JP2009237557A - Optical element having anti-reflection coating, pickup lens for optical information recording/reproducing device and optical information recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element which has an anti-reflection coating having a proper refractive index and excellent scratch resistance, adhesion to a lens, has a high curvature radius and has excellent anti-reflection performance on the whole inside a lens effective diameter region, a pickup lens for an optical information recording/reproducing device using the optical element, and the optical information recording/reproducing device. <P>SOLUTION: The optical element is provided with a lens 1 for having a part S where a surface inclination angle is ≥50° for 10% or more in the projection area S<SB>0</SB>of an effective diameter region and the anti-reflection coating 2 formed on the surface of the lens 1. The anti-reflection coating 2 includes a mesoporous silica coating composed of gathered mesoporous silica nano-particles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention has an antireflection film excellent in scratch resistance and adhesion to a lens, an optical element having an overall antireflection property and a high curvature in the lens effective diameter region, and optical information using the same The present invention relates to a pickup lens for a recording / reproducing apparatus and an optical information recording / reproducing apparatus.

A lens having a high curvature is used as an objective lens of an optical information recording / reproducing apparatus (optical pickup apparatus) or a semiconductor exposure apparatus. A typical example of a lens having a high curvature is a lens having a large numerical aperture (NA). In recent years, an optical pickup device using an objective lens having a laser wavelength of 405 nm and an NA of 0.85 has been proposed. A lens with NA of 0.85 has a shape as shown in FIG. When used as an objective lens, laser light is irradiated from the R ₁ surface side and transmitted to the R ₂ surface side. The laser light is substantially parallel light and is irradiated so as to be perpendicularly incident on the center of the objective lens. For this reason, the light incident angle is very large at the periphery of the lens. In the example shown in FIG. 6, the maximum incident angle of light within the effective diameter region E of the lens is 65 °. The objective lens desirably transmits the irradiated light efficiently, but the amount of reflected light increases in proportion to the incident angle. FIG. 7 shows the reflectivity of the R ₁ surface of a lens made of glass having the shape shown in FIG. 6 and having a reflectivity of 1.72. At the position where the light incident angle is 65 °, 15.5% of the irradiated light is reflected.

In order to reduce the amount of reflected light and efficiently transmit the irradiation light, the surface of the objective lens of the optical pickup device or the semiconductor exposure device is coated with an antireflection film. For example, in a single-layer antireflection film, the optical path difference between the reflected light on the surface and the reflected light at the interface between the antireflection film and the lens becomes an odd multiple of 1/2 of the wavelength, and these lights are caused by interference. It is designed to have a thickness that cancels out. The single-layer antireflection film is designed to have a refractive index smaller than that of the lens and larger than that of an incident medium such as air. It is said that the refractive index of the antireflection film of a lens made of glass having a refractive index of about 1.45 to 1.85 is ideally 1.2 to 1.35. However, since there is no substance having such an ideal refractive index, MgF ₂ having a refractive index of 1.38 is widely used as an antireflection film material.

Conventionally, an antireflection film made of an inorganic material such as MgF ₂ has been formed by vacuum deposition, sputtering, CVD, or the like. However, when the antireflection film is formed by these methods, the antireflection film is generally thinner in the peripheral portion than in the central portion of the lens. In general, the optical film thickness D (θ ′) of the antireflection film at the position of the incident angle θ ′ is an expression: D (θ ′) = D ₀ · (cos θ ′) ^x (where D ₀ is the reflection at the center of the lens) Represents an optical film thickness of the anti-reflection film, and X represents a constant of 0 or more and 1 or less.) When the anti-reflection film is formed by vacuum deposition, X is about 0.7. For this reason, the lens peripheral portion deviates from the designed film thickness, and the light incident angle is large as described above, so that the antireflection effect cannot be sufficiently obtained and the amount of reflected light is very large. Therefore, although such an optical element has a large amount of transmitted light at the center, there is a problem that the amount of transmitted light is not sufficient for the entire element. In addition, a vacuum apparatus is indispensable for forming an antireflection film by vapor deposition, and there is a problem that the cost is high.

  Therefore, JP-A-2006-215542 (Patent Document 1) is composed of a dense layer and a silica airgel porous layer that are sequentially formed on the surface of the substrate, and the refractive index decreases in order from the substrate to the silica airgel porous layer. Proposed anti-reflective coating. This silica airgel porous layer is obtained by (i) reacting sol- or gel-like silicon oxide with an organic modifier to form an organic-modified sol or organic-modified gel, and (ii) converting the organic-modified sol or organic-modified gel into a sol. The resulting organically modified silica gel layer is subjected to a springback phenomenon to form an organically modified silica airgel layer, and (iii) the organically modified silica airgel layer is heat treated to remove the organically modified groups. To form.

  The refractive index of the silica airgel porous layer is as small as about 1.20, and the antireflection film having the silica airgel porous layer has excellent antireflection characteristics in a wide wavelength range. Moreover, since the silica airgel porous layer can be produced by a sol-gel method, it is excellent in cost performance. However, the mechanical strength was weak, the adhesion to the substrate was weak, and the scratch resistance was not sufficient.

  Japanese Patent Laid-Open No. 2006-130889 (Patent Document 2) is a thick film exceeding 1 μm, but does not generate cracks / peeling due to volume shrinkage due to heat treatment, has a small refractive index, and ranges from the visible light region to the near infrared region. As a transparent inorganic porous film having a high transmittance of 90% or more, a mesoporous silica thin film formed on a substrate surface and having nanoscale fine pores is proposed. This mesoporous silica thin film is prepared by applying a mixed solution of a surfactant, a silica raw material such as tetraethoxysilane, water, an organic solvent, and an acid or alkali to a base material to prepare an organic-inorganic composite film. Manufactured by drying and photooxidation to remove organic components.

  Japanese Patent No. 3668126 (Patent Document 3) discloses a ceramic precursor such as tetraethoxysilane, a catalyst, a method of forming a ceramic film having a low dielectric constant (due to high porosity and low refractive index). A method has been proposed in which a liquid comprising a surfactant and a solvent is prepared, applied to a substrate, and the solvent and the surfactant are removed to form a porous silica film.

  However, the mesoporous silica thin film of Patent Document 2 and the porous silica film of Patent Document 3 form a silicate network around the micelles of the surfactant when the coating film is dried, and proceed with hydrolysis and polycondensation. The network is formed by a process for forming a solid thin film. Therefore, even if these films are formed on a lens having a high curvature, hydrolysis and polycondensation after application takes a long time, so that the coating liquid flows and the coating film becomes non-uniform.

JP 2006-215542 A JP 2006-130889 Japanese Patent No. 3668126 Specification

  Accordingly, an object of the present invention is to provide an optical element having an antireflection film excellent in scratch resistance and adhesion to a lens, having an overall antireflection property within the lens effective diameter region, and having a high curvature. An optical information recording / reproducing apparatus pickup lens and an optical information recording / reproducing apparatus used are provided.

  As a result of diligent research in view of the above object, the inventors of the present invention have excellent scratch resistance and adhesion to the lens when a mesoporous silica porous film formed by collecting mesoporous silica nanoparticles is formed on a lens having a high curvature. The present inventors have found that an optical element having an antireflection film and having an antireflective property as a whole in the lens effective diameter region and having a high curvature can be obtained.

  That is, the optical element of the present invention is formed by aggregating a lens having a surface inclination angle of 50 ° or more in a projected area of an effective diameter region of 10% or more and mesoporous silica nanoparticles formed on the surface thereof. It is characterized by comprising an antireflection film made of a mesoporous silica porous film.

  The mesoporous silica nanoparticles preferably have an average particle size of 200 nm or less. The mesoporous silica nanoparticles preferably have a porous structure in which mesopores are arranged in a hexagonal shape.

  The mesoporous silica porous membrane preferably has a structure in which a pore size distribution curve obtained by a nitrogen adsorption method has two peaks. The pore size distribution curve of the mesoporous silica membrane preferably has a peak due to an intraparticle pore size within a range of 2 to 10 nm and a peak due to an interparticle pore size within a range of 5 to 200 nm. The pore volume ratio between the intraparticle pores and the interparticle pores is preferably 1/2 to 1/1. The refractive index of the mesoporous silica porous film is preferably more than 1.10 and not more than 1.35. The mesoporous silica porous membrane preferably has a physical thickness of 15 to 500 nm.

  The optical element of the present invention is suitable as a pickup lens for an optical information recording / reproducing apparatus.

  The optical element of the present invention having an antireflection film composed of a mesoporous silica porous film in which mesoporous silica nanoparticles are aggregated has a high curvature, but the entire lens effective diameter region is excellent in antireflection properties. The antireflection film is also excellent in scratch resistance and adhesion to the lens. An optical element having such characteristics is suitable as a lens used for an optical information recording / reproducing apparatus, a semiconductor exposure apparatus, a camera, an endoscope, an optical communication component, and the like. Since the optical element of the present invention forms an antireflection film by a sol-gel method, it does not require an expensive processing apparatus and can be manufactured at a low cost.

An example of the optical element of this invention is shown, (a) is a longitudinal cross-sectional view, (b) is a top view. It is a partial expanded sectional view of the optical element of FIG. It is a perspective view which shows an example of the mesoporous silica particle which comprises the anti-reflective film of FIG. It is a graph which shows a typical pore size distribution curve. 3 is a graph showing a pore size distribution curve of an antireflection film of Example 1. It is sectional drawing which shows an example of the conventional objective lens of an optical pick-up apparatus. It is a graph which shows the relationship between the light beam incident angle and reflectance of the lens of FIG.

[1] Optical Element The optical element of the present invention will be described in detail below with reference to the accompanying drawings. Of course, the present invention is not limited to the illustrated optical element. FIG. 1 shows an example of the optical element of the present invention. This optical element includes a lens 1 having a convex surface 11 and an antireflection film 2 formed on the convex surface 11. The back surface side of the optical element is a concave surface 12. In this example, the antireflection film 2 is formed only on the convex surface 11 of the lens 1, but the antireflection film 2 may be formed on the convex surface 11 and the concave surface 12. In addition, it is also within the scope of the present invention that the annular surface is formed on the convex surface 11 and / or the concave surface 12 so as to cause diffraction. For the sake of explanation, the antireflection film 2 is shown thicker than the actual thickness.

As shown in FIG. 1B, the projection area S of the portion where the surface inclination angle θ in the effective diameter region E of the lens 1 is 50 ° or more is 10% or more of the projection area S ₀ of the effective diameter region E. . In the case of such a lens, the maximum surface inclination angle θmax in the effective diameter region E is 60 ° to 75 °. As shown in FIG. 2, the surface inclination angle θ at an arbitrary point T on the convex surface 11 of the lens 1 is defined as an angle formed by a surface Fo in contact with the center point 110 of the convex surface 11 and a surface F in contact with the point T. A lens having a maximum surface inclination angle θmax of 60 ° to 75 ° is suitable for an objective lens such as an optical information recording / reproducing apparatus. When the incident light is parallel light such as laser light, the light incident angle θ ′ of the optical element is equal to the surface inclination angle θ.

  The refractive index of the lens 1 is preferably 1.45 to 1.85. If the refractive index is less than 1.45, it is difficult to achieve high NA. If the refractive index is more than 1.85, light having a wavelength in the ultraviolet to blue range is absorbed, and thus is not particularly suitable for laser light having a wavelength of 405 nm. Examples of the material having a refractive index of 1.45 to 1.85 include BK7, LASF01, LASF016, LAK14, SF5, optical glass such as quartz glass, and Pyrex (registered trademark) glass.

  The antireflection film 2 is made of a porous mesoporous silica film in which mesoporous silica nanoparticles are aggregated. FIG. 3 shows an example of mesoporous silica nanoparticles. The particle 20 includes a silica skeleton 20b having a porous structure in which mesopores 20a are arranged in a hexagonal shape. However, the mesoporous silica nanoparticles 20 are not limited to such a hexagonal structure, and may have a cubic structure or a lamellar structure. Therefore, the mesoporous silica porous membrane may be any one of these three types of structured particles or a mixture thereof, but is preferably composed of hexagonal structured particles 20. In the mesoporous silica nanoparticles 20, the mesopores 20a are uniformly formed in a hexagonal shape, so that the mesoporous silica porous film has excellent transparency, mechanical strength, and crack resistance.

  The average particle size of the mesoporous silica nanoparticles 20 is preferably 200 nm or less, and more preferably 20 to 50 nm. If the average particle size exceeds 200 nm, it is difficult to adjust the film thickness, and the flexibility of thin film design is low. In addition, the antireflection property and crack resistance of the mesoporous silica porous film are also low. The average particle diameter of the mesoporous silica nanoparticles 20 is determined by a dynamic light scattering method. The refractive index of the mesoporous silica porous film depends on the porosity, and the larger the porosity, the smaller the refractive index. The porosity of the mesoporous silica porous membrane is preferably 25% or more and less than 75%. The refractive index of the porous mesoporous silica film having a porosity of 25% or more and less than 75% is more than 1.10 to 1.35 or less, preferably 1.15 to 1.30. When the porosity is more than 75%, the scratch resistance, mechanical strength and crack resistance are too small. If the porosity is less than 25%, the refractive index is too large. This porosity is more preferably 35 to 65%.

  As shown in FIG. 4, the pore size distribution curve of the mesoporous silica membrane 20 obtained by the nitrogen adsorption method preferably has two peaks. Specifically, the pore size distribution curve obtained by analyzing by the BJH method from the isothermal desorption curve of nitrogen obtained for the mesoporous silica porous membrane 20 (the horizontal axis is the pore diameter and the vertical axis is the log differential pore volume) Preferably has two peaks. The BJH method is described in, for example, “Method for obtaining mesopore distribution” (E. P. Barrett, L. G. Joyner, and P. P. Halenda, J. Am. Chem. Soc., 73, 373 (1951)). The log differential pore volume is a change amount of the differential pore volume dV with respect to the logarithmic difference value d (logD) of the pore diameter D, and is expressed by dV / d (logD). The first peak on the small pore diameter side indicates the diameter of the intraparticle pores, and the second peak on the large pore diameter side indicates the diameter of the interparticle pores. The mesoporous silica porous membrane preferably has a distribution in which the intraparticle pore diameter is in the range of 2 to 10 nm and the interparticle pore diameter is in the range of 5 to 200 nm. A mesoporous silica porous membrane having an intraparticle pore size and an interparticle pore size within the above range has an appropriate refractive index of more than 1.10 to 1.35 or less, excellent antireflection properties, scratch resistance, and adhesion to the lens 1. .

The ratio of pore volume within a particle V ₁ and inter-particle pore volume V ₂ is preferably 1 / 2-1 / 1. The mesoporous silica porous film 20 having this ratio in the above range is excellent in the balance between antireflection properties and crack resistance. This ratio is more preferably from 1 / 1.9 to 1 / 1.2. The volumes V ₁ and V ₂ are obtained as follows. In FIG. 4, a straight line passing through the minimum point E of the ordinate between the first and second peaks and parallel to the horizontal axis is defined as a base line L _0, and the maximum inclination line of each peak (tangent line at the maximum inclination point) ) The horizontal axis coordinates (D _{A to} D _D ) at the intersections A to D of L _{1 to} L ₄ and the baseline L ₀ are obtained. Analysis data each by the BJH method, and V ₁ calculates the total volume of pores having a diameter in the range of D _A to D _B, calculates a total volume of pores having a diameter in the range of D _C to D _D To V ₂ .

The preferred physical film thickness of the mesoporous silica porous membrane is 15 to 500 nm, more preferably 100 to 150 nm. In FIG. 1A, the ratio D / D ₀ between the physical film thickness D of the antireflection film 2 and the physical film thickness D _{0 at} the center of the lens 1 at the periphery of the lens 1 is COSθ ^{0.7 to} COS (SIN ⁻¹ ( SINθ / n)) ⁻¹ (θ is the surface inclination angle of the antireflection film 2 and n is the refractive index of the antireflection film 2). The peripheral part of the lens 1 is a part having a surface inclination angle θ of 50 ° or more. Although the physical film thickness of the antireflection film 2 gradually decreases from the center of the lens to the periphery, the decrease is relatively small. For this reason, even if the lens is designed to have an optimum film thickness at the center of the lens, the film thickness of the antireflection film 2 in the lens peripheral portion is not too small and exhibits good antireflection properties. When the physical film thickness of the antireflection film 2 in the periphery of the lens 1 is not uniform, any of the maximum value, the minimum value, and the average value may be used as the physical film thickness D.

  In the example shown in FIG. 1, the antireflection film 2 is a single layer, but the present invention is not limited to this, and includes one having a layer other than the mesoporous silica porous film. In the case of the multilayer antireflection film 2, it is preferable to have a porous mesoporous silica film on the outermost surface. By providing the mesoporous silica porous film on the outermost surface, a good antireflection effect with a low refractive index can be obtained.

[2] Optical Element Manufacturing Method The optical element manufacturing method will be described by taking as an example the case where the antireflection film 2 made of only a mesoporous silica porous film is formed on the surface of the lens 1, but is not limited thereto.

  The mesoporous silica porous membrane comprises (i) hydrolyzing and polycondensing alkoxysilane by aging a mixed solution of solvent, acidic catalyst, alkoxysilane, cationic surfactant and nonionic surfactant, and (ii) By adding a basic catalyst to the obtained acidic sol containing silicate, mesoporous silica nanoparticles coated with a nonionic surfactant and having a cationic surfactant in the pores (hereinafter referred to as “surfactant- (Iii) coating the sol on the surface of the lens 1, (iv) drying to remove the solvent, and (v) firing. It can be formed by removing the cationic surfactant and the nonionic surfactant.

(a) Raw material
(a-1) Alkoxysilane The alkoxysilane may be a monomer or an oligomer. The alkoxysilane monomer preferably has 3 or more alkoxyl groups. By using an alkoxysilane having three or more alkoxyl groups as a starting material, a mesoporous silica porous film having excellent uniformity can be obtained. Specific examples of the alkoxysilane monomer include methyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, tetrapropoxysilane, diethoxydimethoxysilane, dimethyldimethoxysilane, dimethyldi An ethoxysilane etc. are mentioned. As the alkoxysilane oligomer, polycondensates of the above-mentioned monomers are preferable. The alkoxysilane oligomer is obtained by hydrolysis and polycondensation of an alkoxysilane monomer. Specific examples of the alkoxysilane oligomer include silsesquioxane represented by the general formula RSiO _1.5 (where R represents an organic functional group).

(a-2) Surfactant
(i) Cationic surfactant Examples of the cationic surfactant include halogenated alkyltrimethylammonium, halogenated alkyltriethylammonium, halogenated dialkyldimethylammonium, halogenated alkylmethylammonium, and halogenated alkoxytrimethylammonium. Examples of the alkyl trimethyl ammonium halide include lauryl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, stearyl trimethyl ammonium chloride, benzyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride and the like. Examples of the halogenated alkyltrimethylammonium include n-hexadecyltrimethylammonium chloride. Examples of the dialkyldimethylammonium halide include distearyldimethylammonium chloride and stearyldimethylbenzylammonium chloride. Examples of the halogenated alkylmethylammonium include dodecylmethylammonium chloride, cetylmethylammonium chloride, stearylmethylammonium chloride, and benzylmethylammonium chloride. Examples of the halogenated alkoxytrimethylammonium include octadecyloxypropyltrimethylammonium chloride.

(ii) Nonionic surfactant Examples of the nonionic surfactant include block copolymers of ethylene oxide and propylene oxide, polyoxyethylene alkyl ethers, and the like. As a block copolymer of ethylene oxide and propylene oxide, for example, the formula: RO (C ₂ H ₄ O) _a- (C ₃ H ₆ O) _b- (C ₂ H ₄ O) _c R (where a and c are each 10 To 120, b represents 30 to 80, and R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms). Examples of commercially available block copolymers include Pluronic (registered trademark, BASF). Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether and the like.

(a-3) Catalyst
(i) Acid catalyst Examples of the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as formic acid and acetic acid.

(ii) Basic catalyst Examples of the basic catalyst include ammonia, amine, NaOH and KOH. Examples of preferred amines include alcohol amines and alkyl amines (methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine, etc.).

(a-4) Pure water is used as the solvent.

(b) Formation method
(b-1) Hydrolysis and polycondensation under acidic conditions An acidic catalyst is added to pure water to prepare an acidic solution, and then a mixed solution of a cationic surfactant and a nonionic surfactant is prepared. Add silane, hydrolyze and polycondensate. The pH of the acidic solution is preferably about 2. Since the isoelectric point of the silanol group of alkoxysilane is about pH 2, the silanol group stably exists in an acidic solution near pH 2. The solvent / alkoxysilane molar ratio is preferably 30-300. When this molar ratio is less than 30, the degree of polymerization of alkoxysilane becomes too high. On the other hand, if it exceeds 300, the degree of polymerization of alkoxysilane becomes too low.

The molar ratio of the cationic surfactant / solvent is preferably 1 × 10 ^{−4 to} 3 × 10 ⁻³ , whereby mesoporous silica nanoparticles having excellent mesopore regularity can be obtained. This molar ratio is more preferably 1.5 × 10 ⁻⁴ to 2 × 10 ⁻³ .

The molar ratio of cationic surfactant / alkoxysilane is preferably 1 × 10 ^{−1 to} 3 × 10 ⁻¹ . If this molar ratio is less than 1 × 10 ⁻¹ , the mesoporous silica nanoparticle mesostructure is not sufficiently formed. On the other hand, if it exceeds 3 × 10 ^−1, the particle size of the mesoporous silica nanoparticles becomes too large. This molar ratio is more preferably 1.5 × 10 ^{−1 to} 2.5 × 10 ⁻¹ .

The nonionic surfactant / alkoxysilane molar ratio is 3.5 × 10 ⁻³ or more and less than 2.5 × 10 ⁻² . If this molar ratio is less than 3.5 × 10 ⁻³ , the refractive index of the porous mesoporous silica film becomes too large. On the other hand, when it is 2.5 × 10 ⁻² or more, the refractive index of the mesoporous silica porous film is 1.10 or less.

  The molar ratio of the cationic surfactant / nonionic surfactant is preferably more than 8 to 60, whereby mesoporous silica nanoparticles having excellent mesopore regularity can be obtained. The molar ratio is more preferably 10-50.

  The solution containing alkoxysilane is aged for 1 to 24 hours. Specifically, the solution is allowed to stand at 20 to 25 ° C. or slowly stirred. Hydrolysis and polycondensation proceed by aging, and an acidic sol containing silicate (an oligomer starting from alkoxysilane) is generated.

(b-2) Hydrolysis and polycondensation under basic conditions A basic catalyst is added to an acidic sol to make the solution basic, followed by hydrolysis and polycondensation to complete the reaction. Thereby, mesoporous silica nanoparticles having an average particle size of 200 nm or less are obtained. The pH of the solution is preferably adjusted to 9-12.

  By adding a basic catalyst, a silicate skeleton is formed around the cationic surfactant micelle, and a regular hexagonal array grows to form particles in which silica and the cationic surfactant are combined. The As the composite particles grow, the effective charge on the surface decreases, so that the nonionic surfactant is adsorbed on the surface. As a result, a solution (sol) of mesoporous silica nanoparticles (see FIG. 3 for the particle shape) coated with a nonionic surfactant and having a cationic surfactant in the pores is obtained [for example, Imai Hiroaki, “Chemical Industry”, Chemical Industry, September 2005, Vol. 56, No. 9, pp.688-693]. In the formation process of the mesoporous silica nanoparticles, the growth of the composite particles is suppressed by the adsorption of the nonionic surfactant. Therefore, the mesoporous silica nanoparticles obtained by the preparation method using the above two types of surfactants The particles have an average particle size of 200 nm or less and excellent regularity of mesopores.

(b-3) Application The surface of the lens 1 is coated with a solution (sol) of a surfactant-mesoporous silica nanoparticle composite. Examples of the sol coating method include a spin coating method, a dip coating method, a spray coating method, a flow coating method, a bar coating method, a reverse coating method, a flexo method, a printing method, and a method using these in combination. The thickness of the obtained porous film can be controlled, for example, by adjusting the rotation speed of the lens in the spin coating method, adjusting the pulling speed in the dipping method, adjusting the concentration of the coating solution, and the like.

  A basic aqueous solution having the same pH as that of the sol may be added as a dispersion medium before coating so that the concentration and fluidity of the sol are in an appropriate range. The ratio of the surfactant-mesoporous silica nanoparticle composite in the coating solution is preferably 10 to 50% by mass. If it is out of this range, it is difficult to form a uniform thin film.

(b-4) Drying The solvent is evaporated from the applied sol. The drying conditions for the coating film are not particularly limited. Natural drying may be performed, or drying may be promoted by heat treatment at a temperature of 50 to 200 ° C. for 15 minutes to 1 hour.

(b-5) Firing The dried membrane is fired to remove the cationic surfactant and the nonionic surfactant, thereby forming a mesoporous silica porous membrane. The firing temperature is preferably higher than 500 ° C, more preferably 550 ° C or higher. If the baking temperature is 500 ° C. or lower, the refractive index is lowered and the mechanical strength of the film may be lowered. The upper limit of the firing temperature is preferably the glass transition temperature of the lens 1, and more preferably the glass transition temperature of the lens 1 -50 ° C. If the firing temperature exceeds the glass transition temperature of the lens 1, the lens 1 is deformed. The firing time is preferably 1 to 6 hours, more preferably 2 to 4 hours. Since the bond between the mesoporous silica particles and the bond between the mesoporous silica particles and the lens 1 are strengthened during firing, the scratch resistance, the adhesion to the lens 1 and the mechanical strength are improved.

[3] Use of optical element The optical element of the present invention has high antireflection characteristics for light in a wide wavelength range from the visible range to the infrared range within the effective lens diameter range. Optical elements having such characteristics include, for example, optical information recording / reproducing apparatuses, semiconductor exposure apparatuses, cameras, endoscopes, optical communication components [for example, laser diode (LD) modules, multiplexers, demultiplexers, etc. It is suitable as a lens used for the above. Light sources with various wavelengths are used for optical information recording / reproducing media [CD, DVD, Blu-ray Disk, HD-DVD, etc.], but the optical element of the present invention is used as a pickup lens for all of them. it can. The shape of the optical element of the present invention can be appropriately selected depending on the application. For example, when it is used as a pickup lens of an optical information recording / reproducing apparatus, it has a shape as shown in FIG. 1, and when it is used for an endoscope or an optical communication part, it has a ball shape.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
pH 2 hydrochloric acid (0.01N) 40 g, n-hexadecyltrimethylammonium chloride (manufactured by Kanto Chemical Co., Inc.) 1.21 g (0.088 mol / L), and block copolymer HO (C ₂ H ₄ O) _106- (C ₃ 1.10 g (0.002 mol / L) of H ₆ O) _70- (C ₂ H ₄ O) ₁₀₆ H (trade name “Pluronic F127”, Sigma-Aldrich) was added and stirred at 23 ° C. for 1 hour. Add Silane (Kanto Chemical Co., Ltd.) 4.00 g (0.45 mol / L), stir at 23 ° C for 3 hours, then add 3.94 g (1.51 mol / L) 28 mass% aqueous ammonia to adjust the pH to 11. And stirred at 23 ° C. for 0.5 hour.

The obtained surfactant-mesoporous silica nanoparticle composite solution (sol) was added to a lens 1 made of LAK14 glass (see FIG. 1, effective diameter of lens: 3 mm, S / S ₀ × 100: 62%, refractive index: 1.718). ) Is applied to the convex surface 11 by spray coating, dried at 80 ° C for 0.5 hours, and then fired at 600 ° C for 3 hours to coat a porous mesoporous silica film having a refractive index of 1.246 and a physical film thickness of 110 nm. I got a lens. For the measurement of the refractive index, a lens reflectometer (model number: USPM-RU, manufactured by Olympus Corporation) was used. The physical film thickness was the film thickness at the center of the lens 1 (site where the incident angle was 0 °) measured using this lens reflectometer.

  The average particle diameter of the mesoporous silica nanoparticles forming the antireflection film was 28 nm. The average particle size of the mesoporous silica nanoparticles was determined by measuring by a dynamic light scattering method [using a dynamic light scattering particle size distribution analyzer LB-550 (manufactured by Horiba, Ltd.). ].

Example 2
Porous mesoporous silica in the same manner as in Example 1 except that the lens 1 made of borosilicate crown glass (BK7) (lens effective diameter: 3 mm, S / S ₀ × 100: 62%, refractive index: 1.530) was used. An antireflection lens having a film was obtained.

Comparative Example 1
Antireflection by forming a MgF ₂ layer with a physical layer thickness of 132 nm on the convex surface 11 of the same LAK14 glass lens 1 as in Example 1 by vacuum evaporation using an apparatus having an electron beam evaporation source. A lens was produced.

Comparative Example 2
Using an apparatus having an electron beam evaporation source, an antireflection film (thickness of film thickness) is formed on the convex surface 11 of the same LAK14 glass lens 1 as in Example 1 by the vacuum evaporation method so as to have the structure shown in Table 1. A total of 391 nm) was formed to produce an antireflection lens.

Comparative Example 3
Antireflection by forming an MgF ₂ layer with a physical layer thickness of 114 nm on the convex surface 11 of the same BK7 glass lens 1 as in Example 2 by vacuum deposition using an apparatus having an electron beam deposition source. A lens was produced.

Comparative Example 4
In the same manner as in Example 1 of JP-A-2006-215542, an antireflection lens is formed by forming an antireflection film comprising an MgF ₂ layer and a silica airgel porous layer on the surface of the same BK7 glass lens 1 as in Example 2. Was made.

  With respect to the antireflection films of Examples 1 and 2 and Comparative Examples 1 to 4, transmittance was measured by the following method, and scratch resistance and adhesion were evaluated by the following methods. Further, as Comparative Examples 5 and 6, transmittance was measured only for the LAK14 glass lens and the BK7 glass lens. The results are shown in Table 1.

Measurement of transmittance A laser beam having a wavelength of 405 nm was incident on the antireflection lens from the convex surface 11, and the transmittance was examined.

Evaluation of scratch resistance The surface after the antireflection film was rubbed 10 times with a nonwoven fabric (trade name “Spic Lens Wiper”, manufactured by Ozu Sangyo Co., Ltd.) at a pressure of 1 kg / cm ² and a speed of 120 times / minute. By observing the above, the scratch resistance was evaluated. The evaluation criteria are: ○: “not scratched at all”, Δ: “slightly scratched but not peeled”, and x: “peeled”.

Evaluation of Adhesiveness After applying a cellophane tape to a 1 cm × 1 cm region of the antireflection film, the adhesiveness was evaluated by peeling the cellophane tape while pulling it in the 45 ° direction. The evaluation criteria are ○: “No peeling at all” and X: “Partial or all peeling”.

Note: (1) Laser wavelength 405 nm.
(2) η represents the refractive index.

Since the samples of Examples 1 and 2 have a mesoporous silica porous film, they have high transmittance with respect to laser light and excellent antireflection properties. On the other hand, the samples of Comparative Examples 1 and 3 have an antireflection film made of MgF _2, and the sample of Comparative Example 2 has a ZrO ₂ / MgF ₂ multilayer film. The antireflection performance was inferior to the sample of 2. Since the antireflection film of Comparative Example 4 had a silica airgel porous layer, the scratch resistance and adhesion were inferior to the antireflection films of Examples 1 and 2. The samples of Comparative Examples 5 and 6 that did not have the antireflection film were significantly inferior in antireflection properties as compared with the samples of Examples 1 and 2.

Measurement of pore size distribution With respect to the antireflection film of Example 1, an isothermal desorption curve of nitrogen gas was obtained with an automatic specific surface area / pore distribution measurement device “Tristar 3000” (Shimadzu Corporation) and analyzed by the BJH method. Thus, a pore size distribution curve (log differential pore volume distribution) was obtained. The results are shown in FIG.

As is clear from FIG. 5, the pore size distribution curve of the antireflection film of Example 1 has two peaks, the intraparticle pore size is in the range of 2 to 10 nm, and the interparticle pore size is 5 to 200 nm. Was in range. The D _A shown in FIG. 4 and 2.1 nm, and 3.2 nm to D _B, a D _C and 14.4 nm, a D _D a 27.7 nm, respectively the analysis data by the BJH method, with a diameter in the range of 2.1-3.2 nm The total volume of the pores is determined as the intraparticle pore volume V _1, and the total volume of the pores having a diameter in the range of 14.2 to 27.7 nm is determined as the interparticle pore volume V ₂ , and the ratio V ₁ / V ₂ As a result, it was 1 / 1.3.

1 ... Lens
11 ... Convex surface
110 ・ ・ ・ Center
12 ... Concave surface 2 ... Antireflection film
20 ・ ・ ・ Mesoporous silica nanoparticles
20a ・ ・ ・ Mesopore
20b ・ ・ ・ Silica skeleton

Claims (11)

An optical element having a lens whose surface inclination angle is 50% or more of the projected area of the effective diameter region is 10% or more, and an antireflection film formed on the surface of the lens, wherein the antireflection film Is an optical element comprising a mesoporous silica porous film in which mesoporous silica nanoparticles are aggregated. 2. The optical element according to claim 1, wherein the mesoporous silica nanoparticles have an average particle size of 200 nm or less. The optical element according to claim 1, wherein the mesoporous silica nanoparticles have a porous structure in which mesopores are arranged in a hexagonal shape. 4. The optical element according to claim 1, wherein the mesoporous silica porous film has a structure in which a pore size distribution curve obtained by a nitrogen adsorption method has two peaks. 5. The optical element according to claim 4, wherein the pore size distribution curve of the porous mesoporous silica film has a peak due to an intraparticle pore size within a range of 2 to 10 nm and an interparticle pore size within a range of 5 to 200 nm. An optical element having a peak due to. 6. The optical element according to claim 5, wherein a pore volume ratio between the intraparticle pores and the interparticle pores is 1/2 to 1/1. The optical element according to any one of claims 1 to 6, wherein the mesoporous silica porous film has a refractive index of more than 1.10 to 1.35 or less. 8. The optical element according to claim 1, wherein the mesoporous silica porous film has a physical film thickness of 15 to 500 nm. The optical element according to any one of claims 1 to 8, wherein the porosity of the mesoporous silica porous film is 25% or more and less than 75%. A pickup lens for an optical information recording / reproducing apparatus comprising the optical element according to claim 1. 11. An optical information recording / reproducing apparatus comprising the pickup lens according to claim 10.

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