JP2007137984A - Composite material and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a combination of light transmittance with stability for environmental variation as compared with the conventional combination while raising refractive index from that of a resin material. <P>SOLUTION: An object lens 7 is produced by molding a composite material composed of inorganic particles and a resin. The composite material has ≥50% light transmittance for light at 405 nm at 3 mm thickness and the moisture absorption coefficient at 90% relative humidity is ≤2%. The inorganic particles are composite particles of SiO<SB>2</SB>with an oxide having ≥1.6 to ≤2.8 refractive index for d lines and the molar fraction of the SiO<SB>2</SB>is ≥0.05 to ≤0.95. The volume-converted particle diameter is ≥2 to ≤100 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composite material and optical elements such as a lens, a filter, a grating, an optical fiber, and a flat optical waveguide.

  Conventionally, information devices such as players, recorders, and drives that read and record information using optical information recording media such as MO, CD, DVD, HD-DVD, and Blu-ray disc have been provided with optical pickup devices. . The optical pickup device includes an optical element unit including an optical element such as a lens for irradiating the optical information recording medium with light having a predetermined wavelength emitted from a light source and causing the light receiving element to receive reflected light. Has been.

  As a material for such an optical element, a plastic such as a copolymer of a cyclic olefin and an α-olefin is used because it can be manufactured at low cost by means such as injection molding (for example, Patent Document 1). reference).

  Here, although the resin material containing the cyclic olefin is excellent in the stability of the refractive index due to a change in humidity, it is inferior in the stability of the refractive index due to a temperature change. There has been proposed a method of suppressing the linear expansion of a resin material by dispersing silica-based inorganic particles in a resin material to obtain an organic-inorganic composite material. Furthermore, in this method, composite particles of metal oxide and silica are used as silica-based particles, so that the refractive index of the composite material is made higher than that of the resin to compensate for the disadvantage of silica having a low refractive index. (For example, refer to Patent Document 2).

  However, when silica and another metal oxide are combined, the hygroscopicity of the composite material increases depending on the type of the metal oxide, and the humidity resistance and the humidity dependency of the refractive index may be significantly deteriorated. In such a case, physical properties, particularly the refractive index, change due to environmental fluctuations such as humidity, and the practicality of the composite material becomes low.

By the way, as a method for controlling the hygroscopicity of the composite material, there is one that regulates the molar ratio of silica and metal oxide within a predetermined range (for example, see Patent Document 3).
JP 2002-105131 A JP 2005-146042 A JP-A-10-67882

  However, in the composite material according to the method disclosed in Patent Document 3, the particle size of the inorganic particles is as large as 0.3 microns or more, and the light transmittance of the molded product is low, so that it is difficult to use for optical elements.

  An object of the present invention is to provide a composite material and an optical element that can improve the combination of light transmittance and stability against environmental fluctuations as compared with the prior art while making the refractive index higher than that of a resin material. It is.

The invention according to claim 1 is a composite material,
A composite material composed of inorganic particles and resin,
The light transmittance of 3 mm thickness is 50% or more for light of 405 nm,
The water absorption rate at a relative humidity of 90% is 2% or less,
The inorganic particles are
Composite particles of SiO ₂ and an oxide having a refractive index with respect to d-line of 1.6 or more and 2.8 or less,
The volume conversion particle diameter is 2 nm or more and 100 nm or less, and the molar fraction of SiO ₂ is 0.05 or more and 0.95 or less.

The invention according to claim 2 is an optical element,
The composite material according to claim 1 is manufactured by molding.

  According to the first or second aspect of the present invention, it is possible to improve the combination of the light transmittance and the stability against environmental fluctuations as compared with the prior art while making the refractive index higher than that of the resin material.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, in the following embodiments, various technically preferable limitations for carrying out the present invention are given, but the scope of the invention is not limited to the following embodiments and illustrated examples.

First, the composite material according to the present invention will be described.
The composite material in the present embodiment contains a resin and inorganic particles, and is molded into a molded product such as an optical element. Hereinafter, (1) resin, (2) inorganic particles, (3) a method for producing a composite material, and (4) a molded product will be described.

(1) Resin The resin in the present invention is not particularly limited as long as it is a transparent resin generally used as an optical material, such as a thermoplastic resin, a thermosetting resin, and a photocurable resin. . However, in terms of processability as an optical element and molding cycle time, it is preferably a thermoplastic resin, such as acrylic resin, cyclic olefin resin, polycarbonate resin, polyester resin, polyether resin, polyamide resin or polyimide resin. More preferably, it is preferably a cyclic olefin resin. Examples of such a resin include compounds described in JP-A No. 2003-73559. Preferred compounds are shown in Table 1 below.

In addition, it is also preferable that the thermoplastic resin mentioned above is used together with other resin with compatibility.
In addition, the water absorption rate of the resin itself in the present embodiment is preferably 2% or less, and more preferably 1% or less, from the viewpoint of reducing the water absorption rate of the entire composite material. Here, when two or more types of resins are used, the water absorption rate of the thermoplastic resin composed of two or more types of resins is considered to be substantially the same as the average value of the water absorption rate of each resin. The water absorption is preferably 2% or less.

(2) Inorganic particles The inorganic particles in the present invention are composite particles of SiO ₂ and an oxide of an element other than silicon, more specifically, an oxide having a refractive index with respect to d-line of 1.6 or more and 2.8 or less. It has become.

Here, as elements other than silicon, Al, Zn, B, Ge, P, Ti, Nb, Zr, Y, W, La, Gd, Ta, etc. are preferable.
The refractive index of the inorganic particles is preferably in the range of 1.6 to 2.8. 2.8 or less is preferable because if the refractive index of the inorganic particles is higher than this, the difference in refractive index from the resin becomes large and causes white turbidity, and 1.6 or higher is preferable. This is because the effect of increasing the refractive index of the composite material is reduced. For this reason, the refractive index of the inorganic oxide compounded with SiO ₂ is in the same range.

The molar fraction of SiO _{2 in} the inorganic particles is 0.05 or more and 0.95 or less.
Further, the water absorption rate of the inorganic particles is preferably 2% or less, and more preferably 1% or less.

  Further, the volume average particle diameter of the inorganic particles is 100 nm or less, preferably 50 nm or less, and more preferably 30 nm or less. This suppresses light scattering caused by inorganic particles and increases the light transmittance.

  The volume average particle diameter of the inorganic particles is 2 nm or more. As a result, the specific surface area of the inorganic particles is prevented from becoming excessive, the required amount of the surface treatment agent for the inorganic particles is set to an appropriate range, and the production of the fine particles and the composite material is facilitated. . This is because when the form of the inorganic particles is spherical and the total volume is the same, the specific surface area is inversely proportional to the average particle diameter, so it is necessary to increase the average particle diameter in order to reduce the specific surface area. Because there is. For example, when the average particle size is changed from 30 nm to 1 nm, the specific surface area is 30 times. Therefore, when the inorganic particles having an average particle size of 30 nm are used, the required amount of the surface treatment agent is 10% of the total volume. When inorganic particles having an average particle diameter of 1 nm are used, the required amount of the surface treatment agent is 30 times, which cannot be realized. In addition, as a surface treating agent with respect to an inorganic particle, there exists a surface treating agent for providing affinity with resin.

The method for producing the above inorganic particles is not particularly limited, and a conventionally known method can be used. For example, a reaction system using a metal halide or an alkoxy metal as a raw material and containing water. The desired oxide fine particles can be obtained by hydrolysis in (hydrolysis method). At this time, a method of using an organic acid, an organic amine or the like in combination is also used for stabilizing the fine particles. In addition, inorganic particles can be produced by mechanical methods (a method for reducing the size of a massive composite material with a grinding device such as a ball mill or attritor) or a thermal decomposition method (a method for obtaining fine particles by thermally decomposing raw materials). , Spray drying method, flame spray method, plasma method, gas phase reaction method, freeze drying method, heated kerosene method, heated petroleum method), precipitation method (coprecipitation method), hydrothermal method (precipitation method, crystallization method, water) Thermal decomposition method, hydrothermal oxidation method) and the like can also be used. Among these, the thermal decomposition method, the precipitation method, and the hydrolysis method are preferable methods from the viewpoint of producing small-sized inorganic particles. A plurality of these methods may be combined.
In addition, as a method of creating composite particles, for example, the method described in Patent Document 2 can be used after obtaining a plurality of metal oxide raw materials by the above method.

  The inorganic particles prepared by such a method are preferably subjected to a surface treatment with a surface treatment agent such as a silane, silicone oil, titanate, aluminate, or amino acid coupling agent.

  Since these coupling agents have different characteristics such as reaction rate, it is preferable to select them appropriately according to the kind of inorganic particles to be used, conditions during surface treatment, and the like. Moreover, only 1 type may be used for a coupling agent and you may use multiple types together. When surface treatment is performed using two or more types of coupling agents, the surface treatment with various coupling agents may be performed simultaneously or at different times.

  Also, depending on the coupling agent used, the properties of the resulting inorganic particles after surface treatment may differ, so the coupling agent to be used is appropriately selected in consideration of the affinity of the thermoplastic resin to be dispersed. It is good to do.

  Silane coupling agents include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetraphenoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, methyltriethoxysilane, methyltriethoxysilane. Phenoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, 3-methylphenyltrimethoxysilane, dimethyldimethoxysilane, diethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiphenoxysilane, trimethylmethoxysilane, triethylethoxysilane, triphenylmethoxy Silane, triphenylphenoxysilane, etc. are mentioned.

  Examples of titanium-based coupling agents include tetrabutyl titanate, tetraoctyl titanate, isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, and bis (dioctyl pyrophosphate) oxyacetate titanate.

  The ratio of the coupling agent to the inorganic particles is not particularly limited, but is preferably in the range of 5 to 200%, and more preferably in the range of 10 to 100%.

  It is also preferable to perform surface treatment using various types of silicone oil. Examples of usable silicone oil include straight silicone oil such as dimethyl silicone oil, methylphenyl silicone oil, and methylhydrogen silicone oil; methacrylic acid modified silicone oil, epoxy modified silicone oil, fluorine modified silicone oil, polyether modified silicone oil, Examples include modified silicone oils such as amino-modified silicone oils.

  Surface treatment methods using such a surface treatment agent include a method of spraying the surface treatment agent into a solution and then drying, a method of adding and reacting the surface treatment agent to a dispersion of inorganic particles, and melt-kneading. Any method can be applied, such as a method of adding a surface treating agent at the time of compounding the resin and the resin.

  The content of the inorganic particles with respect to the composite material is preferably 10% or more and 90% or less, and more preferably 20% or more and 80% or less. If the content of the inorganic particles is 10% or more, the effect of improving the physical properties by mixing the inorganic particles can be exhibited. If the content is 90% or less, the necessary resin ratio is maintained and the original content is maintained. This is because deterioration of various properties such as processability, which is an advantage of the resin, can be prevented.

(3) Production method of composite material As a method of mixing a resin, particularly a thermoplastic resin and inorganic particles, it is preferable to use a melt-kneading method from the viewpoint of reducing the amount of volatile substances used.
Here, when utilizing the melt-kneading method, the thermoplastic resin as a raw material and the inorganic particles may be added and kneaded all at once, or may be added in stages and kneaded. As a method of adding in a divided manner, a method of adding one component in several times, a method of adding one component at a time and adding other components in stages, or a method combining these can be used. The addition of the inorganic particles can be performed in a powder or agglomerated state. Although it is possible to add inorganic particles dispersed in the liquid, in this case, it is necessary to perform a devolatilization treatment after kneading, and the aggregated particles are dispersed in the primary particles in advance. It is preferable to add it later. Also, after kneading the thermoplastic resin and the inorganic particles in advance, when adding components other than the thermoplastic resin that have not been added in advance and further melt-kneading, these may be added all at once and kneaded. Alternatively, it may be added in stages and kneaded.

  When using the melt-kneading method, mixing is performed in an atmosphere of one kind of gas selected from the inert gases nitrogen, helium, neon, argon, krypton and xenon, or two or more kinds of mixed gases. Preferably it is done. However, even general gases such as carbon dioxide, ethylene gas, and hydrogen gas may be used by mixing with the above-described inert gas as long as they are not reactive to the material to be kneaded. .

  Further, when using the melt-kneading method, it is preferable to eliminate the remaining oxygen as much as possible in the reaction system in the melt-kneading apparatus. Specifically, the oxygen amount in the reaction system is 1% or less. Is preferable, and 0.2% or less is more preferable. This is because the resin is deteriorated by the oxidation reaction with oxygen, and coloring is easily generated.

  As an apparatus applicable to the melt kneading method, a closed kneading apparatus or a batch kneading apparatus such as a lab plast mill, a Brabender, a Banbury mixer, a kneader, and a roll can be given. As an apparatus used for the melt kneading method, a continuous melt kneading apparatus such as a single screw extruder or a twin screw extruder can be used. In the case of using a continuous melt-kneading apparatus such as an extruder, it is possible to add components to be added in stages from the middle of the cylinder.

  Further, as a dispersion apparatus for the mixture, various dispersion treatment machines such as a bead mill disperser, an ultrasonic disperser, a high speed stirring disperser, and a high pressure disperser are applicable, but a bead mill disperser can be preferably used. . Examples of the beads used in the bead mill disperser include zirconia beads and glass beads. Zirconia beads are preferably used. Further, the diameter of the beads used is preferably smaller, and more preferably within a range of 0.1 mm or less and 0.001 mm or more.

  In the composite material production process, various additives may be added alone or in combination, if necessary. Additives include antioxidants, light stabilizers, heat stabilizers, weathering stabilizers, stabilizers such as UV absorbers and near infrared absorbers, resin modifiers such as lubricants and plasticizers, soft polymers and alcoholic agents. Examples thereof include white turbidity inhibitors such as compounds, colorants such as dyes and pigments, other antistatic agents, and flame retardants.

  Among these additives, examples of the antioxidant include a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant. By blending these antioxidants, it is possible to prevent lens coloring and strength reduction due to oxidative degradation during molding without reducing transparency, heat resistance, and the like.

  These antioxidants can be used alone or in combination of two or more, and the blending amount thereof is appropriately selected within a range not impairing the object of the present invention. The amount is preferably in the range of 0.001 to 20 parts by weight and more preferably in the range of 0.01 to 10 parts by weight with respect to 100 parts by weight of the composite thermoplastic material of the invention.

  In addition, as a phenolic antioxidant, a conventionally well-known thing can be applied, for example, 2-t-butyl-6- (3-t-butyl-2- 2 of Unexamined-Japanese-Patent No. 63-179953 is mentioned. Hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2,4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate, etc. And acrylate compounds such as octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate described in JP-A-1-168443, and 2,2′-methylene-bis (4 -Methyl-6-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4 -Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ', 5'-di-t-butyl-4'-hydroxyphenylpropionate)) methane, That is, pentaerythrimethyl-tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenylpropionate)), triethylene glycol bis (3- (3-t-butyl-4-hydroxy-5) Alkyl substituted phenolic compounds such as -methylphenyl) propionate), 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4 -Bisoctylthio-1,3,5-triazine, 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1 Triazine group-containing phenol compounds such as 3,5-triazine.

  In addition, the phosphorus antioxidant is not particularly limited as long as it is a substance that is usually used in the general resin industry. For example, triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, Tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) ) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and the like, and 4,4'-butylidene-bis (3-methyl-6-t-butylphenyl- Di-tridecyl phosphite), 4,4'-isopropylidene-bis (phenyl-di-alkyl (C1 -C15) phosphite) diphosphite compounds such as and the like. Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

  Further, as the sulfur-based antioxidant, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- (β-lauryl-thio-propionate), 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.

  Furthermore, in addition to the above-mentioned phenol-based, phosphoric acid-based and sulfur-based antioxidants, amine-based antioxidants such as diphenylamine derivatives, nickel or zinc thiocarbamates, and the like are also applicable as antioxidants.

  Of the additives described above, a compound group having a minimum glass transition temperature of 30 ° C. or less may be blended as the cloudiness inhibitor. Thereby, it is possible to prevent the occurrence of white turbidity in an environment of high temperature and high humidity over a long period of time by suppressing deterioration of various properties such as transparency, heat resistance and mechanical strength.

  Among the additives described above, examples of the light-resistant stabilizer include benzophenone-based light-resistant stabilizer, benzotriazole-based light-resistant stabilizer, hindered amine-based light-resistant stabilizer, and the like. Therefore, it is preferable to use a hindered amine light-resistant stabilizer (hereinafter referred to as HALS). As such HALS, those having a low molecular weight, medium molecular weight and high molecular weight can be appropriately selected. However, when forming a molded body from a composite material, it is preferable to use a low molecular weight or medium molecular weight HALS, and particularly when forming a film-shaped molded body, it is preferable to use a high molecular weight HALS. .

  As HALS having a relatively low molecular weight, LA-77 (manufactured by Asahi Denka), Tinuvin 765 (manufactured by CSC), Tinuvin 123 (manufactured by CSC), Tinuvin 440 (manufactured by CSC), Tinuvin 144 (manufactured by CSC), Hostavin N20 (manufactured by Hoechst), etc. Is mentioned.

  Examples of the medium molecular weight HALS include LA-57 (Asahi Denka), LA-52 (Asahi Denka), LA-67 (Asahi Denka), LA-62 (Asahi Denka) and the like. .

  As HALS having a large molecular weight, LA-68 (Asahi Denka), LA-63 (Asahi Denka), Hostavin N30 (Hoechst), Chimassorb 944 (CSC), Chimassorb 2020 (CSC), Chimassorb 119 (CSC) Tinuvin 622 (manufactured by CSC), CyasorbUV-3346 (manufactured by Cytec), CyasorbUV-3529 (manufactured by Cytec), Uvasil 299 (manufactured by GLC) and the like.

(3.1) Properties of composite material The light transmittance of the composite material manufactured as described above is 50% or more for light of 405 nm when the thickness is 3 mm.
In addition, a higher refractive index of the composite material is often preferable. In particular, when used as a lens material, since the thickness can be reduced when the refractive index is high, there is an advantage that the depth of the entire optical system can be reduced and the lens can be reduced in weight. Further, by reducing the weight of the lens, it is possible to facilitate optical axis adjustment between a plurality of lenses. Therefore, in this Embodiment, it is preferable that the refractive index of a composite material is 1.50 or more, More preferably, it is 1.55 or more, Most preferably, it is 1.60 or more.

  As for the Abbe number of the composite material, various values can be selected by selecting a resin or inorganic particles, but it is preferable to use particles that can obtain anomalous dispersibility. In this case, the composite material can be effectively used for achromatization, and its value may increase.

  Further, the water absorption rate of the composite material is 2% or less, preferably 1% or less, and most preferably 0.5% or less in an environment with a relative humidity of 90%. In the present embodiment, the water absorption rate is expressed in weight% unless otherwise specified. Further, the water absorption rate can be measured from a change in mass when a previously dried material is stored for a certain time or longer under specific high temperature and high humidity conditions. In the present embodiment, the moisture content is calculated more accurately by measuring the amount of water contained when dried by the Karl Fischer method and measuring the change in mass after the subsequent water absorption.

  The composite material is preferably negative in the AMES test. This is because a positive result in the AMES test may impair the health of the user, increase the environmental load, reduce the material stability, and the like.

(4) Molded products Various molded products can be obtained by molding the composite material as described above.
Although it does not specifically limit as a shaping | molding method, From a viewpoint of characteristics, such as the low birefringence in a molding, mechanical strength, and a dimensional accuracy, a melt molding method is preferable. Examples of the melt molding method include press molding, extrusion molding, and injection molding. From the viewpoint of productivity, injection molding is preferable. In the case of a photocurable resin, cast polymerization or the like can be used.

  The molding conditions are appropriately selected according to the purpose of use or the molding method. For example, as the temperature of the composite material in injection molding, an appropriate fluidity is imparted to the resin at the time of molding to reduce sink marks and distortion of the molded product. From the viewpoints of preventing silver streak due to thermal decomposition of the resin and effectively preventing yellowing of the molded product, it is preferably within a range of 150 ° C. to 400 ° C., 200 ° C. It is more preferable to be within a range of ˜350 ° C., and it is particularly preferable to be within a range of 200 ° C. to 330 ° C.

  When injection molding is used, all general methods such as a molding method using carbon dioxide gas as a plasticizer and a method of improving transferability by induction heating of a mold can be applied.

  Further, the molded product in the present embodiment can be used in various forms such as a spherical shape, a rod shape, a plate shape, a columnar shape, a tubular shape, a tube shape, a fiber shape, a film shape or a sheet shape. Moreover, since it is excellent in low birefringence, transparency, mechanical strength, heat resistance, low water absorption, etc., it can be applied to various optical components.

  As a specific application example, as an optical lens or an optical prism, an imaging lens of a camera; a lens such as a microscope, an endoscope or a telescope lens; an all-light transmission lens such as a spectacle lens; a CD or a CD-ROM , WORM (recordable optical disc), MO (rewritable optical disc; magneto-optical disc), MD (mini disc), DVD (digital video disc) and other optical disc pickup lens; laser beam printer fθ lens, sensor lens And a laser scanning system lens such as a camera finder system prism lens.

Other optical uses include light guide plates such as liquid crystal displays; optical films such as polarizing films, retardation films and light diffusion films; light diffusion plates; optical cards; liquid crystal display element substrates.
In addition, the optical element according to the present invention is also suitably used as various filters, gratings, optical fibers, flat optical waveguides, and the like.

  Among the molded products described above, the optical element according to the present invention is preferably used as an optical element such as a pickup lens or a laser scanning system lens that requires low birefringence. The optical pickup device 1 used as the lens 7 will be described.

Here, FIG. 1 is a schematic diagram showing the internal structure of the optical pickup device 1.
As shown in FIG. 1, the optical pickup device 1 in this embodiment includes a semiconductor laser oscillator 2 that is a light source. On the optical axis of the blue light emitted from the semiconductor laser oscillator 2, a collimator 3, a beam splitter 4, a quarter wavelength plate 5, a diaphragm 6, and an objective lens 7 are arranged in a direction away from the semiconductor laser oscillator 2. Are sequentially arranged.
In addition, a sensor lens group 8 and a sensor 9 including two sets of lenses are sequentially disposed in a direction close to the beam splitter 4 and in a direction perpendicular to the optical axis of the blue light described above.

  The objective lens 7 that is an optical element is disposed at a position facing the optical disc D, and condenses the blue light emitted from the semiconductor laser oscillator 2 on one surface of the optical disc D. . Such an objective lens 7 is provided with a two-dimensional actuator 10, and the objective lens 7 is movable on the optical axis by the operation of the two-dimensional actuator 10.

Next, the operation of the optical pickup device 1 will be described.
The optical pickup device 1 in the present embodiment emits blue light from the semiconductor laser oscillator 2 at the time of recording information on the optical disc D or at the time of reproducing information recorded on the optical disc D. As shown in FIG. 1, the emitted blue light becomes a light beam L1, is collimated to infinite parallel light through the collimator 3, and then passes through the beam splitter 4 to pass through the quarter-wave plate 5. To Penetrate. Further, after passing through the diaphragm 6 and the objective lens 7, a condensed spot is formed on the information recording surface D ₂ via the protective substrate D ₁ of the optical disc D.

The light that forms the condensed spot is modulated by the information pits on the information recording surface D ₂ of the optical disc D and reflected by the information recording surface D ₂ . Then, the reflected light is sequentially transmitted through the objective lens 7 and the diaphragm 6, the polarization direction is changed by the quarter wavelength plate 5, and the reflected light is reflected by the beam splitter 4. After that, astigmatism is given through the sensor lens group 8, received by the sensor 9, and finally converted into an electric signal by being photoelectrically converted by the sensor 9.

  Thereafter, such an operation is repeatedly performed, and the operation of recording information on the optical disc D and the operation of reproducing information recorded on the optical disc D are completed.

Incidentally, the magnitude of the thickness and the information pits of the protective substrate D ₁ of the optical disc D, also the numerical aperture NA required for the objective lens 7 different. In the present embodiment, the optical disc D is a high density, and its numerical aperture is set to 0.85.

According to the objective lens 7 of the optical pickup device 1 described above, inorganic particles are contained, and the inorganic particles contain SiO ₂ and an oxide having a refractive index with respect to d-line of 1.6 or more and 2.8 or less. Therefore, unlike the case where only the resin material is contained or the case where only SiO ₂ is contained as the inorganic particles, the refractive index can be increased as compared with the resin material.

Moreover, since inorganic particles are contained in the composite material, the composite material can be stabilized against temperature changes. Further, since SiO _{2 that} is easily hydrophobized is contained in the inorganic particles, the composite material can be stabilized against changes in humidity by hydrophobizing the SiO ₂ . Further, since the water absorption rate at 90% relative humidity is 2% or less, the composite material can be further stabilized against humidity change. Therefore, stability against environmental fluctuations can be improved compared to the conventional case.

Further, since the volume-converted particle diameter of the inorganic particles is 2 nm or more and 100 nm or less, the light transmittance can be increased as compared with the conventional case where the particle diameter is 0.3 microns or more.
Therefore, it is possible to improve the combination of the light transmittance and the stability against environmental fluctuations as compared with the prior art while making the refractive index higher than that of the resin material.

  Hereinafter, the optical element according to the present invention will be described more specifically by giving examples and comparative examples. However, the present invention is not limited to the examples.

(Inorganic particles (1-1); preparation of SiO ₂ / TiO ₂ fine particles, SiO ₂ molar fraction 30%)
A mixed liquid of 463.1 g of pure water, 104.8 g of 26% ammonia water and 4255.0 g of methanol, a mixed liquid of 1368 g of tetramethoxysilane (TMOS) and 229.4 g of methanol, 643.2 g of pure water and 26% ammonia water 104.8 g of the mixed solution was added dropwise over 150 minutes while maintaining the liquid temperature at 25 ° C., and then a mixed solution of 5969 g of titanium tetraisopropoxide and 150 g of isopropyl alcohol was added over 100 minutes to mix silica / titanium. A sol was obtained.

  The sol was distilled by heating under normal pressure, and pure water was added dropwise while keeping the volume constant. When it was confirmed that the top temperature of the distillation tower reached 100 ° C. and the pH became 8 or less, pure water was used. The dropping was finished to obtain a dispersion of inorganic particles.

  Further, 15.4 g of methyltrimethoxysilane was added and stirred at room temperature for 1 hour, and then refluxed for 2 hours. Then, methyl ethyl ketone was added dropwise while keeping the volume constant by heating and distillation under normal pressure, and the addition was terminated when it was confirmed that the tower top temperature reached 79 ° C. and the water content was 1.0% or less. After cooling to room temperature, microfiltration was performed using a 3 μ membrane filter to obtain methyl ethyl ketone-dispersed silica sol. As a result of TEM observation, the volume equivalent average particle diameter of the inorganic particles was 13 nm.

(Inorganic particles (1-2); preparation of SiO ₂ / TiO ₂ fine particles, SiO ₂ molar fraction 80%)
Inorganic particles were prepared in the same manner as the inorganic particles (1-1) except that 3648 g of tetramethoxysilane and 2274 g of titanium tetraisopropoxide were changed. The volume conversion average particle diameter was 7 nm.

(Inorganic particles (1-3): Preparation of SiO ₂ / TiO ₂ fine particles, SiO ₂ molar fraction 80%)
Inorganic particles were prepared in the same manner as the inorganic particles (1-2) except that the amount of methanol added by mixing with tetramethoxysilane was changed to 2100 g. The volume conversion average particle diameter was 30 nm.

(Inorganic particles (1-4); preparation of SiO ₂ / TiO ₂ fine particles, SiO ₂ molar fraction 80%)
Inorganic particles were prepared in the same manner as the inorganic particles (1-2) except that the liquid temperature at the time of dropping the tetramethoxysilane was changed to 40 ° C. The volume conversion average particle diameter was 150 nm.

(Inorganic particles (1-5); preparation of SiO ₂ / TiO ₂ fine particles, SiO ₂ molar fraction 80%)
Inorganic particles were prepared in the same manner as the inorganic particles (1-2) except that the liquid temperature at the time of dropping the tetramethoxysilane was changed to 50 ° C. The volume conversion average particle diameter was 150 nm.

(Inorganic particles (2); Preparation of SiO ₂ / ZnO ₂ fine particles)
A mixture obtained by adding 3066 g of zinc acetate dihydrate in 10 mL of ethanol was stirred at 90 ° C. for 1 hour under heating and refluxing, and then cooled to 0 ° C.
Next, a solution in which 1180 g (1.4 equivalents) of lithium hydroxide monohydrate was dissolved in 400 L of ethanol was added to this solution with stirring at 0 ° C. After stirring the resulting mixture at room temperature for 30 minutes, 816 mL of methyltrimethoxysilane was added while continuing to stir. Further, after stirring at room temperature for 3 hours, 30.6 L of triethylamine was added and further degassed. 1 L of brine was added.

  After that, the reaction liquid which was allowed to stand overnight was concentrated and dried, and this powder was redispersed in 30 L of ethanol to obtain a transparent dispersion. The dispersion was poured into 400 L of n-hexane to reprecipitate, and centrifuged. Separation, decantation, and vacuum drying gave 4322 g of white solid powder. As a result of TEM observation, the volume-converted average particle diameter of the inorganic particles was 10 nm.

(Inorganic particles (3); Preparation of SiO ₂ / Al ₂ O ₃ fine particles)
“Cataloid” as silica sol (trade name; Catalytic Chemical Industry Co., Ltd., particle diameter 5 nm, SiO ₂ concentration 20% by weight) and 176 kg of water were mixed, and 6500 g of 5% by weight NaOH aqueous solution was added thereto. Then, the pH of the dispersion was adjusted to 10.5, and then the temperature of the dispersion was raised to 95 ° C. and maintained at 95 ° C. for 30 minutes to prepare a particle dispersion.

Next, silicic acid obtained by mixing 17744 g of water glass (manufactured by Dokai Chemical Co., Ltd .: JIS No. 3 water glass, SiO ₂ concentration 24 wt%) and 54320 g of water with the particle dispersion maintained at a temperature of 95 ° C. An aqueous alkali solution, an aqueous sodium aluminate solution (Al ₂ O ₃ concentration 22 wt%, Na ₂ O concentration 17 wt%) 5440 g and 10280 g of water mixed with an aqueous solution of sodium aluminate 2280 g of ammonium sulfate and 57360 g of water were mixed. The electrolyte aqueous solution obtained above was added in 11 hours. The addition rate at this time is the total amount of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) in the electrolyte aqueous solution 1.2 g / nuclear particle unit surface area (m ² ) · hour, and the alkali (alkali silicate and alumina) The equivalent ratio EA / EE of the electrolyte was 2.18.

  Next, after aging for 1 hour, washing was performed with an ultrafiltration membrane until the pH of the growth core particle dispersion reached 10. Further, 15.4 g of methyltrimethoxysilane was added and stirred at room temperature for 1 hour, and then refluxed for 2 hours. Then, methyl ethyl ketone was added dropwise while keeping the volume constant by heating and distillation under normal pressure, and the addition was terminated when it was confirmed that the tower top temperature reached 79 ° C. and the water content was 1.0% or less. After cooling to room temperature, microfiltration was performed using a 3 μ membrane filter to obtain a methyl ethyl ketone dispersion sol. As a result of TEM observation, the average particle diameter in terms of volume was 10 nm.

(Inorganic particles (4); Preparation of SiO ₂ fine particles)
A mixed liquid of 463.1 g of pure water, 90.6 g of 26% ammonia water and 4255.0 g of methanol, a mixed liquid of 4560 g of tetramethoxysilane and 229.4 g of methanol, 643.2 g of pure water and 104.8 g of 26% ammonia water. Was added dropwise over 150 minutes while maintaining the liquid temperature at 45 ° C. to obtain a sol dispersion.

  The silica sol was distilled under heating under normal pressure, and pure water was added dropwise while keeping the volume constant. When it was confirmed that the tower top temperature reached 100 ° C and the pH was 8 or less, the addition of pure water was completed. As a result, a fine particle dispersion was obtained.

  Further, 15.4 g of methyltrimethoxysilane was added and stirred at room temperature for 1 hour, and then refluxed for 2 hours. Then, methyl ethyl ketone was added dropwise while keeping the volume constant by heating and distillation under normal pressure, and the addition was terminated when it was confirmed that the tower top temperature reached 79 ° C. and the water content was 1.0% or less. After cooling to room temperature, microfiltration was performed using a 3 μ membrane filter to obtain methyl ethyl ketone-dispersed silica sol. As a result of TEM observation, the volume-converted average particle size was 6 nm.

(Inorganic particles (5); Preparation of TiO ₂ fine particles)
A mixture of pure water 463.1 g, 26% ammonia water 90.6 g and methanol 4255.0 g, titanium tetraisopropoxide 8526.6 g and methanol 229.4 g, pure water 643.2 g and 26% ammonia A mixture of 104.8 g of water was added dropwise over 150 minutes while maintaining the liquid temperature at 45 ° C. to obtain a sol dispersion.

  The silica sol was distilled under heating under normal pressure, and pure water was added dropwise while keeping the volume constant. When it was confirmed that the tower top temperature reached 100 ° C and the pH was 8 or less, the addition of pure water was completed. As a result, a fine particle dispersion was obtained. As a result of TEM observation, the volume-converted average particle size was 18 nm.

(Resin (1), (2))
The resin (1) is cycloolefin resin “APEL5014” (product name, manufactured by Mitsui Chemicals, refractive index 1.54), and the resin (2) is PMMA resin “Acrypet VH” (product name, manufactured by Mitsubishi Rayon). , Refractive index 1.49) was used.

(Making composite materials)
As shown in Table 2 below, each particle dispersion in which the inorganic particles (1) to (5) are dispersed is melt-kneaded while devolatilizing with the resins (1) and (2) to obtain the composite material (1). -(12) was created. The content of the inorganic particles (1) to (5) in the composite material was 50% by weight, respectively. Moreover, when using resin (1), 10 parts of cyclohexylmethyldimethoxysilane was added per 100 parts by weight of the inorganic particles during kneading. When resin (2) was used, 10 parts by weight of γ-methacryloxypropyltrimethoxysilane was added per 100 parts by weight of fine particles during kneading.

  In melt-kneading, a lab plast mill (manufactured by Toyo Seiki Seisakusho Co., Ltd., trade name: lab plast mill KF-6V) is used and kneaded at 100 rpm for 10 minutes under nitrogen, and depressurized at 20 Torr for 2 minutes before completion. I care. Further, at the time of melt kneading, the surface treatment of fine particles was performed by appropriately adding a surface treatment agent.

(Creation of optical elements)
The obtained composite materials (1) to (12) were pressed at 160 ° C. under a reduced pressure of 10 Torr to obtain a molded body having a diameter of 11 mm and a thickness of 3 mm, and then the surface was polished to produce an optical element. Such Examples (1) to (5) and Comparative Examples (1) to (7) were used. These Examples (1) to (5) and Comparative Examples (1) to (7) were used for the following optical property measurements.

(Measurement of transmittance)
The optical transmittance at a wavelength of 405 nm was measured for each optical element. The transmittance measurement method was based on ASTM D 1003. The results are shown in the column of “Transmittance” in Table 2 above. From the viewpoint of practicality, the transmittance needs to be 50% or more.

(Measurement of refractive index and its temperature dependence)
Using an automatic refractometer "KPR-200" (product name, manufactured by Kalnew Optical Industry), the refractive index at a wavelength of 588 nm was measured by changing the temperature of each optical element from 25 ° C to 75 ° C, and the temperature dependence of the refractive index. Sex was calculated. The results are shown in the columns of “refractive index” and “refractive index temperature dependency” in Table 2 above. From the viewpoint of practicality, the temperature dependency of the refractive index needs to be −0.4% or more.

(Hygroscopic test, refractive index humidity dependence measurement)
Using a high-temperature and high-humidity machine “PR-2PK” (product name, manufactured by ESPEC Corporation), the optical element previously dried at 100 ° C. and 10% RH for 100 hours is stored at 60 ° C. and 90% RH for 500 hours. The water absorption was determined from the weight increase before and after. The moisture absorption during drying was measured by dissolving the composite material in cyclohexane, and then measuring the composite material with a dry organic solvent by the Karl Fischer method. The dried Examples (1) to (5) and Comparative Examples (1) to (7) and the absorbed Examples (1) to (5) and Comparative Examples (1) to (7) at 25 ° C. Each refractive index was measured and determined as the humidity dependence of the refractive index. The results are shown in the columns of “Water absorption” and “Refractive index humidity dependency” in Table 2. From the viewpoint of practicality, the humidity dependence of the refractive index needs to be less than 1%.

(Measurement of particle size distribution in composite materials)
A section of about 100 nm is prepared from each optical element using a microtome, and each section is observed at a magnification of 100,000 using a transmission electron microscope “H-800” (product name, manufactured by Hitachi, Ltd.). Was converted into a volume-converted average particle size. The results are shown in the column of “TEM particle size” in Table 2 above.

As is clear from the results shown in Table 2, the optical element of Example (1) has a higher refractive index than that of Resin (1), and light is higher than the optical elements of Comparative Examples (1) to (3). The transmittance and stability against environmental changes are improved respectively.
In addition, the optical elements of Examples (3) to (5) have a refractive index higher than that of the resin (1), and are equally stable against environmental fluctuations as compared with the optical element of Comparative Example (7). The light transmittance is improved, that is, the combination of the light transmittance and the stability against environmental fluctuation is improved as compared with the optical element of Comparative Example (7).

  In addition, the optical elements of Comparative Examples (4) to (6) have a refractive index equal to or lower than the refractive index of the resin material, which is inappropriate as a comparative control for Examples (1) to (5).

It is a schematic diagram which shows the internal structure of the optical pick-up apparatus provided with the objective lens which is the optical element which concerns on this invention.

Explanation of symbols

7 Objective lens (optical element)

Claims (2)

A composite material composed of inorganic particles and resin,
The light transmittance of 3 mm thickness is 50% or more for light of 405 nm,
The water absorption rate at a relative humidity of 90% is 2% or less,
The inorganic particles are
Composite particles of SiO ₂ and an oxide having a refractive index with respect to d-line of 1.6 or more and 2.8 or less,
A composite material having a volume conversion particle diameter of 2 nm to 100 nm and a SiO ₂ molar fraction of 0.05 to 0.95.   An optical element manufactured by molding the composite material according to claim 1.

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