JP2005298226A - Silica sol and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly transparent silica sol and its manufacturing method. <P>SOLUTION: The silica sol essentially comprises an organic liquid medium (other than methanol, ethanol or acetone) having a water solubility at 25°C of 5 wt.% and comprises a silica particle obtained through hydrolysis and/or condensation of a silicon compound. When the inorganic component concentration of the silica gel is adjusted to 10 wt.%, the silica sol shows ≥88% light transmission against a wavelength of 550 nm at an optical path length of 1 mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a silica sol and a method for producing the same. In detail, it is related with the silica sol which gives the hardened | cured material which has the outstanding optical characteristic, and its manufacturing method.

  Silica sols synthesized from alkoxysilane oligomers are widely used in various coating materials and adhesive materials. For example, Patent Document 1 discloses a method in which an alkoxysilane oligomer is hydrolyzed in methanol, ethanol, acetone, or a water solvent, and the silica surface is protected with a silane coupling agent and then used for an inorganic coating film. . Of these, when water is used as a solvent, the storage stability as a coating solution is low, and white turbidity is likely to occur due to aggregation of silica. Therefore, it is necessary to synthesize alkoxysilane, which is a raw material, at a very low concentration. It was disadvantageous. In addition, there is an example in which an oligomer of alkoxysilane and a polyester resin are mixed in an isopropanol or methyl ethyl ketone solvent to form a coating solution, which is then applied and used as a coating film. However, according to the study by the present inventors, in the case of this coating liquid, since the alkoxysilane oligomer is used without hydrolysis, the storage stability in the coating liquid is poor, and the coating film and the molded body are not suitable. When it did, there was a problem that dimensional stability was bad. Deterioration of storage stability due to white turbidity becomes a problem particularly in optical applications that require high transparency.

As described above, only methanol, ethanol, and acetone can be used as a dispersion solvent that maintains the state of nanoparticles that are characteristic of silica synthesized from an oligomer of alkoxysilane and does not cause white turbidity due to silica aggregation. .
JP-A-8-143819

  As described above, only a limited dispersion medium of highly transparent silica sol has been known.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that silica sol dispersed in a specific organic liquid medium solves the above-described problems, and has solved the present invention.
That is, the gist of the present invention is that the main component is an organic liquid medium (excluding methanol, ethanol and acetone) having a solubility in water at 25 ° C. of 5% by weight or more, and by hydrolysis and / or condensation of a silicon compound. A silica sol containing silica particles obtained, wherein the light transmittance at a wavelength of 550 nm at an optical path length of 1 mm when the inorganic component concentration of the silica sol is adjusted to 10% by weight is 88% or more. Exist.

  According to the present invention, a silica sol having high transparency is provided. In addition, it is possible to obtain a composition with a resin that has been poorly compatible with conventional dispersion media, and the number of usable resins increases, and a silica sol that can be used for a wide range of applications is provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to typical examples.
(Organic liquid medium)
The silica sol of the present invention is characterized by containing an organic liquid medium (excluding methanol, ethanol and acetone) having a solubility in water at 25 ° C. of 5% by weight or more as a main component.
The organic liquid medium of the present invention excludes methanol, ethanol and acetone, and has a solubility in water at 25 ° C. of 5% by weight or more. Preferably it is 20 weight% or more, More preferably, it is 50 weight% or more. If the solubility in water is too low, the dispersion stability of the silica particles decreases, and it is not preferred because it tends to cause white turbidity, aggregation, sedimentation, separation, and the like. Although there is no upper limit on the solubility in water, it is easy to absorb moisture in the air during storage of the sol, so care must be taken when using it in applications where moisture content is not preferred, such as liquid crystal materials.

The organic liquid medium is not particularly limited as long as it is a compound that is liquid at 25 ° C. and has the property of dissolving other components, but preferably has an SP value of 9 (cal / cm ³ ) ^1/2 or more. Things are preferable. More preferably, it is 9.2 (cal / cm ³ ) ^1/2 or more. If the SP value is too small, the dispersibility of the silica particles is remarkably lowered, and white turbidity or separation tends to occur, which is not preferable. It is preferably 23.4 (cal / cm ³ ) ^1/2 or less. More preferably, it is 16 (cal / cm ³ ) ^1/2 or less, more preferably 15 (cal / cm ³ ) ^1/2 or less.

  The organic liquid medium preferably has a boiling point of 75 ° C. or higher. More preferably, it is 80 degreeC or more, More preferably, it is 90 degreeC or more. If the boiling point is too low, it is difficult to remove the synthetic dispersion medium used in the silica particle synthesis step described later, which is not preferable. Preferably it is 250 degrees C or less, More preferably, it is 200 degrees C or less. In order to preferably remove the synthetic dispersion medium, it is preferable that the difference in boiling point between the synthetic dispersion medium and the organic liquid medium is 5 ° C. or more. More preferably, it is 10 degreeC or more, More preferably, it is 20 degreeC or more.

  Specific examples of the organic liquid medium include alcohols such as propanol, butanol, diacetone alcohol and benzyl alcohol (excluding methanol and ethanol), esters such as ethyl acetate and methyl acetate, and ketones such as methyl ethyl ketone (however, (Except acetone), cyclic ethers such as tetrahydrofuran, amides such as dimethylformamide, dimethylacetamide, glycols such as ethylene glycol, methylpropylene diglycol, methylpropylene triglycol, ethyl carbitol, butyl carbitol, polyethylene glycol, Such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, methoxypropyl alcohol, methoxybutyl alcohol, polyethylene glycol monomethyl ether acetate Polyhydric alcohol derivatives; styrene, acrylonitrile, vinyl acetate, vinyl toluene, N- vinylpyrrolidone, diallyl adipate, diallyl phthalate, vinyl ethers such as diallyl isophthalate; (meth) acrylates.

The (meth) acrylate is not particularly limited as long as it is a liquid medium containing a (meth) acryl group, but a compound containing one (meth) acryl group and a compound having a plurality of (meth) acryl groups. A compound containing a hydroxyl group.
Examples of the compound containing one (meth) acryl group include (meth) acrylic acid, alkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylate, glycidyl (meth) acrylate, and (meth) acrylic acid. Examples thereof include carbitol, isobornyl (meth) acrylate, acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, and dicyclopentenyl (meth) acrylate.

The alkyl part in the alkyl (meth) acrylate is a linear or branched alkyl having 1 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, such as a phenoxy group, a glycidyl group, and a carboxyl group. May be substituted with one or more. Specific examples of the alkyl (meth) acrylate include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, (meth) acrylic acid 2- Examples include ethylhexyl, isooctyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, and lauryl (meth) acrylate.

  The alkyl part in the dialkylaminoalkyl (meth) acrylate is a linear or branched alkyl having 1 to 20 carbon atoms, more preferably 2 to 8 carbon atoms, and the alkyl in the dialkyl part is independently These may be the same or different, and are linear or branched alkyl having 1 to 20 carbon atoms, more preferably 2 to 8 carbon atoms. Specific examples of the dialkylaminoalkyl (meth) acrylate include, for example, N, N′-dimethylaminoethyl (meth) acrylate, N, N′-diethylaminoethyl (meth) acrylate, and the like.

  Examples of the compound containing two (meth) acrylic groups include alkanediol di (meth) acrylate, polyalkylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, and pentaerythritol di (meth) acrylate. , Dicyclopentanyl di (meth) acrylate, bisphenol A di (meth) acrylate, ethylene oxide-modified bisphenol A di (meth) acrylate, and the like.

  The alkane part in the alkanediol di (meth) acrylate is a linear, branched or cyclic hydrocarbon having preferably 1 to 20 carbon atoms, more preferably 2 to 8 carbon atoms, such as a phenoxy group. One or more may be substituted. Specific examples of the alkanediol di (meth) acrylate include 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, ethylene glycol di (meth) acrylate, butylene glycol di (meth) acrylate. 1,4-butanediol di (meth) acrylate.

  The alkylene in the polyalkylene glycol di (meth) acrylate is a linear or branched alkylene having preferably 1 to 20 carbon atoms, more preferably 2 to 10 carbon atoms. Specific examples of the polyalkylene glycol di (meth) acrylate include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, caprolactam-modified di (meth) acrylate and the like.

  Examples of the compound containing three or more (meth) acryl groups include trimethylolpropane tri (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, Examples thereof include dipentaerythritol hexa (meth) acrylate and N, N, N ′, N′-tetrakis (β-hydroxyethyl) ethyldiamine acrylate.

  Examples of the hydroxyl group-containing (meth) acrylate include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl. Mono (meth) acrylates such as (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, pentaerythritol mono (meth) acrylate; trimethylolpropane di (meth) acrylate, trimethylolethane di (meth) acrylate , Di (meth) acrylates such as pentaerythritol di (meth) acrylate, glycidol dimethacrylate, 2-hydroxy-3- (meth) acrylooxypropyl (meth) acrylate; tetramethylol Tantori (meth) acrylate, tri (meth) acrylates such as pentaerythritol tri (meth) acrylate; dipentaerythritol penta (meth) acrylate.

  As the organic liquid medium, methyl ethyl ketone, tetrahydrofuran, dimethylformamide, polyethylene glycol, polyethylene glycol monomethyl ether acetate, and (meth) acrylates are preferable. Further, when silica sol is used for use in which the organic liquid medium is removed by evaporation or the like, methyl ethyl ketone, tetrahydrofuran, dimethylformamide, polyethylene glycol, or polyethylene glycol monomethyl ether acetate is preferable. When the silica sol is used for an application in which the organic liquid medium is used without being removed by evaporation or the like, (meth) acrylates are preferable. (Meth) acrylates are preferably alicyclic (meth) acrylates such as acryloylmorpholine, and hydroxyl-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, more preferably 2-hydroxyethyl (meth) acrylate. And other hydroxyl group-containing (meth) acrylates.

Among the above, it is preferable to use a compound that is solid at a use temperature, for example, room temperature, in combination with another liquid compound.
The content of the organic liquid medium in the silica sol is usually 95% by weight or less. Preferably, it is 90 weight% or less, More preferably, it is 85 weight% or less. Further, the lower limit of the content of the organic liquid medium is 10% by weight or more, more preferably 20% by weight or more. If the organic liquid medium is too much, that is, if there are too few inorganic components in the silica sol, the silica concentration in the composition will decrease, and the characteristics such as surface hardness, dimensional stability, low curing shrinkage, and low thermal expansion will decrease accordingly. Tend to. On the other hand, when the organic medium is too small, that is, when the inorganic component of the silica sol is too large, the dispersion stability is lowered, the silica particles are aggregated and the transparency is lowered, and flocculation and gelation are liable to occur.
(Silica particles)
The silica sol of the present invention is a silica sol containing silica particles obtained by hydrolysis and / or condensation of a silicon compound. Although there is no limitation in particular as a silicon compound, Water glass, silicon tetrachloride, alkoxysilane, and / or its oligomer are preferable.

When silicon tetrachloride is used as the silicon compound, for example, silica particles can be synthesized by the following method.
First, silicon tetrachloride is uniformly dissolved in a synthetic dispersion medium at room temperature. When stirring is continued for several hours while maintaining at room temperature, the hydrolysis of silicon tetrachloride gradually proceeds, and further hydrolysis and dehydration condensation proceed in an equilibrium reaction by the acid generated as a decomposition product, and silica particles Is synthesized.

When water glass is used as the silicon compound, a known method may be used. For example, silica particles can be synthesized by the following method.
Water glass is uniformly dissolved in the synthetic dispersion medium at room temperature. Thereafter, the system is adjusted to pH = 8 to 10 using ammonia water or other weak alkali reagent, and after maintaining for 30 seconds to 15 minutes, the system is neutralized with an acid reagent to adjust the system to neutral to acidic. Silica particles are synthesized by continuing the stirring for several hours while alternately maintaining the alkalinity adjustment and the acidity adjustment at room temperature for several minutes.

Depending on the pH of the system, the silica particles produced may become coarse. In that case, by controlling the reaction temperature to a low temperature of 5 to 20 ° C. and suppressing the condensation reaction, coarsening of the particles can be prevented and fine particles can be obtained.
Among silicon compounds, a method of obtaining silica particles with an hydrolyzate of an alkoxysilane oligomer is particularly preferably used because the synthesis reaction can be easily controlled and the reaction can be performed under mild conditions. Conventional ordinary silica particles generally have a broad particle size distribution and include particles having a large particle size of, for example, 50 nm or more, and therefore often have poor transparency, and the particles tend to settle. There is also a problem. Although what isolate | separated the particle | grains of a big particle diameter (what is called a cut product) is also known, there exists a tendency which is easy to carry out secondary aggregation and most things which transparency is impaired. In that respect, according to a specific synthesis method of hydrolysis of an oligomer of alkoxysilane, silica particles having a very small particle diameter can be stably obtained, and the silica particles have a property of being difficult to aggregate. There is an advantage that high transparency can be obtained.

Here, the hydrolyzate refers to a product obtained by a reaction including at least a hydrolysis reaction, and may be accompanied by dehydration condensation and the like. The hydrolysis reaction also includes a dealcoholization reaction.
Alkoxysilane is a compound in which an alkoxy group is bonded to a silicon atom, and these produce an alkoxysilane multimer (oligomer) by hydrolysis reaction and dehydration condensation reaction (or dealcoholization condensation). It is preferable that the alkyl chain of the alkoxysilane used in the present invention is not too long, and usually has about 1 to 5 carbon atoms, because the alkoxysilane oligomer is compatible with water or a solvent that is a solvent at the time of synthesis described later. It is preferably about 1 to 3 carbon atoms. Specific examples include tetramethoxysilane and tetraethoxysilane.

  The silica particles that are the subject of the present invention preferably use this alkoxysilane oligomer as a starting material. The reason why the alkoxysilane monomer (monomer) is not used as a starting material is that it is difficult to control the particle size, the particle size distribution tends to be broad, and the particle size is difficult to be uniform. This is because it is difficult to obtain the composition, and there are some kinds of monomers that are toxic, which is undesirable for safety and health. The oligomer can be produced by a known method such as the method described in JP-A-7-48454.

Hydrolysis of the alkoxysilane oligomer is carried out by adding a certain amount of water to the alkoxysilane oligomer in a specific synthetic dispersion medium and causing a catalyst to act. Silica ultrafine particles can be obtained by this hydrolysis reaction.
The synthetic dispersion medium can be used in combination of one or more of water, alcohols, glycol derivatives, hydrocarbons, esters, ketones, ethers, etc., but the synthesis time can be shortened, Among them, alcohols and ketones are particularly preferable in that high-concentration silica ultrafine particles can be obtained.

Specific examples of alcohols include methanol, ethanol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, octanol, n-propyl alcohol, and acetylacetone alcohol. Specific examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.
Among the specific examples of the alcohols and ketones, methanol, ethanol, and acetone are particularly preferable because the synthesis time can be shortened.

  As for the amount of water required for the hydrolysis reaction, the lower limit of the number of moles of alkoxy groups of the alkoxysilane oligomer is usually 0.05 times or more, more preferably 0.3 times or more. If the amount of water is too small, the silica particles do not grow to a sufficient size, and therefore the desired characteristics cannot be exhibited, which is not preferable. However, the upper limit is usually 1 time or less. On the other hand, if the amount is too large, the alkoxysilane oligomer tends to form a gel, which is not preferable.

The alkoxysilane oligomer of the present invention is preferably compatible with the synthetic dispersion medium and water.
As the catalyst used for the hydrolysis, one or more of metal chelate compounds, organic acids, metal alkoxides, boron compounds and the like can be used, and metal chelate compounds and organic acids are particularly preferable.

  Specific examples of the metal chelate compound include aluminum tris (acetylacetonate), titanium tetrakis (acetylacetonate), titanium bis (isopropoxy) bis (acetylacetonate), zirconium tetrakis (acetylacetonate), zirconium bis (butoxy). ) Bis (acetylacetonate), zirconium bis (isopropoxy) bis (acetylacetonate), etc., and one or more of these can be used in combination. Narto) is preferably used.

Specific examples of the organic acid include formic acid, acetic acid, propionic acid, maleic acid and the like. Among these, one or more kinds can be used in combination, and maleic acid is particularly preferably used. When maleic acid is used, there is an advantage that a cured product obtained by radiation curing has a good hue and tends to be less yellowish, which is preferable.
The amount of these catalyst components to be added is not particularly limited as long as the effect is sufficiently exerted, but is usually preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight based on 100 parts by weight of the alkoxysilane oligomer. It is more than part by weight. However, since the action does not change even if the amount is too large, it is usually preferably 10 parts by weight or less, more preferably 5 parts by weight or less.

  In the present invention, the silica particles are preferably ultrafine particles, and the lower limit of the number average particle diameter is preferably 0.5 nm or more, more preferably 1 nm or more. If the number average particle size is too small, the cohesiveness of the ultrafine particles may be extremely increased, and the transparency and mechanical strength of the cured product may be extremely decreased, or the characteristics due to the quantum effect may not be remarkable. The upper limit is preferably 50 nm or less, more preferably 40 nm or less, still more preferably 30 nm or less, particularly preferably less than 15 nm, and most preferably 12 nm or less.

  The silica particles are preferably silica particles having a particle size of more than 30 nm, more preferably silica particles having a particle size of more than 15 nm, preferably 1% by weight or less, more preferably 0.5% by weight, based on silica sol. It is as follows. Alternatively, it is preferably 1% by volume or less, more preferably 0.5% by weight or less, based on the cured product of silica sol. If it is contained in a large amount, light scattering increases, which is not preferable because the transmittance decreases.

  For the determination of the number average particle diameter, a numerical value measured from a transmission electron microscope (TEM) observation image is used. That is, the diameter of a circle having the same area as the observed ultrafine particle image is defined as the particle size of the particle image. The number average particle diameter is calculated using, for example, a known image data statistical processing method using the particle diameter determined in this way, and the number of ultrafine particle images (number of statistical processing data) used for such statistical processing should be as large as possible. Is desirable. For example, in terms of reproducibility, the number of randomly selected particle images is 50 or more, preferably 80 or more, and more preferably 100 or more. Calculation of the volume% in hardened | cured material is converted with the volume of the ball | bowl which makes the particle size determined by the above a diameter.

  In the present invention, by using silica particles composed of hydrolysis and / or condensation of a silicon compound, fine ultrafine particles having a much larger particle diameter than silica particles generally used as a filling component in the past. Can be used as a silica sol. In addition, since the present silica particles have a property of being difficult to aggregate, there is an advantage that they can be uniformly dispersed in silica sol or a cured product thereof. According to this, since light transmittance is not impaired even if a large amount of silica particles are added, a sufficient amount of silica particles can be added to increase dimensional stability and mechanical strength. Furthermore, if silica particles obtained by such a specific production method and surface protection of silica particles such as a silane coupling agent described later are used in combination, a larger amount of monomer and / or oligomer thereof can be added thereto. There is an advantage that silica particles can be dispersed without agglomeration.

The content of silica in the silica sol of the present invention is preferably included in a large amount within a range that can be contained in order to improve the dimensional stability and hardness characteristics of the cured product of the silica sol, and is 5% by weight or more based on the silica sol. It is preferable to include. More preferably, it is 10% by weight or more. Or it is preferable to contain 2 volume% or more with respect to a silica sol. More preferably, it is 5 volume% or more. However, it is preferably not too much to keep the transparency and mechanical strength of the cured product high, and is preferably 90% by weight or less, more preferably 60% by weight, more preferably 40% by weight or less based on the silica sol. Particularly preferably, the content is 30% by weight or less. Or 50 volume% or less with respect to a silica sol, Preferably it is 30 volume% or less.

The silica of the present invention can protect the particle surface by surface treatment, if necessary.
In general, the silica particles synthesized as described above are highly polar and compatible with water, alcohol, and the like, and often have no compatibility with monomers and / or oligomers thereof. In this case, there is a risk of causing aggregation or cloudiness. Further, when obtaining the silica sol of the present invention by the steps described later, problems such as white turbidity and separation may occur.

Therefore, a surface treatment agent having a hydrophilic functional group and a hydrophobic functional group is added to make the surface of the silica particles hydrophobic, thereby preventing problems such as aggregation, white turbidity, and separation as described above.
As the surface treatment method, a method of modifying the surface with the addition of a dispersant or a surfactant or a coupling agent is preferably used.
The dispersant may be selected from polymer dispersants used in fine particle dispersions such as various inks, paints, and electrophotographic toners. As such a polymer dispersant, an acrylic polymer dispersant, a urethane polymer dispersant and the like are appropriately selected and used. Specific examples include trade names such as EFKA (manufactured by Fuka Additives), Disperbyk (manufactured by BYK (BYK)), disparon (manufactured by Enomoto Kasei Co., Ltd.), and the like. The amount of the dispersant used is preferably 10 to 500% by weight, more preferably 20 to 300% by weight, based on the inorganic component.

  The surfactant is not particularly limited, but can be selected from cationic, anionic, nonionic, or amphoteric polymers or low molecular weight non-aqueous surfactants. Specifically, sulfonic acid amide (Avesia Pigments & Additives "Solsperse 3000"), hydrostearic acid (Abesia Pigments & Additives "Solsperse 17000"), fatty acid amine, ε-caprolactone Examples include "Solsperse 24000" manufactured by Avecia Pigments & Additives, 1,2-hydroxystearic acid multimer, beef tallow diamine oleate ("Duomine TDO" manufactured by Lion Akzo), and the like.

The amount of the surfactant used is preferably 10 to 500% by weight, more preferably 20 to 300% by weight, based on the inorganic component.
In particular, the silica particles are preferably surface-treated with a silane coupling agent. A silane coupling agent is a compound having a structure in which an alkoxy group and an alkyl group having a functional group are bonded to a silicon atom, and has a role of making the surface of silica particles hydrophobic.

  The silane coupling agent of the present invention is not particularly limited as long as the purpose is achieved, but those represented by the following general formula (1) are preferable.

(In the formula, R is an alkyl group, R ′ is a group containing a reactive group, and Q ¹ and Q ² are each independently a monovalent organic group.)
R: an alkyl group, preferably C ₁ -C ₆ , more preferably C ₁ -C ₃ , particularly preferably C ₁
, C ₂
Reactive group: Preferably radiation curable group such as alkenyl group, mercapto group, oxylyl group, alkenylcarboxyoxy group, amino group, more preferably C ₆ or less alkenyl group, amino group, mercapto group, oxylyl group, C ₆ The following alkenylcarboxyoxy groups,
A vinyl group, an amino group, a mercapto group, an oxylyl group, and a (meth) acryloyloxy group are preferable, and a vinyl group, a mercapto group, an oxylyl group, and a (meth) acryloyloxy group are more preferable.

R ′ (a group containing a reactive group): a group having the above reactive group at its end, the reactive group may be directly bonded to an Si atom, and a divalent linking group such as an alkylene group or an arylene group It may be bonded to Si via.
Q ¹ and Q ² are preferably a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, or a group containing a reactive group. More preferably, it is a group containing an alkoxy group or a reactive group. When it is a group containing a reactive group, it is preferably the same group as R ′. The alkoxy group is preferably an alkoxy group represented by RO.

A preferred silane coupling agent is trialkoxysilane in which Q ¹ and Q ² are alkoxy groups. Mono and dialkoxysilanes may have low reactivity due to steric hindrance other than alkoxy groups. More preferably, the three alkoxy groups are the same group trialkoxysilane. Specific examples of trialkoxysilanes: epoxycyclohexylethyltrimethoxysilane, glycidoxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, acryloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, mercaptopropyltrimethoxy Silane, mercaptopropyltriethoxysilane In this surface treatment, a Si—O—Si bond is generated through a dealcoholization reaction between the alkoxy group of the silane coupling agent and the hydroxy group on the surface of the silica particle.

  The amount of the silane coupling agent of the present invention used is preferably 1% by weight or more of the silica particles, more preferably 3% by weight or more, and further preferably 5% by weight or more. When the amount of the silane coupling agent used is too small, the surface of the silica particles is not sufficiently hydrophobized, which may hinder uniform mixing with the monomer and / or its oligomer. On the other hand, if the amount is too large, a large number of silane coupling components that do not bind to the silica particles are mixed in, and the transparency and mechanical properties of the resulting cured product are likely to be adversely affected, which is not preferable. Preferably it is 400 weight% or less, More preferably, it is 350 weight% or less, More preferably, it is 300 weight% or less.

The silane coupling agent may be partially hydrolyzed during the surface treatment of the silica particles. Therefore, the silica sol after the surface treatment of the silica particles with the silane coupling agent is performed by a surface treatment with a compound selected from the group consisting of a silane coupling agent, a hydrolysis product of the silane coupling agent, and a condensate thereof. The silica particle which consists of the hydrolyzate of the oligomer of the alkoxysilane currently used is included. In addition, there may be a condensate of silane coupling agents and / or a silane coupling agent and a hydrolysis product thereof. The hydrolysis product of the silane coupling agent refers to a product in which part or all of the alkoxysilane group contained in the silane coupling agent has undergone a hydrolysis reaction to become a hydroxysilane, that is, a silanol group. For example, when the silane coupling agent is epoxycyclohexylethyltrimethoxysilane, epoxycyclohexylethylhydroxydimethoxysilane, epoxycyclohexylethyldihydroxymethoxysilane, and epoxycyclohexylethyltrihydroxysilane are the examples.

Silane coupling agents and / or a condensate of a silane coupling agent and a hydrolysis product thereof are those in which an alkoxy group undergoes a dealcoholization reaction with a silanol group to produce a Si-O-Si bond, or a silanol group Refers to those in which a Si—O—Si bond is produced through a dehydration reaction with other silanol groups.
(Inorganic components other than silica)
The silica sol of the present invention may contain other inorganic components other than silica particles. Although there is no restriction | limiting in particular in another inorganic component, For example, a colorless metal or a colorless metal oxide is used. Specific examples include silver, palladium, alumina, zirconia, aluminum hydroxide, titanium oxide, zinc oxide, calcium carbonate, and clay mineral powder.
Alumina, zinc oxide, or titanium oxide is preferable.

Although there is no particular limitation on the method for producing other inorganic components, a commercially available product is pulverized with a pulverizer such as a ball mill; a method such as sol-gel method is preferable because the particle size can be reduced. More preferably, it is produced by a sol-gel method.
In the present invention, the inorganic component is preferably ultrafine particles, and the lower limit of the number average particle diameter is preferably 0.5 nm or more, more preferably 1 nm or more. If the number average particle size is too small, the cohesiveness of the ultrafine particles may be extremely increased, and the transparency and mechanical strength of the cured product may be extremely decreased, or the characteristics due to the quantum effect may not be remarkable. The upper limit is preferably 50 nm or less, more preferably 40 nm or less, still more preferably 30 nm or less, particularly preferably less than 15 nm, and most preferably 12 nm or less.

  The inorganic component is preferably an inorganic component having a particle size of more than 30 nm, more preferably an inorganic component having a particle size of more than 15 nm, preferably 1% by weight or less, more preferably 0.5% by weight, based on silica sol. It is as follows. Alternatively, it is preferably 1% by volume or less, more preferably 0.5% by weight or less, based on the cured product. If it is contained in a large amount, light scattering increases, which is not preferable because the transmittance decreases. Examples of the method for determining these number average particle diameters include the same methods as described above.

  In order to improve the dimensional stability and hardness characteristics of the cured product, the content of the inorganic component in the silica sol of the present invention is preferably included in a large amount as long as it can be contained, and includes 5% by weight or more based on the silica sol. It is preferable. More preferably, it is 10% by weight or more. Or it is preferable to contain 2 volume% or more with respect to a silica sol. More preferably, it is 5 volume% or more. Or it is 30 volume% or less with respect to a silica sol, More preferably, it is 20 volume% or less, More preferably, you may be 15 volume% or less.

The content ratio of the silica particles in the inorganic component in the silica sol is usually 50% by weight or more, preferably 60% by weight or more, and more preferably 70% by weight or more. The upper limit is 100% by weight or less.
(Radiation curable resin)
The silica sol of the present invention may contain a radiation curable resin as necessary. When (meth) acrylate is used as the organic liquid medium, it has radiation curability. When (meth) acrylate is not used as the liquid medium, it can be used as a radiation curable composition by uniformly mixing a resin having radiation curable properties. Even when (meth) acrylate is used as the organic liquid medium of the silica sol of the present invention, a resin having radiation curability can be further mixed.

The radiation curable resin is not particularly limited, but (meth) acrylate is most preferable because of its high radiation curing reactivity. As the (meth) acrylate, 2) a compound similar to (meth) acrylate that can be used in an organic liquid medium, and a monomer and / or oligomer containing a urethane bond are preferably used.
Among the above, monomers and / or oligomers containing urethane bonds in terms of high heat resistance, high adhesion, or high curability; such as dicyclopentanyl di (meth) acrylate and tricyclodecane dimethanol diacrylate Alicyclic acrylate; 1,6-hexanediol di (meth) acrylate, neopentylglycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, pentaerythritol di (meth) acrylate and other polyhydric alcohol acrylates (Meth) acrylate composed of one or a mixture of two or more selected from the group is most preferably used.

  As a method for producing a monomer having a urethane bond, a method of reacting a chloroformate with ammonia or an amine, a method of reacting an isocyanate with a hydroxyl group-containing compound, a method of reacting urea with a hydroxyl group-containing compound, etc. are known. It may be carried out according to the above method, and when the monomer has a reactive group, it can be oligomerized. Of these, it is generally easy to use a urethane oligomer, and this urethane oligomer is usually added by a conventional method by adding a compound having two or more isocyanate groups in the molecule and a compound containing a hydroxyl group. Produced by reacting.

  Examples of the compound having two or more isocyanate groups in the molecule include tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, isophorone diisocyanate, And polyisocyanates such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, naphthalene diisocyanate.

Of these, one or more of bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate are used in combination because of the favorable hue of the resulting composition. Is preferred.
As the compound containing a hydroxyl group, polyols containing two or more hydroxyl groups are preferably used. Specific examples thereof include ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, trimethylolpropane, and pentaerythritol. , Alkyl polyols such as sorbitol, mannitol, glycerin and the like, polyether polyols that are multimers thereof, polyester polyols synthesized from these polyols and polyhydric alcohols and polybasic acids, polyester polyols such as polycaprolactone polyols, and the like It is done.

The urethane oligomer obtained by these preferably contains the polyether polyol as a compound containing a hydroxyl group, and the average content of structural units derived from the polyether polyol in one molecule of the urethane oligomer is It is preferably 20% by weight or more, more preferably 25% by weight or more, and particularly preferably 30% by weight or more. The upper limit is not particularly limited, but is preferably 90% by weight or less, and 8
It is more preferably 0% by weight or less, and particularly preferably 70% by weight or less.

If the content ratio of this polyether polyol is too small, the cured product becomes brittle, and the elastic modulus is too high and tends to cause internal stress, which tends to cause deformation. Decreases, and it tends to cause problems such as being easily scratched.
The addition reaction between an isocyanate compound and a hydroxyl compound is carried out by a known method, for example, by dropping a mixture of a hydroxyl compound and an addition reaction catalyst such as dibutyltin laurate under conditions of 50 to 90 ° C. in the presence of the isocyanate compound. Can do.

  In particular, when synthesizing a urethane acrylate oligomer, it can be produced by using a part of the compound containing a hydroxyl group as a compound having both a hydroxyl group and a (meth) acryloyl group. The amount used is usually 30 to 70% of the total hydroxyl group-containing compound, and the molecular weight of the resulting oligomer can be controlled according to the proportion.

Examples of compounds having both a hydroxyl group and a (meth) acryloyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, an addition reaction product of a glycidyl ether compound and (meth) acrylic acid, Examples include mono (meth) acrylates of glycol compounds.
Urethane oligomer having (meth) acryloyl groups at both ends by addition reaction of one compound having two or more isocyanate groups in the molecule and two compounds having both a hydroxyl group and a (meth) acryloyl group Can be manufactured.

In particular, urethane oligomers having (meth) acryloyl groups at both ends have the advantage that the adhesiveness and surface curing degree of the resulting resin cured product are further increased.
In the present invention, the monomer having a urethane bond and / or the oligomer thereof may contain an acidic group.
Here, the acidic group means a functional group having acidity, and examples of the acidic group include a sulfonic acid group, a phosphoric acid group, a carboxyl group, and a tertiary amine compound neutralized salt or metal salt thereof. Can be mentioned.

In this case, compounds having these acidic groups may be used as the compounds used in the method for producing the above-mentioned monomer having a urethane bond and / or oligomer thereof, and hydroxyl groups having acidic groups are particularly used during oligomer production. It is preferable to use a group-containing compound.
As the compound containing a hydroxyl group having an acidic group, polyols containing two or more hydroxyl groups are preferably used. Specific examples of the polyol having an acidic group include 2-sulfo-1,4. Alkali metal salts such as butanediol and its sodium salt, alkali metal salts such as 5-sulfo-di-β-hydroxyethylisophthalate and its sodium salt, N, N-bis (2-hydroxyethyl) aminoethylsulfonic acid Sulfonic acids such as tetramethylammonium salt, tetraethylammonium salt, benzyltriethylammonium salt, and the like, and alkali metal salts and amine salts thereof; bis (2-hydroxyethyl) phosphate and tetramethylammonium salt, sodium salt thereof Alkali metal salts, etc. Phosphoric acid esters and their amine and alkali metal salts; dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolheptanoic acid, dimethylolnonanoic acid, dihydroxybenzoic acid, and other alkanol carboxylic acids and their caprolactones Adducts; or compounds having two hydroxyl groups and a carboxyl group in one molecule, such as a half ester compound of polyoxypropylene triol and maleic anhydride or phthalic anhydride, etc. A compound having a carboxyl group as an acidic group is preferred.

  In addition, in order to give an acid group to a monomer having a urethane bond and / or an oligomer thereof, an isocyanate group-containing compound having an acid group as described above is used and / or a hydroxyl group having an acid group is contained. In addition to methods such as using compounds, monomers having urethane bonds and / or oligomers thereof have one or more functional groups other than hydroxyl groups having reactivity with isocyanate groups, such as amino groups, and acidic groups. A method of introducing an acidic group into a monomer having a urethane bond and / or an oligomer thereof by reacting the compound may also be employed. Specific examples of the compound in that case include 1-carboxy-1,5-pentyldiamine, 3,5-diaminobenzoic acid, and the like.

The content of acidic groups in the monomer having an acidic group-containing urethane bond and / or its oligomer is 0.5 × 10 ⁻⁴ eq / g or more with respect to the monomer having a urethane bond and / or its oligomer. It is preferable that it is 1.5 × 10 ⁻⁴ eq / g or more. Further, it is preferably 30 × 10 ⁻⁴ eq / g or less, more preferably 8 × 10 ⁻⁴ eq / g or less.

When the monomer having an acidic group-containing urethane bond and / or its oligomer is used, the amount of the acidic group derived from the monomer and / or oligomer having a radiation curable group in the whole composition is 0.1 × 10. ^-4 eq / g or more is preferably used, more preferably 1 × 10 ⁻⁴ eq / g or more, and more preferably 1.5 × 10 ⁻⁴ eq / g or more. Particularly preferred. Further, it is preferably 13 × 10 ⁻⁴ eq / g or less, more preferably 10 × 10 ⁻⁴ eq / g or less, and particularly preferably 4 × 10 ⁻⁴ eq / g or less.

When the content of the acidic group is too small, the effect of improving the interlayer adhesion as a cured product is insufficient, and not only peeling is likely to occur, but also the cured product combined with silica particles described later tends to be brittle. Conversely, when too large, the softness | flexibility as hardened | cured material will fall, rather, it will become the tendency for interlayer adhesiveness to fall.
The hydroxyalkylene group-containing radiation curable monomer of the present invention mainly means so-called epoxy (meth) acrylate. Epoxy (meth) acrylate is produced by reacting an epoxy compound having at least one epoxy group in one molecule with an unsaturated monobasic acid in the presence of a specific esterification catalyst and a polymerization inhibitor. be able to.

  As an epoxy compound, an epoxy compound obtained by a reaction between a bisphenol A and / or F compound and epichlorohydrin having an epoxy equivalent of 170 to 2000, preferably an epoxy equivalent of 170 to 1000 having a low viscosity can be used. In addition, an epoxy compound obtained by reaction of brominated bisphenol A compound with epichlorohydrin, an epoxy compound obtained by reaction of hydrogenated bisphenol A with epichlorohydrin, a phenol novolac type epoxy compound, cresol novolak Novolac type epoxy compounds such as type epoxy compounds can also be used. These epoxy compounds can be used alone or in admixture of two or more. Among these, bisphenol A and / or F type epoxy compounds are preferable because they are excellent in fluidity, impact resistance, and boiling resistance, and have good adhesion to the adherend.

The unsaturated monobasic acid to be reacted with such an epoxy compound is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, and acrylic acid dimer. These acids can be used alone or in combination of two or more.
The compounding ratio of the epoxy compound and the unsaturated monobasic acid is usually in a range where the carboxyl group in the unsaturated monobasic acid is 0.9 to 1.2 equivalents relative to the epoxy group in the epoxy compound, Among these, a range of 1 ± 0.05 equivalent is preferable in that a resin having excellent curability and storage stability can be obtained. When the blending ratio is smaller than this range, the residual amount of the epoxy group increases, so that a side reaction product of this epoxy group and the secondary hydroxyl group in the epoxy acrylate is generated, and the storage property is also greatly reduced. When the blending ratio is larger than this range, the unsaturated monobasic acid remaining after the reaction is not preferable because the curing time becomes extremely long.

In the present invention, the monomer having a hydroxyalkylene group and / or the oligomer thereof preferably further has an acidic group. Examples of the acidic group include the same as those described in the explanation of the acidic group contained in the monomer having a urethane bond and / or its oligomer, and the acidic group in the monomer having a hydroxyalkylene group and / or its oligomer. There is no particular limitation on the method for forming the surface if a known method is used. For example, a method for introducing a carboxyl group includes a method in which a cyclic acid anhydride is reacted with a hydroxyl group. The acid anhydride in this case is not particularly limited. For example, maleic anhydride, succinic anhydride, phthalic anhydride, pyromellitic anhydride, trimellitic anhydride, naphthalene-1,8: 4,5-tetracarboxylic acid Dianhydride, cyclohexane-1,2,3,4-tetracarboxylic acid = 3,4-anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride, methyl-tetrahydrophthalic anhydride Etc. can be used. Of these, maleic anhydride and succinic anhydride are particularly preferable in terms of excellent transparency and light resistance.

As a method of reacting the cyclic acid anhydride with the hydroxyl group of the radiation-curable resin monomer or oligomer containing a hydroxyalkylene group, the mixture is stirred for several hours at a temperature in the range of room temperature to 150 ° C., more preferably 40 to 100 ° C. after mixing. The method of doing is mentioned.
As the above-mentioned monomer and / or oligomer thereof, a highly transparent material is preferable, and for example, a compound having no aromatic ring is preferable. Resin compositions and cured products using aromatic ring-containing monomers and / or oligomers thereof are colored, or even if they are not initially colored, they are colored during storage or become more colored. There is so-called yellowing. It is thought that this is because the double bond part forming the aromatic ring irreversibly changes its structure by energy rays.

For this reason, the monomer and / or oligomer thereof has a structure that does not have an aromatic ring, so that there is no deterioration in hue and light transmittance does not deteriorate, and applications such as optoelectronics that require colorless and transparent use. There are advantages that make it particularly suitable for applications.
In the monomer having a urethane bond and / or the oligomer thereof, the monomer having no aromatic ring and / or the oligomer thereof are obtained by using the isocyanate group-containing compound not containing an aromatic ring and the hydroxyl group-containing compound not containing an aromatic ring in the above production method. Can be produced by addition reaction.

For example, as the isocyanate compound, it is preferable to use one or more of bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate in combination.
A monomer having a hydroxyalkylene group and / or an oligomer thereof having no aromatic ring is obtained by using an epoxy compound having no aromatic ring and an unsaturated-basic acid having no aromatic ring in the above production method. It can manufacture by making it react. Examples of the epoxy compound having no aromatic ring include a hydrogenated bisphenol A type epoxy compound, a hydrogenated bisphenol F type epoxy compound, or an epoxy not having an aromatic ring such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate. It is preferable to use an epoxy compound obtained by reacting the compound with epichlorohydrin.

  It is a bis (meth) acrylate having an alicyclic skeleton represented by the following general formula (2).

In the general formula (2), R ^a and R ^b are each independently a hydrogen atom or a methyl group, R ^c and R ^d are each independently an alkylene group having 6 or less carbon atoms, and x is 1 or 2 And y represents 0 or 1, respectively.
Specific examples of the component A represented by the general formula (2) include bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = diacrylate, bis (hydroxymethyl) tricyclo [5.2. .1.0 ^2,6] decane = dimethacrylate, bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6] decane = acrylate methacrylate and mixtures thereof, bis (hydroxymethyl) pentacyclo [6.5 1.1 ^3,6 . 0 ^2,7 . 0 ^9,13 ] pentadecane diacrylate, bis (hydroxymethyl) pentacyclo [6.5.1.1 ^3,6 . 0 ^2,7 . 0 ^9,13 ] pentadecane = dimethacrylate, bis (hydroxymethyl) pentacyclo [6.5.1.1 ^3,6 . 0 ^2,7 . ^0,13 ] pentadecane = acrylate methacrylate and mixtures thereof. These tricyclodecane compounds and pentacyclodecane compounds may be used in combination.
Among the above components, bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate has excellent transparency and heat resistance and is particularly preferably used.

[Polymerization initiator]
In the silica sol of the present invention, a polymerization initiator can be added in order to initiate a polymerization reaction that proceeds by active energy rays (for example, ultraviolet rays). As such a polymerization initiator, a radical generator which is a compound having a property of generating radicals by light is generally used, and such known compounds can be used. Such radical generators include benzophenone, benzoin methyl ether, benzoin isopropyl ether, diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,6-dimethylbenzoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and the like. These may be used in combination. Of these, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and benzophenone are preferred. The amount of the polymerization initiator added is usually 0.001 part by weight or more, preferably 0.01 part by weight or more, more preferably 0.05 part by weight, based on 100 parts by weight of the total of the compounds containing radiation-curable functional groups. That's it. However, it is usually 10 parts by weight or less, preferably 8 parts by weight or less. If the amount added is too large, the polymerization reaction may proceed rapidly and not only increase the optical distortion but also deteriorate the hue. If the amount is too small, the composition may not be sufficiently cured. .
Further, when the polymerization reaction is initiated by an electron beam, the above polymerization initiator can be used, but it is preferable not to use the polymerization initiator.

[Surface tension modifier]
The surface tension adjusting agent of the present invention is used for the purpose of reducing the surface tension of the composition and improving the coating property to the substrate.

Specific examples include low and high molecular weight surfactants, silicone compounds and various modified products thereof (polyether modified, fluorine modified, etc.), sorbitan esters, other various leveling agents, antifoaming agents, rheology control agents, mold release Agents and the like. Of these, silicone compounds such as Polyflow KL510 (manufactured by Kyoeisha Chemical Co., Ltd.) are preferred, and polyether modified silicone compounds such as KF351A (manufactured by Shin-Etsu Chemical Co., Ltd.) and fluorine-modified surfactants preferably reduce the surface tension. In addition, it is preferable because it exhibits the property of not causing coating defects and is excellent in antifouling property, slipperiness and environmental resistance.
The addition amount of the surface tension adjusting agent is 5% by weight or less, preferably 3% or less, more preferably 0.01 to 1% by weight with respect to the silica sol, although it depends on the type.

[Auxiliary ingredients]
An auxiliary component such as an additive may be added to the silica sol of the present invention, if necessary, as long as the produced cured resin does not significantly depart from the object of the present invention.

Other auxiliary components include, for example, stabilizers such as antioxidants, heat stabilizers, or light absorbers; fillers such as glass fibers, glass beads, mica, talc, kaolin, metal fibers, metal powders; carbon fibers Carbon materials such as carbon black, graphite, carbon nanotubes, fullerenes such as C ₆₀ (fillers and fullerenes are collectively referred to as inorganic filler components); antistatic agents, plasticizers, mold release agents, Modifiers such as foaming agents, leveling agents, anti-settling agents, surfactants, thixotropy imparting agents; colorants such as pigments, dyes, hue modifiers; necessary for the synthesis of monomers and / or their oligomers or inorganic components Examples include curing agents, catalysts, curing accelerators, and the like. The addition amount of these auxiliary components is not limited as long as the resin cured product to be produced does not deviate significantly from the object of the present invention, but is usually 20% by weight or less of the silica sol.

  The silica sol of the present invention may be further mixed with a monomer other than radiation curable and / or an oligomer thereof for the purpose of improving mechanical properties and heat resistance or balancing various properties. . Although the kind of monomer and / or its oligomer is not specifically limited, Specifically, a thermoplastic resin, a thermosetting resin monomer, and / or its oligomer are used.

  Examples of the thermoplastic resin include polystyrene; polymethyl methacrylate; polyarylate, polyester such as O-PET (manufactured by Kanebo); polycarbonate; polyethersulfone; ZEONEX (manufactured by ZEON Corporation), and fats such as ARTON (manufactured by JSR Corporation). Cyclic thermoplastic resins; cyclic polyolefins such as Apel (manufactured by Mitsui Chemicals) and the like can be mentioned, and polycarbonate or polyethersulfone is preferred from the viewpoint of transparency and dimensional stability. The thermoplastic resin is preferably 20% by weight or less based on the composition other than the inorganic component.

As the thermosetting resin monomer and / or oligomer thereof, an epoxy resin; Rigolite (manufactured by Showa Denko) or the like is used, and a high purity epoxy resin is preferable from the viewpoint of transparency and dimensional stability. The thermosetting resin is preferably 50% by weight or less based on the composition other than the inorganic component.
(Silica sol)
The silica sol of the present invention has a light transmittance of 88% or more at a wavelength of 550 nm at an optical path length of 1 mm when adjusted to an inorganic component concentration of 10% by weight. As a method for adjusting the inorganic component concentration to be 10% by weight, the inorganic component concentration is quantified in advance by a method such as fluorescent X-ray or NMR, and if it is larger than 10% by weight, it is diluted with acetone. When the inorganic component concentration is less than 10% by weight, it is concentrated by evaporation or the like. In this way, the inorganic component concentration is adjusted to 10% by weight, and the light transmittance at a wavelength of 550 nm at an optical path length of 1 mm is measured. At that time, the light transmittance is 88% or more. Preferably, it is 90% or more, more preferably 91% or more.

  The silica sol of the present invention preferably has high transparency. Specifically, the light transmittance at a wavelength of 550 nm at an optical path length of 1 mm is 90% or more, more preferably 95% or more. If the transparency is low, storage stability tends to be low, which is not preferable. In addition, the transparency of dilicasol when cured tends to be greatly impaired, and when the cured product is used for optical applications, read errors increase when reading recorded information, which is not preferable.

  The silica sol of the present invention preferably has a viscosity at 25 ° C. of 1000 centipoise or more. More preferably, it is 2000 poise or more. Moreover, it is preferable that it is 10,000 centipoises or less. More preferably, it is 5000 centipoises or less. If the thickness is less than 1000 centipoise, it is difficult to form a protective film having a thickness of 50 μm or more, which is not preferable because it cannot be used for an information recording medium that requires such a thick protective film. On the contrary, if it is larger than 5000 centipoise, it becomes difficult to form a protective film having a smooth surface, which is not preferable. The viscosity may be measured with an E-type viscometer, a B-type viscometer or a vibration-type viscometer. Methods for adjusting the viscosity include techniques such as addition of diluent, solvent removal, molecular weight control of radiation curable oligomer, addition of thickener or rheology control agent, preferably addition of diluent, radiation The molecular weight control of the curable oligomer and the addition of a thickener are used, and the addition of a diluent is more preferably used.

The silica sol has a surface tension at 25 ° C. of 40 mN / m or less, preferably 35 mN / m or less, more preferably 30 mN / m or less. If the surface tension is too high, the spreadability of the composition at the time of coating deteriorates, and not only the amount of the composition required at the time of coating increases, but also a defect is caused, which is not preferable. The smaller the surface tension, the better, but it is usually 10 mN / m or more. The surface tension may be measured using a surface tension meter (for example, CBVP-A3 type manufactured by Kyowa Interface Science Co., Ltd.). Examples of the method for adjusting the surface tension include addition of the surface tension adjusting agent.
(Method for producing silica sol)
In the method for producing a silica sol of the present invention, after synthesizing silica in a liquid medium by hydrolysis and / or condensation of a silicon compound, the liquid medium is an organic liquid medium having a solubility in water at 25 ° C. of 5% or more (however, , Except for methanol, ethanol and acetone).

Specifically, (a) a step of synthesizing silica particles by hydrolysis and / or condensation of a silicon compound in a synthetic dispersion medium of methanol, ethanol, or acetone, (b) a step of protecting the surface of the silica particles, (C) After the organic liquid medium is mixed, it can be produced by sequentially performing a process of removing the synthetic dispersion medium and replacing the solvent.
According to this production method, a sol in which ultrafine silica particles having a uniform particle diameter are highly dispersed can be obtained more easily.

  The step (a) is performed by the following method when the silicon compound is silicon tetrachloride. First, silicon tetrachloride is uniformly dissolved in a synthetic dispersion medium at room temperature. When stirring is continued for several hours while maintaining at room temperature, the hydrolysis of silicon tetrachloride gradually proceeds, and further hydrolysis and dehydration condensation proceed in an equilibrium reaction by the acid generated as a decomposition product, and silica particles Is synthesized.

In the step (a), when the silicon compound is water glass, the hydrolysis reaction does not occur and only the condensation reaction occurs. Specifically, water glass is uniformly dissolved in a synthetic dispersion medium at room temperature. Thereafter, the pH of the system is adjusted to 8 to 10 using aqueous ammonia and other weak alkaline reagents, and after maintaining for 30 seconds to 15 minutes, the system is neutralized with an acid reagent to adjust the system to neutral to acidic. Silica particles are synthesized by continuing stirring for several hours while alternately maintaining the alkalinity adjustment and the acidity adjustment at room temperature for several minutes.

Depending on the pH of the system, the silica particles produced may become coarse. In that case, by controlling the reaction temperature to a low temperature of 5 to 20 ° C. and suppressing the condensation reaction, coarsening of the particles can be prevented and fine particles can be obtained.
When the silicon compound is an alkoxysilane oligomer, in the step (a), an alkoxysilane oligomer, a catalyst and water are added in a solvent to hydrolyze the alkoxysilane oligomer to synthesize silica particles. The solvent is preferably a solvent of methanol, ethanol, or acetone. These solvents are preferable because they have good compatibility with alkoxysilane oligomers and can stably disperse silica particles synthesized through hydrolysis. The amount of the solvent is preferably 0.3 to 10 times that of the oligomer of alkoxysilane.

Examples of the catalyst include organic acids such as formic acid and maleic acid; inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid; and hydrolytic catalysts such as metal complex compounds such as acetylacetone aluminum, dibutyltin dilaurate and diztiltin dioctate. . The amount used is preferably 0.1 to 3% by weight based on the oligomer of the alkoxysilane.
The water is preferably added in an amount of 10 to 50% by weight based on the oligomer of alkoxysilane. The hydrolysis temperature is 10 to 100 ° C. If it is lower than this, the reaction for forming silica particles does not proceed sufficiently, which is not preferable. On the other hand, if it is too high, an oligomer gelation reaction tends to occur, which is not preferable. The hydrolysis time is preferably 30 minutes to 1 week.

The reaction (b) is a step of protecting the surface of silica particles, and examples of the surface protective agent include surfactants, dispersants, silane coupling agents and the like.
In the case of using a surfactant or a dispersant, a method of adding a surface protective agent and stirring and reacting at room temperature to 60 ° C. for about 30 minutes to 2 hours, after adding and reacting, And a method of aging for several days. When adding, it is important not to select a solvent having a very high solubility in the solvent of the surface protective agent. When a solvent having a very high solubility of the surface protective agent is used, it is not preferable because the protection to the inorganic component is not sufficiently performed or a long time is required for the protection process. When examining the high solubility of the surface protective agent, the solubility value (SP value) in the solvent can be referred to.

  When a silane coupling agent is used, the surface protection reaction proceeds at room temperature (25 ° C.). Usually, stirring is performed for 0.5 to 24 hours to allow the reaction to proceed, but heating may be performed at a temperature of 100 ° C. or lower. When heated, the reaction rate increases and the reaction can be carried out in a shorter time. When a silane coupling agent is used, water may be added. Water is usually added in the range of the amount required for hydrolysis of the alkoxy group derived from the silane coupling agent and the remaining alkoxy group derived from the alkoxysilane. The silane coupling agent may be added in multiple portions. In that case, water may be added in a plurality of times, and the amount thereof is the same as that described in the amount of water added to the silane coupling agent.

The step (c) needs to be performed after the reaction (b) is sufficiently completed. The confirmation can be performed by measuring the residual amount of the silane coupling agent in the reaction solution. Usually, it is when the residual amount of the silane coupling agent in the reaction solution becomes 10% or less with respect to the charged amount. If the operation of (c) is performed before the reaction of (b) sufficiently proceeds, the silica particles are aggregated or coarsened, so that the transparency is impaired. In the step (c), an organic liquid medium is mixed with the reaction liquid obtained in the step (b). The organic liquid medium used at that time must have a boiling point higher than that of the synthetic dispersion medium. At this time, when an organic liquid medium having high solubility in water is used, problems such as white turbidity do not occur. Next, the synthetic dispersion medium is removed by a method such as evaporation. The degree of vacuum during evaporation is preferably 20 kPa or less, more preferably 10 kPa or less, and even more preferably 5 kPa or less. However, in order to avoid gelation and cloudiness, it is preferable to increase the degree of vacuum stepwise from atmospheric pressure. If it is too high, the synthetic dispersion medium cannot be sufficiently removed, and an alkoxy group tends to remain in the alkoxysilane oligomer, which is a raw material for silica particles, and the storage stability of the silica sol is lowered, which is not preferable. Conversely, if it is too low, the dispersion stability of the silica particles is lowered, and the silica particles are likely to be coarsened, aggregated, or gelled. The evaporation temperature may be volatilized at a reduced pressure set by the synthetic dispersion medium, and is usually 30 to 80 ° C. For example, if it is methanol in 15 kPa, the temperature of 30-40 degreeC is preferable. If it is too high, the dispersion stability of the silica particles is lowered, and the silica particles are likely to be coarsened, aggregated, or gelled. If it is too low, the synthetic dispersion medium cannot be sufficiently removed, and when the silica particle raw material is an oligomer of an alkoxysilane, an alkoxy group tends to remain and the storage stability of the silica sol is lowered, which is not preferable.

The above is the method for producing a silica sol of the present invention. Depending on the application, (d) a step of further mixing a radiation curable resin with the silica sol can be performed. Furthermore, it can also be used through the process of removing the volatile component contained in the organic liquid medium at the temperature of (e) 25-150 degreeC depending on a use.
The step (d) is necessary when the silica sol does not have radiation curability or when it is desired to improve the heat resistance, adhesion, and curability of a cured product obtained from the silica sol.

The step (e) is required when it is desired to obtain a solvent-free resin composition using the silica sol. More specifically, it is necessary to form a thick film of 50 microns or more, or to form a thicker film or sheet.
The step (d) can be performed at room temperature (25 ° C.). However, when the viscosity of the radiation curable resin is high, or when the melting point of the radiation curable resin is room temperature (25 ° C.) or more, 30 You may carry out by heating to -90 degreeC. The mixing time is preferably 30 minutes to 5 hours.

  In the step (e), an organic liquid medium or a volatile component contained in the organic liquid medium and an alcohol generated by hydrolysis of an alkoxysilane oligomer (the above are collectively referred to as “volatile components”). Is removed. However, it may be removed within a necessary range, and may not be completely removed. In addition, when temperature is lower than the range described, removal of a volatile component is not fully performed but it is unpreferable. On the other hand, if it is too high, the silica particles are liable to be aggregated, coarsened or gelled, which is not preferable. The temperature may be controlled step by step. The removal time is preferably 1 to 12 hours. Moreover, it is preferable to remove by reducing the pressure to 20 kPa or less, more preferably 10 kPa or less. Moreover, it is preferable to remove at 0.1 kPa or more. The pressure may be gradually reduced.

  By producing silica sol by the above method, a composition in which fine particles of silica particles are uniformly dispersed can be stably produced without causing cloudiness or gelation. In addition, silica sols in which silica particles with a small particle size are dispersed in various resins can be obtained, and coating films and molded articles produced using this silica sol have excellent dimensional stability and weather resistance. .

[Radiation curing conditions]
When the silica sol has radiation curability, the cured product is obtained by so-called “radiation curing” in which a polymerization reaction is started by irradiating the silica sol with radiation (active energy ray or electron beam).
There is no restriction | limiting in the form of a polymerization reaction, For example, well-known polymerization forms, such as radical polymerization, anionic polymerization, cationic polymerization, and coordination polymerization, can be used. Among these polymerization modes, the most preferable polymerization mode is radical polymerization. The reason for this is not clear, but it is presumed to be due to the homogeneity of the product due to the initiation of the polymerization reaction being homogeneous and proceeding in a short time within the polymerization system.

The radiation is an electromagnetic wave (gamma ray, X-ray, ultraviolet ray, visible ray, infrared ray, microwave, etc.) that acts on a polymerization initiator that initiates a necessary polymerization reaction to generate a chemical species that initiates the polymerization reaction. ) Or particle beam (electron beam, α-ray, neutron beam, various atomic beams, etc.).
An example of radiation preferably used in the present invention is preferably ultraviolet rays, visible rays, and electron beams, and most preferably ultraviolet rays and electron beams because energy and a general-purpose light source can be used.

  When ultraviolet rays are used, a method is employed in which a photo radical generator that generates radicals by ultraviolet rays (see the above example) is used as a polymerization initiator and ultraviolet rays are used as radiation. At this time, you may use a sensitizer together as needed. The wavelength of the ultraviolet rays is usually in the range of 200 to 400 nm, and this wavelength range is preferably 250 to 400 nm. As a device for irradiating ultraviolet rays, a known device such as a high-pressure mercury lamp, a metal halide lamp, or an ultraviolet lamp having a structure for generating ultraviolet rays by microwaves can be preferably used. The output of the apparatus is usually 10 to 200 W / cm, and when the apparatus is installed at a distance of 5 to 80 cm with respect to the irradiated object, the light deterioration, thermal deterioration, thermal deformation, etc. of the irradiated object are caused. Less and preferred.

The silica sol of the present invention can also be cured preferably by an electron beam, and a cured product excellent in mechanical properties, particularly tensile elongation properties can be obtained. When an electron beam is used, the light source and the irradiation device are expensive, but the addition of an initiator can be omitted and the polymerization is not inhibited by oxygen. There is a case.
An electron beam irradiation apparatus used for electron beam irradiation is not particularly limited, and examples thereof include a curtain type, an area beam type, a broad beam type, and a pulse beam type. The acceleration voltage during electron beam irradiation is preferably 10 to 1000 kV.

The intensity of the radiation is usually 0.1 J / cm ² or less, preferably irradiated with 0.2 J / cm ² or more energy. In general, irradiation is performed within an energy range of 20 J / cm ² or less, preferably 1
0 J / cm ² or less, more preferably 5 J / cm ² or less, more preferably 3J / cm ² or less, particularly preferably irradiated with 2J / cm ² or less.
If the radiation intensity is within this range, it can be appropriately selected depending on the type of radiation curable compound. For example, in the case of a radiation curable resin composition containing a monomer having a urethane bond or a hydroxyalkylene group and / or an oligomer thereof, the irradiation intensity is preferably ² J / cm ² or less. In the case of a radiation curable resin composition containing a monomer composed of an alicyclic acrylate and / or an oligomer thereof, the irradiation intensity is preferably ³ J / cm ² or less.

  When the irradiation energy or irradiation time of such radiation is extremely small, the heat resistance and mechanical properties of the crosslinked resin composition may not be sufficiently exhibited due to incomplete polymerization. The irradiation time is usually 1 second or longer, preferably 10 seconds or longer. However, when the amount is excessively large, deterioration such as yellowing due to light such as yellowing may occur. Therefore, the irradiation time is usually 3 hours or less, and preferably about 1 hour or less in terms of reaction acceleration and productivity.

The radiation irradiation may be performed in one step or in a plurality of steps. As the radiation source, a diffusion radiation source in which the radiation spreads in all directions is usually used. Irradiation is performed with the liquid composition in a stationary state or a state in which the liquid composition is conveyed by a conveyor, and a radiation source in a stationary state.
It is also possible to use the polymerizable liquid composition as a coating liquid film on a suitable substrate (for example, resin, metal, semiconductor, glass, paper, etc.) and then irradiate radiation to cure the coating liquid film. .

[Radiation cured product]
The radiation-cured product of the silica sol of the present invention usually exhibits insoluble and infusible properties in a solvent or the like, and has advantageous properties for the use of optical members even when it is thickened, and has good adhesion and surface cure. It is preferable that it is excellent. Specifically, it is preferable to exhibit low optical distortion (low birefringence), high light transmittance, dimensional stability, high adhesion, high degree of surface curing, and a certain level of heat resistance. Further, the smaller the curing shrinkage, the better.

This will be described in more detail.
The radiation-cured product of the present invention usually has a thickness of 5 cm or less. Preferably it is 1 cm or less, More preferably, it is 1 mm or less, More preferably, it is 500 micrometers or less. The film thickness is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, more preferably 30 μm or more, particularly preferably 70 μm or more, and most preferably 85 μm or more.

  About transparency of the said hardened | cured material, it is preferable that the light transmittance per 0.1 mm of optical path length in 550 nm is 80% or more, More preferably, it is 85% or more, More preferably, it is 89% or more. More preferably, the light transmittance per optical path length of 0.1 mm at 400 nm is preferably 80% or more, more preferably 85% or more, and still more preferably 89% or more. Particularly preferably, those having the light transmittance per 1 mm of the optical path length are preferable. The light transmittance may be measured at room temperature using, for example, an HP8453 ultraviolet / visible absorptiometer manufactured by Hewlett-Packard Company.

  Moreover, it is preferable that the surface hardness by the pencil hardness test based on JISK5400 of the hardened | cured material of this invention is HB or more, More preferably, it is F or more, More preferably, it is H or more. Moreover, it is preferable that it is 7H or less. In this case, the cured product preferably satisfies the above hardness even on a cured product cured on an inorganic substrate such as glass or metal or a resin substrate, and more preferably cured on a plastic substrate such as polycarbonate. It is preferable that the above-mentioned hardness is also satisfied in the product. If the hardness is too small, it is not preferable because the surface is easily scratched. Although there is no problem with the hardness being too large, the cured product tends to become brittle, and cracks and peeling are likely to occur, which is not preferable.

  Furthermore, curing shrinkage is preferably as small as possible, and is usually 3% by volume or less, more preferably 2% by volume or less. In general, the method is replaced by a method in which silica sol is applied onto a substrate and the amount of concave warpage generated after curing is measured. The measuring method was that a composition film having a thickness of 100 ± 15 microns was formed on a circular polycarbonate plate having a diameter of 130 mm and a thickness of 1.2 ± 0.2 mm using a spin coater, and was irradiated with a prescribed amount of radiation. Then, leave it on the surface plate for 1 hour. After standing, the concave warp of the polycarbonate plate caused by the curing shrinkage of the composition is measured. The concave warp is preferably 1 mm or less, more preferably 0.1 mm or less.

Furthermore, it means that it has better dimensional stability, so that the thermal expansion of hardened | cured material is small. For example, the smaller the linear expansion coefficient, which is one of the specific indicators of thermal expansion, is preferable, preferably 13 × 10 ⁻⁵ / ° C. or less, more preferably 12 × 10 ⁻⁵ / ° C. or less, and still more preferably 10 × 10. ⁻⁵ / ° C. or less, particularly preferably 8 × 10 ⁻⁵ / ° C. or less. The linear expansion coefficient is, for example, a weight of 1 g by a compression method thermomechanical measurement (TMA; SSC / 5200 type; manufactured by Seiko Instruments Inc.) using a plate-shaped test piece of 5 mm × 5 mm × 1 mm, and a heating rate of 10 ℃ /
The linear expansion coefficient can be evaluated in increments of 10 ° C. over a range from 40 ° C. to 100 ° C., and the average value can be used as a representative value.

  In addition, higher adhesion is preferred. The measuring method is to drop 15 drops of the composition on a 10 cm square optically polished glass plate using a dropper, leave it at room temperature for 1 minute, irradiate a prescribed amount of radiation, and then leave it at room temperature for 1 hour. A cut is made in the center of the cured composition portion with a cutter knife so as to reach the glass surface, and after leaving for 14 days at room temperature, the peeling of the interface between the cured composition and the glass surface in the cut portion is visually observed. We evaluated by whether or not. When the number of samples is 5 and no peeling is observed for all the samples, ◎ when no peeling is observed for two or more samples, ○ when no peeling is observed for only one sample, Δ, all The case where peeling was visually observed with respect to the sample was marked with ×. The degree of adhesion is preferably ◯ or ◎, and more preferably ◎.

Further, a plastic substrate such as polycarbonate having the above adhesiveness is more preferable than on the optically polished glass plate.
In addition, it is preferable that the degree of surface hardening is hard. The measurement method is to irradiate the specified amount of ultraviolet light, then sandwich the sample with the right index finger and thumb wearing rubber gloves so that the thumb is on the coated surface side. When the mark is separated from the coated surface, the case where the mark is not visually observed is indicated by ◯, the case where the mark is observed thinly is indicated by Δ, and the case where the mark is observed dark is indicated by X. The surface hardness is preferably ◯.

  The cured product of the present invention is obtained by placing a laminate in which a cured product layer having a film thickness of 100 ± 15 μm is formed on an adherend in an environment of 80 ° C. and 85% RH for 100 hours, more preferably 200 hours. It is preferable that the ratio of the close contact area to the adherend retains 50% or more of the initial close contact area. More preferably, it is 80% or more, and particularly preferably 100%. This adhesion to the adherend is formed as a laminate having a cured product layer with a thickness of 100 ± 15 μm by applying and curing the radiation curable composition of the present invention on the surface of the 10 cm square adherend, The laminate was placed in a constant temperature and humidity chamber set at 80 ° C. and 85% RH for 100 hours, and then a transparent film depicting a 2 cm square was overlaid on the taken out laminate, and the peeled area with respect to the adherend was halved. The following squares are counted, the percentage of the total number of 25 is calculated, and it can be calculated as the ratio of the adhesion area to the adherend.

Or it can obtain | require by measuring the weight of this adherend with a composition film | membrane before and after a constant temperature and humidity test.
The adherend is not particularly limited, and examples thereof include resins, glass, ceramics, inorganic crystals, metals, semiconductors, diamonds, organic crystals, paper pulp, and wood. Preferably, a plastic substrate such as polycarbonate or the plastic substrate is used. A substrate on which an organic or inorganic material is laminated.

As for heat resistance, the glass transition temperature measured by differential thermal analysis (DSC), thermomechanical measurement (TMA) or dynamic viscoelasticity measurement of the cured resin is preferably 120 ° C. or higher. More preferably, it is 150 degreeC or more, More preferably, it is 170 degreeC or more.
Moreover, it is preferable that the hardened | cured material of this invention does not melt | dissolve with respect to various solvents. Typically, it is preferable not to dissolve in a solvent such as toluene, chloroform, acetone, or tetrahydrofuran.

The cured product of the present invention contains ultrafine inorganic substance particles such as silica particles. However, since the fine particles are substances having optical properties different from those of the organic resin matrix, the cured product as a whole is realized by the organic substance alone. There is a case where it has the characteristic that it has the balance of the unusual refractive index and Abbe number which cannot be obtained. Such a balance between the specific refractive index and the Abbe number may be useful in applications where it is desirable that the birefringence is small, utilizing the refraction of light such as a lens or a prism. This refers to the case where the constant term C in the following formula representing the relationship between the refractive index n _D and the Abbe number ν _D measured at ° C. deviates from the range of 1.70 to 1.82.

  In a molded body of a resin material, birefringence generally increases as the thickness increases. In the present invention, by using the above silica particles, the resin cured product of the present invention may acquire the characteristic that the increase rate of birefringence is small compared to the conventional case for the increase in thickness. Therefore, when the cured resin of the present invention is used as a relatively thick molded product having a thickness of 0.1 mm or more as in the optical member of the present invention described later, it is advantageous in terms of lowering the birefringence.

The cured product of the present invention is excellent as an optical material because it has small optical distortion represented by birefringence, good transparency, and excellent functional properties such as dimensional stability and surface hardness.
The optical material here refers to the optical characteristics of the material constituting it, for example, transparency, light absorption and emission characteristics, refractive index difference from the outside, small birefringence, and balance between the above specific refractive index and Abbe number. It refers to general molded articles used for applications that use the above. Specific examples include display panels, touch panels, lenses, prisms, waveguides, optical amplifiers and other optics, and optoelectronic members.

  The optical material of the present invention is roughly classified into two types. The first optical material is an optical material that is a molded body of the cured resin, and the second optical material is an optical material that is a molded body having a thin film of the cured resin as a part of the layer. In other words, the former is an optical material whose main component is the resin cured product and may have an arbitrary thin film (coat layer) made of a material other than the resin cured product, while the latter is the main component of the optical material. Is made of a material that does not have to be the cured resin, and has a thin film of the cured resin as a part of the layers. Any optical material may be formed in close contact with an arbitrary solid material substrate such as resin, glass, ceramics, inorganic crystal, metal, semiconductor, diamond, organic crystal, paper pulp, and wood.

Although there is no restriction | limiting in the dimension of the said 1st optical material, The optical path length of the part of the said resin hardened | cured material is 0.01 mm normally in terms of the mechanical strength of an optical material, Preferably it is 0.1 mm, More preferably, it is 0.2 mm. On the other hand, the upper limit is usually 10,000 mm, preferably 5000 mm, and more preferably 1000 mm in terms of attenuation of light intensity.
The shape of the first optical material is not limited, but examples thereof include a plate shape, a curved plate shape, a lens shape (concave lens, convex lens, concavo-convex lens, half-concave lens, half-convex lens, etc.), prism shape, fiber shape, and the like. Is done.

  Although there is no restriction | limiting in the dimension of the said 2nd optical material, The film thickness of the said resin cured material thin film is 0.05 micrometer normally in terms of mechanical strength or an optical characteristic, Preferably it is 0.1 micrometer, Furthermore, Preferably it is 0.5 micrometer. On the other hand, the upper limit of the film thickness is usually 3000 μm, preferably 2000 μm, more preferably 1000 μm, from the viewpoint of thin film forming processability and cost-effective balance.

The shape of the thin film is not limited, but it is not necessarily flat, and may be formed on a substrate having an arbitrary shape such as a spherical shape, an aspherical curved surface shape, a cylindrical shape, a conical shape, or a bottle shape. Good.
The optical material of the present invention has an optional coating layer, for example, a protective layer that prevents mechanical damage to the coated surface due to friction or wear, and an undesirable wavelength that causes deterioration of semiconductor crystal particles or a substrate. A light-absorbing layer that absorbs light, a transmission shielding layer that suppresses or prevents the transmission of reactive low molecules such as moisture and oxygen gas, an antiglare layer, an antireflection layer, a low refractive index layer, Arbitrary additional function layers such as an undercoat layer and an electrode layer for improving the adhesion may be provided to form a multilayer structure. Specific examples of such an optional coating layer include a transparent conductive film and gas barrier film made of an inorganic oxide coating layer, a gas barrier film made of an organic coating layer, a hard coat, and the like. A known coating method such as a sputtering method, a dip coating method, or a spin coating method can be used.

  Specific examples of the optical material of the present invention are illustrated in more detail. Various lenses such as spectacle lenses, optical connector microlenses, and light-emitting diode condensing lenses, optical switches, optical fibers, optical branches in optical circuits, junction circuits, Optical communication parts such as optical multi-branch circuits, luminous intensity controllers, various display members such as liquid crystal substrates, touch panels, light guide plates, retardation plates, storage / recording applications including optical disk substrates and optical film coatings, and more Are optical adhesives and other optical communication materials, functional films, antireflection films, optical multilayer films (selective reflection films, selective transmission films, etc.), super-resolution films, ultraviolet absorption films, reflection control films, optical waveguides, and Examples include various optical films and coating applications such as an identification function printing surface.

[Optical recording medium]
The optical recording medium referred to in the present invention is not particularly limited, but a next-generation high-density optical recording medium using a blue laser is preferable. Examples of the optical recording medium include optical recording in which a protective film is formed on a surface on which a dielectric film, a recording film, a reflective film, etc. (hereinafter, these layers are collectively referred to as a recording / reproducing functional layer) is formed on a substrate. It means an optical recording medium using a laser beam having a wavelength of 380 to 800 nm, preferably a laser beam having a wavelength of 450 to 350 nm.

  Next, the substrate will be described. An uneven groove for use in recording / reproducing optical information is provided on one main surface of the substrate, and is formed, for example, by injection molding of a light-transmitting resin using a stamper. The material of the substrate is not particularly limited as long as it is a light-transmitting material. For example, thermoplastic resins such as polycarbonate resin, polymethacrylate resin, and polyolefin resin, and glass can be used. Of these, polycarbonate resin is most preferred because it is most widely used in CD-ROMs and is inexpensive. The thickness of the substrate is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, on the other hand, 20 mm or less, preferably 15 mm or less, more preferably 3 mm or less. .2 ± 0.2 mm or so. The outer diameter of the substrate is generally about 130 mm.

  The recording / reproducing functional layer is a layer configured to exhibit a function capable of recording / reproducing an information signal or reproducing the information signal, and may be a single layer or a plurality of layers. The recording / reproducing functional layer is a rewrite that can repeatedly perform recording and erasure when the optical recording medium is a reproduction-only medium (ROM medium), or a write-once medium that can be recorded only once (Write Once medium). Depending on the case of a possible type medium (Rewritable medium), it is possible to adopt a layer structure corresponding to each purpose.

For example, in a read-only medium, the recording / reproducing functional layer is usually composed of a single layer containing a metal such as Al, Ag, Au, etc. For example, the recording / reproducing functional layer is formed of Al, Ag, Au by sputtering. It is formed by forming a reflective layer on a substrate.
In the write-once type medium, the recording / reproducing functional layer is generally configured by providing a reflective layer containing a metal such as Al, Ag, Au, etc. and a recording layer containing an organic dye on the substrate in this order. As such a write-once medium, a medium in which a reflective layer is provided by a sputtering method and then an organic dye layer is formed on a substrate by a spin coating method can be exemplified. As another specific example of the write-once medium, the recording / reproducing functional layer includes a reflective layer containing a metal such as Al, Ag, Au, a dielectric layer, a recording layer, and a dielectric layer. A structure in which the dielectric layer and the recording layer contain an inorganic material is also provided. In such a write-once medium, a reflective layer, a dielectric layer, a recording layer, and a dielectric layer are usually formed by sputtering.

  In a rewritable type medium, the recording / reproducing functional layer is usually formed of a reflective layer containing a metal such as Al, Ag, or Au, a dielectric layer, a recording layer, and a dielectric layer in this order on the substrate. In general, the dielectric layer and the recording layer contain an inorganic material. In such a rewritable medium, a reflective layer, a dielectric layer, a recording layer, and a dielectric layer are usually formed by sputtering. Another specific example of the rewritable medium is a magneto-optical recording medium. A recording / reproducing area is set in the recording / reproducing functional layer. The recording / reproducing area is usually provided in an area having an inner diameter larger than the inner diameter of the recording / reproducing functional layer and an outer diameter smaller than the outer diameter of the recording / reproducing functional layer.

FIG. 1 is a diagram for explaining an example of the recording / reproducing functional layer 5 in the rewritable optical recording medium 10. The recording / reproducing functional layer 5 is provided so as to sandwich the reflective layer 51 formed of a metal material directly provided on the substrate 1, the recording layer 53 formed of a phase change material, and the recording layer 53 from above and below. And two dielectric layers 52 and 54.
The material used for the reflective layer 51 is preferably a substance having a high reflectance, and in particular, a metal such as Au, Ag, or Al, which can be expected to have a heat dissipation effect. A small amount of metal such as Ta, Ti, Cr, Mo, Mg, V, Nb, Zr, or Si may be added to control the thermal conductivity of the reflective layer itself or to improve the corrosion resistance. The amount of metal added in a small amount is usually 0.01 atomic% or more and 20 atomic% or less. Among them, an aluminum alloy containing 15 atomic% or less of Ta and / or Ti, in particular, an alloy of AlαTa _1- α (0 ≦ α ≦ 0.15) has excellent corrosion resistance and is a reliable optical recording medium. It is a particularly preferable reflective layer material for improving the properties. In addition, Ag alloy containing any one of Mg, Ti, Au, Cu, Pd, Pt, Zn, Cr, Si, Ge, and rare earth elements in the range of 0.01 atomic% to 10 atomic% is a reflectance. High thermal conductivity and excellent heat resistance are preferable.

  The thickness of the reflective layer 51 is usually 40 nm or more, preferably 50 nm or more, and is usually 300 nm or less, preferably 200 nm or less. If the thickness of the reflective layer 51 is excessively large, the shape of the tracking groove formed in the substrate 1 changes, and further, it takes time to form a film and the material cost tends to increase. Further, if the thickness of the reflective layer 51 is excessively small, not only does light transmission occur and it does not function as a reflective layer, but also an influence of an island-like structure formed in the initial stage of film growth tends to occur on a part of the reflective layer 51, Reflectance and thermal conductivity may decrease.

  The materials used for the two dielectric layers 52 and 54 are used to prevent evaporation / deformation accompanying the phase change of the recording layer 53 and to control thermal diffusion at that time. The material of the dielectric layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. In general, dielectric materials such as oxides, sulfides, nitrides, carbides, and fluorides such as Ca, Mg, and Li, which are highly transparent and have a high melting point, can be used. These oxides, sulfides, nitrides, carbides, and fluorides do not necessarily have to have a stoichiometric composition, and it is also effective to control the composition for controlling the refractive index, or to mix them. is there.

Specific examples of such a dielectric material include, for example, Sc, Y, Ce, La, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Cr, In, Si, Ge, Sn, Sb, And oxides of metals such as Te; metals such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Zn, B, Al, Ga, In, Si, Ge, Sn, Sb, and Pb Nitrides of Ti; Zr, H
Mention may be made of metal carbides such as f, V, Nb, Ta, Cr, Mo, W, Zn, B, Al, Ga, In, and Si, or mixtures thereof. Further, a sulfide of a metal such as Zn, Y, Cd, Ga, In, Si, Ge, Sn, Pb, Sb, and Bi; a selenide or a telluride; a fluoride such as Mg or Ca, or a mixture thereof. Can be mentioned.

In consideration of repetitive recording characteristics, a mixture of dielectrics is preferable. For example, a mixture of a chalcogen compound such as ZnS or rare earth sulfide and a heat-resistant compound such as oxide, nitride, carbide, or fluoride can be used. For example, a mixture of a heat-resistant compound containing ZnS as a main component and a mixture of a rare-earth sulfate, particularly a heat-resistant compound containing Y ₂ O ₂ S as a main component are examples of a preferable dielectric layer composition. More specifically, ZnS—SiO ₂ , SiN, SiO ₂ , TiO ₂ , CrN, TaS ₂ , Y ₂ O ₂ S and the like can be mentioned. Among these materials, ZnS—SiO ₂ is widely used because of its high deposition rate, low film stress, small volume change rate due to temperature change, and excellent weather resistance. The thickness of the dielectric layer 52 or the dielectric layer 54 is usually 1 nm or more and 500 nm or less. By setting the thickness to 1 nm or more, the effect of preventing deformation of the substrate and the recording layer can be sufficiently secured, and the role as a dielectric layer can be sufficiently achieved. Further, when the thickness is 500 nm or less, the role of the dielectric layer is sufficiently fulfilled, and the internal stress of the dielectric layer itself, the difference in elastic characteristics with respect to the substrate, etc. become remarkable, thereby preventing the occurrence of cracks. be able to.

Examples of the material for forming the recording layer 53 include compounds having a composition such as GeSbTe, InSbTe, AgSbTe, AgInSbTe. Among _{them, {(Sb 2 T e 3} ) 1-x (GeTe) x} 1-y Sb y (0.2 ≦ x ≦ 0.9,0 ≦ y ≦ 0.1) alloy or (Sb _x Te _{1 -x} ) _y M1 _-y (where 0.6≤x≤0.9, 0.7≤y≤1, M is Ge, Ag, In, Ga, Zn, Sn, Si, Cu, Au, Pd) , Pt, Pb, Cr, Co, O, S, Se, V, Nb, Ta) The thin film mainly composed of an alloy is stable in both crystalline and amorphous states. Fast phase transitions between states are possible. Furthermore, there is an advantage that segregation hardly occurs when repeated overwriting, and it is the most practical material.

  The film thickness of the recording layer 53 is usually 5 nm or more, preferably 10 nm or more. With such a range, a sufficient optical contrast between the amorphous state and the crystalline state can be obtained. Further, the film thickness of the recording layer 53 is usually 30 nm or less, preferably 20 nm or less. With such a range, it is possible to obtain an increase in optical contrast due to the light transmitted through the recording layer 53 being reflected by the reflection layer, and the heat capacity can be controlled to an appropriate value, so that high-speed recording is possible. Can also be performed. In particular, if the thickness of the recording layer 53 is 10 nm or more and 20 nm or less, it is possible to achieve both higher speed recording and higher optical contrast. By setting the thickness of the recording layer 53 in such a range, the volume change due to the phase change is reduced, and the recording layer 53 itself and other layers in contact with the upper and lower sides of the recording layer 53 are repeatedly overwritten repeatedly. The effect of volume change can be reduced. Furthermore, accumulation of irreversible microscopic deformation of the recording layer 53 is suppressed, noise is reduced, and repeated overwrite durability is improved.

The reflective layer 51, the recording layer 53, the dielectric layer 52, and the dielectric layer 54 are usually formed by sputtering or the like. In order to prevent oxidation and contamination between layers, it is desirable to form a film with an in-line apparatus in which a target for a recording layer, a target for a dielectric layer, and, if necessary, a target for a reflective layer material are installed in the same vacuum chamber. It is also excellent in terms of productivity.
The protective layer 3 is made of a cured product obtained by spin-coating the silica sol described above and curing it, and is provided in contact with the recording / reproducing functional layer 5 and has a planar annular shape. The protective layer 3 is made of a material that can transmit laser light used for recording and reproduction. The transmittance of the protective layer 3 is usually 80% or more, preferably 85% or more, and more preferably 89% or more at the wavelength of light used for recording / reproduction. Within such a range, loss due to absorption of recording / reproducing light can be minimized. On the other hand, the transmittance is most preferably 100%, but is usually 99% or less because of the performance of the material used.

Such a photocurable resin is sufficiently transparent to blue laser light having a wavelength of about 405 nm used for recording / reproducing of an optical disk, and protects the recording layer 53 formed on the substrate 1 from water and dust. It is desirable to have such properties.
In addition, the surface hardness of the protective film 3 is preferably HB or more, more preferably F or more, and further preferably H or more, according to a pencil hardness test in accordance with JIS K5400. Moreover, it is preferable that it is 7H or less. If the hardness is too small, it is not preferable because the surface is easily scratched. Although there is no problem with the hardness being too large, the cured product tends to become brittle, and cracks and peeling are likely to occur, which is not preferable.

  Furthermore, it is preferable that the adhesion between the protective film 3 and the recording / reproducing functional layer 5 is high. Furthermore, it is preferable that the adhesion with time is higher, and the ratio of the adhesion area between the protective layer 3 and the recording / reproducing functional layer 5 after being placed in an environment of 80 ° C. and 85% RH for 100 hours, more preferably 200 hours is initially It is preferable to hold 50% or more of the contact area. More preferably, it is 80% or more, and particularly preferably 100%.

  The thickness of the protective film 3 is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, still more preferably 70 μm or more, and particularly preferably 85 μm or more. If the film thickness is in such a range, the influence of dust and scratches attached to the surface of the protective film 3 can be reduced, and the thickness is sufficient to protect the recording / reproducing functional layer 5 from the moisture of the outside air. can do. On the other hand, it is usually 300 μm or less, preferably 130 μm or less, more preferably 115 μm or less. When the film thickness is within this range, a uniform film thickness can be easily formed by a general coating method used in spin coating or the like. The protective film 3 is preferably formed with a uniform film thickness in a range covering the recording / reproducing functional layer 5.

The film thickness of the protective film 3 has an important influence on the performance of the objective lens used for recording and reproduction. The objective lens is designed in consideration of the thickness of the protective film 3. Therefore, the thickness of the protective film 3 needs to be strictly set to the thickness determined by the design value of the objective lens according to the optical refractive index. From the viewpoint of obtaining good convergent light by reducing the spherical aberration of the objective lens, the film thickness of the protective film 3 is usually within ± 5% of the average film thickness, and preferably within ± 3%. For example, when an objective lens designed with a blue laser beam of 405 nm, a lens aperture ratio (NA) of 0.85, and a refractive index n = 1.5 of the protective film 3 is used as a recording / reproducing system, the wavefront aberration can be ignored. In order to make it as small as possible, it is necessary to manage the film thickness of the light transmission layer 3 within ± 5% of the average film thickness, preferably within ± 4%, and more preferably within ± 3%.
The optical recording medium obtained as described above may be used as a single plate, or two or more may be bonded together. Then, if necessary, a hub may be attached and incorporated into the cartridge.

Examples of the present invention will be described below. However, the present invention is not limited to these examples as long as the gist of the invention is not exceeded.
(Example 1)
30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of methanol, 6.15 g of 5 wt% aluminum trisacetylacetonate / methanol solution were added to a heat-resistant glass bottle, and 6.51 g of dechlorinated water was added with stirring. . Sealed and allowed to react at 60 ° C. for 2 hours with stirring. 20.0 g of methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., KBM-5103) was added thereto, sealed, and reacted at 60 ° C. for 2 hours while stirring again. The flask was transferred to a flask, and 37.3 g of 2-hydroxyethyl acrylate (Wako Pure Chemical; water solubility: ∞) was added and mixed. This was reduced stepwise by an evaporator to distill off methanol to obtain 74.5 g of silica sol whose organic liquid medium was 2-hydroxyethyl acrylate. (Inorganic component concentration: 43.5 wt%, light transmittance: 91%) To this silica sol, 250 g of acetone was added to adjust the inorganic component concentration to 10 wt%. The light transmittance was measured and found to be 91%.

As a photocurable resin, a mixture in which the following raw materials were uniformly mixed was prepared, and this was designated as photocurable resin A.
SA-1002 (Mitsubishi Chemical; tricyclodecane dimethanol diacrylate): 500 g
A600 (Shin Nakamura Chemical; polyethylene glycol diacrylate): 100 g
APG700 (Shin Nakamura Chemical; polypropylene glycol diacrylate): 100 g
IBXA (Osaka organic chemistry; isobornyl acrylate): 300 g
Add 71.6 g of silica sol whose organic liquid medium is 2-hydroxyethyl acrylate, 141.6 g of photocurable resin A, and 6.43 g of photoinitiator Irgacure 184 (Ciba Specialty Chemicals), and mix evenly. A curable composition (inorganic component concentration: 14.7% by weight; residual methanol 2.2% by weight, light transmittance: 90%) was obtained. The resulting composition was clear and colorless and stable for over 2 weeks.

50 g of the obtained composition was taken, 25 g of acetone was added, and the inorganic component concentration was adjusted to 10% by weight. The light transmittance was measured and found to be 91%.
The photocurable composition was applied to a 10 cm square polycarbonate plate by spin coating to a thickness of about 30 microns, and then photocured by irradiating ultraviolet rays of about 1 J / cm ^{2 with} a high pressure mercury lamp. The obtained cured coating film was colorless and transparent and showed a good appearance.
(Example 2)
30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of methanol, 6.15 g of 5 wt% aluminum trisacetylacetonate / methanol solution were added to a heat-resistant glass bottle, and 6.51 g of dechlorinated water was added with stirring. . Sealed and allowed to react at 60 ° C. for 2 hours with stirring. 20.0 g of methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., KBM-5103) was added thereto, sealed, and reacted at 60 ° C. for 2 hours while stirring again. The flask was transferred to a flask, and 24.0 g of 2-hydroxyethyl acrylate (Wako Pure Chemical; water solubility: ∞) was added and mixed. This was reduced stepwise by an evaporator to distill off methanol, thereby obtaining 58.4 g of silica sol whose organic liquid medium was 2-hydroxyethyl acrylate. (Inorganic component concentration: 55.5 wt%, light transmittance: 91%) To this silica sol, 266 g of acetone was added to adjust the inorganic component concentration to 10 wt%. The light transmittance was measured and found to be 91%.

To this, 157.7 g of photocurable resin A and 6.43 g of photoinitiator Irgacure 184 (Ciba Specialty Chemicals) were added and mixed uniformly to form a photocurable composition (inorganic component concentration: 14.9% by weight; Residual methanol 0.9 wt%, light transmittance 90%). The resulting composition was clear and colorless and stable for over 2 weeks.
When applied and cured in the same manner as in Example 1, the obtained cured coating film was colorless and transparent and showed a good appearance. 50 g of the obtained composition was taken, 25 g of acetone was added, and the inorganic component concentration was adjusted to 10% by weight. The light transmittance was measured and found to be 91%.
(Example 3)
30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of methanol, 6.15 g of 5 wt% aluminum trisacetylacetonate / methanol solution were added to a heat-resistant glass bottle, and 6.51 g of dechlorinated water was added with stirring. . Sealed and allowed to react at 60 ° C. for 2 hours with stirring. To this was added 20.0 g of methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical, KBM-5103), sealed up, and reacted at 60 ° C. for 2 hours while stirring again.
The flask was transferred to a flask, and 23.4 g of acryloylmorpholine (Kojin; water solubility: ∞) was added and mixed. This was reduced stepwise by an evaporator to distill off methanol to obtain 65.1 g of silica sol in which the organic liquid medium was acryloylmorpholine. (Inorganic component concentration: 49.8% by weight, light transmittance: 90%) To this silica sol, 259 g of acetone was added to adjust the inorganic component concentration to 10% by weight. The light transmittance was measured and found to be 91%.

  To this, 151.0 g of photocurable resin A and 6.43 g of photoinitiator Irgacure 184 (Ciba Specialty Chemicals) were added and mixed uniformly to form a photocurable composition (inorganic component concentration: 14.4% by weight; Residual methanol (4.3 wt%, light transmittance: 90%) was obtained. The resulting composition was clear and colorless and stable for over 2 weeks. 50 g of the obtained composition was taken, 25 g of acetone was added, and the inorganic component concentration was adjusted to 10% by weight. The light transmittance was measured and found to be 91%.

When applied and cured in the same manner as in Example 1, the obtained cured coating film was colorless and transparent and showed a good appearance.
(Comparative Example 1)
30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of methanol, 6.15 g of 5 wt% aluminum trisacetylacetonate / methanol solution were added to a heat-resistant glass bottle, and 6.51 g of dechlorinated water was added with stirring. . Sealed and allowed to react at 60 ° C. for 2 hours with stirring. To this was added 20.0 g of methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical, KBM-5103), sealed and reacted again at 60 ° C. for 2 hours with stirring to obtain 74.5 g of silica sol whose organic liquid medium was methanol. . (Inorganic component concentration: 27.0 wt%, light transmittance: 91%) To this silica sol, 204 g of acetone was added to adjust the inorganic component concentration to 10 wt%. The light transmittance was measured and found to be 91%.

  To this, 96.1 g of photocurable resin A and 6.43 g of photoinitiator Irgacure 184 (Ciba Specialty Chemicals) were added and mixed uniformly to form a photocurable composition (inorganic component concentration: 8.9 wt%); Residual methanol 40.5 wt%, light transmittance 90%) was obtained. The resulting composition was clear and colorless and stable for over 2 weeks. 50 g of the obtained composition was taken, 25 g of acetone was added, and the inorganic component concentration was adjusted to 10% by weight. The light transmittance was measured and found to be 91%.

When application and curing were performed in the same manner as in Example 1, innumerable bubbles were generated during ultraviolet irradiation, and the film was cured while containing the bubbles. Therefore, the obtained cured coating film showed the appearance of becoming cloudy.
(Comparative Example 2)
30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of methanol, 6.15 g of 5 wt% aluminum trisacetylacetonate / methanol solution were added to a heat-resistant glass bottle, and 6.51 g of dechlorinated water was added with stirring. . Sealed and allowed to react at 60 ° C. for 2 hours with stirring. To this was added 20.0 g of methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical, KBM-5103), sealed and reacted again at 60 ° C. for 2 hours with stirring to obtain 74.5 g of silica sol whose organic liquid medium was methanol. . (Inorganic component concentration: 27.0 wt%, light transmittance: 91%) To this silica sol, 204 g of acetone was added to adjust the inorganic component concentration to 10 wt%. The light transmittance was measured and found to be 91%.

To this, 96.1 g of photocurable resin A and 6.43 g of photoinitiator Irgacure 184 (Ciba Specialty Chemicals) were added and mixed uniformly, and this was reduced stepwise with an evaporator to distill off methanol. As a result of the operation, white turbidity was generated in the process (inorganic component concentration: 12% by weight). The distillation operation was continued for a while, but the experiment was stopped because the cloudiness did not disappear. It seemed that white turbidity was caused due to low solubility of the photocurable resin A in methanol. To this silica sol, 180 g of acetone was added, and the inorganic component concentration was adjusted to 10% by weight. The light transmittance was measured and found to be 40%.

(Comparative Example 3)
Add 30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of acryloylmorpholine, 6.15 g of 5% by weight aluminum trisacetylacetonate / methanol solution to a heat-resistant glass bottle, and 6.51 g of dechlorinated water with stirring. Added. The mixture was sealed and reacted at 60 ° C. for 2 hours with stirring to obtain a silica sol, but white turbidity was generated in the reaction process (inorganic component concentration: 21% by weight). The reaction was continued for a while, but the experiment was stopped because the cloudiness did not disappear. To this silica sol, 110 g of acetone was added to adjust the inorganic component concentration to 10% by weight. The light transmittance was measured and found to be 30%.

(Comparative Example 4)
Add 30.8 g of methyl silicate oligomer (Mitsubishi Chemical, MS51), 56.6 g of isopropyl alcohol, 6.15 g of 5% by weight aluminum trisacetylacetonate / methanol solution, and 6.51 g of dechlorinated water with stirring. did. It was sealed and stirred for 2 hours at 60 ° C. to obtain silica sol. However, light white turbidity was produced in the reaction process, and the transparency was remarkably reduced (inorganic component concentration: 18% by weight). . After completion of the reaction, a translucent silica dispersion was obtained, but the light transmittance was 45%. To this silica sol, 80 g of acetone was added to adjust the inorganic component concentration to 10% by weight. The light transmittance was measured and found to be 50%.

It is a schematic diagram showing the cross section of the optical recording medium which is one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 3 Protective layer 5 Recording / reproducing functional layer 51 Reflective layer 52, 54 Dielectric layer 53 Recording layer 10 Optical recording medium

Claims (5)

Contains silica particles obtained by hydrolysis and / or condensation of a silicon compound, mainly composed of an organic liquid medium (excluding methanol, ethanol and acetone) having a solubility in water at 25 ° C. of 5% by weight or more. A silica sol having a light transmittance of 88% or more at a wavelength of 550 nm at an optical path length of 1 mm when an inorganic component concentration of the silica sol is adjusted to 10% by weight. 2. The silica sol according to claim 1, wherein the silicon compound is an oligomer of alkoxysilane. The silica sol according to claim 1 or 2, wherein the organic liquid medium contains a (meth) acrylate group. Furthermore, the silica sol as described in any one of Claims 1-3 containing a radiation curable resin. After synthesizing silica particles in a liquid medium by hydrolysis and / or condensation of a silicon compound, the liquid medium is an organic liquid medium having a solubility in water at 25 ° C. of 5% or more (however, excluding methanol, ethanol and acetone) The manufacturing method of the silica sol which has the process substituted to).

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