Photocatalytic coating composition

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a coating composition that is used for coating home appliances such as microwave ovens and ovens and outer panels for office equipment such as cabinets and exhibits photocatalytic activity.

【0002】

[Conventional technology]

TiO₂A coating film formed from a paint containing a photocatalyst, such as the above, exhibits functionality not found in conventional coating films, such as antifouling property, antibacterial property, deodorizing property, and NOx / SOx resolution. Focusing on such photocatalytic action, studies on coating compositions and paints for forming a coating film exhibiting photocatalytic activity are underway, and several kinds of paint compositions have already been proposed.

【0003】

Inorganic materials that do not peel off due to decomposition and chalking due to active oxygen generated by light irradiation are generally used as the base of the coating film to which photocatalytic activity is imparted. For example, an alkoxide such as tetraethoxysilane dissolved in a water / ethanol mixed solvent is dispersed in water.₂Composition mixed with sol (WO96 / 29375), TiO in a solution of organosilica sol in an organic solvent₂A composition in which powder is dispersed (Japanese Patent Laid-Open No. 8-67835), a composition composed of a photocatalytic powder and a binder of a silicone-based polymer (Japanese Patent Laid-Open No. 7-171408), and the like are known.

【0004】

[Problems to be Solved by the Invention]

Silicon tetraethoxydo, which is used as a binder for photocatalysts, is crosslinked and cured by hydrolysis and condensation reactions, so that the volume shrinkage during curing is large. The large volume shrinkage causes a very large shrinkage stress that is not relaxed during and after the film formation, and causes cracks in the coating film. The tendency of cracking to occur becomes more remarkable as the coating film is thicker. Although cracking can be prevented by thinning the coating film, it is very difficult to uniformly apply the thin coating film to a large-area object to be coated, and the coating film is partially formed by slight unevenness or distortion of the surface. Easy to thicken. Even when the surface of an object to be coated having a complicated shape is coated, the coating film is partially thickened according to the unevenness of the object to be coated. In the thickened portion, the occurrence of cracks due to shrinkage stress is still unavoidable.

【0005】

In addition, TiO is added to a solution of organosilica sol in an organic solvent.₂In the paint composition prepared by dispersing the powder, TiO₂Is insufficiently dispersed and easily aggregates. Therefore, a coating film having poor uniformity is formed. TiO₂A coating film made from a paint containing a powder and a silicone-based polymer binder has insufficient weather resistance because the silicone-based polymer is easily decomposed by light irradiation.

【0006】

[Means for solving problems]

The present invention has been devised to solve such a problem, and is TiO.₂By using a photocatalyst-dispersed toner in which acrylic resin and a dispersant are mixed in powder, TiO₂In a well-dispersed state, colloidal silica, partially hydrolyzed condensate of organoalkoxysilane, and finely dispersed TiO₂It is an object of the present invention to provide a coating composition in which particles are incorporated into a three-dimensional network structure of an acrylic resin to form a coating film having excellent photocatalytic activity and a balance between weather resistance and processability.

【0007】

In order to achieve the object, the photocatalytic coating composition of the present invention is TiO.₂Photocatalyst-dispersed toner in which particles, acrylic resin and dispersant are dispersed in an alcohol / glycol derivative mixed solvent is used as a colloidal silica: 10 to 60% by mass, a partially hydrolyzed condensate of organoalkoxysilane: 10 to 60% by mass, and not. Polymer or copolymer of saturated ethylenic monomer: It is characterized in that it is mixed with an organic / inorganic composite binder added to a solvent at a ratio of 20 to 70% by mass. TiO₂As particles, anatase-type TiO with a particle size of 5 to 200 nm₂Is preferable. As the colloidal silica, a mixture of acidic aqueous colloidal silica and non-aqueous colloidal silica in a proportion of 20% by mass or more is preferably used.

【0008】

The partially hydrolyzed condensate of organoalkoxysilane is of the general formula R¹Si (OR²)₃(R¹Is one or two selected from an alkyl group having 1 to 3 carbon atoms, a vinyl group, a 3,4-epoxycyclohexylethyl group, a γ-glycidoxypropyl group, a γ-mercaptopropyl group, and a γ-chloropropyl group. Above, R²Is obtained by hydrolyzing an organoalkoxysilane (one or more selected from an alkyl group, an alkoxyethyl group, and an aryl group) having 1 to 4 carbon atoms in an acidic colloidal silica dispersion, and is obtained by the formula R.¹Si (OH)₃Organoalkoxysilane or a partially hydrolyzed condensate thereof.

【0009】

As the unsaturated ethylenic monomer which is one component of the organic / inorganic composite binder, for example, a monomer selected from an acrylic acid ester and a methacrylic acid ester is used. The organic / inorganic composite binder is selected from lower fatty alcohols, glycol derivatives, and ketone derivatives, and is a solvent containing 10% by mass or more of the glycol derivative, which is a colloidal silica, a partially hydrolyzed condensate of organoalkoxysilane, and unsaturated ethylene. It is prepared by dispersing and mixing a polymer or copolymer of a sex monomer. The organic / inorganic composite binder is preferably adjusted to pH 3 to 6.5. In this case, as the dispersant, a dispersant in which the isoelectric point of the zeta potential deviates from pH 3 to 6.5 of the organic / inorganic composite binder is used.

【0010】

[Action]

Silicone polymer with TiO₂The coating film made from the paint in which is dispersed is TiO when irradiated with light.₂Organic components are 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 an acrylic resin is produced by a polymerization reaction of a (meth) acrylic acid ester and a polymerizable organoalkoxysilane is adopted. Acrylic resin has a three-dimensional network structure, a partially hydrolyzed condensate of colloidal silica and organoalkoxysilane, and TiO.₂The particles are incorporated into the network structure. The three-dimensional network structure of the acrylic resin suppresses the chalking phenomenon and improves the weather resistance of the coating film. The reason is that even if the acrylic resin is partially decomposed and cut by the active oxygen generated by the photocatalytic reaction, it is on the silicate side. It is presumed that this is due to the maintenance of the three-dimensional network structure.

【0011】

To obtain a coating film with excellent weather resistance, use an organic / inorganic composite binder containing a polymer or copolymer of unsaturated ethylenic monomer, and adjust the pH of the organic / inorganic composite binder to 3 to 6.5. This improves the storage stability of the coating composition. For example, TiO₂When anatase-type titanium oxide is used as a paint and a toner in which anatase-type titanium oxide is dispersed in an organic solvent is mixed to form a paint, the anatase-type titanium oxide tends to aggregate and settle at the same time as the toner is mixed. For aggregation and precipitation, the isoelectric point of the zeta potential of anatase-type titanium oxide is in the range of 4.5 to 6.0, and the polymer or copolymer of unsaturated ethylenic monomer contained in the binder and anatase-type titanium oxide. It is presumed that the cause is that the charge on the particle surface becomes zero due to the contact with the particles.

【0012】

On the other hand, TiO₂If organoalkoxysilane (dispersant) and acrylic resin are added to the toner in which the toner is dispersed in a solvent, even if the toner is mixed with the binder, TiO₂A coating composition having good dispersibility can be obtained without agglutination. TiO₂The reason why the agglutination of TiO is suppressed is that TiO₂Is covered with organoalkoxysilane and acrylic resin, so the water content of the binder composition and TiO₂There is no direct contact with TiO in the silicate produced by hydrolysis of organoalkoxysilane.₂Since the surface of the particles is covered, the isoelectric point on the surface of the particles deviates from the pH range of the binder, and the acrylic resin on the surface of the particles easily adapts to the binder component.

【0013】

[Embodiment]

The photocatalytic coating composition according to the present invention is prepared by dissolving an inorganic solid content and an organic solid content in a solvent containing a glycol derivative to form an organic / inorganic composite binder, and mixing the photocatalytic dispersion toner with the organic / inorganic composite binder. Prepared. The photocatalytic dispersion toner is TiO₂It is prepared by dispersing and mixing particles, acrylic resin, and dispersant in an alcohol / glycol derivative mixed solvent. The organic / inorganic composite binder is colloidal silica: 10 to 60% by mass, partially hydrolyzed condensate of organoalkoxysilane: 10 to 60% by mass, polymer or copolymer of unsaturated ethylenic monomer: 20 to It has a solid content composition of 70% by mass.

【0014】

The photocatalytic dispersion toner is TiO with a particle size of 5 to 200 nm.₂It is prepared by adding powder, acrylic resin and dispersant to an alcohol / glycol derivative mixed solvent and sufficiently dispersing and mixing them with a stirrer such as a bead mill or a ball mill. Ultrafine TiO₂Even so, the mixing ratio of alcohol: glycol derivative is (40 to 60) :( 40 to 60), the amount of acrylic resin added is 0.1 to 5% by mass, and the amount of dispersant added is 1 to 10% by mass. By doing so, an excellent dispersed state is realized.

【0015】

The acrylic resin is preferably the same type as the acrylic resin contained in the organic / inorganic composite binder. If the blending amount of the acrylic resin is less than 0.1% by mass, the charge on the particle surface becomes zero when the photocatalyst-dispersed toner is mixed with the organic / inorganic composite binder, and dispersion failure is likely to occur. On the contrary, when the blending amount of acrylic resin exceeds 5% by mass, TiO₂The contact area with the particle surface becomes too large, and the coating film becomes easy to chalk.

【0016】

It is preferable to use a metal alkoxide as a dispersant for the photocatalytic dispersion toner. Of these, metal alkoxides, which are oxides in which the isoelectric point of the zeta potential deviates from the pH of the organic / inorganic composite binder in the final form after hydrolysis, are preferable. Such metal alkoxides include alkoxysilanes, aluminum alkoxides, organoalkoxysilanes in which a part of the alkoxide is replaced with an organic group, and the like. It is also possible to use the same type of organoalkoxysilane as the organoalkoxysilane contained in the organic / inorganic composite binder. The effect of blending the dispersant becomes remarkable at 1% by mass or more, but when an excess amount of the dispersant exceeding 10% by mass is blended, TiO₂The coverage of the particle surface with the dispersant tends to be too high, and the photocatalytic activity after the coating film is formed tends to decrease.

【0017】

The organic / inorganic composite binder is a polymer or copolymer of a solid content and an unsaturated ethylenic monomer composed of a partially hydrolyzed condensate of silica, organoalkoxysilane and organoalkoxysilane, and is organic such as water and / or alcohol. It is prepared by dispersing and mixing in a solvent. As silica, there is colloidal silica, which is used in a state where high molecular weight silicic acid anhydride is dispersed in an organic solvent such as water and / or alcohol. Further, when a mixture of aqueous colloidal silica and non-aqueous colloidal silica is used, the storage stability of the coating composition is improved, and the effect of the non-aqueous colloidal silica on the improvement of storage stability is remarkable at 20% by mass or more. Become. In order to ensure the dispersibility of the colloidal silica dispersion, it is preferable to disperse silica having an average particle size of 150 nm or less (further, 30 nm or less) in a blending amount of 10 to 50% by mass. The colloidal silica dispersion is preferably maintained at an acidic pH in order to prevent the storage stability of the inorganic binder from being lowered.

【0018】

The partially hydrolyzed condensate of organoalkoxysilane contained in the organic / inorganic composite binder is of the general formula R.¹Si (OR²)₃[In the formula, R¹Is selected from alkyl groups with 1 to 3 carbon atoms, vinyl groups, 3,4-epoxycyclohexylethyl groups, γ-glycidoxypropyl groups, γ-methacryloxypropyl groups, γ-mercaptopropyl groups, and γ-chloropropyl groups. 1 type or 2 or more types, R²Indicates an alkyl group having 1 to 4 carbon atoms, an alkoxyethyl group, or an aryl group], which is obtained by hydrolyzing the organoalkoxysilane represented by] in an acidic colloidal silica dispersion.¹Si (OH)₃Organohydroxysilane or a partially hydrolyzed condensate thereof. Methyl hydroxysilane is preferable in consideration of the hardness and economy of the coating film, but it is also possible to mix a small amount of other organoalkoxysilane. It is preferable that 80% by mass or more of the organohydroxysilane is methyltrihydroxysilane. The amount of the partially hydrolyzed condensate of organoalkoxysilane added is adjusted to be in the range of 10 to 60% by mass with respect to the total solid content of the coating composition. When the partially hydrolyzed condensate is added at a ratio of 10% by mass or more, the adhesion of the coating film is improved, but when an excess amount of the partially hydrolyzed condensate exceeding 60% by mass is added, the impact resistance of the film is deteriorated.

【0019】

The unsaturated ethylenic monomer used as an organic source of the organic / inorganic composite binder includes methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, t-butyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and methyl methacrylate. , Ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-ethylhexyl methacrylate, methoxydiethylene glycol acrylate, Examples thereof include acrylic acid esters such as methoxydiethylene glycol methacrylate, methoxytetraethylene glycol methacrylate and allyl methacrylate, and methacrylic acid esters. A small amount of other monomer such as styrene may be added to this unsaturated ethylenic monomer.

【0020】

The amount of the unsaturated ethylenic monomer polymer or copolymer added is adjusted to the range of 20 to 70% by mass with respect to the total solid content of the organic / inorganic composite binder. If the amount added is less than 20% by mass, the coating film cannot have a film thickness of several μm or more, cracks are likely to occur due to heat shrinkage of the coating film, and bending workability is insufficient. On the contrary, if the blending amount exceeds 70% by mass, the chalking phenomenon due to active oxygen is likely to occur, and the life of the coating film is shortened. As the solvent of the organic / inorganic composite binder, a mixed solvent of a lower fatty alcohol and a glycol derivative is used. The glycol derivative is effective in improving the storage stability of the coating composition and the appearance of the coating film, and the effect becomes remarkable when the blending amount is 10% by mass or more.

【0021】

Examples of the lower aliphatic alcohol include methanol, ethanol, propanol, isopropanol, n-butanol, t-butanol and the like. Examples of the glycol derivative include ethylene glycol, propylene glycol, butylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether acetate. The solvent of the organic / inorganic composite binder may contain a small amount of water derived from aqueous colloidal silica or the like.

【0022】

The organic / inorganic composite binder is preferably maintained in the pH range of 3 to 6.5 (further, pH 3 to 5) in order to maintain storage stability. In addition to aqueous ammonia and water, organic amines such as triethanolamine and dimethylamino ether are also used for pH adjustment. The photocatalyst-dispersed toner and the organic / inorganic composite binder prepared as described above are mixed at a predetermined ratio to prepare a coating composition. Photocatalytic dispersion toner: The mixing ratio of the organic / inorganic composite binder is TiO in the coating composition in order to obtain sufficient photocatalytic activity.₂It is preferable to set the ratio of 5 to 5% by mass or more. But TiO₂When the ratio of the above is more than 80% by mass, the adhesion of the formed coating film is lowered.

【0023】

To prepare the photocatalyst-dispersed toner, for example, the photocatalyst-dispersed toner is added to an alcohol / glycol derivative mixed solvent to which a polymer or copolymer of an unsaturated ethylenic monomer and a dispersant are added, and the toner is stirred and mixed with a stirrer and then beads. A horizontal mill filled with toner is used, and a method of flowing into the beads in a stirred state is adopted. At the time of preparation, a colorant such as a pigment or a dye, a thickener or the like may be added as needed.

【0024】

To prepare an organic / inorganic composite binder, for example, aqueous colloidal silica and non-aqueous colloidal silica are placed in a reaction vessel equipped with a stirrer, organoalkoxysilane is added, and the mixture is held at 10 to 80 ° C. for 1 to 5 hours. And react under stirring. Some of the non-aqueous colloidal silica can also be added after the reaction is complete. When the organoalkoxysilane is hydrolyzed, a small amount of catalyst may be added to accelerate the reaction, but the reaction proceeds rapidly even in a system in which no catalyst is present.

【0025】

A polymer or copolymer of an unsaturated ethylenic monomer and an alcohol / glycol derivative mixed solvent are added to a dispersion of a partially hydrolyzed condensate of colloidal silica and organoalkoxysilane obtained after the reaction, and the mixture is sufficiently dispersed and mixed. By doing so, the organic / inorganic composite binder is adjusted. A coating composition is prepared by further stirring while gradually adding an organic / inorganic composite binder to the photocatalyst-dispersed toner in a sufficiently stirred state.

【0026】

The obtained coating composition is applied to the surface of the object to be coated by a spray coating method, a dipping method, a flow coating method, a roll coating method, a screen printing method, an electrostatic coating method, etc. It is baked by heating for 120 minutes. The film thickness of the coating film varies depending on the type and application of the object to be coated and cannot be unconditionally determined, but usually, the coating amount is adjusted so that a coating film having a film thickness of 1 to 100 μm is formed. The coating composition includes metals such as ordinary steel, plated steel, stainless steel, aluminum, aluminum alloy, copper plate, and brass, as well as inorganic substances such as cement, concrete, tile, slate plate, glass, and stone, injection-molded products, and resins. It is also applied to organic substances such as sheets and resin films.

【0027】

[Example]

[TiO₂Preparation of dispersed toner] 2% by mass of acrylic resin and 5% by mass of dispersant are added to a mixed solvent of 50% by mass of isopropanol-50% by mass of butyl cellosolve, and the particle size is adjusted to 40% by mass in the entire coating composition. 20 nm TiO₂The powder was added to the mixed solvent. As the acrylic resin, a resin solution having a solid content of 30% (acrylic resin A) obtained by diluting a mixture of 20 g of methyl methacrylate and 10 g of γ-methacryloxypropyltrimethoxysilane with 70 g of ethylene glycol monobutyl ether and polymerizing at 80 ° C for 6 hours. ), 20 g of n-butyl methacrylate and 10 g of γ-methacryloxypropyltrimethoxysilane were polymerized in the same manner, and a resin solution having a solid content of 30% (acrylic resin B) was used. Acrylic resin, dispersant, TiO₂A photocatalyst-dispersed toner was prepared by charging a mixed solvent to which powder was added into a bead mill and dispersing and mixing the mixture.

【0028】

[Preparation of dispersion of colloidal silica and organoalkoxysilane] 21.2 g of acidic aqueous colloidal silica dispersion (average particle size 10 to 20 nm, solid content 20% by mass) is added to 38.8 g of methanolic colloidal silica dispersion (average). After mixing with a particle size of 10 to 20 nm and a solid content of 30% by mass), 13.9 g of methylmethoxysilane was added, and the mixture was stirred at room temperature for 5 hours to complete the hydrolysis. Isopropanol was added to the obtained product to obtain a dispersion of colloidal silica and organoalkoxysilane having a solid content of 20% by mass.

【0029】

[Preparation of polymer or copolymer of unsaturated ethylenic monomer] The polymer or copolymer of unsaturated ethylenic monomer is a mixture of 20 g of methyl methacrylate and 10 g of n-butyl methacrylate, 20 g of isopropanol and ethylene. It was diluted with a mixed solvent of 50 g of glycol monobutyl ether and polymerized at 80 ° C. for 6 hours to prepare a resin solution having a solid content of 30% by mass.

【0030】

Paint composition 1 An organic / inorganic composite binder having a pH of 4.5 was prepared by mixing 83 g of a dispersion of organoalkoxysilane and colloidal silica and 22 g of acrylic resin A. Acrylic resin A and TiO added with a dispersant₂Disperse toner, TiO in solids₂The mixture was mixed and stirred with an organic / inorganic composite binder so that the content was 40% by mass, filtered using a mesh of 50 μm, and the filtrate was used as a coating composition. The obtained coating composition was sprayed on a pretreated SUS304 stainless steel sheet and heated at 200 ° C. for 20 minutes to form a coating film having a film thickness of 10 μm.

【0031】

Paint composition 2: A paint composition 2 was prepared in the same manner as the paint composition 1 except that the acrylic resin B was used instead of the acrylic resin A, and a coating film having a film thickness of 10 μm was formed. Paint composition 3 (Comparative example): Acrylic resin A and TiO without addition of dispersant₂A coating composition 3 was prepared in the same manner as the coating composition 1 except that a dispersed toner was used, and a coating film having a film thickness of 10 μm was formed.

【0032】

Paint composition 4 (Comparative example): TiO added with either acrylic resin A or a dispersant₂A coating composition 3 was prepared in the same manner as the coating composition 1 except that a dispersed toner was used, and a coating film having a film thickness of 10 μm was formed. Paint composition 5 (Comparative example): TiO added with either acrylic resin B or a dispersant₂A coating composition 3 was prepared in the same manner as the coating composition 1 except that a dispersed toner was used, and a coating film having a film thickness of 10 μm was formed.

【0033】

The dispersibility of each of the prepared coating compositions and the characteristics of the coating film were evaluated by the following methods.

[Evaluation of dispersibility of paint composition] TiO₂After mixing the dispersed toner and the organic / inorganic composite binder to make a paint, TiO by the tube gauge one day later.₂The state of aggregation of particles was investigated. From the survey results, the dispersibility was evaluated by assigning a paint in which no whelk of 10 μm or more was detected as and a paint in which whelk of 10 μm or more was suspended as ×.

【0034】

[Evaluation of coating film characteristics] The appearance of the coating film was observed, and the appearance was evaluated by for the coating film on which a uniform coating film was formed and × for the coating film on which the surface of the coating film was rough and lumps were detected. In addition, the amount of adhesion to the coating film surface is 0.2 mg / cm.²Attach the vegetable oil with 5mW / cm²After irradiating with ultraviolet light for 24 hours, the weight of the salad oil remaining on the surface of the coating film was measured. The weight loss rate before and after irradiation with ultraviolet rays was determined as the oil decomposition rate, and the photocatalytic activity was evaluated with the oil decomposition rate of 40% or more as and less than 40% as x.

【0035】

As is clear from Table 1 showing the test results, TiO without the addition of both acrylic resin and dispersant.₂In the coating composition containing the dispersed toner, TiO₂Aggregation was severe, and a uniform coating film was not formed. TiO₂The dispersion was insufficient even when either the acrylic resin or the dispersant was added. The obtained coating film is TiO.₂It exhibited a lumpy appearance due to the agglutination of, and was inferior in photocatalytic activity. On the other hand, in the coating composition of the example of the present invention, TiO is produced by the action of both the acrylic resin and the dispersant.₂Agglutination of particles was suppressed, and a smooth coating film having excellent photocatalytic activity was formed. Further, even when a relatively thick coating film was formed, cracks did not occur in the coating film.

【0036】

<img file="JP2002249705A_D0001.tif" />【0037】

[Effect of the invention]

As described above, the photocatalytic coating composition of the present invention is TiO.₂By adding acrylic resin and dispersant to the dispersed toner, TiO₂TiO without agglomeration even when the dispersed toner is mixed with an organic / inorganic composite binder₂The particles are uniformly dispersed. When this photocatalytic coating composition is applied to an object to be coated and baked, colloidal silica, a partially hydrolyzed condensate of organoalkoxysilane, and TiO are formed on a three-dimensional network structure of an acrylic resin.₂Particles are involved, and a coating film having excellent photocatalytic activity and having a good balance between weather resistance and processability is formed. In addition, as long as the material can withstand heating of 80 ° C or higher, a coating film with good adhesion is formed without any restrictions on the object to be coated. Therefore, metal panels, concrete walls, tiles, glass windows, and light transmissive. Applies to a wide range of objects such as boards.