Membrane, liquid composition, optical element, and imaging apparatus

Abstract

To provide a membrane which does not require an organosilane compound having a fluoroalkyl group, and which is advantageous in low refractive index coating.SOLUTION: A membrane (1) comprises hollow particles (10), and a binder (20). The hollow particles are formed of a material having a refraction index of 1.15-2.70. The binder (20) is formed of at least polysilsesquioxane, and binds to the hollow particles (10). The membrane (1) satisfies at least one condition out of Ib / Ia≥0.7 and Ib / Ic≥0.3, Ia is absorbance derived from a hydrocarbon group which is not directly coupled to a silicon atom determined by a whole reflection measurement method using a Fourier transformation infrared spectrophotometer, and Ib is absorbance derived from coupling of a silicon atom and a non-reactive functional group, and Ic is absorbance derived from coupling of 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 that are advantageous for low refractive index coating. Additionally, the present invention relates to an optical element and an imaging device. [Background technology]

[0002] BACKGROUND ART Conventionally, from the viewpoint of antireflection, coating using a material having a low refractive index (low refractive index coating) has been performed, and compositions for low refractive index coatings have been known.

[0003] For example, Patent Documents 1 and 2 describe antireflective coating compositions. These coating compositions contain hollow silica particles and a binder formed by polymerizing a specific silane compound and an organosilane compound having a fluoroalkyl group. Additionally, Patent Documents 1 and 2 describe antireflective films that include a low refractive index layer formed by coating the coating composition on the surface of a substrate.

[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 contains a binder formed by polymerizing a specific silane compound and an organosilane compound having a fluoroalkyl group, and hollow silica particles.

[0005] Patent Document 4 describes an optical element having an antireflection coating and a method for manufacturing the same. The manufacturing method includes a step of applying a dispersion containing particles and a dispersion medium onto a substrate. After the dispersion application step, the manufacturing method further includes a step of applying a solution containing a binder-forming component, allowing the solution to penetrate between the particles contained in the previously applied dispersion to form a single layer in which the binder fills the spaces between the particles. The manufacturing method further includes a step of drying the layer to produce an antireflection coating. The solution contains a silane alkoxy condensate with an average particle size of 8 nm to 60 nm and 70 mass % or more of a solvent with a water solubility of 10 wt % or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2015-534104 [Patent Document 2] Special Publication No. 2015-536477 [Patent Document 3] Special Publication No. 2015-535617 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-167271 Summary of the Invention [Problem to be solved by the invention]

[0007] The techniques described in Patent Documents 1 to 3 require an organosilane compound having a fluoroalkyl group. The technique described in Patent Document 4 requires a solution containing a silane alkoxy condensate to penetrate between particles contained in a previously applied dispersion, making the method for producing optical components complicated. Therefore, the present invention provides a film that is advantageous for low refractive index coating without requiring an organosilane compound having a fluoroalkyl group. Additionally, the present invention provides a liquid composition that does not require an organosilane compound having a fluoroalkyl group and can easily produce a low refractive index coating. [Means for solving the problem]

[0008] The present invention provides hollow particles made of a material having a refractive index of 1.15 to 2.70; a binder formed of at least polysilsesquioxane that binds the hollow particles together; When the absorbance attributable to hydrocarbon groups not directly bonded to silicon atoms, the absorbance attributable to bonds between silicon atoms and non-reactive functional groups, and the absorbance attributable to bonds between silicon atoms and hydroxy groups are represented as Ia, Ib, and Ic, respectively, as determined by attenuated total reflectance (ATR) measurement using a Fourier transform infrared spectrophotometer, at least one of the conditions Ib / Ia≧0.7 and Ib / Ic≧0.3 is satisfied. A membrane is provided.

[0009] The present invention also provides A liquid composition comprising: hollow particles made of a material having a refractive index of 1.15 to 2.70; Polysilsesquioxane, a solvent; In a cured product obtained by applying the liquid composition to a substrate and curing the liquid composition, the absorbance attributable to hydrocarbon groups not directly bonded to silicon atoms, the absorbance attributable to bonds between silicon atoms and non-reactive functional groups, and the absorbance attributable to bonds between silicon atoms and hydroxy groups, as determined by total reflection measurement using a Fourier transform infrared spectrophotometer, are expressed as Ia, Ib, and Ic, respectively, and satisfy at least one of the conditions Ib / Ia≧0.7 and Ib / Ic≧0.3. A liquid composition is provided.

[0010] The present invention also provides An optical element is provided that includes the above film.

[0011] The present invention also provides An imaging device is provided that includes the optical element described above. [Effects of the Invention]

[0012] The above-mentioned film does not require an organosilane compound having a fluoroalkyl group, which is advantageous for low refractive index coating. The above-mentioned liquid composition does not require an organosilane compound having a fluoroalkyl group. In addition, low refractive index coating can be easily produced using the above-mentioned liquid composition. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view conceptually showing the structure of an example of a membrane according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of an anti-reflection structure in which a low refractive index coating is applied using the film according to the present invention. [Figure 3A] FIG. 3A is a cross-sectional view showing an example of another antireflection structure in which a low refractive index coating is applied using the film according to the present invention. [Figure 3B] FIG. 3B is a cross-sectional view showing yet another example of an antireflection structure in which a low refractive index coating is applied using the film according to the present invention. [Figure 4A] FIG. 4A is a cross-sectional view showing an example of an imaging device according to the present invention. [Figure 4B] FIG. 4B is a side view of the single lens shown in FIG. 4A. [Figure 5A] FIG. 5A is a cross-sectional view showing another example of an imaging device according to the present invention. [Figure 5B] FIG. 5B is a cross-sectional view showing an example of a cover of the imaging device. [Figure 6] FIG. 6 is a cross-sectional view showing an example of an IR cut filter of an imaging device. [Figure 7] FIG. 7 is a side view showing an optical system in yet another example of an imaging device according to the present invention. [Figure 8] FIG. 8 is a graph showing the absorption spectrum of the film according to Example 1 obtained by the ATR method. [Figure 9] FIG. 9 is a graph showing the absorption spectrum of the film according to Comparative Example 1 obtained by the ATR method. [Figure 10] FIG. 10 is a graph showing the reflection spectra of the antireflection structures according to Examples 1, 7, 10, and 11. [Figure 11] FIG. 11 is a graph showing the reflection spectra of the antireflection structures according to Examples 12 and 13. [Figure 12]FIG. 12 is a graph showing the reflection spectra of the antireflection structures according to Examples 14, 15, and 16. DETAILED DESCRIPTION OF THE INVENTION

[0014] The techniques described in Patent Documents 1 to 3 require an organosilane compound having a fluoroalkyl group. Therefore, the present inventors believed that, in the techniques described in Patent Documents 1 to 3, if the coating liquid contains water as a solvent (dispersion medium), phase separation occurs in the coating liquid due to the water repellency of the fluoroalkyl group. Therefore, the present inventors believed that, in the techniques described in Patent Documents 1 to 3, the addition of an additive such as a surfactant is necessary to obtain a uniform coating liquid. In addition, the present inventors believed that, in the techniques described in Patent Documents 1 to 3, the water and oil repellency of the fluoroalkyl group result in low wettability of the coating liquid to hydrophilic glass substrates and hydrophobic (oleophilic) resin substrates, and that the coating liquid is easily repelled by the substrate when applied to the substrate. Furthermore, the present inventors believed that the technique described in Patent Document 4 requires a solution containing a silane alkoxy condensate to penetrate between the particles after application of a particle-containing dispersion, which requires a complicated process. Therefore, the present inventors have been working day and night to develop a film advantageous for low refractive index coating that does not require an organosilane compound having a fluoroalkyl group. As a result, the present inventors have devised the film according to the present invention. In addition, the present inventors have devised a liquid composition that can easily produce a low refractive index coating without requiring an organosilane compound having a fluoroalkyl group.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following description is an example of the present invention, and the present invention is not limited to the following description.

[0016] As shown in FIG. 1, film 1 includes hollow particles 10 and a binder 20. Hollow particles 10 are made of a material with a refractive index of 1.15 to 2.70. Binder 20 is formed of at least polysilsesquioxane and binds hollow particles 10 together. In film 1, absorbances derived from hydrocarbon groups not directly bonded to silicon atoms, absorbances derived from bonds between silicon atoms and nonreactive functional groups, and absorbances derived from bonds between silicon atoms and hydroxyl groups, as determined by attenuated total reflectance (ATR) using a Fourier transform infrared spectrophotometer, are designated Ia, Ib, and Ic, respectively. Film 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). The absorbance Ia, absorbance Ib, and absorbance Ic can be determined from an absorption spectrum obtained by, for example, the ATR method according to the method described in the Examples.

[0017] The organic-inorganic parameter (D) increases as the amount of hydrocarbon groups not directly bonded to silicon atoms contained in the binder 20 decreases. When 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 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. The hollow particles are fixed to the film 1, and the film 1 has properties that are advantageous for low refractive index coating. If the hollow particles are not fixed sufficiently to the film, 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, if hydroxy groups in the raw materials for the binder 20 condense with each other to form a network of Si-O-Si, 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, a dense network of Si-O-Si develops in the binder 20, and this network can firmly fix the hollow particles 10. 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 properties advantageous for low refractive index coating.

[0019] Preferably, the film 1 further satisfies the conditions Ib / Ia≧0.7 and Ib / Ic≧0.3, which allows the hollow particles 10 to be more reliably and firmly fixed in the film 1, and gives the film 1 advantageous properties for low refractive index coating.

[0020] When silanol groups (Si-OH) are present in the binder 20, the silanol groups form hydrogen bonds with the silanol groups present on the surface of the glass substrate, resulting in high affinity. Therefore, a film with a hydrophobicity parameter (H) of a predetermined value or less easily adheres to a glass substrate. To ensure good adhesion to both substrates with hydrophilic and hydrophobic surfaces, the film 1 preferably satisfies the condition 0.3≦Ib / Ic≦2.0.

[0021] In the film 1, the first absorbance, second absorbance, and third absorbance, determined by the ATR method and resulting from the bond between one oxygen atom and two silicon atoms, are represented as Id, Ie, and If, respectively. The first absorbance Id corresponds to a first wavenumber. The second absorbance Ie corresponds to a second wavenumber greater than the first wavenumber. The third absorbance If corresponds to a third wavenumber greater than the second wavenumber. The film 1 preferably 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 wave number is, for example, 455±50 cm -1 The second wavenumber is the wavenumber at which the maximum value of the absorption spectrum appears. -1 The third wavenumber is the wavenumber at which the maximum value of the absorption spectrum appears. -1 is the wavenumber 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) increase as the number of bonds between oxygen atoms and two silicon atoms (Si-O-Si) in the binder 20 increases. The more developed the Si-O-Si network formed by condensation of hydroxy groups in the raw materials of the binder 20, the larger the first network parameter (N1), the second network parameter (N2), and the third network parameter (N3). Meanwhile, to maintain good film-forming properties, it is important to suppress the aggregation of hollow particles and maintain a uniform thickness of the coating film. To suppress the aggregation of hollow particles, it is desirable to prevent excessive development of the Si-O-Si network. From this perspective, it is desirable for the film 1 to satisfy at least one of the following: N1 is 60 or less, N2 is 20 or less, and N3 is 174 or less. This allows the film 1 to be formed well, and the film 1 can provide an antireflection structure with good antireflection performance.

[0024] More preferably, the film 1 has Id / Ib≦60, Ie / Ib≦20, and If / Ib≦1. 74 further conditions are met.

[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, for example, a hydrophobic functional group 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, a dense Si-O-Si network is easily formed.

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

[0027] The hollow particles 10 are not particularly limited as long as they have a hollow structure, and may have, for example, 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. This makes it easy for the hollow particles 10 to be uniformly dispersed in the film 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 preferably have an average particle diameter of 20 to 100 nm, more preferably 30 to 70 nm. The maximum dimension of the internal space in the hollow particles 10 is, for example, 5 to 100 nm, preferably 10 to 70 nm, more preferably 20 to 50 nm. The hollow particles 10 are preferably 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 preferably a material having a refractive index of 1.20 to 2.00, more preferably a material having a refractive index of 1.30 to 1.50, and even more preferably a material having a refractive index of 1.38 to 1.46. From the viewpoint of resistance to deformation, the hollow particles 10 are preferably 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] In particular, the hollow particles 10 are preferably made of silica or magnesium fluoride to provide an anti-reflection structure with high anti-reflection performance by a low refractive index coating using the film 1. 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 particle 10 are determined so that the hollow particle 10 has a desired refractive index. For example, the material and The proportion of the internal space to the total volume of hollow particle 10 is fixed. Hollow particle 10 has a refractive index of, for example, 1.10 to 1.40, preferably 1.20 to 1.35, and more preferably 1.25 to 1.30. For example, when multiple types of hollow particles made of materials with different refractive indices have the same proportion of the internal space to the total volume of the hollow particles, hollow particles made of a material with a low refractive index have a lower refractive index than hollow particles made of a material with a high refractive index.

[0032] The refractive index of the hollow particles 10 can be measured, for example, by the immersion method (Becke line method). For example, if 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) The dispersion medium of the dispersion liquid of the hollow particles 10 is evaporated and dried to obtain a powder. (ii) The powder obtained in (i) is mixed with a powder having a different refractive index, such as Series A and Series AA manufactured by Gargill. It is mixed with various standard refractive index liquids. (iii) When the mixed solution obtained in (ii) becomes transparent, the refractive index of the standard refractive index solution used is The refractive index is determined to be 10.

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

[0034] In the film 1, the ratio (Wh / Wb) of the mass of the hollow particles 10 to the mass Wb of the binder 20 is, for example, 1 / 5 to 20, preferably 1 / 3 to 10, and more preferably 1 to 5. This makes it possible to provide an antireflection structure with high antireflection performance by using the film 1 as a low refractive index coating.

[0035] The thickness of the film 1 is not particularly limited, but is determined, for example, according to the wavelength of light whose reflection should be prevented. Specifically, the thickness of the film 1 is set so that the optical film thickness (refractive index × physical film thickness) satisfies λ / 4, where λ (nm) is the central wavelength of the wavelengths whose reflection should be prevented. For example, to prevent reflection of light in the visible light range (practically, wavelengths of 380 nm to 780 nm), if the central wavelength λ is λ = 550 nm and the refractive index of the low-refractive index film used is 1.20, the optimal physical film thickness is 115 nm. The practically effective thickness of the film 1 for preventing reflection of visible light is 50 to 300 nm, preferably 70 to 200 nm, and more preferably 90 to 170 nm. This allows for a low-refractive index coating using the film 1 to provide an anti-reflection structure with high anti-reflection performance. Furthermore, to prevent reflection of light with a central wavelength of λ=850 nm, which is close to the visible light region in the near-infrared region (e.g., wavelengths of 800 nm to 2500 nm), the optimal physical film thickness is 177 nm when the refractive index of the low-refractive-index film used is 1.20. The practically effective thickness of film 1 for preventing reflection of near-infrared light is 80 to 350 nm, preferably 130 to 250 nm, and more preferably 150 to 220 nm. This allows the low-refractive-index coating using film 1 to provide an anti-reflection structure with high anti-reflection performance. When a multilayer film is used as the anti-reflection structure, a low-refractive-index layer with a thickness of 50 nm or less may be used. The physical film thickness of the low-refractive-index film is not limited to these, but its cross section can be measured using a SEM, TEM, ellipsometer, or the like.

[0036] The film 1 has a refractive index of, for example, 1.35 or less. This makes it possible to provide an antireflection structure with high antireflection performance by using the film 1 as a low refractive index coating. The film 1 preferably has a refractive index of 1.30 or less, more preferably a refractive index of 1.25 or less. From the viewpoint of reducing the refractive index of the film 1, the film 1 may contain an air space between the hollow particles 10 or in the binder 20. The refractive index of the film 1 can be determined, for example, by the refractive index of the film 1. It can be determined by index 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 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 this liquid composition does not require an organosilane compound having a fluoroalkyl group, phase separation is unlikely to occur in the liquid composition, and the liquid composition is likely to be uniform. Furthermore, the liquid composition has high wettability to glass substrates and resin substrates, making it easy to obtain a film 1 with a uniform structure.

[0039] In the above cured product, it is desirable that the conditions Ib / Ia≧0.7 and Ib / Ic≧0.3 are further satisfied.

[0040] In the above cured product, it is desirable that at least one of the following conditions be satisfied: Id / Ib≦60, Ie / Ib≦20, and If / Ib≦174.

[0041] More preferably, the above cured product further satisfies the conditions Id / Ib≦60, Ie / Ib≦20, and If / Ib≦174.

[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 an average particle size (primary particle size) of, for example, 10 to 150 nm. Furthermore, the hollow particles in the liquid composition are preferably made 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] 2, for example, a liquid composition is applied to the main surface of a substrate 30 and then cured to form a film 1. This provides an antireflection structure 50a that has a low refractive index coating formed using the film 1. By using a liquid composition, a low refractive index coating can be easily formed without the need for an organosilane compound having a fluoroalkyl group.

[0046] The polysilsesquioxane in 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. When silica is contained in the liquid composition in addition to the hollow particles, the 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, tetrafunctional alkoxysilanes form silica (SiO2) through the reactions of the following formulas (1) and (2): R a represents an alkyl group. Trifunctional alkoxysilanes can be converted into polysilsesquioxanes (R b SiO 3 / 2 ) is formed. R b indicates 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 (Equation 4)

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

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

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

[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 considered to be 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 material of the liquid composition.

[0051] In the anti-reflection structure 50a, the film 1 is formed on both main surfaces of the substrate 30, but the film 1 may be formed on only 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 the refractive index and thickness 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 in the near-infrared region that is close to the visible light 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 layered structures (I) to (IV). "A / B" means that B is layered in contact with A. "(A / B)m" or "(A / B)n" means that the structure in which B is layered 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. In the following layered structures, the low refractive index layer has a refractive index of 1.5 or less and a thickness of, for example, 30 to 300 nm. In the following layered structures, film 1 forms at least one low refractive index layer. The low refractive index layer may be a layer made of silica or magnesium fluoride. The medium refractive index layer has a refractive index greater than 1.5 and less than or equal to 1.8 and a thickness of, for example, 30 to 300 nm. The medium refractive index layer may be, for example, an alumina layer or a layer made of a mixture of silica and titania. The high refractive index layer has a refractive index exceeding 1.8 and a thickness of, for example, 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) (IV) Substrate / low refractive index layer / (high refractive index layer / low refractive index layer)

[0053] The antireflection structure 50a may be modified as shown in FIG. 3A as an antireflection structure 50b. The antireflection structure 50b includes a low-refractive-index layer (second low-refractive-index layer 40) separate from the low-refractive-index layer (first low-refractive-index layer) formed by the film 1, located 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 a thickness of, for example, 30 to 300 nm. The second low-refractive-index layer 40 does not contain hollow particles 10, and is, for example, 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 major surfaces of the substrate 30, but the film 1 and the second low-refractive-index layer 40 may be formed on only one major surface of the substrate 30.

[0054] The antireflection structure 50a may be modified as shown in FIG. 3B as an antireflection structure 50c. 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) in addition to 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 a thickness of, for example, 30 to 300 nm. The second low-refractive-index layer 40 does not contain hollow particles 10 and is made of at least one of polysilsesquioxane and silica. The third low-refractive-index layer 60 has a refractive index of, for example, 1.5 or less and 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. Although the film 1, the second low refractive index layer 40, and the third low refractive index layer 60 are formed on both major surfaces of the substrate 30, the film 1, the second low refractive index layer 40, and the third low refractive index layer 60 may be formed on only one major surface of the substrate 30.

[0055] For example, an optical element including the 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 or an infrared (IR) cut filter, a lens, or a cover glass. The film 1 is formed, for example, by applying the above-mentioned liquid composition to the surface of an optical element such as a lens and drying it, and functions as a low refractive index coating. The film 1 can prevent reflection of light of a predetermined wavelength, such as visible light, 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. An optical element including the film 1 but not including a dielectric multilayer film for antireflection is advantageous from the viewpoint of preventing light of a predetermined wavelength while reducing manufacturing costs.

[0056] For example, an imaging device including the optical element can be provided, such as a camera module for an information terminal such as a smartphone or 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 element 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 schematic diagram of the imaging device 70a, and the actual shapes and dimensions of each component and the relative positional relationships between each component are not necessarily accurately depicted in FIG. 4A . In addition, the imaging device 70a may typically include other components such as an adjustment mechanism for the lens system 72 and an aperture. For ease of explanation, these components are omitted from FIG. 4A .

[0058] The lens system 72 is disposed inside the housing 71. The lens system 72 includes a single lens or multiple single lenses (four single lenses 72a, 72b, 72c, and 72d in FIG. 4A). The material of the single lenses is typically glass or resin. The optical filters included in the filter system 73 are not particularly limited. The filter system 73 may include, for example, at least one of a low-pass filter and an IR cut filter. The housing 71 may include, for example, For example, the housing 71 has 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 fluctuations in the environmental conditions of the imaging device 70a.

[0059] As shown in Figures 4A and 4B, for example, in an imaging device 70a, at least one single lens included in a lens system 72 is provided with a film 1. When a single lens is provided with 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, a single lens 72b is provided with a film 1. When the lens system 72 includes multiple single lenses, the single lenses on which the film 1 should be formed are determined appropriately. Although not shown, the lens system 72 may include a laminated lens formed by bonding multiple single lenses together, and the film 1 may be disposed on only one side or both sides of the laminated lens. Typically, the film 1 is formed by applying and drying the above-mentioned liquid composition. Therefore, when a single lens has a surface with a small radius of curvature, the gradient of the lens surface is absorption, and the above-mentioned liquid composition applied to form the film 1 may flow, resulting in spatial variation in the thickness of the film 1. However, by adjusting the conditions for applying and drying the liquid composition, the spatial variation in the thickness of the film 1 can be reduced.

[0060] The imaging device 70a may be modified as in the imaging device 70b shown in FIG. 5A. The imaging device 70b has the same configuration as the imaging device 70a, except for parts that will be specifically described. Components that are the same as or correspond to those of the imaging device 70a are given the same reference numerals, and detailed description thereof will be omitted. The description of the imaging device 70a also applies to the imaging device 70b, unless technically inconsistent.

[0061] As shown in FIG. 5A, in an imaging device 70b, for example, a cover 75 includes a film 1. For example, the film 1 is formed on one main surface of a 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. This prevents deterioration and peeling of the film 1. As shown in FIG. 5B, a dielectric multilayer film 75b, which is an anti-reflection film, may be formed on the other main surface of the glass plate 75a of the cover 75.

[0062] In the imaging devices 70a and 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 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 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. The IR cut filter allows the spectrum of light receivable by the solid-state imaging element 74 including a semiconductor to approach the human visual sensitivity curve (spectrum). The IR cut filter has the function of cutting (blocking) at least infrared light with a wavelength of 700 to 1000 nm, for example.

[0063] The IR cut filter included in the filter system 73 includes, for example, infrared absorbing glass, an infrared reflecting film made of a dielectric multilayer film, an infrared absorbing film, or a combination thereof. The infrared absorbing glass is, for example, glass containing copper phosphate or copper fluorophosphate. The infrared absorbing 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 a 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, an infrared absorbing glass 73a, an infrared absorbing film 73b, and a pair of films 1. The infrared absorbing glass 73b has a plate or sheet shape, and the infrared absorbing film 73b is formed on one main surface of the infrared absorbing glass 73a. Furthermore, the pair of films 1 are formed, for example, to form both main surfaces of the IR cut filter 73x.

[0064] An imaging device equipped with the optical element described above may 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 or digital movie camera). Such an imaging device may include, for example, an optical system 80 shown in FIG. 7. Note that FIG. 7 does not necessarily accurately represent the actual shapes and dimensions of each component and the relative positional relationships of each component. The optical system 80 may include, for example, a plurality of single lenses 81, 82, 83, 84, and 85. For example, a film 1 is formed on both sides of the single lens 82. Although not shown, the optical system 80 may include a cemented lens formed by cementing together 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 constructed by combining a lens having the film 1 with a lens having an anti-reflection film made of a dielectric multilayer film or an anti-reflection 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, methods for evaluating the antireflection structures according to examples and comparative examples and the low refractive index films according to examples and comparative examples will be described.

[0067] [ATR analysis] The absorption spectra of the low refractive index films according to each Example and Comparative Example were measured by the ATR method using a Fourier transform infrared spectrophotometer (manufactured by PerkinElmer, product name: Frontier Gold). In each Example and Comparative Example 1, the low refractive index films formed on the substrates were peeled off to obtain 1 to 10 mg of powder samples, and the absorption spectra of the low refractive index films according to each Example and Comparative Example were measured. The results of the absorption spectra of the low refractive index films according to 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 according to each Example and Comparative Example 1, the maximum absorbance in the absorption band derived from hydrocarbon groups (CH and CH) not directly bonded to silicon atoms was 910±50 cm -1 The maximum absorbance in the absorption band due to the bond between silicon atoms and methyl groups was 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 hydroxy 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 order from the shortest wavenumber side, in FIG. 8. The absorption bands due to the hydrocarbon groups (CH3 and CH2) that are not present 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 spectra of the low refractive index films according to each Example and Comparative Example 1, the absorbance Ia derived from hydrocarbon groups (CH3 and CH2) not directly bonded to silicon atoms was determined as follows. In the absorption band derived from 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 wavenumber 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 above the baseline at the wavenumber where base Expressed 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 due to the bond between a silicon atom and a methyl group (Si—CH3) was determined in the same manner as the absorbance Ia. As shown in the enlarged part (2) of FIG. 1, a baseline was determined, and the absorbance on the baseline at the wavenumber where the maximum absorbance value appears was subtracted from the maximum absorbance value to obtain the absorbance Ib. In other words, the maximum absorbance value was calculated as A max (Si-CH3), and the absorbance on the baseline at the wavenumber where the maximum absorbance appears is A. base When expressed as (Si-CH3), the absorbance Ib is calculated as follows: was determined by Equation 6). 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 absorbance in the absorption band derived from the bond between a silicon atom and a hydroxyl group (Si—OH) was determined as the absorbance Ic derived from that bond. In determining the absorbance Ic, no baseline correction was performed.

[0072] In the absorption spectra of the low refractive index films according to each Example and Comparative Example 1, three maximum values ​​of 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 the bond. Among the absorbance Id, the second absorbance Ie, and the third absorbance If, ​​the first absorbance Id is the smallest. The first absorbance Id and the second absorbance If corresponded to the maximum wavenumber. No baseline correction was performed in determining absorbance Ie and the third absorbance If. It was.

[0073] In the low refractive index films according to each Example and Comparative Example 1, the absorbance Ia, absorbance Ib, absorbance Ic, first absorbance Id, second absorbance Ie, and third absorbance If determined as described above were Based on this, the inorganic-organic parameter (D), hydrophobic parameter (H), and first to third network parameters (N1, N2, and N3) were determined according to the following (Equation 7) to (Equation 11). The results are shown in Table 1. Inorganic-organic parameter (D) = Ib / Ia (Equation 7) Hydrophobicity 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 formation] When the liquid composition of each Example and Comparative Example 1 was applied to a glass substrate or a polycarbonate substrate, if it was confirmed that there were areas where the liquid composition could not be applied or that the thickness of the low refractive index film was uneven, the film-forming ability of the liquid composition was evaluated as "x." If these were not confirmed, the film-forming ability of the liquid composition was evaluated as "a." The results are shown in Table 1.

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

[0076] [Refractive Index] A low refractive index film for each example was formed under the same conditions as those for fabricating the anti-reflection structure for each example, except that a silicon substrate was used as the substrate. A refractive index measurement sample for each example was prepared. The reflectance of the refractive index measurement sample for each example was measured using a spectrophotometer (Hitachi High-Technologies Corporation, product name: U-4000), and the refractive index of the low refractive index film for each example was determined according to reflectance spectroscopy. The results are shown in Table 1.

[0077] Example 1 0.6 g of tetraethoxysilane (TEOS) (Tokyo Chemical Industry Co., Ltd.), 1.18 g of methyltriethoxysilane (MTES) (Tokyo Chemical Industry Co., Ltd.), 0.82 g of 0.3 wt % formic acid (Kishida Chemical Co., Ltd.), 3 g of hollow silica particle sol (JGC Catalysts and Chemicals Co., Ltd., product name: Sururia 4110, silica solid content: approximately 25 wt %), and 22.4 g of ethanol (Kishida Chemical Co., Ltd.) were mixed and reacted at 35°C for 3 hours. In this way, a liquid composition according to Example 1 was obtained. In the hollow silica particle sol, the average particle diameter of the hollow silica particles was approximately 50 nm, the thickness of the silica shell was 10 to 20 nm, the maximum dimension of the internal space of the hollow silica particles was approximately 10 to 30 nm, and the refractive index of the hollow silica particles was 1.25. The solid content of the liquid composition according to Example 1 contained 0.6 wt% silica derived from TEOS, 1.6 wt% polymethylsilsesquioxane derived from MTES, and 2.6 wt% hollow silica particles. The ratio of the amount of MTES to the amount of TEOS added in preparing 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 the silica derived from TEOS and the polymethylsilsesquioxane derived from MTES was 1.3 / 1.1.

[0078] A glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) was washed in ultrapure water for 15 minutes using an ultrasonic cleaner, a commercially available alkaline cleaning solution for 15 minutes, and ultrapure water for 15 minutes. The liquid composition according to Example 1 was applied to both main surfaces of the washed glass substrate by spin coating. Immediately after application, a uniform coating film with good appearance was obtained. The coating film was then dried in an oven at 200°C for 10 minutes to obtain a low refractive index film according to Example 1. This resulted in an antireflection structure according to Example 1, which includes a glass substrate and a low refractive index film formed on the glass substrate, as shown in FIG. 2. Observation of the appearance of the low refractive index film according to Example 1 revealed that 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 molar ratio of polymethylsilsesquioxane to silica was 7 / 3.

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

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

[0081] <Examples 10 and 11> A core-shell structure was prepared by forming a magnesium fluoride shell around a silica core. The silica core of this particle was dissolved in an alkaline solution to prepare hollow magnesium fluoride particles. The magnesium fluoride hollow particles had an average particle diameter of approximately 50 nm, a magnesium fluoride shell thickness of approximately 10 nm, a maximum internal space dimension of approximately 30 nm, and a refractive index of 1.20. Liquid compositions according to Examples 10 and 11 were obtained in the same manner as in Example 1, except that the magnesium fluoride hollow particles were used instead of hollow silica particles. Furthermore, a low refractive index film according to Example 10 and an antireflection structure according to Example 10 were prepared 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. Furthermore, a low refractive index film according to Example 11 and an antireflection structure according to Example 11 were prepared 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 of Example 1, except that the hollow silica particle sol was not added. This coating composition was applied by spin coating 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 alkaline cleaning. The coating film of the coating composition was then 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 applied by spin coating onto the inner low-refractive-index film. The coating film of the liquid composition was then dried in an oven at 200°C for 10 minutes to form a low-refractive-index film of Example 12, and an anti-reflection structure of Example 12 was fabricated, as shown in FIG. 3A . The thickness of the low-refractive-index film of Example 12 was 95 nm. The coating compositions had good film-forming properties on glass substrates, and the liquid composition according to Example 1 had good film-forming properties for the inner low refractive index film.

[0083] Example 13 An antireflection structure of Example 13 was produced 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 1. The liquid composition of Example 10 had 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, a low refractive index film according to Example 14 and an antireflection structure according to Example 14 were produced in the same manner as in Example 1. The liquid composition according to Example 1 had good film-forming properties even when a film was formed to a thickness of 180 nm.

[0085] Example 15 The liquid composition used in Example 1 was applied by spin coating to one main surface of a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) cleaned in the same manner as in Example 1, and the coating was then dried in an oven at 200°C for 10 minutes. A low refractive index film having a thickness of 100 nm was formed. Furthermore, the liquid composition used in Example 1 was applied to the other main surface of the glass substrate by spin coating, and the applied film was then dried in an oven at 200°C for 10 minutes to form a low refractive index film having a thickness of 180 nm, thereby producing the low refractive index film of Example 15 and the antireflection structure of Example 15 as shown in Figure 2. The liquid composition of Example 1 also had good film-forming properties in this case.

[0086] Example 16 The liquid composition used in Example 1 was applied by spin coating to both main surfaces of a glass substrate (float glass, size: 40 mm × 40 mm, thickness: 1 mm, refractive index: 1.52) cleaned in the same manner as in Example 1. The coating film 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, the coating composition used in Example 12 was applied by spin coating to the third low-refractive-index film, and the coating film 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 according to Example 1 was applied by spin coating to the second low-refractive-index film, and the coating film was then 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 producing the anti-reflection structure according to Example 16 shown in FIG. 3B. The liquid composition of Example 1 also had good film-forming properties on glass substrates and low refractive index films, and the coating composition of Example 12 had good film-forming properties on low refractive index films.

[0087] <Comparative Example 1> A liquid composition according to Comparative Example 1 was obtained in the same manner as in Example 1, except that in preparing the liquid composition, the ratio of the molar amount of methyltriethoxysilane (MTES) to the molar amount 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 reflectances of the antireflection structures according to Examples 1 to 5 were 1.6% or less. The visible light reflectances of the antireflection structures according to Examples 6 to 9 were 1.3% or less. The visible light reflectances of the antireflection structures according to Examples 10 and 11 were 1.1% or less. The visible light reflectances of the antireflection structures according to Examples 12 and 13 were 0.2% or less. As such, it was confirmed that the antireflection structures according to each Example were able to exhibit high antireflection performance. As shown in FIG. 10, the spectral reflectances of the antireflection structures according to Examples 1, 7, 10, and 11 were 5% or less across the entire visible light range (wavelength range of 380 nm to 780 nm). As shown in FIG. 11, the spectral reflectance of the antireflection structure according to Example 12 was 4% or less across the entire visible light range, and the spectral reflectance of the antireflection structure according to Example 13 was 3% or less across the entire visible light range.

[0089] As shown in Table 1, the visible light reflectance of the antireflection structure according to Example 14 was 4.2%. Furthermore, 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 range, and in the near-infrared range (wavelengths of 800 nm to 2500 nm), the average spectral reflectance in the wavelength range of 800 nm to 1000 nm, which is close to the visible light range, was 0.4%, and the average spectral reflectance in the wavelength range of 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%. In addition, 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 range, and was 4.8% or less at wavelengths of 80 nm, which are close to the visible light range in the near-infrared range. The average value of the spectral reflectance in the wavelength range of 0 nm to 1000 nm 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%. Furthermore, 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 range, the average spectral reflectance in the near-infrared range of 800 nm to 1000 nm, which is close to the visible light range, was 3.3%, and the average spectral reflectance in the wavelength range of 800 nm to 1100 nm was 3.6%.

[0092] [Table 1] [Explanation of symbols]

[0093] 1 film (first low refractive index layer) 10 hollow particles 20 binder 30 boards 40 Second low refractive index layer 50a, 50b, 50c anti-reflection structure 60 Third low refractive index layer 70a, 70b Imaging device 71 Housing 72 Lens system 72a~72d Single Lens 73 Filters 73a Infrared absorbing glass 73b Infrared absorbing 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. hollow particles made of a material having a refractive index of 1.15 to 2.70; a binder formed of at least polysilsesquioxane that binds the hollow particles together; When the absorbance attributable to hydrocarbon groups not directly bonded to silicon atoms, the absorbance attributable to bonds between silicon atoms and non-reactive functional groups, and the absorbance attributable to bonds between silicon atoms and hydroxy groups are represented by Ia, Ib, and Ic, respectively, as determined by total reflection measurement using a Fourier transform infrared spectrophotometer, at least one of the conditions Ib / Ia≧0.7 and Ib / Ic≧0.3 is satisfied. film.

2. 2. The membrane of claim 1, further satisfying the conditions Ib / Ia≧0.7 and Ib / Ic≧0.

3.

3. When the first absorbance, the second absorbance, and the third absorbance, which are determined by the total reflectance measurement method and are derived from a bond between one oxygen atom and two silicon atoms, are represented by 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 a first wavenumber, the second absorbance Ie corresponds to a second wavenumber that is greater than the first wavenumber, The third absorbance If corresponds to a third wavenumber that is greater than the second wavenumber.

3. The membrane of claim 1 or 2.

4. 4. The membrane of claim 3, further satisfying the conditions Id / Ib≦60, Ie / Ib≦20, and If / Ib≦174.

5. The film according to any one of claims 1 to 4, wherein the polysilsesquioxane is a polysilsesquioxane in which a hydrocarbon group containing 16 or less carbon atoms is bonded to a silicon atom as the non-reactive functional group.

6. The film according to any one of claims 1 to 5, wherein the hollow particles have an average particle size of 10 to 150 nm.

7. 7. The membrane according to claim 1, wherein the hollow particles are made of at least one selected from the group consisting of silica, magnesium fluoride, alumina, aluminosilicate, titania, and zirconia.

8. The film according to any one of claims 1 to 7, having a refractive index of 1.35 or less.

9. A liquid composition comprising: hollow particles made of a material having a refractive index of 1.15 to 2.70; Polysilsesquioxane, a solvent; In a cured product obtained by applying the liquid composition to a substrate and curing the liquid composition, the absorbance attributable to a hydrocarbon group not directly bonded to a silicon atom, the absorbance attributable to a bond between a silicon atom and a non-reactive functional group, and the absorbance attributable to a bond between a silicon atom and a hydroxy group, as determined by total reflection measurement using a Fourier transform infrared spectrophotometer, are expressed as Ia, Ib, and Ic, respectively, and satisfy at least one of the conditions Ib / Ia≧0.7 and Ib / Ic≧0.

3. Liquid composition.

10. The liquid composition according to claim 9 , wherein the cured product further satisfies the conditions Ib / Ia≧0.7 and Ib / Ic≧0.

3.

11. In the cured product, when a first absorbance, a second absorbance, and a third absorbance derived from a bond between one oxygen atom and two silicon atoms as determined by the total reflectance measurement method are represented by 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 a first wavenumber, the second absorbance Ie corresponds to a second wavenumber that is greater than the first wavenumber, The third absorbance If corresponds to a third wavenumber that is greater than the second wavenumber. The liquid composition according to claim 9 or 10.

12. The liquid composition according to claim 11, wherein the cured product further satisfies the conditions Id / Ib≦60, Ie / Ib≦20, and If / Ib≦174.

13. The polysilsesquioxane is a polysilsesquioxane in which a hydrocarbon group containing 16 or less carbon atoms is bonded to a silicon atom as the non-reactive functional group. The liquid composition according to any one of claims 9 to 12.

14. The liquid composition according to any one of claims 9 to 13, wherein the hollow particles have an average particle diameter of 10 to 150 nm.

15. The liquid composition according to any one of claims 9 to 14, wherein the hollow particles are made of at least one selected from the group consisting of silica, magnesium fluoride, alumina, aluminosilicate, titania, and zirconia.

16. An optical element comprising the film according to any one of claims 1 to 8.

17. An imaging device comprising the optical element according to claim 16.

Images