JP7803572B2 - Coating, coating product, and film forming method - Google Patents

Description

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

Patent Document 1 describes that titanium phosphate has non-photocatalytic activity and exhibits antibacterial and deodorizing effects. Furthermore, Patent Document 2 describes coating the surface of an item with a titanium phosphate film to provide an antiviral finish to the item.

JP 2009-233239 Patent Publication No. 2018-058826

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

The coating of the present invention is a coating containing titanium phosphate, and has an uneven surface structure with repeated nanometer-sized irregularities.

With this configuration, the uneven structure increases the specific surface area of the titanium phosphate, enhancing its catalytic activity and imparting stronger antibacterial properties to the substrate coated with this film. 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.

The uneven structure preferably 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.
In this structure, the thin nanostructures increase the specific surface area of the uneven structure, thereby enhancing the catalytic activity of titanium phosphate. Furthermore, a structure in which thin nanostructures intersect and overlap to form voids within it allows substances to move more easily deep into the voids than a porous structure in which the voids are formed by minute holes, thereby increasing the surface area effective for catalytic action.

Preferably, the nanostructures are randomly oriented.
With this configuration, voids of various sizes are formed between the nanostructures, making it possible to exert antibacterial effects against substances of various sizes.

The uneven structure preferably includes the titanium phosphate forming the unevenness and titanium oxide adhering 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, etc. 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.

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

The coated article according to the present invention comprises a coating film containing titanium phosphate and having an uneven structure with repeated nanometer-sized irregularities on the surface, and a substrate that is covered with the coating film and contains iron atoms.
With this configuration, a coating having a larger surface area can be formed by the iron atoms contained in the substrate.

The substrate preferably has a mesh structure.
With this configuration, the titanium phosphate coating can increase the strength of the mesh structure, and at the same time, the catalytic action of the titanium phosphate can act on substances contained in the fluid filtered by the mesh structure. For example, if placed in a ventilation vent, it can prevent bacteria and viruses contained in the air from entering or leaving the vent. In addition, because the mesh structure itself can be given antibacterial properties, 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.

The film forming method according to the present invention is a method in which a substrate is immersed in a dispersion liquid in which titanium phosphate is dispersed, and then the substrate is heated to a temperature of 600°C or higher and 800°C or lower, thereby forming a coating containing titanium phosphate on the substrate.
With this method, titanium phosphate coated on the surface of a substrate can be fixed to the substrate by heating, forming a titanium phosphate film with a surface texture consisting of repeated nanometer-sized irregularities, a large specific surface area, and high catalytic activity.

It is preferable that sodium titanate and iron oxide are further dispersed in the dispersion liquid.
With this method, since sodium titanate and iron oxide are contained in the dispersion liquid, it is possible to form a coating having an uneven structure with nanostructures that rise from the coating surface and have a thin plate-like structure with a thickness of nanometers, and a coating with a larger specific surface area.

The present invention, configured in this way, can provide a titanium phosphate coating with a large specific surface area and high catalytic activity.

1 is an SEM image of the surface of the coating obtained in Example 1. 1 is an SEM image of the surface of the coating obtained in Example 1. 1 is an SEM image of the surface of the coating obtained in Example 1. 1 is an SEM image of the surface of the coating obtained in Example 1. 10 is an SEM image of the surface of the stainless steel mesh obtained in the comparative example. 1 is an SEM image of the surface of the coating obtained in Example 2. 1 is an SEM image of the surface of the coating obtained in Example 3.

The following describes a coating according to one embodiment of the present invention, a coated product having the coating, and a method for forming the thin film, with reference to the drawings.

<Coated products>
The coated product of this embodiment is a titanium phosphate-coated filter that includes a substrate with 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 drawn in through the opening.

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 weave of the mesh structure may also be a twill weave, a dutch weave, or other weaves.

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

The coating comprises a coating structure that tightly covers the surface of the substrate, and a concave-convex structure formed on this coating structure, with repeated nanometer-sized concaves and convexes. The thickness of the coating thus configured is preferably 0.1 μm or more and 10 μm or less.

The coating contains titanium phosphate as its main component, and the coating structure and uneven structure are primarily formed by titanium phosphate. Here, more than 50% of the coating is composed of titanium phosphate. The coating of this embodiment also contains titanium oxide, iron oxide, etc.

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.

The nanostructures of this embodiment are thin, plate-like structures with a nanometer-sized thickness that rise from the coating structure. More specifically, the nanostructures are 100 nm or less in thickness, and the shape, size, extension direction, and posture of each nanostructure are irregular.

The uneven structure is formed by these nanostructures overlapping and joining together, 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.

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

Note that the nanostructures are not limited to the thin plate-like shape described above, but may be spherical with a diameter on the order of nanometers, blocky with a width on the order of nanometers, or needle-like with a thickness on the order of nanometers. Furthermore, the nanostructures may be arranged in a regular pattern.

<Film formation method>
The method for forming the above-mentioned coating will now be described.
The film forming method of this embodiment is a method of forming a film containing titanium phosphate on a substrate by a wet coating method.

(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.

The concentration of the dispersoid in the dispersion is adjusted appropriately depending on the type of substrate and the intended use 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 higher concentration increases the viscosity of the dispersion, resulting in too much adhesion to the substrate, so a concentration of 50 wt% or less is preferred. When applying to a mesh structure, the concentration is preferably 30 wt% or less, more preferably 10% or less, to prevent clogging of the mesh.

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

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

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, and more preferably 10 wt% or more. Furthermore, to ensure the physical strength of the coating, it is preferably 30 wt% or less, and more preferably 15 wt% or less.

(Film forming process)
The dispersion is applied to the surface of the substrate by immersing the substrate in a liquid tank containing the dispersion. 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 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.

(Other processes)
Before the coating step, a pretreatment such as cleaning of the substrate surface may be carried out.
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.

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 within the technical scope of the present invention.

In Example 1, a filter (Sample 1) was produced by the above-described film-forming method, in which a coating containing titanium phosphate was formed on the surface of a stainless steel mesh substrate. The specific conditions were as follows:
(Base material)
Material: Stainless steel Wire diameter: 0.025 mm
Mesh: 500 mesh (film formation conditions)
Dispersion liquid: Dispersion liquid prepared by adding 100 g of a 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

Figures 1 to 4 are SEM images of the coating surface of Sample 1, prepared under the above conditions. Figure 5 is an SEM image of the surface of an uncoated stainless steel mesh (comparative example).

Figures 1 to 4 show that the coating surface has a structure with repeated nanometer-sized irregularities, confirming that the coating of Sample 1 has a characteristic surface structure with a large specific surface area.

Figures 1 to 4 show that thin plate-like structures with nanometer-sized thicknesses are intertwined and overlapped, confirming that the structure has a highly porous surface. The thickness of the observed thin plate-like structures was evaluated and found to be 100 nm or less. Figure 4 also shows that nanometer-sized irregularities have been formed on the surface of the thin plate-like structures.

The coating image shown here is an example of the present invention. When the concentration of 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 with a structure in which nanometer-sized irregularities were repeated on the surface was formed, just as in the previously described examples.

<Effects of this embodiment>
The coating according to this embodiment has an uneven surface structure 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.

The coated product (filter) according to this embodiment is coated with a film containing titanium phosphate, which gives it high corrosion resistance and improves its mechanical strength compared to the strength of the stainless steel mesh substrate alone.

Furthermore, titanium phosphate is a non-photocatalyst, meaning it retains its catalytic activity even in the dark or at night. This means that this filter can be used in more places than filters coated with titanium oxide, a photocatalyst. For example, this filter can perform well even when used in places where light does not reach, such as underwater or in sewage.

In addition, due to its ability to decompose organic matter, it is less likely to become clogged due to the proliferation of attached organisms or the secretions they produce, allowing for long-term use.

In the uneven structure, voids are formed between the thin plate-like nanostructures, resulting in a high porosity and the ability to capture a large amount of material inside. Furthermore, these voids are designed to be wider on the outside and narrower towards the inside, making it easier for materials to penetrate deep into the voids and increasing the surface area available for catalytic reactions. Additionally, larger materials can be captured on the outside of the voids and smaller materials on the inside, making it possible to remove foreign matter of various sizes contained in the fluid. Because the voids are wider on the outside, the captured materials are more likely to be released after the reaction, extending the life of antibacterial effects, etc.

Furthermore, the film-forming method according to this embodiment can form a titanium phosphate film with a surface that has an uneven structure with repeated nanometer-sized irregularities, a large specific surface area, and high catalytic activity, and can be used to manufacture coated products with high antibacterial properties, etc.

Second Embodiment
In the 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. The other film forming conditions are the same as those in the first embodiment.

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

Example 2
The coating according to this embodiment will be described in more detail below with reference to examples.
In Example 2, a filter (sample 2) having a film containing titanium phosphate formed on the surface of a substrate was produced under the following conditions.
(Base material)
Material: Stainless steel Wire diameter: 0.025 mm
Mesh: 500 mesh (film formation conditions)
Dispersion liquid: Dispersion liquid 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

Figure 6 is an SEM image of the coating surface of Sample 2, created under the above conditions. From this image, a structure with 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.

<Effects of the Second Embodiment>
The film-forming method of this embodiment can also form a titanium phosphate film with a rough surface structure consisting of repeated nanometer-sized irregularities, a large specific surface area, and high catalytic activity, and can be used to manufacture coated products with high antibacterial properties, etc.

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

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

Third Embodiment
In this embodiment, the coating is composed of 95% or more of titanium phosphate.
In the film forming 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 liquid. Other film forming conditions are the same as those in the first embodiment.

Example 3
The coating according to this embodiment will be described in more detail below with reference to examples.
In Example 3, a filter (sample 3) having a film containing titanium phosphate formed on the surface of a substrate was produced under the following conditions.
(Base material)
Material: Stainless steel Wire diameter: 0.025 mm or more Mesh: 500 mesh or less (film formation conditions)
Dispersion liquid: Dispersion liquid 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

Figure 7 is an SEM image of the coating surface of Sample 3, created under the above conditions. From this image, it can be seen that the coating surface has a structure with repeated nanometer-sized irregularities, confirming that the coating of Sample 3 has a characteristic surface structure with a large specific surface area. It was also confirmed that randomly shaped nanostructures, such as spherical or lumpy ones, were formed to rise from the coating surface.

<Effects of the Third Embodiment>
The film-forming method of this embodiment can also form a titanium phosphate film with a rough surface structure consisting of repeated nanometer-sized irregularities, a large specific surface area, and high catalytic activity, and can be used to manufacture coated products with high antibacterial properties, etc.

Fourth Embodiment
The uneven structure of this embodiment has titanium oxide attached to the unevenness formed by titanium phosphate. Specifically, titanium oxide is attached to the nanostructures made of titanium phosphate.

This coating is formed by coating a substrate with titanium phosphate using the wet coating method described above, and then coating titanium oxide on top of that. Titanium oxide is coated onto the titanium phosphate using known wet or dry coating methods.

With this configuration, combining titanium oxide, which has photocatalytic properties, with titanium phosphate can further enhance antibacterial performance. Furthermore, by attaching titanium oxide to an 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.

In addition, other metal catalysts may be attached to the surface of the uneven structure, and the metal catalyst to be attached can be selected according to the function desired to be imparted to the substrate.

<Other embodiments>
The coating may be applied to 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.

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

Furthermore, the substrate is not limited to materials containing iron atoms or metals.

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

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.

Claims (14)

A coating comprising titanium phosphate,
The surface has a textured structure with repeated nanometer-sized bumps,
A coating that is composed of over 95% titanium phosphate . the concave-convex structure has a thin plate-like nanostructure having a thickness on the order of nanometers,
The coating according to claim 1 , wherein the unevenness is formed by the nanostructures being arranged at intervals. The coating described in claim 2, wherein the nanostructures are each randomly oriented. The coating described in claim 1, wherein the uneven structure comprises titanium phosphate forming the unevenness and titanium oxide adhering to the unevenness. The coating of claim 1, further containing iron oxide. A coating according to any one of claims 1 to 5;
a substrate that is covered with the coating and contains iron atoms. The coated article according to claim 6, wherein the substrate has a mesh structure. A method for forming the coating according to claim 1 on a substrate, comprising:
The film forming method includes immersing the 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 the coating on the substrate. The film-forming method described in claim 8, wherein sodium titanate and iron oxide are further dispersed in the dispersion liquid. A coating comprising titanium phosphate,
The surface has a textured structure with repeated nanometer-sized bumps,
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 the nanostructures being arranged at intervals. A coating comprising titanium phosphate,
The surface has a textured structure with repeated nanometer-sized bumps,
The uneven structure is a coating having the titanium phosphate forming the unevenness and titanium oxide adhering to the unevenness. A coating comprising titanium phosphate,
The surface has a textured structure with repeated nanometer-sized bumps,
The coating further comprises iron oxide. A coating comprising titanium phosphate,
a coating having an uneven structure in which nanometer-sized unevenness is repeated on the surface;
a substrate that is covered with the coating and contains iron atoms. A coating comprising titanium phosphate,
The surface has a textured structure with repeated nanometer-sized bumps,
A coating that covers a substrate containing iron atoms.