Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-16
2003-05-27
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S437000, C524S497000
Reexamination Certificate
active
06569920
ABSTRACT:
BACKGROUND
Titanium dioxide (TiO
2
) pigments are important pigments in the manufacture of paints, plastics, coatings and paper laminates. Titanium dioxide (TiO
2
) is produced commercially in two crystalline polymorphic forms, namely the rutile form which can be produced by both the chloride and sulfate processes and the anatase form which is produced by the sulfate process. Both of these processes are well known in the art. Generally, in the “chloride” process, rutile crystal is produced while in the sulfate process, both rutile and anatase crystals can be produced.
With regards to rutile TiO
2
it is known to add volatile aluminum compounds in the oxidation reaction of titanium tetrachloride (TiCl
4
), primarily to increase the rutile content of the TiO
2
pigment being produced. Typically, the amount of aluminum compound added is sufficient to form about 1 to 1.5 weight-percent alumina based on the TiO
2
pigment, and this amount helps achieve greater than 99 weight-percent rutile in the pigment. The resulting TiO
2
from the oxidation reaction is then subjected to certain finishing and grinding treatments depending on the desired type of final TiO
2
pigment product.
Finishing and grinding treatment often involve the steps of: a) dispersing the TiO
2
particles in an aqueous medium to form a slurry having a relatively low TiO
2
solids concentration; b) precipitating hydrous inorganic oxide coating, such as for example, alumina, silica and/or other compounds, onto the surface of the TiO
2
particles; c) recovering the inorganic oxide surface-treated TiO
2
particles from the aqueous medium by filtering; d) washing the TiO
2
particles to remove by-product salts and impurities; e) drying the washed TiO
2
pigment particles; f) dry-grinding the dried TiO
2
pigment particles to a desired particle size using a fluid-energy mill, and optionally, if an aqueous TiO
2
pigment slurry is desired, g) dispersing the pigment product in water to produce a slurry typically having a TiO
2
solids content of below about 78 weight-percent.
The titanium dioxide may be finished depending on the end-use application (i.e., paint, plastic etc). For example, some finishing steps involve wet surface treatments with other inorganic metal oxides, such as alumina, silica, phosphate, CeO
2
and the like, for processibility and/or final applications as known in the art. The surface treatment steps then follow by drying and grinding. These steps will give the finished pigment the desired particle size, distribution and properties.
Generally, concentrated rutile TiO
2
slurry products are made by dispersing the finished pigment product in water to produce a slurry having a TiO
2
solids content below about 78 weight-percent. Slurries with solids contents greater than 78 weight-percent typically exhibit negative effects on stability and other physical properties (i.e. difficultly pumping, flocculation, gellation and poor or no fluidity over time).
Slurry stability may be further reduced when the rutile TiO
2
is treated with an inorganic oxide such as amorphous alumina. Dispersants are often added to such slurries to make it maintain viscosity and storage stability so that it can easily be handled during transport from the TiO
2
manufacturers to the customers. However, some prior art slurries, even with dispersants, tend to gel during conventional storage making them difficult to pump and transport.
Based on the foregoing, there is a need for titanium dioxide slurries having improved stability which are useful in the manufacture of paper laminates, plastic, paint and other coatings systems.
SUMMARY OF THE INVENTION
The present invention relates to photodurable slurries having improved stability that comprise: i) below about 78 weight-percent rutile titanium dioxide based on the total weight of the slurry, with a surface treatment comprising an amorphous alumina compound; ii) a polyacrylic acid dispersing agent having a weight average molecular weight (Mw) in the range of from about 2,000 to about 5,000, that is neutralized with a neutralizing agent having a monovalent group, and iii) water, wherein the slurry has a pH of from about 6 to about 8.
Compared to prior art slurries, the slurries of the present invention exhibit improved stability and a reduced tendency toward gellation over time. Accordingly, one advantage of the stable slurries of the present invention is that they can be easily handled and transported to other sites such as a paper laminate manufacturing facilities, while they maintain free flowing and pumpable characteristics.
In another embodiment, the present invention provides methods of making slurries having improved stability comprising mixing rutile titanium dioxide, surface-treated with an amorphous alumina compound, with water and a polyacrylic acid dispersing agent having a molecular weight in the range of from about 2,000 to about 5,000 under conditions so as to form the slurry, wherein the dispersing agent is neutralized with a neutralizing agent having a monovalent group, the mixing is performed at a pH of from about 6 to about 8 and wherein the rutile titanium is present in an amount below about 78 weight-percent based on the total weight of the slurry.
The improved stable slurries of the present invention enable many end-use improvements and expand the limits within which many end users, such as paper manufacturers, were heretofore required to operate.
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Hua Duen-Wu
Wen Fu-Chu
Cain Edward J.
Kalow David A.
Kalow & Springut LLP
Millennium Inorganic Chemicals, Inc.
Schmidt William D.
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