WO2010098366A1

WO2010098366A1 - Metal oxide fine particles, dispersion liquid of metal oxide fine particles, and molded product

Info

Publication number: WO2010098366A1
Application number: PCT/JP2010/052906
Authority: WO
Inventors: Yoshio Tadakuma
Original assignee: Fujifilm Corporation
Priority date: 2009-02-25
Filing date: 2010-02-18
Publication date: 2010-09-02
Also published as: TW201034965A; JP2010195636A

Abstract

To provide metal oxide fine particles having crystallinity, including titanium, wherein crystal structures of the metal oxide fine particles include a rutile structure, and the existence ratio of the rutile structure in all the metal oxide fine particles is 30% or more, wherein the metal oxide fine particles have a water content of 12% by mass or less, and wherein the metal oxide fine particles have a sphere-equivalent average primary particle diameter of 1 nm to 10 nm.

Description

DESCRIPTION Title of Invention

METAL OXIDE FINE PARTICLES, DISPERSION LIQUID OF METAL OXIDE FINE PARTICLES, AND MOLDED PRODUCT

Technical Field

The present invention relates to metal oxide fine particles used for producing a molded product which requires high transparency, a dispersion liquid of metal oxide fine particles which contains the metal oxide fine particles, and a molded product using the dispersion liquid of metal oxide fine particles.

Background Art

Nowadays optical materials are being actively studied. In the field of lenses, in particular, development of optical materials which are highly refractive and superior in heat resistance, light resistance, transparency, moldability, lightness in weight, chemical resistance, solvent resistance, etc. is strongly hoped for.

Since plastic lenses are lighter in weight and less likely to break than lenses made of inorganic materials such as glass and can be formed into a variety of shapes, they are not only used as spectacle lenses but are nowadays used as optical materials such as lenses for portable cameras and pickup lenses and are rapidly becoming common. Accordingly, material itself is required to have a high refractive index so as to reduce the thickness of lenses^ and the size of image pickup devices. For instance, a technique for introducing sulfur atoms into a polymer (refer to PTL 1 and PTL 2), a technique for introducing halogen atoms or aromatic rings into a polymer (refer to PTL 3) and the like have been actively studied. However, plastic material which has a great enough refractive index, favorable transparency and favorable light resistance and can replace glass has not yet been developed. As for optical fibers and optical waveguides, materials having different refractive indexes are used in combination, or materials with refractive index distributions are used. To deal with materials in which the refractive index varies according to sites, such as these materials, development of a technique for freely adjusting the refractive index is hoped for.

Since it is difficult to improve the refractive index with organic materials alone, a method has been reported in which the refractive index of a resin is increased by dispersing an inorganic material having a high refractive index in a resin matrix (refer to PTL 4) . To reduce the attenuation of transmitted light caused by Rayleigh scattering, it is preferable to uniformly disperse inorganic fine particles having a particle size of 15 nm or less in a resin matrix. However, since primary particles having a particle size of 15 nm or less tend to aggregate very easily, it is extremely difficult to disperse them uniformly in the resin matrix. Moreover, in view of the attenuation of transmitted light with respect to an optical path length equivalent to the thickness of a lens, the amount of the inorganic fine particles added has to be limited. Thus, it has been impossible so far to disperse inorganic fine particles in a resin matrix at a high concentration without decreasing the transparency of the resin. Meanwhile, PTL 5 proposes a metal oxide powder having an average particle diameter of 0.1 μm to 2 μm, a BET specific surface area of 2 m²/g to 20 m²/g, and a number-based concentration of isolated OH groups on the particle surface of 3/nm² to 8/nm². In this proposal, however, aggregation of particles cannot be sufficiently controlled. Hence, as things stand at present, further improvement and development are hoped for.

Citation List

Patent Literature [PTL l] Japanese Patent Application Laid-Open (JP-A) No.

2002- 131502

[PTL 2] JP-A No. 10-298287 [PTL 3] JP-A No. 2004-244444 [PTL 4] JP-A No. 2003-73559 [PTL 5] JP-A No. 2005- 139295

Summary of Invention Technical Problem

The present invention is aimed at solving the problems in related art and achieving the following object. An object of the present invention is to provide metal oxide fine particles whitfh have a low water content and make it possible to suppress their aggregation, a dispersion liquid of metal oxide fine particles which can reduce haze caused by light scattering and is highly transparent, and a molded product which is highly transparent and superior in hygrothermal resistance and light resistance.

Solution to Problem

As a result of carrying out a series of earnest examinations to solve the problems, the present inventors have found that when crystal structures of metal oxide fine particles include a rutile structure, and the existence ratio of the rutile structure in all the metal oxide fine particles is 30% or more, it is possible to lower the water content of the metal oxide fine particles and thereby to suppress aggregation of the metal oxide fine particles; also found that a dispersion liquid of metal oxide fine particles which includes the metal oxide fine particles makes it possible to reduce haze caused by light scattering and is highly transparent; and found that a molded product using the dispersion liquid of metal oxide fine particles is highly transparent and superior in hygrothermal resistance and light resistance.

The present invention is based upon the findings of the present inventors, and means for solving the problems are as follows. <1> Metal oxide fine particles having crystallinity, including titanium, wherein crystal structures of the metal oxide fine particles include a rutile structure, and the existence ratio of the rύtile structure in all the metal oxide fine particles is 30% or more, wherein the metal oxide fine particles have a water content of 12% by mass or less, and wherein the metal oxide fine particles have a sphere-equivalent average primary particle diameter of 1 nm to 10 nm.

<2> The metal oxide fine particles according to <1>, further including tin and zirconium. <3> The metal oxide fine particles according to <1> or <2>, wherein the existence ratio of the rutile structure in all the metal oxide fine particles is 60% or more, wherein the metal oxide fine particles have a water content of 5% by mass to 10% by mass, and wherein the metal oxide fine particles have a sphere-equivalent average primary particle diameter of 3 nm to 5 nm. <4> A dispersion liquid of metal oxide fine particles, including 0.1% by mass to 20% by mass of the metal oxide fine particles according to any one of <1> to <3>, wherein the light transmittance of the dispersion liquid at an optical path length of 10 mm and a wavelength of 450 nm is 90% or more. <5> A molded product including a composite composition which contains the dispersion liquid of the metal oxide fine particles according to <4> and a resin.

<6> The molded product according to <5>, having a water content of 5% by mass or less. <7> The molded product according to <5> or <6>, having a refractive index of 1.60 or more at a wavelength of 589 nm, and a light transmittance of 77% or more at a wavelength of 589 nm with respect to a thickness of 1 mm.

<8> The molded product according to any one of <5> to <7>, wherein the amount of the metal oxide fine particles contained is 20% by mass or more.

<9> The molded product according to any one of <5> to <8>, used as a lens base material.

Advantageous Effects of Invention

According to the present invention, it is possible to solve the problems in related art and achieve the above-mentioned object of providing metal oxide fine particles which have a low water content and make it possible to suppress their aggregation, a dispersion liquid of metal oxide fine particles which can reduce haze caused by light scattering and is highly transparent, and a molded product which is highly transparent and superior in hygrothermal resistance and light resistance.

Description of Embodiments (Metal Oxide Fine Particles)

Metal oxide fine particles according to the present invention include titanium and, if necessary, include other component(s).

As the other component(s), a metal oxide containing one metal selected from Zn, Ge, Zr, Hf, Si, Sn, Mn, Ga, Mo, In, Sb, Ta, V, Y and Nb, or a complex metal oxide containing two or more of these metals can be mentioned, for example. It is desirable that the metal oxide fine particles include the metal oxide or the complex metal oxide. Examples of the metal oxide include ZnO, Geθ2, Tiθ2, Zrθ2, HfO₂, SiO₂, Sn₂O₃, Mn₂O₃, Ga₂O₃, Mo₂O₃, In₂O₃, Sb₂O₃, Ta₂O₅, V₂O₅, Y₂O₃ and Nb₂O₅.

Examples of the complex metal oxide include a complex oxide of titanium and zirconium,^' a complex oxide of titanium, zirconia and hafnium; a complex oxide of titanium and barium,' a complex oxide of titanium and silicon; a complex oxide of titanium, zirconium and silicon; a complex oxide of titanium and tin; and a complex oxide of titanium, zirconia and tin.

Regarding these complex metal oxides, it is desirable that titanium occupy 60 at.% or more of all the metal atoms constituting the complex metal oxide, and it is more desirable that titanium and tin occupy 70 at.% or more of all the metal atoms constituting the complex metal oxide. This makes it possible to obtain a dispersion liquid of metal oxide fine particles which has a high refractive index.

It is desirable that the complex metal oxide contain titanium, tin and zirconium, and that titanium and tin occupy 70 at.% to 98 at.% of all the metal atoms constituting the complex metal oxide, with the rest being zirconium.

Additionally, the surface of the metal oxide fine particles may be coated with a material of low photocatalytic activity or doped with a metal for recombining electrons and holes. Preferred examples of such metal oxides include Tiθ2, Zrθ2 and Snθ2, with Tiθ2 being particularly preferable for its high refractive index. Furthermore, by producing a complex oxide of Tiθ2 and tin which has a rutile structure, it is possible to increase the refractive index further. It is particularly desirable that such a rutile -type complex oxide containing tin and titanium be used as a core, and that the surface of the core be covered with Zrθ2, AI2O3, Siθ2 or the like.

The coverage is not particularly limited and may be suitably selected according to the purpose, but it is preferably 10% to 70%, more preferably 20% to 60%, particularly preferably 30% to 50%. Note that the coverage means the ratio of the area of the shell (covering material) to the surface area of the core particles.

Here, the coverage can be worked out by calculation which involves comparing the formulation value of the raw material for an oxide constituting the shell with the reaction rate after the synthesis of the metal oxide fine particles.

Also, these fine particles may be metal oxide fine particles surface-modified with a silane coupling agent, a titanate coupling agent or the like for a purpose such as a reduction in photocatalytic activity, a reduction in water absorption, etc. - Crystallinity -

The metal oxide fine particles have crystallinity. The metal oxide fine particles do not necessarily have to be 100% crystalline but may have regions which have crystal structures and amorphous regions in a mixed manner. The crystal structures are not particularly limited as long as they include a rutile structure when titanium is a main component, and the crystal structures may be suitably selected according to the purpose. For example, the crystal structures may also include an anatase structure and/or a brookite structure in a mixed manner.

Further, the crystal structures may include other crystal structure(s) derived from metal(s) other than titanium.

The existence ratio of the rutile structure in all the metal oxide fine particles is not particularly limited as long as it is 30% or more, and the existence ratio may be suitably selected according to the purpose; however, it is preferably 50% or more, more preferably 60% or more, particularly preferably 80% or more .

When the existence ratio of the rutile structure in all the metal oxide fine particles is less than 30%, the water content of the metal oxide fine particles is high, so that it may be impossible to suppress aggregation of the metal oxide fine particles. Conversely, when the existence ratio of the rutile structure in all the metal oxide fine particles is in the particularly preferable range, it is possible to lower the water content of the metal oxide fine particles, and so there is an advantage in that aggregation of the metal oxide fine particles can be superiorly suppressed. Also, in the case where the metal oxide fine particles are used as a highly refractive material, there is an advantage in that the crystallinity is high and the refractive index increases as the existence ratio of the rutile structure increases. Here, the existence ratio of the rutile structure in all the metal oxide fine particles can be calculated as follows.

The X-ray diffraction of the metal oxide fine particles is measured in an appropriate range, and the X-ray diffraction pattern of the rutile structure is separated from pattern(s) derived from other crystal structure(s) and patterns related to amorphous regions and a background. And it is possible to calculate the existence ratio of the rutile structure by dividing the area of the pattern derived from the rutile structure by the whole area. Such an analysis can be generally carried out by using X-ray diffraction analysis software. - Water Content -

The water content of the metal oxide fine particles is not particularly limited as long as it is 12% by mass or less, and the water content may be suitably selected according to the purpose; however, it is preferably 5% by mass to 10% by mass. When the water content is more than 12% by mass, aggregation of the metal oxide fine particles is conspicuous, and coarse secondary particles, a cause of light scattering, may form.

The water content of the metal oxide fine particles can be adjusted by the addition of an acid and heat treatment. Examples of the acid include carboxylic acids, phosphoric acids and phosphonic acids, with carboxylic acids being particularly preferable. Examples of the carboxylic acids include acetic acid. As for the heat treatment, the temperature is preferably 40⁰C to 90⁰C, and the length of time is preferably 30 minutes or more. The water content is dependent upon the hydroxyl (OH) group density of the surface of the metal oxide fine particles , and can, for example, be measured by the Karl Fischer method.

- Sphere -equivalent Average Primary Particle Diameter -

The sphere-equivalent average primary particle diameter of the metal oxide fine particles is not particularly limited as long as it is in the range of 1 nm to 10 nm, and it may be suitably selected according to the purpose; however, it is preferably in the range of 3 nm to 5 nm. When the sphere-equivalent average primary particle diameter is smaller than 1 nm, it is difficult to obtain sufficient crystallinity, so that the refractive index may decrease. When the sphere-equivalent average primary particle diameter is larger than 10 nm, there is an increase in haze caused by light scattering, so that the required transparency may not be obtained in the case where the metal oxide fine particles are applied to an optical component. Here, the sphere-equivalent average primary particle diameter can be measured using an X-ray diffraction (XRD) apparatus or a transmission electron microscope (TEM), for example.

- Production Method -

The production method of the metal oxide fine particles (and a dispersion liquid thereof) is not particularly limited, and any known method may be used. For instance, desired metal oxide fine particles and a desired dispersion liquid in which the metal oxide fine particles are dispersed can be obtained by hydrolyzing a metal salt or metal alkoxide, used as a raw material, in a reaction system containing water. Examples of the metal salt include chlorides, bromides, iodides, nitrates, sulfates and organic acid salts of desired metals. Examples of the organic acid salts include acetates, propionates, naphthenates, octylates, stearates and oleates. Examples of the metal alkoxide include methoxides, ethoxides, propoxides and butoxides of desired metals. As a method for synthesizing such metal oxide fine particles, the method described in the Japanese Journal of Applied Physics, vol. 37, p. 4603-4608 (in the year of 1998), or in the Langmuir, vol. 16 (l), p. 241 -246 (in the year of 2000) may be used, for example. Especially when the metal oxide fine particles are synthesized by a sol formation method, it is possible to employ a process of forming a precursor such as a hydroxide first, then dehydrating and condensing, or deflocculating the precursor with an acid or alkali so as to form a hydrosol, as in the synthesis of titanium oxide fine particles using titanium tetrachloride as a raw material. Regarding the process of forming the precursor first, it is preferable in terms of purity of a final product to subject the precursor to isolated purification by a method such as filtration or centrifugal separation. Besides the hydrolysis of the raw material in water, the metal oxide fine particles may be produced in an organic solvent or an organic solvent with a thermoplastic resin dissolved therein. The solvents used in these methods are not particularly limited and may be suitably selected according to the purpose, and examples thereof include acetone, 2-butanone, dichloromethane, chloroform, toluene, ethyl acetate, cyclohexanone and anisole. These may be used individually or in combination.

The type(s) of crystal structure(s) or amorphous structure(s) which the metal oxide fine particles have varies/vary depending upon the type(s) of the metal oxide(s) used, the temperature, the pH, the catalyst, etc. In the case where titanium oxide is solely used, an anatase crystal structure generally appears when fine particles thereof are synthesized in an aqueous solution. In such a case, it is possible to allow a rutile crystal structure to appear by adding an appropriate amount of a metal oxide which easily forms a rutile structure . By making titanium oxide coexist with tin oxide, for example, a rutile structure can be obtained more easily. It is inferred that this is because tin oxide has a rutile structure, with its lattice constant being close to the lattice constant of the rutile structure of titanium oxide, and thus their coexistence leads to formation of a rutile complex oxide with the tin oxide serving as a core. (Dispersion Liquid of Metal Oxide Fine Particles)

A dispersion liquid of metal oxide fine particles according to the present invention includes the above-mentioned metal oxide fine particles according to the present invention, preferably includes water and, if necessary, includes other component(s) . - Amount -

The amount of the metal oxide fine particles contained in the dispersion liquid of metal oxide fine particles is not particularly limited as long as it is 0.1% by mass to 20% by mass, and the amount may be suitably selected according to the purpose; however, it is preferably 1% by mass to 10% by mass. When the amount is less than 0.1% by mass, there is an increase in the required amount of solution in the case where a molded product is produced, so that there is a greater load for removing a solvent by evaporation, etc., which could lead to a rise in the cost. When the amount is more than 20% by mass, the distance between each metal oxide fine particle shortens, and their aggregation easily occurs, so that there may be a decrease in temporal stability. The dispersion liquid of metal oxide fine particles preferably includes water, with the amount of the water being desirably 70% by mass or more, more desirably 80% by mass or more. When the amount of the water is less than 70% by mass, gelation arises depending upon the conditions, which makes it difficult to form particles of uniform size, and there may be a decrease in transparency, for example in the case where a metal alkoxide is used as a raw material for the metal oxide fine particles. Alternatively, when a metal salt is used as a raw material, the amount of water cannot be reduced in view of solubility. Further, when the amount of water is small, it may be impossible to use, for example, a device for electrodialysis, etc. in a desalting process, so that the desalting operation could be restricted. - Light Transmittance -

The light transmittance of the dispersion liquid of metal oxide fine particles is preferably 90% or more. When the light transmittance is less than 90%, the light transmittance decreases in the case where the dispersion liquid is formed into a composite molded product, so that use of the dispersion liquid as an optical member is virtually impossible. The light transmittance can, for example, be measured as follows^ the dispersion liquid of metal oxide fine particles is placed in a quartz cell having an optical path length of 10 mm, and the light transmittance of the dispersion liquid is measured at a wavelength of 450 nm using the ultraviolet-visible absorption spectrophotometer UV-3100 (manufactured by SHIMADZU CORPORATION). (Molded Product)

A molded product according to the present invention includes a composite composition which contains the dispersion liquid of metal oxide fine particles according to the present invention, also contains a resin and, if necessary, contains other component(s). - Water Content -

The water content of the molded product is not particularly limited and may be suitably selected according to the purpose; however, it is preferably 5% by mass or less, more preferably 0.5% by mass to 2% by mass. When the water content is more than 5% by mass, water expansion and volume change owing to vaporization occur under high-temperature conditions, causing distortion inside the molded product, so that the transparency of the molded product may decrease owing to light scattering. Here, the water content of the molded product can, for example, be measured by the Karl Fischer method as in the case of the metal oxide fine particles.

- Refractive Index -

The refractive index of the molded product at a wavelength of 589 nm is preferably 1.60 or greater, more preferably 1.65 or greater, even more preferably 1.67 or greater. To reduce the thickness of a lens and the size of a photographic unit, the material for the lens is required to have a high refractive index. The refractive index of a commercially available thermoplastic resin is 1.6 or so. When the above-mentioned refractive index is less than 1.60, such a refractive index can be achieved by a resin alone, so that the formation of the molded product including the composite material has little merit in terms of cost.

The refractive index can, for example, be measured with respect to light having a wavelength of 589 nm, using an Abbe refractometer (DR-M4, manufactured by ATAGO CO., LTD.) .

- Light Transmittance -

The light transmittance of the molded product at a wavelength of 589 nm with respect to a thickness of 1 mm is not particularly limited and may be suitably selected according to the purpose; however, it is preferably 77% or more, more preferably 80% or more. When the light transmittance of the molded product at a wavelength of 589 nm with respect to a thickness of 1 mm is 77% or more, it is easy to obtain a lens base material having superior properties. Here, the light transmittance of the molded product with respect to a thickness of 1 mm is a value obtained as follows^ a base plate having a thickness of 1.0 mm is produced, and the light transmittance of the base plate is measured using an ultraviolet-visible absorption spectrophotometer (UV-3100, manufactured by SHIMADZU CORPORATION). - Amount -

The amount of the metal oxide fine particles contained in the molded product is not particularly limited and may be suitably selected according to the purpose; however, it is preferably 20% by mass or more, more preferably 30% by mass to 50% by mass. When the amount is less than 20% by mass, it may be impossible for the molded product to have a high enough refractive index. <Composite Composition>

The composite composition constituting the molded product of the present invention contains, as required components, a resin and the metal oxide fine particles of the present invention; if necessary, the composite composition may contain other type(s) of resin(s) and/or additive(s) such as a dispersant, a plasticizer, a release agent, etc.

The glass transition temperature of the composite composition is preferably 100⁰C to 400⁰C, more preferably 130⁰C to 380⁰C. When the glass transition temperature is 100⁰C or higher, sufficient heat resistance can easily be obtained. When the glass transition temperature is 400⁰C or lower, there is a tendency for a molding process to be easily performed. — Resin -

The resin is not particularly limited and may be suitably selected according to the purpose. Examples thereof include thermoplastic resin and curable resin. - Thermoplastic Resin -

The thermoplastic resin is not particularly limited and may be suitably selected according to the purpose. Examples thereof include poly(meth)acrylic acid esters, polystyrene, polyamides, polyvinyl ethers, polyvinyl esters, polyvinyl carbazol, polyolefins, polyesters, polycarbonates, polyurethanes, polythiourethanes, polyimides, polyethers, polythioethers, polyetherketones, polysulfones and polyethersulfones. These may be used individually or in combination.

As the thermoplastic resin, it is preferable to use a thermoplastic resin having, at a terminal or a side chain, a functional group capable of forming a chemical bond with the metal oxide fine particles, since aggregation of the metal oxide fine particles can be prevented and uniform dispersion of the metal oxide fine particles can be thereby realized. Suitable examples of the functional group include functional groups represented by the following formulae. OR^{1 1} O R^{1 3}

— P -OR¹² — O— P -OR¹⁴

Il Il o * o

In the above formulae, R¹¹, R¹², R¹³ and R¹⁴ each independently denote a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aryl group, -SO₃H, -OSO₃H, -CO₂H or Si(OR¹S)₁₁₁₁RIe_3-1111 (where R¹S and R¹⁶ each independently denote a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, or a substituted or unsubstituted aryl group, and ml denotes an integer of 1 to 3) .

Here, examples of the chemical bond include a covalent bond, an ionic bond, a coordination bond and a hydrogen bond. In the case where there is a plurality of functional groups, these functional groups may be functional groups capable of forming different chemical bonds with the metal oxide fine particles. Whether or not the functional groups are capable of forming chemical bonds is judged from whether or not the functional groups of the thermoplastic resin are capable of forming chemical bonds with the metal oxide fine particles when the thermoplastic resin and the metal oxide fine particles are mixed together in an organic solvent. All or some of the functional groups of the thermoplastic resin may form chemical bonds with the metal oxide fine particles. The mass average molecular mass of the thermoplastic resin is preferably 1,000 to 500,000, more preferably 3,000 to 300,000, even more preferably 10,000 to 100,000. When the mass average molecular mass is 500,000 or less, the moldability tends to improve. When the mass average molecular mass is 1,000 or greater, the mechanical strength tends to increase. Here, the mass average molecular mass of the thermoplastic resin is a molecular mass expressed as a polystyrene equivalent, detected by means of a differential refractometer, using tetrahydrofuran as a solvent, and a GPC analyzer with the columns TSKGEL GMHXL, TSKGEL G4000HXL and TSKGEL G2000HXL (all of which are the names of products manufactured by TOSOH CORPORATION), for example.

In the thermoplastic resin, the number of the functional groups which bond with the metal oxide fine particles per polymer chain is preferably 0.1 to 20 on average, more preferably 0.5 to 10 on average, even more preferably 1 to 5 on average. When the number of the functional groups per polymer chain is 20 or less on average, the thermoplastic resin coordinates with a plurality of the metal oxide fine particles, so that it tends to be easy to prevent the occurrence of high viscosity and gelation in a solution state. When the number of the functional groups per polymer chain is 0.1 or more on average, it tends to be easy to disperse the metal oxide fine particles stably.

The glass transition temperature of the thermoplastic resin is preferably 80⁰C to 400⁰C, more preferably 130⁰C to 380⁰C. Use of a thermoplastic resin having a glass transition temperature of 80⁰C or higher makes it easier to obtain an optical component with sufficient heat resistance . Use of a thermoplastic resin having a glass transition temperature of 400⁰C or lower makes it easier to perform a molding process. — Curable Resin —

In the case where the resin is a curable resin, such a known mechanism that a curable resin is cured by the action of heat or an active energy ray may be utilized. Specifically, examples of the curable resin include monomers and prepolymers having radical reactive groups (e.g. unsaturated groups such as (meth)acryloyl group, styryl group and allyl group), cationic reactive groups (e. g. epoxy group, oxetanyl group, episulfide group and oxazolyl group) or reactive silyl groups (e.g. alkoxysilyl group). Besides, the sulfur-containing curable resins described in JP-A

Nos. 05- 148340, 05-208950, 06- 192250, 07-252207, 09- 110979, 09-255781, 10-298287, 2001 -342252, 2002- 131502 and so forth can be suitably used.

— Additive — Besides the resin and the metal oxide fine particles, additive(s) may be mixed into the composite composition in view of uniform dispersibility, fluidity at the time of molding, releasability, weatherability, etc. Also, besides the resin, a resin which does not have the functional group(s) may be added. Although the type of such a resin is not particularly limited, it preferably has optical properties, thermal properties and a molecular mass which are similar to those of the above-mentioned resin.

The mixture proportion of the additive(s) varies depending upon the purpose; however, the amount of the additive(s) is preferably 50% by mass or less, more preferably 30% by mass or less, particularly preferably 20% by mass or less, of the total amount of the metal oxide fine particles and the thermoplastic resin. Surface Treating Agent

In the present invention, when the metal oxide fine particles dispersed in water or an alcohol solvent are mixed with the resin as described later, a particle surface treating agent may be added besides the resin, for the purpose of enhancing substitutional properties or extractability to the organic solvent, increasing uniform dispersibility to the resin, decreasing the water absorbability of the fine particles or enhancing weatherability, for example. The mass average molecular mass of the surface treating agent is preferably 50 to 50,000, more preferably 100 to 20,000, even more preferably 200 to 10,000.

As the surface treating agent, a compound having the structure represented by General Formula (l) below is preferable.

A-B (General Formula (I))

In General Formula (l), A denotes a functional group capable of forming a chemical bond with the surface of the metal oxide fine particles in the present invention, and B denotes a polymer or a monovalent group having 1 to 30 carbon atom(s), which has compatibility or reactivity with a resin matrix composed mainly of the resin in the present invention. Here, examples of the chemical bond include a covalent bond, an ionic bond, a coordination bond and a hydrogen bond. Preferred examples of the functional group denoted by A are similar to the above-mentioned suitable examples of the functional group that is capable of forming a chemical bond with the fine particles and is to be introduced into the resin.

Meanwhile, it is desirable in terms of compatibility that the chemical structure of B be the same or similar to the chemical structure of the resin of which the resin matrix is mainly composed. In the present invention, it is desirable, especially in terms of achieving a high refractive index, that the chemical structure of B, as well as the chemical structure of the resin, have aromatic ring(s). The surface treating agent is not particularly limited and may be suitably selected according to the purpose. Examples thereof include p -octyl benzoic acid, p -propyl benzoic acid, acetic acid, propionic acid, cyclopentanecarboxylic acid, dibenzyl phosphate, monobenzyl phosphate, diphenyl phosphate, di-α-naphthyl phosphate, phenylphosphonic acid, phenylphosphonic acid monophenyl ester, KAYAMER PM-21 (product name! manufactured by Nippon Kayaku Co., Ltd.), KAYAMER PM-2 (product name," manufactured by Nippon Kayaku Co., Ltd.), benzenesulfonic acid, naphthalene sulfonic acid, p -octylbenzenesulfonic acid, and the silane coupling agents described in JP-A Nos. 05-221640, 09- 100111, 2002- 187921 and so forth.

These surface treating agents may be used individually or in combination. On a mass basis, the total amount of the surface treating agent(s) is preferably 0.01 times to 2 times, more preferably 0.03 times to 1 time, particularly preferably 0.05 times to 0.5 times, the amount of the metal oxide fine particles. Plasticizer

When the glass transition temperature of the resin in the present invention is high, the molding of the composite composition is not necessarily easy. Accordingly, a plasticizer may be used to lower the molding temperature of the composite composition. When a plasticizer is added, the amount thereof is preferably 1% by mass to 50% by mass, more preferably 2% by mass to 30% by mass, particularly preferably 3% by mass to 20% by mass, of the total amount of the composite composition constituting the transparent molded product.

The selection of the plasticizer needs to be considered so as to create a favorable balance as a whole in terms of compatibility with the resin, weatherability, plasticizing effect, etc., and the most suitable material therefor cannot be unequivocally stated because it varies depending upon other compositions. However, in term of the refractive index, a compound having aromatic ring(s) is preferable, and typical examples thereof include a compound having the structure represented by General Formula (2) below.

General Formula (2)

In General Formula (2), B¹ and B² each independently denote an alkyl group or aryl alkyl group having 6 to 18 carbon atoms, and m denotes 0 or 1. X denotes any one of the following divalent bonding groups.

Regarding the compound represented by General Formula (2), any alkyl group or any aryl alkyl group may be selected for each of B¹ and B², provided that it has 6 to 18 carbon atoms. When it has fewer than six carbon atoms, it has such a low molecular mass that boiling may occur at the melting temperature of the polymer, and foam may form. When it has more than 18 carbon atoms, the compatibility with the polymer may become poor, so that effects obtained by its addition may be insufficient.

Examples of B¹ and B² include straight-chain alkyl groups such as n-hexyl group, n-octyl group, n-decyl group, n-dodecyl group, n-tetradecyl group, n-hexadecyl group and n-octadecyl group ; branched alkyl groups such as 2-hexyldecyl group and methyl-branched octadecyl group,' and arylalkyl groups such as benzyl group and 2-phenylethyl group .

Specific examples of the compound expressed by General Formula (2) include the following compounds, with W- I (KP-L155, product name, manufactured by Kao Corporation) being preferable .

Besides the above-mentioned components, a known release agent such as modified silicone oil may be added to the composite composition for the purpose of improving moldability, and a known degradation preventing agent such as one based upon hindered phenol, amine, phosphorus, thioether, etc. may be added to the composite composition for the purpose of improving light resistance and/or lessening thermal degradation. When the agent(s) is/are mixed into the composite composition, it is desirable that the amount thereof be approximately 0.1% by mass to approximately 5% by mass of the total solid content of the composite composition. - Method of Producing Composite Composition -

Metal oxide fine particles used in the present invention is bonded to a resin having a functional group at a side chain and dispersed in a resin.

The metal oxide fine particles used in the present invention are small in diameter and high in surface energy, so that if they are isolated as a solid, it is difficult to redisperse them. Thus, it is desirable that the metal oxide fine particles be mixed with the resin so as to constitute a stable dispersion while dispersed in a solution. Preferred examples of methods of producing the composite composition include (l) a method of surface-treating the metal oxide fine particles in the presence of the surface treating agent, extracting the surface-treated metal oxide fine particles into an organic solvent, and uniformly mixing the extracted metal oxide fine particles with the resin so as to produce a composite composition composed of the metal oxide fine particles and the resin,^' and (2) a method of uniformly mixing the metal oxide fine particles and the resin together, using a solvent in which both of them can be uniformly dispersed or dissolved, and thusly producing a composite composition composed of the metal oxide fine particles and the resin.

In the case where the composite composition composed of the metal oxide fine particles and the resin is produced by the method of (1), a water-insoluble solvent such as toluene, ethyl acetate, methyl isobutyl ketone, chloroform, dichloroethane, chlorobenzene or methoxybenzene is used as the organic solvent. The resin and the surface treating agent used for extracting the fine particles into the organic solvent may be of the same or different type. Examples of preferably used surface treating agents include the ones already explained with regard to the above-mentioned surface treating agent. When the resin and the metal oxide fine particles extracted into the organic solvent are mixed, additive(s) such as a plasticizer, a release agent, other type of polymer, etc. may be added if necessary.

In the case where the method of (2) is employed, preferred examples of the solvent include hydrophilic polar solvents such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, benzylalcohol, cyclohexanol, ethylene glycol monomethyl ether, l-methoxy-2-propanol, t-butanol, acetic acid and propionic acid, which may be used individually or in combination,' and mixed solvents of the polar solvents and water-insoluble solvents such as chloroform, dichloroethane, dichloromethane, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, chlorobenzene and methoxybenzene. Here, besides the resin, the following may be added if necessary: a dispersant, a plasticizer, a release agent or other type of polymer. When fine particles dispersed in water/methanol are used, a preferred procedure is as follows^ a hydrophilic solvent which dissolves a thermoplastic resin at a boiling point higher than that of water/methanol is added, then the water/methanol is concentrated and distilled away so as to replace the dispersion liquid of the fine particles with a polar organic solvent, and afterward the fine particles are mixed with the resin. In doing so, the surface treating agent may be added.

The composite composition solution produced by the method of (l) or (2) may be directly subjected to cast molding to obtain a transparent molded product; however, in the present invention, it is particularly desirable that the solvent be removed from the solution by a technique such as concentration, freeze-drying, or reprecipitation from a certain poor solvent, and then the powdered solid content be molded by a technique such as injection molding or compression molding. By molding the composite composition, the molded product of the present invention can be produced. Regarding the molded product of the present invention, a molded product having the above-mentioned refractive index and optical properties is advantageous. Also, the molded product of the present invention is particularly advantageously used as an optical component having a maximum thickness of 0.1 mm or greater and a high refractive index, preferably as an optical component having a thickness of 0.1 mm to 5 mm, more preferably as a transparent component having a thickness of 1 mm to 3mm.

Production of such a thick molded product by solution casting is generally not easy because the solvent is hard to remove! however, use of the composite composition of the present invention makes it possible to facilitate molding and easily form a complicated shape such as an aspheric surface and to provide a material having favorable transparency, utilizing the highly refractive properties of the metal oxide fine particles.

Optical components utilizing the molded product of the present invention are not particularly limited as long as they are optical components utilizing the superior optical properties of the composite composition in the present invention, and they may be suitably selected according to the purpose. Suitable examples thereof include lens base materials, particularly light-transmitting optical components (so-called passive optical components). Examples of functional devices equipped with such optical components include display devices (e.g. liquid crystal displays and plasma displays), projector devices (e.g. OHPs and liquid crystal projectors), optical fiber communication devices (e.g. optical waveguides and optical amplifiers) and photographic devices (e.g. cameras and videos). Examples of the passive optical components among the optical functional devices include lenses, prisms, prism sheets, panels, films, optical waveguides, optical discs, and sealants for LEDs.

The molded product of the present invention is particularly suitable as a lens base material. The lens base material has high refractivity, favorable light transmittance and lightness in weight and is superior in optical property. Also, by suitably adjusting the type(s) of monomer(s) which constitute(s) the composite composition and/or the amount of the metal oxide fine particles dispersed, it is possible to freely adjust the refractive index of the lens base material. The term "lens base material" means a single member capable of performing a function of a lens. A film, a member, etc. may be provided on a surface of the lens base material and/or around the lens base material according to the use environment, use, etc. of the lens. For example, a protective film, an antireflection film, a hard coat film or the like may be formed on the surface of the lens base material. Also, the periphery of the lens base material can be fixed by being fitted into a base material holding frame or the like. It should be noted that such a film and a frame are members added to the lens base material as mentioned in the present invention, and are discriminated from the lens base material itself as mentioned in the present invention.

When the lens base material is used as a lens, the lens base material itself may be used alone as a lens>' alternatively, a film, a frame, etc. may be added to the lens base material to constitute a lens as described above. The type and shape of the lens using the lens base material are not particularly limited. The lens base material in the present invention is used as a spectacle lens, a lens for an optical instrument, a lens for optoelectronics, a lens for a laser, a pickup lens, a lens for an onboard camera, a lens for a portable camera, a lens for a digital camera, a lens for an OHP, a microlens array, etc.

Examples

The following explains Examples of the present invention. It should, however, be noted that the present invention is not confined to these Examples in any way.

In the following Examples, the X-ray diffraction spectrum and the mass average molecular mass were measured as follows. <Measurement of X-ray Diffraction (XRD) Spectrum>

The X-ray diffraction spectrum was measured at 23°C using RINT1500 (X-ray source : Cu-Ka radiation, wavelength: 1.5418 A) manufactured by Rigaku Corporation. <Measurement of Mass Average Molecular Mass>

As for the mass average molecular mass, the molecular mass expressed as a polystyrene equivalent, detected by means of a differential refractometer, was calculated, using tetrahydrofuran as a solvent, and a GPC analyzer with the columns TSKGEL GMHXL, TSKGEL G4000HXL and TSKGEL G2000HXL (all of which are the names of products manufactured by TOSOH CORPORATION). (Example l) - Preparation of Dispersion Liquid 1 of Metal Oxide Fine Particles (dispersion liquid of composite metal oxide fine particles obtained by compounding Sn-Ti composite metal oxide with Zr) -

At room temperature, 0.0473 moles of titanium tetraisopropoxide was mixed with 12 ml of ethanol with stirring, and 2ml of concentrated hydrochloric acid was applied dropwise so as to obtain a transparent solution. Apart from this, a solution made by dissolving 0.0142 moles of tin tetrachloride pentahydrate in 101.3 g of water at room temperature was prepared. The solutions were mixed together with stirring at room temperature for a certain period of time, and a transparent solution was thus obtained. The transparent solution was placed in a water bath kept at 70⁰C, and then heated with stirring for 60 minutes so as to obtain a slightly white turbid sol with some transparency. Apart from this, an aqueous solution made by dissolving 0.0236 moles of zirconium chloride oxide octahydrate in 50 ml of water at room temperature was added for 40 minutes to the sol heated in the water bath. After the addition of the aqueous solution, the mixture was aged for 80 minutes with the temperature kept at 80⁰C. Thereafter, by lowering the temperature to room temperature, a transparent sol (dispersion) was obtained.

An X-ray diffraction (XRD) analysis of metal oxide fine particles in the dispersion revealed that the metal oxide fine particles had a rutile structure.

To the dispersion, 4 ml of acetic acid was added, and the mixture was stirred for 30 minutes. Thereafter, the mixture was desalted by ultrafiltration so as to adjust the concentration of the metal oxide fine particles to 4% by mass, and a dispersion liquid 1 of metal oxide fine particles was thus obtained. (Example 2) - Preparation of Dispersion Liquid 2 of Metal Oxide Fine Particles - The same procedure as in Example 1 was followed except that 0.0095 moles of tin tetrachloride pentahydrate was added instead of 0.0142 moles of tin tetrachloride pentahydrate. A transparent dispersion liquid 2 of metal oxide fine particles in which the concentration of the metal oxide fine particles was 4% by mass was thus obtained.

An X-ray diffraction (XRD) analysis of the metal oxide fine particles in the dispersion revealed that a small proportion of the metal oxide fine particles had an anatase structure whereas others of the metal oxide fine particles had a rutile structure. (Example 3)

- Preparation of Dispersion Liquid 3 of Metal Oxide Fine Particles -

At room temperature, 0.0473 moles of titanium tetraisopropoxide was mixed with 8 ml of acetic acid with stirring. Apart from this, a solution made by dissolving 0.0059 moles of tin tetrachloride pentahydrate in 60 g of water at room temperature was prepared. The solutions were mixed together with stirring at room temperature for a certain period of time, and a transparent solution was thus obtained. The transparent solution was applied dropwise to 60 ml of water kept at 50⁰C, which was followed by stirring for 30 minutes,^" afterward, the temperature was raised to 80⁰C, and 2 ml of hydrochloric acid was added, 30 minutes after the temperature had reached 80⁰C, so as to obtain a hydrochloric acid-added solution. Five minutes afterward, apart from this, an aqueous solution made by dissolving 0.0095 moles of zirconium chloride oxide octahydrate in 50 ml of water at room temperature was added for 40 minutes to the heated hydrochloric acid-added solution (sol) . After the addition of the aqueous solution, the mixture was aged for 80 minutes with the temperature kept at 80⁰C. Thereafter, by lowering the temperature to room temperature, a transparent sol (dispersion) was obtained.

An X-ray diffraction (XRD) analysis of metal oxide fine particles in the dispersion reveled that the metal oxide fine particles had a rutile structure.

The dispersion was desalted by ultrafiltration so as to adjust the concentration of the metal oxide fine particles to 4% by mass, and a dispersion liquid 3 of metal oxide fine particles was thus obtained. (Comparative Example l)

- Preparation of Dispersion Liquid 4 of Metal Oxide Fine Particles -

The same procedure as in Example 1 was followed except that tin tetrachloride pentahydrate was not added. A slightly white turbid but transparent dispersion liquid 4 of metal oxide fine particles in which the concentration of the metal oxide fine particles was 4% by mass was thus obtained.

An X-ray diffraction (XRD) analysis of the metal oxide fine particles in the dispersion revealed that the metal oxide fine particles had an anatase structure. (Comparative Example 2)

- Preparation of Dispersion Liquid 5 of Metal Oxide Fine Particles -

The same procedure as in Example 1 was followed except that acetic acid was not at all added before the ultrafiltration. A transparent dispersion liquid 5 of metal oxide fine particles in which the concentration of the metal oxide fine particles was 4% by mass was thus obtained.

An X-ray diffraction (XRD) analysis of the metal oxide fine particles in the dispersion revealed that the metal oxide fine particles had a rutile structure. (Comparative Example 3)

- Preparation of Dispersion Liquid 6 of Metal Oxide Fine Particles -

At room temperature, 0.0473 moles of titanium tetraisopropoxide was mixed with 12 ml of ethanol with stirring, and 2ml of concentrated hydrochloric acid was applied dropwise so as to obtain a transparent solution. Apart from this, a solution made by dissolving 0.00591 moles of tin tetrachloride pentahydrate in 101.3 g of water at room temperature was prepared. The solutions were mixed together with stirring at room temperature for a certain period of time, and a transparent solution was thus obtained. The transparent solution was placed in a pressure-resistant container for heating, and then heated with stirring at 180⁰C for 60 minutes so as to obtain a milk-white sol. Apart from this, an aqueous solution made by dissolving 0.0236 moles of zirconium chloride oxide octahydrate in 50 ml of water at room temperature was added for 40 minutes to the milk-white sol heated in a water bath. After the addition of the aqueous solution, the mixture was aged for 80 minutes with the temperature kept at 80⁰C. Thereafter, by lowering the temperature to room temperature, a transparent sol (dispersion) was obtained.

An X-ray diffraction (XRD) analysis of metal oxide fine particles in the dispersion revealed that the metal oxide fine particles had a rutile structure. To the dispersion, 4 ml of acetic acid was added, and the mixture was stirred for 30 minutes. Thereafter, the mixture was desalted by ultrafiltration so as to adjust the concentration of the metal oxide fine particles to 4% by mass, and a dispersion liquid 6 of metal oxide fine particles was thus obtained. Next, with regard to the metal oxide fine particles contained in each of the obtained dispersion liquids 1 to 6 of metal oxide fine particles, the existence ratio of the rutile structure in all the metal oxide fine particles, the water content and the sphere-equivalent average primary particle diameter were calculated. The results are shown in Table 1.

Also, with regard to each of the obtained dispersion liquids 1 to 6 of metal oxide fine particles, the light transmittance was measured as described below. The results are shown in Table 1. <Calculation of Existence Ratio of Rutile Structure in All Metal Oxide Fine Particles>

The existence ratio of the rutile structure was calculated in the following manner, using the analysis software "crystallinity, multiple peak separation method" for the X-ray diffractometer RINT 2000 Series manufactured by Rigaku Corporation. A predetermined amount of a sample was set on a dedicated sample holder, a signal related to a background was removed from a diffraction pattern obtained in a measurement (29=20° to 80°) using the X-ray diffractometer, such that the diffraction pattern was divided into a pattern of crystalline components and a pattern of amorphous components, and the areas occupied by the respective patterns were calculated. In the case where component(s) other than the rutile structure was/were included in a crystalline peak, the area of only peak components derived from the rutile structure was divided by the area of all components (amorphous components + all crystalline components) so as to calculate the existence ratio of the rutile structure.

Unnecessary salts in the dispersion liquids of metal oxide fine particles were appropriately removed utilizing electrodialysis, ultrafiltration or the like, then the dispersion liquids were dried and left to stand for 24 hours in an atmosphere in which the temperature and the relative humidity were adjusted to 25°C and 80% respectively, and samples were thus prepared. The water content of each sample was measured at 150⁰C, using a Karl Fischer apparatus (AQUACOUNTER AQV-2100) manufactured by Hiranuma Sangyo Co. , Ltd.

The average primary particle diameter of the metal oxide fine particles contained in each dispersion liquid of metal oxide fine particles was measured using H-9000UHR TRANSMISSION ELECTRON MICROSCOPE manufactured by Hitachi, Ltd. (acceleration voltage ^ 200 kV, degree of vacuum at the time of observation: 7.6X lO-⁹Pa). <Measurement of Light Transmittance>

The light transmittance of each dispersion liquid of metal oxide fine particles at an optical path length of 10 mm and a wavelength of 450 nm was measured using the ultraviolet-visible absorption spectrophotometer UV- 3100 (manufactured by SHIMADZU CORPORATION). Table 1

(Production Example l)

- Production of Metal Oxide Fine Particle N,N'-dimethylacetamide Dispersion 1 - Four hundred grams of the dispersion liquid 1 of metal oxide fine particles in Example 1 was added to a solution prepared by adding 1.2 g of p-octylbenzoic acid to 500 g of N,N'-dimethylacetamide, then the mixture was concentrated under reduced pressure until the mixture weighed about 500 g or less so as to perform solvent substitution. Thereafter, the concentration was adjusted by adding N,N'-dimethylacetamide, and 15% by mass of a metal oxide fine particle N,N'-dimethylacetamide dispersion 1 (i.e. dispersion obtained by dispersing metal oxide fine particles in N,N'-dimethylacetamide) was thus produced. (Production Examples 2 to 6)

- Production of Metal Oxide Fine Particle N,N'-dimethylacetamide Dispersions 2 to 6 -

The same procedure as in Production Example 1 was followed except that the dispersion liquids 2 and 3 of metal oxide fine particles in Examples 2 and 3 and the dispersion liquids 4 to 6 of metal oxide fine particles in Comparative Examples 1 to 3 were used instead of the dispersion liquid 1 of metal oxide fine particles in Example 1. Metal oxide fine particle N,N'-dimethylacetamide dispersions 2 to 6 were thus produced. (Synthesis Example l)

- Synthesis of Thermoplastic Resin -

In 107.1 g of ethyl acetate were dissolved 247.5 g of styrene, 2.50 g of β-carboxyethyl acrylate and 2.5 g of a polymerization initiator (V-601 (product name), manufactured by Wako Pure

Chemical Industries, Ltd.), then polymerization was effected at 80⁰C in a nitrogen atmosphere to thereby synthesize a thermoplastic resin. The mass average molecular mass of the thermoplastic resin, measured by GPC, was 35,000. The refractive index of the thermoplastic resin, measured using an Abbe refractometer, was 1.59. (Examples 4 to 6 and Comparative Examples 4 to 6)

- Preparation of Material Composition and Production of Transparent Molded Product -

The thermoplastic resin, n-octyl benzoic acid and KP-L155 were added to each of the metal oxide fine particle

N,N'-dimethylacetamide dispersions 1 to 6 of Production Examples 1 to 6 such that the mass ratio of the metal oxide fine particle solid content to the thermoplastic resin to n-octyl benzoic acid to KP-L155 was 41.7 • 53.1 : 12.5 : 5. The mixture was uniformly stirred and mixed, then the dimethylacetamide solvent was concentrated with heating under reduced pressure.

The concentrated residue was subjected to thermal compression molding (temperature : 180⁰C, pressure : 13.7 MPa, time : 2 minutes) so as to produce a transparent molded product (lens base material) having a thickness of 1 mm.

Next, properties of each molded product were evaluated as described below. The results are shown in Table 2. <Measurement of Water Content of Molded Product>

Each molded product was pulverized and, as explained in relation to the metal oxide fine particles, left to stand for 24 hours in an atmosphere in which the temperature and the relative humidity were adjusted to 25°C and 80% respectively, and samples were thus prepared. The water content of each sample was measured at 150⁰C, using a Karl Fischer apparatus (AQUACOUNTER AQV 2100) manufactured by Hiranuma Sangyo Co., Ltd.

The refractive index of each molded product was measured with respect to light having a wavelength of 589 nm, using an Abbe refractometer (DR-M4, manufactured by ATAGO CO., LTD.). <Measurement of Light Transmittance of Molded Product>

The light transmittance of each molded product was measured as follows: a base plate having a thickness of 1.0 mm was produced, and the light transmittance of the base plate at a wavelength of 589 nm was measured using an ultraviolet-visible absorption spectrophotometer (UV-3100, manufactured by SHIMADZU CORPORATION).

As for the evaluation of the hygrothermal resistance of each molded product, the temporal degradation of the molded product was evaluated by leaving it to stand under a high-temperature and high-humidity condition (temperature: 65°C, humidity: 90%) for 168 hours. The evaluation was carried out by judging the extent of cracking in the molded product by visual observation. No cracking whatsoever was detected in molded products with favorable hygrothermal resistance, whereas cracking was detected in molded products with poor hygrothermal resistance and, in an extreme case, a molded product broke into several pieces. <Evaluation of Light Resistance of Molded Product>

The light resistance of each molded product was measured as follows: a transparent molded product having a thickness of 1 mm was produced, and simulated sunlight was continuously applied for 168 hours, using a sunshine weather meter (S300(H), manufactured by Suga Test Instruments Co., Ltd.), to an optical component made by placing a filter (SO39, manufactured by FUJIFILM Corporation) on the transparent molded product's surface on the side where the light is applied. The light resistance was evaluated in terms of the change in transmittance at a wavelength of 450 nm caused by coloration.

When the value obtained by dividing the transmittance after the application by the transmittance before the application is 0.9 or greater, there is virtually no problem.

The transmittance was measured using the ultraviolet-visible absorption spectrophotometer UV- 3100 (manufactured by SHIMADZU CORPORATION). Table 2

Industrial Applicability

Having both favorable light transmittance and lightness in weight, the molded product obtained by molding a composite composition which contains the dispersion liquid of metal oxide fine particles according to the present invention and a resin makes it possible to relatively easily provide, for example, a lens whose refractive index can be freely adjusted. Also, the molded product makes it possible to provide, for example, a lens having favorable mechanical strength, heat resistance and light resistance. Therefore, the molded product of the present invention is useful for providing a variety of optical components including a lens base material which constitutes, for example, a spectacle lens, a lens for an optical instrument, a lens for optoelectronics, a lens for a laser, a pickup lens, a lens for an onboard camera, a lens for a portable camera, a lens for a digital camera, a lens for an OHP, a microlens array, etc., and thus the molded product has high industrial applicability.

Claims

1. Metal oxide fine particles having crystallinity, comprising: titanium, wherein crystal structures of the metal oxide fine particles include a rutile structure, and the existence ratio of the rutile structure in all the metal oxide fine particles is 30% or more, wherein the metal oxide fine particles have a water content of 12% by mass or less, and wherein the metal oxide fine particles have a sphere-equivalent average primary particle diameter of 1 nm to 10 nm.

2. The metal oxide fine particles according to claim 1, further comprising tin and zirconium.

3. The metal oxide fine particles according to claim 1 or 2, wherein the existence ratio of the rutile structure in all the metal oxide fine particles is 60% or more, wherein the metal oxide fine particles have a water content of 5% by mass to 10% by mass, and wherein the metal oxide fine particles have a sphere-equivalent average primary particle diameter of 3 nm to 5 nm.

4. A dispersion liquid of metal oxide fine particles, comprising: 0.1% by mass to 20% by mass of the metal oxide fine particles according to any one of claims 1 to 3, wherein the light transmittance of the dispersion liquid at an optical path length of 10 mm and a wavelength of 450 nm is 90% or more.

5. A molded product comprising- a composite composition which contains the dispersion liquid of the metal oxide fine particles according to claim 4 and a resin.

6. The molded product according to claim 5, having a water content of 5% by mass or less.

7. The molded product according to claim 5 or 6, having a refractive index of 1.60 or more at a wavelength of 589 nm, and a light transmittance of 77% or more at a wavelength of 589 nm with respect to a thickness of 1 mm.

8. The molded product according to any one of claims 5 to 7, wherein the amount of the metal oxide fine particles contained is 20% by mass or more.

9. The molded product according to any one of claims 5 to 8, used as a lens base material.