Anti-reflective coating, lens, imaging device and liquid composition

Abstract

The membrane (1) of the present invention comprises hollow particles (10) and an adhesive (20). The hollow particles are formed of a material having a refractive index of 1.15 to 2.70. The adhesive (20) is formed of at least polysilsesquioxane and binds the hollow particles (10). The membrane (1) satisfies at least one of the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3. Ia is the absorbance derived from hydrocarbon groups not directly bonded to silicon atoms, determined by total reflectance measurement using a Fourier transform infrared spectrophotometer. Ib is the absorbance derived from the bond between silicon atoms and non-reactive functional groups. Ic is the absorbance derived from the bond between silicon atoms and hydroxyl groups.

Description

[Technical Field]

[0001] This invention relates to a film and liquid composition that are advantageous for coating low refractive indices. Additionally, this invention relates to an optical element and a camera device. [Previous Technology]

[0002] In the past, from the point of view of anti-reflection, there are known methods for coating with a material having a low refractive index (low refractive index coating) and compositions for low refractive index coating.

[0003] For example, Patent Documents 1 and 2 disclose an antireflective coating composition. This coating composition contains an adhesive and hollow silica particles. The adhesive is formed by polymerizing a specific silane compound with an organosilicon compound having a fluoroalkyl group. Additionally, Patent Documents 1 and 2 disclose an antireflective film containing a low-refractive-index layer formed by coating the coating composition onto the surface of a substrate.

[0004] Patent Document 3 discloses an antireflective film having a laminated structure comprising a transparent substrate, a high-refractive-index layer, and a low-refractive-index layer. The low-refractive-index layer contains an adhesive and hollow silica particles, the adhesive being formed by polymerizing a specific silane compound with an organosilicon compound having a fluoroalkyl group.

[0005] Patent Document 4 discloses an optical component having an anti-reflective film and a method for manufacturing the same. The manufacturing method includes a step of coating a substrate with a dispersion containing particles and a dispersion medium. After the dispersion coating step, the method further includes the step of coating a solution containing a binder-forming component, allowing the solution to penetrate between the particles contained in the previously coated dispersion to form a single layer with binder filling the interparticle spaces. The manufacturing method further includes a step of drying the layer to produce the anti-reflective film. The solution contains silane alkoxy condensates with an average particle size of 8 nm or more and 60 nm or less, and a solvent containing at least 70% by mass of water with a solubility of at least 10% by weight. (Prior Art Documents, Patent Documents)

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-534104; Patent Document 2: Japanese Patent Application Publication No. 2015-536477; Patent Document 3: Japanese Patent Application Publication No. 2015-535617; Patent Document 4: Japanese Patent Application Publication No. 2017-167271 [Summary of the Invention]

[0007] [Problem to be Solved by the Invention] According to the technology described in Patent Documents 1-3, there is a need for organosilicon compounds containing fluoroalkyl groups. According to the technology described in Patent Document 4, it is necessary to allow a solution containing a silane alkoxy condensate to permeate between particles contained in a pre-coated dispersion, making the manufacturing method of optical components complex. Therefore, the present invention provides a film that does not require organosilicon compounds containing fluoroalkyl groups and is advantageous for low-refractive-index coating. Furthermore, the present invention provides a liquid composition that does not require organosilicon compounds containing fluoroalkyl groups and allows for simple low-refractive-index coating. [Technical Means for Solving the Problem]

[0008] The present invention provides a membrane comprising: hollow particles formed of a material having a refractive index of 1.15 to 2.70, and an adhesive formed of at least polysilsesquioxane to bond the hollow particles; when the absorbance derived from hydrocarbon groups not directly bonded to silicon atoms, the absorbance derived from the bonding between silicon atoms and non-reactive functional groups, and the absorbance derived from the bonding between silicon atoms and hydroxyl groups, determined by total reflectance measurement using Fourier transform infrared spectrophotometer (ATR method), is expressed as Ia, Ib, and Ic respectively, at least one of the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3 is satisfied.

[0009] Furthermore, the present invention provides a liquid composition comprising: hollow particles formed from a material having a refractive index of 1.15 to 2.70, polysilsesquioxane, and a solvent; and in a cured product obtained by coating the liquid composition onto a substrate and hardening the liquid composition, when the absorbance derived from hydrocarbon groups not directly bonded to silicon atoms, the absorbance derived from the bonding between silicon atoms and non-reactive functional groups, and the absorbance derived from the bonding between silicon atoms and hydroxyl groups, determined by total reflectance measurement using a Fourier transform infrared spectrophotometer, are expressed as Ia, Ib, and Ic respectively, at least one of the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3 is satisfied.

[0010] Furthermore, the present invention provides an optical element having the above-described film.

[0011] Furthermore, the present invention provides a camera device equipped with the above-described optical elements. [Effects of the Invention]

[0012] The above-described film does not require organosilane compounds containing fluoroalkyl groups and is advantageous for low-refractive-index coating. The above-described liquid composition does not require organosilane compounds containing fluoroalkyl groups. Furthermore, low-refractive-index coating can be easily performed using the above-described liquid composition.

Implementation Method

[0014] According to the technology described in Patent Documents 1-3, organosilicon compounds containing fluoroalkyl groups are required. Therefore, the inventors believe that in the technology described in Patent Documents 1-3, if the coating solution contains water as a solvent (dispersion medium), phase separation will occur in the coating solution due to the water-repellent properties of the fluoroalkyl groups. Therefore, according to the technology described in Patent Documents 1-3, the inventors believe that additives such as surfactants need to be added in order to obtain a uniform coating solution. In addition, the inventors believe that the technology described in Patent Documents 1-3 will result in low wettability of the coating solution on hydrophilic glass substrates and hydrophobic (oleophilic) resin substrates due to the water-repellent and oil-repellent properties of the fluoroalkyl groups, making it easy for the coating solution to be repelled on the substrate when it is coated. Furthermore, the inventors believe that the technology described in Patent Document 4 requires a complicated step of allowing a solution containing silane alkoxy condensates to penetrate between the particles after coating a dispersion containing particles. Therefore, the inventors conducted round-the-clock research to develop a film that is advantageous for low-refractive-index coating without requiring organosilane compounds containing fluoroalkyl groups. As a result, the inventors developed the film of the present invention. In addition, the inventors developed a liquid composition that does not require organosilane compounds containing fluoroalkyl groups and can be easily coated with low-refractive-index materials.

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the following description is only one example of the present invention, and the present invention is not limited to what is described below.

[0016] As shown in Figure 1, the membrane 1 comprises hollow particles 10 and an adhesive 20. The hollow particles 10 are formed of a material having a refractive index of 1.15 to 2.70. The adhesive 20 is formed of at least polysilsesquioxane and binds the hollow particles 10. In the membrane 1, the absorbance derived from hydrocarbon groups not directly bonded to silicon atoms, the absorbance derived from the bonding between silicon atoms and non-reactive functional groups, and the absorbance derived from the bonding between silicon atoms and hydroxyl groups, determined by total reflectance measurement using Fourier transform infrared spectrophotometry (ATR method), are respectively expressed as Ia, Ib, and Ic. The membrane 1 satisfies at least one of the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3. In this specification, Ib / Ia is also referred to as the organic-inorganic parameter (D), and Ib / Ic is also referred to as the hydrophobic parameter (H). Absorbance Ia, absorbance Ib and absorbance Ic can be determined, for example, based on the absorption spectrum obtained by the ATR method according to the method described in the examples.

[0017] The less hydrocarbon groups not directly bonded to silicon atoms contained in the binder 20, the larger the organic-inorganic parameter (D). If the amount of hydrocarbon groups not directly bonded to silicon atoms contained in the binder 20 is small, the Si-O-Si network in the binder 20 is dense, and the density of the inorganic components in the binder 20 becomes higher. Thus, the hollow particles 10 are firmly fixed by the Si-O-Si network. Therefore, if Ib / Ia ≥ 0.7 in the film 1, the hollow particles 10 are firmly fixed in the film 1, thereby giving the film 1 a property advantageous for low refractive index coating. If the fixation of hollow particles in the film is insufficient, there is a possibility of a decrease in the mechanical strength of the film.

[0018] The fewer hydroxyl groups bonded to silicon atoms in the adhesive 20, the larger the hydrophobic parameter (H). For example, if the hydroxyl groups in the raw material of the adhesive 20 condense with each other to develop into a network composed of Si-O-Si, then the number of hydroxyl groups bonded to silicon atoms in the adhesive 20 decreases. If the hydrophobic parameter (H) is above a certain value, then the network composed of Si-O-Si in the adhesive 20 develops densely, and the hollow particles 10 can be firmly fixed by this network. Therefore, if Ib / Ic ≥ 0.3 in the film 1, the hollow particles 10 are firmly fixed in the film 1, and thus the film 1 has the characteristic of being advantageous for low refractive index coating.

[0019] Ideally, film 1 should satisfy the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3. In this way, the hollow particles 10 in film 1 are more securely fixed, and film 1 has the characteristic of being advantageous for coating low refractive index.

[0020] When silanol groups (Si-OH) are present in the adhesive 20, the silanol groups form hydrogen bonds with the silanol groups present on the surface of the glass substrate, thus exhibiting high affinity. Therefore, films with hydrophobic parameters (H) below a certain value can also easily adhere to the glass substrate. Ideally, film 1 should satisfy the condition of 0.3≦Ib / Ic≦2.0 to exhibit good adhesion to both substrates with hydrophilic and hydrophobic surfaces.

[0021] In membrane 1, the first absorbance, second absorbance, and third absorbance, determined by the ATR method, originating from the bond between one oxygen atom and two silicon atoms, are denoted as Id, Ie, and If, respectively. The first absorbance Id corresponds to the first wavenumber. The second absorbance Ie corresponds to the second wavenumber, which is greater than the first wavenumber. The third absorbance If corresponds to the third wavenumber, which is greater than the second wavenumber. Ideally, membrane 1 satisfies at least one of the following conditions: Id / Ib ≤ 60, Ie / Ib ≤ 20, and If / Ib ≤ 174. In this specification, Id / Ib is also referred to as the first network parameter (N1), Ie / Ib is also referred to as the second network parameter (N2), and If / Ib is also referred to as the third network parameter (N3).

[0022] The first wavenumber is, for example, the wavenumber in which the absorption spectrum reaches its maximum value at 455 ± 50 cm⁻¹. The second wavenumber is, for example, the wavenumber in which the absorption spectrum reaches its maximum value at 780 ± 50 cm⁻¹. The third wavenumber is, for example, the wavenumber in which the absorption spectrum reaches its maximum value at 1065 ± 50 cm⁻¹.

[0023] The more bonds (Si-O-Si) between oxygen atoms and two silicon atoms in the adhesive 20, the larger the first network parameter (N1), the second network parameter (N2), and the third network parameter (N3) become. The more developed the Si-O-Si network formed by the condensation of hydroxyl groups in the raw materials of the adhesive 20, the larger the first network parameter (N1), the second network parameter (N2), and the third network parameter (N3) become. On the other hand, in order to maintain good film-forming properties, it is important to suppress the aggregation of hollow particles and maintain a uniform coating thickness. To suppress the aggregation of hollow particles, it is ideal to prevent the excessive development of the Si-O-Si network. From this point of view, it is ideal for at least one of N1 being 60 or less, N2 being 20 or less, and N3 being 174 or less in the film 1. In this way, the film 1 can be formed well, and an anti-reflective structure with good anti-reflective properties can be provided by the film 1.

[0024] Membrane 1 is more ideal to satisfy the conditions Id / Ib≦60, Ie / Ib≦20 and If / Ib≦174.

[0025] Typically, the polysilsesquioxane of adhesive 20 has non-reactive functional groups bonded to silicon atoms. To enable the polysilsesquioxane of adhesive 20 to exhibit appropriate hydrophobic properties, the non-reactive functional groups are, for example, alkyl groups exhibiting hydrophobicity. Ideally, the polysilsesquioxane of adhesive 20 is a polysilsesquioxane containing hydrocarbon groups with 16 or fewer carbon atoms bonded to silicon atoms as non-reactive functional groups. In this case, since the non-reactive functional groups are small in size, the Si-O-Si network can be easily and densely formed.

[0026] The adhesive 20 may also be formed of silicon dioxide, for example. In this case, the polysilsesquioxane contained in the adhesive 20 readily exhibits hydrophobic properties, and the silicon dioxide contained in the adhesive 20 readily exhibits hydrophilic properties. Therefore, in the adhesive 20, the hydrophilicity or hydrophobicity of the film 1 can be adjusted to an appropriate level by adjusting the ratio (Mp / Ms) of the mass of polysilsesquioxane Mp to the mass of silicon dioxide Ms. In this way, the film 1 can be appropriately formed on substrates with hydrophilic surfaces, such as glass substrates, and also on substrates with hydrophobic surfaces, such as resins. From this perspective, the ratio (Mp / Ms) of the mass of polysilsesquioxane Mp to the mass of silicon dioxide Ms in adhesive 20 is, for example, 3 / 7 or more, ideally 1 to 9, and even more ideally 3 / 2 to 4.

[0027] The hollow particles 10 are not particularly limited as long as they have a hollow structure, such as having a spherical, cylindrical, or sheet-like shape. The hollow particles 10 have, for example, an average particle size (primary particle size) of 10 to 150 nm. In this way, the hollow particles 10 can be easily and uniformly dispersed in the membrane 1. The average particle size of the hollow particles 10 can be determined, for example, by taking the arithmetic mean of the particle sizes of more than 50 hollow particles 10 observed using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Furthermore, the particle size of each particle refers to the maximum diameter.

[0028] Ideally, the hollow particles 10 have an average particle size of 20–100 nm, and more ideally, an average particle size of 30–70 nm. Furthermore, the maximum size of the internal space within the hollow particles 10 is, for example, 5–100 nm, more ideally 10–70 nm, and more ideally 20–50 nm. Ideally, the hollow particles 10 are monodisperse particles with a coefficient of variation of 0.1 or less.

[0029] The material of the hollow particles 10 can be either inorganic or organic, as long as it has a refractive index of 1.15 to 2.70. Ideally, the material of the hollow particles 10 should have a refractive index of 1.20 to 2.00, more ideally it should have a refractive index of 1.30 to 1.50, and even more ideally it should have a refractive index of 1.38 to 1.46. From the viewpoint of the difficulty of deformation under external force, the hollow particles 10 should ideally be formed of an inorganic material. In this case, the hollow particles 10 may be formed, for example, of at least one material selected from the group consisting of silicon dioxide, magnesium fluoride, aluminum oxide, aluminum silicate, titanium dioxide, and zirconium oxide.

[0030] In order to provide an anti-reflective structure with high anti-reflective properties by using the low refractive index coating of film 1, the hollow particles 10 are preferably formed of silicon dioxide or magnesium fluoride. Furthermore, the refractive index of silicon dioxide is 1.46, and the refractive index of magnesium fluoride is 1.38.

[0031] The structure and material of the hollow particle 10 are determined in a way that the hollow particle 10 has a desired refractive index. For example, the material of the hollow particle 10 and the ratio of its internal space to the total volume of the hollow particle 10 are determined in a way that the hollow particle 10 has a desired refractive index. For example, the hollow particle 10 has a refractive index of 1.10 to 1.40, more ideally it has a refractive index of 1.20 to 1.35, and even more ideally it has a refractive index of 1.25 to 1.30. For example, among various hollow particles formed from materials with different refractive indices, when the ratio of the internal space to the total volume of the hollow particle is the same, the hollow particle formed from the low refractive index material has a lower refractive index than the hollow particle formed from the high refractive index material.

[0032] The refractive index of the hollow particles 10 can be determined, for example, by the immersion method (Becker line method). For example, when the hollow particles 10 are formed of silicon dioxide, the refractive index of the hollow particles 10 can be determined in the following order: (i) Evaporate and dry the dispersion medium of the dispersion of the hollow particles 10 to obtain a powder. (ii) Mix the powder obtained in (i) with various standard refractive index liquids of different refractive indices, such as Series A and Series AA manufactured by GARGILL. (iii) Determine the refractive index of the standard refractive index liquid used when the mixture obtained in (ii) becomes transparent as the refractive index of the hollow particles 10.

[0033] The hollow particles 10 can be commercially available or manufactured using specific methods. For example, the hollow particles 10 can also be manufactured by forming a shell around a core and removing the core. For example, a shell made of silicon dioxide or a shell made of magnesium fluoride can be formed around a polymer core having a particle size of tens of nanometers. Then, the polymer core can be removed by dissolving it in a solvent or by combustion, thereby obtaining hollow particles 10 that are hollow silicon dioxide particles or hollow magnesium fluoride particles. Alternatively, a shell made of magnesium fluoride can be formed around a core made of silicon dioxide, and the core made of silicon dioxide can be dissolved using an alkali, thereby also obtaining hollow particles 10 that are hollow magnesium fluoride particles.

[0034] In the film 1, the ratio (Wh / Wb) of the mass Wh of the hollow particles 10 to the mass Wb of the binder 20 is, for example, 1 / 5 to 20, more ideally 1 / 3 to 10, and even more ideally 1 to 5. In this way, an antireflective structure with high antireflective properties can be provided by using the low refractive index coating of the film 1.

[0035] The thickness of film 1 is not particularly limited, and is determined, for example, according to the wavelength of the light to be prevented from being reflected. Specifically, when the center wavelength of the light to be prevented from being reflected is set to λ (nm), the thickness of film 1 is set such that the optical film thickness (refractive index × physical film thickness) satisfies λ / 4. For example, in order to prevent the reflection of light belonging to the visible light region (practically speaking, wavelengths of 380 nm to 780 nm), when the center wavelength λ is set to λ = 550 nm and the refractive index of the low-refractive-index film used is set to 1.20, the optimal physical film thickness is 115 nm. The thickness of film 1 that is practically effective in preventing the reflection of visible light is 50 to 300 nm, more ideally 70 to 200 nm, and even more ideally 90 to 170 nm. In this way, an anti-reflection structure with high anti-reflection performance can be provided by using a low-refractive-index coating of film 1. Furthermore, to prevent reflection of light in the near-infrared region (e.g., wavelengths from 800 nm to 2500 nm) that is close to the visible light region and centered at λ = 850 nm, the optimal physical film thickness is 177 nm when the refractive index of the low-refractive-index film used is set to 1.20. The thickness of film 1, which is practically effective in preventing near-infrared reflection, is 80–350 nm, more ideally 130–250 nm, and even more ideally 150–220 nm. Thus, an anti-reflection structure with high anti-reflection performance can be provided by using a low-refractive-index coating of film 1. When using a multilayer film as the anti-reflection structure, a low-refractive-index layer with a thickness of 50 nm or less can also be used. Moreover, the physical film thickness of the low-refractive-index film is not limited to these specifications; its profile can be measured using SEM, TEM, or an ellipsometry.

[0036] The film 1 has, for example, a refractive index of 1.35 or lower. Therefore, an antireflective structure with high antireflective properties can be provided by using the low refractive index coating of the film 1. Ideally, the film 1 should have a refractive index of 1.30 or lower, and more ideally, a refractive index of 1.25 or lower. From the viewpoint of reducing the refractive index of the film 1, the film 1 may also contain an air space in the spaces between the hollow particles 10 or in the adhesive 20. The refractive index of the film 1 can be determined, for example, by reflectance spectroscopy.

[0037] Film 1 is, for example, a cured product obtained by curing a specific liquid composition. The liquid composition contains hollow particles, polysilsesquioxane, and a solvent. The hollow particles are formed from a material having a refractive index of 1.15 to 2.70. In the cured product obtained by coating the liquid composition onto a substrate and curing the liquid composition, at least one of the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3 is satisfied. The solvent contained in the liquid composition is, for example, an alcohol such as ethanol or water.

[0038] Since the liquid composition does not require organosilicon compounds with fluoroalkyl groups, phase separation is less likely to occur in the liquid composition, and the liquid composition can easily become uniform. In addition, the liquid composition has high wettability to glass substrates and resin substrates, and a film 1 with a uniform structure can be easily obtained by means of the liquid composition.

[0039] Ideally, the hardened material should satisfy the conditions that Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3.

[0040] Ideally, the hardened material should satisfy at least one of the following conditions: Id / Ib≦60, Ie / Ib≦20, and If / Ib≦174.

[0041] In the above-mentioned hardened material, it is even more ideal to satisfy the conditions Id / Ib≦60, Ie / Ib≦20 and If / Ib≦174.

[0042] The polysilsesquioxane in the liquid composition is, for example, a polysilsesquioxane containing a hydrocarbon group with 16 or fewer carbon atoms as a non-reactive functional group bonded to silicon atoms.

[0043] The characteristics of the hollow particles 10 in the membrane 1 are typically also suitable for hollow particles in liquid compositions. Therefore, the hollow particles in the liquid composition, for example, have an average particle size (primary particle size) of 10–150 nm. Furthermore, the hollow particles in the liquid composition are preferably formed from at least one of the following: silicon dioxide, magnesium fluoride, aluminum oxide, aluminum silicate, titanium dioxide, and zirconium oxide.

[0044] Liquid components may also contain silicon dioxide in addition to hollow particles.

[0045] As shown in FIG2, for example, a film 1 is formed by coating a liquid composition onto the main surface of a substrate 30 and then hardening the liquid composition. This provides an anti-reflective structure 50a formed by low-refractive-index coating using the film 1. By using a liquid composition, low-refractive-index coating can be easily performed without the need for organosilicon compounds containing fluoroalkyl groups.

[0046] The polysilsesquioxane of the liquid composition is formed, for example, by hydrolysis and dehydration condensation of a trifunctional alkoxysilane contained in the raw material of the liquid composition. Furthermore, when the liquid composition contains silicon dioxide in addition to hollow particles, the silicon dioxide is formed, for example, by hydrolysis and dehydration condensation of a tetrafunctional alkoxysilane contained in the raw material of the liquid composition. For example, the tetrafunctional alkoxysilane forms silicon dioxide (SiO2) by the reactions described in (Formula 1) and (Formula 2) below. Ra represents an alkyl group. The trifunctional alkoxysilane forms polysilsesquioxane (RbSiO3 / 2) by the reactions described in (Formula 3) and (Formula 4) below. Rb represents a non-reactive functional group, and Rc represents an alkyl group. Si(ORa)4+4H2O→Si(OH)4+4RaOH (Formula 1) Si(OH)4→SiO2+2H2O (Formula 2) RbSi(ORc)3+3H2O→RbSi(OH)3+3RcOH (Formula 3) RbSi(OH)3→RbSiO3 / 2+3 / 2H2O (Formula 4)

[0047] The hydrolysis catalyst contained in the raw materials of the liquid composition is, for example, a carboxylic acid such as formic acid and acetic acid.

[0048] The substrate 30 is, for example, a substrate formed of glass or resin.

[0049] For example, the liquid composition can be hardened by heating a coating film formed by applying a liquid composition to the main surface of the substrate 30. In this case, typically, the coating film is heated at a temperature below the thermal decomposition temperature (decomposition temperature) of the trifunctional alkoxysilane. Ideally, the coating film is heated at a temperature below 450°C. When the substrate 30 is formed from a resin with low heat resistance, the coating film can also be heated at a temperature below 100°C. For example, even if the coating film is heated at an environment of 80°C, a refractive index of 1.35 or less (e.g., 1.20) can be imparted to the film 1.

[0050] The ratio of the mass of polysilsesquioxane Mp to the mass of silica Ms in the adhesive 20 of membrane 1 (Mp / Ms) can be considered, for example, as equal to the ratio of the mass of trifunctional alkoxysilane Mr to the mass of tetrafunctional alkoxysilane Me contained in the raw material of the liquid composition (Mr / Me).

[0051] In the anti-reflection structure 50a, a film 1 is formed on both main surfaces of the substrate 30, but it is also possible to form the film 1 on only one main surface of the substrate 30. Furthermore, when the film 1 is formed on both main surfaces of the substrate 30, the refractive index and thickness of the film 1 formed on one main surface can be the same as or different from the refractive index and thickness of the film 1 formed on the other main surface. For example, it can also be configured such that the film 1 formed on one main surface prevents the reflection of light in the visible light region, and the film 1 formed on the other main surface prevents the reflection of light in the near-infrared region that is close to the visible light region.

[0052] The anti-reflective structure 50a can be modified based on various viewpoints. For example, the anti-reflective structure 50a can also be modified to have the following stacked structures (I) to (IV). Furthermore, "A / B" means that B and A are stacked together. Also, "(A / B)m" or "(A / B)n" means that the structure formed by stacking B on A is repeated m or n times. m is an integer of 2 or more, and n is an integer of 1 or more. Furthermore, in the following stacked structures, the low refractive index layer has a refractive index of 1.5 or less, for example, a thickness of 30 to 300 nm. In the following stacked structures, film 1 forms at least one low refractive index layer. The low refractive index layer can be a layer formed of silicon dioxide or magnesium fluoride. The medium refractive index layer has a refractive index of more than 1.5 and less than 1.8, for example, a thickness of 30 to 300 nm. The intermediate refractive index layer is, for example, a layer formed of alumina or a mixture of silicon dioxide and titanium oxide. The high refractive index layer has a refractive index exceeding 1.8, for example, a thickness of 30–300 nm. The high refractive index layer is, for example, a layer formed of titanium oxide, zirconium oxide, tantalum oxide, or niobium oxide. Such laminated structures may be formed on only one main surface of the substrate or on both main surfaces of the substrate. (I) Substrate / High refractive index layer / Low refractive index layer (II) Substrate / Intermediate refractive index layer / High refractive index layer / Low refractive index layer (III) Substrate / (High refractive index layer / Low refractive index layer)m (IV) Substrate / Low refractive index layer / (High refractive index layer / Low refractive index layer)n

[0053] Furthermore, the anti-reflection structure 50a can be modified as shown in Figure 3A as the anti-reflection structure 50b. The anti-reflection structure 50b has a low-refractive-index layer (second low-refractive-index layer 40) different from the low-refractive-index layer (first low-refractive-index layer) formed on the film 1 between the film 1 and the substrate 30 in the thickness direction of the substrate 30. The second low-refractive-index layer 40 has a refractive index of 1.5 or less, and for example, a thickness of 30 to 300 nm. The second low-refractive-index layer 40 is, for example, a layer composed of at least one of polysilsesquioxane and silicon dioxide without containing hollow particles 10. In the anti-reflection structure 50b, the film 1 and the second low-refractive-index layer 40 are formed on both main surfaces of the substrate 30, but it is also possible to form the film 1 and the second low-refractive-index layer 40 only on one main surface of the substrate 30.

[0054] Furthermore, the anti-reflective structure 50a can also be modified as shown in Figure 3B as the anti-reflective structure 50c. The anti-reflective structure 50c has multiple low-refractive-index layers (a second low-refractive-index layer 40 and a third low-refractive-index layer 60) that are different from the low-refractive-index layer (first low-refractive-index layer) formed on the film 1 between the film 1 and the substrate 30 in the thickness direction of the substrate 30. The second low-refractive-index layer 40 has a refractive index of 1.5 or less, and for example, a thickness of 30 to 300 nm. The second low-refractive-index layer 40 is, for example, a layer composed of at least one of polysilsesquioxane and silicon dioxide without containing hollow particles 10. The third low-refractive-index layer 60 has, for example, a refractive index of 1.5 or less, and for example, a thickness of 30 to 300 nm. The third low-refractive-index layer 60 may also have the same refractive index and thickness as the first low-refractive-index layer. Although film 1, second low refractive index layer 40 and third low refractive index layer 60 are formed on both main surfaces of substrate 30, film 1, second low refractive index layer 40 and third low refractive index layer 60 may also be formed on only one main surface of substrate 30.

[0055] For example, an optical element having a film 1 can be provided. The optical element having film 1 can be, for example, an optical filter such as a low-pass filter and an infrared (IR) cutoff filter, a lens, or a cover glass. Film 1 is formed, for example, by coating and drying the aforementioned liquid composition onto the surface of the optical element such as a lens, and functions as a low-refractive-index coating. With film 1, reflection of light of specific wavelengths, such as visible light, can be prevented in the optical element. The optical element may further have a dielectric multilayer film for anti-reflection, or it may not have a dielectric multilayer film for anti-reflection. From the viewpoint of suppressing manufacturing costs and preventing light of specific wavelengths, it is more advantageous for the optical element to have film 1 but not to have a dielectric multilayer film for anti-reflection.

[0056] For example, a camera device equipped with the above-mentioned optical elements may be provided. The camera device may be, for example, a camera module of an information terminal such as a smartphone or a digital camera.

[0057] As shown in FIG4A, the camera device 70a includes, for example, a housing 71, a lens system 72, a filter system 73, a solid-state imaging element 74, and a cover 75. The camera device 70a is, for example, a camera module of an information terminal such as a smartphone. Furthermore, FIG4A is a schematic diagram of the camera device 70a, and the shape and size of each part and the relative positional relationship of each part in the actual object may not be accurately shown in FIG4A. In addition, typically, the camera device 70a may include an adjustment mechanism for the lens system 72 and other constituent elements such as an aperture. In FIG4A, these constituent elements are omitted for ease of explanation.

[0058] The lens system 72 is disposed inside the housing 71. The lens system 72 has a single lens or multiple single lenses (four single lenses 72a, 72b, 72c and 72d in FIG. 4A). Typically, the single lens is made of glass or resin. The optical filter included in the filter system 73 is not particularly limited. The filter system 73 may, for example, include at least one of a low-pass filter and an infrared cutoff filter. The housing 71 has, for example, an opening formed around the optical axis of the lens system 72. This opening is covered by a cover 75. The cover 75 is preferably made of glass. The cover 75 can withstand collisions with objects outside the housing 71 and variations in environmental conditions of the imaging device 70a.

[0059] As shown in Figures 4A and 4B, for example, in the imaging device 70a, at least one single lens included in the lens system 72 has a film 1. When a single lens has a film 1, the film 1 may be disposed on only one side of the single lens or on both sides of the single lens. For example, single lens 72b has a film 1. When the lens system 72 contains multiple single lenses, the single lens to which the film 1 should be formed is appropriately determined. Although the figures are omitted, the lens system 72 may contain a bonded lens formed by bonding multiple single lenses together, and the film 1 may be disposed on only one or both sides of the bonded lens. Furthermore, typically, the film 1 is formed by coating and drying the liquid composition described above. Therefore, when a single lens has a surface with a small radius of curvature, it is possible that the slope of the lens surface is absorbed, the liquid composition coated to form the film 1 flows, and thus the thickness of the film 1 is not uniform in space. However, by adjusting the coating and drying conditions of the liquid components, the spatial non-uniformity of the thickness of film 1 can be reduced.

[0060] The camera device 70a can also be modified like the camera device 70b shown in FIG5A. Except for the parts specifically described, the camera device 70b is constructed in the same way as the camera device 70a. The same symbols are used for the constituent elements that are the same as or correspond to those of the camera device 70a, and detailed descriptions are omitted. The description of the camera device 70a is also applicable to the camera device 70b as long as it is not technically contradictory.

[0061] As shown in FIG. 5A, in the imaging device 70b, for example, the cover portion 75 includes a film 1. For example, the film 1 is formed on one main surface of the glass plate 75a of the cover portion 75. For example, the cover portion 75 is arranged such that the film 1 faces the interior of the housing 71. This prevents the film 1 from deteriorating and peeling. As shown in FIG. 5B, a dielectric multilayer film 75b (an anti-reflective film) may also be formed on the other main surface of the glass plate 75a of the cover portion 75.

[0062] In both imaging devices 70a and 70b, at least one optical filter included in the filter system 73 may also have a membrane 1. In this case, the membrane 1 may be omitted from the single lens of the lens system 72 of the imaging device 70a and the cover 75 of the imaging device 70b. The optical filter with membrane 1 in the filter system 73 can be either a low-pass filter or an infrared cutoff filter. The membrane 1 is disposed on the surface of the optical filter. By means of the infrared cutoff filter, the spectrum of light that can be received in the solid-state imaging element 74 containing semiconductors can be made close to the human visibility curve (spectrum). For example, the infrared cutoff filter has the function of filtering (blocking) infrared light with wavelengths of at least 700 to 1000 nm.

[0063] The infrared cutoff filter included in the filter system 73 may, for example, include an infrared-absorbing glass, an infrared-reflective film composed of a dielectric multilayer film, an infrared-absorbing film, or a combination thereof. The infrared-absorbing glass may, for example, be a glass containing copper phosphate or copper fluorophosphate. The infrared-absorbing film is a film in which a pigment or dye that absorbs infrared light is dispersed in a matrix resin. For example, such an infrared cutoff filter may include film 1. For example, the filter system 73 includes the infrared cutoff filter 73x shown in FIG. 6. The infrared cutoff filter 73x may, for example, include an infrared-absorbing glass 73a, an infrared-absorbing film 73b, and a pair of films 1. The infrared-absorbing glass 73a has a plate-like or sheet-like shape, and the infrared-absorbing film 73b is formed on one of the main surfaces of the infrared-absorbing glass 73a. Furthermore, the pair of films 1 may, for example, be formed in a manner that forms both main surfaces of the infrared cutoff filter 73x.

[0064] The imaging device equipped with the above-mentioned optical elements can be a digital camera (digital still camera and digital camcorder), other than the camera module of an information terminal such as a smartphone. Such an imaging device may, for example, have the optical system 80 shown in FIG7. Furthermore, FIG7 may not accurately show the shape and size of each part in the actual object, as well as the relative positional relationship of each part. The optical system 80 may, for example, have multiple single lenses 81, 82, 83, 84 and 85. For example, a film 1 is formed on both sides of the single lens 82. Although the figure is omitted, the optical system 80 may contain a bonded lens formed by bonding multiple single lenses together, or the film 1 may be disposed on only one or both sides of the bonded lens.

[0065] In the imaging device 70a, imaging device 70b, and optical system 80, a lens system can also be constructed by combining a "lens having a film 1" with a "lens having an anti-reflective film composed of a dielectric multilayer film or an anti-reflective structure composed of a moth-eye structure". Example

[0066] The present invention will be described in more detail through embodiments. Furthermore, the present invention is not limited to the following embodiments. First, the anti-reflection structures of the embodiments and comparative examples, and the evaluation methods of the low refractive index films of the embodiments and comparative examples, will be described.

[0067] [Analysis using ATR method] The absorption spectra of the low-refractive-index films of each example and comparative example were determined by ATR method using a Fourier transform infrared spectrophotometer (PerkinElmer, product name: Frontier Gold). In each example and Comparative Example 1, 1-10 mg of powder samples obtained by peeling off the low-refractive-index film deposited on a substrate were used to measure the absorption spectra of the low-refractive-index films of each example and comparative example. The results of the absorption spectra of the low-refractive-index films of Example 1 and Comparative Example 1 are shown in Figures 8 and 9, respectively.

[0068] In the absorption spectra of the low-refractive-index films of each embodiment and Comparative Example 1, the maximum absorbance value originating from the absorption bands of hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms appears in the wavenumber range of 910 ± 50 cm⁻¹. Furthermore, the maximum absorbance value originating from the absorption band of the bond between silicon atoms and methyl groups appears in the wavenumber range of 1276 ± 50 cm⁻¹. Also, the maximum absorbance value originating from the absorption band of the bond between silicon atoms and hydroxyl groups appears in the wavenumber range of 3438 ± 50 cm⁻¹. Moreover, the maximum absorbance value originating from the absorption band of the bond between one oxygen atom and two silicon atoms (siloxane bond) appears in the wavenumber ranges of 455 ± 50 cm⁻¹, 780 ± 50 cm⁻¹, and 1065 ± 50 cm⁻¹. In Figures 8 and 9, symbol a indicates the absorption band originating from hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms, symbol b indicates the absorption band originating from the bond between silicon atoms and methyl groups, and symbol c indicates the absorption band originating from the bond between silicon atoms and hydroxyl groups. From the short wavenumber side, symbols d, e, and f sequentially indicate the absorption band originating from the bond between one oxygen atom and two silicon atoms. Furthermore, in Figure 8, the absorption bands originating from hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms and the absorption bands originating from the bond between silicon atoms and methyl groups are magnified and displayed in magnified sections (1) and (2), respectively.

[0069] In the absorption spectra of the low-refractive-index films of each embodiment and Comparative Example 1, the absorbance Ia originating from hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms is determined as follows. In the absorption bands originating from hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms, a baseline is determined as shown in the enlarged portion (1) of FIG8. The absorbance Ia is determined by subtracting the absorbance on the baseline line from the maximum absorbance value. In other words, if the maximum absorbance value is represented as Amax (CH3 and CH2), and the absorbance on the baseline line of the wavenumber where the maximum absorbance value appears is represented as absorbance Abase (CH3 and CH2), then the absorbance Ia is determined by the following (Equation 5). Ia = Amax (CH3 and CH2) - Abase (CH3 and CH2) (Equation 5)

[0070] In the absorption spectra of the low-refractive-index films of each embodiment and Comparative Example 1, the absorbance Ib originating from the bond between silicon atoms and methyl groups (Si-CH3) is determined in the same manner as absorbance Ia. As shown in the enlarged portion (2) of FIG8, a baseline is determined by subtracting the absorbance on the baseline line of the wavenumber in which the absorbance maximum occurs from the maximum absorbance value, and the absorbance Ib is obtained. In other words, if the maximum absorbance value is represented as Amax(Si-CH3), and the absorbance on the baseline line of the wavenumber in which the absorbance maximum occurs is represented as Abase(Si-CH3), then the absorbance Ib is determined by the following (Equation 6). Ib = Amax(Si-CH3) - Abase(Si-CH3) (Equation 6)

[0071] In the absorption spectra of the low-refractive-index films of each embodiment and Comparative Example 1, the maximum value of absorbance in the absorption band originating from the bond between silicon atoms and hydroxyl groups (Si-OH) is determined as the absorbance Ic originating from that bond. When determining the absorbance Ic, no correction using a reference line is performed.

[0072] In the absorption spectra of the low-refractive-index films of each embodiment and Comparative Example 1, the three maxima of absorbance originating from the bond between one oxygen atom and two silicon atoms (Si-O-Si) are determined as the first absorbance Id, the second absorbance Ie, and the third absorbance If originating from this bond. Among the first absorbance Id, the second absorbance Ie, and the third absorbance If, ​​the first absorbance Id corresponds to the minimum wavenumber, and the third absorbance If corresponds to the maximum wavenumber. Furthermore, no correction using a reference line is performed when determining the first absorbance Id, the second absorbance Ie, and the third absorbance If.

[0073] In the low-refractive-index films of each embodiment and Comparative Example 1, based on the absorbance Ia, absorbance Ib, absorbance Ic, first absorbance Id, second absorbance Ie, and third absorbance If determined in the manner described above, the inorganic-organic parameter (D), hydrophobic parameter (H), and first to third network parameters (N1, N2, and N3) were determined according to the following (Equations 7) to (Equations 11). The results are shown in Table 1. Inorganic-organic parameter (D) = Ib / Ia (Equation 7) Hydrophobic parameter (H) = Ib / Ic (Equation 8) First network parameter (N1) = Id / Ib (Equation 9) Second network parameter (N2) = Ie / Ib (Equation 10) Third network parameter (N3) = If / Ib (Equation 11)

[0074] [Evaluation of Film-Forming Properties] When the liquid composition of each embodiment and Comparative Example 1 was coated onto a glass substrate or a substrate made of polycarbonate, and it was confirmed that either an area without liquid composition was coated or the thickness of the low-refractive-index film was uneven, the film-forming properties of the liquid composition were evaluated as "×". Furthermore, when such cases were not confirmed, the film-forming properties of the liquid composition were evaluated as "a". The results are shown in Table 1.

[0075] [Reflectivity] In the anti-reflection structures of each embodiment, the reflectivity (visible light reflectivity) of the visible light region (380-780 nm) of the anti-reflection structure formed by depositing a low refractive index film on a substrate was first measured using a spectrophotometer (manufactured by Hitachi Global Advanced Technology Co., Ltd., product name: U-4000), and calculated based on this spectrophotometric reflectivity according to Japanese Industrial Standard (JIS) R 3106:1998. In the measurement of this spectrophotometric reflectivity, the reflection angle was set to 12°. The spectrophotometric reflectivity of the anti-reflection structures of Examples 1, 7, 10 and 11 is shown in Figure 10, and the spectrophotometric reflectivity spectra of the anti-reflection structures of Examples 12 and 13 are shown in Figure 11. Furthermore, the visible light reflectivity of the anti-reflection structures of each embodiment is shown in Table 1.

[0076] [Refractive Index] Except for using a silicon substrate as the substrate, low-refractive-index films of each embodiment were formed under the same conditions as those used in the fabrication of the anti-reflection structures of each embodiment, and samples for refractive index measurement of each embodiment were prepared. The reflectance of the samples for refractive index measurement of each embodiment was measured using a spectrophotometer (manufactured by Hitachi Global Advanced Technology Co., Ltd., product name: U-4000), and the refractive index of the low-refractive-index films of each embodiment was determined according to the reflectance spectroscopy method. The results are shown in Table 1.

[0077] <Example 1> 0.6 g of tetraethoxysilane (TEOS) (manufactured by Tokyo Chemical Industry Co., Ltd.), 1.18 g of methyltriethoxysilane (MTES) (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.82 g of 0.3% formic acid (manufactured by Kishida Chemical Co., Ltd.), 3 g of sol of hollow silica particles (manufactured by Nichibukai Chemical Co., Ltd., product name: Surulia 4110, silica solids content: approximately 25% by weight), and 22.4 g of ethanol (manufactured by Kishida Chemical Co., Ltd.) were mixed and reacted at 35°C for 3 hours. The liquid composition of Example 1 was obtained in this manner. In the sol of hollow silica particles, the average particle size of the hollow silica particles is approximately 50 nm, the thickness of the shell formed by silica is 10–20 nm, the maximum size of the internal space of the hollow silica particles is approximately 10–30 nm, and the refractive index of the hollow silica particles is 1.25. The solid component of the liquid composition of Example 1 contains 0.6 wt% of TEOS-derived silica, 1.6 wt% of MTES-derived polymethylsilsesquioxane, and 2.6 wt% of hollow silica particles. The mass ratio of MTES added to the liquid composition of Example 1 to the mass ratio of TEOS is 7 / 3. The weight ratio of the hollow silica particles to the total weight of the solid components of TEOS-derived silica and MTES-derived polymethylsilsesquioxane is 1.3 / 1.1.

[0078] A glass substrate (float glass, dimensions: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) was cleaned using an ultrasonic cleaner for 15 minutes in ultrapure water, 15 minutes in a commercially available alkaline cleaning solution, and 15 minutes in ultrapure water. The liquid composition of Example 1 was then applied to both main surfaces of the cleaned glass substrate using a spin-coating method. The appearance immediately after coating was good, and a uniform coating was obtained. The coating was then dried in an oven at 200°C for 10 minutes to obtain the low-refractive-index film of Example 1. Thus, the anti-reflective structure of Example 1, comprising a glass substrate and a low-refractive-index film formed on the glass substrate, as shown in FIG. 2, was obtained. The appearance of the low-refractive-index film of Example 1 was observed, and it exhibited a uniform thickness. The thickness of the low-refractive-index film of Example 1 was 120 nm. In the adhesive for the low refractive index film of Example 1, the mass ratio of polymethylsilsesquioxane to silicon dioxide is 7 / 3.

[0079] <Examples 2-5> In preparing the liquid compositions, the mass ratio of methyltriethoxysilane (MTES) to tetraethoxysilane (TEOS) was adjusted as shown in Table 1. Otherwise, the liquid compositions of Examples 2-5 were obtained in the same manner as in Example 1. The low-refractive-index films of Examples 2-5 and the anti-reflective structures of Examples 2-5 were fabricated in the same manner as in Example 1, except that the liquid compositions of Examples 2-5 were used instead of the liquid composition of Example 1. The liquid compositions of Examples 2-5 all exhibit good film-forming properties.

[0080] <Examples 6-9> In preparing the liquid compositions, the mass of methyltriethoxysilane (MTES) relative to the mass of tetraethoxysilane (TEOS) was adjusted as shown in Table 1. Otherwise, the liquid compositions of Examples 6-9 were obtained in the same manner as in Example 1. A substrate made of polycarbonate (PC) (size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.59) was used instead of a glass substrate, and the liquid compositions of Examples 6-9 were used instead of the liquid composition of Example 1. Otherwise, the low refractive index films of Examples 6-9 and the anti-reflective structures of Examples 6-9 were fabricated in the same manner as in Example 1.

[0081] <Examples 10 and 11> A core-shell structure particles were formed by forming a shell of magnesium fluoride around a core formed of silicon dioxide. The silicon dioxide core of the particles was dissolved in an alkaline solution to produce hollow magnesium fluoride particles. In the hollow magnesium fluoride particles, the average particle size was about 50 nm, the thickness of the shell formed of magnesium fluoride was about 10 nm, the maximum size of the internal space was about 30 nm, and the refractive index of the hollow particles was 1.20. Except that the hollow magnesium fluoride particles were used instead of the hollow silicon dioxide particles, the liquid compositions of Examples 10 and 11 were obtained in the same manner as in Example 1. In addition, except that the liquid composition of Example 10 was used instead of the liquid composition of Example 1, the low refractive index film of Example 10 and the anti-reflection structure of Example 10 were produced in the same manner as in Example 1. Furthermore, except that the liquid composition of Example 11 was used instead of the liquid composition of Example 7, the low refractive index film of Example 11 and the anti-reflection structure of Example 11 were fabricated in the same manner as in Example 7. The thickness of the low refractive index film of Example 10 and the thickness of the low refractive index film of Example 11 are 118 nm.

[0082] <Example 12> A coating composition was prepared in the same manner as the liquid composition of Example 1, except that no hollow silicon dioxide particles were added to the sol. The coating composition was applied to both main surfaces of a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) that had been pre-cleaned by alkali cleaning using a spin coating method. Next, the coating film was dried in an oven at 200°C for 10 minutes to form an inner low-refractive-index film. The refractive index of the inner low-refractive-index film was 1.46, and the thickness of the inner low-refractive-index film was 260 nm. The liquid composition of Example 1 was then applied to the inner low-refractive-index film using a spin coating method. Next, the liquid composition coating was dried in an oven at 200°C for 10 minutes to form the low refractive index film of Example 12, thereby fabricating the anti-reflective structure of Example 12 as shown in FIG. 3A. The thickness of the low refractive index film of Example 12 is 95 nm. The coating composition has good film-forming properties on the glass substrate, and the liquid composition of Example 1 has good film-forming properties on the inner low refractive index film.

[0083] <Example 13> The antireflective structure of Example 13 was fabricated in the same manner as in Example 12, except that the liquid composition of Example 10 was used instead of the liquid composition of Example 10. The liquid composition of Example 10 has good film-forming properties for the inner low refractive index film.

[0084] <Example 14> Except for changing the thickness of the low refractive index film to 180 nm, the low refractive index film of Example 14 and the anti-reflection structure of Example 14 were fabricated in the same manner as in Example 1. The liquid composition of Example 1 also has good film-forming properties when the film thickness is 180 nm.

[0085] <Example 15> On one main surface of a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) after being cleaned in the same manner as in Example 1, the liquid composition used in Example 1 was coated by spin coating. The coating was then dried in an oven at 200°C for 10 minutes to form a low refractive index film with a thickness of 100 nm. Furthermore, on the other main surface of the glass substrate, the liquid composition used in Example 1 was coated by spin coating. The coating was then dried in an oven at 200°C for 10 minutes to form a low refractive index film with a thickness of 180 nm, thereby fabricating the low refractive index film of Example 15 and the anti-reflective structure of Example 15 as shown in FIG. 2. The liquid composition of Example 1 also exhibits good film-forming properties in this case.

[0086] <Example 16> On both main surfaces of a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) after being cleaned in the same manner as in Example 1, the liquid composition used in Example 1 was coated by spin coating. The coating was then dried in an oven at 200°C for 10 minutes to form a third low-refractive-index film with a thickness of 30 nm. Next, on the third low-refractive-index film, the coating composition used in Example 12 was coated by spin coating. The coating was then dried in an oven at 200°C for 10 minutes to form a second low-refractive-index film with a thickness of 40 nm. Furthermore, the liquid composition of Example 1 was applied to the second low-refractive-index film by spin coating, and then the coating was dried in an oven at 200°C for 10 minutes to form a first low-refractive-index film with a thickness of 30 nm, thereby fabricating the anti-reflective structure of Example 16 as shown in FIG. 3B. The liquid composition of Example 1 also exhibits good film-forming properties for glass substrates or low-refractive-index films in this case, and the coating composition of Example 12 exhibits good film-forming properties for low-refractive-index films.

[0087] <Comparative Example 1> In preparing the liquid composition, the mass ratio of methyltriethoxysilane (MTES) to tetraethoxysilane (TEOS) was adjusted as shown in Table 1. Otherwise, the liquid composition of Comparative Example 1 was obtained in the same manner as in Example 1. Except that the liquid composition of Comparative Example 1 was used instead of the liquid composition of Example 1, the low refractive index film and the anti-reflection structure of Comparative Example 1 were prepared in the same manner as in Example 1. Observing the appearance of the low refractive index film of Comparative Example 1, it was clearly confirmed that the thickness of the low refractive index film was uneven.

[0088] As shown in Table 1, the visible light reflectance of the anti-reflection structures of Examples 1-5 is 1.6% or less. The visible light reflectance of the anti-reflection structures of Examples 6-9 is 1.3% or less. The visible light reflectance of the anti-reflection structures of Examples 10 and 11 is 1.1% or less. The visible light reflectance of the anti-reflection structures of Examples 12 and 13 is 0.2% or less. Thus, it can be confirmed that the anti-reflection structures of each embodiment can exhibit high anti-reflection performance. Furthermore, as shown in FIG10, the spectral reflectance of the anti-reflection structures of Examples 1, 7, 10, and 11 is 5% or less in the entire visible light region (wavelength range of 380 nm to 780 nm). Also, as shown in FIG11, the spectral reflectance of the anti-reflection structure of Example 12 is 4% or less in the entire visible light region, and the spectral reflectance of the anti-reflection structure of Example 13 is 3% or less in the entire visible light region.

[0089] As shown in Table 1, the visible light reflectance of the anti-reflection structure of Example 14 is 4.2%. Furthermore, as shown in Figure 12, the spectral reflectance of the anti-reflection structure of Example 14 is less than 8.5% in the entire visible light region, and the average spectral reflectance in the near-infrared region (wavelength 800 nm to 2500 nm), specifically in the wavelength range of 800 nm to 1000 nm, is 0.4%, and the average spectral reflectance in the wavelength range of 800 nm to 1100 nm is 0.6%.

[0090] As shown in Table 1, the visible light reflectance of the anti-reflection structure of Example 15 is 2.3%. Furthermore, as shown in Figure 12, the spectral reflectance of the anti-reflection structure of Example 15 is less than 4.8% in the entire visible light region, and the average spectral reflectance in the near-infrared region, specifically in the wavelength range of 800 nm to 1000 nm (close to the visible light region), is 2.2%, and the average spectral reflectance in the wavelength range of 800 nm to 1100 nm is 2.4%.

[0091] As shown in Table 1, the visible light reflectance of the anti-reflection structure of Example 16 is 0.7%. Furthermore, as shown in Figure 12, the spectral reflectance of the anti-reflection structure of Example 16 is less than 3.5% in the entire visible light region, and the average spectral reflectance in the near-infrared region, specifically in the wavelength range of 800 nm to 1000 nm (close to the visible light region), is 3.3%, and the average spectral reflectance in the wavelength range of 800 nm to 1100 nm is 3.6%.

[0092] [Table 1] substrate Composition of anti-reflective structure Materials of hollow particles Mass ratio of silane compounds Inorganic and organic parameters (D) Hydrophobic parameters (H) First network parameter (N1) Second network parameters (N2) Third network parameter (N3) Refractive index of low refractive index film Film-forming properties Visible light reflectance [%] MTES TEOS Example 1 Glass single layer Silicon dioxide 7 3 1.1 0.6 17 8 41 1.19 a 1.4 Example 2 Glass single layer Silicon dioxide 5 5 1.5 0.5 twenty two 9 55 1.18 a 1.4 Example 3 Glass single layer Silicon dioxide 10 0 1.2 1.2 7 6 11 1.20 a 1.6 Example 4 Glass single layer Silicon dioxide 9 1 1.0 1.6 9 6 18 1.20 a 1.5 Example 5 Glass single layer Silicon dioxide 3 7 0.7 0.3 60 20 174 1.18 a 1.5 Example 6 PC single layer Silicon dioxide 6 4 1.3 0.5 20 9 48 1.19 a 1.2 Example 7 PC single layer Silicon dioxide 8 2 1.2 0.8 17 8 25 1.19 a 1.2 Example 8 PC single layer Silicon dioxide 10 0 1.2 1.2 7 6 11 1.19 a 1.1 Example 9 PC single layer Silicon dioxide 4 6 1.7 0.5 27 10 67 1.18 a 1.3 Example 10 Glass single layer MgF2 7 3 1.2 0.5 18 9 43 1.17 a 0.8 Example 11 PC single layer MgF2 7 3 1.3 0.6 16 9 41 1.17 a 1.1 Example 12 Glass 2nd floor Silicon dioxide 7 3 1.0 0.8 17 8 40 1.19 a 0.2 Example 13 Glass 2nd floor MgF2 7 3 1.2 0.6 19 8 42 1.17 a 0.2 Example 14 Glass single layer Silicon dioxide 7 3 1.1 0.7 19 8 46 1.19 a 4.2 Example 15 Glass single layer Silicon dioxide 7 3 1.1 0.7 18 8 44 1.19 a 2.3 Example 16 Glass 3 floors Silicon dioxide 7 3 1.2 0.8 19 9 47 1.19 a 0.7 Comparative Example 1 Glass single layer Silicon dioxide 2 8 0.5 0.2 73 twenty two 196 - × 5.3 [Simplified Explanation of the Diagram]

[0013] [Fig. 1] is a cross-sectional view conceptually illustrating the structure of one example of the film of the present invention. [Fig. 2] is a cross-sectional view illustrating an example of an anti-reflection structure formed by low-refractive-index coating using the film of the present invention. [Fig. 3A] is a cross-sectional view illustrating another example of an anti-reflection structure formed by low-refractive-index coating using the film of the present invention. [Fig. 3B] is a cross-sectional view illustrating yet another example of an anti-reflection structure formed by low-refractive-index coating using the film of the present invention. [Fig. 4A] is a cross-sectional view illustrating an example of the imaging device of the present invention. [Fig. 4B] is a side view of the single lens shown in Fig. 4A. [Fig. 5A] is a cross-sectional view illustrating another example of the imaging device of the present invention. [Fig. 5B] is a cross-sectional view illustrating an example of the cover portion of the imaging device. [Fig. 6] is a cross-sectional view illustrating an example of an infrared cutoff filter of the imaging device. [Fig. 7] is a side view illustrating the optical system in yet another example of the imaging device of the present invention. [Figure 8] is a graph showing the absorption spectrum of the membrane of Example 1 obtained by the ATR method. [Figure 9] is a graph showing the absorption spectrum of the membrane of Comparative Example 1 obtained by the ATR method. [Figure 10] is a graph showing the reflection spectrum of the antireflection structures of Examples 1, 7, 10 and 11. [Figure 11] is a graph showing the reflection spectrum of the antireflection structures of Examples 12 and 13. [Figure 12] is a graph showing the reflection spectrum of the antireflection structures of Examples 14, 15 and 16.

Claims

1. An antireflective film comprising a first layer, characterized in that: the first layer comprises: hollow particles having an average primary particle size of 10 to 150 nm and a refractive index of 1.10 to 1.40, and an adhesive containing polysilsesquioxane to bind the hollow particles; the first layer has a thickness of 50 to 300 nm and a refractive index of 1.25 or less; the mass ratio of the hollow particles to the adhesive is in the range of 1 / 5 to 20; and the polysilsesquioxane is a polysilsesquioxane containing hydrocarbon groups with 16 or fewer carbon atoms as non-reactive functional groups bonded to silicon atoms.

2. As in claim 1, the antireflective film, wherein, The aforementioned adhesive further comprises silicon dioxide.

3. The antireflective film as requested in item 1 or 2, wherein, The aforementioned hollow particles include materials having a refractive index of 1.15 to 2.

70.

4. The antireflective film as requested in item 1 or 2, wherein, In the first layer mentioned above, when the absorbance derived from hydrocarbon groups not directly bonded to silicon atoms, the absorbance derived from the bond between silicon atoms and non-reactive functional groups, and the absorbance derived from the bond between silicon atoms and hydroxyl groups, determined by total reflectance measurement using a Fourier transform infrared spectrophotometer, are expressed as Ia, Ib, and Ic respectively, at least one of the conditions Ib / Ia≧0.7 and Ib / Ic≧0.3 must be satisfied.

5. The antireflective film of claim 4 further satisfies the conditions Ib / Ia≧0.7 and Ib / Ic≧0.

3.

6. As in claim 4, the antireflective film, wherein, In the first layer described above, when the first absorbance, second absorbance, and third absorbance, which are determined by the total internal reflection measurement method and originate from the bond between one oxygen atom and two silicon atoms, are represented as Id, Ie, and If respectively, at least one of the following conditions must be satisfied: Id / Ib≦60, Ie / Ib≦20, and If / Ib≦174. The first absorbance Id corresponds to the first wavenumber, the second absorbance Ie corresponds to the second wavenumber which is greater than the first wavenumber, and the third absorbance If corresponds to the third wavenumber which is greater than the second wavenumber.

7. The antireflective film of claim 6 further satisfies the conditions Id / Ib≦60, Ie / Ib≦20 and If / Ib≦174.

8. The antireflective film as requested in item 1 or 2, wherein, The aforementioned hollow particles are formed from at least one of the following groups: silicon dioxide, magnesium fluoride, aluminum oxide, aluminum silicate, titanium dioxide, and zirconium oxide.

9. The antireflective film of claim 1 or 2 further comprises a second layer having a thickness of 30 to 300 nm and a refractive index greater than 1.5 and less than 1.

8.

10. The antireflective film of claim 9 further comprises a third layer having a thickness of 30 to 300 nm and a refractive index greater than 1.

8.

11. A lens having an antireflective coating of claim 1 or 2 disposed on its surface.

12. A camera device comprising the lens of claim 11.

13. A liquid composition comprising: an adhesive component containing a trifunctional alkoxysilane or a hydrolysate of the aforementioned trifunctional alkoxysilane, and hollow particles having an average primary particle size of 10 to 150 nm and a refractive index of 1.10 to 1.40; wherein the hollow particles are in a mass ratio of 1 / 5 to 20 of the adhesive obtained from the aforementioned adhesive component, and the film formed by the liquid composition has a refractive index of 1.25 or less.

14. The liquid composition as claimed in claim 13, wherein, The adhesive components further include: tetrafunctional alkoxysilanes or hydrolyzed products of the aforementioned tetrafunctional alkoxysilanes.

15. The liquid composition as claimed in claim 13 or 14, wherein, In the film formed by the above liquid composition, when the absorbance derived from hydrocarbon groups not directly bonded to silicon atoms, the absorbance derived from the bonding between silicon atoms and non-reactive functional groups, and the absorbance derived from the bonding between silicon atoms and hydroxyl groups are expressed as Ia, Ib, and Ic respectively, determined by total reflectance measurement using a Fourier transform infrared spectrophotometer, at least one of the following conditions must be satisfied: Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.

3.

16. The liquid composition of claim 15 further satisfies the conditions Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.

3.

17. The liquid composition as claimed in claim 15, wherein, In the film formed by the above-mentioned liquid composition, when the first absorbance, second absorbance and third absorbance, which are determined by the above-mentioned total internal reflection measurement method and originating from the bond between 1 oxygen atom and 2 silicon atoms, are represented as Id, Ie and If respectively, at least one of the following conditions is satisfied: Id / Ib≦60, Ie / Ib≦20 and If / Ib≦174. The first absorbance Id corresponds to the first wavenumber, the second absorbance Ie corresponds to the second wavenumber which is greater than the first wavenumber, and the third absorbance If corresponds to the third wavenumber which is greater than the second wavenumber.

18. The liquid composition of claim 17 further satisfies the conditions Id / Ib≦60, Ie / Ib≦20 and If / Ib≦174.

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