organic solvent to which a glycol derivative is added, and colloidal silica: 10 to 60% by weight, a partial hydrolysis condensate of organoalkoxysilane: Prepare a base resin consisting of 10 to 60% by weight, a polymer or copolymer of unsaturated ethylenic monomer: 20 to 70% by weight, and TiO with a particle size of 200 nm or more based on 100 parts by weight of the base resin.₂ It is manufactured by dispersing 10 to 150 parts by weight of particles to prepare a paint, and applying the paint of a steel plate or a steel plate having an intermediate layer formed therein.

【0008】

[Action]

TiO in a base resin containing an inorganic silica resin and an acrylic resin₂ In a coating film made from a paint in which is dispersed, TiO is usually used when irradiated with light.₂ The acrylic resin is decomposed by the active oxygen generated by the photocatalytic reaction of the above, causing a chalking phenomenon in the coating film and deteriorating the weather resistance. On the other hand, in the present invention, a resin composition in which acrylic silicate is produced by a polymerization reaction of acrylic and organoalkoxysilane is adopted. Acrylic silicates are colloidal silica and TiO₂ It has a three-dimensional network structure involving particles. TiO₂ And the network structure of acrylic silicate in which colloidal silica is dispersed does not lead to the choking phenomenon because the three-dimensional network structure is maintained on the silicate side even if a part of acrylic is decomposed and cut by active oxygen, and the weather resistance of the coating film is not reached. It is presumed to improve the sex. In addition, the introduction of the acrylic component imparts flexibility to the coating film and improves workability. Moreover, TiO₂ Since the particles can be dispersed in the coating film to a relatively high concentration, excellent photocatalytic activity can be imparted.

【0009】

[Embodiment]

TiO₂ The dispersed coating film can be provided directly on the surface of the steel sheet (Fig. 1) or on the surface of the steel sheet (Fig. 2) via an intermediate layer. TiO provided on the surface of the steel plate 1₂ The dispersed coating film 2 contains colloidal silica: 10 to 60% by weight, partially hydrolyzed condensate of organoalkoxysilane: 10 to 60% by weight, polymer or copolymer of unsaturated ethylenic monomer: 20 to 70. TiO with a particle size of 200 nm or less in 100 parts by weight of the base resin made of% by weight₂ It is made from a paint containing 10 to 150 parts by weight of particles 3. If the blending amount of colloidal silica is less than 10% by weight, the hardness of the coating film is lowered, and conversely, if the blending amount is more than 60% by weight, the impact resistance is lowered.

【0010】

The partially hydrolyzed condensate of organoalkoxysilane is an organohydroxysilane or a partial condensate thereof obtained by hydrolyzing organoalkoxysilane in a mixed dispersion of acidic aqueous colloidal silica and non-aqueous colloidal silica according to the following formula. It is a thing. If the amount of the partially hydrolyzed condensate of organoalkoxysilane is less than 10% by weight, the adhesion of the coating film is lowered, and conversely, if the amount is more than 60% by weight, the impact resistance is deteriorated. R¹ Si (OR² )₃ R¹ Si (OH)₃However, R¹ : Select from alkyl group with 1 to 3 carbon atoms, vinyl group, 3,4-epoxycyclohexylethyl group, γ-glycidoxypropyl group, γ-methacryloxypropyl group, γ-mercaptopropyl group, γ-chloropropyl group Propyl group R² : Alkyl group or aryl group with 1 to 3 carbon atoms [0011]

Examples of the unsaturated ethylenic monomer used in the polymer or copolymer of the unsaturated ethylenic monomer include methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, t-butyl acrylate, and 2-hydroxymethyl acrylate. , 2-Hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, Acrylate esters such as 2-ethylhexyl methacrylate, methoxydiethylene glycol acrylate, methoxydiethylene glycol methacrylate, methoxytetraethylene glycol methacrylate, allyl methacrylate and the like are used, and other monomers such as styrene may be blended in a small amount. .. If the compounding amount of the unsaturated ethylenic monomer polymer or copolymer is less than 20% by weight, the coating film cannot be made into a thick film of several μm or more, and cracks caused by heat shrinkage of the coating film are suppressed. , It becomes difficult to improve workability. On the contrary, when the blending amount exceeds 70% by weight, the choking phenomenon due to the photocatalytic property is likely to occur, and the life of the coating film is shortened.

【0012】

TiO₂ As the particles, anatase type, rutile type and the like having a particle size of 200 nm or less are used. TiO₂ The particles are dispersed in the coating film at a ratio of 10 to 150 parts by weight with respect to 100 parts by weight of the base resin. TiO with a particle size exceeding 200 nm₂ For particles, TiO dispersed in the coating film₂ The specific surface area of the particles becomes small, and sufficient photocatalytic activity cannot be obtained. TiO₂ Sufficient photocatalytic activity cannot be obtained even when the amount of dispersed particles is less than 10 parts by weight. However, a large amount of TiO exceeding 150 parts by weight₂ When the particles are blended, a dense coating film is not formed due to the lack of the resin component, and the particles are easily broken by processing or the like. TiO₂ The dispersed coating film preferably forms the surface of the steel sheet with a film thickness of 0.2 to 10 μm. If the film thickness is less than 0.2 μm, the unevenness on the surface of the steel sheet cannot be absorbed, and the coating film peeling easily occurs starting from the film breakage at the convex portion. On the contrary, if the film is thicker than 10 μm, the processability required for building materials, home appliances, etc. cannot be obtained.

【0013】

TiO₂ The processability of the dispersed coating film is the surface of the steel sheet 1 and TiO.₂ This is improved by interposing an intermediate layer 4 having excellent adhesion to both of the dispersed coating films 2 (Fig. 2). Intermediate layer 4 is tentatively TiO₂ Even if cracks occur in the dispersed coating film 2 during processing, the steel plate 1 to TiO₂ Prevents the dispersed coating film 2 from peeling off. TiO₂ Particle 3 is TiO₂It exhibits the desired photocatalytic activity regardless of the presence or absence of cracks in the dispersed coating film 2. As the intermediate layer 4, TiO₂ An organic coating film or an organic / inorganic composite coating film is used because it is required to have better workability than the dispersed coating film 2. The organic coating film used for the intermediate layer 4 includes steel plate 1 and TiO.₂ Considering the adhesion to the dispersed coating film, a resin coating having a polar group is preferable, and specifically, an epoxy resin, a polyurethane resin, a polyester resin, an acrylic resin, a fluorine-acrylic mixed resin and the like are used. As the organic / inorganic composite coating film, acrylic silicate type, polyester silicate type, fluorine-acrylic silicate type and the like are suitable. The intermediate layer 4 is a surface layer of TiO.₂ It may be decomposed by the active oxygen generated in the dispersed coating film 2. Therefore, it is preferable to add a radical inhibitor such as benzotriazole or diphenylpicrylhydrazil to the intermediate layer 4. Radical inhibitor is TiO₂ It has the effect of trapping radicals generated in the dispersed coating film 2 and suppressing the decomposition of organic components forming the intermediate layer 4.

【0014】

[Example]

After mixing the acidic aqueous colloidal silica dispersion with the methanoly colloidal silica dispersion, methyltriethoxysilane was added, and the mixture was stirred at room temperature for about 5 hours to complete the hydrolysis. Isopropyl alcohol was added to the obtained product to prepare a colloidal silica-dispersed organoalkoxysilane solution (hereinafter referred to as silica dispersion) having a solid content of about 20% by weight. Acrylic acid ester (methyl methacrylate: n-butyl methacrylate = 2: 1 mixture) is diluted with a mixture of isopropanol and ethylene glycol monobutyl ether (mixture ratio 2: 5), and AIBN (azobisisobuty) is used in a nitrogen-substituted atmosphere. (Bonitrile) was added and polymerized at 80 ° C. for about 6 hours to prepare an acrylic resin solution having a solid content of about 30% by weight (hereinafter, simply referred to as acrylic resin solution). After blending the acrylic resin liquid with the silica dispersion liquid, anatase type TiO₂ Disperse the powder and list the following multiple types of TiO₂ A paint for forming a dispersed coating film was prepared.

【0015】

Painting condition 1 (example of the present invention) Anatase type TiO with a particle size of 100 nm₂ Using powder, colloidal silica: 10% by weight, methyltriethoxysilane: 10% by weight, acrylic acid ester: 70% by weight, anatase type TiO in solid content ratio₂ 10 Prepared to a coating composition of% by weight. A stainless steel strip with a thickness of 0.4 mm is degreased, paint is applied with a roll coater, and TiO with a film thickness of 3 μm is fired at 250 ° C for 1 minute.₂ A dispersed coating film was formed. Obtained TiO₂ The dispersed coating is white and TiO in the acrylic silicate.₂ It was confirmed by SEM observation of the cross section of the coating film that the particles were uniformly dispersed. Painting condition 2 (example of the present invention) 20% by weight of acrylic ester concentration in solid content ratio, anatase type TiO₂TiO with a film thickness of 3 μm in the same manner as in Example 1 except that the amount of powder dispersed is 60% by weight.₂ A dispersed coating film was formed.

【0016】

Painting condition 3 (example of the present invention) TiO with a film thickness of 3 μm in the same manner as in Example 1 except that the concentration of colloidal silica is 60% by weight and the acrylic acid ester is 20% by weight in terms of solid content ratio.₂ A dispersed coating film was formed. Painting condition 4 (example of the present invention) TiO with a film thickness of 3 μm in the same manner as in Example 1 except that the concentration of methyltriethoxysilane is 60% by weight and the acrylic acid ester is 20% by weight in terms of solid content ratio.₂ A dispersed coating film was formed. Painting condition 5 (example of the present invention) After degreasing a stainless steel sheet with a thickness of 0.4 mm, an acrylic resin solution was used for the intermediate layer, the acrylic resin solution was applied to the surface of the steel sheet with a roll coater, and the intermediate layer was formed by firing at 230 ° C for 1 minute. .. Next, the coating condition 1 is the same as TiO.₂ Disperse paint is applied on the intermediate layer with a roll coater, and TiO with a film thickness of 3 μm is fired at 250 ° C for 1 minute.₂A dispersed coating film was formed.

【0017】

Painting condition 6 (example of the present invention) TiO for intermediate layer formation₂ Using a mixed solution of silica dispersion and acrylic resin solution that does not contain TiO₂ Same as coating condition 1 for forming a dispersed coating film TiO₂ Dispersive paint was used. After degreasing a stainless steel sheet with a thickness of 0.4 mm, a paint for forming an intermediate layer is applied with a roll coater, fired at 230 ° C for 1 minute, and then TiO.₂ Disperse paint is applied with a roll coater and fired at 250 ° C for 1 minute to obtain a TiO with a film thickness of 3 μm.₂ A dispersed coating film was formed. Painting condition 7 (example of the present invention) An intermediate layer with a film thickness of 1 μm and a TiO with a film thickness of 3 μm under the same conditions as coating condition 5, except that 1% by weight of benzotriazole is added to the paint for forming the intermediate layer.₂ A dispersed coating film was formed.

【0018】

Painting condition 8 (comparative example) Anatase type TiO with a particle size of 250 nm₂ TiO with a film thickness of 3 μm, as in coating condition 2, except that powder is used.₂ A dispersed coating film was formed. Painting condition 9 (comparative example) The concentration of methyltriethoxysilane in the solid content ratio is 15% by weight, anatase type TiO₂ TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the powder is 5% by weight.₂ A dispersed coating film was formed. Painting condition 10 (comparative example) Anatase-type TiO with a solid content ratio of 15% by weight of anatase ester₂TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the powder is 65% by weight.₂ A dispersed coating film was formed. Painting condition 11 (comparative example) Anatase-type TiO with a solid content ratio of 15% by weight of anatase ester₂TiO with a film thickness of 3 μm under the same conditions as coating condition 3 except that the powder is 15% by weight.₂ A dispersed coating film was formed.

【0019】

Painting condition 12 (comparative example) TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the concentration of colloidal silica is 5% by weight, methyltriethoxysilane is 5% by weight, and acrylic acid ester is 80% by weight in terms of solid content ratio.₂ A dispersed coating film was formed. Painting condition 13 (comparative example) Anatase-type TiO in solid content ratio without the addition of methyltriethoxysilane₂ TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the powder concentration is 20% by weight.₂ A dispersed coating film was formed. Painting condition 14 (comparative example) Anatase-type TiO in solid content ratio without adding colloidal silica₂ TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the powder concentration is 20% by weight.₂ A dispersed coating film was formed.

【0020】

Painting condition 15 (comparative example) TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the concentration of colloidal silica is 65% by weight and the acrylic acid ester is 15% by weight in terms of solid content ratio.₂ A dispersed coating film was formed. Painting condition 16 (comparative example) TiO with a film thickness of 3 μm under the same conditions as coating condition 1 except that the concentration of methyltriethoxysilane is 65% by weight and the acrylic acid ester is 15% by weight in terms of solid content ratio.₂ A dispersed coating film was formed. Painting condition 17 (comparative example) Roll coater applicator TiO under the same conditions as coating condition 1 except that the peripheral speed of the roll is reduced to adjust the film thickness to 0.1 μm.₂ A dispersed coating film was formed. Painting condition 18 (comparative example) Roll coater applicator TiO under the same conditions as coating condition 1 except that the peripheral speed of the roll is increased to adjust the film thickness to 15 μm.₂ A dispersed coating film was formed.

【0021】

Test pieces were cut out from the coated steel sheets obtained under the respective coating conditions 1 to 18 and subjected to workability test, weather resistance test and photocatalytic activity test. In the workability test, the test piece was T-bent and then tape peeled. Visually observe the residual state of the coating film after the tape is peeled off, and apply if the coating film is not detected by bending at 0T, and if the coating film is not detected by bending at 2T or less. Those in which no peeling was detected in the film were evaluated as Δ, and those in which peeling occurred in the coating film by bending at 5T were evaluated as ×. In the weather resistance test, the test piece was held in a 63 ° C sunshine weather acceleration tester for 1000 hours, and the weather resistance was investigated by the gloss retention before and after the test. A gloss retention rate of 90% or more was evaluated as , 80% or more was evaluated as , 70% or more was evaluated as Δ, and less than 70% was evaluated as ×. In the photocatalytic activity test, the adhesion amount was 0.2 mg / cm² Adhere the vegetable oil to the surface of the test piece with 5mW / cm² After irradiating with ultraviolet light for 24 hours, the weight of the salad oil remaining on the test piece was measured. Then, the weight reduction rate of the salad oil after the ultraviolet light irradiation was obtained as compared with the salad oil before the ultraviolet light irradiation, and the photocatalytic activity was determined by using this weight reduction rate as the oil decomposition rate. Less than% was evaluated as x.

【0022】

The investigation results are shown in Table 1 (Example of the present invention) and Table 2 (Comparative Example) together with the coating film composition. As is clear from the comparison between Table 1 and Table 2, colloidal silica and TiO are formed in the three-dimensional network structure of acrylic silicate.₂ The pre-coated steel sheet of the present invention example in which the above is dispersed has a good balance between workability, weather resistance and photocatalytic activity, and is a coated steel sheet having a self-cleaning action for applications such as building materials and home appliances that require workability. It turns out that it can be used as. Among them, the base steel plate and TiO₂ Excellent processability was obtained in Test Nos. 5 to 7 in which an intermediate layer was interposed between the dispersed coating film, and weather resistance was also improved in Test No. 7 to which a radical inhibitor was added.

【0023】

<img file="JP2000317393A_D0001.tif" />【0024】

<img file="JP2000317393A_D0002.tif" />【0025】

[Effect of the invention]

As described above, the precoated steel sheet of the present invention is a colloidal silica and TiO in a form of being involved in a three-dimensional network structure of acrylic silicate produced by the reaction / polymerization of acrylic and organoalkoxysilane.₂ A coating film in which particles are dispersed is formed on the surface of the steel sheet. Due to this coating film structure, the chalking phenomenon of the coating film due to active oxygen generated by the photocatalytic reaction is suppressed, and TiO₂ Weather resistance and workability are improved while maintaining the photocatalytic activity of the particles. The pre-coated steel sheet thus obtained utilizes excellent photocatalytic activity, weather resistance, and workability, and is used in a wide range of fields including building materials and housings for home appliances.

[Simple explanation of drawings]

[Figure 1]

TiO on the surface of the steel plate₂ Pre-coated steel sheet directly provided with a dispersed coating film [Figure 2]

TiO via the intermediate layer₂ Pre-coated steel sheet directly provided with a dispersed coating film [Explanation of symbols]

1: Steel plate 2: TiO₂ Dispersed coating 3: TiO₂ Particle 4: Intermediate layer