JP3882227B2 - Highly cleanable design member and method for cleaning design member - Google Patents

Description

【００７０】
この結果から、膜厚０．２μm 以上では意匠性を損う可能性のある干渉縞が生じることが判明した。そして、膜厚０．２未満では、問題となるほどの干渉縞や白濁は生じないことが分った。
比較のため、上述した方法と同様の方法でシリコーンとチタニアの重量比が１：９となるような膜厚０．１μm の塗膜（トップコート）を形成した。このとき成膜された膜の屈折率は２．３であった。この試料について塗膜外観を観察したところ表１の試料Ｄと比較してややギラギラと反射する感じが観察された。
【００７１】
【発明の効果】
以上の説明から明らかなように、本発明は、雨水や簡単なシャワー程度でも十分に清浄性を維持でき、かつ意匠性は損なわれない高清浄性意匠部材、及び、そのような高清浄性意匠部材を得るための意匠部材の清浄化方法を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a member having design properties such as a laminated steel sheet building material and an automobile paint outer plate, and a cleaning method thereof. In particular, a high cleanliness design member that can maintain sufficient cleanliness only by washing with rain water or a simple shower and that does not impair the designability, and a design member for obtaining such a high cleanliness design member It relates to a cleaning method.
[0002]
[Prior art]
The prior art will be described using a laminated steel sheet building material as an example.
Laminated steel sheets can produce various designs by stacking one or more colored films, patterned films, transparent films, embossed films, etc., and bonding them onto the steel sheet. Widely used as a material.
[0003]
[Problems to be solved by the invention]
However, the surface of the laminated steel building material is gradually soiled by exposure for a long period of time outdoors, and the design properties thereof deteriorate. In order to avoid such a situation as much as possible, measures have been taken to make the material of the design film a water-repellent fluororesin, but the water-repellent film is likely to be attached with hydrophobic dirt (oil). Some point out that it is easy to get dirty in areas and cities.
[0004]
After all, in the past, when the surface of the building material is soiled, there has been no effective means other than cleaning mainly by human power in order to recover the cleanliness and design.
An object of the present invention is to provide a highly clean design member that can sufficiently maintain cleanliness only by washing with rainwater or a simple shower and that does not impair the design. Moreover, it aims at providing the cleaning method of the design member for obtaining such a highly clean design member.
[0005]
[Means for Solving the Problems]
  In order to solve the above problems, a highly clean design member of the present invention comprises a base material that has been subjected to an aesthetic treatment, and a surface layer that includes an optical semiconductor formed on the surface of the base material, the surface of which is Shows hydrophilicity with a contact angle with water of less than 10 °, and the thickness of the surface layer is less than 0.2 μmThe refractive index of the surface layer is 2 or lessIt is characterized by that.
[0006]
If the surface of the member is sufficiently hydrophilic, hydrophobic dirt (oil, fat, carbon black, smoke, etc.) does not adhere to the surface of the member in the presence of water. In addition, dirt adhered when no water is present can be removed by rinsing with water and rubbing lightly. On the other hand, hydrophilic dirt (mud dirt, dust, etc.) adheres to the surface of the member, but the dirt is removed by rinsing with water or rubbing lightly.
In the design member of the present invention, the reason why the thickness of the surface layer containing the optical semiconductor is less than 0.2 μm is to prevent white turbidity and interference fringes that impair the aesthetics. The quantitative basis will be described later.
[0007]
  In the present invention, the refractive index of the surface layer is set to 2 or less.TheThe reason for this is to reduce the reflection by the surface layer and to eliminate the glare caused by the formation of the surface layer.
  The refractive index of anatase-type titanium oxide that can be most suitably used as the optical semiconductor particles is 2.5. Therefore, when the surface layer is formed only with anatase-type titanium oxide, the above-mentioned glittering feeling remains, and in this case, it is preferable to add a substance having a refractive index smaller than 2. As a material having a refractive index smaller than 2, silica (1.48), silicone (about 1.5), alumina (1.6), tin oxide (1.9) and the like can be used. Among these, since silicone is hydrophobic as it is, at least a part of the organo group bonded to the silicon atom is substituted with a hydroxyl group by a method described later.
  In the present invention, the average particle diameter of the optical semiconductor particles contained in the surface layer is preferably 0.1 μm or less. The reason is to eliminate white turbidity due to light scattering caused by the optical semiconductor particles.
  Furthermore, in the present invention, the water absorption rate of the surface layer is preferably 1% or less. The reason for this is to make it difficult to cause corrosion and deterioration of the underlying metal or film, thereby preventing changes in design.
[0008]
Further, the design member cleaning method of the present invention includes a step of forming a surface layer having a thickness of less than 0.2 μm including an optical semiconductor on the surface of a substrate subjected to aesthetic treatment, Irradiating light having a wavelength shorter than the excitation light wavelength of the semiconductor to make the surface hydrophilic.
By this method, it is possible to provide a highly clean design member that can maintain design properties by rain water or simple water washing.
[0009]
Next, the relationship between the optical semiconductor and hydrophilicity will be described.
The present inventor has found that the surface of the optical semiconductor is highly hydrophilized when the optical semiconductor is photoexcited. That is, when the photoconductive titania is photoexcited with ultraviolet rays, the surface is highly hydrophilized so that the contact angle with water is 10 ° or less, more specifically 5 ° or less, particularly about 0 °, and It was discovered that high hydrophilicity is maintained and restored by light irradiation, and further, under certain conditions, a state of once highly hydrophilic is maintained even in a dark place for 3 weeks or more.
[0010]
When light having a wavelength of energy higher than the band gap energy of the optical semiconductor is irradiated for a sufficient time at a sufficient illuminance, the surface of the optical semiconductor-containing layer becomes super hydrophilic.
The superhydrophilization phenomenon of the surface caused by photoexcitation of the optical semiconductor cannot be clearly explained at present. It seems that the superhydrophilization phenomenon by the optical semiconductor is not necessarily the same as the photodegradation of the substance by the photocatalytic oxidation-reduction reaction conventionally known in the field related to the chemical reaction of the optical semiconductor. In this regard, the conventional theory regarding the photocatalytic oxidation-reduction reaction is that an electron-hole pair is generated by photoexcitation, and the generated electron reduces surface oxygen to superoxide ion (O₂ ^-), And holes oxidize surface hydroxyl groups to produce hydroxyl radicals (.OH), which are highly reactive reactive oxygen species (O₂ ^-The substance was decomposed by the redox reaction of (.OH).
[0011]
However, the superhydrophilization phenomenon by the optical semiconductor does not agree with the conventional knowledge about the photocatalytic decomposition of the substance in at least two points. First, in the conventional theory, optical semiconductors such as rutile and tin oxide do not proceed with the reduction reaction because the energy level of the conductor is not sufficiently high, and as a result, electrons photoexcited by the conductor It was thought that electron-hole pairs generated by photoexcitation recombine without participating in the redox reaction. On the other hand, it was confirmed that the hydrophilization phenomenon caused by the optical semiconductor also occurs in an optical semiconductor such as rutile or tin oxide.
[0012]
Secondly, conventionally, it is considered that decomposition of a substance by a photocatalytic oxidation-reduction reaction does not occur unless the thickness of the optical semiconductor layer is at least 100 nm or more. On the other hand, it was observed that superhydrophilicity by the optical semiconductor occurs even when the film thickness of the photocatalyst containing layer is on the order of several nm.
[0013]
Therefore, although it is not possible to conclude clearly, it is considered that the superhydrophilization phenomenon by the photo semiconductor is a slightly different phenomenon from the photodegradation of the substance by the photocatalytic oxidation-reduction reaction. However, it was confirmed that the surface would not be superhydrophilic unless irradiated with light having an energy higher than the band gap energy of the optical semiconductor. Presumably, the surface of the photosemiconductor-containing layer is given polarity by the conduction electrons and holes generated by excitation of the photosemiconductor, and water becomes a hydroxyl group (OH^- ), And a physical adsorption water layer is formed thereon, and the surface is considered to be superhydrophilic.
[0014]
Once the surface of the photosemiconductor-containing layer is highly hydrophilized by photoexcitation, the hydrophilicity of the surface lasts for a certain period even if the substrate is kept in a dark place. When contaminants are adsorbed on the surface hydroxyl groups with the passage of time and the surface gradually loses super hydrophilicity, the super hydrophilicity is restored by photoexcitation again.
[0015]
In order to first hydrophilize the optical semiconductor-containing layer, any light source having a wavelength of energy higher than the band gap energy of the optical semiconductor can be used. In the case of an optical semiconductor whose photoexcitation wavelength is located in the ultraviolet region, such as titania, the ultraviolet rays contained in the sunlight are preferably used under the condition that sunlight hits the substrate coated with the optical semiconductor-containing layer. be able to. The optical semiconductor can be photoexcited by an artificial light source indoors or at night. As will be described later, when the optical semiconductor-containing layer is made of silica-containing titania, it can be easily hydrophilized even with weak ultraviolet rays contained in a fluorescent lamp.
[0016]
After the surface of the optical semiconductor-containing layer is once made superhydrophilic, it can be maintained or recovered by relatively weak light. For example, in the case of titania, the maintenance and recovery of hydrophilicity can be sufficiently performed even with the weak ultraviolet rays contained in indoor lighting such as a fluorescent lamp.
[0017]
Even if the optical semiconductor-containing layer is very thin, it exhibits hydrophilicity. In particular, since the photocatalytic semiconductor material made of a metal oxide has sufficient hardness, the optical semiconductor-containing layer has sufficient durability and wear resistance.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Base material
In the present invention, the base material is, for example, metal, ceramics, glass, plastics, wood, stone, cement, cement mortar, concrete, precast reinforced concrete, lightweight cellular concrete (ALC) panel, asbestos slate, pulp cement board, asbestos Cement calcium silicate board, gypsum plaster, gypsum board, combinations thereof, laminates, or building exteriors, window frames, structural members, window glass; automobiles, rail cars, aircraft, ships Vehicle exteriors and paints such as: machinery and equipment exteriors, dust covers and paints; traffic signs, various display devices, advertising tower exteriors and paints. The surface of the substrate is coated with a photosemiconductor coating.
Examples of the substrate that are particularly excellent in terms of heat resistance, light weight, low cost, and strength include ALC panels, asbestos slate, and asbestos cement calcium silicate plates.
Examples of the base conditioner (undercoat) to be coated on the substrate include special rubber-based elastic sealers, acrylic resin-based sealers, epoxy resin sealers, organic fillers, inorganic fillers, and the like.
For example, a silicone resin paint, an acrylic resin paint, an acrylic urethane resin paint, a fluororesin paint, and a combination thereof (overcoat) are suitable as the colored paint (intercoat) applied on the undercoat.
A photocatalyst-containing siloxane resin or the like can be used as a coating film mainly composed of a photocatalyst and a silicone-based resin as an example of the top coat.
[0018]
Mechanical devices and articles placed outside buildings and outdoors are exposed to sunlight during the day, so that the surface of the photosemiconductor coating is highly hydrophilic. In addition, the surface is occasionally exposed to rainfall. Every time the hydrophilized surface receives rainfall, soot and contaminants adhering to the surface of the substrate are washed away by raindrops and the surface is self-purified.
[0019]
The surface of the photo-semiconductor coating is highly hydrophilized so that the contact angle with water is 10 ° or less, preferably 5 ° or less, particularly about 0 °, so that not only urban dust containing a large amount of lipophilic components Inorganic dust such as clay minerals can be easily washed away from the surface. Thus, the surface of the substrate is highly self-cleaned and kept clean by natural action.
[0020]
If the substrate is made of a non-heat-resistant material such as plastics, or if the substrate is painted with paint, apply a photo-oxidation-resistant paint containing an optical semiconductor to the surface as described later. By photocuring and curing, an optical semiconductor coating can be formed.
[0021]
Optical semiconductor
As an optical semiconductor used for the hydrophilic fiber of the present invention, titania (TiO 2) is used.₂ ) Is most preferred. Titania is harmless, chemically stable, and available at low cost. Further, titania has a high band gap energy, and therefore requires ultraviolet light for photoexcitation and does not absorb visible light in the process of photoexcitation, so that no color formation due to complementary color components occurs.
[0022]
As titania, both anatase and rutile can be used. The advantage of anatase type titania is that a sol in which very fine particles are dispersed can be easily obtained on the market, and a very thin thin film can be easily formed. Rutile-type titania has a conduction band level lower than that of anatase-type, but it can be used for the purpose of superhydrophilicity with an optical semiconductor. When the substrate is coated with an optical semiconductor coating made of titania, and titania is photoexcited by ultraviolet rays, water becomes hydroxyl (OH)^- ), And a physical adsorption water layer is formed on the surface. As a result, the surface is considered to be superhydrophilic.
[0023]
Other optical semiconductors that can be used in the present invention include ZnO and SnO.₂ , SrTiO_Three , WO_Three , Bi₂ O_Three , Fe₂ O_Three There are metal oxides such as These metal oxides, like titania, have metal elements and oxygen on the surface, so that surface hydroxyl groups (OH^- ).
Moreover, you may mix the particle | grains of an optical semiconductor with the metal oxides which are not optical semiconductors, such as a silica. In particular, when an optical semiconductor is blended with silica or tin oxide, the surface can be highly hydrophilized.
[0024]
As an example of a method for producing such an optical semiconductor layer composed of silica-containing titania, a precursor of amorphous silica (for example, tetraethoxysilane, tetraisopropoxysilane, tetra n-propoxysilane, tetrabutoxysilane, tetramethoxysilane, A mixture of silanol which is a hydrolyzate thereof; or a polysiloxane having an average molecular weight of 3,000 or less) and a crystalline titania sol is applied to the surface of the substrate and hydrolyzed as necessary. After the silanol is formed, the optical semiconductor layer in which titania is bound with amorphous silica is formed by heating the silanol to room temperature or if necessary and subjecting it to dehydration condensation polymerization.
[0025]
Formation of photocatalytic layer by firing amorphous titania
When the substrate is made of a heat-resistant material such as metal, ceramics, or glass, it has super-hydrophilic properties such that the contact angle with water is 0 °. One preferred way of forming the coating is to first coat the surface of the substrate with amorphous titania and then phase change the amorphous titania to crystalline titania (anatase or rutile) by firing. Any of the following methods can be employed for forming the amorphous titania.
[0026]
(1) Hydrolysis and dehydration condensation polymerization of organic titanium compounds
Add a hydrolysis inhibitor such as hydrochloric acid or ethylamine to titanium alkoxide, for example, tetraethoxy titanium, tetraisopropoxy titanium, tetra n-propoxy titanium, tetrabutoxy titanium, tetramethoxy titanium, After diluting with alcohol, with partial or full hydrolysis, the mixture can be spray coated, flow coated, spin coated, dip coated, roll coated or other coating methods to form a substrate It is applied to the surface of and dried at room temperature to 200 ° C. By drying, the hydrolysis of titanium alkoxide is completed to produce titanium hydroxide, and an amorphous titania layer is formed on the surface of the substrate by dehydration condensation polymerization of titanium hydroxide.
Instead of the titanium alkoxide, other organic titanium compounds such as titanium chelate or titanium acetate may be used.
[0027]
(2) Formation of amorphous titania from inorganic titanium compounds
Inorganic titanium compounds such as TiCl_Four Or Ti (SO_Four)₂ Is applied to the surface of the substrate by spray coating, flow coating, spin coating, dip coating or roll coating. Next, the inorganic titanium compound is dried at a temperature of about 100 to 200 ° C. to be subjected to hydrolysis and dehydration condensation polymerization to form an amorphous titania layer on the surface of the substrate. Or TiCl_Four Amorphous titania may be formed on the surface of the substrate by chemical vapor deposition.
[0028]
(3) Formation of amorphous titania by sputtering
Amorphous titania is deposited on the surface of the substrate by irradiating a metal titanium target with an electron beam in an oxidizing atmosphere.
[0029]
(4) Firing temperature
Amorphous titania is baked at a temperature at least equal to or higher than the crystallization temperature of anatase. Amorphous titania can be converted to anatase titania by baking at a temperature of 400 to 500 ° C. or higher. Amorphous titania can be converted to rutile titania by baking at a temperature of 600 to 700 ° C. or higher.
[0030]
Photocatalytic layer made of silica-containing titania
Another preferred method of forming a photo-semiconductor coating with excellent wear resistance that exhibits superhydrophilicity with a contact angle with water of 0 ° is based on a photo-semiconductor coating comprising a mixture of titania and silica. It is to be formed on the surface of the material. The ratio of silica to the total of titania and silica can be 5 to 90 mol%, preferably 10 to 70 mol%, more preferably 10 to 50 mol%. Any one of the following methods can be employed to form an optical semiconductor coating made of silica-containing titania.
[0031]
(1) A suspension containing anatase-type or rutile-type titania particles and silica particles is applied to the surface of the substrate and sintered at a temperature below the softening point of the substrate.
(2) Amorphous silica precursors (for example, tetraalkoxysilanes such as tetraethoxysilane, tetraisopropoxysilane, tetra n-propoxysilane, tetrabutoxysilane, tetramethoxysilane; silanols that are hydrolysates thereof; Or a polysiloxane having an average molecular weight of 3,000 or less) and a crystalline titania sol are applied to the surface of the substrate, and if necessary, hydrolyzed to form silanol, and then heated at a temperature of about 100 ° C. or higher. By subjecting silanol to dehydration condensation polymerization, an optical semiconducting coating in which titania is bound with amorphous silica is formed. In particular, if the dehydration condensation polymerization temperature of silanol is performed at a temperature of about 200 ° C. or more, the degree of polymerization of silanol can be increased and the alkali resistance performance of the optical semiconductor coating can be improved.
[0032]
(3) Amorphous titania precursors (organic titanium compounds such as titanium alkoxides, chelates, or acetates, or TiCl_Four Or Ti (SO_Four)₂ By applying a suspension obtained by dispersing silica particles in a solution of an inorganic titanium compound) to the surface of the substrate, and subjecting the titanium compound to hydrolysis and dehydration condensation polymerization at a temperature from room temperature to 200 ° C. Then, an amorphous titania thin film in which silica particles are dispersed is formed. Next, amorphous titania is phase-changed to crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and to a temperature equal to or lower than the softening point of the substrate.
[0033]
(4) Amorphous titania precursor (organic titanium compound such as titanium alkoxide, chelate, or acetate, or TiCl_Four Or Ti (SO_Four)₂ A precursor of amorphous silica (e.g., tetraethoxysilane, tetraisopropoxysilane, tetra n-propoxysilane, tetrabutoxysilane, tetramethoxysilane, etc.) to a solution of an inorganic titanium compound); Hydrolyzate silanol; or polysiloxane having an average molecular weight of 3,000 or less) is mixed and applied to the surface of the substrate. Subsequently, these precursors are subjected to hydrolysis and dehydration condensation polymerization to form a thin film made of a mixture of amorphous titania and amorphous silica. Next, amorphous titania is phase-changed to crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and to a temperature equal to or lower than the softening point of the substrate.
[0034]
An optical semiconductor layer made of titania-containing titania
Still another preferred method of forming a photo-semiconductor coating with excellent wear resistance that exhibits superhydrophilicity such that the contact angle with water is 0 ° is based on a photo-semiconductor coating comprising a mixture of titania and tin oxide. It is to be formed on the surface of the material. The ratio of tin oxide to the total of titania and tin oxide can be 1 to 95% by weight, preferably 1 to 50% by weight. Any one of the following methods can be employed for forming an optical semiconductor coating comprising titania containing tin oxide.
[0035]
(1) A suspension containing anatase-type or rutile-type titania particles and tin oxide particles is applied to the surface of the substrate and sintered at a temperature below the softening point of the substrate.
(2) Amorphous titania precursors (organic titanium compounds such as titanium alkoxides, chelates, or acetates, or TiCl_Four Or Ti (SO_Four)₂ A suspension obtained by dispersing tin oxide particles in a solution of an inorganic titanium compound such as the above is applied to the surface of a substrate, and the titanium compound is subjected to hydrolysis and dehydration condensation polymerization at a temperature from room temperature to 200 ° C. Thus, an amorphous titania thin film in which tin oxide particles are dispersed is formed. Next, amorphous titania is phase-changed to crystalline titania by heating to a temperature equal to or higher than the crystallization temperature of titania and to a temperature equal to or lower than the softening point of the substrate.
[0036]
Silicone paint containing optical semiconductor
Still another preferred way of forming a photo-semiconductor layer exhibiting superhydrophilicity with a water contact angle of 0 ° is an uncured or partially cured silicone (organopolysiloxane) or a silicone precursor Using a composition in which particles of an optical semiconductor are dispersed in a coating film-forming element comprising: After this composition is applied to the surface of the substrate and the coating film forming element is cured, when the optical semiconductor is photoexcited, the organic group bonded to the silicon atom of the silicone molecule is replaced with a hydroxyl group by the action of the optical semiconductor, The surface of the semiconductor-containing layer is superhydrophilic.
[0037]
This approach has several advantages. Since the photo-semiconductor-containing silicone coating can be cured at room temperature or at a relatively low temperature, it can also be applied to non-heat resistant materials such as plastics and organic substances. This coating composition containing an optical semiconductor can be applied to an existing base material that requires superhydrophilization of the surface at any time by dipping, brushing, spray coating, roll coating or the like. Superhydrophilicity by photoexcitation of an optical semiconductor can be easily performed with a light source such as sunlight.
[0038]
Furthermore, when a coating film is formed on a plastically workable substrate such as a steel plate, the steel plate can be easily plastically processed as necessary before photoexcitation after the coating film is cured. Before photoexcitation, an organic group is bonded to the silicon atom of the silicone molecule, so the coating film is sufficiently flexible, so that the steel sheet can be easily plastic processed without damaging the coating film. Can do. After the plastic working, if the optical semiconductor is photoexcited, the organic group bonded to the silicon atom of the silicone molecule is replaced with a hydroxyl group by the optical semiconductor action, and the surface of the coating film becomes superhydrophilic.
[0039]
Since the photo-semiconductor-containing silicone composition has a siloxane bond, the photo-semiconductor-containing silicone composition has sufficient resistance to the photo-oxidation action of the photo semiconductor (photo semiconductor).
Still another advantage of the optical semiconductor coating comprising the optical semiconductor-containing silicone paint is that once the surface is made superhydrophilic, it remains superhydrophilic for a long time even if kept in a dark place, and like a fluorescent lamp. It is to recover the super hydrophilicity even with the light of an indoor lamp.
[0040]
Examples of coating film forming elements include methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltri-t-butoxysilane; ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxy Silane, ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-t-butoxysilane; n-propyltrichlorosilane, n-propyltribromosilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltri Isopropoxysilane, n-propyltri-t-butoxysilane; n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane n-hexyltriisopropoxysilane, n-hexyltri-t-butoxysilane; n-decyltrichlorosilane, n-decyltribromosilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, n-decyltriisopropoxysilane N-decyltri-t-butoxysilane; n-octadecyltrichlorosilane, n-octadecyltribromosilane, n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane, n-octadecyltri-t- Butoxysilane; phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltrit-butoxysilane; tetrac Silane, tetrabromosilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane; dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane; diphenyldichlorosilane, diphenyldibromo Silane, diphenyldimethoxysilane, diphenyldiethoxysilane; phenylmethyldichlorosilane, phenylmethyldibromosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane; trichlorohydrosilane, tribromohydrosilane, trimethoxyhydrosilane, triethoxyhydrosilane, tri Isopropoxyhydrosilane, tri-t-butoxyhydrosilane; vinyltrichlorosilane, vinyltribromosilane, Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltri-t-butoxysilane; trifluoropropyltrichlorosilane, trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tri Fluoropropyltriisopropoxysilane, trifluoropropyltri-t-butoxysilane; γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycyl Sidoxypropyltriethoxysilane, γ-glycidoxypropyltriisopropoxysilane, γ-glycidoxypropyltri-t-butoxysilane; γ-methacryloxypropyl Tildimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltriisopropoxysilane, γ-methacrylic Roxypropyltri-t-butoxysilane; γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriisopropoxysilane, γ-aminopropyltri-t-butoxysilane; γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropi Lutriethoxysilane, γ-mercaptopropyltriisopropoxysilane, γ-mercaptopropyltri-t-butoxysilane; β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltri Ethoxysilanes; and their partial hydrolysates; and mixtures thereof can be used.
[0041]
In order to ensure good hardness and smoothness of the silicone coating film, it is preferable to contain 10 mol% or more of a three-dimensional crosslinkable siloxane. Furthermore, in order to provide sufficient flexibility of the coating film while ensuring good hardness and smoothness, it is preferable to contain 60 mol% or less of a two-dimensional crosslinked siloxane. In addition, in order to increase the rate at which the organic group bonded to the silicon atom of the silicone molecule is replaced with a hydroxyl group by photoexcitation, a silicone in which the organic group bonded to the silicon atom of the silicone molecule is an n-propyl group or a phenyl group is used. Is preferred. Instead of silicone having a siloxane bond, an organopolysilazane compound having a silazane bond can also be used.
[0042]
Add antibacterial enhancer
The optical semiconductor-containing layer can be doped with a metal such as Ag, Cu, or Zn. In order to dope an optical semiconductor with Ag, Cu, or Zn, a soluble salt of these metals is added to a suspension of optical semiconductor particles, and an optical semiconductor-containing layer is formed using the resulting solution. it can. Alternatively, after forming the photosemiconductor-containing layer, a soluble salt of these metals may be applied and photoreduced by light irradiation.
[0043]
The photosemiconductor-containing layer doped with Ag, Cu, or Zn can kill bacteria attached to the surface. Furthermore, this photosemiconductor-containing layer suppresses the growth of microorganisms such as cocoons, algae, and moss. Therefore, the surface of the design member can be kept clean for a long period of time.
[0044]
Addition of photoactivity enhancer
The optical semiconductor-containing layer can be further doped with a platinum group metal such as Pt, Pd, Rh, Ru, Os, and Ir. These metals can be similarly doped into the optical semiconductor by photoreduction deposition or addition of soluble salts. When the optical semiconductor is doped with a platinum group metal, the redox activity of the optical semiconductor can be enhanced, and contaminants attached to the surface can be decomposed.
[0045]
Photoexcitation / UV irradiation
In the present invention, the optical semiconductor-containing layer is preferably formed of an optical semiconductor that has a high band gap energy and is photoexcited only by ultraviolet rays, such as titania. If it does so, visible light will not be absorbed by the optical-semiconductor content layer, and a member will not color by a complementary color component. Anatase type titania can be photoexcited with ultraviolet light having a wavelength of 387 nm or less, rutile type titania is 431 nm or less, tin oxide is 344 nm or less, and zinc oxide is 387 nm or less.
[0046]
As the ultraviolet light source, a room lamp such as a fluorescent lamp, an incandescent lamp, a metal halide lamp, or a mercury lamp can be used. Under conditions exposed to sunlight, the optical semiconductor is advantageously photoexcited naturally by the ultraviolet light contained in the sunlight.
[0047]
Photoexcitation can or can be carried out until the contact angle of the surface with water is about 10 ° or less, preferably about 5 ° or less, especially about 0 °. In general, 0.001mW / cm²Can be made superhydrophilic until the contact angle with water reaches about 0 ° within a few days. The illuminance of ultraviolet rays contained in sunlight falling on the earth's surface is about 0.1-1 mW / cm²Therefore, when exposed to sunlight, the surface can be made superhydrophilic in a shorter time.
[0048]
When the surface of the design member is self-cleaned by rain (self-cleaning) or prevents the adhesion of contaminants, the optical semiconductor-containing layer can be formed of an optical semiconductor that can be photoexcited with ultraviolet light or visible light. The hydrophilic design member covered with the optical semiconductor-containing layer is placed outdoors and exposed to sunlight and rain.
[0049]
When the photo-semiconductor-containing layer is formed of titania-containing silicone, it is preferable to photoexcite the photocatalyst with sufficient illuminance so that a sufficient amount of surface organic groups bonded to silicon atoms of the silicone molecule are replaced with hydroxyl groups. . The most advantageous way for this is to use sunlight. Once the surface is highly hydrophilized, the hydrophilicity persists at night. The hydrophilicity is restored and maintained every time it is exposed to sunlight again.
[0050]
When providing the user with the design member of the present invention, it is desirable to make the design member superhydrophilic in advance.
[0051]
Principle of surface layer thickness determination
A phenomenon in which a thin transparent film such as a soap bubble or oil flowing on water exhibits a beautiful color is caused by light interference. A thin film of an optical semiconductor material may also produce a striped interference color due to light interference.
The interference color is determined by the refractive index n of the thin film, the film thickness t, the light refraction angle r, and the light wavelength λ.
2n · t · cos r = m · (λ / 2) (m: natural number)
If m is an odd number, the light is strengthened as a result of the interference, and if it is an even number, the light appears to change depending on the angle of the light. ("Physics Handbook" by Morikazu Toda, Ryuko Miyajima, Asakura Shoten, p.282)
[0052]
By reducing the film thickness t, interference fringes can be reduced,
n · t ≦ λ₀ / 4 (λ₀ Is a purple wavelength: 0.35 μm)
When the relationship is established, the interference fringes are completely eliminated.
When n = 1.5, t ≦ 0.058 μm
When n = 2.0, t ≦ 0.044 μm
When n = 2.5, t ≦ 0.035 μm
From the results of such quantitative examination and the examples described later, the thickness of the surface layer was set to less than 0.2 μm.
[0053]
In this invention, it is preferable that the protection treatment for protecting the said designable film or designable coating from the photoredox reaction by the photocatalytic action of the said optical semiconductor is given.
As one form of such a treatment, there is one in which the photo-semiconductor-containing layer has a weak redox-reducing hydrophilic function. Such an idea is based on the discovery that the hydrophilicity phenomenon on the surface of the member by the optical semiconductor is fundamentally different from the photooxidation-reduction reaction by the optical semiconductor. Based on this discovery, the present inventor has found that there is a structure that exhibits a hydrophilization phenomenon, although the photooxidation-reduction reaction is hardly exhibited in the design of the optical semiconductor thin film.
[0054]
The first mode of weak redox hydrophilization is to place the energy level of the conduction band of the optical semiconductor at a positive value when the hydrogen generation level is 0 eV.
The conventional theory concerning the photo-redox reaction is that a conduction electron-hole pair is generated by photoexcitation, and then the reduction reaction by the generated conduction electron and the oxidation reaction by the hole are simultaneously promoted and proceed.
Therefore, tin oxide or rutile, whose lower end of the energy level of the conduction band of the optical semiconductor is not sufficiently high on the negative side, has a structure in which the reduction reaction due to conduction electrons does not proceed easily and only the oxidation reaction due to holes tends to be promoted. In such a structure, conduction electrons become excessive, and electron-hole pairs generated by photoexcitation recombine without participating in the oxidation-reduction reaction, so that practically neither an oxidation reaction nor a reduction reaction occurs. However, the hydrophilization phenomenon by photoexcitation proceeds.
[0055]
When the photoredox reaction of an optical semiconductor is used for decomposition of an organic substance, the decomposition reaction is performed using water or oxygen in the environment. In other words, the conduction electrons generated by photoexcitation reduce oxygen to superoxide ions (O₂ ^-), And holes oxidize hydroxyl groups to generate hydroxyl radicals (.OH), which are highly reactive active oxygen species (O₂ ^-Organic substances are decomposed by the redox reaction of (.OH).
Therefore, in order to effectively photodeoxidize and decompose organic matter, the energy level at the upper end of the valence band that generates holes is positioned on the positive side of the oxygen generation level (+0.82 eV) from which the hydroxyl group emits electrons. In addition, the energy level at the lower end of the conduction band generated by conduction electrons may be positioned on the negative side from the hydrogen generation level (0 eV) that hydrogen releases electrons and donates to the oxygen side.
Therefore, conversely, in order to prevent the organic matter from being effectively photooxidatively reduced, (1) the energy level at the top of the valence band is positioned on the negative side from the oxygen generation level (+0.82 eV), or (2) The energy level at the bottom of the conduction band may be positioned on the positive side of the hydrogen generation level (0 eV).
[0056]
When photoredox reactions of optical semiconductors are used for precipitation of metal ions in water, metal ions are reduced and deposited by conduction electrons generated by photoexcitation (at the same time holes oxidize hydroxyl groups in water to generate hydroxides. It is considered that a radical (.OH) is generated.) Therefore, for example, in order to effectively precipitate and remove iron ions from water, the energy level at the lower end of the conduction band generated by conduction electrons needs to be located on the more negative side than the iron generation level (−0.44 eV).
Therefore, conversely, in order not to deposit metal ions from water, the energy level at the lower end of the conduction band may be positioned on the positive side of the metal generation level. If the noble metal is excluded, the metal generation level is on the negative side of the hydrogen generation level, so that the energy level at the bottom of the conduction band should be positioned on the positive side of the hydrogen generation level (0 eV). Become.
As the optical semiconductor in which the lower end of the energy level of the conduction band usable for this is a positive value when the hydrogen generation level is 0 eV, tin oxide, tungsten trioxide, dibismuth trioxide, second oxide Examples thereof include metal oxides such as iron and rutile type titanium oxide.
[0057]
From the above, as one method for photohydrophilization while suppressing decomposition of resin and precipitation of dissolved metal ions in water, when the energy level of the conduction band of the optical semiconductor is set to 0 eV, It can be seen that there is a method located at a positive value.
[0058]
In the second mode of weak redox hydrophilization, a layer containing an optical semiconductor and a hydrophilic substance that is not an optical semiconductor is formed on the surface of the base material, and the optical semiconductor is hardly in contact with the outside air.
In such a state, most of the conduction electrons and holes generated by photoexcitation of the optical semiconductor do not diffuse to the surface, and the probability of contact with surface reactive species such as water, oxygen and metal ions is drastically reduced. The reduction reaction is suppressed.
And excitation light illuminance 1mW / cm²Photooxidation-reduction reaction under the amount of conduction electrons and holes generated in a coating film having a thin film thickness and / or a low photo-semiconductor particle content to the extent that sufficient abrasion resistance can be exhibited below. It can be suppressed to the extent that does not occur. Nevertheless, the photohydrophilization reaction proceeds.
[0059]
In the third mode of weak redox hydrophilization, a layer containing a photo-semiconductor and a substance that inhibits the photo-redox reaction of the photo-semiconductor is formed on the substrate surface.
The mechanism is not clear, but alkali metal, alkaline earth metal, alumina, zirconia, silica, antimony oxide, amorphous titanium oxide, aluminum, manganese, etc. weaken the photo-redox performance of optical semiconductors (“titanium oxide” Gihodo (1991)).
And excitation light illuminance 1mW / cm²In the following, and under the amount of conduction electrons and holes generated in a coating film that is thin enough to exhibit sufficient wear resistance and / or has a low content of photo semiconductor particles, almost no photo-redox reaction occurs. It can be suppressed to the extent that it does not occur. However, even if these substances are contained in the layer, the photohydrophilization reaction proceeds.
[0060]
In the second and third aspects of weak redox hydrophilization, the thinner the film thickness, the better. The thickness is preferably 1 μm or less, more preferably 0.2 μm or less.
If it does so, the absolute amount of the optical semiconductor fixed to a base material can be reduced, and photoredox property can be lowered more. Also, wear resistance is improved.
In particular, when the thickness is 0.2 μm or less, the transparency of the thin film containing the optical semiconductor can be easily secured, and the design and transparency of the base can be maintained.
[0061]
In the second mode of weak redox hydrophilicity, the photosemiconductor content is preferably 5 to 80% by weight, more preferably about 10 to 50% by weight with respect to the photosemiconductor-containing layer. This is because the smaller the content of the optical semiconductor, the lower the photooxidation / reduction property. However, since the photohydrophilization phenomenon is a phenomenon based on the photoexcitation phenomenon of the optical semiconductor, it is necessary to contain about 5% or more.
[0062]
In the second and third embodiments of weak redox hydrophilization, the illuminance of light having a wavelength shorter than the excitation wavelength is preferably 0.0001 to 1 mW / cm.², More preferably 0.001-1 mW / cm²The degree is good. This is because, as the illuminance of light having a wavelength shorter than the excitation wavelength is lower, the amount of electron-hole pairs to be generated is reduced, so that the photoredox property can be lowered. However, since the photohydrophilization phenomenon is also a phenomenon based on the photoexcitation phenomenon of an optical semiconductor, it is about 0.0001 mW / cm.²The above excitation light illuminance is required.
[0063]
In the present invention, as another aspect of the treatment for protecting the designable film or the designable coating from the photo-oxidation-reduction reaction due to the photocatalytic action of the optical semiconductor, an intermediate layer is provided between the base material and the optical semiconductor-containing layer. It may be provided. Thereby, adhesiveness with a base material increases and abrasion resistance improves.
[0064]
Manufacturing process example of laminated steel building materials
(1) Steel plate base treatment: Hot dip galvanizing is performed on the steel plate, nickel plating is performed thereon, and then chromate treatment is performed.
(2) Preparation of PVC design film: A design pattern is printed on the PVC film, and PVC film doubling (embossing) is performed thereon. Furthermore, a silicone resin containing an optical semiconductor is coated thereon.
(3) Lamination: An adhesive is applied on the steel sheet, and the film is laminated.
(4) Irradiate photocatalytic excitation light as necessary. However, this step is not necessarily performed because the outdoor use member is exposed to sunlight and rainfall.
[0065]
Manufacturing process example of ceramic siding building materials
(1) A primer resin is applied onto a building material (for example, a hard calcium silicate plate), and a hard coat resin is further applied thereon as necessary.
(2) Surface treatment is performed by a method such as corona discharge, alkali treatment, or plasma treatment.
(3) A silicone resin containing an optical semiconductor is coated.
(4) Irradiate photocatalytic excitation light as necessary. However, this step is not necessarily performed because the outdoor use member is exposed to sunlight and rainfall.
[0066]
【Example】
Example 1
An experiment conducted for selecting the thickness of the surface layer including the optical semiconductor so as not to cause white turbidity or interference fringes will be described.
A 10 cm square aluminum substrate was used as the substrate. In order to smooth the surface of the substrate, it was previously coated with a silicone layer. As coating materials for this coating, liquid composition A (silica sol, solid content 13%, mixed solvent of water and alcohol) and liquid B (methyltrimethoxy) of the coating composition “Glaska” (T2202) of Nippon Synthetic Rubber (Tokyo) Silane, silane content 98%, methanol solvent) were mixed so that the weight ratio of A liquid and B liquid was 3, and the composition for silicone resin coating materials was prepared. The coating composition was applied to the aluminum substrate and cured at a temperature of 150 ° C. to obtain a plurality of aluminum substrates (# 1 sample) covered with a 3 μm-thick silicone base coat.
[0067]
Next, solution A (silica sol, solid content 13%) of anatase type titania sol (Nissan Chemical Co., Ltd., TA-15, solid content 15%, aqueous solvent) and silicone resin paint (“Glaska” (T2202) manufactured by Nippon Synthetic Rubber Co., Ltd.) Water and alcohol mixed solvent) and B liquid (methyltrimethoxysilane, silane content 98%, methanol solvent)) were mixed and diluted with ethanol to prepare a titania-containing coating composition. The weight ratio of titania sol, silica sol, and methyltrimethoxysilane solution was 56:33:11.
This coating composition was applied onto a sample # 1 and cured at a temperature of 150 ° C. to form a top coat in which anatase-type titania particles were dispersed in a silicone coating film. The weight ratio of silicone and titania in the top coat formed here was set to 1. As shown in Table 1, the film thickness of the top coat of each sample was 0.02 to 2.5 μm.
[0068]
Next, 0.5 mW / cm was used for this sample using a BLB fluorescent lamp.²Were irradiated with ultraviolet rays for 1 day. When the contact angle of the surface of this sample with water was measured with a contact angle measuring device (CA-X150), the contact angle reading was 0 °.
Table 1 shows the observation results of the film thickness and coating film appearance of each sample obtained. The refractive index of the formed film was 1.8.
[0069]
[Table 1]

[0070]
From this result, it has been found that interference fringes that may impair the design properties occur when the film thickness is 0.2 μm or more. It has been found that when the film thickness is less than 0.2, there are no problematic interference fringes and white turbidity.
For comparison, a 0.1 μm thick coating film (top coat) was formed so that the weight ratio of silicone to titania was 1: 9 by the same method as described above. The refractive index of the film formed at this time was 2.3. As a result of observing the appearance of the coating film on this sample, a feeling of slight glare reflection was observed as compared with Sample D in Table 1.
[0071]
【The invention's effect】
As is clear from the above description, the present invention is a highly clean design member capable of maintaining sufficient cleanliness even in rainwater or a simple shower, and whose design is not impaired, and such a highly clean design. The cleaning method of the design member for obtaining a member can be provided.

Claims (12)

A substrate subjected to aesthetic treatment, and a surface layer including an optical semiconductor formed on the surface of the substrate;
The surface exhibits hydrophilicity with a contact angle with water of less than 10 °,
Thickness is 0.2μm less than der of the surface layer is,
A highly clean design member, wherein the refractive index of the surface layer is 2 or less . The average particle diameter of the high cleanliness design member of claim 1 Symbol placement is 0.1μm or less of the optical semiconductor particles contained in the surface layer. Optical semiconductor particles contained in the surface layer is anatase type titanium oxide particles, in addition to anatase titanium oxide particles to the surface layer, according to claim 1 or 2, wherein the refractive index is smaller substance than 2 is added Highly clean design member. The material having a refractive index smaller than 2 is at least one selected from the group consisting of silica, alumina, tin oxide, and silicone in which at least a part of an organo group bonded to a silicon atom is substituted with a hydroxyl group. The highly clean design member according to claim 3 .   The high cleanliness design member according to claim 1, wherein the water absorption rate of the surface layer is 1% or less. The highly clean design member according to any one of claims 1 to 5 , wherein the substrate has a designable film attached to the surface thereof. The highly clean design member according to claim 6 , wherein the base material is a laminated steel sheet building material. The highly clean design member according to any one of claims 1 to 5 , wherein the base material has a design coating applied to the surface thereof. The highly clean design member according to claim 8 , wherein the base material is an automobile outer plate. The high cleanliness design member of any one of Claims 6-9 in which the protection treatment for protecting the said designable film or designable coating from the photoredox reaction by the photocatalytic action of the said optical semiconductor is given. Forming a surface layer having a thickness of less than 0.2 μm including the optical semiconductor on the surface of the aesthetically treated substrate;
Irradiating the surface layer with light having a wavelength shorter than the excitation light wavelength of the optical semiconductor to make the surface hydrophilic;
The cleaning method of the design member characterized by including. Forming a surface layer having a thickness of less than 0.2 μm, including an optical semiconductor and silicone, on the surface of the aesthetically treated substrate;
Irradiating the surface layer with light having a wavelength equal to or less than the excitation light wavelength of the optical semiconductor to replace the organic group bonded to the silicon atom in the silicone with a hydroxyl group, thereby hydrophilizing the surface;
The cleaning method of the design member characterized by including.