JPH04187512A - Silica sol and its production - Google Patents

Abstract

PURPOSE:To improve bonding strength in use as a binder and eliminate occurrence of cracks when formed into films by regulating a silica sol so that the gradient of a straight line indicating correlation between the silica concentration and reduced viscosity thereof may satisfy a specific relationship. CONSTITUTION:In the aforementioned silica sol, the gradient ( [log(etasp/C)]/ C) of a straight line indicating the correlation between the reduced viscosity (etasp/C) and the silica concentration (C) satisfies a relationship of 0.02<= [log(etasp/ C)]/ C<=0.20. The above-mentioned silica sol is obtained by the following steps. That is (a) a step for adding silicic acid liquid to an aqueous solution of an alkali metallic silicate at 0.05-5.0wt.% concentration expressed in terms of SiO2 and regulating the SiO2/M2O (molar ratio, M is alkali metal or quaternary ammonium) to 30-60, (b) a step for adding one or two or more metallic compounds selected from Ca, Mg, Al, Ti, Cu, rare earth metals, etc., before, during or after the step for adding the silicic acid liquid, (c) a step for keeping the resultant mixture solution at an optional temperature of >=60 deg.C for a prescribed time and (d) a step for reading the silicic acid liquid to the reaction solution and keeping the SiO2/M2O (molar ratio) in the reaction solution at 60-100.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a novel silica sol and a method for producing the same.

[Prior art]

Silica sol is used as a binder for inorganic materials, a filler for plastics, a coating agent, etc., and the shape of the dispersed silica particles in conventional silica sol is all spherical or close to spherical.

As a method for producing these silica sols, for example, a method of adding a silicic acid solution to an aqueous solution of an alkali metal silicate is known (Japanese Patent Application Laid-Open No. 1964-1964.58-15022゜62-7).
(See Publication No. 622).

These conventional silica sols do not have sufficient bonding strength when used as a binder in sand molds for casting or as binders for inorganic fibers.
When a film was formed using the silica sol, there were problems such as cracks occurring in the film.

In order to solve these problems, a silica sol made of elongated silica particles and a method for producing the same have been proposed (see Japanese Patent Application Laid-open No. 1-317115), but no other methods are known yet. do not have.

〔the purpose〕

The purpose of the present invention is to provide a new type of silica sol and a method for producing the same, which solves the above-mentioned problems such as insufficient bonding strength when used as a binder and occurrence of cracks when formed into a film. It is in.

Another object of the present invention is to provide a new method for producing a new type of silica sol consisting of elongated silica particles.

〔composition〕

The first aspect of the present invention is the slope of the straight line (△[log(η
The present invention relates to a silica sol characterized in that sp/C)]/ΔC) satisfies the following relationship.

0.02≦Δ [log(71SP/C)]/ΔC≦0
．． 20 The second aspect of the present invention is S10□ of 0.05 to 5.
0L1t% alkali metal silicate aqueous solution.

(a) 5j02/Mz of the mixed liquid by adding silicic acid liquid
Step (b) in which O (molar ratio, M is an alkali metal or quaternary ammonium) is 30 to 60: Ca, Mg, AL In, Tj before, during or after the silicic acid solution addition step.

Step of adding a compound of one or more metals selected from the group consisting of Zr, Sn, Si, Sb, Fe, Cu, and rare earth metals'(C) Adding this mixed solution to 6
Step (d) of maintaining at an arbitrary temperature of 0° C. or higher for a certain period of time: Adding a silicic acid solution to the reaction solution again to adjust the 5i02/M20 (molar ratio) in the reaction solution to 60 to 100. Regarding the manufacturing method.

[Characteristics of the silica sol of the present invention]

The reduced viscosity of the silica sol of the present invention is concentration dependent, and as the silica concentration increases, the reduced viscosity also increases. In contrast, conventional silica sols have little or no concentration dependence.

Reduced viscosity = (specific viscosity) / (silica concentration) In general, regarding the shape of the polymer in a polymer sol and the reduced viscosity of the sol, if the shape is spherical, the reduced viscosity is constant regardless of the polymer concentration. Takes a value. On the other hand, in the case of chain or linear polymers, there is concentration dependence, and as the polymer concentration increases, the reduced viscosity also increases.

The silica sol of the present invention is different from the conventional silica sol in which spherical silica particles are dispersed, and shows the same tendency as in the case of polymer sol.1 The silica particles of the present invention are considered to be silica sol in which chain or linear particles are dispersed. It will be done. And this is also confirmed by @photography.

The silica sol of the present invention has a higher viscosity than the conventional spherical silica sol even at the same concentration, and is stable despite the high viscosity.
This is thought to be due to the fact that it is a sol in which chain (linear) particles are dispersed.

Reduced viscosity of the silica sol of the present invention (ηs p / C+C
, P, /lyt%) and concentration (C, wt%), and the vertical axis shows the reduced viscosity on a logarithmic scale, as shown in Figure 1.

When expressed as concentration on an arithmetic scale on the horizontal axis, it becomes a straight line, and its slope Δ[log(77SP/C)]/ΔC is 0.02
~0°20.

Furthermore, the silica sol of the present invention has an average particle diameter D1 of less than 4On+n as measured by a dynamic light scattering method, and a ratio of D1/D2×5, where D2 is the average particle diameter measured by a N2 gas adsorption method. Note that the silica particles of JP-A-1-317115 have this D1/D2≧5, and the present invention has /
They are exactly the opposite in relation to D2.

A method for measuring particle size using dynamic light scattering is described in the Journal of Chemical Physics (Journalof C
Chemical Physjcs) Volume 57 No. 11 (
(December 1972), page 4814, and the particle size can be easily measured, for example, using a commercially available device called N4 manufactured by Coulter, Inc. in the United States. From the specific surface area Sm2/g measured by the normal BET method
The particle size D2mμ given by the formula D2=□ means the diameter of a hypothetical spherical colloidal silica particle having the same specific surface area Sm2/g as the elongated colloidal silica particle. Therefore, the ratio of the particle diameter mμ measured by the above dynamic light scattering method to the above mμ
The size of D2 means the degree of elongation of the elongated colloidal silica particles in the same plane.

〔Production method〕

The aqueous alkali metal silicate solution is an aqueous solution of sodium silicate, potassium silicate, etc., and is usually Sl, 02/M
20 (molar ratio, M: alkali metal or quaternary ammonium) is about 1 to 4.5.

The silicic acid solution is an aqueous solution of a low polymer of silicic acid obtained by dealkalizing the same alkali metal silicate aqueous solution as described above by a method such as treatment with a cation exchange resin. This type of silicic acid solution usually has a pH of 2 to 4. SjO□ concentration approximately 7w
Those with a content of t% or less are preferable raw materials because they are relatively stable.

The addition of the silicic acid liquid is carried out at 50°C or lower, preferably 40°C or lower, and the SiO2/M2O of the mixed liquid after addition is 30~30°C.
60, preferably in the range of 35 to 55.

If the SiO2/M2O (mole ratio) is less than 30, the shape of the dispersed particles in the final sol will be close to spherical, and if it exceeds 60, the stability of the sol will deteriorate.

The metal compound used in the present invention includes Sl.

Zr, Al, Ti, In, Sb, Sn, F
e, Cu.

Examples include inorganic and organic salts such as Mg, Ca, and rare earths, and organic compounds such as alkoxides. It may also be a colloid such as a hydrated metal oxide.

The metal compound is usually added as an aqueous solution of one type or a mixture of two or more types.

When the metal compound is a colloid, the metal compound may be added before, simultaneously with, or after the addition of the silicic acid solution. However, when using the metal compound in a form other than a colloid, if the aqueous solution of the metal compound is acidic, it is better to add it at the same time as the silicic acid solution, since if it is blended before adding the silicic acid solution, the mixed solution tends to become unstable.

When adding colloids and other metal salts, they may be added at the same time, or the colloids may be added to an aqueous alkali metal silicate solution in advance, and then the silicate solution and other metal salts may be added. You can also take the following method.

The amount of the metal compound added is 0.5 to 5 (ht%, preferably 5 to 30t%) as an oxide based on the total solid content in the final product.

When the metal compound is a metal salt, the stability deteriorates as the amount of residual salt in the sol increases, so it is preferable that the amount of the metal salt as an oxide does not exceed about 5 ut%.

The mixed liquid to which the silicic acid liquid and the metal compound have been added is then stirred at 60°C or higher, preferably 80 to 95°C for 30 minutes or more.

Through this operation, nucleation and nucleation are carried out for ripening of the mixed solution and single particle growth.

After the aging process, silicic acid solution is added again. At this time, since gelation may occur if a predetermined amount is added at a time, it is preferable to add it gradually. The maturing step stabilizes the connected nuclei, and the re-addition of the silicic acid solution strengthens the connected nuclei.

The amount of silicic acid solution added is such that 5i02/M20 (molar ratio) in the final sol is 60 to 100. Also, the temperature is 6
The temperature is 0°C or higher.

The silica sol obtained as described above may be used as is for the intended purpose, or depending on the purpose,
Concentrate by ultrafiltration, evaporation, etc. Furthermore, by a method such as solvent substitution, an organic solvent such as alcohol or glycol can be substituted to obtain an organic sol.

〔Example〕

Example-1 24w in a 5Ω separable flask with reflux and stirrer
t% (concentration as 5in2) of sodium silicate (Sin
, / Na2O molar ratio 3) 21.5 g was added, and further 300 g of water was added.

Next, 3 wt% sodium silicate (Sin) was added to this solution.
2/Na2O molar ratio 3) was prepared by passing it through a cation exchange resin tower.
A mixture of 2408 g of H2,5) and 31 g of an aluminum chloride aqueous solution of IIIt% (concentration as Al□03) was gradually added with stirring to obtain S10□/Na.
A liquid with a 2O molar ratio of 44.9 was obtained.

Then, the obtained liquid was heated and aged at a temperature of 80° C. for 30 minutes. Thereafter, while the temperature was further maintained at 80°C, 1427 g of 3 wt% silicic acid solution was added to this solution at a rate of 6.4 g/min, and the solid content was 2.89 w at pH 1 O.
A silica sol of t% was obtained.

Next, this silica sol was concentrated using an evaporator to a solid content concentration of 20 wt% to prepare silica sol A.

This silica sol A is diluted with water to give a solid concentration (
Viscosity (ηc, p) at 25°C by changing C, wt%)
was measured using a rotational vibration viscometer (Viscomate VM-LA, manufactured by Yama-Denki Kogyo Co., Ltd.) to determine the value of reduced viscosity (ηsp/C). The relationship between reduced viscosity (ηsp/C) and concentration (C) is shown in Table 1 and FIG. 1. In FIG. 1, the vertical axis represents the reduced viscosity (ηsp/C) on a logarithmic scale, and the horizontal axis represents the concentration (C') on an arithmetic scale. Reduced viscosity of silica sol A (
The value of the straight mA slope Δ[log(rt sp/C)]/ΔC, which shows the correlation between ηsp/C) and concentration (C), is 0;
It was 4.

Example-2 24t in a 5g separable flask with reflux and stirrer
<t% (concentration as S10□) of sodium silicate, (5
io2/Na2O molar ratio 3) 21.5 g was added, and further 300 g of water was added.

Next, 1irt% (A1
20. Sodium aluminate aqueous solution with a concentration of 100
g was added. Then, 3 wt % silicic acid solution (pH 2,5) obtained by passing 3 t = t % sodium silicate into this solution through a cation exchange resin tower was prepared.
8 g was added with stirring to obtain a solution with a 5in2/Na2O molar ratio of 31.3.

Then, the obtained liquid was heated and aged at a temperature of 80° C. for 30 minutes. After that, 6.4 g of 3800 g of 3111 g% silicic acid solution was added to this solution while the temperature was further maintained at 80°C.
, added at a rate of 7 minutes to achieve a solids concentration of 2 at p) 19.5.
．． A 9vt% silica sol was obtained.

Next, this silica sol was concentrated to a solid content concentration of 2 (ht%) using an evaporator to prepare silica sol B.

Regarding this silica sol B, the relationship between the reduction concentration (ηsp/C) and the concentration (C) was determined in the same manner as in Example 1. The results are shown in Table 1 and Figure 1.

Direct graph showing the correlation between the reduced viscosity and concentration of this silica sol B
The value of the slope ΔE log(ηSJ)/C)]/ΔC of B was 0.19.

Comparative Example-1 24t in 5Q separable flask with reflux and stirrer
at% (concentration as SiO□) of sodium silicate (Sx
21.5 g of O□/Na2O molar ratio 3) was added, and further 300 g of water was added.

Next, this liquid was heated and aged at a temperature of 80° C. for 30 minutes. Furthermore, add 3
3wt% silicic acid solution (pH 2,5) obtained by preparing txt% sodium silicate (Sin2/Na2O molar ratio 3) through a cation exchange resin tower 3835
A mixture of 31 g of aluminum chloride aqueous solution of g and t% (concentration as A1203) was added at a rate of 6.4 g/min, and the solid content concentration was 2.9 w at p) 110.1.
A silica sol of t% was obtained.

Next, this silica sol was concentrated to a solid content concentration of 20 vt% using an evaporator to prepare silica sol C.

Regarding this silica sol C, the relationship between reduced viscosity (ηsp/C) and concentration (C) was determined in the same manner as in Example 1. The results are shown in Table 1 and Figure 1.

The value of the slope Δ[log(ηsp/C)]/ΔC of the straight line C showing the correlation between the reduced viscosity and the concentration of this silica sol C is 0.
．． It was 00.

Example-3 In Example-2, instead of adding 100 g of 1 tst% (concentration as Al□03) sodium aluminate aqueous solution, 10 g of 1 wt% (concentration as A120-) sodium aluminate aqueous solution was added. 21 g of 1tvt% (concentration as ZrO2) zirconyl ammonium carbonate aqueous solution
Silica sol D was prepared in exactly the same manner as in Example 2, except that .

In the same manner as in Example 1, the slope of the straight line Δ[log
Properties such as the value of (ηsp/C)]/ΔC are shown in Table 2.

Examples 4 to 9 Silica sols E to 9 were prepared in exactly the same manner as in Example 1, except that instead of adding the aluminum chloride aqueous solution in Example 1, an aqueous solution of the metal compound shown in Table 2 was added. 1J was prepared. The properties of these silica sols are shown in Table-2.

Example 10 In Example 2, an aqueous solution of the metal compound shown in Table 2 was added instead of adding an aqueous solution of sodium aluminate, and the amount of silicic acid solution added after heating was changed to 1427 g. , Silica sol K was prepared in exactly the same manner as in Example-2. The properties of this sol are shown in Table 2.

Example 11 Silica vine L was prepared in exactly the same manner as in Example 2, except that instead of adding the sodium aluminate aqueous solution, an aqueous solution of the metal compound shown in Table 2 was added. The properties of this silica sol are shown in Table 2.
t% (concentration as Sj02) of sodium silicate (Sin
2/Na2O molar ratio 3)2], 5 g was added, and further 300 g of water was added.

Next, 3 wt% of sodium silicate (S]0 was added to this solution.
2/Na2O molar ratio 3) was prepared by passing it through a cation exchange resin column.
pH2,5) 1900g,! l: 1 wt% (
Al□0. A mixture of aluminum chloride aqueous solution 3], g of a specific concentration) was gradually added with stirring to obtain a solution with a S]0□/Na2O molar ratio of 36.1.

Then, the obtained liquid was heated to a temperature of 70'C for 30
Aged for minutes. Thereafter, while the temperature was further maintained at 70°C, 6.4 g of 3tyt% silicic acid solution was added to this solution.
g at a rate of 7 minutes to obtain a silica sol with a pH of 10.0 and a solid content concentration of 9 wt%.

Next, this silica sol was treated in the same manner as in Example-1 to prepare silica sol M. The properties of this silica sol are shown below.
Shown in 2.

Example-13 24-
t% (concentration as S]02) of sodium silicate (Sin
21.5 g of 2/Na2 (molar ratio 3) was added, and further 300 g of water was added.

Then, 3 wt% of silica soda (Sj0
3 wt% silicic acid solution (pH
2,5) A mixture of 3]00 g and 31 g of an aluminum chloride aqueous solution of ]ut% (concentration as A120.) was gradually added with stirring to form a solution with a S]02/Na2O molar ratio of 57.0. Obtained.

The resulting liquid was then heated and aged at a temperature of 90'C for 30 minutes. Thereafter, 7.3% of 3 wt% silicic acid solution was added to this solution while maintaining 90'Cj2. ”+g to 6
．． It was added at a rate of 4 g/min to obtain a silica sol with a pH of 9.9 and a solid content concentration of 2.9 wt%.

Next, this silica sol was treated in the same manner as in Example-1 to prepare silica sol N. The properties of this silica sol are shown below.
2, Example-] 4 In a 5FJ separable flask with a reflux device and a stirrer, 24
-t% (concentration as Sin2) of sodium silicate (Si
30.0 g of n2/\a20 molar ratio 3) was added, and further 300 g of water was added.

Next, this sodium silicate aqueous solution had an average particle size of 170
4kt% (concentration as SiO□) Silica sol [Catalyst Chemical Industry Co., Ltd., Cataloid 5I-40] 45g
was added. Then, 1808 g of 3 wt % silicic acid solution (pH 2,5) obtained by passing 3 wt % sodium silicate into this liquid through a cation exchange resin column.
was gradually added with stirring, and then 2 wt% (
Concentration as ZrO□) Add 50g of zirconyl ammonium carbonate aqueous solution to make SiO□/N820 molar ratio 30
．． A liquid No. 8 was obtained.

The resulting liquid was then heated and aged at a temperature of 80'C for 30 minutes. Thereafter, while maintaining the temperature at 80°C, 3000 g of 3vt% silicic acid solution was added to this solution at a rate of 6.4g/min to obtain a solid content concentration of 2°9vt at pH 9.5.
% of silica sol was obtained.

Next, this silica sol was treated in the same manner as in Example-1 to prepare silica sol ○. The properties of this silica sol are shown below.
Shown in 2.

Comparative Example-2 21.5 g of 24-t% (concentration as SiO□) sodium silicate (SjO2/\820 molar ratio 3) was placed in a 10Q autoclave container, and 300 g of water was added.

Next, 3 wt% sodium silicate (Sin) was added to this solution.
2/Na2O molar ratio 3) was prepared by passing it through a cation exchange resin tower.
H2,5) 3835 g were added. and.

This solution was heated at a temperature of 150°C for 60 minutes, and the pH was adjusted to 9.
3, a silica sol with a solid content concentration of 2*9 bt% was obtained.

Next, this silica sol was concentrated using an evaporator to a solid content concentration of 20t; t% to prepare silica sol P.

The properties of this silica sol are shown in Table-2.

Comparative Example-3 24w in a 5Q separable flask with reflux and stirrer
t% (concentration as Sin2) of sodium silicate (510
2/11ia20 molar ratio 3) 21.5g was added, and further 300g of water was added.

Next, 3 tpt% of sodium silicate (Si) was added to this solution.
3 t% silicic acid liquid (p
H2,5) A mixture of 3835 g and 31 g of aluminum chloride aqueous solution at 11°C% (concentration as A'l□03) was gradually added with stirring to form SiO□/Na2.
A liquid with an O molar ratio of 69.8 was obtained.

Then, the obtained liquid was heated and aged at 80°C for 30 minutes, and then further heated to a solid content concentration of 2 (ht%) using an evaporator.
When the solution was concentrated to 100%, the solution turned into a gel.

Table 11 [Effects] According to the present invention, it is possible to provide a new type of silica sol having excellent properties such as high bonding strength when used as a binder and no cranking in the film when used as a film, and a method for producing the same. did it.

[Brief explanation of drawings]

FIG. 1 is a graph showing the correlation between reduced viscosity and concentration of the silica sols obtained in Examples 1 and 2 and Comparative Example 1, respectively. FIG. 2 is a transmission electron micrograph of the silica particle structure of silica sol A obtained in Example 1, and FIG. 3 is a transmission electron micrograph of the silica particle structure of silica sol P obtained in Comparative Example 2. It's a photo. Patent applicant: Catalysts Chemical Industry Co., Ltd. Representative Patent Attorney Eiji Tomo Matsu ・′・, -2
Effect Figure 1 □ Concentration C (w?%) Figure 3

Claims (1)

[Claims] 1. The slope of the straight line showing the correlation between reduced viscosity (ηsp/C) and silica concentration (C) (Δ[log(ηsp/C)]/Δ
A silica sol characterized in that C) satisfies the following relationship. 0.02≦Δ[log(ηsp/C)]/ΔC≦0.2
02. (a) Silicic acid solution is added to an aqueous alkali metal silicate solution containing 0.05 to 5.0 wt% as SiO_2 to form a mixed solution of SiO_2/M_2
Step (b) of setting O (molar ratio, M is an alkali metal or quaternary ammonium) to 30 to 60: Ca, Mg, Al, In, Ti before, during or after the silicic acid solution addition step. , Zr, Sn,
Step of adding a compound of one or more metals selected from the group consisting of Si, Sb, Fe, Cu, and rare earth metals (c) Maintaining this mixed solution at an arbitrary temperature of 60 ° C. or higher for a certain period of time Step (d) A method for producing silica sol comprising the step of adding a silicic acid solution to the reaction solution again to adjust the SiO_2/M_2O (molar ratio) in the reaction solution to 60 to 100.