JPH02160613A - Production of surface-modified silica - Google Patents

Abstract

PURPOSE:To obtain a surface-modified silica having remarkably improved stability in hydrophobic organic solvent and useful for the reaction with a specific organic silicon compound by specifying the properties of fine particles of porous silica having alkoxylated surface. CONSTITUTION:1mol of a tetraalkoxysilane is hydrolyzed in an alcohol containing 2.5-6mol of water and 0.1-3mol of an alkali catalyst to obtain an alcoholic dispersion of porous fine. particles of silica containing >=3.5mumol/m<2> of alkoxy group directly bonded to surface Si, having a silanol group density of <=2mumol/m<2> and satisfying the formula SXD>=5,000 wherein S (m<2>/g) is specific surface area and D (nm) is average particle diameter. An organic silicon compound expressed by the general formula I or II is added to the dispersion and made to react with the silica fine particles. In the formula, R<1> to R<3> are H or 1-20C substituted or unsubstituted hydrocarbon group, X and Y<1> are OH or 1-4C alkoxy group, Y<2> is H or 1-4C alkyl group, n is 1-3 and m is 1-20.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a sol that is stable in any organic solvent and is suitable for use as a hard coat for plastic lenses, a fiber treatment agent, a thickener for oil, etc. The present invention relates to a method for producing surface-modified silica.

(Conventional Technique IN) Conventionally, silica that can be dispersed in organic solvents has been known to have alkoxy groups on its surface, and a method for producing it is to obtain it by hydrolyzing alkoxysilanes in the presence of an alkali catalyst. It has been known.

The obtained silica is generally hydrophilic, so if you try to disperse it in a highly hydrophobic organic solvent, the silica particles will aggregate or gel, resulting in phase separation and making it difficult to disperse them uniformly. could not. Therefore, up until now, organic solvent-dispersed silica has only been treated with solvents that are not very hydrophobic.

The use of alcohols such as methanol, 2-propanol, and 1-butanol was limited.

(Problem to be Solved by the Invention) Therefore, as a method for dispersing fine particles of inorganic oxides such as silica in a more hydrophobic organic solvent, there are two methods: - Hydrolysis of alkoxides such as silicon, titanium, zirconium, aluminum, etc. possible organometallic compounds,
Hydrolyze in an alcohol-containing solution to form a suspension of hydrate fine particles in an alcoholic solution; and has. A method has been proposed in which, after surface modification is performed by adding a coupling agent such as silane, titanate, or aluminum, (1) the alcoholic solvent is replaced with an organic solvent (Japanese Patent Application Laid-Open No. 182204/1983).

However, when attempting to modify the surface of silica fine particles using tetraalkoxysilane as an organometallic compound using this surface modification method, the molar ratio of tetraalkoxysilane to water is greater than 6, resulting in a large number of silanol groups on the silica surface. Furthermore, the silica fine particles used as an intermediate have an average particle diameter of 0.05.
Applicable only to ~5μs and average particle size of 0.0
It was virtually impossible to modify the surface of ultrafine particles of 5μ or less.

Therefore, if the organic solvent-dispersed silica obtained by this method is used as a thickener for hard coats or oils, problems may arise in performance such as hard coat strength and transparency and oil thickening properties, impairing practicality. was.

Therefore, the object of the present invention is to use silica as a raw material, which is obtained by hydrolyzing tetraalkoxysilane in alcohol containing water and an alkali catalyst, and which has a high density of alkoxy groups and porous surface characteristics. The objective is to produce silica with excellent dispersibility in organic solvents by surface modification using an organosilicon compound.

(Means for Solving the Problems) The method for producing surface-modified silica according to the present invention is a method for producing surface-modified silica, which is produced by hydrolyzing tetraalkoxysilane in an alcohol containing water and an alkali catalyst. The group density is 3.5 μmol/- or more, the silanol group density is 2 μmol/% or less, and the specific surface area s (r
rr/g) and the average particle diameter D (nm) is S
An alcohol dispersion of porous silica particles whose surface is alkoxylated and has XD≧5,000 has the general formula: R′4-n5iXn, (R″, Si), NH
.

(Here, R", R", and R3 are each a hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms; X and Yl are each a hydroxy group or an alkoxy group having 1 to 4 carbon atoms. Group; Y2 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, n is 1 to 3, m is 1 to 20
It consists of adding an organosilicon compound represented by ) to perform a silica surface modification reaction.

To explain this in more detail, the surface-alkoxylated porous silica particles used in the production of the surface-modified silica of the present invention have a density of alkoxy groups directly bonded to silicon on the surface of 3.5 μwool/rd or more, The density of silanol groups is 2 μmol/rd or less, the specific surface area is 5 (rrf
/g) and the average particle diameter D (nm) is SXD≧s
, ooo.

In general, the specific surface area s (
What is the relationship between rrr/g) and average particle diameter D (nm)?

vatson (Anal, Chew, 20.576
(1948)), S X D = 2,720
It is. At this time, if SXD≧2,720, this silica is a porous material having pores. The larger this value (SXD) is, the more the particles deviate from the spherical shape, become more porous, increase the surface area, and increase the reactivity with organosilicon compounds.

In conventional alcohol-dispersed silica sol, 5XD=3,0
The silica sol used in the present invention has a low porosity of 00 to 4,000, but since it is a very porous silica with S×D≧5,000, it has high reactivity with organosilicon compounds.

In addition, the silica surface where 3.5 μmol/rrr or more of alkoxy groups directly bonded to silicon and 2 μmol/n (or less of silanol groups) are present is hydrophobic due to the presence of many alkoxy groups.On the other hand, as mentioned above, Unexamined Japanese Patent Publication No. 1986-
The silica made from alkoxysilane described in Japanese Patent No. 182204 has few alkoxy groups and many silanol groups on the surface, so its surface is substantially hydrophilic.

Comparing the reactivity of these silicas with organosilicon compounds, it was found that silica produced by conventional methods has a hydrophilic surface, so many water molecules are adsorbed there, and the organic silica compounds, which are naturally hydrophobic, It prevents the access of elementary compounds and prevents the progress of surface modification reactions. However, since the silica used in the present invention has a hydrophobic surface, less water molecules are adsorbed, and even more alcohol molecules are adsorbed. therefore.

The organosilicon compound can easily approach the surface of the silica particles and allow the surface modification reaction to proceed smoothly.

This is one reason why porous fine particles having the above-mentioned properties are used in the method of the present invention.

The production of porous silica particles with such characteristics is
Tetraalkoxysilane or an alcoholic solution thereof having a concentration of 0.1 to 6 mol/Ω is maintained at a predetermined temperature and sufficiently stirred. This is carried out by gradually introducing the water-alcohol-alkali catalyst mixture solution containing 2.5 to 5.0 times the mole of water and 0.1 to 3 times the mole of the alkali catalyst. If stirring is insufficient at this time, it is undesirable because sedimentary silica particles will form.Also, if the water-alcohol-alkali catalyst mixed solution is left open, the alcohol and alkali catalyst will volatilize, and their concentration will change from time to time. It is desirable to carry out the process in a closed system, as this makes it difficult to produce a product that changes and is reproducible.

This tetraalkoxysilane has the general formula Si(OR)4
In the compound represented by, the alkyl group defined by R is methyl or ethyl having 4 or less carbon atoms.

Propyl, butyl, etc. are preferred, for example.

Tetramethoxysilane, tetraethoxysilane.

Examples include tetra-1-propoxysilane and tetra-1-butoxysilane.

When the number of carbon atoms in this alkyl group increases, 5
~500n, 100~2.50on for ethyl group,
The particle size of silica produced by one reaction increases, such as 250 to 3,500 nm for propyl groups and 500 to 5,000 nm for butyl groups. Therefore, it is desirable to select and use tetraalkoxysilanes having different numbers of carbon atoms in their alkyl groups depending on the desired particle size.

The concentration of tetraalkoxysilane relative to alcohol as reaction medium is 0.1 to 6 mol/Ω, in particular 0.1 to 6 mol/Ω.
Preferably 2 to 2 mol/Q, the concentration is 0
．． If it is lower than 1 ol/Q, an excessive reaction volume is required, resulting in low productivity and poor economic efficiency. 6 pho again. If l/Q is exceeded, the concentration is too high, causing dissociation between particles, resulting in decreased dispersibility and further phase separation of silica due to aggregation.

The alcohol used as the reaction medium is a lower aliphatic alcohol represented by the general formula ROM, and methanol in which the alkyl group defined by R has 4 or less carbon atoms.

Ethanol, 2-propertool, 1-butanol, etc. are preferred. These are usually commercially available products, but as the number of carbon atoms in this alcohol increases, the particle size of the silica produced increases, so the desired silica particle size It is desirable to select the type of alcohol depending on the situation.

Alkali catalysts added to the reaction medium system include ammonia or alkylamines whose alkyl group is methyl, ethyl, propyl, butyl, etc.
Monoalkylamines, dialkylamines, trialkylamines, etc. can be used. However, alkylamines have a weak catalytic effect and the rate of hydrolysis of tetraalkoxysilane is slow, and depending on the concentration, they can act as flocculants to promote the dissociation of silica particles, so they do not have this effect and are highly reactive and volatile. Ammonia is more suitable because it has a high carbon content and can be easily removed in subsequent steps.

The concentration of this alkali catalyst to tetraalkoxysilane, i.e. the molar ratio to silica (e.g. alkali/
Si) is 0.1 to 3, particularly preferably 0.3 to 2. If it is less than 0.1, silica will be dispersed as very fine particles, and the necessary charge to be able to exist stably will not be applied to the particle surface. Unable to grant.

During the reaction or some time after the reaction, the particles will coalesce and form a gel, and adding more than 3 particles will not improve the catalytic effect and will not be economical. However, if the catalyst concentration is within the above range, When the silica particles are changed, the particle size of the silica changes, so the size of the silica particles can also be adjusted using this property.

What is the theoretical amount (stoichiometric value) of water required for hydrolysis?

H, O/alkoxysilane; 2 0 In the present invention, for producing silica having an alkoxy group on the surface.

The amount of water must be close to the theoretical value, and the amount is 2.5 to 6.0 times the mole of tetraalkoxysilane.
Particularly preferred is 3.0 to 6.0 times the mole, which is 2.
If it is less than 5 times the mole, the tetraalkoxysilane will not be sufficiently hydrolyzed, so unreacted tetraalkoxysilane will remain or a soluble polymer, which is a partial hydrolyzate, will be produced, which is not preferable, and if it exceeds 6.0 times the mole. Hydrolysis proceeds sufficiently and the number of silanol groups on the surface increases, which is undesirable.

The hydrolysis mechanism when alkoxysilane grows into silica particles is shown by the following equation.

Si(OR)4+XH2O-4SL(OH)X(OR)
4-x+XROH"'■=Si-OH+HO-8i=→
=Si-0-8iE+H,O...■=Si-O
H+RO-8iE→ESi-0-5iE+ROH...
The hydrolyzed monomer produced by formula 00 condenses its silanol groups with each other (formula 0) or the silanol group and an alkoxy group directly bonded to silicon (formula 0), and the molecular weight (condensation) gradually changes from oligomer to polymer to fine particles. degree) and eventually grow to the desired size. The hydrolysis temperature at this time is 10 to 50℃, especially 20 to 40℃.
The temperature is preferably 1°C (below 1°C, the rate of coordination of alkali ions to the surface of the silica particles is reduced more than the rate of hydrolysis reaction and condensation reaction, and the ionic stability of the particles is reduced, resulting in the formation of bonds between particles. This is undesirable because it promotes fusion, and if the temperature exceeds 50°C, the rate of coordination of alkali ions to the surface of the silica particles increases more than the rate of hydrolysis reaction or condensation reaction, resulting in a stable state with a low degree of condensation and small particles. Undesirable as it produces too much silica particles.
However, since the particle diameter of silica can be changed by changing the reaction temperature within this range, the silica particles can also be adjusted under these conditions.

As described above, in the method of the present invention, the particle size of silica can be controlled by controlling the number of carbon atoms in the tetraalkoxysilane and alcohol used as raw materials, the concentration of the alkali catalyst, the amount of water added to the reaction system, and the reaction temperature. It is possible.

In general, this control is carried out by first selecting a tetraalkoxysilane with an appropriate number of carbon atoms depending on the desired particle size, and then controlling the silica particle size within the aforementioned range of silica particles, for example, in the range of 5 to 500 nm for tetramethoxysilane. decide. If more precise particle size control within this range is required, silica of any particle size can be produced by selecting each condition according to the trends in the conditions shown in Table 1. can.

Table 1 The organosilicon compound used in the reaction with the porous silica fine particles thus obtained has the general formula R'4. ．． 5
iXn, (R13S i), N H1 (here, R″
, R2, and R1 each have a hydrogen atom or a carbon atom number of 1
~20 substituted or unsubstituted hydrocarbon groups; x, y' are each a hydroxy group or an alkoxy group having 1 to 4 carbon atoms; Y'' is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, n is 1 to 3, m is 1 to 20).

Specific examples of such compounds include trimethylmethoxysilane, triethylmethoxysilane, triphenylmethoxysilane, dimethylvinyltrimethoxysilane, trifluoropropyldimethylmethoxysilane, 3-aminopropyldimethylmethoxysilane, dimethyldimethoxysilane, methylvinyl Dimethoxysilane, diphenyldimethoxysilane, 3-aminopropylmethyldimethoxysilane, methyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane.

3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane.

Alkoxysilanes such as 3-aminopropyltrimethoxysilane, silazanes such as hexamethyldisilazane and tetramethyldivinyldisilazane, trimethylsilanol, and triethylsilanol.

triphenylsilanol, diphenylsilanediol,
Examples include silanols such as dimethylsiloxane oligomers having terminal OH groups and methylphenylsiloxane oligomers having terminal OH groups, and these may be used alone or as a mixture of two or more thereof.

The amount of the organosilicon compound to be used is preferably 0.01 to 10°, particularly 0.1 to 1 in molar ratio to the amount of Sin contained in the silica particles. The amount of organosilicon compounds introduced to the surface is small,
The properties of this compound cannot be fully exhibited on the silica surface, and if it exceeds 10, the reaction between the silica surface and the organosilicon compound will not be completed and an excess of the organosilicon compound will remain, which is undesirable. .

The reaction is carried out by slowly adding the metal organosilicate in the above amount ratio while stirring the alcohol-dispersed silica sol obtained in the previous step, and then heating at 0°C or higher, preferably 10°C or higher, at 1 to 8°C.
This is carried out by stirring for a period of time, preferably 3 to 5 hours.

In this reaction, if the temperature is below 0°C, the reaction is slow and requires a long time, which is uneconomical.

The alcohol-dispersed silica sol obtained by the method described above is
It is suitable for this reaction because it has a small amount of silanol groups and a large amount of alkoxy groups directly bonded to silicon. The hydrolyzable group in the organosilicon compound added at this time reacts with water in the hydrous alcohol serving as a dispersion medium and changes into an =si-oH group. At this time, in order to produce silica with a large number of silanol groups by the method described in JP-A No. 63-182204, when Hz O/S i is set to 6, the hydrolysis of the organosilicon compound proceeds quickly and a large number of Mi5i-
OH groups are generated. Then, these Mi5i-OH
The groups undergo a condensation reaction to produce oligomers of organosilicon compounds, and the amount actually consumed in the silica surface modification reaction decreases, reducing efficiency.

On the other hand, since there is very little water in the dispersion medium when producing the silica of the present invention, the amount of ESi-OH groups produced is small, so the condensation reaction between organosilicon compounds is small and the reaction with silica is efficient. becomes possible.

In the dispersed silica obtained by this reaction, the dispersion medium alcohol can be replaced with another organic solvent by adding any organic solvent thereto and removing the alcohol by distillation or the like.

As this organic solvent, hydrocarbons such as hexane, cyclohexane, toluene, and xylene are preferable.

(Examples) Next, specific embodiments of the present invention will be explained using Examples and Comparative Examples. The silanol groups, alkoxy groups directly bonded to silicon, and organosilicon substituents on each side were quantified by the following method.

(2) Silanol group The silanol group on the surface of the silica was reacted with methanol in an autoclave, the carbon content of the obtained silica was quantified, and the amount of silanol group was calculated from the increase using the following formula.

ΔC1: Difference in carbon content before and after reaction (wt%) S: N,
Specific surface area due to adsorption (bo/g) ■ Alkoxy group directly bonded to silicon Nisilica was dissolved in a 10% NaOH aqueous solution, and the amount of alcohol produced was determined by gas chromatography.
It was calculated using the following formula.

W: Amount of alcohol produced from silica per unit weight (μ■ol/g) S: N, specific surface area due to adsorption (po/g) ■Organosilicon substituent: Alkoxy groups on the silica surface are After detachment,
Quantify the amount of carbon contained in silica.

From that value, the amount of organosilicon substituents was determined using the following formula.

Carbon content (weight%) S: N
, specific surface area by adsorption (i/g) n2: total number of carbons contained in organosilicon substituent Example 1゜IO with stirring motor, dropping funnel, and thermometer
In glass flask A, add 182 d of 28% ammonia water.
, ion exchange water 110d, and ethanol 5542d
were added, and the reaction solution was heated to 38°C while stirring vigorously.
A mixed solution of tetramethoxysilane 518- and ethanol 648tQ was added dropwise thereto over 1 hour. The particle size of the obtained ethanol-dispersed silica sol was measured with a submicron analyzer (Model N4-64SO, manufactured by Coulter Co., Ltd.) and found to be 40 n-.

After drying this silica sol, the specific surface area due to nitrogen adsorption was measured using an automatic specific surface area measuring device (Model 2200, manufactured by Shimabara Seisakusho) and found to be 250 rrf/g.

Next, this silica powder was subjected to "Si-
NMR and "C-NMR" are measured using an NMR measuring device (GSX-2
70 type 1 manufactured by JEOL Ltd.), and the results are shown in FIGS. 1(a) and 1(b). Note that the amount of the ethoxy group at this time was 12 μ@ol/rrr, and the amount of silanol group was 1.8 μmol/rrr.

The above ethanol-dispersed silica sol was concentrated under reduced pressure using a rotary evaporator to obtain 100% silica sol with a silica concentration of 20% by weight. I got it. After 0.5 g of hexamethyldisilazane was added and stirred at 20° C. for 3 hours, 120 g of xylene was added and ethanol was removed by vacuum distillation to obtain a xylene-dispersed silica sol (xylene 99.5%). After drying this silica sol, "Si-NMR" and "C-NMR" were measured by CP-MAS method, and the respective results are shown in FIGS. 2(a) and (b).

Comparative Example 1 An alcohol-dispersed silica sol was produced in the same manner as in Example 1, except that the types of tetraalkoxysilane and alcohol, the concentration of each raw material relative to the entire solution, and the reaction temperature were as shown in Table 2.

The reaction conditions and analysis results at this time are also listed in Table 1. CP- of the silica powder obtained by drying this silica sol
"Si-NMR" and "c-NMR" by MAS method are NM
R measurement device! (Model GSX-270, manufactured by JEOL Ltd.), and the results are shown in FIGS. 3(a) and 3(b).

Next, the above silica sol was used to react with the same organosilicon compound as in Example 1 under the conditions shown in Table 3. As a result, when the alcohol concentration in the obtained xylene sol became 15% or less, it gelled and the silica and xylene separated into phases. After drying this silica sol, CP-MA
211Si,-NMR and 3C-NMR were measured by the S method, and the results are shown in FIGS. 4(,) and (b).

The measurement results of the raw material silica sol in the present invention and the prior art can be evaluated by comparing and contrasting FIGS. 1 and 3. That is, based on (=SiO), Si signal ■, (yo5iO), 5i(OH) (7) signal ■, and (=sio), 5iOH signal ■
It can be seen that the number of hydroxyl groups in the present invention is small compared to the number in the prior art. ■ is each signal caused by a methoxy group.

Furthermore, modified silica can be evaluated by comparing Figures 2 and 4. From the results of Figure 2 according to the present invention, ■, which indicates a signal of a hydroxyl group, decreases, indicating that it is caused by the trimethylsilyl group of the modified group. The increase in the signal ■■ indicates that the reaction of the modifying group is well carried out, but in the case of the conventional method, the signal ■ due to the hydroxyl group almost decreases, as shown in Figure 4. I haven't done it,
Furthermore, the signal (■) due to the trimethylsilyl group of the modifying group was also low, indicating that this reaction was not carried out sufficiently.

Examples 2-4. and Comparative Examples 2 to 4 Alcohol-dispersed silica sol was produced in the same manner as in Example 1, except that the types of tetraalkoxysilane and alcohol, the concentration of each raw material in the entire solution, and the reaction temperature were as shown in Table 2. did.

The reaction conditions and analysis results at this time are also listed in Table 2. The obtained silica sol was reacted with various organosilicon compounds under the conditions shown in Table 3, and the results are also shown in Table 3. In each comparative example, gelation occurred when the alcohol concentration in the obtained xylene sol decreased to 2 to 8% or less, and in each case, silica and xylene separated into phases.

(Effects of the Invention) Since the surface of the surface-modified silica obtained by the method of the present invention is modified with an organosilicon compound, it not only has significantly improved stability in hydrophobic organic solvents, but also
By selecting different types of organic silicon compounds, organic solvent-dispersed sol consisting of silica particles with various surface modifications can be obtained. Therefore, in addition to improving the performance of conventional plastic lens hard coats and fiber treatment agents, it is expected to expand into new applications such as oil thickeners.

[Brief explanation of the drawing]

Figures 1 and 2 show the CP of porous silica fine particles and surface-modified silica obtained in Example 1, respectively.
-2gSi-NMR by MAS method (each figure a) and “C-
Graphs showing the measurement results of NMR spectra (each figure b), Figures 3 and 4 respectively show the cp - This is a graph showing the measurement results of Si-NMR (each figure a) and L3cm NMR (each figure b) spectrum measured by the MAS method. Figure 1 Figure 2 (b) 13C-NMR spectrum Figure 3 (a) 29Si-NMR spectrum (b) t3C-NMR spectrum Figure 4 (b) 13C-NMR spectrum

Claims (1)

[Claims] 1. The density of alkoxy groups directly bonded to silicon on the surface obtained by hydrolyzing tetraalkoxysilane in alcohol containing water and an alkali catalyst is 3.5 μmol/
m^2 or more, the density of silanol groups is 2 μmol/m^2
Below, specific surface area S (m^2/g) and average particle diameter D (nm
), the alcohol dispersion of porous silica fine particles whose surface is alkoxylated has a relationship of S x D ≧ 5,000, and the general formula:
i)_2NH, or ▲Mathematical formula, chemical formula, table, etc.▼ (Here, R^1, R^2, R^3 are each a hydrogen atom or a substituted or unsubstituted hydrocarbon having 1 to 20 carbon atoms. Groups: X and Y^1 are each a hydroxy group or an alkoxy group having 1 to 4 carbon atoms; Y^2 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, n is 1 to 3, m
is 1 to 20) and reacts with the porous silica fine particles. 2. The surface-modified silica according to claim 1, wherein the hydrolysis of the tetraalkoxysilane is carried out in the presence of water in an amount of 2.5 to 6 times and an alkali catalyst in an amount of 0.1 to 3 times the amount of the tetraalkoxysilane. Production method. 3. The surface-modified silica according to claim 1, wherein the amount of the organosilicon compound added to the alcohol dispersion is within a molar ratio of 0.01 to 10 with respect to the amount of SiO_2 in the porous silica fine particles. manufacturing method.