Patent Publication Number: US-2012040819-A1

Title: Method of producing photocatalyst layer

Description:
TECHNICAL FIELD 
     The present invention relates to a method of producing a photocatalyst layer. 
     BACKGROUND ART 
     In the past, it is known that photocatalyst has a function of resolving and removing material (dirt) of organic-system or the like based on a photocatalyst effect with irradiation of light. Therefore, it is known that, by forming a photocatalyst layer on a surface of a grass product, a plastic product, or the like, dirt adhered to the surface of the grass product, the plastic product, or the like is self-cleaned. As a method of forming such a phtocatalyst layer, for example, there is used a method of applying an ultraviolet ray (ultraviolet light) to a titanium oxide layer having a hydrophilic effect formed on a surface of a substrate, and applying an aqueous solution containing fine particles of titanium oxide having a photocatalyst effect. In the method, an aqueous solution of titanium oxide is uniformly dispersed with the hydrophilic effect, a solvent is evaporated with drying, and a thin layer of fine particles of titanium oxide is uniformly formed (please see Patent Document No. 1). 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document No. 1: Japanese Patent Laid-open No. 2008-260667 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the invention disclosed in Patent Document No. 1 mentioned above, however, a thin layer of photocatalyst is uniformly formed on a surface of a substrate as mentioned above, so it is necessary to increase light irradiation energy for activation in order to increase a photocatalyst effect. 
     The present invention has been accomplished in view of such circumstances, and therefore, it is a main object of the invention to provide a method of producing a photocatalyst layer which can increase a photocatalyst effect without increasing light irradiation energy for activation. 
     Means for Solving the Problems 
     In order to solve the above problems, the invention according to claim  1  relates to a method of producing a photocatalyst layer, comprising: 
     a light irradiation process of irradiating an ultraviolet ray on a titanium oxide layer formed on a substrate, 
     an aqueous photocatalyst solution application process of applying an aqueous photocatalyst solution containing fine particles on the titanium oxide layer, and 
     a drying process of drying the aqueous photocatalyst solution to form a photocalalyst layer, 
     wherein in the aqueous photocatalyst solution application process, the aqueous photocatalyst solution is applied on the titanium oxide layer in such a way that a thickness of the aqueous photocatalyst solution is ununiform, and 
     in the drying process, when the drying is carried out, a boundary portion between the aqueous photocatalyst solution and the titanium oxide layer moves gradually from a portion of the aqueous photocatalyst solution whose thickness is thin. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flowchart of explaining a method of producing a phtocatalyst layer in accordance with a first embodiment. 
         FIG. 2  is a schematic cross-sectional view of showing a substrate and a titanium oxide layer in the first embodiment. 
         FIG. 3  is a schematic view of showing that light is irradiated. 
         FIG. 4  is a schematic view of showing that an aqueous photocatalyst solution is applied. 
         FIG. 5  is a schematic cross-sectional view of a photocatalyst layer. 
         FIG. 6  is a schematic view of a substrate and a titanium oxide layer seen from the above. 
         FIG. 7  is a schematic view of a phtocatalyst layer seen from the above. 
         FIG. 8  is a flowchart of explaining a method of producing a phtocatalyst layer in accordance with a second embodiment. 
         FIG. 9  is a schematic cross-sectional view of showing a substrate and a titanium oxide layer in the second embodiment. 
         FIG. 10  is a schematic view of showing that light is irradiated. 
         FIG. 11  is a schematic cross-sectional view of explaining a blocking frame 
         FIG. 12  is a schematic view of showing that an aqueous phtocatalyst solution is applied. 
         FIG. 13  is a schematic cross-sectional view of showing a phtocatalyst layer. 
         FIG. 14  is a schematic view of a photocatalyst layer seen from the above. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     Referring now to  FIG. 1  to  FIG. 7 , a method of producing a photocatalyst layer according to an embodiment of the present invention will be explained. 
     A method of producing a photocatalyst layer according to the present embodiment comprises, as essential processes, a light irradiation process (step S 11 ), a process of applying an aqueous photocatalyst solution (step S 13 ), and a drying process (step S 14 ), as shown in  FIG. 1 . Now, each process will be explained in sequence. First, a substrate will be explained. 
     As shown in  FIG. 2 , material of a substrate  1  is not limited particularly, but grass, resin, or the like is listed. 
     A spherical shape, a plane shape, or the like is listed as a shape of the substrate  1 . In the present embodiment, a case where a substrate  1  of a spherical shape is used, and a photocatalyst layer is produced, as shown in  FIG. 2 , and  FIG. 6 , will be explained. A substrate of a spherical shape is not limited particularly. For example, as shown in  FIG. 2 , it may be possible to have a flat portion  2 , and a curved portion  4 . Further, a thickness of the substrate  1  is not limited particularly. 
     A titanium-oxide layer  6  formed on the substrate  1  is a layer with a hydrophilic effect, and may comprise, as a main component, titanium oxide of a rutile type. 
     A thickness of the titanium oxide layer  6  is not limited particularly, but it is sufficient that the titanium oxide layer  6  is as thick as the titanium oxide layer  6  covers an area in which the titanium oxide layer  6  is to be formed. Although a method of forming the titanium oxide layer  6  is not limited particularly, a vapor deposition method, and a spattering method are listed. 
     &lt;Light Irradiation Process&gt; 
     A light irradiation process is a process of irradiating an ultraviolet ray  8  on the titanium oxide layer  6  formed on the substrate  1  (step S 11 ). 
     As shown in  FIG. 3 , an irradiation method is a method Of collecting and irradiating the ultraviolet ray  8  emitted from an Hg—Xe lamp or the like on the substrate  1  for a predetermined period of time in such a way that a contact angle (not shown) indicative of a hydrophilic effect is approximately 10 degree for the titanium oxide layer  6  whose main component is titanium oxide of low crystalline. Further, it is preferable that the energy of the ultraviolet ray  8  to be irradiated is, for example, approximately 2800 J/cm 2  or more, as disclosed in Patent Document No. 1. 
     &lt;Blocking Frame Forming Process&gt; 
     A blocking frame forming process is a process of forming a blocking frame  7  for an aqueous phtocatalyst solution  9  on the periphery of the substrate  1  (step S 12 ). In a case where a member (hereinafter, referred to as “a blocking frame”) of functioning to block the aqueous photocatalyst solution  9  is already provided on the periphery of the substrate  1 , this process is not necessary. 
     As shown in  FIG. 4 , the blocking frame  7  is provided to prevent the aqueous photocatalyst solution  9  from leaking to the periphery of the substrate  1  when the aqueous photocatalyst solution  9  is applied on the titanium oxide layer  6 . 
     A shape of the blocking frame  7  is not limited particularly, as long as it has a shape of blocking the aqueous photocatalyst solution  9  on the periphery of the substrate  1 , for example, as shown in  FIG. 4 . 
     It is preferable that a height of the blocking frame  7  is higher than the position of a top  5  of the substrate  1  of a spherical shape. As mentioned below, in order to apply the aqueous photocatalyst solution  9  to the degree to which the top  5  of the substrate  1  of a spherical shape is covered, by making a height of the blocking frame  7  higher than the position of the top  5  of the substrate  1  of a spherical shape, it is possible to prevent the aqueous photocatalyst solution  9  from leaking to the outside. 
     &lt;Process of Applying an Aqueous Photocatalyst Solution&gt; 
     This process is a process of applying the aqueous photocatalyst solution  9  containing fine particles  10  on the titanium oxide layer  6  to form a photocatalyst layer  11  (step S 13 ). 
     Here, it is a characterizing feature to apply the aqueous photocatalyst solution containing fine particles to form a photocatalyst layer. 
     As shown in  FIG. 4 , the aqueous photocatalyst solution  9  is not limited particularly, as long as it has a phtocatalyst effect. An aqueous solution containing the fine particles  10  and whose main component is titanium oxide of an anatase type having a photocatalyst effect, or the like, is listed. Distilled water, ammonia water, or the like is listed as a solvent. 
     The concentration of fine particles in the aqueous photocatalyst solution  9  affects a thickness of a film, so it is selected at the request of a necessary thickness of a film. 
     Thus, by making the aqueous photocatalyst solution contain fine particles, in the case where the drying is carried out in a drying process mentioned below, it is possible to generate a step on a surface of a photocatalyst layer after the aqueous photocatalyst solution has been dried. 
     As a method of applying the aqueous photocatalyst solution  9 , a method of dripping a proper quantity on the substrate  1  with a microsyringe or the like is listed. 
     Here, it is a characterizing feature to apply the aqueous phtocatalyst solution  9  on the titanium oxide  6  in such a way that a thickness of the aqueous phtocatalyst solution  9  is ununiform. 
     Since the substrate  1  is a substrate having the flat portion  2  and the curved portion  4 , by applying the aqueous photocatalyst solution  9  as shown in  FIG. 4 , a thickness of the aqueous photocatalyst solution  9  accumulated at the flat portion  2  is different from a thickness of the aqueous photocatalyst solution  9  accumulated at the curved portion  4 . Therefore, the aqueous photocatalyst solution  9  is ununiformly applied on the titanium oxide layer  6 . 
     Thus, by applying an aqueous photocatalyst solution on a titanium oxide layer in such a way that a thickness of the aqueous phtocatalyst solution is ununiform, in the case where the drying is carried out in a drying process mentioned below, it is possible to generate a step on a surface of a photocatalyst layer after an aqueous photocatalyst solution has been dried. 
     Further, it is necessary to apply an amount of the aqueous phtocatalyst solution  9  more than an amount required for the aqueous phtocatalyst solution  9  to be uniformly applied. 
     Furthermore, as shown in  FIG. 4 , it may be possible to apply an amount of the aqueous phtocatalyst solution  9  by which the top  5  of the substrate  1  of a spherical shape is covered. Thus, it is also possible to generate a step on a surface in the vicinity of the top of the substrate for the phtocatalyst layer after the aqueous phtocatalyst solution has been dried. 
     &lt;Drying Process&gt; 
     A drying process is a process of drying a photocatalyst layer  11  (step S 14 ). 
     Although a drying temperature is not limited particularly, it is preferably from a room temperature to approximately 80 degree. A drying period of time is a period of time for which an aqueous potocatalyst solution is evaporated, so it varies with an applied amount of the aqueous potocatalyst solution  9 . 
     Here, a mechanism of producing a step is thought as follows: it is generally known that, when an aqueous fine-particle solution uniformly applied on a plane substrate is dried, a step is generated at a boundary between the aqueous solution and the substrate by a evaporating speed, and the diffusion of concentration of the aqueous solution. In this case, a step is formed in one ring-shape along a shape of the boundary, since the aqueous solution is dispersed in a circular shape on the plane substrate. 
     It is the present invention that this situation is realized over a whole surface of a plane substrate or a spherical substrate. That is, by applying an aqueous solution on the substrate  1  to the extent to which the aqueous solution is accumulated over the whole of the substrate  1 , and making an thickness of the aqueous solution on the substrate be ununiform, a thickness of the aqueous solution moves gradually from a thin portion due to the drying in such a way that a boundary portion moves on the substrate (in the case where the substrate  1  has a spherical shape, a diameter of a ring-shaped boundary portion extends with the top  5  being a center), resulting in the above steps being generated continuously. 
     Thus, based on the drying, as shown in  FIG. 5 , and  FIG. 7 , steps  12  can be generated on a surface of the photocatalyst layer  11 . 
     In the case where a blocking frame is formed in a blocking frame process, there may be provided a process of removing a blocking frame after a drying process. 
     Second Embodiment 
     Referring now to  FIG. 8  to  FIG. 14 , a method of producing a photocatalyst layer according to an embodiment of the present invention will be explained. 
     In the first embodiment, a case where a phtocatalyst layer is produced by using a spherical-shaped substrate has been explained. In the present embodiment, a case where a phtocatalyst layer is produced by using a plane-shaped substrate will be explained hereinafter. 
     A method of producing a photocatalyst layer according to the present embodiment comprises a light irradiation process (step S 21 ), a process of forming a blocking frame (step S 22 ), a process of locating a substrate (step S 23 ), a process of applying an aqueous photocatalyst solution (step S 24 ), and a drying process (step S 25 ), as shown in  FIG. 8 . Now, each process will be explained in sequence. First, a substrate on which a titanium oxide layer is formed and which is used in a light irradiation process will be explained. 
     As shown in  FIG. 9 , material of a substrate  21  is the same as material explained in the first embodiment. 
     A shape of the substrate  21  is plane, and a thickness of the substrate  21  is not limited particularly. 
     Material, a thickness, and a forming method of a titanium-oxide layer  22  formed on the substrate  21  are the same as ones explained in the first embodiment. 
     &lt;Light Irradiation Process&gt; 
     A light irradiation process is a process of irradiating an ultraviolet ray on the titanium oxide layer  22  formed on the substrate  21  (step S 21 ). 
     As shown in  FIG. 10 , a ultraviolet ray  23  to be irradiated, an irradiation process, and the like are the same as the cases explained in the first embodiment. 
     &lt;Blocking Frame Forming Process&gt; 
     A blocking frame forming process is a process of forming a blocking frame  24  (step S 22 ). 
       FIG. 11  is a view of showing a blocking frame seen from the above. 
     A shape of the blocking frame  24  is not limited particularly, as long as it is a shape capable of locating the substrate  21  in an inclined condition, as mentioned below. As shown in  FIG. 11 , a U-shape is listed. 
     A size of the blocking frame  24  is not limited particularly, as long as it is a size capable of locating the substrate  21 , as mentioned below. A size in which one substrate  21  or a plurality of substrates  21  can be located may be possible. 
     &lt;Substrate Locating Process&gt; 
     A substrate locating process is a process of locating a substrate on a blocking frame formed in a blocking frame forming process in an inclined condition (step S 23 ). 
     As shown in  FIG. 12 , by locating the substrate  21  on the blocking frame  24  in an inclined condition, when an aqueous photocatalyst solution  25  is applied as mentioned below, it is possible that an amount of the aqueous photocatalyst solution  25  accumulated on the substrate  21  varies with the position. 
     Therefore, in the case where the drying is carried out in a drying process mentioned below, steps are generated on a surface of a photocatalyst layer after an aqueous photocatalyst layer has been dried. 
     &lt;Process of Applying an Aqueous Photocatalyst Solution&gt; 
     A process of applying an aqueous photocatalyst solution is a process of applying the aqueous photocatalyst solution  25  containing fine particles  26  on the titanium oxide layer  22  to form a photocatalyst layer  27  (step S 24 ). 
     A process of applying the aqueous photocatalyst solution  25  is the same as a process explained in the first embodiment. 
     Here, it is a characterizing feature to apply the aqueous photocatalyst solution  25  on the titanium oxide layer  22  in such a way that a thickness of the aqueous photocatalyst solution  25  is ununiform. 
     As shown in  FIG. 12 , by applying the aqueous photocatalyst solution  25  in a condition in which the substrate  21  is located on the blocking frame  24  mentioned above in an inclined condition, a thickness to which the aqueous photocatalyst solution  25  is accumulated varies with the position on the substrate  21 . Therefore, the aqueous photocatalyst solution  25  is applied on the titanium oxide layer  22  ununiformly. 
     Thus, in the case where the drying is carried out in a drying process mentioned below, it is possible to generate steps on a surface of the photocatalyst layer after the aqueous photocatalyst solution has been dried. 
     It is necessary that an amount of the aqueous photocatalyst solution  25  to be applied is larger than an amount of the aqueous photocatalyst solution  25  which are applied uniformly. An amount of the aqueous photocatalyst solution  25  is large in the case where the blocking frame  24  is used, and the aqueous photocatalyst solution  25  is applied in a condition where the substrate  21  is inclined and located, as compared with the case where the blocking frame  24  is not used, and the aqueous photocatalyst solution  25  is applied uniformly in a condition where the substrate  21  is located in a plane condition. 
     &lt;Drying Process&gt; 
     The drying process is the same as the case explained in the first embodiment (step S 14 ). The drying is carried out in a condition where the substrate  21  is located on the blocking frame  25 . 
     By such a drying process, a step  28  can be generated on a surface of the photocatalyst layer  27 , as shown in  FIG. 13 , and  FIG. 14 . 
     It may be possible to provide a process of removing a blocking frame after a drying process. 
     As mentioned above, since the aqueous photocatalyst solution  9  contains fine particles  10 , in the case where the drying is carried out in a drying process, a step  12  can be generated on a surface of the photocatalyst layer  11  after the aqueous photocatalyst solution  9  is dried. Further, by applying the aqueous photocatalyst solution  9  on the titanium oxide layer  6  in such a way that a thickness of the aqueous photocatalyst solution  9  is ununiform, when the drying is carried out, a boundary portion between the aqueous solution and the titanium oxide layer  6  moves gradually from a thin portion of the thickness of the aqueous solution, so that continuous steps can be generated on a surface of the phtocatalyst layer  11 . 
     Thus, by generating a step  12 , a surface area of the photocatalyst layer  11  can become large, and therefore, it is possible to dissolve and remove more material of an organic system (dirt) adhered to a surface of the substrate  1  which is a photocatalyst effect. 
     Further, the substrate  1  has a spherical shape, and by applying an amount of the aqueous photocatalyst solution  9  which is larger than an amount of the aqueous photocatalyst solution  9  which is applied uniformly, in the case where the drying is carried out in a drying process, a step can be generated on a surface of the photocatalyst layer  11  after the aqueous photocatalyst solution  9  has been dried. 
     Further, by applying an amount of the aqueous photocatalyst solution by which the top of the substrate having a spherical shape is covered, after the aqueous photocatalyst solution  9  has been dried, a step  12  can be also generated on a surface of the photocatalyst layer  11  in the vicinity of the top  4  of the substrate. 
     Further when the aqueous photocatalyst solution  9  is applied on the titanium oxide layer  22 , by forming the blocking frame  7  for the aqueous photocatalyst solution  9  on the periphery of the substrate  1  in such a way that the aqueous photocatalyst solution  9  does not leak to the periphery of the substrate  1 , the aqueous photocatalyst solution  9  does not leak to the periphery of the substrate  1  so that the aqueous photocatalyst solution  9  can be accumulated on the substrate  1 . Thus, in the case where the drying is carried out in a drying process, a step can be generated on a surface of the photocatalyst layer  11  after the aqueous photocatalyst solution  9  has been dried. 
     Further, the substrate  21  is a plane shape, and when the aqueous photocatalyst solution  25  is applied on the titanium oxide layer  22 , the blocking frame for the aqueous photocatalyst solution  25  is formed in such a way that the aqueous photocatalyst solution  25  does not leak to the outside of the substrate  21 , and the substrate is located on the blocking frame  24  thus formed in an inclined condition. Thus, in the case where the drying is carried out in a drying process, a step can be generated on a surface of the photocatalyst layer  27  after the aqueous photocatalyst solution  25  has been dried. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1 : substrate (spherical shape) 
           2 : flat portion 
           3 : boundary between a flat portion and a curved portion 
           4 : curved portion 
           5 : top 
           6 ,  22 : titanium oxide layer 
           7 ,  24 : blocking frame 
           8 ,  23 : ultraviolet ray 
           9 ,  25 : aqueous photocatalyst solution 
           10 ,  26 : photocatalyst fine particle 
           11 ,  27 : photocatalyst layer 
           12 ,  28 : step 
           21 : plane-shaped substrate