JP7151509B2 - Photocatalyst coated body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a photocatalyst-coated body suitable for exterior applications such as buildings.

When a photocatalyst layer is provided on a base material, an intermediate layer is provided in order to prevent deterioration due to adhesion to the base material and photocatalyst. For example, Japanese Patent Application Laid-Open No. 2001-259432 (Patent Document 1) describes the use of an intermediate layer made of polysiloxane or silicone resin, which is a material that is difficult to decompose with a photocatalyst.

On the other hand, the above-mentioned polysiloxane and silicone resin have low versatility and are expensive, and in order to simplify the manufacturing process and reduce the cost, a technique of omitting the intermediate layer has been proposed. For example, Japanese Patent Application Laid-Open No. 2008-264747 (Patent Document 2) discloses that the photocatalyst concentration in the photocatalyst layer is relatively low at about 1 to 20%, so that the photocatalyst layer is directly applied to the organic substrate without providing an intermediate layer. A photocatalytic coating solution and coated body capable of forming a are disclosed. Lowering the photocatalyst concentration lowers the photocatalytic activity, but in order to prevent such a decline in activity, Patent Document 2 discloses that the photocatalyst layer is mainly made of particles to increase the permeability of harmful gases and prevent contact with the photocatalyst particles. Taking the opportunity, gas decomposability is ensured.

Furthermore, in the technical field of paints, it is widely practiced to add an ultraviolet absorber to improve the weather resistance of the paint film, that is, to prevent deterioration. UV absorbers include organic and inorganic materials, and cerium oxide is known as an inorganic UV absorber. Examples are given in paragraphs 0052 and 0053 of Patent Document 1, for example, but there is no description of examples in which cerium oxide is actually used in the patent document.

JP-A-2001-259432 JP 2008-264747 A

The present inventors have recently found that cerium oxide, which has been conventionally known as an ultraviolet absorber, improves the weather resistance of photocatalyst-coated bodies, a phenomenon that cannot be explained by its ultraviolet absorption action. The present invention is based on such findings.

Accordingly, an object of the present invention is to provide a photocatalyst-coated article having excellent weather resistance.

And the photocatalyst-coated body according to the present invention is
A base material, a first layer containing an organic resin on the surface of the base material, and a second layer containing a photocatalyst provided in contact with the first layer,
wherein the first layer further comprises cerium oxide (CeO ₂ );
The second layer has a photocatalytic activity value of 5 nmol/L/min or more and 30 nmol/L/min or less as determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014.

Photocatalyst-coated body according to the present invention A photocatalyst-coated body according to the present invention comprises a first layer containing an organic resin and a second layer containing a photocatalyst provided in contact with the first layer on the surface of a substrate. It has a basic configuration, the first layer further contains cerium oxide (CeO ₂ ), and the photocatalytic activity of the second layer is determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2: 2014. It has a relatively high activity of 5 nmol/L/min or more and 30 nmol/L/min or less, preferably 5 nmol/L/min or more and 23 nmol/L/min or less. The photocatalyst-coated body according to the present invention exhibits excellent weather resistance while maintaining photocatalytic activity for a long period of time by providing such a configuration. Specifically, the photocatalyst-coated body according to the present invention has the effect that the photocatalyst layer stably adheres to the substrate for a long period of time, does not peel off, and is less susceptible to deterioration such as discoloration or fading. Therefore, for example, it is preferably used for exterior applications such as buildings.

In the present invention, the presence of cerium oxide is considered to be the main cause of the development of this excellent weather resistance. Cerium oxide is known to have an ultraviolet absorbing effect, but the excellent weather resistance of the present invention is a phenomenon that cannot be explained by the ultraviolet absorbing effect of cerium oxide. This is clarified by the fact that conventionally known UV absorbers, which are equivalent to cerium oxide as UV absorbers, do not exhibit such remarkable improvement in weather resistance as the present invention. It can be said that such effects of cerium oxide were unexpected for those skilled in the art.

Substrate The substrate used in the present invention may be any material, whether inorganic or organic, as long as the first layer containing an organic resin can be formed thereon, and its shape is not limited. Preferred examples of substrates from the viewpoint of materials include metals, ceramics, glass, plastics, rubber, stone, cement, concrete, fibers, fabrics, wood, paper, combinations thereof, laminates thereof, and laminates thereof. Examples include those having at least one layer of coating on the surface. Preferable examples of the substrate from the viewpoint of use include building materials, building exteriors, window frames, window glass, structural members, exteriors and coatings of vehicles, exteriors of machinery and articles, dustproof covers and coatings, traffic signs, and various displays. Equipment, advertising towers, sound insulation walls for roads, sound insulation walls for railways, bridges, exterior and painting of guardrails, interior and painting of tunnels, insulators, solar cell covers, solar water heater heat collection covers, vinyl houses, vehicle lighting covers , outdoor lighting fixtures, stands, and exterior materials in general such as films, sheets, seals, etc. to be adhered to the surfaces of the articles.

First Layer Containing Organic Resin In the present invention, the first layer containing an organic resin is provided between the base material and the second layer, which is a photocatalyst layer, and serves as a protective layer for preventing deterioration of the base material due to the photocatalyst. It has a function. In addition, the surface of the base material may be additionally modified in design.

In the present invention, the organic resin that constitutes the first layer is not particularly limited as long as it ensures adhesion to the substrate and allows a photocatalyst layer to be provided in contact therewith. Examples include fluororesin, silicone, acrylic silicone, vinyl acetate, vinyl acetate acrylic, acrylic urethane, acrylic, epoxy, vinyl chloride vinyl acetate, vinylidene chloride, SBR, alkyd, melamine, polyester, nylon, polyolefin, polycarbonate and the like.

Further, according to another aspect of the present invention, the organic resin may be applied to the substrate as a first layer in the form of a composition such as an aqueous dispersion, emulsion, dispersion, or the like. Therefore, in the present invention, the method of forming the first layer containing the organic resin is not particularly limited, but it may be formed by appropriately applying a paint or coating composition containing the organic resin to the substrate. Alternatively, a dispersion may be formed by dispersing the organic resin in a solvent and applied to the substrate.

According to one aspect of the present invention, there is an advantage that the organic resin of the first layer does not necessarily have to be composed of a silicone-based resin such as polysiloxane or silicone resin, which is a material that is difficult to decompose. In the present invention, the use of silicone-based resins is not excluded, but according to one aspect of the present invention, a resin containing no Si or containing less than 2% by weight of Si is used. It is an extremely versatile technology that can be used and therefore can be used with a wide range of resins.

In the present invention, the first layer containing organic resin contains cerium oxide. The form of cerium oxide is not particularly limited as long as it can be added to the first layer containing the organic resin, but it is preferably added to the organic resin composition in the form of a sol dispersed in water.

The amount of cerium oxide to be added to the first layer is not particularly limited as long as the effect of the addition is exhibited. is preferred, and more preferably in the range of 0.3 wt% to 3 wt%.

According to one aspect of the invention, the first layer can contain inorganic pigments, inorganic particles. Inorganic pigments are added as extender pigments or as color pigments. Inorganic particles are added to form an uneven surface, to control gloss, or as a filler, and silica sand, for example, can be used.

Although the film thickness of the first layer is not particularly limited in the present invention, it is preferably 1 μm to 200 μm, more preferably 5 μm to 100 μm.

In the present invention, the method for forming the first layer is not particularly limited as long as a stable layer can be formed on the base material. For example, a coating composition containing an organic resin and cerium oxide is prepared and applied to the base material. may be formed by solidifying and drying. A method for applying the coating composition may be selected as appropriate, and for example, methods such as roller, spray, roll coater, flow coater, dip coat, flow coating, screen printing, electrodeposition, and vapor deposition can be used.

Second Layer Containing Photocatalyst In the present invention, the second layer is a photocatalyst layer, which may be a known photocatalyst layer. If it is 5 nmol/L/min or more, which is the value specified by law, it has sufficient activity and has practical antifouling properties, and if it is 10 nmol/L/min or more, it has even higher antifouling properties. is.

In the present invention, the photocatalyst constituting the second layer is not limited as long as it can be used as a photocatalyst, but titanium oxide is preferably used. In the present invention, titanium oxide is available in various forms such as powder, sol, and solution, and any form can be used as long as it exhibits photocatalytic activity. According to a preferred embodiment of the present invention, the photocatalyst particles preferably have an average particle size of 10 nm or more and 100 nm or less, more preferably 10 nm or more and 60 nm or less. Within this range, weather resistance, decomposability of harmful gases, and various desired film properties (ultraviolet absorption, transparency, film strength, etc.) are efficiently exhibited. Moreover, a photocatalyst layer with good transparency can be obtained by using a commercially available sol photocatalyst and adjusting the particle size to 30 nm or less, preferably 20 nm or less.

In the present invention, the particle size of the photocatalyst is calculated as the number average value obtained by measuring the length of arbitrary 100 particles entering a 200,000-fold field of view with a scanning electron microscope. As for the shape of the particles, a true sphere is most preferable, but a substantially circular or elliptical shape is also preferable.

In the present invention, the second layer is a photocatalyst layer that is stable and active at a value determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014 of 5 nmol / L / min or more and 30 nmol / L / min or less. Although it is not particularly limited as long as it can be formed, for example, it may be formed by preparing a coating composition containing a photocatalyst, applying it on the first layer, solidifying it, and drying it. A method for applying the coating composition may be selected as appropriate, and for example, methods such as roller, spray, roll coater, flow coater, dip coat, flow coating, screen printing, electrodeposition, and vapor deposition can be used.

Although the film thickness of the second layer is not particularly limited, it is preferably 0.1 μm to 3 μm, more preferably 0.5 μm to 1.5 μm.

According to a preferred embodiment of the invention, the second layer contains inorganic particles. Inorganic particles include single oxides such as silica, alumina, zirconia, ceria, yttria, boronia, magnesia, calcia, ferrite, amorphous titania, and hafnia, as well as complex oxides such as barium titanate and calcium silicate. can be used, and silica particles can be preferably used. These inorganic oxides are preferably in the form of aqueous colloids using water as a dispersion medium, or organosols in which they are colloidally dispersed in a hydrophilic solvent such as ethyl alcohol, isopropyl alcohol or ethylene glycol, and the use of colloidal silica is particularly preferred. . The particle size of the inorganic particles is preferably 10 nm or more and less than 40 nm, more preferably 10 nm or more and 30 nm or less, when the inorganic particles are in the form of aqueous colloid or organosol.

Here, the average particle diameter is calculated as a number average value obtained by measuring the length of arbitrary 100 particles entering a 200,000-fold field of view with a scanning electron microscope. As for the shape of the particles, a true sphere is most preferable, but a substantially circular or elliptical shape is also preferable.

It may also contain water-soluble inorganic amorphous materials, examples of which are selected from the group consisting of metal phosphates such as alkali silicates, alkali borosilicates, alkali zirconates, and alkali phosphates. and those containing one or more of the These substances can easily form a chemisorbed water layer in the presence of water and can exhibit high hydrophilicity over a long period of time. Among these, alkali silicates are preferred, and at least one of sodium silicate, potassium silicate, lithium silicate and ammonium silicate is more preferred. In general, sodium silicate and potassium silicate have the highest adhesiveness, and ammonium silicate and lithium silicate have the highest water resistance. Considering film properties, film hardness, water resistance, etc., lithium silicate is more preferable.

In addition, other inorganic binders may be included, such as hydrolyzable silicone. Hydrolyzable silicone is a general term for organosiloxanes having alkoxy groups and/or partial hydrolysis condensates thereof. As the hydrolyzable silicone, tetrafunctional silicone compounds are often used. base) (both manufactured by Colcoat).

In the present invention, the content of the photocatalyst particles in the second layer and the coating composition is generally 1 part by mass or more and less than 50 parts by mass with respect to the total amount of 100 parts by mass of the photocatalyst particles and the inorganic oxide particles. , photocatalytic activity, appearance, durability, and other performances can be taken into account and selected as appropriate.

The invention is further illustrated by the following examples, but the invention is not limited to these examples.

Materials The following materials were prepared for the preparation of the photocatalyst-coated body.
The following materials were prepared for the coating composition for the first layer.
(1) Resin Resin 1 Silicone-modified acrylic resin having a silicon content of less than 2% by mass relative to the solid content of the silicone-modified resin Resin 2 Silicon content having a silicon content of approximately 30% by mass relative to the solid content of the silicone-modified resin Silicone-modified acrylic resin Resin 3 Acrylic resin containing no silicone component (2) Metal oxides Aqueous sols or powders of the following various oxides were used.
1. Cerium Oxide _CeO2
2. Metal oxides other than cerium oxide 2-1. A metal oxide that exhibits absorption in the middle to long wavelength range of ultraviolet rays Iron oxide Fe2O3
manganese oxide _MnO2
Niobium Oxide _Nb2O5
2-2. _Lanthanide metal oxide Lanthanum oxide _{La2O3
Neodymium} Oxide _Nd2O3
2-3. Common Metal Oxide Aluminum _{Oxide Al2O3}
Zirconium oxide _ZrO2
(3) dispersion medium: deionized water (4) pigment:
Iron-manganese composite oxide (manufactured by Dainichiseika Co., Ltd., trade name: MF-5533 Black) (used for resins 1 and 2)
Titanium oxide (manufactured by Dainichiseika Co., Ltd., trade name: MF-5765 White) (used for resin 3)
(5) UV absorber: hydroxyphenyltriazine-based UV absorber (UVA)
(6) film-forming aid: Texanol (manufactured by KH Neochem, trade name: Kyowanol M)
(7) Thickener:
Thickener 1: Hectorite Thickener 2: Alkali-swelling viscosity modifier (8) Curing agent: Hydrolyzable silicone compound (used for Resin 2)
(9) light stabilizer: hindered amine light stabilizer

The following materials were prepared for the coating composition for the second layer.
(1) Photocatalyst Titanium oxide aqueous dispersion (anatase type, particle size: X90 = 72.5 nm by laser diffraction/scattering method (JIS Z 8825: 2013), basic)
(2) Binder Water-dispersed colloidal silica (manufactured by Nissan Chemical Industries, trade name: Snowtex S, solid content 30%)
(3) Dispersion medium: deionized water (4) Additive: polyether-modified silicone surfactant

Various additions of (1) resin, (2) metal oxide, (3) dispersion medium, and (4) to (9) so that the composition shown in Preparation Table 1 of the coating composition for the first layer is obtained. A coating composition for the first layer was prepared by appropriately mixing the above agents. Here, the metal oxide concentration in Table 1 means the ratio of the solid content concentration to the resin solid content. Concentration of other additives refers to the concentration of active ingredients in the paint. Thickener 2 was added last, and the amount was such that the viscosity was 500 to 1000 mPa·s (approximately 0.5 to 3.0% by mass). The viscosity was measured at a paint temperature of 25° C. and a Brookfield viscometer M3 rotor at 60 rpm.

(1) Titanium oxide aqueous dispersion, ( 2 ) Water-dispersed colloidal silica, (3) Dispersion medium: ion-exchanged water, and (4) Additive: A photocatalyst coating liquid was obtained by mixing with a polyether-modified silicone surfactant. The total solid concentration of the photocatalyst and binder in the photocatalyst coating liquid was set to 5.5% by mass. Here, the solid content concentration means mass % when the coating liquid is dried at 105 to 110° C. and becomes a constant weight.

Fabrication of Base Material An aluminum plate was coated with an epoxy sealer and dried at room temperature to obtain a sealer-coated body. Furthermore, acrylic white enamel was applied to the sealer-coated body and dried sufficiently to obtain a base material.

The base material obtained in the preparation of the photocatalyst-coated body test body was heated to a plate temperature of 60°C, and the coating composition for the first layer was applied to the surface thereof with an air spray at a coating amount of 150 ± 50 g / m ² . and dried at 80° C. for 5 minutes to form a first layer on the substrate.

Next, the substrate coated with the first layer is heated to a plate temperature of 60°C, and the coating composition for the second layer is applied with an air spray in an amount of 10 ± 2.5 g/m ² and dried naturally. to form a second layer. The photocatalyst-coated body thus obtained was used as a test body.

The photocatalyst-coated body obtained in the evaluation test of the photocatalyst-coated body was evaluated by the following methods.
(1) Photocatalytic Activity Evaluation Test Evaluation was made in accordance with the methylene blue decomposition activity measurement method (JIS R 1703-2:2014).
(2) Weather resistance evaluation test (2-1) Adhesive tape test method (evaluated according to the following procedures 1 to 6 with reference to JIS Z 0237: 2009)
1. Test sample preparation: After painting, leave at 23±1° C., 50±5% RH for 24 hours or more, repeat the cycle of irradiation and rainfall with a metering weather meter (manufactured by Toyo Seiki Co., Ltd.), accumulated energy 162 MJ / m ² The test specimens before and after were evaluated.
2. Test atmosphere: The following steps 3 and 4 were performed at 23±1° C. and 50±5% RH.
3. Pressing of tape: A total of 2 reciprocations of a 2 kg rubber roller at a speed of 10±0.5 mm/sec4. Peeling speed: 5.0±0.2 mm/sec for tape folding at 180°5. Measurements: Ignore the first 30 mm of tape displacement and average the subsequent 20 mm stress measurements6. Calculation of tape adhesion rate maintenance rate: Calculate the percentage of the measured value after the metering weather meter test to the measured value before the test. Incidentally, a tape adhesion rate maintenance rate of 80% or more according to this evaluation test is a practically preferable value.
(2-2) Gloss retention rate According to JIS Z8741, the gloss value at 60 ° is measured with a gloss meter (VG2000 manufactured by Nippon Denshoku Industries), and the measured value after the metering weather meter test is the measured value before the test. We calculated what percentage of
Test specimen preparation: After painting, leave at 23 ± 1 ° C., 50 ± 5% RH for 24 hours or more, repeat the cycle of irradiation and rainfall with a metering weather meter (manufactured by Toyo Seiki Co., Ltd.), accumulated energy 90 MJ / m ² The test specimens before and after were evaluated.

Evaluation results
test 1
Coated bodies having combinations of the first layer and the second layer shown in Table 3 below were prepared, and the above weather resistance evaluation tests were conducted using these as test bodies. The results were as shown in Table 3.

The results in Table 3 show that even with a resin with a small Si content (less than 2% by weight), by including cerium oxide, the weather resistance is equivalent to that of a resin with a relatively large Si content (about 30% by weight). It shows that you can get sexuality.

test 2
Coated bodies of combinations of the first layer and the second layer shown in Table 4 below were prepared, and the above photocatalytic activity evaluation test and weather resistance evaluation test were performed using these as test specimens. The results were as shown in Table 4.

The results in Table 4 clearly show that the addition of cerium oxide effectively prevents deterioration of the weather resistance in comparison with the coated body to which it is not added.

test 3
Coated bodies having combinations of the first layer and the second layer shown in Table 5 below were prepared, and the above weather resistance evaluation tests were conducted using these as test bodies. The results were as shown in Table 5.

The results in Table 5 show that among various metal oxides, only cerium oxide significantly improves the weather resistance.

test 4
Coated bodies having combinations of the first layer and the second layer shown in Table 6 below were prepared, and the above weather resistance evaluation tests were conducted using these as test bodies. The results were as shown in Table 6.

The results in Table 6 show that only cerium oxide has the effect of improving weather resistance even when an ultraviolet absorber or light stabilizer is added. In this test, the amount of the ultraviolet absorber to be added is set to be equal to or greater than the ultraviolet absorbability of cerium oxide. Therefore, it is suggested that the effect of improving the weather resistance of cerium oxide is not due to its ultraviolet absorption effect.

Claims (7)

A base material, a first layer containing an organic resin on the surface of the base material, and a second layer containing a photocatalyst provided in contact with the first layer,
wherein the first layer further comprises cerium oxide (CeO ₂ );
A photocatalyst coating in which the second layer has a photocatalytic activity value of 5 nmol/L/min or more and 30 nmol/L/min or less as determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014. body. The second layer has a photocatalytic activity value of 10 nmol/L/min or more and 23 nmol/L/min or less as determined by the methylene blue decomposition activity measurement method specified in JIS R 1703-2:2014. 2. The photocatalyst-coated body according to 1. 3. The photocatalyst-coated body according to claim 1, wherein the organic resin does not contain Si, or if it contains Si, the resin has a Si concentration of less than 2 wt %. 4. The photocatalyst-coated body according to claim 1, wherein the amount of cerium oxide added in said first layer is 0.3% by weight to 10% by weight relative to the solid content of said organic resin. The photocatalyst-coated body according to any one of claims 1 to 4, wherein the first layer further contains an inorganic pigment or inorganic particles. The photocatalyst-coated body according to any one of claims 1 to 5, wherein the photocatalyst is titanium oxide. A coating composition for producing a photocatalyst-coated body according to any one of claims 1 to 6, comprising an organic resin and cerium oxide.