JP7423261B2 - Transparent member, imaging device, and method for manufacturing transparent member - Google Patents

Description

The present invention relates to a hydrophilic transparent member, a method for manufacturing the same, and an imaging device using the transparent member as a protective cover.

In recent years, surveillance cameras have been installed in various places such as stores, hotels, banks, and train stations for the purpose of crime prevention. Surveillance cameras are installed by attaching them to ceilings, external walls, pillars, etc. via installation parts, or by embedding them.

A transparent protective cover is attached to the surveillance camera body to protect it from the surrounding environment and does not interfere with imaging. The protective cover uses resin materials such as polycarbonate and acrylic resin, which have excellent transparency and impact resistance. In the case of surveillance cameras installed outdoors, water droplets from rain or condensation adhere to the protective cover, distorting the image or making it unclear, so a hydrophilic film is provided on the protective cover to prevent water droplets from adhering Prevention techniques are widely used.

Patent Document 1 proposes a hydrophilic film that obtains a silica particle film with high hydrophilicity and high adhesion by infiltrating silica sol into a resin base material.

Japanese Patent Application Publication No. 2013-203774

Generally, when a resin base material such as polycarbonate or acrylic resin used for a protective cover of a surveillance camera or the like is installed outdoors for a long period of time, it deteriorates due to sunlight and cracks such as cracks occur. Therefore, even when a hydrophilic film is formed on the protective cover, as cracks occur in the resin base material that is the protective cover, cracks also occur in the hydrophilic film, resulting in an increase in haze that distorts the photographed image. There is. Another problem is that when the cracks extend, the hydrophilic film falls off from the protective cover, making it impossible to maintain hydrophilicity.

Therefore, it is preferable that the hydrophilic film provided on the protective cover can suppress the occurrence of cracks, suppress the increase in haze, and maintain hydrophilicity when the protective cover is installed outdoors for a long period of time. However, the hydrophilic film with the structure proposed in Patent Document 1 cannot suppress the deterioration of the base material due to sunlight when it is installed outdoors for a long period of time, so it is difficult to suppress the occurrence of cracks in the hydrophilic film. Therefore, it is impossible to suppress the increase in haze and maintain hydrophilicity over a long period of time.

The present invention has been made in view of the above problems, and is a hydrophilic coating that can suppress the occurrence of cracks in a hydrophilic coating when installed outdoors for a long period of time, suppress an increase in haze, and maintain hydrophilicity. The present invention provides a transparent member having the following.

The transparent member according to the present invention is a transparent member having a porous layer on a resin base material, the porous layer having a network structure in which silica particles are bonded to each other with a binder, and the resin base material: The resin has a mixed layer in which the network structure has invaded the surface layer on the side where the porous layer is provided, the mixed layer has a thickness of 20 nm or more and 160 nm or less, and the resin in a cross section in the thickness direction of the mixed layer. It is characterized in that the film thickness variation in a 1 μm length range along the film surface on the surface of the base material is 15% or less.

Further, the imaging device according to the present invention includes an optical system and an image sensor that acquires an image via the optical system, in a space surrounded by the housing and the transparent member.

Further, the method for manufacturing a transparent member according to the present invention is a method for manufacturing a transparent member in which a layer containing silica is formed on a resin base material, the method comprising: forming a layer containing silica particles on the resin base material and a component to be a binder. and forming a mixed layer in which a network structure in which the silica particles are bonded to each other with a binder invades the porous layer and the resin base material by applying a dispersion containing the mixture and curing the dispersion, The film thickness of the mixed layer is 20 nm or more and 160 nm or less, and the film thickness variation in a 1 μm length range along the film surface of the cross section in a direction intersecting the film surface of the mixed layer is 15% or less. It is characterized by

According to the present invention, it is possible to provide a transparent member formed with a highly reliable hydrophilic film that can suppress an increase in haze and maintain hydrophilicity even when exposed to an outdoor environment for a long period of time.

FIG. 1 is a schematic diagram showing a cross section in the thickness direction of an embodiment of a transparent member according to the present invention. 1 is a schematic diagram showing an embodiment of an imaging device according to the present invention. 1 is a schematic diagram showing a configuration example of an imaging device according to the present invention. 1 is an observation image of a cross section of a transparent member prepared in Example 1 using a scanning transmission electron microscope.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments, and changes can be made as appropriate without departing from the spirit of the present invention.

≪Transparent member≫
FIG. 1 is a schematic diagram showing a cross section in the thickness direction (direction parallel to the normal to the surface of the base material) of an embodiment of the transparent member according to the present invention. In the figure, a transparent member 10 according to the present invention has a hydrophilic coating on a resin base material 16, which is composed of a porous layer 14 and a mixed layer 15 in which the porous layer penetrates into the resin base material 16. . In the present invention, "transparent" means a property of transmittance of visible light of 20% or more.

The porous layer 14 includes a plurality of silica particles (silicon oxide particles) 12 and a binder 11 interposed between the plurality of silica particles 12. The plurality of silica particles 12 are fixed to each other by the binder 11, and are porous due to voids 13 formed between the silica particles 12 and between the binders 11.

When a conventional hydrophilic film formed on a resin base material is installed in an outdoor environment, stress is applied to the hydrophilic film formed on the resin base material due to the following two phenomena, and cracks occur.
(1) The surface of the resin base material deteriorates due to oxidation due to sunlight and oxygen.
(2) The resin base material expands and contracts due to water absorption due to rain and temperature changes due to sunlight.

On the other hand, with the above configuration, the resin base material 16 is first covered with the mixed layer 15, which reduces the surface area of the resin base material 16 exposed to the surface. This prevents oxidative deterioration and also relieves stress caused by expansion and contraction of the resin base material 16. Furthermore, since the silica particles of the mixed layer 15 and the porous layer 14 have a network structure, stress associated with oxidative deterioration of the resin base material 16 is alleviated, and the occurrence of cracks in the resin base material 16 is suppressed. As a result, even when the transparent member according to the present invention is installed in an outdoor environment, it is possible to suppress the occurrence of cracks in the hydrophilic coating, suppress an increase in haze for a long period of time, and maintain hydrophilicity.

Each layer will be explained in detail below.
<Porous layer>
The porous layer 14 has a network structure in which silica particles 12 are bonded to each other by a binder 11 and includes voids 13 between the silica particles 12 and within the binder 11. In other words, the network structure is a structure formed by bonding silica particles to each other with a binder. The porosity of the porous layer 14 is preferably 40% or more and 55% or less. When the porosity of the porous layer 14 is 40% or more, by maintaining the internal stress of the film at an appropriate level, it is possible to suppress the occurrence of cracks in the film during outdoor exposure, suppress the increase in haze, and improve hydrophilicity. You can maintain your sexuality. Further, when the porosity of the porous layer 14 is 55% or less, the haze of the hydrophilic film can be reduced and transparency can be maintained. Furthermore, since the binder 11 and the silica particles 12 are hydrophilic, the porous layer 14 is hydrophilic, and the contact angle with water on the surface of the porous layer 14 is 30° or less. Further, the thickness of the porous layer 14 is preferably 100 nm or more and 800 nm or less. If the film thickness of the porous layer 14 is smaller than 100 nm, the network structure of the mixed layer 15 and the porous layer 14 will not sufficiently suppress the occurrence of cracks in the resin base material 16, and cracks will occur in the film. It may not be possible to suppress the increase in haze and maintain hydrophilicity. Furthermore, if the thickness of the porous layer 14 is greater than 800 nm, the internal stress of the hydrophilic coating will increase, causing cracks in the film, thereby suppressing the increase in haze and maintaining hydrophilicity. may not be possible.

Here, the porosity of the porous layer 14 is a value representing the volume ratio of voids included in the porous layer 14 to the porous layer 14. The porosity can be calculated using equation 1 using a spectroscopic ellipsometer from the refractive index of the porous layer, the refractive index of silica of 1.46, and the refractive index of air of 1.00.
(Formula 1) Porosity = 100 x (Refractive index of porous layer - 1.46) ÷ (1.00 - 1.46)

Furthermore, it is preferable that the surface of the porous layer 14, that is, the surface of the transparent member according to the present invention on which the porous layer 14 is provided, has an average surface roughness Ra of 2 nm or more and 10 nm or less. The average surface roughness Ra is calculated by the calculation method defined in JIS B 0601:2001, and when Ra is a small value, the porous layer 14 has a dense and uniform structure. Therefore, when Ra is 10 nm or less, even if the transparent member according to the present invention is installed outdoors for a long period of time, oxidative deterioration of the base material and cracking of the hydrophilic coating can be suppressed, which is preferable. On the other hand, in view of the relationship with the porosity, Ra is preferably 2 nm or more.

[Silica particles]
The average particle diameter of the silica particles 12 is preferably 10 nm or more and 60 nm or less. When the average particle diameter of the silica particles 12 is 10 nm or more, the voids 13 formed between the particles can be appropriately enlarged, a desired porosity can be achieved, and the internal stress of the film can be maintained appropriately. Therefore, generation of cracks in the film can be suppressed during outdoor exposure, an increase in haze can be suppressed, and hydrophilicity can be maintained. Further, when the average particle diameter of the silica particles 12 is 60 nm or less, the size of the voids 13 formed between the particles can be appropriately reduced, and the haze can be reduced without causing light scattering by the voids 13 or the silica particles 12. This is preferable because it can suppress the increase in .

Here, the average particle diameter of the silica particles 12 is the average Feret diameter. This average Feret diameter can be measured by image processing of an image observed using a transmission electron microscope. As the image processing method, commercially available image processing such as image Pro PLUS (manufactured by Media Cybernetics) can be used. In a predetermined image area, contrast adjustment may be performed as necessary, and the average Feret diameter of each particle can be measured using commercially available particle measurement software to determine the average value.

Although solid silica particles or hollow silica particles can be used as the silica particles 12, chain-shaped silica particles in which these particles are connected are particularly preferable. By using chain-shaped silica particles, the porosity can be increased without creating large voids. Chain-like silica particles may be mixed with solid silica particles or hollow silica particles. In the case of chain-shaped silica particles, it is preferable that the average particle diameter of individual particles connected to each other is 10 nm or more and 60 nm or less.

The silica particles 12 contain SiO ₂ as a main component, but may also contain metal oxides such as Al ₂ O ₃ , TiO ₂ , ZnO ₂ , and ZrO ₂ in the particles. However, if 30% or more of the silanol (Si-OH) groups on the surface of the silica particles 12 are modified with organic groups or composited with other metals, hydrophilicity is lost. The porous layer 14 made of such silica particles has low hydrophilicity and also has poor self-cleaning properties.

Therefore, in order to develop good hydrophilicity in the porous layer 14, it is preferable to use silica particles in which silanol (Si-OH) groups remain on 70% or more of the particle surface; It is more preferable to use silica particles in which silanol groups remain.

[binder]
The binder 11 can be selected as appropriate depending on the abrasion resistance and environmental reliability of the hydrophilic film and the adhesion strength with the silica particles 12, but it is preferable that the binder 11 has a high affinity with the silica particles 12 and has a high abrasion resistance of the porous layer. It is preferable to use a silica binder, which improves the Among silica (SiO ₂ ) binders, it is more preferable to use a hydrolyzed condensate of silicate, and even more preferable to use a hydrolyzed condensate of a tetrafunctional silicate.

The content of the binder 11 is preferably from 3% by mass to 20% by mass, more preferably from 10% by mass to 20% by mass, based on the entire mass of the porous layer 14. If the content of the binder 11 with respect to the entire mass of the porous layer 14 is less than 3% by mass, the force for fixing the silica particles 12 is weak, and the silica particles 12 may peel off. Moreover, when the content of the binder 11 in the porous layer 14 exceeds 20% by mass, the spaces between the silica particles 12 are filled with the binder, the porosity in the porous layer 14 decreases, and the internal stress of the hydrophilic coating increases. There is a tendency.

<Mixed layer>
The mixed layer 15 is a layer in which a resin base material 16 penetrates into the voids of a network structure formed by bonding silica particles to each other with a binder, and is provided on the side of the resin base material 16 where the porous layer 14 is provided. ing. The range from the top of the resin base material 16 that has entered the voids of the network structure formed by the binder and silica particles to the bottom of the network structure is the mixed layer 15. When installed in an outdoor environment, the resin base material 16 may be oxidized and deteriorated by sunlight and oxygen. However, since the surface area of the resin base material 16 that comes into contact with oxygen can be reduced by the mixed layer, oxidative deterioration of the resin base material 16 can be suppressed. Furthermore, since the mixed layer 15 and the porous layer 14 have a continuous network structure, the stress associated with oxidative deterioration of the resin base material 16 is alleviated and the occurrence of cracks is suppressed.

The thickness of the mixed layer 15 is preferably 20 nm or more and 160 nm or less. If the thickness of the mixed layer 15 is less than 20 nm, the resin base material 16 will not penetrate into the network structure sufficiently, and the stress caused by oxidative deterioration of the resin base material 16 will not be alleviated. It is not possible to suppress the occurrence of cracks. Furthermore, if the thickness of the mixed layer 15 is greater than 160 nm, scattering due to the resin base material 16 and silica particles 12 will occur, which will increase the haze, which is not preferable. Further, the thickness of the mixed layer is preferably larger than the average particle diameter of the silica particles. Since the thickness of the mixed layer is larger than the average particle diameter of the silica particles, the strength of the network structure of the mixed layer 15 can be increased, so that cracks can be suppressed more reliably. In addition, when chain-shaped silica particles are used, it is preferable that the thickness of the mixed layer is larger than the average particle diameter of individual particles connected to each other.

Further, the volume ratio of the network structure in the mixed layer 15 is preferably 20% or more and 80% or less, and more preferably 30% or more and 70% or less. When the volume ratio of the network structure in the mixed layer 15 is 20% or more, oxidative deterioration of the resin base material 16 during outdoor exposure can be sufficiently suppressed, and the occurrence of cracks can be suppressed. When the volume ratio of the network structure in the mixed layer 15 is 80% or less, stress during outdoor exposure can be alleviated and generation of cracks can be suppressed.

Further, the mixed layer 15 relieves stress caused by expansion and contraction of the resin base material 16 due to water absorption due to rain and temperature changes due to sunlight. The thickness of the mixed layer 15 has a thickness variation of 15% or less in an arbitrary length range of 1 μm along the surface of the resin base material 16 in the cross section in the thickness direction. If the film thickness variation of the mixed layer within the film surface is greater than 15%, the stress due to expansion and contraction of the resin base material will be concentrated in the part where the mixed layer film thickness is smaller than the surrounding area. Cracks occur in the material 16, and cracks occur in the hydrophilic coating. Therefore, it is not possible to suppress an increase in haze and maintain hydrophilicity.

The film thickness variation is the ratio of the height of the unevenness occurring at the interface between the resin base material 16 and the mixed layer 15 to the average film thickness of the mixed layer 15. The average thickness of the mixed layer 15 and the height of the unevenness occurring at the interface between the resin base material 16 and the mixed layer 15 are determined by cutting the transparent member of the present invention into a thin section and observing the cross section using a scanning transmission electron microscope or the like. Here, the height of the unevenness occurring at the interface between the resin base material 16 and the mixed layer 15 refers to the portion of the interface consisting only of the resin base material 16 that is closest to the mixed layer side and the portion of the mixed layer 15 that is closest to the resin base material 16 side at the interface. This is the absolute value of the height difference in the thickness direction with the part. When calculating the film thickness variation, it is preferable to binarize the obtained image using image processing software, as this makes it easier to distinguish between the base material and the mixed layer (silica particles or binder). As shown in FIG. 4, when an arbitrary length of 1 μm along the surface of the resin base material 16 in the cross section in the thickness direction is represented by the range of the solid line in the figure, the distance between the resin base material 16 and the mixed layer 15 is The height of the unevenness (film thickness variation) occurring at the interface corresponds to the ratio of the height of the unevenness to the average film thickness of the distance between the two white broken lines (the distance indicated by the white arrow).

<Resin base material 16>
As the material of the resin base material 16, resins such as transparent acrylic resin, polycarbonate, and polyester can be used. The shape of the resin base material 16 is not limited, and may be plate-like or film-like, and even if it is flat, it may have a curved, concave, or convex shape, such as a hemispherical shape. It may have a dome shape or the like. Note that the transmittance of the resin base material to visible light is preferably 50% or more.

<Manufacturing method>
Next, an example of the method for manufacturing a transparent member according to the present invention will be explained.
The method for manufacturing a transparent member according to the present invention includes a step of forming a porous layer 14 and a mixed layer 15 on a resin base material 16.

The process of forming the porous layer 14 and the mixed layer 15 includes a method of sequentially applying and drying a dispersion of silica particles 12 and a binder solution onto the resin base material 16, and a method of coating and drying a dispersion of silica particles 12 and a binder solution on the resin base material 16, or a method of coating and drying a dispersion of silica particles 12 and a binder solution, or a method of coating and drying a dispersion of silica particles 12 and a binder solution. A method of applying and drying a dispersion containing both onto the resin base material 16 can be used. A method in which a dispersion containing both the silica particles 12 and the components to become the binder 11 is applied is more preferable in that the composition inside the porous layer 14 becomes uniform.

The dispersion liquid of silica particles 12 is a liquid in which silica particles 12 are dispersed in a solvent, and the content of silica particles 12 is preferably 2% by mass or more and 10% by mass or less. A silane coupling agent or a surfactant may be added to the dispersion liquid of the silica particles 12 in order to improve the dispersibility of the silica particles 12. However, if these compounds react with many of the silanol groups on the surface of the silica particles 12, the bond between the silica particles 12 and the binder 11 will be weakened, and the abrasion resistance of the porous layer 14 will decrease, and the porous The hydrophilicity of the layer 14 may deteriorate. Therefore, the content of additives such as silane coupling agents and surfactants in the dispersion is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass of silica particles 12.

It is preferable to use a silica binder solution that has a strong binding force with the silica particles 12 as the binder solution. The silica binder solution is mainly composed of a silicate hydrolyzed condensate, which is produced by adding water, an acid, or a base to a silicate ester such as methyl silicate or ethyl silicate in a solvent, and then hydrolyzing and condensing it. A solution is preferred.

The type of acid or base to be used may be appropriately selected in consideration of solubility in the solvent and reactivity with the silicate ester. The acid used in the hydrolysis reaction is preferably hydrochloric acid or nitric acid, and the base is preferably ammonia or various amines. Silicate hydrolysis condensates can be prepared by neutralizing and condensing not only silicate esters but also silicates such as sodium silicate in water. Acids that can be used in the neutralization reaction include hydrochloric acid and nitric acid. When preparing the silica binder solution, it may be heated at a temperature of 80° C. or lower.

When using a silica binder as the binder 11, trifunctional silane alkoxide substituted with an organic group such as methyltriethoxysilane or ethyltriethoxysilane may be added to the silica binder solution for the purpose of improving solubility and coating properties. can. The amount of trifunctional silane alkoxide added is preferably 10 mol % or less of the total silane alkoxide contained in the silica binder solution. When the amount added exceeds 10 mol %, the organic groups inhibit hydrogen bonding between silanol groups within the binder, resulting in a decrease in wear resistance.

When using a dispersion containing both the silica particles 12 and the components to become the binder 11, the dispersion of the silica particles 12 and the binder solution described above may be prepared in advance and then mixed. Alternatively, a dispersion liquid may be prepared by adding a component to become the binder 11 to a dispersion liquid of silica particles 12 and causing the mixture to react. When using the latter method to obtain a dispersion containing silica particles 12 and a silica binder as a component to become binder 11, a silicate ester, water, and an acid catalyst are added to the dispersion of silica particles 12 and reacted. It is possible to prepare. A method in which a binder solution is prepared in advance and then mixed is preferred because it allows the reaction of the components that will become the binder 11 to be controlled and preparation can be made while checking the reaction state.

The amount of the component to become the binder 11 in the dispersion containing both the silica particles 12 and the component to become the binder 11 is preferably 3 parts by mass or more and 20 parts by mass or less, based on 100 parts by mass of the silica particles and the component to become the binder. , more preferably 10 parts by mass or more and 20 parts by mass or less.

The solvent that can be used for the dispersion liquid of the silica particles 12 and the silica binder solution needs to be able to dissolve or disperse them uniformly and form a film with a uniform thickness of the mixed layer 15. . Therefore, it is desirable to combine a solvent with relatively high solubility of the resin base material 16 and a solvent with relatively low solubility. Further, it is desirable that the boiling point of the solvent in which the resin base material 16 has a relatively high solubility is higher than the boiling point of the solvent in which the resin base material 16 has a relatively low solubility. By selecting the solvent in this manner, the silica particles are encouraged to be uniformly arranged in the early stage of the film formation process, and a porous network structure with highly uniform arrangement is formed. In the later stages of the film formation process, the proportion of the solvent with a high boiling point and relatively high solubility increases, and the resin base material 16 rapidly dissolves, so that the porous network formed at the beginning of the film formation process The structure penetrates into the resin substrate 16 and a uniform mixed layer 15 is formed.

Examples of solvents in which the resin base material 16 has relatively high solubility include ethers such as dimethoxyethane, diglyme, dioxane, diisopropyl ether, dibutyl ether, and cyclopentyl methyl ether; ethyl acetate, n-butyl acetate, and ethylene glycol monomethyl. Esters such as ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate; various aliphatic or esters such as n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane; Alicyclic hydrocarbons; various aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; various ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, 2-heptanone, and cyclohexanone; chloroform, Various chlorinated hydrocarbons, such as methylene chloride, carbon tetrachloride, and tetrachloroethane; aprotic, such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and ethylene carbonate. Examples include polar solvents. As the solvent in which the resin base material 16 has relatively high solubility, diglyme, dibutyl ether, propylene glycol monomethyl ether acetate, and 2-heptanone are preferably used.

Examples of solvents in which the resin base material 16 has relatively low solubility include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methylpropanol, 1-pentanol, -Pentanol, cyclopentanol, 2-methylbutanol, 3-methylbutanol, 1-hexanol, 2-hexanol, 3-hexanol, 4-methyl-2-pentanol, 2-methyl-1-pentanol, 2- Monohydric alcohols such as ethylbutanol, 2,4-dimethyl-3-pentanol, 3-ethylbutanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol; ethylene glycol, triethylene glycol, etc. Dihydric or higher alcohols; ether alcohols such as methoxyethanol, ethoxyethanol, propoxyethanol, isopropoxyethanol, butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, etc. Examples include: As the solvent in which the resin base material 16 has relatively low solubility, 2-propanol is preferably used.

In order to obtain the transparent member according to the present invention, it is necessary to use a solvent in which the solubility of the resin base material 16 is relatively high and a solvent in which the solubility of the resin base material 16 is relatively low from among these exemplified solvents. They should be selected and used so that there is a difference in boiling point. Further, considering the boiling point of the solvent, it is also possible to use a mixture of two or more solvents selected from among a solvent with relatively high solubility and a solvent with relatively low solubility.

When using a mixture of a solvent with relatively high solubility and a solvent with relatively low solubility, the proportion of the solvent with relatively high solubility should be 2% by mass or more and 30% by mass or less. It is preferably 10% by mass or more and 20% by mass or less. When the content is 2% by mass or more, a sufficient mixed layer can be formed, and when it is 30% by mass or less, the thickness of the mixed layer does not become too thick and the haze can be maintained well. .

Examples of methods for applying a dispersion of silica particles 12, a binder solution, or a dispersion in which they are mixed include a spin coating method, a blade coating method, a roll coating method, a slit coating method, a printing method, and a dip coating method. . When manufacturing a transparent member having a three-dimensionally complex shape such as a concave surface, a spin coating method is preferable from the viewpoint of uniformity of film thickness.

After applying a dispersion of silica particles 12 and a binder solution, or a dispersion of a mixture thereof, the amount of solvent remaining in the porous layer and the mixed layer can be suppressed to improve wear resistance. Therefore, it is preferable to form the porous layer and the mixed layer by providing a drying step and a curing step. The drying step and the curing step are steps for removing the solvent, promoting the reaction of the component to become the binder 11, or the reaction between the component to become the binder 11 and the silica particles 12. The temperature of the drying step and the curing step is preferably 20°C or more and 200°C or less, more preferably 60°C or more and 150°C or less. If the temperature in the drying step and curing step is less than 20° C., the solvent will remain and the abrasion resistance will decrease. Moreover, if the temperature of the drying step and the curing step exceeds 200° C., the hardening of the binder 11 proceeds too much, and as a result, cracks are likely to occur in the porous layer 14.
The amount of solvent remaining in the porous layer 14 is preferably 3.0 mg/cm ³ or less.

When applying a dispersion of silica particles 12 and a binder solution in sequence, the dispersion of silica particles 12 is applied and a firing process is performed once, and then the binder solution is applied and a drying process and a curing process are performed. Porous layers and mixed layers can also be formed.

In order to make the porous layer 14 a desired thickness, the above-described coating step, drying step, and curing step may be alternately repeated multiple times.

≪Imaging device≫
FIG. 2 is a schematic diagram showing an embodiment of the imaging device of the present invention, in which FIG. 2(a) is a fixed-point observation type surveillance camera, and FIG. 2(b) is a rotating type capable of pan/tilt/zoom driving. This is a surveillance camera. The imaging device shown in FIGS. 2(a) and 2(b) has a transparent member (protective cover) 3 according to the present invention that functions as a protective cover in device bodies 1 and 2, and Equipped with an optical system for acquiring data. Further, the transparent member 3 covers at least the optical systems of the device bodies 1 and 2 and protects them from dust and impact from the outside. Although the protective cover 3 in FIG. 2(a) has a planar box shape, and the protective cover 3 in FIG. 2(b) has a hemispherical dome shape, the shape of the protective cover 3 is not limited to these.

FIG. 3 shows an example of the configuration of an imaging device according to the present invention. The imaging device 30 has a space surrounded by a transparent member 10 including a porous layer 14, a mixed layer 15, and a resin base material 16, and a casing 36. In the space, an optical system 31, an image sensor 32, It includes a video engine 33, a compression output circuit 34, and an output section 35.

An image acquired through the transparent member 10 is guided to an image sensor 32 by an optical system (lens) 31, converted into an image analog signal (electrical signal) by the image sensor 32, and output. The video analog signal output from the image sensor 32 is converted into a video digital signal by the video engine 33, and the video digital signal output from the video engine 33 is compressed into a digital file by the compression output circuit 34. The video engine 33 may perform processing to adjust image quality such as brightness, contrast, color correction, and noise removal in the process of converting a video analog signal into a video digital signal. The signal output from the compression output circuit 34 is output from the output section 35 to an external device via wiring.

The transparent member 10 is installed so that the surface on which the porous layer 14 is provided faces the outside. Such a configuration protects against dust and impact from the outside, and also turns water droplets that adhere to the surface of the transparent member 10 due to changes in the external environment into a liquid film, thereby suppressing distortion of images acquired by the image sensor 32. be able to.

Furthermore, the imaging device 30 includes a pan/tilt controller for adjusting the angle of view, a controller for controlling imaging conditions, a storage device for storing acquired video data, a transfer means for externally transmitting data outputted from the output unit 35, etc. , an imaging system can be configured.

Hereinafter, a specific method for manufacturing the transparent member according to the present invention will be explained.
(Preparation of coating liquid)
First, the coating liquid used for manufacturing the transparent member according to the present invention will be explained.

(1) Preparation of silica binder solution 13.82 g of ethanol and an aqueous nitric acid solution (3% concentration) were added to 12.48 g of ethyl silicate, stirred at room temperature for 10 hours, and the silica binder solution (solid concentration 12.0% by mass) was added. was prepared.

(2-1) Preparation of silica particle coating liquid A 2-propanol (IPA) dispersion of chain silica particles (trade name: IPA-ST-UP, manufactured by Nissan Chemical Industries, Ltd., solid content concentration 15.5 mass) %) was diluted with 85.00 g of IPA (boiling point: 82.5°C) and 15.00 g of diglyme (boiling point: 162.0°C) as solvents, and then the silica binder solution 2 prepared in (1) was obtained. .60 g was added and stirred at room temperature for 10 minutes. Thereafter, the mixture was stirred at 50° C. for 1 hour to prepare silica particle coating liquid A. Particle size distribution measurement using a dynamic light scattering method (trade name: Zetasizer Nano ZS, manufactured by Malvern) revealed that silica particles with an average particle size of 15 nm were connected to an average circular equivalent diameter of 95 nm in silica particle coating liquid A. It was confirmed that chain silica particles were dispersed.

(2-2) Preparation of silica particle coating liquid B Silica particle coating was carried out in the same manner as silica particle coating liquid A, except that 85.00 g of IPA and 15.00 g of dibutyl ether (boiling point: 140.8°C) were used as solvents. Work solution B was prepared.

(2-3) Preparation of silica particle coating liquid C The procedure was the same as silica particle coating liquid A except that 85.00 g of IPA and 15.00 g of propylene glycol monomethyl ether acetate (boiling point: 140.0°C) were used as the solvent. Silica particle coating liquid C was prepared.

(2-4) Preparation of silica particle coating liquid D Silica particle Coating liquid D was prepared.

(2-5) Preparation of Silica Particle Coating Solution E Silica Particle Coating Solution E was prepared in the same manner as Silica Particle Coating Solution A except that 70.00 g of IPA and 30.00 g of diglyme were used as solvents.

(2-6) Preparation of Silica Particle Coating Solution F Silica Particle Coating Solution F was prepared in the same manner as Silica Particle Coating Solution A except that 100.00 g of IPA was used as the solvent.

(2-7) Preparation of silica particle coating liquid G Silica particle coating was performed in the same manner as silica particle coating liquid A except that 70.00 g of IPA and 30.00 g of tetrahydrofuran (boiling point: 66.0°C) were used as solvents. Solution G was prepared.

(2-8) Preparation of Silica Particle Coating Solution H Silica Particle Coating Solution H was prepared in the same manner as Silica Particle Coating Solution A except that 105.00 g of IPA and 30.00 g of diglyme were used as solvents.

(Example 1)
An appropriate amount of silica particle coating liquid A was dropped onto a polycarbonate base material (nd = 1.58, νd = 30.2) with a diameter (φ) of 50 mm and a thickness of 4 mm with a light transmittance of approximately 80%, and the coating was applied at 2000 rpm for 20 seconds. Spin coating was performed. Thereafter, it was heated in a hot air circulation oven at 90° C. for 15 minutes to produce a transparent member in which a porous layer and a mixed layer were formed. The average Feret diameter of the silica particles was 15 nm.

FIG. 4 is a cross-sectional observation image of the transparent member produced in Example 1. It can be seen that three layers are formed from the bottom of the observed image: a resin base material 16, a mixed layer 15 of resin base material and silica particles, and a porous layer 14. The film thickness variation of the mixed layer 15, which will be described later, was calculated using this cross-sectional observation image, and the film thickness variation was 8%.

(Example 2)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid B was used instead of silica particle coating liquid A.

(Example 3)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid C was used instead of silica particle coating liquid A.

(Example 4)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid D was used instead of silica particle coating liquid A.

(Example 5)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid E was used instead of silica particle coating liquid A.

(Example 6)
A transparent member prepared in the same manner as in Example 1 was further coated with silica particle coating liquid F. For coating, a series of steps of dropping an appropriate amount of silica particle coating solution F, performing spin coating at 2000 rpm for 20 seconds, and heating in a hot air circulation oven at 90° C. for 15 minutes was repeated twice to create a transparent member.

(Comparative example 1)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid F was used instead of silica particle coating liquid A.

(Comparative example 2)
A transparent member with a hydrophilic film prepared in the same manner as in Example 1 was further coated with silica particle coating liquid F. To coat, drop an appropriate amount of silica particle coating solution F, spin coat at 2000 rpm for 20 seconds, and repeat the series of steps of heating at 90°C for 15 minutes in a hot air circulation oven three times to create a transparent member with a hydrophilic coating. did.

(Comparative example 3)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid G was used instead of silica particle coating liquid A.

(Comparative example 4)
A transparent member was produced in the same manner as in Example 1 except that silica particle coating liquid H was used instead of silica particle coating liquid A.

(Evaluation method for transparent members)
Next, a method for evaluating transparent members produced in Examples and Comparative Examples will be described.
(1) Measurement of the film thickness of the porous layer and mixed layer Using a spectroscopic ellipsometer (product name: VASE, manufactured by JA Woollam Japan), the thickness of the porous layer and mixed layer was measured in the wavelength range of 380 nm to 800 nm. The film thickness was determined.

(2) Measurement of the porosity of the porous layer Using a spectroscopic ellipsometer (product name: VASE, manufactured by JA Woollam Japan), measurement was performed from a wavelength of 380 nm to 800 nm, and the refractive index of the porous layer was determined from the analysis. The porosity of the porous layer was calculated using Equation 1.

(3) Measurement of film thickness variation of mixed layer The film was cut out using a focused ion beam device (trade name: SMI3050, manufactured by SII Nanotechnology), and the film was thinned so that the cross section of the mixed layer in the film thickness direction could be observed. The cross-sectional state of the mixed layer in the film thickness direction was observed in bright field using a scanning transmission electron microscope (trade name: S-5500, manufactured by Hitachi High-Technologies) at a magnification of 100,000 times. Thereafter, the observed images were subjected to image processing. As an image processing method, commercially available image processing software such as image Pro PLUS (manufactured by Media Cybernetics) was used. In a predetermined image area, the film thickness of the mixed layer was calculated by appropriately adjusting the contrast if necessary, and the film thickness variation in a length range of 1 μm was calculated.

(4) Measurement of contact angle Using a fully automatic contact angle meter (product name: DM-701, manufactured by Kyowa Interface Science Co., Ltd.), measure the contact angle when a droplet of 2 μl of pure water is brought into contact at 23°C and 50% RH. It was measured.

(5) Haze measurement Haze was measured using a haze meter (trade name: NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

(6) Outdoor exposure test The transparent member was placed in a xenon weather meter (trade name: Super Xenon Weather Meter SX75, manufactured by Suga Test Instruments Co., Ltd.). The light irradiation intensity was set at 180 W/m ² , and one cycle of light irradiation and water spraying was 18 minutes, and only light irradiation was 1 hour and 42 minutes, making the test and evaluation for a total of 300 cycles for a total of 600 hours. The contact angle of the transparent member after the test was measured in the same manner as (4) Measurement of contact angle. This outdoor exposure test corresponds to 100 hours of actual outdoor exposure for 1 year.

(7) Evaluation If the contact angle is 30° or less, formation of water droplets on the surface of the transparent member can be sufficiently suppressed. Further, if the haze is 1 or less, a clear image can be obtained during photographing. Therefore, the initial value and the value after the outdoor exposure test are evaluated as good if the contact angle is 30° or less and the haze is 1 or less. If it is large, it is considered defective.

(8) Measurement of surface roughness Using SPM (trade name: L-trace & NanoNavi II, manufactured by SII Nano Technology Co., Ltd.), the surface shape in an area of 2 μm×2 μm was measured, and Ra was calculated therefrom.
Table 1 shows the measurement results and evaluation results for Examples 1 to 6 and Comparative Examples 1 to 4.

As shown in Table 1, it was confirmed that with the configuration of this example, the contact angle was 30° or less and the haze was 1 or less both at the initial value and after outdoor exposure, indicating that hydrophilicity and haze could be maintained. was confirmed. On the other hand, Comparative Example 1 which is outside the scope of the present invention because no mixed layer is provided, Comparative Example 2 where the thickness of the porous layer is thicker than the range specified by the present invention, and Comparative Example 2 where the thickness of the porous layer is outside the scope of the present invention. Comparative Example 4, which is thinner than the range specified by the invention, and Comparative Example 3, where the thickness variation of the mixed layer is larger than the range specified by the invention, maintains hydrophilicity after outdoor exposure and suppresses increase in haze. I couldn't do that.

The transparent member according to the present invention can be used not only for imaging devices such as flat covers and dome covers for outdoor cameras and surveillance cameras, but also for general applications such as window glass, mirrors, lenses, and transparent films, as well as for imaging systems and projection systems. It can be used for optical lenses, optical mirrors, optical filters, eyepieces, and optical components.

10 Transparent member 11 Binder 12 Silica particles 13 Voids 14 Porous layer 15 Mixed layer 16 Resin base material 1 Device body 2 Device body 3 Transparent member (protective cover)
30 Imaging device 31 Optical system (lens)
32 Image sensor 33 Video engine 34 Compression output circuit 35 Output section 36 Housing

Claims (16)

a resin layer made of resin;
a mixed layer comprising a plurality of silica particles, a binder for bonding the plurality of silica particles, and the resin, and disposed on the resin layer;
a porous layer comprising the plurality of silica particles and a binder for bonding the plurality of silica particles, a porous layer provided with voids and disposed on the mixed layer;
The thickness of the mixed layer is 20 nm or more and 160 nm or less,
The film thickness variation in a length range of 1 μm along the surface of the resin layer in the cross section in the thickness direction of the mixed layer is 15% or less,
A transparent member characterized in that the porous layer has a thickness of 100 nm or more and 800 nm or less. The transparent member according to claim 1, wherein the surface of the porous layer opposite to the side on which the mixed layer is provided has an average surface roughness Ra of 2 nm or more and 10 nm or less. The transparent member according to claim 1 or 2, wherein the thickness of the mixed layer is larger than the average Feret diameter of the silica particles. 4. The transparent member according to claim 1, wherein the silica particles have an average Feret diameter of 10 nm or more and 60 nm or less. The transparent member according to any one of claims 1 to 4, wherein the binder is a silica binder. The plurality of silica particles of the mixed layer are bonded to the plurality of silica particles of the porous layer via the binder, according to any one of claims 1 to 5. Transparent member. 7. The transparent member according to claim 1, wherein the resin layer has a transmittance of 50% or more to visible light. 8. The transparent member according to claim 7, wherein the resin material is one or more selected from the group consisting of acrylic resin, polycarbonate, and polyester. The transparent member according to any one of claims 1 to 8, wherein a contact angle with water on a surface of the porous layer opposite to the side on which the mixed layer is provided is 30° or less. An imaging device comprising an optical system and an image sensor that acquires an image via the optical system, in a space surrounded by a housing and the transparent member according to any one of claims 1 to 9. A method for manufacturing a transparent member in which a layer containing silica is formed on a resin layer made of resin, the method comprising:
A dispersion containing a plurality of silica particles and a component serving as a binder is applied onto a resin base material made of the resin, and the dispersion is cured to join the plurality of silica particles and the plurality of silica particles. a mixed layer having a binder and the resin, and a porous layer having voids and having a binder bonding the plurality of silica particles and the plurality of silica particles,
The thickness of the mixed layer is 20 nm or more and 160 nm or less,
The film thickness variation in a length range of 1 μm along the surface of the resin layer in the cross section in the thickness direction of the mixed layer is 15% or less,
The thickness of the porous layer is 100 nm or more and 800 nm or less,
A method for manufacturing a transparent member, characterized by: 12. The method for manufacturing a transparent member according to claim 11, wherein the average Feret diameter of the silica particles is smaller than the thickness of the mixed layer. The silica particles are chain silica particles,
13. The method for manufacturing a transparent member according to claim 11 or 12, wherein the average Feret diameter of each particle constituting the chain silica particles is smaller than the thickness of the mixed layer. 14. The dispersion liquid includes a solvent in which the resin has a relatively high solubility and a solvent in which the resin has a relatively low solubility. A method for manufacturing a transparent member. 15. The method of manufacturing a transparent member according to claim 14, wherein the boiling point of the solvent in which the resin has a relatively high solubility is higher than the boiling point of the solvent in which the resin has a relatively low solubility. the resin is polycarbonate,
The solvent in which the resin has relatively high solubility is selected from diglyme, dibutyl ether, propylene glycol monomethyl ether acetate, and 2-heptanone,
16. The method for manufacturing a transparent member according to claim 14, wherein the solvent in which the resin has relatively low solubility is 2-propanol.

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