JP2010143806A - Surface-treated silica-based particle and process of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide surface-treated silica-based particles which have high hydrophobicity in spite of their nano order fine particle size and a very high dispersibility in a transparent resin. <P>SOLUTION: The particles are silica-based particles having an average particle size in the range of 1-50 nm as microscopically determined. Each of the particles are surface-treated with a hydrophobic silane coupling agent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to surface-treated silica-based particles and a method for producing the same, and more particularly to silica-based particles that have been surface-treated so as to exhibit high hydrophobicity and a method for producing the same.

  In general, resin materials have the advantage of being lighter and more flexible in molding than inorganic materials, but on the other hand, they have disadvantages such as a large thermal expansion coefficient and a low hardness that makes the surface easily damaged. . In order to overcome the drawbacks of such resin materials, generally, particles of inorganic oxides such as silica are blended as fillers, especially when blended with transparent resin materials. In order to improve various mechanical properties without impairing the properties, inorganic oxide particles having a fine particle size are used.

  By the way, fine particles (nanoparticles) of an inorganic oxide having a nano-order particle diameter in the range of 1 to 50 nm in average particle diameter are generally very hydrophilic for hydrophilic resins because the particle surface is hydrophilic. Dispersibility is also good, but since many of the industrially used resins are hydrophobic, hydrophilic nanoparticles have poor compatibility with transparent resins and are often not sufficiently dispersed. Effects (improved transparency and surface hardness) are often not exhibited. Therefore, use of inorganic oxide nanoparticles to which hydrophobicity is imparted by surface treatment using a silane coupling agent by adding a dispersant to improve the compatibility of the inorganic oxide nanoparticles with the resin. Etc. have been proposed (see Patent Documents 1 to 6).

JP 2004-175915 A JP 2003-73558 A JP 2007-314484 A JP 2008-7381 A JP 10-36415 A JP 2002-169007 A

  In the method using a dispersant or a silane coupling agent as in the above-mentioned patent document, compared with the case where these are not used, compatibility with a transparent resin is improved to some extent, and a decrease in transparency can be avoided. The degree is not enough.

  Accordingly, an object of the present invention is to provide a surface-treated silica-based particle having a nano-order fine particle size, exhibiting high hydrophobicity, and having significantly improved dispersibility in a transparent resin, and a method for producing the same. It is to provide.

  As a result of repeated investigations on nano-order silica-based particles surface-treated with a hydrophobic silane coupling agent, the inventors of the present invention have conventionally reported that silica-based particles surface-treated by a known method have a particle size of However, the surface treatment is not sufficiently performed because of the nano-order, and as a result, the dispersibility to the transparent resin is not effectively improved. It has been found that a sufficient surface treatment can be performed with a functional silane coupling agent to significantly improve the dispersibility of the transparent resin, and the present invention has been completed.

That is, according to the present invention, silica-based particles having an average particle diameter in the range of 1 to 50 nm as measured with an electron microscope, each particle being surface-treated with a hydrophobic silane coupling agent, and isopropyl A surface-treated silica characterized in that when dispersed in a 1: 1 (weight ratio) mixed solvent of alcohol and n-heptane at a concentration of 3% by mass, the dispersion exhibits a visible light transmittance of 80% or more. System particles are provided.
In the surface-treated silica-based particles of the present invention,
(1) The hydrophobic silane coupling agent has the following formula (1):
R ¹ —Si (OR ² ) ₃ (1)
In the formula, R ¹ is an alkyl group, an alkenyl group or an aryl group,
R ² is an alkyl group,
A trialkoxysilane represented by:
Is preferred.

According to the invention,
A step of preparing a liquid in which silica-based particles having a particle diameter of 1 to 50 nm are dispersed by a wet method as measured with an electron microscope;
Partially hydrolyzing the hydrophobic silane coupling agent in the presence of water;
Mixing the liquid containing the partial hydrolyzate and the liquid in which the silica-based fine particles are dispersed, and reacting the partial hydrolyzate with the silica-based fine particles at a pH of 9 to 12;
A step of subjecting the dispersion obtained by the reaction of the partially hydrolyzed product and the silica-based fine particles to solvent replacement by ultrafiltration, removing unreacted coupling agent and the like and replacing with a single solvent;
A method for producing a surface-treated silica is provided.
According to the present invention, there is further provided a resin composite comprising 1 to 50% by mass of the surface-treated silica-based particles.

In the production method of the present invention,
(1) using a trialkoxysilane represented by the formula (1) as the hydrophobic silane coupling agent;
(2) performing partial hydrolysis of the hydrophobic silane coupling agent with 1 to 3 equivalents of water relative to the coupling agent;
Is preferred.

  The surface-treated silica-based particles of the present invention are not only extremely fine with an average particle diameter of 1 to 50 nm, but also 1: 1 (weight) of a hydrophilic organic solvent (isopropyl alcohol) and a lipophilic organic solvent (n-heptane). Ratio) It has a remarkable feature in that it shows a high visible light transmittance of 80% or more when dispersed in a mixed solvent. That is, high transparency is ensured even when dispersed in such a highly hydrophobic mixed solvent, although the surface-treated silica-based particles have a remarkably fine particle size. The particles are bonded to each other and hardly agglomerate, substantially exist in the form of so-called primary particles, and each particle is effectively surface-treated with a hydrophobic silane coupling agent. (That is, the surface coverage by the silane coupling agent is extremely high). That is, when some of the particles are aggregated or some of the particles are not surface-treated, the hydrophilic solvent (isopropyl alcohol) and the hydrophobic solvent (n-heptane) as described above are used. This is because the dispersion liquid when dispersed in the mixed solvent becomes cloudy, and the visible light transmittance becomes lower than 80%.

  Therefore, the surface-treated silica-based particles of the present invention are particularly excellent in dispersibility with respect to the transparent resin. Reduction can be effectively avoided and a resin composite with high transparency (visible light transmittance) can be obtained.

  The surface-treated silica-based particles of the present invention having the above characteristics use silica-based particles obtained by a wet method as a raw material, and fine silica-based particles having a predetermined nano-order particle size are dispersed in a solvent. This dispersion is used, and the dispersion is prepared by adding a liquid of a hydrophobic silane coupling agent partially hydrolyzed with water in advance to cause a reaction.

That is, surface treatment of inorganic oxide nanoparticles with a silane coupling agent is very commonly performed, but it is difficult to perform surface treatment with a conventional method to a high degree. It was not possible to carry out a uniform and high coverage treatment on the inorganic particles.
For example, once the particles having a primary particle size of nano-order are dried once, the particles are extremely strongly aggregated, so that redispersion is almost impossible. Although such agglomerated dry particles can be surface treated with a coupling agent, it is difficult to break up the originally agglomerated powder to primary particles, and the coupling agent itself may polymerize. Alternatively, the particles may be chemically bonded by a coupling agent. Therefore, it can be said that it is virtually impossible to effectively perform surface treatment with a silane coupling agent on fine inorganic particles of nano-order obtained by a dry method.
On the other hand, in the inorganic particles obtained by the wet method, even if the primary particle diameter is nano-order of 50 nm or less, if the particles are not dried and are present in the liquid, the form of the primary particles is maintained without aggregation. Therefore, if the treatment with the silane coupling agent can be performed satisfactorily in that state, there is a possibility that a surface treatment with a high coverage can be realized. However, as a matter of course, the hydrophobic silane coupling agent has a relatively hydrophobic organic functional group (for example, an alkyl group), whereas inorganic particles obtained by a wet method are generally hydrophilic. In a form dispersed in a high solvent. Therefore, the inorganic particles having a nano-order particle size dispersed in the hydrophilic solvent are surface-treated with the hydrophobic silane coupling agent, and it is difficult to effectively perform the surface treatment. It has become.

  However, in the production method of the present invention, since the hydrophobic silane coupling agent is partially hydrolyzed with water and then added to the dispersion of silica-based particles to perform surface treatment, the hydrophobic coupling agent has an appropriate hydrophilicity. As a result, the surface treatment is performed with a hydrophobic silane coupling agent and has a nano-order fine particle size as described above. However, surface-treated silica-based particles that can maintain high transparency even when the individual particles are surface-treated and blended with a transparent resin are obtained.

Production of surface-treated silica-based particles;
The surface-treated silica-based particles of the present invention use a dispersion in which silica-based particles obtained by a wet method (hereinafter sometimes referred to as raw material silica-based particles) are dispersed, and hydrophobic silane is used in the dispersion. It is manufactured by adding the liquid to the partially hydrolyzed product of the coupling agent and performing surface treatment.

<Raw silica particles>
In the present invention, the raw silica particles used for the surface treatment have a predetermined nano-sized average particle size, specifically 1 to 50 nm, preferably 1 to 35 nm, most preferably 5 to 25 nm. As long as it is obtained by a wet process, it is not limited to silica particles, and may be fine particles of silica-based composite oxide such as silica-titania or silica-zirconia.
In addition, those having a particle size smaller than the above range are difficult to produce and surface treatment with a silane coupling agent is difficult, and particles larger than the above range have a large scattering of visible light. When blended with a transparent resin, the transparency is lowered.

  Many methods such as hydrolysis method, neutralization method, ion exchange method and precipitation method have been proposed and implemented for the wet method, but the fine nanoparticles dispersed in the solvent are easily and relatively small in particle size. It is most preferable to use a sol-gel method in which a silane compound is hydrolyzed and condensed from the viewpoint that it can be obtained in a uniform form.

In the sol-gel method, the raw material silane compound has the following general formula:
Si (OR) ₄
Or
SiR ′ _n (OR) _4-n
In the formula, R and R ′ are alkyl groups, preferably a lower alkyl group having 4 or less carbon atoms such as a methyl group, an ethyl group, an isopropyl group, and a butyl group,
n is an integer of 1 to 3,
The alkoxysilane represented by these is suitable, and such an alkoxysilane can also be used individually by 1 type, and can also use 2 or more types together. In the present invention, tetramethoxysilane and tetraethoxysilane are most preferable.
The alkoxysilane as described above can be obtained in the form of a partially hydrolyzed low condensate, and such a condensate can also be used.

Silica-based composite oxide particles such as silica-titania and silica-zirconia can be obtained by using titanium or zirconium alkoxides such as titanium isopropoxide, titanium butoxide, zirconium butoxide, etc. together with the above alkoxysilanes. can get.
In such a silica-based composite oxide particle, it is preferable to use the alkoxysilane described above in an amount of at least 50 mol% or more so that the characteristics of the silica are not impaired. Moreover, physical properties, such as a refractive index of particle | grains, can be adjusted by combined use of such a titanium alkoxide and a zirconium alkoxide.

  In the sol-gel method, the silane compound is added to an aqueous solution containing a catalyst, whereby the silane compound is hydrolyzed and condensed to obtain a liquid in which desired fine silica particles are dispersed.

Examples of the catalyst include those that function as hydrolysis catalysts for metal alkoxides such as alkoxysilanes as described above, such as amine compounds such as N (CH ₃ ) ₃ , ammonia, or LiOH, NaOH, KOH, N (CH ₃ ) A base such as ₄ OH is preferably used. Among these, ammonia is very suitable as a catalyst for hydrolysis because it is easily vaporized and can be easily removed after synthesis.

Since the amount of the catalyst varies depending on the type of catalyst used and the like, it cannot generally be said. However, generally, the pH of the reaction system, that is, the pH of the solution when the silane compound described above is added is 8 to 8. The above catalyst is used in an amount such that it is maintained in the range of 12, preferably 9 to 11.5, most preferably 10 to 11. For example, in the most suitable ammonia as the catalyst, the NH ₃ content in the catalyst aqueous solution is preferably 0.01 to 5% by weight, particularly 0.03 to ₃ % by weight. Moreover, the particle diameter of the silica nanoparticle finally obtained can also be controlled by changing such a catalyst amount. In general, the smaller the catalyst amount, the smaller the nanoparticle diameter.

  Since water is essential for hydrolysis of the silane compound, water or a mixed solvent of water and a water-soluble organic solvent is used as the solvent. In this case, the amount of water in the reaction solution is preferably 3% by weight or more, particularly 5% by weight or more, although it depends on the type of silane compound used. In this case, it is necessary to prevent water in the reaction solution from becoming zero during the reaction.

  Examples of water-soluble organic solvents to be mixed with water include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, and propylene glycol, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane and tetrahydrofuran, and acetic acid. Esters such as ethyl can be mentioned, and these can be used alone or in combination. Among these, lower alcohols such as methanol, ethanol, and isopropanol are extremely preferably used because they have high compatibility with alkoxysilane and water and low viscosity.

The use of the water-soluble organic solvent as described above is advantageous in adjusting the generated silica-based particles to a nano-order fine particle diameter, and is used in an amount within a range that can ensure the amount of water described above.
In addition, since alcohol will produce | generate when alkoxides, such as alkoxysilane, hydrolyze, the ratio of the alcohol in a reaction liquid will increase after completion | finish of synthesis | combination. Even if the initial reaction liquid is only a catalyst and water, it contains alcohol produced by hydrolysis of alkoxysilane or the like after the synthesis is completed.

In the hydrolysis condensation of the raw material silane compound, this raw material silane compound is dropped into the reaction solution (catalyst aqueous solution or catalyst aqueous solution / water-soluble organic solvent mixed solvent solution) filled in the reaction vessel under mixing and stirring. Is preferred.
The dropping in the liquid means that the tip of the dropping nozzle (tip of the dropping port) is immersed in the reaction solution when the raw material is dropped into the reaction solution. The position of the tip of the dropping port is not particularly limited as long as it is in the liquid, but a position where stirring is sufficiently performed such as in the vicinity of the stirring blade is desirable. For example, when the liquid is dropped from the upper part of the reaction liquid without dropping in the liquid, it is not preferable because the particles are likely to aggregate.

The temperature of the reaction tank when performing the hydrolysis may be in the range of 0 to 60 ° C., and is appropriately selected depending on the type of the silane compound (alkoxysilane) to be used. In some cases, the particle size of the nanoparticles can be controlled by changing the temperature.
In addition, a well-known thing is employ | adopted as a reaction container used for a hydrolysis, reaction conditions other than the above, without any limitation.

  As described above, silicon compounds such as alkoxysilanes are hydrolyzed / condensed to have the above-mentioned nano-order average particle diameter (1 to 50 nm, preferably 1 to 35 nm, most preferably 5 to 25 nm). Thus, spherical silica nanoparticles are obtained in the form of a dispersion dispersed in the reaction solution. Since such nanoparticles generally do not scatter visible light, they are often obtained as transparent dispersions in appearance.

The average particle diameter of the obtained nanoparticles can be confirmed by analyzing a photographed image of a scanning electron microscope or a transmission electron microscope. Moreover, the specific surface area of the dried particle | grains can be measured, and an average particle diameter can also be computed from a following formula.
d = 6 / (S × D)
In formula, d is an average particle diameter (micrometer).
S is specific surface area (m ² / g)
D is the density of the particles (g / cm ³ )

  In the above description, a method for producing a silica-based particle having a nano-order particle size is described by taking the sol-gel method as an example. Of course it is also possible.

<Dispersion of silica-based particles>
The dispersion liquid in which nano-order silica-based particles obtained as described above are dispersed contains a catalyst such as ammonia, water, and an alcohol or an organic solvent generated by hydrolysis of a metal alkoxide. In order to perform the surface treatment operation with a silane coupling agent with good reproducibility, it is preferable to perform solvent substitution with a single solvent. In particular, it is optimal to perform solvent substitution with alcohols such as methanol that are compatible with both hydrophilic and hydrophobic solvents.

  As a solvent replacement method, a distillation method, an ultrafiltration method, or the like can be employed. The distillation method is a method in which a single solvent to be replaced is continuously added while the solvent of the dispersion is distilled off, and the solvent is replaced. In addition, the ultrafiltration method is a method in which solvent replacement is performed by adding a single solvent to be replaced to the dispersion side while separating and removing the solvent of the dispersion solution through a filtration membrane. is there.

In addition, the concentration of the silica-based particles in the dispersion of silica-based particles obtained by solvent substitution is such that it can be uniformly mixed with the silane coupling agent solution (partial hydrolysis solution) in the surface treatment described later. Although not particularly limited, it is generally in the range of about 1 to 15% by weight, preferably in the range of about 2 to 8% by weight.
Moreover, it is preferable to adjust pH of the said dispersion to the range of 9-12, especially 10-11 by addition of alkali hydroxide, sodium carbonate, etc., such as ammonia, an amine, and sodium hydroxide. By such pH adjustment, aggregation of silica-based nanoparticles can be effectively prevented. The pH regulator is suitable because ammonia is easily vaporized and easily removed.

<Silane coupling agent>
In the present invention, a hydrophobic silane coupling agent is used as a surface treatment agent for imparting hydrophobicity to the silica-based particles in the dispersion. This silane coupling agent is a hydrolyzable functional group that generates an essentially hydrophobic functional group such as an alkyl group or an aryl group and a group capable of reacting with a hydrophilic group such as a silanol group on the surface of a silica-based particle. A silane compound having one hydrophobic functional group and three hydrolyzable functional groups is preferably used from the viewpoint of reactivity with the surface of the silica-based particle and hydrophobicity. Is done.

As a typical example of such a hydrophobic silane coupling agent, the following formula (1):
R ¹ —Si (OR ² ) ₃ (1)
In the formula, R ¹ is an alkyl group, an alkenyl group or an aryl group,
R ² is an alkyl group,
The trialkoxysilane represented by these can be mentioned.

In the trialkoxysilane, the group R ¹ is a hydrophobic group, and examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, and a dodecyl group. Group, hexadecyl group, octadecyl group and the like can be exemplified, and these may have a cyclic structure or may have a branched structure. There is a tendency for the degree of hydrophobicity to be large. Examples of alkenyl groups include vinyl groups, allyl groups, butenyl groups, and examples of aryl groups include phenyl groups, naphthyl groups, and the like.

  In addition, the above alkyl group, alkenyl group, and aryl group may have various substituents as long as the hydrophobicity is not inhibited, for example, a halogen atom such as a fluorine atom, a bromine atom, a chlorine atom, or an iodine atom Alternatively, it may have a hydrophobic group such as a cyano group, an isocyanate group, or a (meth) acryloxy group as a substituent. Furthermore, the alkyl group may have the aryl group exemplified above as a hydrophobic substituent, and the aryl group may have an alkyl group as a hydrophobic substituent.

Further, the alkoxy group (OR ² ) in the trialkoxysilane is a hydrolyzable group, and examples of the alkyl group R ² in the alkoxy group include those exemplified for the group R ^1. However, a lower alkyl group having 4 or less carbon atoms is particularly preferred from the viewpoint of hydrolyzability and ease of synthesis. In particular, a methoxy group and an ethoxy group are most preferably employed as the alkoxy group (OR ² ).

As a suitable example of the trialkoxysilane mentioned above,
Methyltrimethoxysilane,
Ethyltrimethoxysilane,
n-propyltrimethoxysilane,
Isopropyltrimethoxysilane,
n-butyltrimethoxysilane,
Isobutyltrimethoxysilane,
Pentiltrimethoxysilane,
n-hexyltrimethoxysilane,
n-octyltrimethoxysilane,
Isooctyltrimethoxysilane,
n-decyltrimethoxysilane,
Dodecyltrimethoxysilane,
Hexadecyltrimethoxysilane,
n-octadecyltrimethoxysilane,
Styrylethyltrimethoxysilane,
Phenethyltrimethoxysilane,
Cyclohexyltrimethoxysilane,
Cyclopentyltrimethoxysilane,
Phenyltrimethoxysilane,
Benzyltrimethoxysilane,
3- (pentafluorophenyl) propyltrimethoxysilane,
(3,3,3-trifluoropropyl) trimethoxysilane,
Chlorophenyltrimethoxysilane,
(Chloromethyl) phenylethyltrimethoxysilane,
3-chloropropyltrimethoxysilane,
3-bromopropyltrimethoxysilane,
3-iodopropyltrimethoxysilane,
Vinyltrimethoxysilane,
Allyltrimethoxysilane,
Vinyl-tris (β-methoxyethoxy) silane,
3-acryloxypropyltrimethoxysilane,
3-methacryloxypropyltrimethoxysilane,
3-isocyanatopropyltrimethoxysilane,
2-cyanoethyltrimethoxysilane,
3-cyanopropyltrimethoxysilane,
These can be used alone or in combination of two or more. Furthermore, compounds obtained by substituting ethoxy groups for methoxy groups in the compounds exemplified above (for example, methyltriethoxysilane) can also be suitably used as the hydrophobic silane coupling agent in the same manner as described above.

  In the present invention, among the compounds exemplified above, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxy, and the like, can be used to increase the coverage of nanoparticles, and to facilitate surface treatment with high hydrophobicity. Silane and the like are preferable, and those having the fluorine atom as the hydrophobic substituent such as (3,3,3-trifluoropropyl) trimethoxysilane are preferable as the one that most improves the hydrophobicity. . Furthermore, it has a functional group having a copolymerizability with a monomer constituting the resin, such as an alkenyl group or a (meth) acryloxy group, in that the compatibility with a resin, particularly a transparent resin, is directly improved. Among them, 3-methacryloxypropyltrimethoxysilane is preferable.

<Partial hydrolysis of silane coupling agent>
In the present invention, it is important to partially hydrolyze the silane coupling agent prior to the surface treatment using the hydrophobic silane coupling agent as described above. That is, by this partial hydrolysis treatment, a silanol group (SiOH group) is generated in the silane compound used as the silane coupling agent, and this silane coupling agent is dispersed in water or a hydrophilic organic solvent. Surface treatment can be performed by effectively reacting with the surface of the silica-based particles. In this case, when all the alkoxy groups, which are hydrolyzable groups in the silane coupling agent, are hydrolyzed, the dehydration condensation reaction between the silane coupling agents proceeds so that it cannot be ignored, and the oligomer of the coupling agent As a result, it is difficult to effectively perform the surface treatment. That is, the surface of the silica-based particle having a nano-order particle size cannot be effectively coated with the silane coupling agent, and the dispersibility particularly with respect to the transparent resin becomes insufficient.

  The partial hydrolysis treatment of the silane coupling agent as described above is carried out by mixing this coupling agent with 1 to 3 equivalents, preferably 1 to 2 equivalents of water. If an excessive amount of water is used, the hydrolysis proceeds too much and the dehydration condensation reaction between the coupling agents becomes remarkable, and the coupling agent is liable to be oligomerized, and the amount of water is too small. And, the partial hydrolysis rate of the silane coupling agent is low, so that the surface treatment of the silica-based particles in the dispersion cannot be effectively performed, and in this case also, the dispersibility to the transparent resin is improved. It becomes difficult. In the partial hydrolysis treatment, at least one of the alkoxy groups of the raw material silane coupling agent is preferably 80% or more, preferably 90% or more partially hydrolyzed to form a silanol group. The partial hydrolysis rate of the coupling agent can be confirmed using a gas chromatograph or the like.

Moreover, it is preferable that pH is adjusted to acidity or alkalinity by addition of an acid or an alkali to said water, Thereby, it becomes possible to advance partial hydrolysis rapidly. For example, in the case of acidity, the pH is preferably adjusted to a range of 2 to 5, particularly around pH 4, with sulfuric acid, hydrochloric acid, nitric acid, etc., and in the case of alkali, ammonia, sodium hydroxide, hydroxide It is preferable that the pH is adjusted in the range of 9 to 11, particularly around pH 10, with potassium or the like. In this case, from the viewpoint of suppressing the dehydration / condensation reaction subsequent to hydrolysis, it is preferable that the pH is adjusted to the acidic side.
The partial hydrolysis treatment time depends on the type (reactivity) of the silane coupling agent to be used and the amount of the catalyst used, so it cannot be generally stated, but it is preferably in the range of 5 minutes to several hours.
In the partial hydrolysis, heating may be performed as necessary.

<Surface treatment>
In the present invention, the liquid in which the silane coupling agent partially hydrolyzed as described above is dispersed or dissolved is mixed with the dispersion liquid in which the silica-based nanoparticles having the nano-order size are dispersed. Thus, the surface treatment of the particles is performed. In general, the above mixing is preferably performed by dropping a liquid in which a partially hydrolyzed silane coupling agent is dispersed or dissolved in a dispersion liquid in which silica-based nanoparticles are dispersed.

  In the above surface treatment, the pH of the mixed solution should be adjusted to a range of 9 to 12, particularly 10 to 11, by adding an alkali hydroxide such as ammonia or sodium hydroxide, or sodium carbonate. Is preferred. Such pH adjustment can prevent aggregation of silica-based nanoparticles and promotes dehydration condensation reaction between silanol groups generated by partial hydrolysis of the coupling agent and silanol groups on the surface of silica-based nanoparticles. Surface treatment can be effectively performed on silica-based nanoparticles.

The amount of the silane coupling agent used for the surface treatment is such an amount that the visible light transmittance of the obtained surface-treated silica-based particles (nanoparticles) in a predetermined mixed solvent is 80% or more. However, the theoretical use amount (g) for uniformly coating the nanoparticles with the silane coupling agent can be obtained by the following formula.
[Theoretical use amount of coupling agent] = A · B / C
In the formula, A is the weight (g) of silica-based nanoparticles to be surface-treated,
B is the specific surface area (m ² / g) of the nanoparticles,
C is the minimum coating area (m ² / g) of the coupling agent.
Further, the minimum covering area C (m ² / g) of the above coupling agent is obtained by the following formula.
Minimum covering area C
= (6.02 × 10 ²³ × 13 × 10 ⁻²⁰ ) / (Molecular weight of silane coupling agent)

  In this invention, the usage-amount of the silane coupling agent for obtaining a predetermined | prescribed visible light transmittance | permeability is 1-3 times amount of the theoretical usage-amount calculated above, Preferably it is 1-2 times amount, More preferably, it is 1 .1 to 1.5 times better. When the amount used is less than the above range, the coating ratio of the coupling agent to the nanoparticles becomes low, the degree of hydrophobicity imparted becomes insufficient, particularly the dispersibility with respect to the transparent resin decreases, and the above range. When used in a larger amount, there is a concern about polymerization of coupling agents and aggregation of nanoparticles, which is not preferable.

  The surface-treated silica-based particles obtained as described above are obtained in a state of being dispersed in a water-soluble organic solvent containing water or the like. Such a dispersion is subjected to solvent replacement by ultrafiltration, It is necessary to carry out the step of substituting with a solvent. That is, as described above, in the ultrafiltration method, the solvent replacement is performed by adding the single solvent to be replaced to the dispersion side while separating and removing the solvent of the dispersion solution through the filtration membrane. By performing this operation, the coupling agent released in the solvent can be removed together with the solvent passing through the filtration membrane, and the surface-treated silica-based particles can be re-agglomerated. Can be effectively prevented, and the surface-treated silica particles of the present invention having excellent transparency in the dispersion can be obtained.

Surface-treated silica-based particles;
The surface-treated silica-based particles (nanoparticles) of the present invention thus obtained have an extremely fine nano-order particle size as in the case of the raw material silica-based particles described above, and the average particle size is measured by an electron microscope. 1 to 50 nm, preferably in the range of 1 to 35 nm, most preferably in the range of 5 to 25 nm, are not agglomerated and the individual particles are coated with the hydrophobic silane coupling agent described above, Very high hydrophobicity.

  Further, since it exhibits high hydrophobicity and has a nano-order fine particle size and is not agglomerated, the particles are mixed in a mixed solvent of isopropyl alcohol and n-heptane having a weight ratio of 1: 1. In the dispersion containing mass%, the visible light transmittance is 80% or more, particularly 85% or more, and most preferably 90% or more, and the dispersion has high transparency.

  That is, since the surface-treated silica-based nanoparticles of the present invention are highly hydrophobic, they are no longer dispersed in water, but are well dispersed in a low molecular weight alcohol such as methanol and remain transparent. On the other hand, saturated hydrocarbons with extremely high hydrophobicity such as n-heptane are not completely compatible, and the dispersion may become cloudy. From the data of the particle size distribution meter and the like, the cause of the white turbidity that occurs when the degree of hydrophobicity of the nanoparticles is insufficient is that the particles are aggregated and the particle size is increased. As described above, the nanoparticles have high hydrophobicity because of high visible light transmittance at 1: 1 (weight ratio) of isopropyl alcohol, which is a hydrophilic organic solvent, and n-heptane, which is a hydrophobic organic solvent. At the same time, aggregation of particles is effectively suppressed, and it can be said that the particles exist in a so-called monodispersed state.

Resin composites;
The above-mentioned surface-treated silica-based nanoparticles of the present invention are nano-order particles having a remarkably fine particle diameter, and hardly cause aggregation, and exhibit high monodispersity and extremely high hydrophobicity. Thus, mechanical properties such as heat resistance (thermal expansion coefficient), surface hardness and strength of the resin can be adjusted. For example, the resin composite containing the surface-treated silica-based nanoparticles of the present invention in the range of 1 to 50% by mass, particularly 1 to 30% by mass, most preferably 3 to 20% by mass, The mechanical properties are effectively improved. Furthermore, when a transparent resin is used, the nanoparticles are uniformly dispersed without agglomeration, so that the excellent transparency is maintained.

  The resin with which the surface-treated silica-based nanoparticles are mixed may be not only a thermoplastic resin but also a curable resin.

In addition, as a means for mixing the surface-treated silica-based nanoparticles and the resin, a known method can be used without limitation.
For example, when mixing with a resin that is soluble in a solvent, both are dispersed in an organic solvent that is compatible with both the transparent resin and the surface-treated nanoparticles, the two dispersions are mixed, and then the solvent is removed. Thereby, both can be mixed uniformly.
Also, using nanoparticles dispersed in an organic solvent compatible with the monomer that forms the resin, mixing the monomer and nanoparticles, then removing the solvent and polymerizing the monomer in which the nanoparticles are dispersed Can do. In this case, the nanoparticles can be uniformly dispersed in the curable resin by using a crosslinking agent, a thermal polymerization initiator, or a photopolymerization initiator together with the monomer. In particular, when mixed with such a monomer, a silane compound having an organic functional group copolymerizable with the monomer (for example, a vinyl group or a (meth) acryl group) is preferably used as the silane coupling agent. Is done.
Furthermore, since the surface-treated silica-based nanoparticles of the present invention have a characteristic that the coverage of the silane coupling agent is very high and hardly aggregates even when dried, the solvent was removed and dried. The nanoparticles and the resin can be mixed by melt kneading.

  As described above, the surface-treated silica-based nanoparticle of the present invention has a fine particle size of nano-order of 50 nm or less, exhibits high hydrophobicity, and is difficult to aggregate. It is extremely useful for use as a resin composite, particularly as a transparent resin composite, but it can also be applied to other uses by utilizing its properties. For example, it can be applied to applications such as adjusting the viscosity of various media and resins, developing thixotropic properties, and improving heat resistance and reinforcing properties while maintaining transparency.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
In the following examples, various measurements were performed by the following methods.

(Measurement of particle size)
The average particle diameter was obtained by analyzing data of 100 or more particles using a scanning image of a scanning electron microscope or a transmission electron microscope.

(Visible light transmittance)
The surface-treated nanoparticles were dispersed in a mixed solvent of isopropyl alcohol and n-heptane at a weight ratio of 1: 1 so that the solid content concentration was 3% by mass.
The dispersion was placed in a quartz cell having an optical path length of 1 cm and set in a spectrophotometer, and the transmittance at a wavelength of 593 nm was measured to obtain the visible light transmittance. A quartz cell with an optical path length of 1 cm filled with pure water was used as a reference cell.

(Floatability)
Highly hydrophobic powder has the property of floating in water and not precipitating. This phenomenon was expressed numerically as follows. First, the surface-treated nanoparticles were dried to obtain a powder. A mixed solvent of water and methanol with various volume ratios was prepared. Next, the powder was slowly added to various mixed solvents, and it was confirmed whether or not they settled. The content (volume fraction) of methanol in the mixed solvent when the powder began to settle was defined as floatability and recorded.
Specifically, a highly hydrophilic powder that is not surface-treated (for example, untreated silica) has a good flowability and is often 0% because it is compatible with water. For example, a powder having a very high water repellency such as Teflon does not sink in water, so that the flowability is almost 100%.

(Production Example 1 of Raw Silica Particles)
1776 g and 4.4 g of pure water and ammonia water (25% by mass) were charged in a 4 liter glass reactor equipped with stirring blades, respectively, and stirred at 90 rpm while maintaining the temperature of the reaction solution at 40 ° C.
Next, in a 2 liter Erlenmeyer flask,
Tetramethoxysilane [(Si (OMe) ₄ , manufactured by Tama Chemical Industry Co., Ltd.]] 304 g
152g of methanol
Was prepared to prepare an alkoxysilane solution.
This solution was dropped into the reaction solution at a rate of 3 g / min to synthesize silica nanoparticles A. Stirring was continued for 60 minutes after completion of dropping, and then the solution was taken out. The removed solution was clear.
Subsequently, the solvent was replaced using an ultrafiltration apparatus (Advantech Toyo Co., Ltd., UHP-62K equipped with an ultrafilter having a molecular weight cut off of 50,000 manufactured by the same company). As a method, dilution with methanol and concentration with an ultrafiltration device were repeated, and the solvent of the solution containing the silica nanoparticles A was replaced with methanol. The ultrafiltration conditions were 10 hours at a pressure of 0.3 MPa. The solid concentration of silica in the final solution was adjusted to 5%. When the dispersion substituted with the solvent under the above conditions was analyzed using a gas chromatograph, 99% by weight or more of the solvent was replaced with methanol. The pH of the dispersion was 8.2 at 25 ° C.
Further, as a result of observing the obtained silica nanoparticles A with a transmission electron microscope, the particle shape was almost spherical, and no coarse particles were observed in the range of the observed field of view. The average particle size was 8.1 nm, and the variation coefficient of the particle size was 9.6%.

(Production Example 2 of Raw Material Silica Particles)
Use methanol instead of pure water, charge methanol and ammonia water to 2091 g and 249 g, respectively, set the reaction liquid temperature to 50 ° C., use the raw material tetramethoxysilane to 124 g, and methanol to 62 g. Prepared silica nanoparticles B in the same manner as in Production Example 1, and prepared a dispersion in which the solvent was replaced with methanol.
As a result of analysis, the particle shape was almost spherical, no coarse particles were observed in the range of the observed field of view, the average particle size was 23 nm, and the variation coefficient of the particle size was 11.2%.

(Production Example 3 of Raw Material Silica Particles)
Methanol is used in place of pure water, the charge amounts of methanol and ammonia water are 1161 g and 139 g, respectively, the temperature of the reaction solution is 40 ° C., the amount of raw material tetramethoxysilane used is 242 g, and methanol is 121 g. Prepared silica nanoparticles C in the same manner as in Production Example 1 and prepared a dispersion in which the solvent was replaced with methanol.
As a result of analysis, the particle shape was almost spherical, and no coarse particles were observed in the range of the observed field of view. The average particle size was 66 nm, and the variation coefficient of the particle size was 8.5%.

Example 1
Using the methanol dispersion of silica nanoparticles A obtained in Production Example 1, surface treatment with a silane coupling agent was performed. As the silane coupling agent, methyltrimethoxysilane, which is a kind of trialkoxysilane having three alkoxy groups in the molecule, was used.
First, in a 2 liter glass reactor with stirring blades,
700 g of a methanol dispersion of silica nanoparticles A having a solid content concentration of 5%,
Ammonia water (25% by mass) 40 g
Was stirred at 200 rpm while maintaining the temperature of the reaction solution at 40 ° C. The pH of the reaction solution having the above composition was 10.9 at 25 ° C.
Since the average particle diameter (primary particle diameter) of the silica nanoparticles A is 8.1 nm, the theoretical specific surface area is calculated as 370 m ² / g using the above formula. The density of silica was 2.0 g / cm3. Since the minimum covering area of methyltrimethoxysilane is 575 m ² / g calculated using the above formula, the theoretical usage of the coupling agent is calculated to be 22.5 g.
A coupling agent 1.2 times the theoretical amount used was prepared, diluted with methanol 2 times by weight, and stirred. Subsequently, a pH 4 aqueous hydrochloric acid solution containing 1 equivalent of water to the coupling agent was added and stirred for about 60 minutes.
In addition, when the said liquid of 1 hour after was analyzed by GC / MS, it was confirmed that 94% of the raw material silane coupling agent hydrolyzed the alkoxy group and produced | generated the silanol group.

Subsequently, a solution containing a coupling agent was dropped into the reactor over 2 hours. After completion of the dropwise addition, the solution was taken out after stirring for 24 hours or more.
The extracted solution was replaced with methanol by using the above ultrafiltration apparatus.
The said solution was moved to the evaporator apparatus, isopropyl alcohol was added little by little to the solvent, distilling methanol, and the solvent was substituted from methanol to isopropyl alcohol. At this time, the solid content concentration of the nanoparticles was 15%.
Next, using the isopropyl alcohol dispersion having a solid content concentration of 15%, isopropyl alcohol and n-heptane, the weight ratio of isopropyl alcohol to n-heptane is 1: 1 and the solid content concentration is 3%. In this way, the three solutions were mixed. As a result, a dispersion liquid in which the surface-treated silica particles were dispersed at a concentration of 3% by mass in a 1: 1 (weight ratio) mixed solvent of isopropyl alcohol and n-heptane was prepared.
The visible light transmittance of the dispersion was measured and found to be 96%. Further, the floatability was 30%. When the particles in the dispersion were observed with a transmission electron microscope, the results were the same as those described in Production Example 1 for Nanoparticle A.

(Example 2)
As the silane coupling agent, n-propyltrimethoxysilane, which is a kind of trialkoxysilane having three alkoxy groups in the molecule, is used instead of methyltrimethoxysilane. Surface treatment was performed in the same manner as in Example 1 except that an aqueous hydrochloric acid solution having a pH of 4 containing water was added and stirred for about 10 minutes.
As a result, the visible light transmittance was 93% and the flowability was 35%.
(Example 3)
As the silane coupling agent, (3,3,3-trifluoropropyl) trimethoxysilane, which is a kind of trialkoxysilane having three alkoxy groups in the molecule, is used instead of methyltrimethoxysilane. Surface treatment was performed in the same manner as in Example 1 except that an aqueous hydrochloric acid solution having a pH of 4 containing 2 equivalents of water to the agent was added and stirred for about 60 minutes.
As a result, the visible light transmittance was 88% and the flowability was 55%.

(Comparative Example 1)
Surface-treated nanoparticles were prepared and evaluated in the same manner as in Example 1 except that an aqueous hydrochloric acid solution having a pH of 4 containing 0.7 times equivalent water relative to the coupling agent was added.
As a result, the dispersion was visually cloudy, visible light transmittance was 28%, and flowability was 10%.

(Comparative Example 2)
Surface-treated nanoparticles were prepared and evaluated in the same manner as in Example 1 except that an aqueous hydrochloric acid solution having a pH of 4 containing 3.5 times the equivalent amount of water relative to the coupling agent was added.
As a result, the visible light transmittance was 54% and the flowability was 35%.

(Comparative Example 3)
Surface-treated nanoparticles were prepared and evaluated in the same manner as in Example 1 except that ammonia water (25% by mass) was not added to the reaction solution. The pH of the reaction solution at this time was 8.2 at 25 ° C.
As a result, the dispersion liquid was also white turbid, visible light transmittance was 21%, and flowability was 10%.

Example 4
Surface-treated nanoparticles were prepared and evaluated in the same manner as in Example 1 except that the amount of ammonia water (25% by mass) added to the reaction solution was 4 g. In addition, the pH of the reaction liquid at this time was 10.2 at 25 degreeC.
As a result, the dispersion was transparent, the visible light transmittance was 90%, and the flowability was 30%.

(Comparative Example 4)
Surface treatment was performed in the same manner as in Example 1 except that dimethyldimethoxysilane, which is a kind of dialkoxysilane having two alkoxy groups in the molecule, was used as the silane coupling agent instead of methyltrimethoxysilane. It was. At this time, since the minimum coating area of the coupling agent is 651 m ² / g, a coupling agent 1.2 times the theoretical amount used was prepared, diluted with methanol twice the weight ratio, and stirred. . Subsequently, a pH 4 aqueous hydrochloric acid solution containing 1.5 times the equivalent of water as the coupling agent was added, and the mixture was stirred for about 60 minutes.
As a result, the visible light transmittance was 58% and the flowability was 15%.

(Example 5 and Comparative Example 5)
Surface treatment was performed in the same manner as in Example 1 except that silica nanoparticle B of Example 2 (Example 5) and silica nanoparticle C of Example 3 (Comparative Example 5) were used instead of silica nanoparticle A. .
As a result, the visible light transmittance of Example 5 was as good as 90%, but the visible light transmittance of Comparative Example 5 was 53%. Further, both floatability were 30%.
Since the flowability of the particles of Comparative Example 5 was 30%, it is considered that the hydrophobization treatment was carried out with almost the same coupling agent as in Example 1 and Example 5, but the particle size of the nanoparticles was It is considered that the visible light transmittance was low because it was considerably larger than 50 nm.

(Example 7)
Using the surface-treated silica nanoparticles obtained in Example 2, experiments on nanocomposites were conducted.
Dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) 20g
Photopolymerization initiator (Irgacure-184) 0.2g
Were mixed to prepare an ultraviolet curable resin.
Using the isopropyl alcohol dispersion of silica nanoparticles surface-treated with n-propyltrimethoxysilane obtained in Example 2, the content of nanoparticles was 10% by weight with respect to the ultraviolet curable resin. Were added and stirred well. The solvent isopropyl alcohol was distilled off using an evaporator to obtain an ultraviolet curable resin composition with nanoparticles added. The resin composition was transparent.
Next, the UV curable resin composition was coated on a transparent polyester film using a bar coater, and the resin was cured by irradiation with an 80 W high pressure mercury lamp for 30 seconds to obtain a coating film.
The film was transparent and the pencil hardness was 2H.

(Example 8)
A highly hydrophobic surface-treated silica nanoparticle was obtained in the same manner as in Example 3 except that 3-methacryloxypropyltrimethoxysilane was used as the silane coupling agent. When the visible light transmittance was measured in the same manner as in Example 1, it was 88% and the flowability was 45%.
An ultraviolet curable resin composition was prepared in the same manner as in Example 7 except that the above nanoparticles were used, and a coating film was produced.
As a result, the resin composition was transparent, the film was also transparent, and the pencil hardness was 3H. Since the main component of the ultraviolet curable resin has a polymerizable acrylic group, and the surface treatment agent for the nanoparticles also has a polymerizable acrylic group, the surface hardness is improved as compared with Example 7. Guessed.

(Comparative Example 6)
An ultraviolet curable resin composition was prepared in the same manner as in Example 7 except that the silica nanoparticles A of Production Example 1 that had not been subjected to surface treatment were used as nanoparticles, and a coating film was produced.
As a result, it was confirmed that the above-mentioned ultraviolet curable resin composition was markedly clouded and the nanoparticles were aggregated. The coating film was not completely transparent, and turbidity was observed.

Claims (6)

  Silica-based particles having an average particle diameter in the range of 1 to 50 nm as measured with an electron microscope, each particle is surface-treated with a hydrophobic silane coupling agent, and 1 of isopropyl alcohol and n-heptane 1: Surface-treated silica-based particles, wherein the dispersion exhibits a visible light transmittance of 80% or more when dispersed in a mixed solvent at a concentration of 3% by mass (by weight). The hydrophobic silane coupling agent has the following formula (1):
R ¹ —Si (OR ² ) ₃ (1)
In the formula, R ¹ is an alkyl group, an alkenyl group or an aryl group,
R ² is an alkyl group,
The surface-treated silica-based particle according to claim 1, which is a trialkoxysilane represented by the formula: A step of preparing a liquid in which silica-based particles having a particle diameter of 1 to 50 nm are dispersed by a wet method as measured with an electron microscope;
Partially hydrolyzing the hydrophobic silane coupling agent in the presence of water;
Mixing the liquid containing the partial hydrolyzate and the liquid in which the silica-based fine particles are dispersed, and reacting the partial hydrolyzate with the silica-based fine particles at a pH of 9 to 12;
A step of subjecting the dispersion obtained by the reaction of the partially hydrolyzed product and the silica-based fine particles to solvent replacement by ultrafiltration, removing unreacted coupling agent and the like and replacing with a single solvent;
A method for producing surface-treated silica-based particles, comprising: As the hydrophobic silane coupling agent, the following formula (1):
R ¹ —Si (OR ² ) ₃ (1)
In the formula, R ¹ is an alkyl group, an alkenyl group or an aryl group,
R ² is an alkyl group,
The manufacturing method of Claim 3 using the trialkoxysilane represented by these.   The manufacturing method of Claim 3 or 4 which performs the partial hydrolysis of a hydrophobic silane coupling agent with 1-3 times equivalent water with respect to this coupling agent.   A resin composite comprising 1 to 50% by mass of the surface-treated silica-based particles according to claim 1 or 2.