Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2000-06-27
2002-11-26
Metzmaier, Daniel S. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C423S338000, C106S482000, C162S181600
Reexamination Certificate
active
06486216
ABSTRACT:
BACKGROUND OF THE INVENTION
Colloidal silicas are known materials that are known to be useful in papermaking to enhance the retention and drainage of pulps used to make paper.
U.S. Pat. Nos. 5,643,414 and 5,368,833 describe a colloidal silica microparticle consisting of high surface area, i.e., greater than 700 m
2
/g and an S-value between 20 and 40 which is useful in papermaking. These patents teach the need for surface treatment of the colloidal silica particle with aluminum in order to stabilize the surface area and thereby the product. U.S. Pat. No. 5,603,805 also describes a colloidal silica having a surface area less than 700 m
2
/g and with an S-value of 20 to 40 which can be used in the making of paper. This patent clearly teaches that surface areas of less than 700 m
2
/g are needed in order to obtain a stable colloidal silica product without aluminum surface treatment that is useful in the paper making application.
It would be highly useful to have additional colloidal silica aquasols available for use in various applications, including papermaking applications.
SUMMARY OF THE INVENTION
The instant claimed invention is a stable aquasol comprising colloidal silica having a surface area of from about 700 m
2
/g to about 1100 m
2
/g, and an S-value of from about 20 to about 50; wherein said colloidal silica is not surface treated; wherein the molar ratio of SiO
2
/Na
2
O in said colloidal silica is greater than about 13.0:1 and is less than about 17.0:1; and wherein said aquasols have a percent by weight SiO
2
solids level of from about 7.00 percent to about 16.80 percent.
DETAILED DESCRIPTION OF THE INVENTION
The instant claimed invention is a stable aquasol comprising colloidal silica having a surface area of from about 700 m
2
/g to about 1100 m
2
/g, and an S-value of from about 20 to about 50; wherein said colloidal silica is not surface treated; wherein the molar ratio of SiO
2
/Na
2
O in said colloidal silica is greater than about 13.0:1 and is less than about 17.0:1; and wherein said aquasols have a percent by weight SiO
2
solids level of from about 7.00 percent to about 16.80 percent.
These stable aquasols are useful in the application of making paper.
Contrary to the teachings of the known art, the aquasols of the present invention advantageously provide a colloidal silica that remains stable without the addition of an aluminum surface treatment. Furthermore, the colloidal silica aquasols of the present invention advantageously exhibit excellent activity not only in alkaline furnishes but also in acid furnishes in papermaking. The colloidal silica aquasols of the present invention are useful, among other areas, in the papermaking industry, for example, as retention and dewatering aids.
The aquasols of the present invention comprise colloidal silica having a surface area of from about 700 m
2
/g to about 1100 m
2
/g. The surface area is determined using the Sears Method, as described in
Anal. Chem.,
28, 1981(1956). Preferably the colloidal silica has a surface area greater than about 700 m
2
/g, more preferably greater than about 790 m
2
/g, and most preferably greater than about 857 m
2
/g. Preferably, the colloidal silica has a surface area less than about 1100 m
2
/g, more preferably, less than about 970 m
2
/g.
The colloidal silica in the aquasols has an S-value, of from about 20 to about 50, preferably from about 22.5 to about 50. The S-value is determined using the procedure described in
J. Phys. Chem
., Iler and Dalton, 60, 955(1956).
As used herein, a “stable aquasol” is defined as one comprising colloidal silica with a surface area above 700 m
2
/g and whose S-value remains in the range of from about 20 to about 50 as the aquasol is aged at room temperature for a period of at least 30 days. Aquasols of the present invention can be produced and stored and remain stable at room temperature for at least 30 days.
Aquasols of the present invention can be produced and stored at concentrations of from about 7.00 percent by weight SiO
2
solids to about 16.80 percent by weight SiO
2
solids. More preferably the percent by weight SiO
2
solids is from about 7.00 percent to about 14.00 percent. Most preferably, the percent by weight SiO
2
solids is from about 11.50 percent to about 13.70 percent.
Aquasols of the present invention can be made by following this process. A process for making a stable colloidal silica aquasol comprising:
(a) forming a heel, with said heel containing water, an alkali metal silicate wherein the molar ratio of SiO
2
to Na
2
O or K
2
O is greater than about 1:1 and is less than about 15:1; an acid (and/or a corresponding salt thereof), wherein said heel has a pH of at least 10, wherein the alkali metal silicate and acid are initially present in a ratio by weight of at least 63:1, wherein the temperature of the heel is below 100 degrees F.;
(b) adding to the initial composition an aqueous silicic acid composition typically having a SiO
2
content in the range of from about 5.0 to about 7.2 percent by weight, while maintaining the temperature of the composition below 100 degrees F., wherein the aqueous silicic acid composition is added slowly and continuously until from about one-half to about three-quarters of the silicic acid composition has been added to the initial composition;
(c) increasing the temperature of the composition from below 100 degrees F. to between about 115 degrees F. and about 125 degrees F. in a time period of from about 10 to about 35 minutes, and maintaining the temperature until the addition of all the silicic acid composition is complete;
(d) optionally, maintaining the temperature of the composition below 125 degrees F for about an hour; and
(e) discontinuing the heating and
(f) optionally removing water from the resulting composition until the solids content based on SiO
2
of the resulting aquasol is at least about 7.00 percent by weight.
The process begins with the preparation of an initial composition, known as a “heel”, followed by addition of a source of active silica, usually in the form of silicic acid or polysilicic acid, over a specified time. In the above process, the initial heel is composed of water, any of a number of commercially available silicates or alkali water glasses, and an acid and/or a corresponding salt thereof in a prescribed ratio. While the order of addition is not important, for purposes of ease of manufacture, it has been discovered that the acid preferably should be added to the dilution water, prior to the addition of the silicate.
During the addition of the active silica, the reaction temperature is controlled within a specified reaction temperature profile. The alkali water glasses or silicates can be any number of conventional materials. These are normally potassium or sodium salts. The mole ratio of SiO
2
to Na
2
O or K
2
O, is from about 1:1 to about 15:1 and is preferably within the range of from about 2.5:1 to 3.9:1. Such water glass solutions typically will have a pH in excess of 10, typically around 11.
The acid used in the above process can be any number of organic or mineral acids. Examples of such acids include, but are not limited to: mineral acids such as hydrochloric, phosphoric or sulfuric or such materials as carbon dioxide. Organic acids include but are not limited to: acetic acid, formic acid and propionic acid. Examples of suitable salts include: sodium sulfate, sodium acetate, potassium sulfate, potassium acetate, trisodium phosphate and sodium monohydrogen phosphate.
Once the heel is prepared in the above process, the temperature of the composition is reduced to 85 degrees F. or lower, typically to 80 degrees F. or lower, and usually in a range of from 60 to 85 degrees F. At this point, silicic acid or poly silicic acid is slowly added to the composition, for example over a total period of about 4 hours. Silicic acid suitable for the present invention can be prepared via known methods in the art, such as the cation exchange of dilute solutions of alkali water glasses as described above. Typically, the dilute solutions contain from 3.0 to 9.0 percent
Huang Cheng-Sung
Keiser Bruce A.
MacDonald Dennis L.
Nunn Maureen B.
Breininger Thomas M.
Brumm Margaret M.
Metzmaier Daniel S.
Ondeo Nalco Company
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