METHOD FOR PRODUCING SILICA SOL HAVING ELONGATED PARTICLE SHAPE
20200392004 ยท 2020-12-17
Assignee
Inventors
- Satoru MURAKAMI (Sodegaura-shi, JP)
- Takuya FUKUOKA (Sodegaura-shi, JP)
- Kazuya KUROIWA (Sodegaura-shi, JP)
Cpc classification
C01P2004/61
CHEMISTRY; METALLURGY
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
C01P2004/62
CHEMISTRY; METALLURGY
International classification
Abstract
A method for producing a silica sol containing a small amount of metal impurities and wherein colloidal silica having an elongated particle shape is dispersed in a solvent, by addition of a compound as an anion source and ammonia as an alkali source and heating of the resultant mixture at a predetermined temperature, includes the following steps: (a) preparing a raw material liquid by adding at least one compound as an anion source selected from the group of inorganic acids, organic acids, and ammonium salts of these acids, and ammonia to a silica sol as a raw material having SiO.sub.2 of 1% by mass to 30% by mass and a pH of 2 to 5 so the mass ratio of the compound to SiO.sub.2 is 0.5% to 1.9%; and (b) heating the raw material liquid prepared in step (a) at 80 C. to 200 C. for 0.5 hours to 20 hours.
Claims
1. A method for producing a silica sol containing elongated amorphous colloidal silica particles dispersed in a liquid medium and having an SiO.sub.2 concentration of 6% by mass to 30% by mass, wherein the silica particles contained in the silica sol exhibit a D.sub.L/D.sub.B ratio of 2.5 or more and a D.sub.L of 30 nm to 300 nm wherein D.sub.L is an average particle diameter (nm) as measured by the dynamic light scattering method, and D.sub.B is a primary particle diameter (nm) as measured by the nitrogen gas adsorption method, and the silica particles have a particle length of 50 nm to 1,000 nm as determined by observation with an electron microscope, the production method comprising the following steps (a) and (b): (a) a step of preparing a raw material liquid by adding at least one compound as an anion source selected from the group consisting of inorganic acids, organic acids, and ammonium salts of these acids, and ammonia to a silica sol as a raw material having an SiO.sub.2 concentration of 1% by mass to 30% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 0.5% to 1.9%; and (b) a step of heating the raw material liquid prepared in the step (a) at 80 C. to 200 C. for 0.5 hours to 20 hours, to thereby produce a silica sol.
2. The method for producing a silica sol according to claim 1, wherein the silica sol as a raw material used in the step (a) is produced from a colloidal aqueous solution of activated silica prepared by bringing an aqueous alkali silicate solution exhibiting a ratio by mole of SiO.sub.2/M.sub.2O (wherein M is sodium or potassium) of 1 to 4.5 into contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
3. The method for producing a silica sol according to claim 2, wherein the silica sol as a raw material used in the step (a) is produced from a colloidal aqueous solution of activated silica prepared by treating the aqueous alkali silicate solution with a strong acid at a temperature of 1 C. to 98 C., and then bringing the treated aqueous solution into contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
4. The method for producing a silica sol according to claim 2, wherein the silica sol as a raw material used in the step (a) is produced from a colloidal aqueous solution of activated silica prepared by bringing the aqueous alkali solution or the treated aqueous solution into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin before or after contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
5. The method for producing a silica sol according to claim 1, wherein the compound as an anion source used in the step (a) is at least one compound as an anion source selected from the group consisting of nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid, acetic acid, formic acid, oxalic acid, citric acid, lactic acid, malic acid, gluconic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and an ammonium salt of any of these.
6. The method for producing a silica sol according to claim 1, wherein the silica sol as a raw material used in the step (a) contains colloidal particles having a primary particle diameter (D.sub.B or D.sub.s) of 5 nm to 50 nm.
7. The method for producing a silica sol according to claim 1, wherein the ammonia added in the step (a) is in the form of ammonia gas or an aqueous ammonia solution.
8. The method for producing a silica sol according to claim 1, wherein the step (a) comprises a step of adding the compound as an anion source to the silica sol as a raw material, followed by addition of the ammonia.
9. The method for producing a silica sol according to claim 1, wherein the step (a) comprises a step of adding the ammonia to the silica sol as a raw material, followed by addition of the compound as an anion source and subsequent addition of the ammonia.
10. The method for producing a silica sol according to claim 1, wherein the raw material liquid prepared in the step (a) has a pH of 8 to 12.
11. The method for producing a silica sol according to claim 1, wherein, in the step (b), the raw material liquid is heated in an autoclave apparatus at 100 C. to 180 C.
12. The method for producing a silica sol according to claim 1, wherein the method further comprises a step of bringing the silica sol produced in the step (b) into contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin.
13. The method for producing a silica sol according to claim 12, wherein the method further comprises a step of bringing the silica sol produced in the step (b) into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin before or after contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin.
14. The method for producing a silica sol according to claim 1, wherein the method further comprises a step of replacing the aqueous medium of the produced silica sol with an organic medium.
15. The method for producing a silica sol according to claim 1, wherein the mass ratio of each of Ca and Mg to SiO.sub.2 is 0.01 ppm to 50 ppm in the silica sol.
16. The method for producing a silica sol according to claim 1, wherein the mass ratio of Na to SiO.sub.2 is 0.1 ppm to 50 ppm, and the mass ratio of K to SiO.sub.2 is 0.1 to 50 ppm in the silica sol.
17. The method for producing a silica sol according to claim 1, wherein the amorphous colloidal silica particles exhibit a D.sub.L/D.sub.B ratio of 3 to 30 wherein D.sub.L is an average particle diameter (nm) as measured by the dynamic light scattering method, and D.sub.B is a primary particle diameter (nm) as measured by the nitrogen gas adsorption method.
18. The method for producing a silica sol according to claim 1, wherein the silica sol is an acidic silica sol or an ammonia-containing alkaline silica sol.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0038]
[0039]
[0040]
[0041]
[0042]
[0043]
[0044]
[0045]
[0046]
[0047]
MODES FOR CARRYING OUT THE INVENTION
[0048] The present invention is directed to a method for producing a silica sol containing elongated amorphous colloidal silica particles dispersed in a liquid medium and having an SiO.sub.2 concentration of 6% by mass to 30% by mass, wherein the silica particles contained in the silica sol exhibit a D.sub.L/D.sub.B ratio of 2.5 or more and a D.sub.L of 30 nm to 300 nm wherein D.sub.L is an average particle diameter (nm) as measured by the dynamic light scattering method, and D.sub.B is a primary particle diameter (nm) as measured by the nitrogen gas adsorption method, and the silica particles have a particle length of 50 nm to 1,000 nm as determined by observation with an electron microscope, the production method comprising the following steps (a) and (b):
[0049] (a) a step of preparing a raw material liquid by adding at least one compound as an anion source selected from the group consisting of inorganic acids, organic acids, and ammonium salts of these acids, and ammonia to a silica sol as a raw material having an SiO.sub.2 concentration of 1% by mass to 30% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 0.5% to 1.9%; and
[0050] (b) a step of heating the raw material liquid prepared in the step (a) at 80 C. to 200 C. for 0.5 hours to 20 hours, to thereby produce a silica sol.
[0051] The aforementioned liquid medium is an aqueous medium (water) or an organic medium (organic solvent).
[0052] The mass ratio of the compound as an anion source to SiO.sub.2 may be adjusted to fall within a range of 0.5 to 1.9%, or 0.5 to 1.9, or 0.5 to 1.5.
[0053] The principle of measurement of the average particle diameter D.sub.L (nm) is based on the dynamic light scattering method. For example, the average particle diameter can be measured with a dynamic light scattering particle diameter measuring apparatus (Zetasizer Nano, available from Spectris Co., Ltd.). The average particle diameter D.sub.L (nm) measured by the dynamic light scattering method falls within a range of 30 nm to 300 nm.
[0054] The primary particle diameter D.sub.B (nm) is calculated from the following formula: (D.sub.B nm)=2720/S wherein S is a specific surface area (m.sup.2/g) measured by the nitrogen gas adsorption method (BET method). The primary particle diameter refers to the diameter of a virtual spherical silica particle having a specific surface area equal to that of an elongated silica particle. Thus, the D.sub.L/D.sub.B ratio probably corresponds to the degree of elongation of a silica particle. An elongated silica particle neither has a three-dimensional aggregation structure formed of particles, nor has a three-dimensional network structure. An elongated silica particle has a structure in which particles are connected in a rosary form or a chain form. Conceivably, silica particles having the same particle diameter and/or different particle diameters are connected in a rosary form or a chain form.
[0055] In the present invention, the D.sub.L/D.sub.B ratio is 2.5 or more and may be, for example, 2.5 to 50.0, or 3.0 to 30.0, or 3.0 to 15.0.
[0056] The particle length of the silica particles can be determined by observation of the particle shape with an electron microscope (transmission electron microscope). The length is 50 nm to 1,000 nm or 100 nm to 700 nm.
[0057] The silica sol as a raw material used in the step (a) can be produced from a colloidal aqueous solution of activated silica prepared by bringing an aqueous alkali silicate solution exhibiting a ratio by mole of SiO.sub.2/M.sub.2O (wherein M is sodium or potassium) of 1 to 4.5 into contact with an ion exchange resin, for example, a strong acid-type cation exchange resin, or both a strong acid-type cation exchange resin and a strong base-type anion exchange resin.
[0058] The colloidal aqueous solution of activated silica can be produced by preparing the aforementioned aqueous alkali silicate solution so as to have a solid content of 1% by mass to 10% by mass, and then bringing the aqueous alkali silicate solution into contact with the ion exchange resin. The solid content as used herein corresponds to the total amount of all components of the aqueous solution or the silica gel, except for the amount of the aqueous medium or organic medium component. The aqueous alkali silicate solution may be prepared by dilution of commercially available sodium silicate No. 1, No. 2, or No. 3 with, for example, pure water.
[0059] The strong acid-type cation exchange resin is a hydrogen-type cation exchange resin, and the hydrogen-type cation exchange resin may be prepared by passing an aqueous strong acid solution through a cation exchange resin charged in a column. Specific examples of the strong acid-type cation exchange resin include Amberlite IR-120B, Amberjet 1020, and DOWEX MARATHON GH (available from The Dow Chemical Company); Diaion SK104 and Diaion PK208 (available from Mitsubishi Chemical Holdings Corporation); and Duolite C20J (available from Sumika Chemtex Company, Limited).
[0060] The strong base-type anion exchange resin is a hydroxyl group-type anion exchange resin, and the hydroxyl group-type anion exchange resin may be prepared by passing an aqueous strong alkali solution through an anion exchange resin charged in a column. Specific examples of the strong base-type anion exchange resin include Amberlite IRA400J, Amberlite IRA410J, and Amberjet 4400 (available from The Dow Chemical Company); Diaion SA10A and Diaion SA20A (available from Mitsubishi Chemical Holdings Corporation); and Duolite UBA120 (available from Sumika Chemtex Company, Limited).
[0061] The aforementioned colloidal aqueous solution of activated silica used may have an SiO.sub.2 solid content of 1% by mass to 10% by mass, preferably 1% by mass to 6% by mass.
[0062] The silica sol as a raw material used in the step (a) can be produced from the colloidal aqueous solution of activated silica prepared by further bringing the solution into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin.
[0063] Such a chelating resin contains two or more electron-donating atoms such as N, S, O, and P. Examples of such a chelating resin include NO type, SN type, NN type, and OO type chelating resins; for example, iminodiacetic acid-type (N(CH.sub.2COO).sub.2) and polyamine-type (NH(CH.sub.2CH.sub.2NH)nH) chelating resins. Specific examples of the aforementioned chelating resin include Diaion CR11, Diaion CR20, Diaion CRB03, and Diaion CRB05 (available from Mitsubishi Chemical Holdings Corporation). A chelating resin containing adsorbed metal ions can be recycled by removing the metal ions with an aqueous mineral acid solution (aqueous hydrochloric acid solution or aqueous sulfuric acid solution).
[0064] The silica sol as a raw material used in the step (a) can be produced from the colloidal aqueous solution of activated silica highly purified by repeatedly bringing the solution into contact with the aforementioned ion exchange resin or chelating resin.
[0065] The column can be filled with the aforementioned ion exchange resin or chelating resin, and the aforementioned aqueous solution can be passed through the column at a space velocity of 1 h.sup.1 to 30 h.sup.1 or 1 h.sup.1 to 15 h.sup.1.
[0066] The silica sol as a raw material used in the step (a) can be highly purified through production of the silica sol from the colloidal aqueous solution of activated silica prepared by treating the solution with a strong acid at a temperature of 1 C. to 98 C., and then bringing the treated solution into contact with a strong acid-type cation exchange resin or with both a strong acid-type cation exchange resin and a strong base-type anion exchange resin. The colloidal aqueous solution of activated silica probably contains colloidal fine particles (e.g., a particle diameter of 5 nm or less, or 3 nm or less, or 1 nm or less) formed in the aqueous solution. In some cases, such colloidal particles may contain metal impurities. When the metal impurities contained in the colloidal particles cannot be removed with the ion exchange resin or the chelating resin, the colloidal aqueous solution of activated silica can be treated with an aqueous acid solution at 1 C. to 98 C., preferably at room temperature, to thereby elute the metal impurities from the interior of the colloidal particles into the aqueous solution. The metal impurities are separated (through adsorption) from the aqueous solution by bringing the solution into contact with the aforementioned ion exchange resin or chelating resin. Thus, the purity of the colloidal aqueous solution of activated silica can be increased, to thereby increase the purity of the finally produced silica sol.
[0067] The silica sol as a raw material used in the step (a) may be a silica sol containing colloidal particles having a primary particle diameter (D.sub.B or D.sub.S) of 5 nm to 50 nm, or 5 nm to 30 nm, or 5 nm to 10 nm.
[0068] The primary particle diameter of colloidal particles contained in the silica sol can be measured by a common method, such as the Sears titration method or the nitrogen adsorption method.
[0069] The silica sol as a raw material used in the step (a) may be a silica sol having an SiO.sub.2 concentration of 1% by mass to 30% by mass, or 3% by mass to 25% by mass, or 10% by mass to 25% by mass.
[0070] The compound as an anion source used in the step (a) may be at least one compound as an anion source selected from the group consisting of nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid, acetic acid, formic acid, oxalic acid, citric acid, lactic acid, malic acid, gluconic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and an ammonium salt of any of these. For example, an aqueous solution of, for example, nitric acid, sulfuric acid, or oxalic acid may be used. Such an anion source may be added in the form of an ammonium salt, or may be used as an ammonium salt converted by ammonia used for pH adjustment. The concentration of the aqueous solution used may be, for example, 0.1% by mass to 50% by mass, or 0.1% by mass to 10% by mass, or 0.1% by mass to 5% by mass, or 0.1% by mass to 1% by mass, or 0.1% by mass to 0.2% by mass.
[0071] The ammonia used in the step (a) for pH adjustment may be in the form of ammonia gas or an aqueous ammonia solution. The pH adjustment is performed by introducing ammonia gas directly into the silica sol as a raw material, or adding an aqueous ammonia solution to the silica sol as a raw material. The aqueous ammonia solution may be used at a concentration of 28% by mass, or may be used after being diluted with pure water to a concentration of 1% by mass to less than 28% by mass.
[0072] The step (a) includes, for example, a step of adding the aforementioned compound as an anion source to the silica sol as a raw material, followed by addition of the aforementioned ammonia.
[0073] The step (a) includes, for example, a step of adding the aforementioned ammonia to the silica sol as a raw material, followed by addition of the aforementioned compound as an anion source and subsequent addition of the aforementioned ammonia.
[0074] The pH of the raw material liquid prepared in the step (a) (silica sol as a raw material) may be adjusted to 8 to 12, or 9 toll, or 9 to 10.
[0075] The step (b) involves heating of the raw material liquid prepared in the step (a) (silica sol as a raw material) at 80 C. to 200 C., or 100 C. to 180 C., or 120 C. to 150 C. with stirring for 0.5 hours to 20 hours, to thereby produce a silica sol. The heating of the raw material liquid with an autoclave apparatus at a temperature of 100 C. to 200 C. or 100 C. to 180 C. can produce a silica sol containing elongated colloidal particles having a high degree of deformation. An ammonia-containing alkaline silica sol having a pH of 8 to 11 or 9 to 11 is produced through the step (b).
[0076] The silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity. For example, the silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin, or with both a strongly acidic ion exchange resin and a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity.
[0077] The silica sol produced in the step (b) can be brought into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin before or after contact with a strongly acidic ion exchange resin and/or a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity. For example, the silica sol produced in the step (b) can be brought into contact with a carboxylic acid-type chelating resin, a hydroxyl group-type chelating resin, and/or an amine-type chelating resin after contact with a strongly acidic ion exchange resin or with both a strongly acidic ion exchange resin and a strongly basic ion exchange resin, to thereby prepare a silica sol of high purity.
[0078] The silica sol produced in the step (b) may be optionally subjected to concentration with an ultrafiltration membrane, or evaporative concentration under reduced pressure or at ambient pressure, so as to adjust the concentration of SiO.sub.2 to 6% by mass to 30% by mass.
[0079] The silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin, to thereby produce an acidic silica sol.
[0080] The aqueous medium of the aforementioned acidic silica sol can be replaced with an organic medium (organic solvent), to thereby produce an organosilica sol. This solvent replacement can be performed by evaporation with an apparatus such as a rotary evaporator. The solvent replacement does not cause a change in the D.sub.L/D.sub.B ratio of colloidal silica particles.
[0081] Examples of usable organic solvents include alcohols, glycols, esters, ketones, nitrogen-containing solvents, and aromatic solvents. Specific examples of such solvents include organic solvents, such as methanol, ethanol, propanol, ethylene glycol, propylene glycol, glycerin, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether, propylene glycol monoethyl ether acetate, acetone, methyl ethyl ketone, dimethylformamide, N-methyl-2-pyrrolidone, toluene, xylene, and dimethylethane. Other examples of usable solvents include polyethylene glycol, silicone oil, and reactive diluents containing radical-polymerizable vinyl or epoxy groups.
[0082] The surfaces of silica particles may be treated with a silane coupling agent such as tetraethoxysilane, trimethylmonoethoxysilane, or hexamethyldisilane.
[0083] The resultant silica sol may contain Ca and Mg as metal impurities, wherein the mass ratio of Ca to SiO.sub.2 is 0.01 ppm to 100 ppm or 0.01 ppm to 50 ppm, and the mass ratio of Mg to SiO.sub.2 is 0.01 ppm to 100 ppm or 0.01 ppm to 50 ppm.
[0084] The silica sol may also contain Na and K, wherein the mass ratio of Na to SiO.sub.2 is 0.1 ppm to 1,000 ppm or 0.1 ppm to 500 ppm, and the mass ratio of K to SiO.sub.2 is 0.1 ppm to 100 ppm or 0.1 ppm to 50 ppm.
[0085] The silica sol produced in the step (b) can be brought into contact with a strongly acidic ion exchange resin, to thereby prepare an acidic silica sol, and then high-purity ammonia gas or aqueous ammonia solution can be added to the acidic silica sol, to thereby prepare an ammonia-containing alkaline silica sol.
EXAMPLES
[0086] [Evaluation of Physical Properties of Silica Sol] [0087] 1) pH [0088] The pH was measured with a pH meter (available from DKK-TOA CORPORATION). [0089] 2) Electrical conductivity [0090] The electrical conductivity was measured with an electrical conductivity meter (available from DKK-TOA CORPORATION). [0091] 3) SiO.sub.2 concentration [0092] The weighing method was used for measurement. [0093] The mass of SiO.sub.2 was determined from the difference between the mass of a residue obtained by baking of the silica sol at 1,000 C. and the mass of metal elements (in terms of oxide) contained in the silica sol in an amount of 1 ppm or more among all metal elements measured by the metal element analysis as described in 8) below. The SiO.sub.2 concentration was calculated on the basis of the determined mass of SiO.sub.2. [0094] 4) D.sub.L particle diameter (average particle diameter as measured by the dynamic light scattering method) [0095] The D.sub.L particle diameter was measured with a dynamic light scattering particle diameter measuring apparatus (Zetasizer Nano, available from Spectris Co., Ltd.). [0096] 5) D.sub.B particle diameter (primary particle diameter as measured by the nitrogen adsorption method) [0097] An aqueous silica sol was brought into contact with a hydrogen-type strongly acidic cation exchange resin, to thereby remove sodium adsorbed on the surface of the silica sol. Thereafter, the silica sol was dried at 300 C. and then ground to prepare a powder sample. The specific surface area Si (m.sup.2/g) of the resultant powder sample was measured by the BET method with a nitrogen adsorption specific surface area measuring apparatus (Monosorb MS-16, available from Yuasa Ionics Co., Ltd.), to thereby determine the D.sub.B particle diameter (nm). [0098] The D.sub.B particle diameter was calculated by the following formula (II) (through conversion of colloidal silica particles into spherical particles).
D.sub.B(nm)=2720/S.sub.1(m.sup.2/g)(II) [0099] 6) D.sub.S particle diameter (primary particle diameter as measured by the Sears titration method) [0100] Firstly, 1.50 g of a silica gel (solid content) was added to a 200-ml beaker, and about 100 ml of pure water was added to the silica gel to thereby prepare a slurry. Thereafter, 30 g of NaCl was added to and dissolved in the slurry. Subsequently, the pH of the slurry was adjusted to about 3 by addition of 1N-HCl, and then pure water was added so that the volume of the slurry was 150 nil. The slurry was subjected to pH titration with 0.1NNaOH at 25 C., to thereby determine the volume V (ml) of 0.1NNaOH solution required for increasing the pH from 4.00 to 9.00. The specific surface area (S.sub.2) was determined by the Sears titration method, and the primary particle diameter (D.sub.S) was calculated by using the following Formulae (III) and (TV).
S.sub.2(m.sup.2/g)=32V(ml)25(III)
D.sub.S(nm)=2720/S.sub.2(m.sup.2/g)(IV) [0101] 7) Electron microscopic observation [0102] The particles were photographed with a transmission electron microscope (JEM-1010, available from JEOL Ltd.) at an acceleration voltage of 100 kV. For measurement of the particle length (L) of silica particles, a series of silica particles connected in a rosary form and a chain form were regarded as a single particle, and the particle was projected onto a plane. The particle length was defined as the long side of a rectangle circumscribing the projected image and having the smallest area (see
[0106] [Determination of Deformation] [0107] : D.sub.L particle diameter/D.sub.B particle diameter=2.5 or more [0108] Determination of growth of elongated silica particles by observation with a transmission electron microscope. [0109] x: D.sub.L p article diameter/D.sub.B particle diameter=less than 2.5 [0110] Insufficient growth of elongated silica particles. [0111] Gelation: Gelation refers to formation of a gel.
Example 1
[0112] A stirring bar was added to a 500-ml styrol bottle, and the styrol bottle was charged with 363.2 g of an aqueous silica sol [Snowtex (registered trademark) ST-OXS, available from Nissan Chemical Corporation, particle diameter as measured by the Sears method (D.sub.S)=5.0 nm, average particle diameter as measured by the dynamic light scattering method (D.sub.L)=9.0 nm, SiO.sub.2 concentration: 10.5% by mass, produced from an aqueous sodium silicate solution having a ratio by mole of SiO.sub.2/Na.sub.2O of 3.1 to 3.3]. Subsequently, while the silica sol was stirred with a magnetic stirrer, 3.0 g of 10% by mass aqueous nitric acid solution (serving as an anion source) was added, and then 3.7 g of 28% by mass aqueous ammonia solution was added. The resultant mixture was stirred for one hour to thereby prepare a raw material liquid.
[0113] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 2
[0114] A stirring bar was added to a 500-ml styrol bottle, and the styrol bottle was charged with 361.4 g of an aqueous silica sol [Snowtex (registered trademark) ST-OXS, available from Nissan Chemical Corporation, particle diameter as measured by the Sears method (D.sub.S)=5.0 nm, average particle diameter as measured by the dynamic light scattering method (D.sub.L)=9.0 nm, SiO.sub.2 concentration: 10.5% by mass, produced from an aqueous sodium silicate solution having a ratio by mole of SiO.sub.2/Na.sub.2O of 3.1 to 3.3]. Subsequently, while the silica sol was stirred with a magnetic stirrer, 4.5 g of 10% by mass aqueous nitric acid solution (serving as an anion source) was added, and then 4.1 g of 28% by mass aqueous ammonia solution was added. The resultant mixture was stirred for one hour to thereby prepare a raw material liquid.
[0115] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 3
[0116] A sodium-stabilized alkaline aqueous silica sol [Snowtex (registered trademark) ST-14K, available from Nissan Chemical Corporation, primary particle diameter as measured by the nitrogen gas adsorption method (D.sub.B)=7.2 nm, average particle diameter as measured by the dynamic light scattering method (D.sub.L)=16.0 nm, SiO.sub.2 concentration: 18.0% by mass, produced from an aqueous sodium silicate solution having a ratio by mole of SiO.sub.2/Na.sub.2O of 3.1 to 3.3] was passed through a column filled with a hydrogen-type strongly acidic cation exchange resin (Amberlite IR-120B, available from The Dow Chemical Company) and then passed through a column filled with a hydroxyl group-type strongly basic anion exchange resin (Amberlite IRA-410J, available from The Dow Chemical Company), to thereby prepare an acidic aqueous silica sol having an SiO.sub.2 concentration of 13.2% by mass and a pH of 3.9. Subsequently, 132.2 g of 28% by mass aqueous ammonia solution was added to 21,325 g of the acidic aqueous silica sol, to thereby prepare an ammonia-stabilized raw material silica sol.
[0117] A stirring bar was added to a 500-ml styrol bottle, and 71.6 g of pure water was added thereto. While the pure water was stirred with a magnetic stirrer, 294.3 g of the above-prepared ammonia-stabilized raw material silica sol was added, and the resultant mixture was stirred for 10 minutes to achieve homogeneity. Subsequently, 3.3 g of 10% by mass aqueous nitric acid solution (serving as an anion source) was added, and then 0.8 g of 28% by mass aqueous ammonia solution was added. The resultant mixture was stirred for one hour to thereby prepare a raw material liquid.
[0118] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 4
[0119] A raw material liquid of Example 4 was produced in the same manner as in Example 3, except that the amount of pure water was changed to 71.8 g, the amount of 10% by mass aqueous nitric acid solution added was changed to 3.0 g, and the amount of 28% by mass aqueous ammonia solution was changed to 1.0 g.
[0120] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 5
[0121] A stirring bar was added to a 500-ml styrol bottle, and 170.8 g of pure water was added thereto. While the pure water was stirred with a magnetic stirrer, the styrol bottle was charged with 190.6 g of an aqueous silica sol [Snowtex (registered trademark) ST-OS, available from Nissan Chemical Corporation, primary particle diameter as measured by the nitrogen gas adsorption method (D.sub.B)=9.2 nm, average particle diameter as measured by the dynamic light scattering method (D.sub.L)=15.2 nm, SiO.sub.2 concentration: 20.5% by mass, produced from an aqueous sodium silicate solution having a ratio by mole of SiO.sub.2/Na.sub.2O of 3.1 to 3.3], and the mixture was stirred for 10 minutes to achieve homogeneity. Subsequently, 5.2 g of 10% by mass aqueous nitric acid solution (serving as an anion source) was added, and then 3.4 g of 28% by mass aqueous ammonia solution was added. The resultant mixture was stirred for one hour to thereby prepare a raw material liquid. A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 6
[0122] A raw material liquid of Example 6 was produced in the same manner as in Example 3, except that the amount of pure water was changed to 73.1 g, 10% by mass nitric acid serving as an anion source was changed to 0.3 g of oxalic acid dihydrate, and the amount of 28% by mass aqueous ammonia solution was changed to 2.3 g.
[0123] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 7
[0124] A raw material liquid of Example 7 was produced in the same manner as in Example 3, except that the amount of pure water was changed to 70.1 g, 10% by mass nitric acid serving as an anion source was changed to 3.8 g of 8% by mass sulfuric acid, and the amount of 28% by mass aqueous ammonia solution was changed to 1.9 g.
[0125] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 8
[0126] A raw material liquid of Example 9 was produced in the same manner as in Example 3, except that the amount of pure water was changed to 72.7 g, 10% by mass nitric acid serving as an anion source was changed to 1.3 g of ethylenediaminetetraacetic acid (Chelest 3N-50 available from Chelest Corporation, EDTA.H.3(NH.sub.4), containing 50.4% by mass EDTA), and the amount of 28% by mass aqueous ammonia solution was changed to 1.7 g.
[0127] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Example 9
[0128] 130 g of the deformed silica sol produced in Example 6 was sequentially passed through a column filled with a hydrogen-type strongly acidic cation exchange resin (Amberlite IR-120B, available from The Dow Chemical Company), a column filled with a hydroxyl group-type strongly basic anion exchange resin (Amberlite IRA-410J, available from The Dow Chemical Company), and a column filled with a hydrogen-type strongly acidic cation exchange resin (Amberlite IR-120B, available from The Dow Chemical Company), to thereby prepare an acidic silica sol having an SiO.sub.2 concentration of 10.5% by mass and a pH of 5.1. Subsequently, 0.28 g of 28% by mass aqueous ammonia solution was added to 63 g of the acidic silica sol, to thereby prepare an ammonia-stabilized silica sol having a pH of 9.6.
Example 10
[0129] 130 g of the silica sol produced in Example 7 was sequentially passed through a column filled with a hydrogen-type strongly acidic cation exchange resin (Amberlite IR-120B, available from The Dow Chemical Company), a column filled with a hydroxyl group-type strongly basic anion exchange resin (Amberlite IRA-410J, available from The Dow Chemical Company), and a column filled with a hydrogen-type strongly acidic cation exchange resin (Amberlite IR-120B, available from The Dow Chemical Company), to thereby prepare an acidic silica sol having an SiO.sub.2 concentration of 10.5% by mass and a pH of 4.9. Subsequently, 0.29 g of 28% by mass aqueous ammonia solution was added to 68 g of the acidic silica sol, to thereby prepare an ammonia-stabilized silica sol having a pH of 9.6.
Comparative Example 1
[0130] A raw material liquid of Comparative Example 2 was produced in the same manner as in Example 3, except that the amount of pure water was changed to 72.5 g, the amount of 10% by mass nitric acid added was changed to 1.5 g, and the amount of 28% by mass aqueous ammonia solution was changed to 1.7 g.
[0131] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. Thereafter, the resultant silica sol was removed from the autoclave. The silica sol was evaluated according to the aforementioned evaluation of physical properties of silica sol and determination of deformation.
Comparative Example 2
[0132] A raw material liquid of Comparative Example 2 was produced in the same manner as in Example 3, except that the amount of pure water was changed to 63.9 g, the amount of 10% by mass nitric acid added was changed to 7.8 g, and the amount of 28% by mass aqueous ammonia solution was changed to 4.0 g.
[0133] A SUS autoclave (inner volume: 300 ml) was charged with 260 g of the raw material liquid, and the raw material liquid was heated at 140 C. for eight hours and then cooled to room temperature. The product removed from the autoclave was found to undergo gelation.
[0134] Tables 1 to 3 show the silica source, SiO.sub.2 concentration, and pH of the aqueous silica sol used for the production of each of the raw material liquids of Examples 1 to 8 and Comparative Examples 1 and 2, and the type and amount of an anion source added.
[0135] Tables 4 to 6 show the physical properties and heating conditions of the raw material liquids prepared in Examples 1 to 8 and Comparative Examples 1 and 2.
[0136] Tables 7 to 10 show the results of evaluation of the physical properties and determination of deformation of the silica sols produced in Examples 1 to 10 and Comparative Examples 1 and 2.
[0137]
TABLE-US-00001 TABLE 1 (a) Raw material liquid Example 1 Example 2 Example 3 Example 4 Raw material silica Silica sol Silica sol Silica sol Silica sol source SiO.sub.2 concentration 10.5 10.5 13.2 3.6 (wt %) pH 2.8 2.8 3.9 2.9 Anion source Nitric acid Nitric acid Nitric acid Nitric acid Anion/silica (wt %) 0.8 1.2 0.9 0.8
TABLE-US-00002 TABLE 2 (a) Raw material liquid Example 5 Example 6 Example 7 Example 8 Raw material silica Silica sol Silica sol Silica sol Silica sol source SiO.sub.2 concentration 20.5 13.2 13.2 13.2 (wt %) pH 2.6 3.9 3.9 3.9 Anion source Nitric acid Oxalic acid Sulfuric acid EDTA Anion/silica (wt %) 1.3 0.6 0.8 1.4
TABLE-US-00003 TABLE 3 Comparative Comparative (a) Raw material liquid Example 1 Example 2 Raw material silica source Silica sol Silica sol SiO.sub.2 concentration (wt %) 13.2 13.2 pH 3.9 3.9 Anion source Nitric acid Nitric acid Anion/silica (wt %) 0.4 2.0
TABLE-US-00004 TABLE 4 Example 1 Example 2 Example 3 Example 4 (a) Physical properties of raw material liquid pH 9.6 9.6 9.6 9.2 Electrical conductivity 3570 4380 3830 3080 S/cm (b) Heating conditions Temperature ( C.) 140 140 140 140 Time (hr) 8 8 8 8
TABLE-US-00005 TABLE 5 Example 5 Example 6 Example 7 Example 8 (a) Physical properties of raw material liquid pH 9.6 9.6 9.7 9.6 Electrical conductivity 4210 3530 3940 3530 S/cm (b) Heating conditions Temperature ( C.) 140 140 140 140 Time (hr) 8 8 8 8
TABLE-US-00006 TABLE 6 Comparative Comparative Example 1 Example 2 (a) Physical properties of raw material liquid pH 9.6 9.6 Electrical conductivity S/cm 2480 3830 (b) Heating conditions Temperature ( C.) 140 140 Time (hr) 8 8
TABLE-US-00007 TABLE 7 Physical properties of silica sol Example 1 Example 3 pH 10.0 9.9 Electrical conductivity S/cm 2820 3080 D.sub.L particle diameter (nm) 32.3 55.5 D.sub.B particle diameter (nm) 11.6 12.8 D.sub.L/D.sub.B ratio 2.8 4.3 Deformation Particle diameter (nm) by observation 108 491 with electron microscope SiO.sub.2 % by mass 10.3 10.5 Na/SiO.sub.2 (ppm) 753 198 K/SiO.sub.2 (ppm) 4 1 Mg/SiO.sub.2 (ppm) 11 1 Ca/SiO.sub.2 (ppm) 10 6
TABLE-US-00008 TABLE 8 Exam- Exam- Exam- Exam- Physical properties of silica sol ple 5 ple 6 ple 7 ple 8 pH 9.8 10.0 10.0 9.9 Electrical conductivity S/cm 3820 2800 3140 2810 D.sub.L particle diameter (nm) 66.7 42.7 73.6 47.3 D.sub.B particle diameter (nm) 12.4 12.9 12.8 12.8 D.sub.L/D.sub.B ratio 5.4 3.3 5.7 3.7 Deformation Particle diameter (nm) by 538 223 446 169 observation with electron microscope SiO.sub.2 % by mass 10.6 10.5 10.5 10.5 Na/SiO.sub.2 (ppm) 814 345 347 358 K/SiO.sub.2 (ppm) 5 12 3 5 Mg/SiO.sub.2 (ppm) 10 12 11 13 Ca/SiO.sub.2 (ppm) 12 6 5 6
TABLE-US-00009 TABLE 9 Physical properties of silica sol Example 9 Example 10 pH 9.4 9.3 Electrical conductivity S/cm 596 566 D.sub.L particle diameter (nm) 42.7 73.6 D.sub.B particle diameter (nm) 12.9 12.8 D.sub.L/D.sub.B ratio 3.3 5.7 Deformation Particle diameter (nm) by observation 223 446 with electron microscope SiO.sub.2 % by mass 10.3 10.2 Na/SiO.sub.2 (ppm) 2.9 3.2 K/SiO.sub.2 (ppm) 0.6 0.3 Mg/SiO.sub.2 (ppm) 0.2 0.6 Ca/SiCO.sub.2 (ppm) 0.5 1.5
TABLE-US-00010 TABLE 10 Compar- Compar- Physical properties of silica Exam- Exam- ative ative sol ple 2 ple 4 Example 1 Example 2 pH 9.2 9.6 10.0 Gelation Electrical conductivity S/cm 3610 2540 2010 Gelation D.sub.L particle diameter (nm) 122.6 55.2 27.3 Gelation D.sub.B particle diameter (nm) 11.7 14.8 13.9 Gelation D.sub.L/D.sub.B ratio 10.5 3.7 2.0 Gelation Deformation X Gelation Particle diameter (nm) by 509 564 43 Gelation observation with electron microscope SiO.sub.2 % by mass 10.3 10.5 10.5 Gelation
INDUSTRIAL APPLICABILITY
[0138] A silica sol which contains a small amount of metal impurities and in which colloidal silica having an elongated particle shape is dispersed in a solvent can be readily produced by addition of a compound as an anion source and ammonia as an alkali source to a silica sol and heating of the resultant mixture at a predetermined temperature.
[0139] A silica sol containing non-spherical silica particles is expected to exhibit various effects (e.g., bonding force, adsorption force, and optical transparency) depending on the shape of the particles. Thus, the silica sol can be used in a variety of applications including microfillers for various coating agents, binders, modifiers, catalyst carriers, and abrasives for electronic materials (e.g., an abrasive for a silicon wafer, and a CMP abrasive for a device wafer for polishing a silicon oxide film or a metal such as copper or aluminum).