JP7638672B2 - Optical member, optical device, imaging device, and method for manufacturing optical member - Google Patents

Description

The present invention relates to an optical member having excellent anti-fogging properties and optical performance, and a method for manufacturing the optical member.

When the surface of a transparent substrate such as glass or plastic falls below the dew point temperature, minute water droplets adhere to the substrate surface, scattering transmitted light and impairing transparency, resulting in a so-called "cloudy" state. Therefore, transparent components in particular are often required to have anti-fog properties in addition to optical properties such as anti-reflection.

Patent Document 1 discloses an optical component that provides anti-reflection and anti-fogging properties by providing a porous structure on a substrate in which metal oxide particles are bound with a binder and by absorbing moisture from the air into the porous structure.

JP 2013-105846 A

When moisture is adsorbed into the voids of the porous structure, the air in the voids is replaced with water, causing an increase in the refractive index. Therefore, when the component of Patent Document 1 is exposed to an environment where anti-fogging performance is required and the porous structure adsorbs moisture, the refractive index increases. This causes a change from the optically designed state in a non-moisture state, resulting in a significant decrease in anti-reflection performance.

The present invention is devised to solve the above-mentioned problems, and has an object to provide a component and a method for manufacturing the component, in which moisture absorption by a porous layer is suppressed.

The member according to the present invention is a member having a porous layer on a substrate, the porous layer having, in order from the substrate side, a first region, a second region, and a third region, the first region containing first particles, the third region containing second particles having a shape different from that of the first particles, and the second region containing the first particles and the second particles, and the average porosity of the second region is larger than the average porosity of the first region and smaller than the average porosity of the third region.

According to the present invention, it is possible to realize a member and a method for manufacturing a member in which moisture absorption by a porous layer is suppressed.

1A is a schematic diagram showing one embodiment of an optical member according to the present invention, and FIG. 1B is an enlarged view of a porous layer. FIG. 1A shows a member in which only a porous layer is formed on a substrate, and FIG. 1B shows a member in which a vapor-deposited film layer is formed between the porous layer and the substrate. FIG. 1 is a schematic diagram of an embodiment of an optical member according to the present invention, which has a surface antireflection layer. FIG. 1 is a schematic diagram of an embodiment of an optical member according to the present invention, the member having an underlying anti-reflection layer. FIG. 1 is a schematic diagram of an embodiment of an optical member according to the present invention, which has a hydrophilic polymer layer. 1 is a schematic diagram showing an example of the configuration of an imaging device according to the present invention; FIG. 1 is a diagram showing reflectance characteristics before and after water absorption in Example 1. FIG. 13 is a diagram showing reflectance characteristics before and after water absorption in Comparative Example 1.

The following describes embodiments of the present invention, but unless otherwise specified, the present invention is not limited to these embodiments.

[Optical components]
FIG. 1(a) is a schematic diagram showing one embodiment of a member of the present invention.

The member 100 of the present invention has a porous layer 20 including, in order from the substrate side, a first region 21, a second region 22, and a third region 23 on a substrate 10, and has anti-fogging properties and anti-reflection layer properties. In the figure, a configuration having a porous layer 20 on one side of the substrate 10 is shown, but the porous layer 20 may be provided on both sides of the substrate 10 depending on the application.

By appropriately selecting the substrate 10, the member 100 of the present invention can be used for a wide range of applications, such as window glass, mirrors, lenses, and transparent films. It is particularly suitable for applications such as optical lenses for imaging and projection systems, optical mirrors, optical filters, eyepieces, flat covers and dome covers for outdoor cameras and surveillance cameras, face shields, and mouth shields.

(Substrate)
The material of the substrate 10 may be glass, resin, etc. The shape of the substrate 10 is not limited, and may be flat, curved, concave, convex, or film-like.

For the glass, inorganic glass containing zirconium oxide, titanium oxide, tantalum oxide, niobium oxide, hafnium oxide, lanthanum oxide, gadolinium oxide, silicon oxide, calcium oxide, barium oxide, sodium oxide, potassium oxide, boron oxide, aluminum oxide, etc. can be used. The glass substrate can be shaped by grinding and polishing, molding, float forming, etc.

Resins that can be used include polyethylene terephthalate, polyethylene naphthalate, triacetyl cellulose, acrylic resin, polycarbonate, cycloolefin polymer, polyvinyl alcohol, etc.

In order to improve the strength and flatness of the substrate 10 and the adhesion of the film in contact with the substrate 10, the surface of the substrate 10 may be cleaned or polished, or a functional layer such as an adhesive layer or a hard coat layer may be provided.

(Porous Layer)
Fig. 1(b) shows an enlarged view of the porous layer 20. The first region includes first particles 24, the third region includes second particles 25 that are different in shape from the first particles, and the second region includes both the first particles 24 and the second particles 25. "Different shapes" here also includes similar shapes that simply differ in size. Fig. 1(b) shows a case where the first particles 24 are spherical particles and the second particles 25 are chain-like particles.

Gaps are formed between the particles contained in the porous layer 20, and they are three-dimensionally connected to each other and to the outside air. With this porous structure, when the humidity of the external environment of the component increases, the moisture contained in the air that has infiltrated into the voids in the porous layer 20 is condensed and adsorbed, thereby exhibiting anti-fogging properties. In addition, because the voids in the porous layer 20 are connected to each other, it is possible to adsorb moisture by utilizing all of the voids in the layer, thereby achieving high anti-fogging performance.

In the porous layer 20 of the member according to the present invention, the average porosity of the second region 22 is greater than the average porosity of the first region 21 and less than the average porosity of the third region 23. Within the porous layer 20, the third region 23 has the greatest average porosity and is primarily responsible for adsorbing moisture. Therefore, if anti-fogging performance is the only requirement for the porous layer 20, it is sufficient to have only the third region, but if anti-reflection performance is also required in addition to anti-fogging performance, the third region alone is insufficient. The reason for this is explained below.

2(a), consider the case where a porous layer 220 with a large porosity for anti-fogging purposes is formed directly on a substrate 10. The refractive index of the substrate 10 made of glass or resin is about 1.5, whereas the refractive index of the porous layer 220 provided for anti-fogging purposes is about 1.2 to 1.3. When the difference in refractive index is large in this way, light reflection _R1 occurs at the interface between the substrate 10 and the porous layer 220.

In order to reduce the light reflection occurring at the interface between the substrate 10 and the porous layer 220, a configuration shown in FIG. 2(b) is considered in which a layer 221 having a refractive index intermediate between the refractive index of the porous layer 220 and the refractive index of the substrate 10 is provided between the porous layer 220 and the substrate 10. The refractive index difference between the porous layer 220 and the layer 221 is set to be approximately the same as the refractive index difference between the substrate 10 and the porous layer 220, and the film thickness of the layer 221 is set to an integer multiple of λ/4 of the wavelength λ to be reduced. With this configuration, it is possible to reduce the reflected light by interference between the reflected light _R1 at the interface between the layer 221 and the substrate 10 and the reflected light _R2 at the interface between the porous layer 220 and the layer 221.

However, the configuration of Fig. 2(b) has the following problem. When the optical member is exposed to a high humidity environment and the porous layer 220 absorbs moisture (moisture), the air in the pores is replaced with water, and the refractive index of the porous layer 220 increases. When the layer 221 is a layer with a low porosity such as a vapor deposition film, the refractive index of the layer 221 hardly changes even if it absorbs moisture, so the refractive index difference between the porous layer 220 and the layer 221 becomes smaller than the refractive index difference between the porous layer 220 and the substrate _10. Then, the balance of the intensities of the reflected light _R1 and the reflected light R2 is lost, and the reflected light cannot be sufficiently reduced due to interference.

Therefore, it was found that if layer 221 is made into porous layer 221' whose porosity is adjusted to be intermediate between that of porous layer 220 and that of substrate 10, and porous layer 221' is also made to absorb moisture, in an attempt to reduce the difference in refractive index caused by moisture absorption, a new problem would arise.

When the porous layer 220 is formed on the porous layer 221' after it is formed, a dense region with a small porosity is formed at the interface between the porous layer 221' and the porous layer 220, blocking the movement of moisture. Therefore, the moisture adsorbed by the porous layer 220 cannot move to the porous layer 221' and remains within the porous layer 220. If only the refractive index of the porous layer 220 that adsorbs moisture increases and the refractive index of the porous layer 221' does not change, the balance of the intensity of the reflected light at each interface will be lost for the same reason as when the layer 221' is a vapor deposition film, and the reflected light will not be sufficiently reduced.

The dense region formed at the interface between the porous layer 221' and the porous layer 220 is believed to be due to the particles densely agglomerating at the surface of the coating liquid where drying first begins when the coating liquid dries to form the porous layer 221'. Therefore, in the present invention, as shown in FIG. 1(b), a second region 22 containing first particles 24 and second particles 25 is provided between the first region 21 corresponding to the porous layer 221' and the third region 23 corresponding to the porous layer 220.

The second region can be formed by applying a coating liquid for forming the first region 21 to the substrate, and applying a coating liquid for forming the third region 23 before the coating liquid dries. The second region 22 contains both the first particles 24 and the second particles 25, and therefore has a porosity intermediate between the porosity of the first region 21 and the porosity of the third region, and the formation of a dense region can be suppressed. The second region may be formed by applying a coating liquid for forming the first region 21 to the substrate, applying a coating liquid containing the first particles and the second particles before the coating liquid dries, and applying a coating liquid for forming the third region 23 before the coating liquid dries.

If there is no dense region between the first region 21 and the third region 23 that prevents the movement of moisture, the moisture adsorbed in the third region 23 will move to the first region 21 via the second region 22. The refractive index of the first region 21 and the second region 22 also increases due to moisture adsorption, just like the third region 23. As a result, even when the porous layer 20 adsorbs moisture, the refractive index difference between the first region 21 and the third region 23 and the refractive index difference between the third region 23 and the substrate 10 become approximately the same, and the intensity of the light reflected at each interface also becomes approximately the same, making it possible to maintain anti-reflection performance.

From the viewpoint of anti-fogging and anti-reflection, the porosity of the first region is preferably 10% or more and 30% or less, and the porosity of the third region is preferably 40% or more and 60% or less. Here, the porosity refers to the ratio of the combined area of the voids contained in any region in the cross section of the porous layer.

The porosity can be calculated by the following method. First, the porous layer 20 is sliced in the film thickness direction at any position, and an observation image is obtained using a scanning transmission electron microscope (STEM). The acquired image is processed using Image Pro PLUS (manufactured by Media Cybernetics, Inc.) or the like, and the void and non-void parts are binarized to calculate the combined area of the voids in each region. Then, the ratio of the area occupied by the voids in each region of the porous layer is calculated to obtain the porosity. It is preferable to calculate the porosity for a region of 150 nm x 150 nm or more including each region in the cross section of the porous layer 20.

Figure 1 (b) shows a case where the first particles 24 are spherical particles and the second particles 25 are chain-like particles, but this is not limited as long as the average porosity of the third region can be made larger than the average porosity of the first region. For example, the first particles 24 and the second particles 25 may both be spherical particles, and the particle diameter of the second particles 25 may be larger than that of the first particles 24. It is preferable to select a shape and particle diameter for the first particles 24 that results in fewer voids being formed between the particles than the second particles 25.

The first particles 24 and the second particles 25 can be selected from a variety of shapes, such as spherical, chain-like, disk-like, elliptical, rod-like, needle-like, and angular, and can be used alone or in combination. Spherical or chain-like shapes are particularly preferred because they have excellent film-forming properties and can increase the porosity while providing sufficient film hardness. In addition, multiple types of particles with different shapes may be mixed and used.

Chain particles are an aggregate of multiple particles that are linked together in a chain (also called a rosary shape) in a straight or curved manner. The shape of the particles that form the chain particles may be such that the individual particles can be clearly observed, or they may be fused together and lose their shape, and the chain-like structure is maintained even when they become a film. Therefore, the gaps between the particles can be made larger than when particles of other shapes are used, and a porous layer with a large pore volume can be formed.

When spherical, discoidal, or elliptical particles are used for the first particles 24 or the second particles 25, the average particle diameter is preferably 5 nm or more and 100 nm or less. If the average particle diameter is 5 nm or more, the compressive stress during film formation can be released, and cracks tend not to occur easily. If the average particle diameter is 100 nm or less, light scattering due to the particle size is unlikely to occur, and a highly transparent film is likely to be obtained. A more preferable average particle diameter is 10 nm or more and 60 nm or less.

When chain-, rod-, or needle-shaped particles are used for the first particles 24 or the second particles 25, the average short diameter is preferably 5 nm or more and 40 nm or less, and more preferably 8 nm or more and 30 nm or less. If the average short diameter is 5 nm or more and 40 nm or less, reliability deterioration and scattering due to the incorporation of moisture and chemical substances in the atmosphere are unlikely to occur. The ratio of long diameter/short diameter is preferably 3 or more and 12 or less, and more preferably 4 or more and 10 or less. If the ratio of long diameter/short diameter is within this range, it is easy to increase the pore volume, and at the same time, it is easy to suppress light scattering and obtain high transparency.

Here, the average particle size of the particles is the average Feret's diameter. This average Feret's diameter can be measured by image processing of images observed under a transmission electron microscope. As an image processing method, a commercially available image processing program such as Image Pro PLUS (manufactured by Media Cybernetics) can be used. In a specified image area, the contrast is appropriately adjusted if necessary, the average Feret's diameter of each particle is measured by particle measurement, and the average value is calculated.

The first particles 24 and the second particles 25 may each be particles of a single metal oxide mainly composed of silicon oxide or zirconium oxide, or some of the elements may be replaced with other elements such as Al, Ti, Zn, Zr, or B, or organic groups may be bonded to them. Particles mainly composed of silicon oxide are particularly preferred because they reduce the refractive index of the porous layer 20 and have excellent chemical stability.

In order to increase the strength (scratch resistance) of the porous layer 20, it is advisable to bond the particles together. Methods for bonding the particles together include a method of physically bonding the particles using a binder, and a method of chemically bonding the particles together by treating the surfaces of the particles. As the binder, either an organic binder or an inorganic binder can be used, but a chemically stable inorganic binder is preferred, and a silicon oxide compound is particularly preferred. A suitable example of a silicon oxide compound is a silicon oxide oligomer obtained by hydrolyzing and condensing a silicate ester.

The average pore size of the pores contained in the porous layer 20 is preferably 3 nm or more and 50 nm or less, as obtained by measuring the pore distribution by nitrogen gas adsorption. If the average pore size is 3 nm or more, air and moisture can move smoothly within the porous layer 20, making it possible to achieve sufficient anti-fogging performance. If the average pore size is 50 nm or less, there are few pores with a pore size exceeding 100 nm that cause light scattering, making it possible to achieve high transparency. A more preferred pore size is 5 nm or more and 20 nm or less.

The amount of voids contained in the porous layer 20 can be determined as pore volume by nitrogen gas adsorption. The pore volume is preferably 0.1 cm3/g or more and 1.0 cm3/g or less. If the pore volume is 0.1 cm3/g or more, the porous layer 20 can retain a sufficient amount of water to obtain anti-fogging properties. If the pore volume is 1.0 cm3/g or less, sufficient scratch resistance can be obtained without reducing the hardness of the skeleton. A more preferable pore volume is 0.3 cm3/g or more and 0.6 cm3/g or less.

The third region 23 of the porous layer 20, which is exposed to the external environment, is mainly responsible for absorbing moisture, so it is desirable for it to have voids capable of absorbing the amount of moisture required for the application. Therefore, it is advisable to set the thickness of the third region 23 according to the required anti-fogging performance. The thicker the third region is, the higher the anti-fogging performance will be, but if the porous layer 30 is made of an inorganic material, if the film thickness is too thick, cracks will occur due to stress, so a thickness of 0.2 μm or more and 2 μm or less is preferable. More preferably, it is 0.2 μm or more and 1.5 μm or less.

The thickness of each of the first region 21 and the second region 22 may be determined according to the optical design. The first region 21 may have a thickness that is an integer multiple of λ/4 of the wavelength λ to be reduced, but is preferably 50 nm or more and 150 nm or less. Within this range, the reflection of the wavelength λ of visible light can be reduced under interference conditions.

The physical thickness of each region can be measured by slicing the laminated film on the optical component using an electron beam processing device to expose its cross section, and then measuring the image obtained using a scanning transmission electron microscope (STEM).

(Surface Antireflection Layer)
In order to further enhance the anti-reflection effect of the member, it is also preferable to provide a front-surface anti-reflection layer 30 on the porous layer 20 as shown in FIG. 3 to reduce reflection occurring at the interface between air and the porous layer 20 .

The surface antireflection layer 30 has antireflection performance that suppresses reflection at the light input/output interface of the component, and moisture permeability that allows moisture to move between the outside and the porous layer 20. The surface antireflection layer 30 is a laminate of multiple layers with different refractive indices, and high-, medium-, and low-refractive index layers are appropriately combined according to the optical design. In order to reduce the difference in refractive index between the surface antireflection layer 30 and air and suppress reflection, a low-refractive index layer is provided on the outermost surface of the surface antireflection layer 30. The surface antireflection layer 30 is preferably formed by a vapor deposition method.

In the present invention, a layer having a refractive index of 1.8 or more is called a high refractive index layer, a layer having a refractive index of 1.4 or more and less than 1.8 is called a medium refractive index layer, and a layer having a refractive index of less than 1.4 is called a low refractive index layer. In the present invention, "transparent" refers to a state in which the transmittance of visible light is 70% or more, and the refractive index is represented by the value (n _d ) at the sodium d line (wavelength 589.3 nm).

The low refractive index layer can be a film containing an inorganic material such as silicon oxide (SiO ₂ , n _d =1.46), magnesium fluoride (MgF ₂ , n _d =1.38), or calcium fluoride (CaF ₂ , n _d =1.43).

For the medium refractive index layer, a film containing an inorganic material such as aluminum oxide (Al ₂ O ₃ , n _d =1.77), silicon oxide, or calcium fluoride can be used.

Examples of the high refractive index layer include films containing inorganic materials such as zirconium oxide (ZrO ₂ , n _d =2.13), titanium oxide (TiO ₂ , n _d =2.52 to 2.72), tantalum oxide (Ta _{2 O 5} , n _d =2.17), niobium oxide (Nb 2 O ₅ , n _d =2.32), hafnium oxide ( _{Hf 2} O 5 , n _d =1.91), etc. The high refractive index layer may contain two types selected from these metal oxides, or may be mixed with another metal oxide to adjust the refractive index.

The thickness of each layer in the anti-reflection layer 30 is preferably 10 nm or more and 200 nm or less. By setting the thickness of each layer within this range, it is possible to reduce the reflection of visible light over a wide wavelength range. In order to suppress the reflectance over a wide wavelength range, the number of layers is preferably 2 or more, and more preferably 3 or more.

The moisture permeability of the surface antireflection layer 30 allows the movement of moisture between the outside and the porous layer 20, and the moisture can be retained in the porous layer 20 or released into the outside air depending on the humidity, thereby repeatedly exerting antifogging properties. In order to give the surface antireflection layer 30 moisture permeability, it is preferable to form each layer so that it contains pores. A layer having pores within the film can be formed by appropriately adjusting the deposition conditions, such as the introduction pressure of the film-forming gas during deposition, the temperature of the substrate, and the angle of the deposition material flying to the base material. Among these, non-heated deposition and oblique deposition, in which deposition is performed without heating, are preferable.

The refractive index of a film is determined by the composition and density of the film. For example, the refractive index n _d of magnesium fluoride (MgF ₂ ) in the true density state is 1.38, but if there are 30% voids in the film, n _d is reduced to 1.27. This is because the refractive index of the film as a whole decreases due to the presence of air with n _d = 1.0 in the voids in the film. In this way, in the case of layers made of the same composition, the denser the film, the higher the refractive index, and the lower the density of the film, the lower the refractive index. And, by making each layer constituting the anti-reflection layer a low-density film containing voids, it is possible to make the film easy to transmit moisture.

To prevent the component from fogging, the relative humidity near the surface of the component must be kept below 100%. Since the amount of moisture that the porous layer 20 can hold is limited, it is desirable for the porous layer 20 to start absorbing moisture at a relative humidity as close to 100% as possible.

Moisture near the surface of the member passes through the surface anti-reflection layer 30 and is adsorbed by the porous layer 20. For example, if the pores of the surface anti-reflection layer 30 are made smaller than those of the porous layer 20, a higher pressure is required for the moisture to move through the surface anti-reflection layer 30 than when moving through the porous layer 20. In other words, in order for water to diffuse through the surface anti-reflection layer 30 into the porous layer 20, the relative pressure (relative humidity) of the water must be higher than that of the porous layer 20 alone. In this way, by laminating the surface anti-reflection layer 30, which has smaller pores than the porous layer 20, on top of the porous layer 20, water adsorption begins at a higher relative humidity than the porous layer 20 alone, and the anti-fogging properties can be further improved.

If the adsorption of moisture into pores follows the Kelvin law, the humidity at the time when moisture condenses within the porous layer and adsorption begins will move to the higher humidity side as the pores become larger. Since the pores in the front-surface antireflection layer 30 are sufficiently smaller than the pores in the porous layer 20, the front-surface antireflection layer 30 will begin to adsorb moisture even in a low-humidity environment where adsorption does not begin in the porous layer 20. For example, if the contact angle of the front-surface antireflection layer 30 with water is 10 degrees and the pore diameter is 3 nm in diameter, it is expected that moisture adsorption will begin at a relative humidity of 50%.

In this way, the front-surface antireflection layer 30 begins to adsorb moisture in a lower humidity environment than the porous layer 20, and as the humidity increases, the moisture adsorbed in the front-surface antireflection layer 30 moves to the porous layer 20. As a result, the optical member according to the present invention can exhibit antifogging performance over a wide humidity range.

The surface anti-reflection layer 30 of the present invention can only retain a small amount of moisture, so even if it absorbs moisture, the refractive index does not change significantly. Therefore, it is possible to exhibit anti-reflection performance even in a high humidity environment.

(Base Anti-Reflection Layer)
In order to further enhance the antireflection effect, it is also preferable to provide an underlying antireflection layer 40 between the porous layer 20 and the substrate 10 as shown in FIG. 4, thereby reducing the reflection occurring at the interface between the porous layer 20 and the substrate 10.

The base anti-reflection layer 40 is preferably a single film having a refractive index between the porous layer 20 and the substrate 10, or a laminated body combining multiple layers having different refractive indices, such as a high refractive index layer, a medium refractive index layer, and a low refractive index layer. By utilizing interference within the base anti-reflection layer 40, it is possible to reduce reflection not only at wavelength λ but also over a wider wavelength range. The high refractive index layer, the medium refractive index layer, and the low refractive index layer can each be made of the films exemplified for the surface anti-reflection layer. The base anti-reflection layer 40 can be formed by a vacuum film-forming method such as deposition or sputtering, or a wet film-forming method using a sol-gel liquid or a particle dispersion.

A configuration including a top anti-reflective layer 30 in addition to a base anti-reflective layer 40 is also preferable because it enhances the anti-reflective effect.

(Method of manufacturing components)
A method for manufacturing the member shown in FIG. 4 will now be described.

The method for manufacturing the component 100 of the present invention includes a step of forming a porous layer 20 on the substrate 10.

A wet film formation method is used in the process of forming the porous layer 20. When forming the porous layer 20 by a wet method, it is possible to form the layer by forming a coating film on a substrate using a coating liquid containing a metal oxide precursor or metal oxide particles synthesized by a sol-gel method or the like, and drying the coating liquid at 15°C to 200°C. The coating liquid is not limited to a coating liquid containing a metal oxide precursor or metal oxide particles, and a coating liquid containing polymer particles may also be used.

The solvent that can be used in the coating liquid for forming the porous layer 20 may be any solvent in which the raw materials dissolve uniformly and the reactants do not precipitate. For example, water can be used. In addition, monohydric alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methylpropanol, 1-pentanol, 2-pentanol, cyclopentanol, 2-methylbutanol, 3-methylbutanol, 1-hexanol, 2-hexanol, 3-hexanol, 4-methyl-2-pentanol, 2-methyl-1-pentanol, 2-ethylbutanol, 2,4-dimethyl-3-pentanol, 3-ethylbutanol, 1-heptanol, 2-heptanol, 1-octanol, and 2-octanol can be used. Dihydric or higher alcohols such as ethylene glycol and triethylene glycol can also be used. In addition, ether alcohols such as methoxyethanol, ethoxyethanol, propoxyethanol, isopropoxyethanol, butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, and 1-propoxy-2-propanol, and ethers such as dimethoxyethane, diglyme, tetrahydrofuran, dioxane, diisopropyl ether, dibutyl ether, and cyclopentyl methyl ether can be used. In addition, esters such as ethyl formate, ethyl acetate, n-butyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and propylene glycol monomethyl ether acetate can be used. Various ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone can be used. In addition, aprotic polar solvents such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and ethylene carbonate can be used. Two or more selected solvents from these can also be mixed and used.

Additives can be added to the coating liquid used to form the porous layer 20 for the purposes of improving the wettability between the coating liquid and the coating surface, increasing the uniformity of the layer thickness, and improving the adhesion between the porous layer 20 and the coating surface. Examples of additives include surfactants, leveling agents, adhesion promoters, acid catalysts, etc., and the amount added is preferably 2 parts by weight or less based on the solid components forming the porous layer 20.

Methods for forming the porous layer 20 using a coating liquid containing a metal oxide precursor or metal oxide particles include spin coating, spraying, blade coating, roll coating, slit coating, printing, and dip coating. When manufacturing a component having a three-dimensional complex shape such as a concave surface, the spin coating and spraying methods are preferred from the viewpoint of uniformity of film thickness.

The first region 21, the second region 22, and the third region 23 can be formed by applying a coating liquid containing the first particles 24 to form a coating film, and then applying a coating liquid containing the second particles 25 before the surface of the coating film dries. The time from applying the coating liquid containing the first particles 24 to form a coating film to applying the coating liquid containing the second particles 25 depends on the type and temperature of the solvent, the thickness of the second region, etc., but is preferably within 2 minutes, and more preferably within 1 minute.

The thickness and porosity of the first region 21 and the third region 23 can be controlled by controlling the individual component content, viscosity, and coating conditions of the coating liquid forming each region. The thickness and porosity of the second region 22 can be controlled by the drying conditions after application of the coating liquid containing the first particles 24. For example, if the drying time is short, the second region 22 will be thicker, and if the drying time is long, the second region 22 will be thinner.

In addition, a process of applying a coating liquid containing the first particles and the second particles may be added between the application of the coating liquid for forming the first region 21 and the application of the coating liquid for forming the third region 23 to form the second region 22. The coating liquid containing the first particles and the second particles and the coating liquid for forming the third region 23 are applied before the surface of the film made of the previously applied coating liquid dries. In this case, the thickness of the second region can be adjusted by the thickness of the coating film of the coating liquid containing the first particles 24 and the second particles 25.

After the coating liquid containing the first particles 24 and the coating liquid containing the second particles 25 are applied onto the substrate 10, drying and/or curing are performed. The drying and curing are performed to remove the solvent and to promote the reaction of the binder itself or the reaction between the binder and the particles. From the viewpoint of suppressing the influence of residual solvent and the occurrence of cracks in the layer, the drying and/or curing temperature is preferably 15°C or higher and 200°C or lower, and more preferably 60°C or higher and 150°C or lower. The drying and/or curing time is preferably 5 minutes or higher and 24 hours or lower, and more preferably 15 minutes or higher and 5 hours or lower.

As mentioned above, it is preferable that silicon oxide particles are dispersed in the coating liquid used to form the porous layer 20, because it is easy to manufacture and has relatively high stability. Below, a detailed explanation is given of the case where the coating liquid for forming the porous layer 20 is formed using a liquid in which silicon oxide particles are dispersed. Below, both the coating liquid containing the first particles 24 and the coating liquid containing the second particles 25 are explained.

The coating liquid used to form the porous layer 20 can be prepared by mixing a liquid in which silicon oxide particles are dispersed, a binder solution containing a binder component, a solvent, etc.

The liquid in which silicon oxide particles are dispersed can be prepared by adding water or a solvent to a dispersion of spherical or chain-shaped silicon oxide particles prepared by a wet method such as hydrothermal synthesis to dilute it. Alternatively, it can be prepared by replacing the solvent of a dispersion of silicon oxide particles prepared by a similar wet method with a desired solvent by distillation or ultrafiltration, or by dispersing silicon oxide particles synthesized by a dry method such as fumed silica in water or a solvent by ultrasonic waves or a bead mill. When chain-shaped silicon oxide particles are used, particles of shapes other than chain-shaped, such as perfect circles, ellipses, disks, rods, needles, and squares, may be appropriately mixed and used. The ratio of particles of shapes other than chain-shaped to the total particles can be appropriately determined taking into account the refractive index of the substrate and the film to be laminated.

A silicon oxide compound is preferably used as a binder to bind silicon oxide particles together. A suitable example of a silicon oxide compound is a silicon oxide oligomer obtained by hydrolysis and condensation of a silicate ester.

From the viewpoint of scratch resistance and anti-fogging properties, the amount of silicon oxide compound added to the coating liquid is preferably 1% by mass or more and 30% by mass or less, and more preferably 4% by mass or more and 20% by mass or less, relative to the silicon oxide particles.

There are several possible methods for adding silicon oxide oligomers to a silicon oxide particle dispersion. For example, a silicon oxide oligomer solution prepared in advance in water or a solvent can be mixed with the silicon oxide particle dispersion, or the raw material for the silicon oxide oligomer can be mixed with the silicon oxide particle dispersion and then converted into the silicon oxide oligomer.

Silicon oxide oligomers can be prepared by adding water, an acid, or a base to a silicate ester such as methyl silicate or ethyl silicate in a solvent or dispersion to cause hydrolysis and condensation. Examples of acids that can be added to the silicate ester include hydrochloric acid, nitric acid, methanesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, phosphoric acid, and p-toluenesulfonic acid. The base can be selected from ammonia or various amines, taking into consideration the solubility in the solvent and the reactivity of the silicate ester. When preparing the binder solution, it is also possible to heat it to a temperature of 80°C or less.

The weight-average molecular weight of the silicon oxide condensate contained in the binder solution is preferably 500 or more and 3000 or less in polystyrene equivalent. If the weight-average molecular weight is less than 500, cracks are likely to occur after curing, and the stability as a coating liquid decreases. Furthermore, if the weight-average molecular weight exceeds 3000, the viscosity increases, making the voids inside the binder more likely to become non-uniform, and large voids are more likely to occur.

When chemically bonding silicon oxide particles together, a method can be used in which silicon oxide particles are bonded together via highly activated silanol groups. Specifically, this can include a method of treating the surface of silicon oxide particles with a strong acid or a method of attaching silanol groups to the surface of silicon oxide particles.

The solvent that can be used for the dispersion of silicon oxide particles may be any solvent in which the raw materials dissolve uniformly and the reactants do not precipitate. The above-mentioned monohydric alcohols, dihydric or higher alcohols, ether alcohols, ethers, esters, ketones, aprotic polar solvents, etc. can be used. In addition, various aliphatic or alicyclic hydrocarbons such as n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane, various aromatic hydrocarbons such as toluene, xylene, and ethylbenzene, and various chlorinated hydrocarbons such as chloroform, methylene chloride, carbon tetrachloride, and tetrachloroethane can also be used. Two or more solvents selected from these can also be mixed and used.

[Second embodiment]
Depending on the application, such as when a member having the front-surface antireflection layer 30 is incorporated into a device, the metal oxide film of the front-surface antireflection layer 30 may be exposed to the atmosphere, and a siloxane-based organic substance may adhere to the surface of the layer, increasing the contact angle of water. If the contact angle of water on the surface of the front-surface antireflection layer 30 becomes high and moisture exceeds the amount that the member can retain, water droplets will form on the surface of the member, causing fogging.

Therefore, in this embodiment, as shown in FIG. 5, a hydrophilic polymer layer 50 is provided on the surface of the component that comes into contact with air (the surface of the anti-reflection layer 40) to suppress an increase in the contact angle of the component surface with water.

(Hydrophilic Polymer Layer)
The hydrophilic polymer layer 50 can be made of any compound containing a hydrophilic functional group, but is particularly preferably made of a polymer having a hydrophilic group of an amphoteric ion. The presence of the hydrophilic group of an amphoteric ion increases the hydrophilicity of the surface and reduces the electrical resistance, making it difficult for contaminants to adhere to the surface. As a result, it is possible to maintain high hydrophilicity for a long period of time. The presence of a hydrophilic polymer layer on the surface of the optical member prevents moisture that cannot be retained by the optical member from forming a water film on the surface of the optical member instead of water droplets, thereby suppressing the occurrence of fogging.

As the amphoteric ionic hydrophilic group, any one selected from the group consisting of sulfobetaine group, carbobetaine group, phosphorcholine group, sulfone group, phosphonate group, and carboxylic acid anhydride can be preferably used. In addition, the organic skeleton of the polymer having the amphoteric ionic hydrophilic group is not particularly limited.

In order to increase the adhesion between the hydrophilic polymer layer 50 and the front-surface antireflection layer 30, it is preferable to select the chemical composition of the front-surface antireflection layer 30 that is in contact with the hydrophilic polymer layer 50. For example, in order to react with the silanol groups of the silane coupling agent contained in the solution for forming the hydrophilic polymer layer 50, it is preferable to use silicon oxide on the surface of the front-surface antireflection layer 30 on which the hydrophilic layer is formed.

In general, to improve the anti-reflection performance of a multilayer film, it is preferable to lower the refractive index of the layer in contact with air. However, the compounds used to form the hydrophilic polymer layer 50 are generally silane coupling agents or hydrophilic polymers, and many of these compounds have a refractive index of more than 1.4. Therefore, in order to maintain hydrophilicity by suppressing adhesion of siloxane-based organic matter to the surface without affecting the anti-reflection performance of the front-surface anti-reflection layer 30, it is preferable to set the layer thickness of the hydrophilic polymer layer 50 to 1 nm or more and 20 nm or less.

With a hydrophilic polymer layer of this thickness, it is possible to achieve high anti-reflection performance even when a hydrophilic layer is formed by designing the refractive index and film thickness of each layer of the anti-reflection layer.

The thickness of the hydrophilic polymer layer can be measured by the following method using an X-ray photoelectron spectrometer. The surface of the member is irradiated with an X-ray beam, and the concentration of elements derived from the hydrophilic polymer is measured from the intensity of the detected photoelectron peak. The elements derived from the hydrophilic polymer can be measured, for example, using sulfur if the hydrophilic group of the hydrophilic polymer is a sulfobetaine group, phosphorus if the hydrophilic group is a phosphorocholine group, and nitrogen if the hydrophilic group is a carbobetaine group. Next, after etching an arbitrary predetermined area of the surface of the member with an ion beam for a certain period of time, an X-ray beam is irradiated into the etched area to measure the concentration of elements derived from the hydrophilic polymer. The set of measuring the concentration of elements derived from the hydrophilic polymer and etching is repeated multiple times, and the depth D of the groove from the surface is physically measured. The layer thickness of the hydrophilic polymer layer 50 etched in one etching process can be calculated from the number of etchings and the depth D of the groove.

Under the etching conditions calculated for the layer thickness etched in one etching process, etching and measurement of the concentration of elements derived from the hydrophilic polymer are repeated for the hydrophilic polymer layer 50 formed on the surface of the optical element until the elements derived from the hydrophilic polymer can no longer be detected. In the present invention, the layer thickness of the hydrophilic polymer layer 50 is determined by multiplying the number of etchings at the point when the detection intensity of the elements derived from the hydrophilic polymer disappears by the layer thickness etched in one etching process.

The hydrophilic polymer layer 50 can be formed by applying a solution containing a compound that contains a functional group having hydrophilicity onto the anti-reflection layer by a method such as spin coating, blade coating, roll coating, slit coating, printing, or dip coating, and then curing the solution.

The compound containing a functional group having hydrophilic properties is particularly preferably a polymer having a hydrophilic group of an amphoteric ion. Preferred main chain structures of hydrophilic polymers include acrylic resins, methacrylic resins, polyurethane resins, polyimide resins, polyamide resins, epoxy resins, polystyrene resins, polyester resins, etc.

As the solvent for the hydrophilic polymer solution, it is preferable to select a solvent that is highly compatible with the hydrophilic polymer to be used from among alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, and propylene glycol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether and tetrahydrofuran; aromatic hydrocarbon compounds such as benzene, toluene, and xylene; aliphatic hydrocarbon compounds such as n-hexane; alicyclic hydrocarbon compounds such as cyclohexane; and acetate esters such as methyl acetate and ethyl acetate.

[Third embodiment]
FIG. 6 shows an example of a preferred embodiment of an imaging apparatus according to the present invention, and illustrates the configuration of a single-lens reflex digital camera to which a lens barrel (interchangeable lens) which is an example of the optical device of the present invention is coupled.

The optical device of the present invention refers to devices such as binoculars, microscopes, semiconductor exposure devices, and interchangeable lenses that are equipped with an optical system including the member of the present invention, in which a porous layer is formed on a transparent substrate. Alternatively, the optical device refers to devices that generate images using light that has passed through the member of the present invention.

The imaging device of the present invention refers to a camera system such as a digital still camera or digital video camera, or an electronic device such as a mobile phone that is equipped with an imaging element that receives light that has passed through the member of the present invention. Note that a modular form mounted on an electronic device, such as a camera module, may also be considered an imaging device.

In FIG. 6, the camera body 320 and the lens barrel 310, which is an optical device, are connected, but the lens barrel 310 is a so-called interchangeable lens that can be attached and detached from the camera body 320.

Light from a subject passes through an optical system consisting of multiple lenses 312, 313, etc., arranged on the optical axis of the photographing optical system inside the housing 311 of the lens barrel 310, and is received by the image sensor. The member according to the present invention is preferably used for, for example, lens 312, which is the lens most likely to become cloudy inside the housing, but may be used for any of the lenses that make up the optical system.

Here, the lens 313 is supported by an inner tube 314 and is movably supported relative to the outer tube of the lens barrel 311 for focusing and zooming.

During the observation period before shooting, light from the subject is reflected by the main mirror 322 in the housing 321 of the camera body, passes through the prism 323, and then the captured image is displayed to the photographer through the viewfinder lens 324. The main mirror 322 is, for example, a half mirror, and the light that passes through the main mirror is reflected by the sub-mirror 325 in the direction of the AF (autofocus) unit 326, and this reflected light is used, for example, for distance measurement. The main mirror 322 is attached and supported by a main mirror holder 327, for example, by gluing. During shooting, the main mirror 322 and the sub-mirror 325 are moved out of the optical path via a driving mechanism (not shown), the shutter 328 is opened, and the shooting light image incident from the lens barrel 310 is formed on the image sensor 329. The aperture 315 is configured so that the brightness and focal depth during shooting can be changed by changing the opening area.

As shown in Figure 6, by using the components of the present invention, it is possible to prevent the optical system from fogging due to changes in the external environment, and to obtain a clear image.

The following describes examples and comparative examples of the present invention. However, the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

(1) Preparation of silicon oxide particle dispersion 1 for forming a first region of a porous layer 1-ethoxy-2-propanol was added to 370 g of a 1-methoxy-2-propanol (hereinafter, PGME) dispersion of spherical silicon oxide particles (PGM-ST manufactured by Nissan Chemical Industries, Ltd., average particle size 12 nm, solid content concentration 30 mass%) to prepare 2,018.2 g of a 1-ethoxy-2-propanol dispersion of spherical silicon oxide particles with a solid content concentration of 5.5 mass%.

In a separate container, 54 g of 0.01 mol/l dilute hydrochloric acid was slowly added to a solution of 62.6 g of ethyl silicate and 36.8 g of 1-ethoxy-2-propanol, and the mixture was stirred at room temperature for 90 minutes, and then heated at 40°C for 1 hour to prepare a silicon oxide oligomer solution with a solids concentration of 11.8% by mass.

94.1 g of silicon oxide binder solution was slowly added to the resulting 1-ethoxy-2-propanol dispersion of spherical silicon oxide particles, and the mixture was stirred at room temperature for 2 hours to prepare silicon oxide particle coating solution 1.

The particle size distribution of the coating liquid was measured using dynamic light scattering (Zetasizer Nano ZS, manufactured by Malvern Instruments) to confirm that spherical silicon oxide particles with an average particle size of 15 nm were dispersed.

(2) Preparation of silicon oxide particle dispersion 2 for forming third region of porous layer 1-propoxy-2-propanol was added to 500 g of a 2-propanol (IPA) dispersion of chain-like silicon oxide particles (IPA-ST-UP, manufactured by Nissan Chemical Industries, Ltd., average particle size 12 nm, solid content concentration 15% by mass) while distilling off the IPA, to prepare 433.3 g of a 1-propoxy-2-propanol dispersion of chain-like silicon oxide particles with a solid content concentration of 17.3% by mass.
In a separate vessel, 54 g of 0.01 mol/l dilute hydrochloric acid was slowly added to a solution of 62.6 g of ethyl silicate and 36.8 g of 1-propoxy-2-propanol, and the mixture was stirred at room temperature for 90 minutes, and then heated at 40° C. for 1 hour to prepare a silicon oxide oligomer solution with a solid content of 11.8% by mass.

25.4 g of the silicon oxide oligomer solution was slowly added to the 1-propoxy-2-propanol dispersion of the chain-like silicon oxide particles, and the mixture was stirred at room temperature for 2 hours to prepare silicon oxide particle coating solution 2.

The particle size distribution of the coating liquid was measured using dynamic light scattering (Zetasizer Nano ZS, manufactured by Malvern Instruments) to confirm that chain-like silicon oxide particles with a minor axis of 11 nm and a major axis of 77 nm were dispersed.

(3) Measurement of film thickness and voids After coating the anti-reflection layer formed on the substrate with a carbon film and a Pt-Pd film, the anti-reflection layer was sliced in an electron beam processing device (FIB-SEM; Nova 600 manufactured by FEI) and observed with a scanning transmission electron microscope (STEM; S-5500 manufactured by Hitachi). The film thickness of each layer was measured from the obtained secondary electron image. The presence or absence of the second region can be determined by binarizing the obtained secondary electron image, calculating the amount of voids from the substrate side to the surface side, and determining the change in void ratio.

(4) Measurement of refractive index The change in the polarization state of incident light and reflected light was measured in the wavelength range from 380 nm to 800 nm using a spectroscopic ellipsometer, and the refractive index was calculated. n _d is shown as a representative value of the refractive index. The film thickness measured in (3) was used to calculate the refractive index.

(5) Antifogging Evaluation Using an antifogging evaluation device (AFA-2 manufactured by Kyowa Interface Science Co., Ltd.), a transparent substrate held at 25° C. was left in an atmosphere of 25° C. and 70% RH while being cooled to 15° C., and a transmission image was recorded every second for up to 300 seconds. A compression antifogging index analysis was performed from the transmission image, and the time change of the compression antifogging index was plotted.

The time until the compression antifogging index started to decrease from the initial value was read from the obtained plot, and the antifogging property was evaluated according to the following criteria. The longer the time until the compression antifogging index started to decrease from the initial value, the better the antifogging property. A 40 mm square, 3 mm thick flat glass plate (S-BSL7, n _d =1.52, manufactured by OHARA Co., Ltd.) without a porous layer began to fog up in 68 seconds.

(6) Reflectance Evaluation The absolute reflectance was measured at wavelengths of 380 nm to 780 nm using a reflectance measuring device (USPM-RU manufactured by Olympus Corporation), and the average value of the reflectance at wavelengths of 400 to 700 nm (average reflectance) was calculated and evaluated according to the following criteria: The smaller the average reflectance before and after water absorption, the better the reflective performance.

Example 1
An appropriate amount of silicon oxide particle dispersion 1 was dropped onto a 40 mm square, 3 mm thick flat glass plate (S-BSL7, n _d =1.52, manufactured by Ohara Corporation) and spin-coated at 4000 rpm for 12 seconds to form a coating film. Then, before the coating film made of silicon oxide particle dispersion 1 dried, an appropriate amount of silicon oxide particle dispersion 2 was subsequently dropped onto the plate and spin-coated at 1500 rpm for 30 seconds to form a coating film. Thereafter, the plate was heated at 140°C for 30 minutes in a hot air circulating oven to harden the coating film, thereby producing a member having a porous layer.

Example 2
A member having a porous layer was obtained in the same manner as in Example 1, except that an appropriate amount of silicon oxide particle dispersion liquid 1 was dropped and spin-coated at 4000 rpm for 16 seconds.

Example 3
A member having a porous layer was produced in the same manner as in Example 1, except that a coating liquid for forming a porous layer was applied in the following procedure.

An appropriate amount of silicon oxide particle dispersion liquid 1 was dripped and spin-coated at 5000 rpm for 20 seconds. Next, an appropriate amount of a liquid made by mixing silicon oxide particle dispersion liquid 1 and silicon oxide particle dispersion liquid 2 in a 10:1 ratio was dripped and spin-coated at 5000 rpm for 10 seconds, and then an appropriate amount of silicon oxide particle dispersion liquid 2 was dripped and spin-coated at 1500 rpm for 30 seconds.

Example 4
After forming the porous layer, a surface antireflection layer consisting of a combination of a layer containing silicon oxide, a layer containing titanium oxide, and a layer containing magnesium fluoride was formed based on a design taking antireflection performance into consideration, and a porous layer was formed in the same manner as in Example 1, to obtain a member.

When forming the front-surface antireflection layer, the temperature of the substrate, the ultimate vacuum pressure, and the pressure during film formation of each layer were adjusted so as to obtain the desired refractive index. In addition, silicon oxide pellets (SiO2E type manufactured by Canon Optron Inc.), pellets containing titanium oxide (manufactured by Nichia Corporation), and magnesium fluoride pellets ( _MgF2 manufactured by Rare Metals Co., Ltd.) were used for film formation of each layer. The refractive index and film thickness of each layer of the front-surface antireflection layer are shown in Table 1.

(Comparative Example 1)
A magnesium fluoride film was formed as an undercoat film by vapor deposition on a 40 mm square, 3 mm thick flat glass plate (S-BSL7, n _d =1.52, manufactured by Ohara Corporation), and then an appropriate amount of silicon oxide particle dispersion liquid 2 was dropped and spin-coated at 1500 rpm for 30 seconds. This was then heated at 140°C for 30 minutes in a hot air circulating oven and cured to produce a member having a porous layer. The magnesium fluoride undercoat film is a layer provided to reduce the difference in refractive index between the substrate and the porous layer and reduce reflection.

(Comparative Example 2)
Except for forming the porous layer and then the front-surface antireflection film successively, a member having a porous layer was produced in the same manner as in Comparative Example 1. The front-surface antireflection film was a vapor-deposited film consisting of multiple layers as shown in Table 1, as in Example 4.

(Evaluation of Examples 1 to 3 and Comparative Examples 1 and 2)
The configurations and evaluation results of the members produced in Examples 1 to 4 are summarized in Table 2, and the configurations and evaluation results of the members produced in Comparative Examples 1 and 2 are summarized in Table 3.

In the anti-fogging evaluation, the members produced in Comparative Examples 1 and 2 became fogged up in 102 seconds, whereas the members produced in Examples 1 to 4 did not fog up at less than 110 seconds, confirming their excellent anti-fogging properties. The glass substrate fogged up in 68 seconds in the anti-fogging evaluation, proving that it has anti-fogging properties.

The results of Examples 1 to 3 and Comparative Example 1 show that the configuration of Comparative Example 1, which has a base layer for anti-reflection, has a higher average reflectance due to water absorption than the configurations of Examples 1 to 3 according to the present invention. Figures 7 and 8 show the reflection characteristics measured before and after water absorption for each of the members of Example 1 and Comparative Example 1. The average reflectance difference before and after water absorption for Example 1 was 1.53%, while the average reflectance difference before and after water absorption for Comparative Example 1 was 1.65%, meaning that Example 1 had superior anti-reflection properties.

Both the members of Example 4 and Comparative Example 2 have a surface anti-reflection layer formed on the porous layer. It was confirmed that the anti-reflection properties of both are enhanced by combining them with an anti-reflection layer. However, although the average reflectance before water absorption was the same in Example 4 and Comparative Example 2, a large difference in the average refractive index occurred after water absorption, and it was confirmed that Example 4 has superior anti-reflection properties. The average reflectance difference before and after water absorption in Example 4 was 0.73%, and the average reflectance difference before and after water absorption in Comparative Example 2 was 1.03%.

These results confirm that the members of the present invention have excellent anti-fogging and anti-reflection properties before and after moisture absorption.

The members of the present invention can be used for general purposes such as window glass, mirrors, lenses, transparent shields, and transparent films. They can also be used as optical components such as optical lenses for imaging and projection systems, optical mirrors, optical filters, eyepieces, and flat and dome covers for outdoor and surveillance cameras.

REFERENCE SIGNS LIST 100 Member 10 Substrate 20 Porous layer 21 First region 22 Second region 23 Third region 24 First particle 25 Second particle 30 Front surface antireflection layer 40 Base antireflection layer 50 Hydrophilic polymer layer 310 Lens barrel 320 Camera body 312, 313 Lens 328 Shutter 329 Imaging element

Claims (23)

An optical member comprising a porous layer on a substrate,
the porous layer has, in this order from the substrate side, a first region, a second region, and a third region;
the first region includes first particles, the third region includes second particles having a shape different from that of the first particles, and the second region includes the first particles and the second particles,
the average porosity of the second region is greater than the average porosity of the first region;
An optical member, wherein the average porosity of the third region is greater than the average porosity of the second region. The optical member according to claim 1, characterized in that the porosity of the first region is 10% or more and 30% or less, and the porosity of the third region is 40% or more and 60% or less. The optical member according to claim 1 or 2, characterized in that the thickness of the third region is 0.2 μm or more and 2 μm or less. The optical member according to any one of claims 1 to 3, characterized in that the thickness of the first region is 50 nm or more and 150 nm or less. The optical member according to any one of claims 1 to 4, characterized in that the average pore size of the pores contained in the porous layer is 3 nm or more and 50 nm or less. 6. The optical member according to claim 1, wherein the pore volume of the pores contained in the porous layer is 0.1 cm ³ /g or more and 1.0 cm ³ /g or less. The optical member according to any one of claims 1 to 6, characterized in that the first particles are spherical silicon oxide particles, and the second particles are chain-like silicon oxide particles. The optical member according to claim 7, characterized in that the average particle size of the spherical silicon oxide particles is 5 nm or more and 100 nm or less, and the average short diameter of the chain-like silicon oxide particles is 5 nm or more and 40 nm or less. The optical member according to any one of claims 1 to 8, characterized in that it has a laminate of multiple layers having mutually different refractive indices on the surface of the porous layer and/or between the porous layer and the substrate. The optical member according to claim 9, characterized in that the laminate includes at least two layers selected from a low refractive index layer having a refractive index of less than 1.4, a medium refractive index layer having a refractive index of 1.4 or more and less than 1.8, and a high refractive index layer having a refractive index of 1.8 or more. 11. The optical member according to claim 1, further comprising a hydrophilic polymer layer on a surface of the optical member that is in contact with air. The optical member according to claim 11, characterized in that the hydrophilic polymer layer is a polymer having a zwitterionic hydrophilic group. The optical member according to claim 12, characterized in that the hydrophilic group of the zwitterion is any one selected from the group consisting of a sulfobetaine group, a carbobetaine group, a phosphorocholine group, a sulfone group, a phosphonate group, and a carboxylic acid anhydride. The optical member according to any one of claims 11 to 13, characterized in that the thickness of the hydrophilic polymer layer is 1 nm or more and 20 nm or less. An optical device comprising a housing and an optical system made up of a plurality of lenses in the housing,
An optical device, wherein at least one of the lenses is the optical member according to claim 1 . An imaging device comprising a housing, an optical system including a plurality of lenses disposed within the housing, and an imaging element that receives light that has passed through the optical system,
An imaging device, wherein at least one of the lenses is an optical member according to claim 1 . A method for producing an optical member according to any one of claims 1 to 14, comprising the steps of:
A step of supplying a first coating liquid containing first particles onto the substrate to form a first coating film;
supplying a second coating liquid containing second particles having a shape different from that of the first particles onto a substrate to form a second coating film;
Including,
A method for producing an optical member, comprising forming the second coating film after the first coating film is formed and before the first coating film is dried. The method for producing an optical member according to claim 17, characterized in that the first coating liquid contains spherical silicon oxide particles, and the second coating liquid contains chain-like silicon oxide particles. The method for manufacturing an optical member according to claim 17 or 18, characterized in that the first coating liquid and the second coating liquid contain a binder component. The method for producing an optical member according to claim 19, further comprising a step of forming a laminate of multiple layers having different refractive indices between the substrate and the porous layer by a vapor deposition method. The method for manufacturing an optical member according to any one of claims 17 to 20, characterized in that it includes a step of forming a laminate of multiple layers having different refractive indices on the surface of the porous layer by a vapor deposition method. 22. The method for manufacturing an optical member according to claim 17, further comprising a step of supplying a solution containing a compound having a hydrophilic functional group to a surface of the optical member in contact with air to form a hydrophilic polymer layer. The method for producing an optical member according to claim 22, characterized in that the hydrophilic functional group is any one selected from the group consisting of a sulfobetaine group, a carbobetaine group, a phosphorocholine group, a sulfone group, a phosphonate group, and a carboxylic acid anhydride.

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