Method for producing purified active silicic acid solution and silica sol

Patent metadata

Field	Value
Publication number	US-10550300-B2
Application number	US-201615205571-A
Country	US
Kind code	B2
Filing date	Jul 8, 2016
Priority date	Sep 16, 2011
Publication date	Feb 4, 2020
Grant date	Feb 4, 2020

Abstract

A method for producing an active silicic acid solution in which the existing amount of foreign matters as plate-like fine particles is reduced and a method for producing a silica sol in which such foreign matters are reduced. The method fulfills the following condition; the existing amount of plate-like fine particles having a length of one side of 0.2 to 4.0 μm and a thickness of 1 to 100 nm is measured to be 0% to 30% in accordance with measuring method A, the method including the steps of: preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components; and filtering the active silicic acid solution through a filter whose removal rate of particles having a primary particle size of 1.0 μm is 50% or more.

First claim

The invention claimed is:

1. A method for producing a purified active silicic acid solution, the method comprising:
preparing an active silicic acid solution by subjecting an alkali silicate aqueous solution having a silica concentration of 0.5% by mass to 10.0% by mass to cation-exchange to remove alkaline components wherein the active silicic acid solution that is prepared contains an amount of plate-like fine particles having a length of one side of 0.2 to 4.0 μm and a thickness of 1 to 100 nm; and
filtering the active silicic acid solution through a filter selected from the group consisting of a membrane filter, a pleated filter, a depth filter, a yarn-wound filter, a surface filter, a roll filter, a pleated depth filter, a diatomaceous-earth-containing filter, and combinations thereof, the filter having:
a removal rate of particles having a primary particle size of 1.0 μm of 50% or more, and
a filtering rate in a range of from 13 L/min to 400 L/min per 1 m 2 of a filtration area of the filter;

wherein:
an amount of plate-like fine particles having a length of one side of 0.2 to 4.0 μm and a thickness of 1 to 100 nm in the purified active silicic acid solution is in a range of from 0% to 30% as measured by a measuring method A;
the measuring method A comprises:
observing under a scanning electron microscope at a magnification of 5,000 times a membrane filter through which 30 mL of a solution to be observed has been passed, the solution to be observed having a silica concentration of 4% by mass and a temperature of 25° C., and the membrane filter having a filtration area of 4.90 cm 2 and an absolute pore size of 0.4 μm;
measuring as one count a state in which one or more of the plate-like fine particles exist within one visual field area having a length of 15 μm and a width of 20 μm; and
determining the presence or absence of the count with respect to each visual field area of 100 non-overlapping visual field areas to measure a total number of counts as the amount (%) of the plate-like fine particles; and

the solution to be observed in the measuring method A is the purified active silicic acid solution.

2. The method according to claim 1 , wherein the removal rate is 60% or more.

3. The method according to claim 1 , wherein the removal rate is 70% or more.

4. The method according to claim 1 , wherein the removal rate is 80% or more.

5. The method according to claim 1 , wherein the removal rate is 90% or more.

6. The method according to claim 1 , wherein the filter is a membrane filter having an absolute pore size of 0.3 μm to 3.0 μm.

7. The method according to claim 1 , wherein the alkaline components of the alkali silicate aqueous solution are at least one selected from the group consisting of a sodium ion, a potassium ion, a lithium ion, a rubidium ion, and a cesium ion.

8. A method for producing a silica sol, the method comprising:
adding the purified active silicic acid solution produced by the method according to claim 1 into an alkaline aqueous solution to obtain a mixture; and
heating the mixture to polymerize active silicic acid;

wherein an amount of plate-like fine particles having a length of one side of 0.2 to 4.0 μm and a thickness of 1 to 100 nm in the silica sol is in a range of from 0% to 30% as measured by the measuring method A in which the solution to be observed is the silica sol.

9. The method according to claim 8 , wherein the alkaline components of the alkaline aqueous solution are at least one selected from the group consisting of an alkali metal ion, an ammonium ion, amine, and a quaternary ammonium ion.

10. The method according to claim 1 , wherein
the amount as measured by the measuring method A of the plate-like fine particles in the purified active silicic acid solution is reduced relative to an amount as measured by the measuring method A of the plate-like fine particles contained in the active silicic acid solution.

11. The method according to claim 1 , wherein the alkali silicate aqueous solution has a silica concentration in a range of from 0.5% by mass to 4% by mass.

12. The method according to claim 1 , wherein the filter is selected from the group consisting of a pleated filter, a depth filter, a yarn-wound filter, a surface filter, a roll filter, a pleated depth filter, a diatomaceous-earth-containing filter, and combinations thereof.

13. The method according to claim 1 , wherein the active silicic acid solution contains an amount of the plate-like fine particles as measured by the measuring method A in a range of from 73% to 75%.

Assignees

• Nissan Chemical Ind Ltd

Inventors

• Ema Kiyomi
• Takakuma Noriyuki
• Nishimura Tohru
• Kawashita Naoki
• Yamaguchi Kouji

Classifications

• C09K3/1463 Primary

  Aqueous liquid suspensions · CPC title

• C01B33/1435

  using ion exchangers · CPC title

• C01B33/1412

  by oxidation of silicon in basic medium · CPC title

• C01B33/141 Primary

  Preparation of hydrosols or aqueous dispersions · CPC title

• C01B33/1485

  Stabilisation, e.g. prevention of gelling; Purification · CPC title