JP3379570B2 - Method for removing solid contaminants having hydrophilic groups and fatty acid-based oil attached to composite material surface - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a bathtub, a bathroom wall material,
Parts such as bathroom flooring materials for bathrooms, kitchen utensils such as ventilation fans, tableware, kitchen bags, and glass articles such as displays and window glasses that easily adhere to dirt, food oil, and fatty acid oils such as fingerprints. In a member such as a urinal or bath apron that easily adheres to inorganic acid calcium salt-based stains, such as a toilet bowl that easily adheres to carbohydrate-based stains, a photocatalyst-containing layer is formed on the surface to make the surface hydrophilic. The present invention relates to a technique for improving the rinsing and removing performance by using the composite material. More specifically, the present invention relates to a method of using the above composite material without impairing the ability of the solid contaminant having a hydrophilic group such as the above fatty acid oil and the like to be removed by washing with water for a long period of time.

[0002]

The present inventor has previously proposed a method of highly hydrophilizing the surface of an article by the action of a photocatalyst (WO
96/29375). According to this method, the surface of the article is coated by coating a semiconductor photocatalyst such as anatase-type titania. When the photocatalyst is photoexcited with sufficient illuminance for a sufficient time by irradiating the photocatalytic coating with light, the surface of the photocatalytic coating becomes highly hydrophilic. This hydrophilization phenomenon is explained as follows. In general, the surface energy −γ _{s at} the interface between a solid and a gas is the molecular dispersion force component γ _s ^d.
And it is possible to be composed of three components of the dipole component gamma _s ^p and hydrogen bond component gamma _s ^h are known, photocatalytic co - When the photocatalyst in the coating is optically pumped, the hydrogen bonds among the three components only components gamma _s ^h is significantly increased, thereby co - because the physically adsorbed water of coating surface increases.

The surface energy −γ _{l at} the interface between the liquid and the gas is the molecular dispersion force component γ _l ^d and the dipole component γ _l ^p.
Although be composed of three components of the hydrogen bond component gamma _l ^h are known as hydrogen bonding component by photoexcitation of the photocatalyst gamma _s ^h
Increases not only the hydrophilization phenomenon but also the wettability with other solvents. That is, the wettability with the solvent having the hydrogen bond component γ _l ^h is improved.

The present inventors have also found that in water, the contact angle between a solvent having a smaller hydrogen bonding component γ _l ^h than water, that is, many organic solvents, increases. In particular, it exhibits a high oil repellency in water for hydrocarbon-based oils such as petroleum and organic solvents having a hydrogen bonding component γ _l ^h of 0, such as methylene iodide, and the photocatalytic properties of the organic solvent adhered to the surface thereof. When the coating is immersed in water, the phenomenon that the above organic solvent is rapidly separated from the surface is recognized.

When the photocatalytic coating is immersed in water, the phenomenon that the organic solvent is rapidly released from the surface is, for example, oleic acid, trioleic acid glyceride, linoleic acid.
Even in oils having a hydrogen bond component γ _l ^h due to a carbonyl group such as acid and lauric acid, hydrogen bond component γ _l ^h
Occurs due to the small value of.

[0006]

However, in a solvent having a hydrogen bond component γ _l ^h due to these carbonyl groups, oriented adsorption of solvent molecules occurs, and the carbonyl groups are likely to be bonded to the photocatalytic coating surface by hydrogen bonds. The photocatalytic coating is cleaned by the immersion in water because the organic groups are discretely adsorbed and the organic groups are discretely directed to the outside. It was found that the contact angle was slightly increased by the operation. Therefore, after washing the adhered oil with water, the photocatalyst is not photoexcited, and when the operation of washing with water is repeated, the contact angle of the photocatalytic coating surface with water gradually increases. As a result, the hydrogen bonding component γsh on the photocatalytic coating surface is gradually reduced, so that it does not exhibit high oil repellency in water, and the performance of the adhering fatty acid oil removed by washing with water decreases. It is considered that such a tendency can occur not only in fatty acid oils but also in all solid contaminants having a hydrophilic group. The present invention has been made in view of the above circumstances, and an object thereof is to use a composite material having a photocatalytic coating that does not deteriorate the performance of washing out solid contaminants having a hydrophilic group such as fatty acid oil by washing. To provide a method.

[0007]

In the present invention, in order to solve the above problems, a photocatalyst-containing layer is formed on the surface of a substrate, and the photocatalyst is photoexcited to make the surface of the composite material hydrophilic. A method for removing solid contaminants having a hydrophilic group attached to, the method comprising the steps of washing the composite material surface with water, photoexciting the photocatalyst, and remaining by the water washing step by photocatalytic action. A method for removing a solid contaminant having a hydrophilic group attached to the surface of a composite material, comprising the step of substituting a hydrophilic group derived from the solid contaminant with adsorbed water. A method of removing a fatty acid-based oil adhering to the surface of a composite material in which a photocatalyst-containing layer is formed on the surface of a substrate and the photocatalyst is photoexcited so that the surface becomes hydrophilic; And a step of photoexciting the photocatalyst to replace the carbonyl group derived from the fatty acid remaining by the water washing step by photocatalysis with adsorbed water. A method for removing fatty acid oil is provided. The hydrophilic group derived from the solid contaminant such as the carbonyl group derived from the fatty acid remaining in the water washing step may be removed from the surface of the composite material during the water washing step or after the water washing step by photoexciting the photocatalyst and substituting it with adsorbed water. As a result, it is possible to suppress the deterioration of the water washing removal performance due to the oriented adsorption of the solid dirt component having a hydrophilic group such as a fatty acid molecule.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. For the photocatalyst of the present invention, a photocatalyst composed of an oxide semiconductor can be preferably used, and for example, anatase type titanium oxide,
Zinc oxide, tin oxide, strontium titanate, tungsten trioxide, dibismuth trioxide, ferric oxide, rutile type titanium oxide, and brookite type titanium oxide can be preferably used.

Photoexcitation of the photocatalyst is carried out by irradiating the photocatalyst with light having an energy larger than the band gap of the semiconductor photocatalyst. For example, anatase-type titanium oxide is photoexcited with ultraviolet rays having a wavelength of 387 nm or less, zinc oxide having a wavelength of 387 nm or less, tin oxide having a wavelength of 344 nm or less, and strontium titanate having a wavelength of 387 nm or less. Thus, in order to use a photocatalyst having an excitation wavelength in the ultraviolet region, as a light source, at least a trace amount of ultraviolet rays, such as fluorescent lamps, sunlight, incandescent lamps, mercury lamps, fluorescent mercury lamps, metal halide lamps, and high-pressure sodium lamps, is used. Use a light source that can illuminate. In order to replace the hydrophilic group in a solid contaminant such as a carbonyl group derived from fatty acid with adsorbed water by photoexcitation of the photocatalyst, the illuminance of excitation light is 0.
001 mW / cm ² or more, preferably 0.01 mW / c
m ² or more, more preferably 0.1 mW / cm ² or more. Therefore, a light source having a luminous body improved to have such an illuminance may be used.

The photocatalyst-containing layer has a structure in which the surface exhibits hydrophilicity by photoexcitation of the photocatalyst. This is to ensure the cleanability of the appearance only by washing with water. for that purpose,
The exposed surface of the photocatalyst containing layer is an inorganic oxide such as silica, alumina, titania, zirconia, ceria, yttria, zinc oxide, tin oxide, strontium titanate, tungsten trioxide, dibismuth trioxide, ferric oxide, molybdenum oxide. Objects, TiO ₂ / WO ₃ , TiO ₂ / Mo ₂ O ₃ , Si
O ₂ · Al ₂ O ₃ , WO ₃ / SnO ₂ , TiO ₂ / Al ₂ O ₃ ,
It is composed of a solid acid such as TiO ₂ / SiO ₂ or silicon. When the exposed surface is made of an inorganic oxide, the physically adsorbed water that hydrogen-bonds to the OH group on the surface of the inorganic oxide increases in response to photoexcitation of the photocatalyst, and the surface becomes hydrophilic. If the exposed surface is made of zirconia or ceria, the alkali resistance is improved. When the exposed surface consists of a solid acid, the amount of physically adsorbed water that is electrostatically adsorbed on the electron acceptor surface (in the case of Lewis acid) or the proton donor surface (in the case of Bronsted acid) depends on the photoexcitation of the photocatalyst. Increase and the surface becomes hydrophilic. When the exposed surface is composed of silicone, first, the organo group bonded to the silicon atom in the silicon is replaced by a hydroxyl group by photoexcitation of the photocatalyst, and the physically adsorbed water bonded to the substituted hydroxyl group by hydrogen bond is generated. , Increases in response to photoexcitation of the photocatalyst, and the surface becomes hydrophilic.

Solid contaminants having a hydrophilic group which can be used in the present invention include fatty acid oils, fatty acid salts, inorganic acid calcium salts, proteins, hydrocarbons and amino acids.
The fatty acid oil that can be used in the present invention includes, for example, linoleic acid, oleic acid, trioleic acid glyceride, edible oil,
Oils secreted by animals, fingerprints, dirt, free fatty acids, linolenic acid, arachidonic acid, glyceryl ether, stearic acid, palmitic acid, wax, phosphatidic acid, acylglycerol, lauric acid, prostaglandin, vaccenic acid, Talylic acid, isanic acid, lactobadic acid, vernolic acid, lignoceric acid, calcium oleate, behenic acid, arachidic acid, myristic acid, caproic acid, decanoic acid, butyric acid, propionic acid, acetic acid, mevalonic acid, prostacyclin, thromboxane. A2, Ryu Kotorien D
4, adipic acid, maleic acid, sterols, phospholipids,
Examples thereof include bile acids such as lithocolic acid and deoxycholic acid. Fatty acid salts that can be used in the present invention include soap dregs, calcium oleate, calcium linoleate, calcium stearate, calcium palmitate, calcium laurate, and the like. Examples of the inorganic acid calcium salt that can be used in the present invention include urinary stones, scales, calcium phosphate, calcium carbonate and the like. Hydrocarbons that can be used in the present invention include feces, cellulose, starch, amylose,
Examples thereof include saccharose.

The solid contaminants having a hydrophilic group such as fatty acid oil adhered thereto can be washed with water by, for example, immersing in water, rinsing with water, lightly rubbing while rinsing with water, and the like. it can.

The composite material to which the present invention can be applied includes, for example,
Bathtub, bathroom interior, ventilation fan, dishes, dishwasher, dish dryer, sink, cooking range, kitchen hood, kitchen utensils, window frame, window glass, washbasin, kitchen back, kitchen interior, lighting, cathode ray tube, large Toilet bowl, urinal, tile joint, tile, bathroom mirror, washbasin, sink and washbasin trap, gray
Examples include chings, bathroom ceilings, bathtub aprons, toilet mats, bath lids, shower curtains, bath chairs, and films to be attached to the above articles.

Ag, Cu, Pt and P are contained in the photocatalyst containing layer.
Metals such as d and Ru can be added. The metal is added to the photocatalyst sol by adding a compound containing the above metal, and if necessary, photoreducing the metal in a solution and applying the liquid fixed on the photocatalyst particles to the article surface, or forming on the article surface. The photocatalyst-containing layer may be added with a compound containing the above metal, photoreduced, and fixed on the photocatalyst particles. The addition of the above metal improves the oxidation / decomposition power of the photocatalyst, and accelerates the reaction of substituting the adsorbed water for the hydrophilic group derived from the solid contaminants remaining in the water washing step. Also A
When a metal such as g, Cu, or Zn is added, the metal-added layer can kill bacteria attached to the surface. In addition, this layer inhibits the growth of microorganisms such as mold, algae and moss. Therefore, it is possible to more effectively suppress the attachment of stains on the surface of the member due to the microorganisms.

[0015]

【Example】

Example. Ethyl silicate (Corcort, tetramer)
7.5 g and tetraethoxysilane (Wako Pure Chemical Industries) 7.5
g and then diluted with 111.8 g of methanol and then 2
% Aqueous nitric acid solution (23.3 g) was added, and the mixture was stirred and hydrolyzed to obtain a stock solution. Then, the stock solution was diluted 5-fold with isopropanol to obtain a primer solution. The above primer solution is PET
The (polyethylene terephthalate) film was applied by the flow coating method and then dried at room temperature (20 ° C.) for 20 minutes to cure the primer coating film. Next, 75 parts by weight of a 98% tetraethoxysilane solution and a photocatalytic coating liquid STK01 (Anatar.
25 parts by weight of a composition comprising ze type titanium oxide, an alkyl silicate, water, methanol and propanol) are mixed,
After mixing, the mixture was stirred for 1.5 hours to hydrolyze tetraethoxysilane and then diluted 25 times with ethanol to obtain a top coating solution. After applying the above-mentioned top coating solution on the primer coating film by the flow coating method, it is dried at room temperature (20 ° C.) for 20 minutes to obtain a primer coating.
The coating was cured to give a # 1 sample. For comparison with the # 1 sample, the surface of the PET film was irradiated with a BLB lamp having an illuminance of 0.1 mW / cm ² for 24 hours. As a result, the contact angle of the PET film surface with water was 78 °,
The contact angle of the surface of the # 1 sample with water showed a hydrophilic property of 0 °. Here, as the contact angle with water, a value 15 seconds after a water drop was dropped from a microsyringe using a contact angle measuring device (CA-X150, manufactured by Kyowa Interface Science Co., Ltd.) was used. next,#
After coating oleic acid on the surface of sample 1, sample # 1 was lightly rinsed in a water bath to obtain sample # 2. The # 2 sample was clean in appearance. Similarly, after oleic acid was applied to the surface of the PET film, it was lightly rinsed in a water bath, but oleic acid remained in appearance. It is considered that this difference is due to the fact that the surface of sample # 1 is highly hydrophilic and the contact angle with oleic acid in water is increased. When the contact angle with water of the # 2 sample was measured, it showed a slightly high value of 20 °. It is considered that this is because the oriented adsorption of oleic acid molecules occurred, whereby the carbonyl group was adsorbed to the photocatalytic coating surface by hydrogen bonding to form a portion in which the organo group was discretely oriented to the outside. Next, illuminance of 0.1m on sample # 2
A # 3 sample was obtained by irradiating a W / cm ² BLB lamp for 8 hours. The contact angle with water of the # 3 sample surface was 0 °. Next, the surfaces of the # 2 sample and # 3 sample were coated with oleic acid again, and after lightly rinsing in a water bath, the contact angle of each sample surface with water was measured. As a result, it was 3 for sample # 3.
While rising to 0 °, the # 2 sample stayed at 20 °, maintaining a higher degree of hydrophilicity.

Example 2 (Metal-supported photocatalyst) 100 g of ST-K01 (solid content concentration 10 wt%, pH 1.5) having a titania / silicate ratio of 80/20 was used for an inner diameter of 7.
Put a 4cm 300ml polypropylene beaker,
1.0 to 10 wt% of the titania weight 1. Ag (S
0.13-1.3 g for 100 g of T-K01 stock solution
Of AgNo3) was added and UV irradiation (20 W of B
Three LB lamps were arranged at intervals of 10 cm and irradiated at a distance of 30 cm. The reaction temperature was constant at 30 ° C. ) Then, silver was photoreduced on the surface of the titania to obtain a coating solution.
(For a photocatalyst of 100 g, the calculation is performed by irradiating the energy of 620 J as the ultraviolet energy).

Regarding 10 g of the dried product of the above coating solution, the form of silver photo-reduced and plated was metallic silver.
Confirmed by line diffraction. The silver-supported photocatalyst solution was diluted 100 times with normal propanol so that the solid content concentration of the photocatalyst was 0.1 wt%. On the other hand, a large slide glass (Matsunami Glass, thickness 1.3 mm, 76 mm
X52 mm, pre-cleaned, water edge polishing), and the contact angle of water was measured after 1 hour of natural drying. When the contact angle of water was measured with time while irradiating with ultraviolet light of 10 and 100 μW / cm ^{2 with} a BLB lamp,
The contact angle of water was maintained at 300 degrees or more and 10 degrees or less. Even when a sample having a contact angle with water of 10 degrees or less was left in a dark place, it was maintained at 10 degrees or less for 300 hours or more. Even when the same test as above was carried out with the amount of silver supported being 10 wt%, the contact angle of water of the coating film was 10 degrees or less, which was not significantly different from the case where silver was not supported, and the hydrophilicity was inhibited. There wasn't.

Since silver reacts with chlorine to form insoluble silver chloride, antibacterial performance may be improved by pre-supporting by blending silver and copper so as to form a eutectic (75:25). It is also effective to carry out photoreduction plating of a plurality of metals.
Not only silver but also copper may be supported. Even when copper is photoreductively plated on a photocatalyst in the same manner as above, the rate of hydrophilization in response to photoexcitation tends to decrease slightly, but the contact angle with water decreases to 10 degrees or less, and in the dark. It was confirmed that the contact angle with water of 10 degrees or less was maintained for 300 hours or more even when left standing.

Addition of a fragrance to a liquid obtained by photoreducing a titania with a metal such as silver or copper did not impair the hydrophilicity of the coating film. Samples of mint type fragrance (SX-7523) and citrus type fragrance (SX-2033) were obtained from Fragrance Laboratory, Takasago International Corporation. 0.3 wt% of the above fragrance was added to a silver-supported photocatalyst solution diluted 100 times with normal propanol. Addition of any of the fragrances was found to have an effect of maintaining hydrophilicity even under a low illuminance of 10 μW / cm ² or less, and the contact angle of water was maintained at 10 ° or less for 300 hours or more. Further, the tendency of extending the pot life of the liquid was recognized, and the hydrophilicity was maintained at 10 degrees or less even when the liquid was left to stand at room temperature for 2 weeks after coating.

As the pH of the photocatalyst became closer to neutral, the titania particles were more likely to aggregate, and a remarkable concentration dependence was recognized. However, the conditions under which aggregation did not occur could be understood from the relationship between the titania concentration and pH. In ST-K01 (manufactured by Ishihara Sangyo), if the solid content concentration was 5 wt% or less, aggregation and gelation of the liquid were not observed even when the pH was adjusted to 4 by adding sodium hydroxide. At pH 4, silver could be supported in a short time.

The film coated with the photocatalyst was colorless and transparent even when 10 wt% of silver was titrated to the titania by photoreduction, no black coloring peculiar to silver was observed, and decolorization was not necessary.

Example 3 (Toilet bowl, Urinal) An attempt was made to make the toilet bowl and urinal superhydrophilic and antibacterial to prevent black stains and dirt from the rim and prevent microbial slime stains. The above metal-supported photocatalyst coating solution was coated on a toilet bowl. Toilet bowl was pre-treated by cleaning with sun pole, dried on the left side and then coated on the left half, and then dried on the left side (the purpose of dryer drying is to reduce the uneven coating by applying heat to the substrate surface before coating. And to accelerate the dehydration condensation reaction of the silicate after coating to increase the adhesion). Normal use was used to compare stains on treated and untreated surfaces. The hydrophilicity of the urinal-treated surface was maintained for 3 weeks or longer, and the generation of odor was suppressed. (Odor intensity 0) On the other hand, odor was generated on the untreated surface after 1 week. (Odor intensity 2) The hydrophilicity of the surface treated with a toilet bowl was maintained for 3 weeks or longer, and no adhesion of dirt was observed. In the case of a toilet bowl, the pretreatment (pre-cleaning) showed a more remarkable cleaning effect on the waste. On the other hand, adhesion of dirt was observed on the untreated surface.

Example 4 (bathroom floor) A DAP (diallyl phthalate) bed in a bathroom was coated with a photocatalyst (ST-K01, titania / silicate ratio 8/2) carrying 1 wt% of silver with respect to titania, and then dried naturally. , When a shower was applied, the water film was extremely thin at the hydrophilized part due to superhydrophilicity, and no puddle was observed,
A large puddle was formed in the untreated part. 14 in this state
A large puddle remained in the untreated portion even after standing for a while, whereas the hydrophilized portion was completely dried. Due to the superhydrophilic effect of the silver-supported photocatalyst, the effect of promoting the drying of the DAP bed in the bathroom was observed. It is also expected that the super antibacterial action of silver will suppress the generation of mold on the floor.

Example 5 (Bathroom tile) After coating a silver-supported photocatalyst on a bathroom tile, 11 days after, the untreated portion was colored purple by the ninhydrin reaction (purified by reacting with protein and amino acid), but the coated portion Since no coloring was observed, the antifouling effect of the silver-supported photocatalyst was confirmed. In addition, the mold growth was suppressed by coating the silver-supported photocatalyst on the moldy joint. Mold was thickened on the uncoated part. The bathroom had only 60W incandescent light bulbs and windows for illumination, but the antibacterial effect of silver allowed it to exhibit an antifungal effect even in low light.

Example 6 (bathroom wall, evaluation of antifouling) Silver was post-supported by photoreduction plating on the photocatalytic coating surface of a sample prepared by the same method as above. The loading condition is that the photocatalytic coating surface is irradiated with a BLB lamp having an ultraviolet illuminance of 1 mW / cm ² for about 24 hours in advance, and then a 1 wt% silver nitrate aqueous solution is applied to the photocatalytic coating surface by brushing or dipping to obtain an ultraviolet illuminance of 1 mW. / C
The BLB lamp of m ² was irradiated for a predetermined time (about 5 to 30 minutes). After irradiation, the surface of the photocatalytic coating was washed with water and then dried. The sample coated with the photocatalytic coating was placed on the wall of the bathroom, and four people took a bath a day to evaluate the antifouling property. For the installation location, we chose the lower part of the wall of the washroom where it is easy to get dirty and has a large load of dirt. After bathing every day, it was irradiated with ultraviolet light having an ultraviolet illuminance of 10 μW / cm ^{2 with} a white fluorescent lamp at night. The stains that adhere are soap stains, sebum stains, etc., and the gloss retention rate that is close to the visual feeling was used as an index for evaluating this stain. A gloss meter manufactured by Nippon Denshoku Industries Co., Ltd. was used to measure the gloss ratio.

[0026]

[Table 1]

As shown by the antifouling evaluation results, the normal P
It was confirmed that it is less likely to get dirty than the ET steel plate. The appearance of visible stains was in good agreement with the gloss retention data.

Example 7 (additional function, antibacterial performance of actual urine) Photocatalytic coating liquid ST-K01 and S manufactured by Ishihara Sangyo
Equal amounts of T-K03 were mixed, and copper acetate was mixed so that the concentration of Cu was several% (about 1 to 10 wt%) with respect to the amount of Ti in this equal amount mixed solution. 30 while hitting the BLB lamp
The mixture was stirred at 4 ° C with a 4 hrs stirrer. This copper pre-supported photocatalytic coating liquid is nPA (normaporopanol)
It was diluted by 20 times to obtain a top coating solution. The primer-treated PET film was applied by the flow coating method, dried at room temperature, and then baked at 120 ° C. for 30 minutes. 0.5 ml of urine was dropped on the surface of the photocatalytic coating on which copper was carried by photoreduction plating, and the mixture was left for 24 hours in the room. (UV illuminance in the room was about 1 μW / cm ² for about 8 hours when indoor fluorescent lamp illumination was turned on) After 24 hours, bacteria were collected and cultured to evaluate antibacterial performance.

[0029]

[Table 2]

It can be confirmed that the general inorganic antibacterial material-coated PET film has an antibacterial effect below the detection level for the copper-supported photocatalytic PET, whereas the bacteria greatly grow after 24 hours. An antibacterial test was carried out on a sample obtained by post-supporting copper on a photocatalytic coating by photoreduction plating in the same manner as in the case of post-supporting copper. The supporting condition is that the photocatalytic coating surface is irradiated with a BLB lamp having an ultraviolet illuminance of 1 mW / cm ² for about 24 hours in advance, and then a 1 wt% aqueous solution of copper acetate is applied to the photocatalytic coating surface by brushing or dipping to obtain an ultraviolet illuminance of mW. / Cm ²
The BLB lamp was irradiated for a predetermined time (about 5 to 30 minutes). After irradiation, the surface of the photocatalytic coating was washed with water and then dried.

Example 8 (Addition of Oxide) The addition of a metal oxide such as zirconia or ceria improves the durability of the photocatalytic coating. For indoor water supply parts, in addition to mechanical properties such as scratch resistance and abrasion resistance, durability tests of materials require heat resistance such as hot water resistance and chemical resistance such as acid resistance and alkali resistance. Many. For example, an alkaline detergent is used to remove oil stains around kitchen stoves, or an alkaline detergent is used to remove clogging of drain pipes due to oils and fats accumulated in kitchen, washbasin, and bathroom drainage holes. The drug is used. Also,
Alkaline bleach is also used to remove mold and bacteria that have propagated in the bathroom. The photocatalytic coating whose exposed surface is made of silicone, which is used in the above-mentioned embodiments, may have a problem in durability with a strong alkaline agent. Even in such a case, it was possible to improve the alkali resistance performance without impairing the photocatalytic property, as shown in the table below, by only slightly adding ZnO ₂ or the like.

[0032]

[Table 3]

Further, when CeO _{2 was} added, it was also confirmed that the hydrophilization performance in response to photoexcitation of the photocatalyst was improved in the low temperature fixing type coating using the above silicon-based binder. Similar effects can be expected for hot water resistance and others.

In the production of the photocatalytically coated PET steel sheet, there is a step of applying tension to the PET film and adhering it to the vinyl chloride steel sheet (laminating). When the photocatalytic coating is applied to the PET film in advance, if the coating layer does not have elasticity, the tension applied to the PET film at the time of lamination may cause cracks in the coating layer and reduce durability.
In such a case, first, a PET film and a vinyl chloride steel plate are laminated. Then, a primer layer for facilitating the photocatalytic coating is applied, and the photocatalytic coating is applied thereon. Alternatively, only the primer layer is coated and laminated with a vinyl chloride steel plate. After that, if a photocatalytic coating is applied, this crack can be eliminated.
Actually, the photocatalytic PET steel plate prototyped by painting after this,
The characteristics (durability, appearance, photocatalytic property, etc.) comparable to those of the photocatalytically coated PET film were obtained. Alternatively,
Similar effects can be expected by adding, for example, trifunctional silicone to the photocatalytic coating layer so as to have elasticity.

Since the contact angle of water is repeatedly kept low by washing away the dirt with water and decomposing the remaining dirt, for example, the drop effect of the mirror (water is not formed into water drops because the contact angle of water is low). It can be expected to be a water film and improve the visibility of the mirror) and to maintain the antifogging effect and extend the recovery effect.

Further, the antifouling property is further improved by washing with a tap water shower or by using it together with weakly acidic soft water. Metal ions attached to the photocatalytic coating surface can also be eluted and removed by washing with weakly acidic soft water or acidic water. In addition, the bacteriostatic effect of water accumulated in traps can be expected. Furthermore, as a method of cleaning when soiled for a long period of time, a neutral or acidic detergent may be applied to further enhance the soil removal effect. Acid is particularly effective. It goes without saying that the dirt can be removed more quickly by rubbing it lightly compared with mere washing with water. Water spots (water stains) due to Ca in tap water can be easily removed from stains as compared with ordinary PET steel sheets by using the above acidic detergent and have an easy cleaning effect.

Further, when the UV illuminance is low and the photocatalytic effect is weak, the effect of the surfactant in the detergent can assist the initial hydrophilic property or provide gloss.

The above-mentioned dripping property can be expected not only on the mirror but also on the wall and the like, and it is possible to prevent the growth of microorganisms such as mold due to residual water droplets and the adhesion of organic hydrophobic stains due to the water film formation due to the dripping property. You can expect dirt.

Further, when applying a photocatalytic coating to a large product, it is preferable to add a leveling agent to the coating liquid, but many leveling agents give off an offensive odor at the time of coating, so if a perfume is added to suppress the offensive odor, Good. As described in the above Examples, for example, in the mint-based fragrance, the offensive odor can be suppressed without inhibiting the hydrophilization reaction by the photoexcitation of the photocatalyst.

[0040]

EFFECTS OF THE INVENTION According to the method of the present invention, it is possible to prevent permanently lowering the ability of solid contaminants having a hydrophilic group such as fatty acid oil attached to the composite material having photocatalytic coating and having a hydrophilic group to be washed off. It becomes possible to do.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI C11D 7/00 C11D 7/00 C23G 5/00 C23G 5/00 // B32B 33/00 B32B 33/00 (58) Fields investigated (Int.Cl. ⁷ , DB name) B08B 3/10 B01J 21/08 B01J 35/02 B05D 3/00 B08B 17/00 C11D 7/00 C23G 5/00 B32B 33/00

Claims (2)

(57) [Claims] 1. A method of removing a solid contaminant having a hydrophilic group attached to the surface of a composite material in which a photocatalyst-containing layer is formed on the surface of a substrate and the photocatalyst is photoexcited to make the surface hydrophilic. In the method, the step of washing the surface of the composite material with water, photoexciting the photocatalyst, and replacing the hydrophilic group derived from the solid contaminants remaining by the washing step by photocatalysis with adsorbed water. A method for removing solid contaminants having a hydrophilic group attached to the surface of a composite material, which comprises: 2. A method for removing a fatty acid-based oil adhering to a surface of a composite material, wherein a photocatalyst-containing layer is formed on a surface of a base material, and the photocatalyst is photoexcited to make the surface of the composite material hydrophilic. The method comprises a step of washing the surface of the composite material with water, a step of photoexciting the photocatalyst, and replacing the carbonyl group derived from the fatty acid remaining by the washing step by photocatalysis with adsorbed water. A method for removing fatty acid oil adhered to the surface of a composite material.