Antifouling member and antifouling coating composition

Field of the Invention

0001The present invention relates to a member having a surface on which a material is less likely to be deposited, more specifically a member having an antifouling surface on which the so-called "stains," such as deposits and contaminants, are less likely to be deposited.

Background Art

0002In the field of buildings and coatings, the pollution of the environment has posed a problem of contamination of exterior materials for buildings, outdoor buildings, and coatings provided thereon.

0003Dust and particles floating in the air deposit on the roof and the outer wall of buildings in fine weather. Upon exposure to rainfall, the deposits flow together with rainwater and flow down along the outer wall of the building. Further, in rainy weather, dust and particles floating in the air are carried by rain and flow down on the outer wall of the building and the surface of the outdoor building. As a result, the contaminant adheres on the surface along the course of the rainwater. As the surface dries, soil appears in a stripe pattern on the surface.

0004Combustion products, such as carbon black, municipal dust, and contaminants of inorganic materials, such as clay particles, constitute the soil on the coating of the exterior material for the building. Such a wide variety of contaminants are considered to render measures for antifouling complicate (<nplcit id="ncit0001" npl-type="s"><text>Yoshinori Kitsutaka, "Gaiheki Shiage Zairyou No Osen No Sokushin Shiken Houhou (Accelerated Testing Method for Contamination of Finish Materials of Outer Wall)," Journal of Structural and Construction Engineering (Transactions of AIJ), No. 404, October 1989, pp. 15-24</text></nplcit>).

0005The use of a water-repellent paint, such as polytetrafluoroethylene (PTFE), has hitherto been considered preferable for preventing the exterior of the building and the like from being soiled. In recent years, however, that the surface of the coating is made hydrophilic as much as possible has become recognized as more effective for municipal dust containing a large amount of a hydrophobic component (<nplcit id="ncit0002" npl-type="s"><text>Kobunshi, Vol. 44, May 1995. p. 307</text></nplcit>). Accordingly, coating of buildings with a hydrophilic graft polymer has been proposed in a newspaper ("<nplcit id="ncit0003" npl-type="s"><text>Japan Chemical Week", January 30, 1995</text></nplcit>). According to this report, the coating has a hydrophilicity of 30 to 40° in terms of contact angle thereof with water.

0006Inorganic dust typified by clay minerals has a contact angle thereof with water of 20° to 50° and, hence, has affinity for the graft polymer having a contact angle thereof with water of 30° to 40° and is likely to adhere on the surface of the graft polymer. Therefore, it is considered that the coating of the graft polymer cannot satisfactorily prevent soiling with inorganic dust.

0007<patcit id="pcit0001" dnum="US5331074A"><text>US-A-5 331 074</text></patcit>, <patcit id="pcit0002" dnum="JP8134437A"><text>JP-A-8 134 437</text></patcit>, <patcit id="pcit0003" dnum="JP8034973A"><text>JP-A-8 034 973</text></patcit>, <patcit id="pcit0004" dnum="JP8003544A"><text>JP-A-8 003 544</text></patcit> and <patcit id="pcit0005" dnum="JP8134381A"><text>JP-A-8 134 381</text></patcit> relate to a substrate with a surface having water-repellant properties.

0008Although there are proposals wherein the surface of a member is rendered water-repellent or hydrophilic to keep the surface clean, such as those described above, there is still room for improvement in the surface cleaning activity.

[SUMMARY OF THE INVENTION]

0009The present inventors have now found that a surface having both a hydrophobic portion, and a hydrophilic portion induced by a photocatalyst has a very good antifouling property. The present invention has been made based on such finding.

0010Accordingly, an object of the present invention is to provide a member having a surface on which a material is less likely to be deposited, having an antifouling surface on which the so-called "stains," such as deposits and contaminants, are less likely to be deposited, and having both a hydrophobic portion, and a hydrophilic portion induced by a photocatalyst, the hydrophobic portion and the hydrophilic portion being present in a microscopically dispersed and exposed state on the surface of the member.

0011According to the present invention, there is provided a member comprising: a substrate; and a surface layer provided on the substrate, the surface layer comprising a hydrophobic resin and a photocatalytic oxide as defined in claim 1, the hydrophobic resin and the photocatalytic oxide being present in a microscopically dispersed and exposed state on the outermost surface of the member, the photocatalytic oxide being self-hydrophilified or functioning to hydrophilify the photocatalytic oxide still remaining unhydrophilified present around the photocatalytic oxide by photocatalytic action created in response to photoexcitation.

0012According to the present invention, the hydrophobic portion derived from the hydrophobic resin and the hydrophilic portion induced by the photocatalyst are present in a microscopically dispersed state on the outermost surface of the member. As a result of the hydrophobic portion and the hydrophilic portion adjacent to each other, a hydrophilic deposit having affinity for the hydrophilic portion does not have affinity for the adjacent water-repellent portion. On the other hand, a hydrophobic deposit having affinity for the hydrophobic portion does not have affinity for the adjacent hydrophilic portion. Therefore, it is considered that both the hydrophilic deposit and the hydrophobic deposit cannot deposit on the surface of the member, and, even when deposited on the surface of the member, are unstable and hence are easily removed, permitting the surface of the member to be kept clean. In this connection, however, it should be noted that the above description is hypothetical and the present invention is not limited to the above mechanism alone.

[BRIEF DESCRIPTION OF THE DRAWINGS]

0013<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a diagram illustrating how to install a test sample in Example 2. In the drawing, the member 1 according to the present invention is installed on the wall surface of a house 11 so as to be exposed to sunlight from the sun 10.</li><li><figref idref="f0002">Fig. 2</figref> is a diagram showing the structure of a member according to the present invention. A member 21 according to the present invention comprises a surface layer 23 provided on a substrate 22. The surface layer 23 comprises a hydrophobic resin layer 24 and a photocatalytic oxide 25 dispersed in the layer 24, the photocatalytic oxide 25 being present in an exposed state on the outermost surface of the layer 24.</li><li><figref idref="f0002">Fig. 3</figref> is a diagram of a member having the same construction as the member according to the aspect shown in <figref idref="f0002">Fig. 2</figref>, except that the surface layer 23 further comprises an inorganic oxide 26.</li><li><figref idref="f0002">Fig. 4</figref> is a diagram showing a second embodiment of the present invention. A member 21 according to the present invention comprises a layer 24, formed of a photocatalytic oxide, and a layer 28, formed of a hydrophobic resin, provided on the layer 24. In this case, the layer 28 formed of a hydrophobic resin is laminated onto a part of the layer 24. As a result, the hydrophobic resin and the photocatalytic oxide are present in a microscopically dispersed and exposed state on the outermost surface of the surface layer 23.</li><li><figref idref="f0002">Fig. 5</figref> is a diagram of a member having the same construction as the member according to the embodiment shown in <figref idref="f0002">Fig. 4</figref>, except that the layer 24 comprising a photocatalytic oxide further comprises an inorganic oxide 29.</li></ul>

[DETAILED DESCRIPTION OF THE INVENTION]

Definition

0014In the present invention, the terms "antifouling property" and "antifouling activity" are used to mean any of such properties that a certain surface is inert to deposition of a material thereon, that is, a property that various materials are less likely to be deposited on a certain surface, and a property that materials, even when once deposited on a certain surface, can be easily removed.

0015Further, in the present invention, the presence of the hydrophobic portion and the hydrophilic portion in a "microscopically dispersed state" on the surface means that the hydrophobic portion and the hydrophilic portion are homogeneously present per unit area of not more than about 0.1 mm².

0016Further, in the present invention, the term "photocatalyst" used herein refers to a material which, when exposed to light (excitation light) having higher energy (i.e., shorter wavelength) than the energy gap between the conduction band and the valence band of the crystal, can cause excitation (photoexcitation) of electrons in the valence band to produce a conduction electron and a hole. Photocatalytic oxides used herein are selected from anatase form of titanium oxide, zinc oxide, tin oxide, ferric oxide, dibismuth trioxide, tungsten trioxide, and strontium titanate.

Antifouling member according to the present invention

0017The member according to the present invention comprises a substrate and a surface layer provided on the substrate, the surface layer comprising a hydrophobic resin and a photocatalytic oxide as defined in claim 1. The hydrophobic resin and the photocatalytic oxide are present in a microscopically dispersed and exposed state on the outermost surface of the surface layer.

0018The member according to the present invention has, on its outermost surface, a hydrophobic portion, and a hydrophilic portion induced by a photocatalyst. As a result, both hydrophilic deposits and hydrophobic deposits cannot be deposited on the surface of the member, and, even when deposited on the surface of the member, are unstable and hence are easily removed, permitting the surface of the member to be kept clean. Therefore, the member according to the present invention may be used in the following applications.

0019Specifically, examples of applications include building materials, exterior of buidlings, interior of buildings, sashes, windowpanes, structural members, plates, exterior and coating of vehicles, exterior of machineries and articles, dustproof covers and coatings, reflector plates for traffic signs, various display devices, advertising towers or poster columns, noise barriers for roads, noise barriers for rail roads, decorative plates for roads, light source covers for signals, display panels for outdoors, bridges, exterior and coating of guard rails, interior and coating of tunnels, lighting apparatuses for interior of tunnels, insulators, covers for solar cells, covers for solar energy collectors of solar water heaters, vinyl plastic hothouses, covers for lighting of vehicles, mirrors for roads, mirrors for vehicles, instrument covers and instrument panels for two-wheeled vehicles, glass lenses, plastic lenses, helmet shields, windowpanes for housings, automobiles and railway vehicles, showcases, showcase for retention of heat, film structures, fins for heat exchangers, glass surfaces for various places, window shades (blinds), tire wheels, roof materials, antennas, power lines, households, stools, bath tubs, wash basins, lighting equipment, covers for lighting, kitchenwares, tablewares, cabinets for tablewares, dishwashers, dishdryers, sinks, cooking ranges, kitchen hoods, ventilation fans, anti-thrombotenic material, anti-protein-depositable materials, bottoms of ships, and films for application on the above articles.

0020According to a preferred embodiment of the present invention, the surface layer of the member of the present invention further comprises an inorganic oxide. This inorganic oxide, together with the hydrophobic resin and the photocatalytic oxide, is present in a microscopically dispersed and exposed state on the outermost surface of the surface layer. Further, the inorganic oxide is hydrophilified by photocatalytic action created in response to photoexcitation of the photocatalytic oxide. This means that the hydrophilic portion induced by the photocatalyst is further provided in the surface layer by the inorganic oxide.

0021A first preferred embodiment of the present invention is shown in <figref idref="f0002">Fig. 2</figref>. The member 21 shown in this drawing comprises a surface layer 23 provided on a substrate 22. The surface layer 23 comprises a hydrophobic resin layer 24 and a photocatalytic oxide 25 dispersed in this layer 24. The photocatalytic oxide 25 is present in an exposed state on the outermost surface of the layer 24. In the embodiment shown in this drawing, the photocatalytic oxide is provided as a particle.

0022In the embodiment shown in <figref idref="f0002">Fig. 2</figref>, the surface layer 23 may contain an inorganic oxide, and this embodiment is shown in <figref idref="f0002">Fig. 3</figref>. The embodiment shown in <figref idref="f0002">Fig. 3</figref>, a particulate inorganic oxide 26, together with the photocatalytic oxide 25, is dispersed in the hydrophobic resin layer 24. The inorganic oxide 26 also is present in an exposed state on the outermost surface of the layer 23.

0023A second preferred embodiment of the present invention is as shown in <figref idref="f0002">Fig. 4</figref>. The member 21 shown in this drawing comprises a layer 24, formed of a photocatalytic oxide, and a layer 28, formed of a hydrophobic resin, provided on the layer 24. In this case, the layer 28 formed of a hydrophobic resin is laminated onto a part of the layer 24. Consequently, the hydrophobic resin and the photocatalytic oxide are present in a microscopically dispersed and exposed state on the outermost surface of the surface layer 23.

0024Further, in the embodiment shown in <figref idref="f0002">Fig. 4</figref>, the layer 24 formed of a photocatalytic oxide may further contain an inorganic oxide. This embodiment is shown in <figref idref="f0002">Fig. 5</figref>. In the embodiment shown in <figref idref="f0002">Fig. 5</figref>, a particulate inorganic oxide 29 is dispersed in the layer formed of a photocatalytic inorganic oxide. This inorganic oxide 29 also is present in an exposed state on the outermost surface of the layer 23.

0025In the present invention, photocatalytic oxides include those as described above. Further, light sources and irradiation intensity of light may be as follows. Light from sunlight, a room lamp, a fluorescent lamp, a mercury lamp, an incandescent lamp, a xenon lamp, a high pressure sodium lamp, a metal halide lamp, a BLB lamp and the like is preferred. On the other hand, when the photocatalytic oxide is tin oxide, light from a bactericidal lamp, a BLB lamp and the like is preferred. The irradiation intensity of light applied may be suitably determined by taking into consideration the composition of the member, applications of the member and the like. In order to highly hydrophilify the hydrophilic portion of the surface of the member and maintain the highly hydrophilified state, the irradiation intensity of the excitation light is preferably not less than 0.001 mW/cm², more preferably not less than 0.01 mW/cm², most preferably not less than 0.1 mW/cm².

0026In the present invention, hydrophobic resins include fluororesins, acrylic resins, urethane resins, polyester resins, vinyl resins, PET, and acrylic silicone.

0027According to a preferred embodiment of the present invention, a fluororesin is utilized as the hydrophobic resin from the viewpoint of lightfastness. Preferred fluororesins include polymers containing a fluoro group, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polychlorotrifluoroethylene, tetrafluoroethylene/hexafluoropropylene copolymer, ethylene/tetrafluoroethylene copolymer, ethylene/chlorotrifluoroethylene copolymer, tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, perfluorocyclo polymer, vinyl ether/fluoroolefin copolymer, vinyl ester/fluoroolefin copolymer, tetrafluoroethylene/vinyl ether copolymer, chlorotrifluoroethylene/vinyl ether copolymer, urethane-crosslinked tetrafluoroethylene, epoxy-crosslinked tetrafluoroethylene, acryl-crosslinked tetrafluoroethylene, and melamine-crosslinked tetrafluoroethylene. In the present invention, the silicone resin, as compared with the photocatalytic oxide, is present in an amount large enough to serve substantially as a hydrophobic resin.

0028In the present invention, the level of the hydrophobicity of the hydrophobic resin may be suitably determined so far as the effect of the present invention is attained. For example, the level of the hydrophobicity is preferably not less than 60°, more preferably not less than 120°, in terms of the contact angle of the hydrophobic resin with water.

0029Inorganic oxides, which are preferably added in the present invention, are not particularly limited so far as they can be hydrophilified by photocatalytic action of the photocatalytic oxide. Examples thereof include silica, alumina, water glass, silicate, aluminosilicate, zirconia, ceria, tin oxide, calcia, magnesia, amorphous titania and other metal oxides. Among them, silica or alumina is particularly preferred from the viewpoint of retention of the hydrophilicity of the hydrophilic portion in a dark place.

0030The substrate also is not particularly limited. The substrate may be suitably determined by taking the applications of the member into consideration. Specific examples of substrates usable herein include those include metals, ceramics, glasses, plastics, woods, stones, cements, concretes, fibers, woven fabrics, and combinations of the above materials and laminates of the above materials.

0031The content of the photocatalytic oxide in the surface layer of the member according to the present invention is not particularly limited. For example, the content of the photocatalytic oxide in the surface layer is preferably about 10 to 80% by weight, more preferably about 20 to 50% by weight.

0032According to a preferred embodiment of the present invention, the thickness of the surface layer may be suitably determined by taking into consideration the composition of the surface layer, applications of the member and the like. For example, when a transparent surface layer is contemplated, the thickness is preferably not more than about 0.4 µm. This can prevent haze development derived from irregular reflection of light, rendering the surface layer substantially transparent. The thickness of the surface layer is more preferably not more than about 0.2 µm from the viewpoint of effectively preventing the color development of the surface layer derived from the interference of light. The smaller the thickness of the surface layer, the better the transparency of the surface layer. However, it is apparent that a given thickness is preferred from the viewpoint of abrasion resistance.

0033The photocatalytic oxide may be utilized as a particle. Although the particle diameter (crystallite diameter) may be suitably determined, the particle diameter is preferably about 1 to 100 nm, more preferably about 5 to 20 nm.

0034Also when the inorganic oxide is used as a particle, the particle diameter thereof may be suitably determined. However, the particle diameter is preferably about 1 nm to 1 µm, more preferably about 5 to 100 nm.

0035For the embodiments shown in the drawings, preferred conditions are as follows.

0036At the outset, in the embodiment shown in <figref idref="f0002">Fig. 2</figref>, the thickness of the hydrophobic resin layer 24 is preferably about 10 nm to 10 µm, more preferably about 100 nm to 1 µm. The content of the photocatalytic oxide particle in the layer 24 is preferably about 10 to 80% by weight, more preferably about 20 to 50% by weight. In the embodiment shown in <figref idref="f0002">Fig. 3</figref>, the content of the photocatalytic oxide particle is preferably about 1 to 80% by weight, more preferably about 20 to 50% by weight, while the content of the inorganic oxide particle is preferably about 1 to 70% by weight, more preferably about 5 to 55% by weight.

0037Further, in the embodiment shown in <figref idref="f0002">Fig. 4</figref>, the thickness of the photocatalytic oxide layer 27 is preferably about 10 nm to 1 µm, more preferably about 50 to 400 nm. The thickness of the hydrophobic resin layer overlying the photocatalytic oxide layer 27 is preferably about 1 to 100 nm, more preferably about 5 to 50 nm. In the embodiment shown in <figref idref="f0002">Fig. 5</figref>, the content of the photocatalytic oxide particle is preferably about 10 to 99% by weight, more preferably about 50 to 99% by weight, while the content of the inorganic oxide particle is preferably about 50 to 90% by weight, more preferably about 5 to 50% by weight.

0038In the present invention, the proportion of the hydrophobic portion and the hydrophilic portion present on the surface layer also may be suitably determined by taking applications of the member into consideration.

0039Specifically, the member, wherein the hydrophobic portion and the hydrophilic portion each are present in at least one place per 10 to 100 nm² on the outermost surface of the surface layer, has such a property that biopolymers are less likely to be deposited thereon. Therefore, this member can be applied to anti-thrombotenic materials, anti-protein-depositable materials, anti-lipid-adhesion materials and the like. More specifically, the member may be used as contact lenses and disposable medical instruments, such as urinary catheters, percutaneous devices, various artificial organs, blood bags, urine-collecting bags, lung drainages, and tubes for connection between the above members.

0040On the other hand, the member, wherein the hydrophobic portion and the hydrophilic portion each are present in at least one place per 10 nm² to 1 µm² on the outermost surface of the surface layer, has such a property that organisms are less likely to be deposited thereon. Therefore, this member may be used as materials for the bottom of ships, outer wall materials, bathroom materials, bathtub materials, materials for water tanks for the appreciation, and surface materials (for example, design tiles) for equipment utilizing circulating water (for example, artificial waterfalls in parks) in its area which comes into contact with the circulating water.

0041Further, the member, wherein the hydrophobic portion and the hydrophilic portion each are present in at least one place per mm² on the outermost surface of the surface layer, has such a property that a stain derived from suspended smoke and soot in the air is less likely to be deposited thereon, or the stain, even when once deposited thereon, can be easily removed. Therefore, this member may be used as building materials for outdoors, covers for solar batteries, covers for heat collectors for solar water heaters, handrails, internal walls for tunnels, sound insulating walls, sound barriers, guard fences, road structures, such as decorative plates for roads, window shades (blinds), insulators, wheels, and bodies for vehicles, such as automobiles.

0042Specifically, the member, wherein a hydrophobic portion derived from the water-repellent fluororesin and a hydrophilic portion derived from the silicone or silica each are present in at least one place per 10 to 100 nm² on the outermost surface of the surface layer, has such a property that biopolymers are less likely to be deposited thereon. Therefore, this member can be applied to anti-thrombotenic materials, anti-protein-depositable materials, anti-lipid-adhesion materials and the like. More specifically, the member may be used as contact lenses and disposable medical instruments, such as urinary catheters, percutaneous devices, various artificial organs, blood bags, urine-collecting bags, lung drainages, and tubes for connection between the above members.

0043On the other hand, the member, wherein a hydrophobic portion derived from the water-repellent fluororesin and a hydrophilic portion derived from the silicone or silica each are present in at least one place per 10 nm² to 1 µm² on the outermost surface of the surface layer, has such a property that organisms are less likely to be deposited thereon. Therefore, this member may be used as materials for the bottom of ships, outer wall materials, bathroom materials, bathtub materials, materials for water tanks for the appreciation, and surface materials (for example, design tiles) for equipment utilizing circulating water (for example, artificial waterfalls in parks) in its area which comes into contact with the circulating water.

0044Further, the member, wherein a hydrophobic portion derived from the water-repellent fluororesin and a hydrophilic portion derived from the silicone or silica each are present in at least one place per 0.1 mm² on the outermost surface of the surface layer, has such a property that a stain derived from suspended smoke and soot in the air is less likely to be deposited thereon, or the stain, even when once deposited thereon, can be easily removed. Therefore, this member may be used as building materials for outdoors, covers for solar batteries, covers for heat collectors for solar water heaters, handrails, internal walls for tunnels, sound insulating walls, sound barriers, guard fences, road structures, such as decorative plates for roads, window shades (blinds), insulators, wheels, and bodies for vehicles, such as automobiles.

0045In the member according to the present invention, the contact angle of the surface layer with water is not basically limited so far as the member has an antifouling activity. In general, however, the apparent contact angle of the member with water is about 10 to 120°.

0046Photocatalytic oxides are known to have antifouling, antimicrobial, and deodorant activities based on the oxidative degradation action. It is believed that, also in the member according to the present invention, this action is maintained. It is believed that the oxidative degradation action of the photocatalyst is more preferably exhibited in the case where the hydrophobic portion derived from the water-repellent fluororesin and the hydrophilic portion derived from the silicone or silica each are present in at least one place per 0.1 mm² on the outermost surface of the surface layer.

0047Further, the member according to the present invention can effectively prevent the growth of water droplets deposited thereon, and water droplets deposited on the member are rolled over the surface by the action of slight force and easily removed from the surface. Further, ice and snow are not easily deposited on the surface of the member according to the present invention. That is, the member according to the present invention has inhibitory activity against the growth of water droplets, deposition of water droplets, and deposition of ice and snow.

0048Because the member of the present invention has inhibitory activity against the growth of water droplets, application of the member to glasses, mirrors and the like can effectively prevent the growth of water droplets to such an extent that water droplets scatter light. More specifically, the member can be applied for preventing fogging or ensuring the visibility of glasses, mirrors, lenses, prisms and the like. More specifically, the member can be used as windowpanes for buildings, windowpanes for vehicles, windshields for vehicles, mirrors for vehicles, road mirrors, lavatory mirrors, covers for instrument boards, lenses for spectacles, helmet shields, goggles, and showcases for retention of heat. It is believed that the above action is more preferably exhibited in the case where the hydrophobic portion derived from the water-repellent fluororesin and the hydrophilic portion derived from the silicone or silica each are present in at least one place per 0.2 µm² on the outermost surface of the surface layer.

0049Further, since the member according to the present invention has inhibitory activity against the deposition of water droplets and against the deposition of ice and snow, the member according to the present invention can be used in applications, such as the prevention of a lowering in efficiency of a heat exchanger due to the deposition of water droplets between fins in an aluminum fin of the heat exchanger, the prevention of a lowering in the insulating property of a bath surface due to the deposition of water (salt) onto the surface of an insulator, the prevention of a deterioration in design due to the deposition of water droplets onto an apron portion of a bathtub, the prevention of accumulation of ice and snow on a roof, the prevention of the formation of an icicle, the prevention of accumulation of ice and snow on an antenna, the prevention of communication troubles, the prevention of accumulation of ice and snow on a power line, and the prevention of conical discharge. More specifically, the member can be used as fins for heat exchangers, insulators, bathtubs, counters for lavatories, kitchen counters, roof materials, roof gutters, antennas, and power lines. According to a preferred embodiment of the present invention, it is believed that the inhibitory activity against the deposition of water droplets and the inhibitory activity against the deposition of ice and snow are more preferably exhibited in the case where the hydrophobic portion derived from the water-repellent fluororesin and the hydrophilic portion derived from the silicone or silica each are present in at least one place per mm² on the outermost surface of the surface layer.

0050Further, according to the present invention, preferably, a metal, such as silver, copper, or zinc, is added to the surface layer. The surface layer with the above metal added thereto can kill bacteria and mold deposited on the surface thereof even in a dark place and hence can further improve the antifouling property. Further, a platinum group metal, such as platinum, palladium, ruthenium, rhodium, iridium, or osmium, may be added to the surface layer. The surface layer with the above metal added thereto can enhance the redox activity of the photocatalyst and can improve the degradability of organic stains and the degradability of harmful gases and bad smells.

Production of antifouling member according to the present invention

0051Preferably, the member according to the present invention is produced as follows.

0052The member having a construction shown in <figref idref="f0002">Fig. 2 or 3</figref> may be produced by coating a substrate with a layer comprising a hydrophobic resin containing a photocatalytic oxide and optionally an inorganic oxide dispersed therein. More specifically, a hydrophobic resin is dissolved in a solvent capable of dissolving the hydrophobic resin, and a photocatalytic oxide and optionally an inorganic oxide are dispersed in the solution to prepare a coating liquid which is then coated on a substrate. Thereafter, the solvent is removed by evaporation to dry the coating and to form a resin layer. Thus, a surface layer is formed on the substrate.

0053Basically, the photocatalytic oxide and the inorganic oxide are present in an exposed state on the outermost surface of the surface layer, the degree of the exposure of the photocatalytic oxide and the inorganic oxide on the outermost surface of the surface layer being basically proportional to the concentration of the photocatalytic oxide and the inorganic oxide in the coating liquid. In some cases, however, even when the concentration of these materials in the coating liquid is increased, it is difficult to expose the photocatalytic oxide and the inorganic oxide on the outermost surface. In this case, after the formation of the resin layer, the surface of the resin layer may be removed to expose a desired amount of the photocatalytic oxide and the inorganic oxide, present within the layer, on the surface thereof.

0054Alternatively, the members having constructions as shown in <figref idref="f0002">Figs. 2 and 3</figref> may be produced as follows. Specifically, at the outset, a hydrophobic resin precursor composition capable of forming a hydrophobic resin layer is coated on a substrate. An example of the precursor composition is a solution of a hydrophobic resin in a solvent capable of dissolving the hydrophobic resin. On the other hand, the surface of the inorganic oxide and the surface of the photocatalytic oxide are hydrophobified with a hydrophobifying agent. Specific examples of hydrophobifying agents include, for example, silane coupling agents. The hydrophobified photocatalytic oxide and inorganic oxide are coated on the coating of the hydrophobic resin precursor composition formed on the substrate. The surface of the photocatalytic oxide and the surface of the inorganic oxide are now in a hydrophobified state, and, hence, the photocatalytic oxide and the inorganic oxide have good affinity for and can be evenly present on the hydrophobic resin coating. Thereafter, the hydrophobifying agent is removed from the surface of the photocatalytic oxide and the inorganic oxide. The hydrophobifying agent may be removed by a suitable method determined depending upon the type of the hydrophobifying agent. For example, a silane coupling agent can be easily removed by ultraviolet irradiation or etching. The assembly is then cured or dried to induce such a reaction that the precursor composition is converted to a hydrophobic resin layer. Thus, members as shown in the drawings are obtained.

0055The members having constructions as shown in <figref idref="f0002">Figs. 4 and 5</figref> may be produced, for example, by forming a layer comprising a photocatalytic oxide and optionally an inorganic oxide on the surface of a substrate, applying a hydrophobic resin precursor composition, capable of forming a hydrophobic resin layer, on a part of the above layer to form a coating, and subjecting the coating to such a reaction that the coating is converted to a hydrophobic resin layer. More specifically, a composition containing photocatalytic oxide particles and optionally a binder is provided. The composition is coated on a substrate. The coating is subjected to such a reaction that photocatalytic oxide particles are bonded to one another through the binder, thereby forming a photocatalytic oxide layer. A solution containing a hydrophobic resin precursor composition dissolved therein is then applied on a part of the photocatalytic oxide layer. The application of the solution on a part of the photocatalytic oxide layer may be carried out, for example, by applying the precursor composition through a slit having a specific opening pattern. Thereafter, the coating is then subjected to such a reaction that the precursor composition is converted to a hydrophobic resin layer, thereby forming a member.

0056Alternatively, members having constructions as shown in <figref idref="f0002">Figs. 4 and 5</figref> may be produced as follows. Specifically, at the outset, a layer comprising a photocatalytic oxide and optionally an inorganic oxide is formed on the surface of a substrate in the same manner as described above. A composition comprising a photodecomposable hydrophobic material and a hydrophobic resin is applied on the above layer to form a coating. The coating is then irradiated with light to decompose and remove the photodecomposable hydrophobic material, and the coating is subjected to such a reaction that the coating is converted to a hydrophobic resin layer.

0057Further, members having constructions as shown in <figref idref="f0002">Figs. 4 and 5</figref> may be produced as follows. Specifically, at the outset, a layer comprising a photocatalytic oxide and optionally an inorganic oxide is formed on the surface of a substrate in the same manner as described above. A composition comprising a hydrophobic material, dissolvable in a specific solvent, and a hydrophobic resin is applied onto the above layer to form a coating. The specific solvent is brought into contact with the surface of the coating to remove the hydrophobic material, thereby converting the coating layer to a hydrophobic layer to prepare a member. Hydrophobic materials dissolvable in specific solvents are known in the art. Examples of combinations of hydrophobic materials with specific solvents capable of dissolving them include: a combination of polyethylene or polystyrene with a petroleum; a combination of polyacetal or polyamide with a strong alkali; a combination of polyacetal, ABS, or acryl with a strong acid; a combination of low-density polyethylene, polyphenyl oxide, polystyrene, polysulfone, or polyvinyl chloride with a chloro compound solvent; a combination of polyacetal, ABS, polystyrene, or polyvinyl chloride with an amine compound; a combination or acryl, polystyrene, polysulfone, or polyvinyl chloride with a ketone, an ester, an ether; and a combination of ABS, acryl, polyphenylene oxide, polystyrene, or polyvinyl chloride with an aromatic acid compound solvent.

[EXAMPLES]

Example 1

0058A titanium oxide (anatase form) sol (Nissan Chemical Industries Ltd., TA-15), a silica sol (Japan Synthetic Rubber Co., Ltd., liquid A of Glasca), methyltrimethoxysilane (Japan Synthetic Rubber Co., Ltd., liquid B of Glasca), polytetrafluoroethylene (PTFE) particles (Daikin Industries, Ltd., Ruburon L-5), and ethanol were mixed together. The mixture was stirred for 2 to 3 min to prepare a coating liquid. The coating liquid was spray-coated (spray diameter: 0.5 mm) on the surface of a glazed tile substrate having a size of 5 x 10 cm square (TOTO, LTD., AB02E11). The coating was heat treated for 15 min at 200°C to form a surface layer comprising 33 parts by weight, based on charge weight, of titanium oxide (anatase form) particles, 66 parts by weight, based on charge weight, of polytetrafluoroethylene, 6 parts by weight, based on charge weight, of silica, and 5 parts by weight, based on charge weight, of silicone. The member thus formed was used as sample 4. The contact angle of sample 4 with water was 110°.

0059The surface of sample 4 was then irradiated with ultraviolet light from an ultraviolet light source (Sankyo Denki, a black light blue (BLB) fluorescent lamp) at an ultraviolet irradiation intensity of 0.3 mW/cm² for one day. The member thus prepared was used as sample 5. The contact angle of sample 5 with water was 97.4°, that is, was somewhat lower than that before the ultraviolet light irradiation. It is expected that photocatalytic action permits organic groups bonded to silicon atoms in a silicone molecule were substituted by hydroxyl groups, resulting in hydrophilification. Therefore, it is considered that the contact angle of the sample with water was somewhat lowered by the hydrophilification. That is, it is considered that, due to the photocatalytic action, organic groups on the surface of sample 5 was substituted by hydroxyl groups, resulting in the formation of a structure wherein both a hydrophilic portion, where a hydrophilified silicone was exposed to the outside air, and a water-repellent portion, where a water-repellent fluororesin was exposed to the outside air, were microscopically dispersed.

Example 2

0060Sample 5 prepared in Example 1 was disposed outdoors to determine the capability of the surface of the sample to retain the cleanness against deposits and contaminants. For comparison, a glazed tile plate was disposed outdoors in the same manner as the sample 5.

0061The capability of the surface of the sample to retain the cleanness against deposits and contaminants was determined by disposing the sample under a roofed portion in the rooftop of a building as shown in <figref idref="f0001">Fig. 1</figref> and exposing the sample for four months.

0062As a result, the glazed title plate was found to be somewhat soiled, whereas no soil was found for sample 5.

0063Before and after the 4-month outdoor exposure test, the color difference was measured for the surface of the member. The color difference was measured with a color difference meter (Tokyo Denshoku Co., Ltd.). ΔE* was used as the color difference according to the Japanese Industrial Standards (JIS) H0201. As a result, the change in color difference between before and after the outdoor exposure test was 2 for the glazed tile plate, whereas the change in color difference was as small as 0.5 for sample 5.

Example 3

0064Photocatalytic titania particles (Ishihara Sangyo Kaisha Ltd., ST-41, 5 g), the surface of which had been coated with 1,3,5,7-tetramethylcyclotetrasiloxane by bringing 1,3,5,7-tetramethylcyclotetrasiloxane into contact in a gaseous phase with the photocatalytic titania particles, Voncoat (Dainippon Ink and Chemicals, Inc., vinyl acetate/acryl copolymer, 0.6 g), and 25 ml of water were mixed together in a paint shaker. The mixture was coated on an aluminum substrate. In this case, the proportion of the resin component to the titania was 1 in terms of the volume ratio. The coating was cured at 120°C to prepare sample 19.

0065The contact angle of sample 19 with water was measured and found to be 70°.

0066Further, the surface of the sample was treated with an aqueous sodium hydroxide solution having pH 10, further treated with dilute hydrochloric acid, and then irradiated with sunlight to prepare sample 20.

0067The contact angle of sample 20 with water was measured. As a result, it was found that the contact angle was reduced to 56°.

0068The surface of sample 20 was coated with an aqueous Methylene Blue solution, and the coated sample was irradiated with sunlight in the same manner as described above. One day after the initiation of the irradiation, it was found that the dye was faded, confirming that antifouling effect by the photocatalytic decomposition could be attained.

Example 4

0069A titanium oxide (anatase form) sol (Ishihara Sangyo Kaisha Ltd., STS-11), polytetrafluoroethylene (PTFE) particles (Daikin Industries, Ltd., D-1), and distilled water were mixed together. The mixture was stirred for 30 min to prepare a coating liquid. The coating liquid was coated on a soda lime glass substrate having a size of 10 cm square by spray coating. The coating was heat-treated at 380°C for 3 min, thereby forming a surface layer comprising 4 parts by weight of titanium oxide (anatase form) particles and 6 parts by weight of polytetrafluoroethylene particles. Next, a reflective coating of aluminum was formed by vacuum deposition on the backside of the glass plate to prepare mirror sample 11.

0070Observation of the surface of sample 11 showed that this sample had a surface layer having such a structure that both a hydrophilic portion, where photocatalytic oxide particles were exposed so as to contact with the outside air, and a water-repellent portion, where a water-repellent fluororesin were exposed to so as to contact with the outside air, were microscopically dispersed on the surface thereof.

0071The contact angle of the surface of sample 11 with water was measured. In this case, the contact angle of the sample with water was measured with a contact angle goniometer (Kyowa Interface Science Co., Ltd., CA-X150). The contact angle was measured 30 sec after dropping of a water droplet on the surface of the sample. As a result, the contact angle of the sample with water was 120°, that is, a value more than 90°. When.sample 11 was inclined, water droplets were rolled down.

0072The surface of sample 11 was then irradiated with ultraviolet light from an ultraviolet light source (Sankyo Denki, a black light blue (BLB) fluorescent lamp) at an irradiation intensity of 0.5 mW/cm² for about one day to prepare sample 12. The contact angle of sample 12 with water was measured and found to be 110°. When sample 12 was inclined, water droplets were rolled down.

Example 5

0073A titanium oxide (anatase form) sol (Ishihara Sangyo Kaisha Ltd., STS-11), polytetrafluoroethylene (PTFE) particles (Daikin Industries, Ltd., D-1), and distilled water were mixed together. The mixture was stirred for 30 min to prepare a coating liquid. The coating liquid was coated on a slate substrate by spray coating. The coating was heat-treated at 380°C for 3 min, thereby forming a surface layer comprising 4 parts by weight of titanium oxide (anatase form) particles and 6 parts by weight of polytetrafluoroethylene particles. Thus, sample 21 was obtained.

0074Observation of the surface of sample 21 showed that this sample had a surface layer having such a structure that both a hydrophilic portion, where photocatalytic oxide particles were exposed so as to contact with the outside air, and a water-repellent portion, where a water-repellent fluororesin were exposed to so as to contact with the outside air, were microscopically dispersed on the surface thereof.

0075The contact angle of the surface of sample 21 with water was then measured. In this case, the contact angle of the sample with water was measured with a contact angle goniometer (Kyowa Interface Science Co., Ltd., CA-X150). The contact angle was measured 30 sec after dropping of a water droplet on the surface of the sample. As a result, the contact angle of the sample with water was 120°, that is, a value more than 90°. When sample 21 was inclined, water droplets were rolled down.

0076The surface of sample 21 was then irradiated with ultraviolet light from an ultraviolet light source (Sankyo Denki, a black light blue (BLB) fluorescent lamp) at an ultraviolet irradiation intensity of 0.5 mW/cm² for about one day to prepare sample 22. The contact angle of sample 22 with water was measured and found to be 110°. When sample 22 was inclined, water droplets were rolled down.