Anti-reflection film, method for manufacturing anti-reflection film, lens, and imaging device

Abstract

To provide a film that is advantageous for low refractive index coating, without requiring an organosilane compound having a fluoroalkyl group.SOLUTION: A film (1) includes hollow particles (10) and a binder (20). The hollow particles are made of a material having a refractive index of 1.15 to 2.70. The binder (20) is formed of at least a polysilsesquioxane and binds the hollow particles (10). The film (1) satisfies at least one of conditions Ib / Ia≥0.7 and Ib / Ic≥0.3. Ia is an absorbance derived from a hydrocarbon group not directly bonded to a silicon atom, the absorbance being determined by attenuated total reflection using a Fourier transform infrared spectrophotometer. Ib is an absorbance derived from a bond between a silicon atom and a non-reactive functional group. Ic is an absorbance derived from a bond between a silicon atom and a hydroxy group.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a film and a liquid composition advantageous for a low refractive index coating. In addition, the present invention relates to an optical element and an imaging device.

Background Art

[0002] Conventionally, coating with a material having a low refractive index (low refractive index coating) from the viewpoint of antireflection, and a composition for low refractive index coating are known.

[0003] For example, Patent Documents 1 and 2 describe an antireflection coating composition. This coating composition includes a binder formed by polymerizing a predetermined silane compound and an organosilane compound having a fluoroalkyl group, and hollow silica particles. In addition, Patent Documents 1 and 2 describe an antireflection film including a low refractive index layer formed by coating the surface of a substrate with this coating composition.

[0004] Patent Document 3 describes an antireflection film having a laminated structure of a transparent substrate, a high refractive index layer, and a low refractive index layer. The low refractive index layer includes a binder formed by polymerizing a predetermined silane compound and an organosilane compound having a fluoroalkyl group, and hollow silica particles.

[0005] Patent Document 4 describes an optical member having an antireflection film and a method for manufacturing the same. The manufacturing method includes a step of coating a dispersion containing particles and a dispersion medium on a substrate. The manufacturing method further includes a step of coating a solution containing a component for forming a binder after the step of coating the dispersion, and infiltrating the solution between the particles contained in the previously coated dispersion to form a single layer in which the binder is filled between the particles. The manufacturing method further includes a step of drying the layer to produce an antireflection film. The solution contains a silane alkoxy condensate having an average particle diameter of 8 nm or more and 60 nm or less, and contains 70% by mass or more of a solvent having a water solubility of 10% by weight or less.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention provides an antireflection structure having high antireflection properties.

Means for Solving the Problems

[0008] The present invention includes a first layer containing hollow particles having an average primary particle diameter of 10 to 150 nm and having a thickness of 80 to 350 nm and a refractive index of 1.25 or less, and a second layer having a thickness of 30 to 300 nm and a refractive index of 1.5 or less See The hollow particles have a refractive index of 1.15 to 2.70, The first layer contains polysilsesquioxane and a binder that binds the hollow particles, When the absorbance derived from a hydrocarbon group not directly bonded to a silicon atom, the absorbance derived from the bond between a silicon atom and a non-reactive functional group, and the absorbance derived from the bond between a silicon atom and a hydroxy group, which are determined by the total reflection measurement method using a Fourier transform infrared spectrophotometer, are represented by Ia, Ib, and Ic, respectively, the first layer satisfies at least one of the conditions of Ib / Ia ≧ 0.7 and Ib / Ic ≧ 0.3. provides an antireflection film.

[0009] Moreover, the present invention is a method for manufacturing an antireflection film, including applying a first liquid composition that is a precursor of the first layer and a second liquid composition that is a precursor of the second layer to an optical element. The first liquid composition contains an alkoxysilane represented by the following formula and hollow particles, and provides the above method for manufacturing an antireflection film. (Formula) R b Si(OR c ) 3 (R b represents a non-reactive functional group, and R crepresents an alkyl group.)

[0010] In addition, the present invention A lens provided with the above antireflection film provides.

[0011] In addition, the present invention An imaging device provided with the above lens provides.

Advantages of the Invention

[0012] The above antireflection film can have high antireflection properties.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 3B

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Figure 12

Mode for Carrying Out the Invention

[0014] According to the techniques described in Patent Documents 1 to 3, an organosilane compound having a fluoroalkyl group is required. For this reason, the inventors considered that in the techniques described in Patent Documents 1 to 3, when the coating solution contains water as a solvent (dispersion medium), phase separation occurs in the coating solution due to the water repellency of the fluoroalkyl group. Therefore, according to the techniques of Patent Documents 1 to 3, the inventors considered that it is necessary to add an additive such as a surfactant to obtain a uniform coating solution. In addition, the inventors considered that the techniques described in Patent Documents 1 to 3 have low wettability of the coating solution with respect to a hydrophilic glass substrate and a hydrophobic (lipophilic) resin substrate due to the water repellency and oil repellency of the fluoroalkyl group, and the coating solution is likely to be repelled on the substrate during coating of the coating solution on the substrate. Further, the inventors considered that according to the technique described in Patent Document 4, it is necessary to infiltrate a solution containing a silane alkoxy condensate between particles after a dispersion liquid containing particles is coated, which requires a complicated process. Therefore, the inventors repeatedly studied day and night to develop a film advantageous for a low refractive index coating that does not require an organosilane compound having a fluoroalkyl group. As a result, the inventors devised the film according to the present invention. In addition, the inventors devised a liquid composition that does not require an organosilane compound having a fluoroalkyl group and can easily achieve a low refractive index coating.

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following description relates to an example of the present invention, and the present invention is not limited to what is described below.

[0016] As shown in FIG. 1, the film 1 includes hollow particles 10 and a binder 20. The hollow particles 10 are made of a material having a refractive index of 1.15 to 2.70. The binder 20 is formed of at least polysilsesquioxane and binds the hollow particles 10. In the film 1, the absorbance derived from a hydrocarbon group not directly bonded to a silicon atom, the absorbance derived from the bond between a silicon atom and a non-reactive functional group, and the absorbance derived from the bond between a silicon atom and a hydroxy group, which are determined by the total reflection measurement method (ATR method) using a Fourier transform infrared spectrophotometer, are represented by Ia, Ib, and Ic, respectively. The film 1 satisfies at least one of the conditions of 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). The absorbance Ia, the absorbance Ib, and the absorbance Ic can be determined, for example, from the absorption spectrum obtained by the ATR method according to the method described in the examples.

[0017] The organic-inorganic parameter (D) increases as the amount of the hydrocarbon group not directly bonded to the silicon atom contained in the binder 20 decreases. When the amount of the hydrocarbon group not directly bonded to the silicon atom contained in the binder 20 is small, the Si-O-Si network in the binder 20 is dense, and the density of the inorganic component in the binder 20 increases. As a result, 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, and the film 1 has advantageous properties for a low refractive index coating. If the fixing of the hollow particles in the film is not sufficient, the mechanical strength of the film may decrease.

[0018] The hydrophobic parameter (H) increases as the number of hydroxy groups bonded to silicon atoms in the binder 20 decreases. For example, in the raw materials of the binder 20, when the hydroxy groups condense with each other and a network composed of Si-O-Si develops, the number of hydroxy groups bonded to silicon atoms in the binder 20 decreases. If the hydrophobic parameter (H) is equal to or greater than a predetermined value, in the binder 20, a network composed of Si-O-Si 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 the film 1 has characteristics advantageous for low refractive index coating.

[0019] The film 1 preferably further satisfies the conditions of Ib / Ia ≧ 0.7 and Ib / Ic ≧ 0.3. Thereby, the hollow particles 10 are more surely and firmly fixed in the film 1, and the film 1 has characteristics advantageous for low refractive index coating.

[0020] When a silanol group (Si-OH) is present in the binder 20, the silanol group has a high affinity because it forms a hydrogen bond with the silanol group present on the surface of the glass substrate. Therefore, a film with a hydrophobic parameter (H) equal to or less than a predetermined value also easily adheres to the glass substrate. The film 1 more preferably satisfies the condition of 0.3 ≦ Ib / Ic ≦ 2.0 so as to exhibit good adhesion to both a substrate having a hydrophilic surface and a substrate having a hydrophobic surface.

[0021] In the film 1, the first absorbance, the second absorbance, and the third absorbance, which are derived from the bond of one oxygen atom and two silicon atoms determined by the ATR method, are represented by Id, Ie, and If, respectively. The first absorbance Id corresponds to the first wave number. The second absorbance Ie corresponds to the second wave number that is larger than the first wave number. The third absorbance If corresponds to the third wave number that is larger than the second wave number. The film 1 preferably satisfies at least one of the conditions of 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 wave number is, for example, the wave number at which the maximum value of the absorption spectrum appears at 455±50 cm -1 The second wave number is, for example, the wave number at which the maximum value of the absorption spectrum appears at 780±50 cm -1 The third wave number is, for example, the wave number at which the maximum value of the absorption spectrum appears at 1065±50 cm -1 The wave number at which the maximum value of the absorption spectrum appears.

[0023] The first network parameter (N1), the second network parameter (N2), and the third network parameter (N3) are larger as the number of bonds (Si-O-Si) between an oxygen atom and two silicon atoms in the binder 20 is greater. The more the Si-O-Si network formed by the condensation of hydroxyl groups in the raw material of the binder 20 develops, 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 the hollow particles and keep the thickness of the coating film uniform. To suppress the aggregation of the hollow particles, it is desirable to prevent excessive development of the Si-O-Si network. From such a perspective, in the film 1, it is desirable that at least one of N1 being 60 or less, N2 being 20 or less, and N3 being 174 or less is satisfied. Thereby, the film 1 can be formed well, and an antireflection structure having good antireflection performance can be provided by the film 1.

[0024] The film 1 more preferably further satisfies the conditions of Id / Ib ≦ 60, Ie / Ib ≦ 20, and If / Ib ≦ 1 74.

[0025] Typically, the polysilsesquioxane of the binder 20 has a non-reactive functional group bonded to a silicon atom. In order for the polysilsesquioxane of the binder 20 to exhibit an appropriate hydrophobic effect, the non-reactive functional group is a functional group exhibiting hydrophobicity such as an alkyl group. Desirably, the polysilsesquioxane of the binder 20 is a polysilsesquioxane in which a hydrocarbon group containing 16 or fewer carbon atoms is bonded to a silicon atom as a non-reactive functional group. In this case, since the non-reactive functional group is not bulky, the Si-O-Si network is likely to be formed densely.

[0026] The binder 20 may, for example, be further formed of silica. In this case, the polysilsesquioxane contained in the binder 20 tends to exhibit a hydrophobic effect, and the silica contained in the binder 20 tends to exhibit a hydrophilic effect. Therefore, by adjusting the ratio (Mp / Ms) of the amount of substance Mp of the polysilsesquioxane to the amount of substance Ms of the silica in the binder 20, the hydrophilicity or hydrophobicity of the membrane 1 can be adjusted to an appropriate level. Thereby, the membrane 1 can be appropriately formed on a substrate having a hydrophilic surface such as a glass substrate, and the membrane 1 can also be appropriately formed on a substrate having a hydrophobic surface such as a resin. From such a viewpoint, the ratio (Mp / Ms) of the amount of substance Mp of the polysilsesquioxane to the amount of substance Ms of the silica in the binder 20 is, for example, 3 / 7 or more, desirably 1 to 9, and more desirably 3 / 2 to 4.

[0027] The hollow particles 10 are not particularly limited as long as they have a hollow structure. For example, they have a spherical, cylindrical, or sheet-like shape. The hollow particles 10 have, for example, an average particle diameter (primary particle diameter) of 10 to 150 nm. Thereby, the hollow particles 10 are likely to be uniformly dispersed in the membrane 1. The average particle diameter of the hollow particles 10 can be determined, for example, by arithmetically averaging the particle diameters of 50 or more hollow particles 10 observed using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Note that the particle diameter of each particle means the maximum diameter.

[0028] The hollow particles 10 desirably have an average particle diameter of 20 to 100 nm, and more desirably have an average particle diameter of 30 to 70 nm. Note that the maximum dimension of the internal space in the hollow particles 10 is, for example, 5 to 100 nm, desirably 10 to 70 nm, and more desirably 20 to 50 nm. The hollow particles 10 are desirably monodisperse particles having a coefficient of variation of 0.1 or less.

[0029] The material of the hollow particles 10 may be an inorganic material or an organic material as long as it has a refractive index of 1.15 to 2.70. The material of the hollow particles 10 is desirably a material having a refractive index of 1.20 to 2.00, more desirably a material having a refractive index of 1.30 to 1.50, and even more desirably a material having a refractive index of 1.38 to 1.46. From the viewpoint of the difficulty of deformation against external force the hollow particles 10 are desirably made of an inorganic material. In this case, the hollow particles 10 are made of, for example, at least one selected from the group consisting of silica, magnesium fluoride, alumina, aluminosilicate, titania, and zirconia.

[0030] Among them, in order to provide an antireflection structure having high antireflection performance by the low refractive index coating using the film 1, the hollow particles 10 are desirably made of silica or magnesium fluoride. The refractive index of silica is 1.46, and the refractive index of magnesium fluoride is 1.38.

[0031] The structure and material of the hollow particles 10 are determined so that the hollow particles 10 have a desired refractive index. For example, so that the hollow particles 10 have a desired refractive index, the material of the hollow particles 10 and the ratio of the internal space to the total volume of the hollow particles 10 is determined. The hollow particles 10 have, for example, a refractive index of 1.10 to 1.40, desirably a refractive index of 1.20 to 1.35, and more desirably a refractive index of 1.25 to 1.30. For example, in a plurality of types of hollow particles made of materials having different refractive indices, when the ratio of the internal space to the total volume of the hollow particles is the same, the hollow particles made of a low refractive index material have a lower refractive index than the hollow particles made of a high refractive index material.

[0032] The refractive index of the hollow particles 10 can be measured, for example, by the immersion method (Becke line method). For example, when the hollow particles 10 are made of silica, the refractive index of the hollow particles 10 can be measured according to the following procedure. (i) Evaporate and dry the dispersion medium of the dispersion liquid of the hollow particles 10 to obtain a powder. (ii) Mix the powder obtained in (i) with various standard refractive index liquids having different refractive indices such as Series A and Series AA manufactured by GARGILL. (iii) When the mixed liquid obtained in (ii) becomes transparent, determine the refractive index of the standard refractive index liquid used as the refractive index of the hollow particles 10.

[0033] The hollow particles 10 may be commercially available or may be produced by a predetermined method. For example, the hollow particles 10 may be produced by forming a shell around a core and then removing the core. For example, a shell made of silica or a shell made of magnesium fluoride is formed around a polymer core having a particle diameter of several tens of nanometers. Then, the polymer core is removed by dissolution or combustion in a solvent to obtain the hollow particles 10 which are hollow silica particles or hollow magnesium fluoride particles. Also, the hollow particles 10 which are hollow magnesium fluoride particles can be obtained by forming a shell made of magnesium fluoride around a core made of silica and dissolving the core made of silica with an alkali.

[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, from 1 / 5 to 20, desirably from 1 / 3 to 10, and more desirably from 1 to 5. Thereby, an antireflection structure having high antireflection performance can be provided by the low refractive index coating using the film 1.

[0035] The thickness of the film 1 is not particularly limited, but is determined, for example, according to the wavelength of the light to be anti-reflected. Specifically, when the central wavelength of the wavelength of the light to be anti-reflected is λ (nm), the optical thickness (refractive index × physical thickness) of the film 1 is set to satisfy λ / 4. For example, in order to prevent reflection of light belonging to the visible light region (practically wavelengths of 380 nm to 780 nm), when λ, which is the central wavelength, is set to λ = 550 nm and the refractive index of the low refractive index film used is 1.20, the optimum physical thickness is 115 nm. The practically effective thickness of the film 1 for preventing reflection of visible light is 50 to 300 nm, desirably 70 to 200 nm, and more desirably 90 to 170 nm. Thereby, an anti-reflection structure having high anti-reflection performance can be provided by the low refractive index coating using the film 1. Further, in order to prevent reflection of light having a central wavelength of λ = 850 nm, which is close to the visible light region in the near-infrared region (for example, wavelengths of 800 nm to 2500 nm), when the refractive index of the low refractive index film used is 1.20, the optimum physical thickness is 177 nm. The practically effective thickness of the film 1 for preventing reflection of near-infrared light is 80 to 350 nm, desirably 130 to 250 nm, and more desirably 150 to 220 nm. Thereby, an anti-reflection structure having high anti-reflection performance can be provided by the low refractive index coating using the film 1. When a multilayer film is used as the anti-reflection structure, a low refractive index layer having a thickness of 50 nm or less may be used. Further, the physical thickness of the low refractive index film is not limited to these, but its cross section can be measured by SEM, TEM, or an ellipsometer or the like.

[0036] The film 1 has a refractive index of, for example, 1.35 or less. Thereby, an anti-reflection structure having high anti-reflection performance can be provided by the low refractive index coating using the film 1. The film 1 desirably has a refractive index of 1.30 or less, and more desirably 1.25 or less. From the viewpoint of reducing the refractive index of the film 1, the film 1 may contain an air space in the space between the hollow particles 10 or in the binder 20. The refractive index of the film 1 can be determined, for example, by reflection spectroscopy.

[0037] The film 1 is, for example, a cured product obtained by curing a predetermined liquid composition. This liquid composition contains hollow particles, polysilsesquioxane, and a solvent. The hollow particles are made of a material having a refractive index of 1.15 to 2.70. In the cured product obtained by applying the liquid composition to a substrate and curing the liquid composition, at least one of the conditions of 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] In this liquid composition, since an organosilane compound having a fluoroalkyl group is unnecessary, phase separation hardly occurs in the liquid composition, and the liquid composition tends to be uniform. In addition, the wettability of the liquid composition with respect to a glass substrate and a resin substrate is high, and a film 1 having a uniform structure is easily obtained by the liquid composition.

[0039] In the above cured product, desirably, the conditions of Ib / Ia≥0.7 and Ib / Ic≥0.3 are further satisfied.

[0040] In the above cured product, desirably, at least one of the conditions of Id / Ib≤60, Ie / Ib≤20, and If / Ib≤174 is satisfied.

[0041] In the above cured product, more desirably, the conditions of Id / Ib≤60, Ie / Ib≤20, and If / Ib≤174 are further satisfied.

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

[0043] The characteristics of the hollow particles 10 in the film 1 typically also apply to the hollow particles in the liquid composition. Therefore, the hollow particles in the liquid composition have, for example, an average particle diameter (primary particle diameter) of 10 to 150 nm. Further, the hollow particles in the liquid composition are preferably composed of at least one selected from the group consisting of silica, magnesium fluoride, alumina, aluminosilicate, titania, and zirconia.

[0044] The liquid composition may contain, for example, silica in addition to the hollow particles.

[0045] As shown in FIG. 2, for example, the film 1 is formed by applying the liquid composition to the main surface of the substrate 30 and curing the liquid composition. Thereby, an antireflection structure 50a having a low refractive index coating using the film 1 is provided. By using the liquid composition, an organosilane compound having a fluoroalkyl group is not required, and the low refractive index coating can be simplified.

[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. Further, when silica is contained in the liquid composition in addition to the hollow particles, this silica 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 silica (SiO2) by the reactions of the following (Formula 1) and (Formula 2). R a represents an alkyl group. The trifunctional alkoxysilane forms polysilsesquioxane (R b SiO 3 / 2 ) by the reactions of the following (Formula 3) and (Formula 4). R b represents a non-reactive functional group, and R c represents an alkyl group. Si(OR a )4 + 4H2O → Si(OH)4 + 4R a OH (Formula 1) Si(OH)4 → SiO2 + 2H2O (Formula 2) R b Si(OR c )3 + 3H2O → R b Si(OH)3 + 3R c OH (Formula 3) R b Si(OH)3 → R b SiO 3 / 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 a substrate made of, for example, glass or resin.

[0049] For example, the liquid composition can be cured by heating a coating film formed by applying the liquid composition to the main surface of the substrate 30. In this case, the coating film is typically exposed to and heated in an environment at a temperature lower than the thermal decomposition temperature (decomposition temperature) of the trifunctional alkoxysilane. The coating film is desirably exposed to and heated in an environment at a temperature lower than 450°C. When the substrate 30 is made of a resin with low heat resistance, the coating film may be exposed to and heated in an environment at a temperature of, for example, 100°C or lower. For example, it is possible to impart a refractive index of 1.35 or less (for example, 1.20) to the film 1 by exposing the coating film to an environment at 80°C and heating it.

[0050] The ratio (Mp / Ms) of the amount of substance Mp of polysilsesquioxane to the amount of substance Ms of silica in the binder 20 of the film 1 can be regarded as equal to, for example, the ratio (Mr / Me) of the amount of substance Mr of trifunctional alkoxysilane to the amount of substance Me of tetrafunctional alkoxysilane contained in the raw materials of the liquid composition.

[0051] In the antireflection structure 50a, although the film 1 is formed on both main surfaces of the substrate 30, the film 1 may be formed only on one main surface of the substrate 30. 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 may be the same as or different from those of the film 1 formed on the other main surface. For example, the film 1 formed on one main surface may be configured to prevent reflection of light in the visible light region, and the film 1 formed on the other main surface may be configured to prevent reflection of light close to the visible light region in the near-infrared region.

[0052] The antireflection structure 50a can be modified from various viewpoints. For example, the antireflection structure 50a may be modified to have the following laminated structures (I) to (IV). Note that "A / B" means that B is laminated in contact with A. Also, "(A / B)m" or "(A / B)n" means that the structure in which B is laminated on A is repeated m times or n times. m is an integer of 2 or more, and n is an integer of 1 or more. In the following laminated structures, the low refractive index layer has a refractive index of 1.5 or less and, for example, a thickness of 30 to 300 nm. In the following laminated structures, the film 1 forms at least one of the low refractive index layers. The low refractive index layer can be a layer made of silica or magnesium fluoride. The medium refractive index layer has a refractive index exceeding 1.5 and not exceeding 1.8 and, for example, a thickness of 30 to 300 nm. The medium refractive index layer is, for example, a layer made of alumina or a layer made of a mixture of silica and titania. The high refractive index layer has a refractive index exceeding 1.8 and, for example, a thickness of 30 to 300 nm. The high refractive index layer is, for example, a layer made of titania, zirconia, tantalum oxide, or niobium oxide. These 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 / Medium 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] Further, the antireflection structure 50a may be changed to be like the antireflection structure 50b shown in FIG. 3A. The antireflection structure 50b includes a low refractive index layer (second low refractive index layer 40) different from the low refractive index layer (first low refractive index layer) formed by 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 has a thickness of, for example, 30 to 300 nm. The second low refractive index layer 40 does not contain, for example, the hollow particles 10 and is a layer made of at least one of polysilsesquioxane and silica. In the antireflection structure 50b, the film 1 and the second low refractive index layer 40 are formed on both main surfaces of the substrate 30, but the film 1 and the second low refractive index layer 40 may be formed on only one main surface of the substrate 30.

[0054] Further, the antireflection structure 50a may be changed to be like the antireflection structure 50c shown in FIG. 3B. The antireflection structure 50c includes a plurality of low refractive index layers (second low refractive index layer 40 and third low refractive index layer 60) different from the low refractive index layer (first low refractive index layer) formed by 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 has a thickness of, for example, 30 to 300 nm. The second low refractive index layer 40 does not contain, for example, the hollow particles 10 and is a layer made of at least one of polysilsesquioxane and silica. The third low refractive index layer 60 has a refractive index of 1.5 or less, for example, and has a thickness of, for example, 30 to 300 nm. The third low refractive index layer 60 may have the same refractive index and thickness as the first low refractive index layer. The film 1, the second low refractive index layer 40, and the third low refractive index layer 60 are formed on both main surfaces of the substrate 30, but the film 1, the second low refractive index layer 40, and the third low refractive index layer 60 may be formed on only one main surface of the substrate 30.

[0055] For example, an optical element including a film 1 can be provided. The optical element including the film 1 can be, for example, an optical filter such as a low-pass filter and an infrared (IR) cut filter, a lens, or a cover glass. The film 1 is formed, for example, by applying and drying the above liquid composition on the surface of an optical element such as a lens, and functions as a low refractive index coating. By the film 1, reflection of light having a predetermined wavelength such as visible light can be prevented in the optical element. The optical element may further include a dielectric multilayer film for antireflection, or may not include a dielectric multilayer film for antireflection. The optical element including the film 1 and not including a dielectric multilayer film for antireflection is advantageous from the viewpoint of preventing light having a predetermined wavelength while suppressing the manufacturing cost.

[0056] For example, an imaging device including the above optical element can be provided. This imaging device is, for example, a camera module of an information terminal such as a smartphone and a digital camera.

[0057] As shown in FIG. 4A, the imaging device 70a includes, for example, a housing 71, a lens system 72, a filter system 73, a solid-state imaging device 74, and a cover 75. The imaging device 70a is, for example, a camera module of an information terminal such as a smartphone. Note that FIG. 4A is a diagram schematically showing the imaging device 70a, and in FIG. 4A, the shapes and dimensions of each component in the actual object and the relative positional relationship between each component are not necessarily accurately represented. In addition, the imaging device 70a typically may include an adjustment mechanism for the lens system 72 and other components such as an aperture. In FIG. 4A, for convenience of explanation, these components are omitted.

[0058] The lens system 72 is disposed inside the housing 71. The lens system 72 includes a single single lens or a plurality of single lenses (in FIG. 4A, four single lenses 72a, 72b, 72c, and 72d). The material of the single lens is typically glass or resin. The optical filter included in the filter system 73 is not particularly limited. The filter system 73 can include, for example, at least one of a low-pass filter and an IR cut filter. The housing 71 is, for example It has an aperture formed around the optical axis of the lens system 72. This aperture is covered by a cover 75. The cover 75 is preferably made of glass. The cover 75 can withstand collisions with external objects of the housing 71 and fluctuations in the environmental conditions of the imaging device 70a.

[0059] As shown in FIGS. 4A and 4B, for example, in the imaging device 70a, at least one single lens included in the lens system 72 is provided with a film 1. When the single lens is provided with the film 1, the film 1 may be disposed on only one side of the single lens, or the film 1 may be disposed on both sides of the single lens. For example, the single lens 72b is provided with the film 1. When the lens system 72 includes a plurality of single lenses, the single lens on which the film 1 is to be formed is appropriately determined. Although not shown, the lens system 72 may include a cemented lens formed by cementing a plurality of single lenses, and the film 1 may be disposed on only one side or both sides of the cemented lens. Typically, the film 1 is formed by applying and drying the above liquid composition. Therefore, when the single lens has a surface with a small radius of curvature, the gradient of the lens surface is absorbed, and the above liquid composition applied for forming the film 1 may flow, and the thickness of the film 1 may vary spatially. However, by adjusting the application and drying conditions of the above liquid composition, the spatial variation in the thickness of the film 1 can be reduced.

[0060] The imaging device 70a may be modified like the imaging device 70b shown in FIG. 5A. The imaging device 70b is configured in the same manner as the imaging device 70a except for the parts to be specifically described. The components identical or corresponding to those of the imaging device 70a are denoted by the same reference numerals, and detailed descriptions thereof are omitted. The description of the imaging device 70a also applies to the imaging device 70b as long as there is no technical contradiction.

[0061] As shown in FIG. 5A, in the imaging device 70b, for example, the cover 75 includes the film 1. For example, the film 1 is formed on one main surface of the glass plate 75a of the cover 75. For example, the cover 75 is arranged so that the film 1 faces the inside of the housing 71. Thereby, deterioration and peeling of the film 1 can be prevented. As shown in FIG. 5B, a dielectric multilayer film 75b, which is an antireflection film, may be formed on the other main surface of the glass plate 75a of the cover 75.

[0062] In the imaging device 70a and the imaging device 70b, at least one optical filter included in the filter system 73 may include the film 1. In this case, the film 1 may be omitted in 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 including the film 1 in the filter system 73 may be a low-pass filter or an IR cut filter. The film 1 is disposed on the surface of the optical filter. By the IR cut filter, the spectrum of light that can be received by the solid-state imaging device 74 including a semiconductor can be made closer to the human visual sensitivity curve (spectrum). The IR cut filter has a function of cutting (shielding) infrared rays having a wavelength of, for example, at least 700 to 1000 nm.

[0063] The IR cut filter included in the filter system 73 includes, for example, infrared-absorbing glass, an infrared reflection film made of a dielectric multilayer film, an infrared absorption film, or a combination thereof. The infrared-absorbing glass is, for example, glass containing copper phosphate or potassium phosphate. The infrared absorption film is a film in which a dye or pigment that absorbs infrared rays is dispersed in a matrix resin. For example, such an IR cut filter may include the film 1. For example, the filter system 73 includes an IR cut filter 73x shown in FIG. 6. The IR cut filter 73x includes, for example, infrared-absorbing glass 73a, an infrared absorption film 73b, and a pair of films 1. The infrared-absorbing glass 73b has a plate-like or sheet-like shape, and the infrared absorption film 73b is formed on one main surface of the infrared-absorbing glass 73a. Also, the pair of films 1 are formed so as to form both main surfaces of the IR cut filter 73x, for example.

[0064] The imaging device provided with the above-described optical element can be an imaging device other than a camera module of an information terminal such as a smartphone, such as a digital camera (digital still camera and digital movie camera). Such an imaging device includes, for example, an optical system 80 shown in FIG. 7. Note that in FIG. 7, the shape and dimensions of each component in the actual object and the relative positional relationship between each component are not necessarily accurately represented. The optical system 80 includes, for example, a plurality of single lenses 81, 82, 83, 84, and 85. For example, a film 1 is formed on both surfaces of the single lens 82. Although not shown, the optical system 80 may include a cemented lens formed by cementing a plurality of single lenses, and the film 1 may be disposed on only one side or both sides of the cemented lens.

[0065] In the imaging device 70a, the imaging device 70b, and the optical system 80, a lens system may be configured by combining a lens provided with the film 1 and a lens provided with an antireflection film made of a dielectric multilayer film or an antireflection structure made of a moth-eye structure.

Example

[0066] The present invention will be described in more detail with reference to examples. Note that the present invention is not limited to the following examples. First, the antireflection structure according to the examples and comparative examples and the evaluation method of the low refractive index film according to the examples and comparative examples will be described.

[0067] [Analysis by ATR method] Using a Fourier transform infrared spectrophotometer (manufactured by PerkinElmer, product name: Frontier Gold), the absorption spectra of the low refractive index films according to the respective examples and comparative examples were measured by the ATR method. The absorption spectra of the low refractive index films according to Example 1 and Comparative Example 1 were measured using 1 to 10 mg of powdery samples obtained by peeling off the low refractive index films formed on the substrates in each of the examples and Comparative Example 1. The results of the absorption spectra of the low refractive index films according to Example 1 and Comparative Example 1 are shown in FIGS. 8 and 9, respectively.

[0068] In the absorption spectrum of the low refractive index film according to each Example and Comparative Example 1, the maximum value of absorbance in the absorption band derived from the hydrocarbon group (CH3 and CH2) not directly bonded to a silicon atom is 910±50 cm -1 The maximum absorbance in the absorption band due to the bond between silicon atoms and methyl groups appeared in the wave number range of 1276 ± 50 cm -1 The maximum absorbance in the absorption band due to the bond between silicon atoms and hydroxyl groups was 3438 ± 50 cm -1 Furthermore, the maximum absorbance in the absorption band resulting from the bond between one oxygen atom and two silicon atoms (siloxane bond) was observed at 455 ± 50 cm -1 , 780±50cm -1 , and 1065±50cm -1 8 and 9, the absorption bands resulting from hydrocarbon groups (CH3 and CH2) that are not directly bonded to silicon atoms are indicated by the symbol a, the absorption bands resulting from bonds between silicon atoms and methyl groups are indicated by the symbol b, the absorption bands resulting from bonds between silicon atoms and hydroxyl groups are indicated by the symbol c, and the absorption bands resulting from bonds between one oxygen atom and two silicon atoms are indicated by the symbols d, e, and f, in that order from the short wavenumber side. The absorption bands due to the free hydrocarbon groups (CH3 and CH2) and the absorption bands due to the bond between the silicon atom and the methyl group are shown enlarged in enlarged areas (1) and (2), respectively.

[0069] In the absorption spectrum of the low refractive index film according to each Example and Comparative Example 1, the absorbance Ia derived from the hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms was determined as follows. In the absorption band derived from the hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms, a baseline was set as shown in the enlarged portion (1) of FIG. 8, and the absorbance on the baseline at the wave number where the maximum value of absorbance appears was subtracted from the maximum value of absorbance to determine the absorbance Ia. In other words, the maximum value of absorbance was taken as A max (CH3 and CH2) and the maximum absorbance The absorbance on the baseline at the wave number at which it appears is defined as absorbance A base When represented as (CH3 and CH2), the absorbance Ia was determined by the following (Equation 5). Ia = A max (CH3 and CH2) - A base (CH3 and CH2) (Equation 5)

[0070] In the absorption spectra of the low refractive index films according to each Example and Comparative Example 1, the absorbance Ib derived from the bond between the silicon atom and the methyl group (Si-CH3) was determined in the same manner as the absorbance Ia. Figure 8 As shown in the enlarged portion (2) of FIG. 8, the baseline was defined, and the absorbance on the baseline at the wave number at which the maximum value of the absorbance appears was subtracted from the maximum value of the absorbance to obtain the absorbance Ib. In other words, the maximum value of the absorbance is represented as A max (Si-CH3), and the absorbance on the baseline at the wave number at which the maximum value of the absorbance appears is represented as A base (Si-CH3), then the absorbance Ib is as follows ( Equation 6) was determined. Ib = A max (Si-CH3) - A base (Si-CH3) (Equation 6)

[0071] In the absorption spectra of the low refractive index films according to each Example and Comparative Example 1, the maximum value of the absorbance in the absorption band derived from the bond between one oxygen atom and two silicon atoms (Si-O-Si) was determined as the absorbance Ic derived from that bond. In the determination of the absorbance Ic, correction by the baseline was not performed.

[0072] In the absorption spectra of the low refractive index films according to each Example and Comparative Example 1, the three maximum values of the absorbance derived from the bond between one oxygen atom and two silicon atoms (Si-O-Si) were determined as the first absorbance Id, the second absorbance Ie, and the third absorbance If derived from that bond. First In the first absorbance Id, the second absorbance Ie, and the third absorbance If, the first absorbance Id corresponded to the wave number with the minimum value, and the third absorbance If corresponded to the wave number with the maximum value. Note that the first absorbance Id, the second Even in the determination of the absorbance Ie and the third absorbance If, baseline correction was not performed. was not.

[0073] In the low refractive index films according to each of the examples and Comparative Example 1, based on the absorbances Ia, Ib, Ic, the first absorbance Id, the second absorbance Ie, and the third absorbance If determined as described above, the inorganic-organic parameter (D), the hydrophobic parameter (H), and the first to third network parameters (N1, N2, and N3) were determined according to the following (Equations 7) to (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 property] When applying the liquid compositions according to each of the examples and Comparative Example 1 onto a glass substrate or a substrate made of polycarbonate, if it was confirmed that there was a portion where the liquid composition could not be applied or the thickness of the low refractive index film was uneven, the film-forming property of the liquid composition was evaluated as "x". Also, when these were not confirmed, the film-forming property of the liquid composition was evaluated as "a". The results are shown in Table 1.

[0075] [Reflectance] In the antireflection structure according to each example, the reflectance (visible light reflectance) in the visible light region (380 to 780 nm) of the antireflection structure in which the low refractive index film was formed on the substrate was first measured by a spectrophotometer (manufactured by Hitachi High-Technologies Corporation, product name: U-4000) for the spectral reflectance of the antireflection structure, and calculated according to Japanese Industrial Standard (JIS) R 3106:1998 based on this spectral reflectance. 。 This In the measurement of the spectral reflectance, the reflection angle was set to 12°. Examples 1, 7, 10, and 1 The spectral reflectance of the antireflection structure according to 1 is shown in FIG. 10, and the spectral reflectance spectra of the antireflection structures according to Example 12 and Example 13 are shown in FIG. 11. Also, the visible light reflectance of the antireflection structure according to each example is shown in Table 1.

[0076] [Refractive index] Except for using a silicon substrate as the substrate, the low refractive index films according to each example were formed under the same conditions as the production of the antireflection structures according to each example, and the samples for measuring the refractive index according to each example were produced. Using a spectrophotometer (manufactured by Hitachi High-Technologies Corporation, product name: U-4000), the reflectance of the sample for measuring the refractive index according to each example was measured, and the refractive index of the low refractive index film according to each example 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 wt% formic acid (manufactured by Kishida Chemical Co., Ltd.), 3 g of a sol of hollow silica particles (manufactured by JGC Catalysts & Chemicals Ltd., product name: Throughia 4110, silica solid content: about 25 wt%), and 22.4 g of ethanol (manufactured by Kishida Chemical Co., Ltd.) were mixed and reacted at 35° C. for 3 hours. In this way, the liquid composition according to Example 1 was obtained. In the sol of hollow silica particles, the average particle diameter of the hollow silica particles was about 50 nm, the thickness of the shell made of silica was 10 to 20 nm, the maximum dimension of the internal space of the hollow silica particles was about 10 to 30 nm, and the refractive index of the hollow silica particles was 1.25. The solid content in the liquid composition according to Example 1 contained 0.6 wt% of silica derived from TEOS, 1.6 wt% of polymethylsilsesquioxane derived from MTES, and 2.6 wt% of hollow silica particles. The ratio of the amount of substance of MTES to the amount of substance of TEOS added in the production of the liquid composition according to Example 1 was 7 / 3. The ratio of the weight of the hollow silica particles to the total weight of the solid content of silica derived from TEOS and polymethylsilsesquioxane derived from MTES was 1.3 / 1.1.

[0078] For a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52), using an ultrasonic cleaner, cleaning was performed in ultrapure water for 15 minutes, cleaning was performed with a commercially available alkaline cleaning solution for 15 minutes, and cleaning was performed in ultrapure water for 15 minutes. On both main surfaces of the cleaned glass substrate, the liquid composition according to Example 1 was applied by the spin coating method. The appearance immediately after application was good, and a uniform coating film was obtained. Then, the coating film was dried in an oven under the conditions of 200 °C for 10 minutes to obtain a low refractive index film according to Example 1. As a result, an antireflection structure according to Example 1 including a glass substrate and a low refractive index film formed on the glass substrate as shown in FIG. 2 was obtained. When observing the appearance of the low refractive index film according to Example 1, it had a uniform thickness. The thickness of the low refractive index film according to Example 1 was 120 nm. In the binder of the low refractive index film according to Example 1, the ratio of the amount of substance of polymethylsilsesquioxane to the amount of substance of silica was 7 / 3.

[0079] <Examples 2 to 5> In the preparation of the liquid composition, except that the ratio of the amount of substance of methyltriethoxysilane (MTES) to the amount of substance of tetraethoxysilane (TEOS) was adjusted as shown in Table 1, the liquid compositions according to Examples 2 to 5 were obtained in the same manner as in Example 1. Except that the liquid compositions according to Examples 2 to 5 were used instead of the liquid composition according to Example 1, the low refractive index films according to Examples 2 to 5 and the antireflection structures according to Examples 2 to 5 were produced in the same manner as in Example 1. All of the liquid compositions according to Examples 2 to 5 had good film-forming properties.

[0080] <Examples 6 to 9> In the preparation of the liquid composition, except that the ratio of the amount of substance of methyltriethoxysilane (MTES) to the amount of substance of tetraethoxysilane (TEOS) was adjusted as shown in Table 1, the same as in Example 1 In the same manner as in Example 1, liquid compositions according to Examples 6 to 9 were obtained. A substrate made of polycarbonate (PC) (size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.59) was used instead of the glass substrate, and a low refractive index film according to Examples 6 to 9 and an antireflection structure according to Examples 6 to 9 were produced in the same manner as in Example 1, except that the liquid compositions according to Examples 6 to 9 were used instead of the liquid composition according to Example 1.

[0081] <Examples 10 and 11> A shell made of magnesium fluoride was formed around a core made of silica to produce core-shell structured particles. The core of silica in these particles was dissolved in an alkaline solution to produce hollow particles of magnesium fluoride. In these hollow particles of magnesium fluoride, the average particle diameter was about 50 nm, the thickness of the outer shell made of magnesium fluoride was about 10 nm, the maximum dimension of the internal space was about 30 nm, and the refractive index of the hollow particles was 1.20. Liquid compositions according to Examples 10 and 11 were obtained in the same manner as in Example 1, except that these hollow particles of magnesium fluoride were used instead of the hollow silica particles. Also, a low refractive index film according to Example 10 and an antireflection structure according to Example 10 were produced in the same manner as in Example 1, except that the liquid composition according to Example 10 was used instead of the liquid composition according to Example 1. Further, a low refractive index film according to Example 11 and an antireflection structure according to Example 11 were produced in the same manner as in Example 7, except that the liquid composition according to Example 11 was used instead of the liquid composition according to Example 7. The thickness of the low refractive index film according to Example 10 and the thickness of the low refractive index film according to Example 11 were 118 nm.

[0082] <Example 12> A coating composition was prepared in the same manner as the liquid composition according to Example 1, except that the sol of hollow silica particles was not added. This coating composition was spin-coated onto 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. Next, the coating film of the coating composition was dried in an oven under the conditions of 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 according to Example 1 was spin-coated onto the inner low-refractive-index film. Next, the coating film of the liquid composition was dried in an oven under the conditions of 200°C for 10 minutes to form a low-refractive-index film according to Example 12, and an antireflection structure according to Example 12 as shown in Fig. 3A was fabricated. The thickness of the low-refractive-index film according to Example 12 was 95 nm. The coating composition had good film-forming properties on the glass substrate, and the liquid composition according to Example 1 had good film-forming properties on the inner low-refractive-index film.

[0083] <Example 13> An antireflection structure according to Example 13 was fabricated in the same manner as Example 12, except that the liquid composition according to Example 10 was used instead of the liquid composition according to Example 1. The liquid composition according to Example 10 had good film-forming properties on the inner low-refractive-index film.

[0084] <Example 14> A low-refractive-index film according to Example 14 and an antireflection structure according to Example 14 were fabricated in the same manner as Example 1, except that the thickness of the low-refractive-index film was changed to 180 nm. The liquid composition according to Example 1 also had good film-forming properties when the film was formed to a thickness of 180 nm.

[0085] <Example 15> The liquid composition used in Example 1 was spin-coated onto one main surface of a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) that had been cleaned in the same manner as Example 1, and then the coating film was dried in an oven under the conditions of 200°C for 10 minutes A low refractive index film with a thickness of 100 nm was formed. Further, on the other main surface of the glass substrate, the liquid composition used in Example 1 was applied by spin coating, and then the coating film was dried in an oven under the conditions of 200 °C for 10 minutes to form a low refractive index film with a thickness of 180 nm. A low refractive index film according to Example 15 and an antireflection structure according to Example 15 as shown in FIG. 2 were produced. The liquid composition according to Example 1 also had 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) washed in the same manner as in Example 1, the liquid composition used in Example 1 was applied by spin coating, and then the coating film was dried in an oven under the conditions of 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 applied by spin coating, and then the coating film was dried in an oven under the conditions of 200 °C for 10 minutes to form a second low refractive index film with a thickness of 40 nm. Further, on the second low refractive index film, the liquid composition according to Example 1 was applied by spin coating, and then the coating film was dried in an oven under the conditions of 200 °C for 10 minutes to form a first low refractive index film with a thickness of 30 nm. An antireflection structure according to Example 16 as shown in FIG. 3B was produced. The liquid composition according to Example 1 also had good film-forming properties with respect to the glass substrate and the low refractive index film, and the coating composition according to Example 12 had good film-forming properties with respect to the low refractive index film.

[0087] <Comparative Example 1> In the preparation of the liquid composition, a liquid composition according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the ratio of the amount of substance of methyltriethoxysilane (MTES) to the amount of substance of tetraethoxysilane (TEOS) was adjusted as shown in Table 1. A low refractive index film according to Comparative Example 1 and an antireflection structure according to Comparative Example 1 were produced in the same manner as in Example 1, except that the liquid composition according to Comparative Example 1 was used instead of the liquid composition according to Example 1. When the appearance of the low refractive index film according to Comparative Example 1 was observed, it was clearly confirmed that the thickness of the low refractive index film was non-uniform.

[0088] As shown in Table 1, the visible light reflectance of the antireflection structures according to Examples 1 to 5 was 1.6% or less. The visible light reflectance of the antireflection structures according to Examples 6 to 9 was 1.3% or less. The visible light reflectance of the antireflection structures according to Examples 10 and 11 was 1.1% or less. The visible light reflectance of the antireflection structures according to Examples 12 and 13 was 0.2% or less. Thus, it was confirmed that the antireflection structures according to the respective examples could exhibit high antireflection performance. As shown in FIG. 10, the spectral reflectance of the antireflection structures according to Examples 1, 7, 10, and 11 was 5% or less over the entire visible light region (range of wavelength 380 nm to 780 nm). Also, as shown in FIG. 11, the spectral reflectance of the antireflection structure according to Example 12 was 4% or less over the entire visible light region, and the spectral reflectance of the antireflection structure according to Example 13 was 3% or less over the entire visible light region.

[0089] As shown in Table 1, the visible light reflectance of the antireflection structure according to Example 14 was 4.2%. Also, as shown in FIG. 12, the spectral reflectance of the antireflection structure according to Example 14 was 8.5% or less over the entire visible light region, and the average value of the spectral reflectance in the range of wavelength 800 nm to 1000 nm, which is close to the visible light region, among the near-infrared region (wavelength 800 nm to 2500 nm) was 0.4%, and the average value of the spectral reflectance in the range of wavelength 800 nm to 1100 nm was 0.6%.

[0090] As shown in Table 1, the visible light reflectance of the antireflection structure according to Example 15 was 2.3%. Also, as shown in FIG. 12, the spectral reflectance of the antireflection structure according to Example 15 was 4.8% or less over the entire visible light region, and among the near-infrared regions, the average value of the spectral reflectance in the wavelength range of 80 0 nm to 1000 nm close to the visible light region was 2.2%, and the average value of the spectral reflectance in the wavelength range of 800 nm to 1100 nm was 2.4%.

[0091] As shown in Table 1, the visible light reflectance of the antireflection structure according to Example 16 was 0.7%. Also, as shown in FIG. 12, the spectral reflectance of the antireflection structure according to Example 16 was 3.5% or less over the entire visible light region, and among the near-infrared regions, the average value of the spectral reflectance in the wavelength range of 800 nm to 1000 nm close to the visible light region was 3.3%, and the average value of the spectral reflectance in the wavelength range of 800 nm to 1100 nm was 3.6%.

[0092]

Table 1

Explanation of Signs

[0093] 1 Film (first low refractive index layer) 10 Hollow particles 20 Binder 30 Substrate 40 Second low refractive index layer 50a, 50b, 50c Antireflection structure 60 Third low refractive index layer 70a, 70b Imaging device 71 Housing 72 Lens system 72a to 72d Single lens 73 Filter system 73a Infrared absorption glass 73b Infrared absorption film 73x IR cut filter 74 Solid-state imaging device 75 Cover 75a glass plate 75b dielectric multilayer film 80 optical system 81 - 85 single lens

Claims

1. A first layer containing hollow particles having an average primary particle diameter of 10 to 150 nm, having a thickness of 80 to 350 nm and a refractive index of 1.25 or less, and a second layer having a thickness of 30 to 300 nm and a refractive index of 1.5 or less, wherein the hollow particles have a refractive index of 1.15 to 2.70, the first layer contains polysilsesquioxane and a binder that binds the hollow particles, when the absorbance derived from a hydrocarbon group not directly bonded to a silicon atom, the absorbance derived from the bond between a silicon atom and a non-reactive functional group, and the absorbance derived from the bond between a silicon atom and a hydroxy group, which are determined by the total reflection measurement method using a Fourier transform infrared spectrophotometer, are represented by Ia, Ib, and Ic, respectively, the first layer satisfies at least one of the conditions of Ib / Ia ≥ 0.7 and Ib / Ic ≥ 0.3, an antireflection film.

2. In the absorbance spectrum obtained by the total reflection measurement method using a Fourier transform infrared spectrophotometer, when the maximum value of absorbance within the range of a wave number of 455 ± 50 cm -1 is defined as Id, the maximum value of absorbance within the range of a wave number of 780 ± 50 cm -1 is defined as Ie, and the maximum value of absorbance within the range of a wave number of 1065 ± 50 cm -1 is defined as If, satisfies at least one selected from the group consisting of Id / Ib ≤ 60, Ie / Ib ≤ 20, and If / Ib ≤ 174, The antireflection film according to claim 1.

3. The antireflection film according to claim 1 or 2, wherein the polysilsesquioxane has a hydrocarbon group containing 16 or fewer carbon atoms bonded to a silicon atom.

4. The antireflection film according to any one of claims 1 to 3, wherein the hollow particles contain at least one selected from the group consisting of silica, magnesium fluoride, alumina, aluminosilicate, titania, and zirconia.

5. The antireflection film according to any one of claims 1 to 4, wherein the second layer contains at least one selected from the group consisting of polysilsesquioxane and silica.

6. The first layer contains silica, The antireflection film according to any one of claims 1 to 5, wherein the ratio (Mp / Ms) of the amount of substance of the polysilsesquioxane to the amount of substance of the silica (Ms) is 3 / 7 or more.

7. A method for manufacturing an antireflection film, including applying a first liquid composition which is a precursor of the first layer and a second liquid composition which is a precursor of the second layer to an optical element, wherein the first liquid composition contains an alkoxysilane represented by the following formula and hollow particles, The method for manufacturing an antireflection film according to any one of claims 1 to 6. (Formula) R b Si(OR c ) 3 (R b represents a non-reactive functional group, and R c represents an alkyl group.)

8. A lens provided with the antireflection film according to any one of claims 1 to 6.

9. An imaging device provided with the lens according to claim 8.

Images