Coating film, coating product, and film forming method

Abstract

Provided is a titanium phosphate coating film having a large specific surface area and high catalytic activity. This coating film, which contains titanium phosphate, is configured so as to have an uneven structure in which nanometer-sized dips and bumps are repeated on a surface.

Description

Coating, coating product and film forming method

[0001] The present invention relates to a coating containing titanium phosphate, a coated article having the coating, and a method for forming the coating.

[0002] Patent Document 1 describes that titanium phosphate has non-photocatalytic activity and exhibits antibacterial and deodorizing effects, while Patent Document 2 describes coating the surface of an article with a titanium phosphate film to provide an antiviral treatment to the article.

[0003] JP 2009-233239 JP 2018-058826

[0004] The activity of a catalyst depends on its specific surface area, and increasing the specific surface area increases its activity, further strengthening its antibacterial action, etc. Therefore, the main object of the present invention is to provide a titanium phosphate coating with a large specific surface area and high catalytic activity.

[0005] The coating according to the present invention is a coating containing titanium phosphate, and has an uneven structure in which nanometer-sized irregularities are repeated on the surface.

[0006] This structure allows the specific surface area of ​​titanium phosphate to be increased by the uneven structure, enhancing the catalytic activity of titanium phosphate and imparting a stronger antibacterial effect to the substrate coated with this coating. In addition, the nanometer-sized unevenness makes it easier to capture viruses and other microorganisms of a similar scale. Furthermore, using titanium phosphate as a coating can impart high corrosion resistance to the substrate and improve its mechanical strength.

[0007] The uneven structure preferably has thin plate-like nanostructures with a thickness on the order of nanometers, and the unevenness is formed by arranging the nanostructures at intervals. With this configuration, the thin plate-like nanostructures increase the specific surface area of ​​the uneven structure, thereby enhancing the catalytic activity of titanium phosphate. Furthermore, a structure in which thin plate-like nanostructures intersect and overlap to form voids within it allows substances to move deeper into the voids than a porous structure in which voids are formed by fine pores, thereby increasing the surface area effective for catalytic action.

[0008] It is preferable that the nanostructures are oriented in random directions, since this configuration results in voids of various sizes being formed between the nanostructures, allowing the nanostructures to exert antibacterial and other effects on substances of various sizes.

[0009] The uneven structure preferably includes the titanium phosphate forming the unevenness and titanium oxide attached to the unevenness. With this configuration, by combining titanium oxide, which has photocatalytic activity, with titanium phosphate, it is possible to further enhance antibacterial performance. Furthermore, by attaching titanium oxide to the uneven structure, the specific surface area of ​​the titanium oxide can be increased compared to when it is attached to a flat surface, thereby enhancing its catalytic activity.

[0010] The coating preferably further contains iron oxide. With this configuration, the catalytic action of iron oxide can be utilized to enhance the decomposition performance of organic matter. In addition, inexpensive ilmenite (FeTiO ３ ) can be used as a raw material for film formation.

[0011] The coated article of the present invention comprises a coating containing titanium phosphate and having a surface with a concave-convex structure in which nanometer-sized concaves and convexes are repeated, and a substrate that is covered with the coating and contains iron atoms. With this configuration, a coating with a larger surface area can be formed by the iron atoms contained in the substrate.

[0012] It is preferable that the substrate has a mesh structure. With this configuration, the strength of the mesh structure can be increased by coating it with titanium phosphate, and at the same time, the catalytic action of titanium phosphate can act on substances contained in the fluid filtered by the mesh structure. For example, if it is placed in a ventilation vent, it can prevent bacteria and viruses contained in the air from entering or leaving the vent. Furthermore, since the mesh structure itself can be given an antibacterial effect, if it is placed in, for example, a drain, it is less likely to encounter situations where bacteria and other microorganisms grow and cause clogging.

[0013] The film formation method according to the present invention is a method of forming a coating containing titanium phosphate on a substrate by immersing the substrate in a dispersion liquid in which titanium phosphate is dispersed, and then heating the substrate to a temperature of 600° C. to 800° C. With this method, titanium phosphate applied to the surface of the substrate is fixed to the substrate by heating, thereby forming a titanium phosphate film having a surface with an uneven structure in which nanometer-sized irregularities are repeated, a large specific surface area, and high catalytic activity.

[0014] It is preferable that sodium titanate and iron oxide are further dispersed in the dispersion liquid. In this method, the inclusion of sodium titanate and iron oxide in the dispersion liquid makes it possible to form a coating having an uneven structure with nanostructures that rise from the coating surface and have a thin plate-like thickness on the order of nanometers, thereby enabling the formation of a coating having a larger specific surface area.

[0015] According to the present invention thus configured, it is possible to provide a titanium phosphate coating having a large specific surface area and high catalytic activity.

[0016] SEM image of the surface of the coating obtained in Example 1. SEM image of the surface of the coating obtained in Example 1. SEM image of the surface of the coating obtained in Example 1. SEM image of the surface of the coating obtained in Example 1. SEM image of the surface of the coating obtained in Example 1. SEM image of the surface of the stainless steel mesh obtained in the comparative example. SEM image of the surface of the coating obtained in Example 2. SEM image of the surface of the coating obtained in Example 3.

[0017] Hereinafter, a coating according to one embodiment of the present invention, a coated product having the coating, and a method for forming the thin film will be described with reference to the drawings.

[0018] <Coated Product> The coated product of this embodiment is a filter coated with titanium phosphate, and includes a substrate having a mesh structure and a coating containing titanium phosphate that covers the substrate. This filter physically filters objects in a fluid using the mesh structure, and also chemically filters bacteria, viruses, and the like in the fluid by decomposing them using the catalytic action of the titanium phosphate. For example, it can be installed in a ventilation opening and function as a screen while removing bacteria and viruses contained in the outside air that is taken in through the opening.

[0019] The substrate here is a wire mesh (so-called stainless steel mesh) made by plain weaving stainless steel wires formed by shaping stainless steel (SUS) into a linear shape. Various metal wires may be used as threads for weaving the mesh, but those containing iron atoms are particularly preferred. The weaving method of the mesh structure may be twill weave, dutch weave, or the like.

[0020] The mesh structure is preferably as follows: Wire diameter (thread diameter in mm): 0.025 or more Mesh (number of threads per inch): 500 mesh or less is preferred, and 50 mesh or more and 200 mesh or less is more preferred.

[0021] The coating film has a coating structure that tightly covers the surface of the substrate, and a concavo-convex structure formed on the coating structure and having repeated nanometer-sized concaves and convexes. The thickness of the coating film thus configured is preferably 0.1 μm or more and 10 μm or less.

[0022] The coating contains titanium phosphate as a main component, and the coating structure and the uneven structure are mainly formed of titanium phosphate. Here, 50% or more of the coating is composed of titanium phosphate. The coating of this embodiment further contains titanium oxide, iron oxide, etc.

[0023] The uneven structure has nanometer-sized structures (hereinafter referred to as nanostructures), and the unevenness is formed by arranging these nanostructures at intervals on the coating surface. Here, nanometer size refers to a width, height, thickness, etc. of 1000 nm or less.

[0024] The nanostructures of this embodiment are thin, nanometer-sized plates rising from the coating structure. More specifically, the nanostructures are 100 nm or less in thickness, and the shapes, sizes, extension directions, and orientations of the individual nanostructures are irregular.

[0025] The uneven structure is formed by overlapping and joining such nanostructures, and the density of the nanostructures decreases from the inside (closer to the substrate) to the outside (farther from the substrate) of the uneven structure.

[0026] Between the nanostructures, voids of irregular size and shape are formed, and these voids become smaller from the outside to the inside of the uneven structure, reaching nanometer size at the inside.

[0027] The nanostructure is not limited to the above-mentioned thin plate shape, but may be a sphere with a diameter on the order of nanometers, a block with a width on the order of nanometers, a needle with a thickness on the order of nanometers, etc. Furthermore, the nanostructure may be arranged regularly.

[0028] <Film Forming Method> A film forming method for the above-described coating will be described below. The film forming method of this embodiment is a method for forming a coating containing titanium phosphate on a substrate by a wet coating method.

[0029] (Preparation of Dispersion) A dispersoid obtained by adding a mixed powder of iron oxide and sodium titanate (hereinafter also referred to as brown powder) to a titanium phosphate-containing powder is added to water and stirred to prepare a dispersion in which these are dispersed.

[0030] The concentration of the dispersoid in the dispersion is adjusted appropriately depending on the type of substrate and the application of the coated product. It is preferably 1 wt % or more, more preferably 3% or more, so that a coating of at least sufficient thickness can be formed. Furthermore, a high concentration increases the viscosity of the dispersion, resulting in excessive adhesion to the substrate, so the concentration is preferably 50 wt % or less. When applying to a mesh structure, the concentration is preferably 30 wt % or less, more preferably 10% or less, so as to prevent clogging of the mesh.

[0031] The titanium phosphate-containing powder contains titanium phosphate and impurities such as iron oxide, and is highly pure with an impurity content of less than 5 wt%. This titanium phosphate-containing powder may also be pure titanium phosphate powder that does not contain impurities. The titanium phosphate-containing powder can be purified, for example, by refluxing the brown powder in phosphoric acid at 150°C, separating it into solid and liquid phases after sufficient reaction, and drying the solid phase.

[0032] The brown powder contains iron oxide and sodium titanate in a molar ratio of 4:1. The brown powder here is produced by, for example, mixing ilmenite and sodium hydroxide and heating the mixture. Iron oxide powder may be used instead of the brown powder.

[0033] The brown powder is added to the dispersoid to increase the specific surface area of ​​the coating. To increase the specific surface area, the brown powder content of the dispersoid is preferably 5 wt% or more, more preferably 10 wt% or more. To ensure the physical strength of the coating, the content is preferably 30 wt% or less, more preferably 15 wt% or less.

[0034] (Film-forming step) The substrate is immersed in a liquid tank containing the dispersion liquid, thereby coating the surface of the substrate with the dispersion liquid. The substrate is then removed from the tank and placed in an electric furnace, where it is heated until the substrate temperature reaches 600°C or higher and 800°C or lower, thereby hardening the titanium phosphate on the substrate and forming a coating. The application of the dispersion liquid is not limited to immersion, and various methods such as spraying may be used. Heating is also not limited to an electric furnace, and various existing heating devices may be used.

[0035] (Other Steps) A pretreatment such as cleaning of the surface of the substrate may be carried out before the coating step. Furthermore, between the coating step and the heating step, the substrate wetted with the dispersion may be dried to volatilize the water serving as the dispersion medium.

[0036] <Example 1> The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and modifications can be made within the scope of the above and below-described aims, and all such modifications are included within the technical scope of the present invention.

[0037] In Example 1, a filter (Sample 1) was produced using the above-described film-forming method, in which a titanium phosphate-containing coating was formed on the surface of a stainless steel mesh substrate. Specific conditions were as follows: (Substrate) Material: Stainless steel Wire diameter: 0.025 mm Mesh: 500 mesh (Film-forming conditions) Dispersion: Dispersion prepared by adding 100 g of dispersoid consisting of titanium phosphate-containing powder (90 wt%) and brown powder (10 wt%) to 2 L of water and stirring Heating temperature: Approximately 700°C Drying conditions: Room temperature

[0038] 1 to 4 are SEM images of the coating surface of Sample 1 prepared under the above conditions. Note that Fig. 5 is an SEM image of the surface of an uncoated stainless steel mesh (comparative example).

[0039] 1 to 4, a structure in which nanometer-sized irregularities are repeated can be seen on the surface of the coating, and it was confirmed that the coating of Sample 1 has a characteristic surface structure with a large specific surface area.

[0040] 1 to 4, it was possible to see that thin plate-like structures having a thickness of nanometer order were intertwined and overlapped, and it was confirmed that the structure had a highly porous surface. When the thickness of the observed thin plate-like structures was evaluated, it was found to be 100 nm or less. Furthermore, in FIG. 4, it was possible to see that nanometer-sized irregularities were formed on the surface of the thin plate-like structures.

[0041] The coating image shown here is an example of the present invention, and even when the concentration of the dispersoid in the dispersion was changed between 1 and 50%, when the amount of brown powder in the dispersoid was changed between 5 wt% and 30 wt%, and when the heating temperature was changed between 600°C and 800°C, a coating having a structure in which nanometer-sized irregularities were repeated on the surface was formed, as in the above-mentioned examples.

[0042] <Effects of this embodiment> The coating according to this embodiment has an uneven structure on its surface and a large specific surface area, which enhances the catalytic activity of the titanium phosphate contained in the coating, enabling it to exhibit high antibacterial, antiviral, deodorizing, and organic matter decomposition effects, etc. Furthermore, because this uneven structure is formed by nanometer-sized unevenness, it is easy to capture viruses and the like of a similar scale.

[0043] The coated product (filter) according to this embodiment is coated with a film containing titanium phosphate, and therefore has high corrosion resistance and mechanical strength that is greater than that of the stainless steel mesh substrate alone.

[0044] Furthermore, titanium phosphate is a non-photocatalyst and maintains catalytic activity even in the dark or at night, so this filter can be used in more places than filters coated with titanium oxide, a photocatalyst. For example, this filter can demonstrate its performance even when used in places where light does not reach, such as underwater or in sewage.

[0045] Furthermore, due to the organic matter decomposition function, clogging caused by the proliferation of attached organisms or the secretions of those organisms is unlikely to occur, and the filter can be used for a long period of time.

[0046] In the uneven structure, voids are formed between the thin plate-like nanostructures, resulting in a high porosity and the ability to capture many substances inside. Furthermore, these voids are designed to be wider on the outside and narrower toward the inside, making it easier for substances to penetrate deep into the voids and providing a large surface area effective for catalytic reactions. Additionally, larger substances can be captured on the outside of the voids and smaller substances on the inside, making it possible to remove foreign substances of various sizes contained in fluids. Because the voids are wider on the outside, the captured substances are more likely to be released after the reaction, extending the life of antibacterial and other effects.

[0047] Furthermore, according to the film-forming method of this embodiment, it is possible to form a titanium phosphate film having an uneven structure with repeated nanometer-sized irregularities on the surface, a large specific surface area, and high catalytic activity, and this film can be used to manufacture coated products with high antibacterial properties, etc.

[0048] Second Embodiment In a film forming method of this embodiment, a dispersion liquid is prepared using a titanium phosphate-containing powder containing more impurities than in the first embodiment as a dispersoid, and a coating is formed using the dispersion liquid. Other film forming conditions are the same as those in the first embodiment.

[0049] The titanium phosphate-containing powder herein contains 5 wt % to 30 wt % of impurities, for example, 10 wt % of iron oxide as an impurity, and is refined from, for example, the aforementioned brown powder so that the impurity content falls within the above range.

[0050] Example 2 The coating according to this embodiment will be described in more detail below with reference to an example. In Example 2, a filter (Sample 2) was produced under the following conditions, in which a coating containing titanium phosphate was formed on the surface of a substrate. (Substrate) Material: Stainless steel Wire diameter: 0.025 mm Mesh: 500 mesh (Coating conditions) Dispersion: Dispersion prepared by adding 100 g of dispersoid made of titanium phosphate-containing powder containing 10 wt % iron oxide as an impurity to 2 L of water and stirring Heating temperature: Approximately 700°C Drying conditions: Room temperature

[0051] Figure 6 is an SEM image of the coating surface of Sample 2, created under the above conditions. From this image, a structure of repeated nanometer-sized irregularities can be seen on the coating surface, confirming that the coating of Sample 1 has a characteristic surface structure with a large specific surface area. It was also confirmed that nanostructures with random shapes, such as thin plates, spheres, and chunks, were formed to rise from the coating surface.

[0052] <Effects of the Second Embodiment> The film-forming method of this embodiment also makes it possible to form a titanium phosphate film having an uneven structure with repeated nanometer-sized irregularities on the surface, a large specific surface area, and high catalytic activity, and can be used to manufacture coated products with high antibacterial properties, etc.

[0053] The iron oxide contained in the coating also exerts its catalytic action on the surface of the coating, improving, for example, the decomposition performance of organic matter.

[0054] A dispersion can be prepared using a titanium phosphate-containing powder with a low degree of refinement as the dispersoid, which is more advantageous in terms of production costs than using a titanium phosphate-containing powder with a high degree of refinement.

[0055] Third Embodiment The coating of this embodiment is one in which 95% or more of the coating is made of titanium phosphate. In the coating method according to this embodiment, titanium phosphate-containing powder without brown powder added is added as a dispersoid to water and stirred to prepare a dispersion. The other coating conditions are the same as those of the first embodiment.

[0056] Example 3 The coating according to this embodiment will be described in more detail below with reference to an example. In Example 3, a filter (Sample 3) was produced in which a coating containing titanium phosphate was formed on the surface of a substrate under the following conditions. (Substrate) Material: Stainless steel Wire diameter: 0.025 mm or more Mesh: 500 mesh or less (Coating conditions) Dispersion: Dispersion prepared by adding 100 g of titanium phosphate-containing powder to 2 L of water and stirring Heating temperature: 700°C Drying conditions: Room temperature

[0057] Figure 7 is an SEM image of the coating surface of Sample 3, created under the above conditions. From this image, a structure of repeated nanometer-sized irregularities can be seen on the coating surface, confirming that the coating of Sample 3 has a characteristic surface structure with a large specific surface area. It was also confirmed that nanostructures with random shapes, such as spheres and chunks, were formed to rise from the coating surface.

[0058] <Effects of the Third Embodiment> The film-forming method of this embodiment also makes it possible to form a titanium phosphate film having an uneven structure with repeated nanometer-sized irregularities on the surface, a large specific surface area, and high catalytic activity, and can be used to manufacture coated products with high antibacterial properties, etc.

[0059] Fourth Embodiment The uneven structure of this embodiment has titanium oxide adhered to unevenness formed by titanium phosphate. Specifically, in this embodiment, titanium oxide is adhered to a nanostructure made of titanium phosphate.

[0060] This coating is formed by coating the substrate with titanium phosphate using the wet coating method described above, followed by a further coating of titanium oxide, which is then coated onto the titanium phosphate using known wet or dry coating methods.

[0061] With this configuration, combining titanium oxide, which has photocatalytic activity, with titanium phosphate can further enhance antibacterial performance. Furthermore, by attaching titanium oxide to a textured structure, the specific surface area of ​​the titanium oxide can be increased, thereby enhancing its catalytic activity, compared to when it is attached to a flat surface. Furthermore, in the coating of this embodiment, in which titanium oxide is partially attached to a titanium phosphate film, a strong reduction reaction of titanium phosphate and a strong oxidation reaction of titanium oxide can occur on the surface. This improves decomposition efficiency through the synergistic effect of the two catalytic reactions. Furthermore, the occurrence of multiple oxidation and reduction reactions enables the decomposition of complex organic substances and mixtures that are difficult to treat with a single catalyst.

[0062] Other metal catalysts may be attached to the surface of the uneven structure, and the metal catalyst to be attached may be selected according to the function to be imparted to the substrate.

[0063] Other Embodiments The coating may cover a coarse mesh structure such as a screen door, which can impart antibacterial properties to the screen door and improve its mechanical strength, reducing the risk of breakage.

[0064] The coating may also be used to coat other substrates that do not have a mesh structure, such as the surfaces of pipes and tanks that require corrosion resistance. Coating the bottom of a ship can prevent not only corrosion but also the attachment of marine organisms such as barnacles.

[0065] Furthermore, the substrate is not limited to one containing iron atoms or metal.

[0066] The coating containing titanium phosphate does not need to be formed directly on the substrate, and for example, another metal film formed by plating may be provided between the coating and the substrate.

[0067] It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, it will be understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following aspects.

[0068] According to the present invention, it is possible to provide a titanium phosphate coating having a large specific surface area and high catalytic activity.

Claims

1. A coating containing titanium phosphate, which has an uneven structure with repeated nanometer-sized irregularities on its surface.

2. The coating according to claim 1, wherein the uneven structure has nanostructures in the form of thin plates with a thickness on the order of nanometers, and the unevenness is formed by arranging the nanostructures at intervals.

3. The coating of claim 2, wherein the nanostructures are each randomly oriented.

4. The coating according to claim 1, wherein the uneven structure comprises titanium phosphate forming the unevenness and titanium oxide adhering to the unevenness.

5. The coating of claim 1 further comprising iron oxide.

6. A coated article comprising the coating according to any one of claims 1 to 5 and a substrate that is covered with the coating and contains iron atoms.

7. The coated article according to claim 6, wherein the substrate has a mesh structure.

8. A film forming method comprising immersing a substrate in a dispersion liquid in which titanium phosphate is dispersed, and then heating the substrate to a temperature of 600°C or higher and 800°C or lower, thereby forming a film containing titanium phosphate on the substrate.

9. The film forming method according to claim 8, wherein sodium titanate and iron oxide are further dispersed in the dispersion liquid.

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