Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-03-09
2003-12-02
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S436000, C106S438000
Reexamination Certificate
active
06656261
ABSTRACT:
BACKGROUND OF THE INVENTION
Titanium dioxide (TiO
2
) is an important pigment in the manufacture of paints, plastics, and coatings. There has been a considerable research effort to make titanium dioxide pigments with desirable properties (i.e., fine particle size, gloss and durability).
Titanium dioxide 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. These processes are well known in the art.
Anatase and rutile forms of TiO
2
differ not only in their crystallographic structures but also in the type and amount of surface and other impurities resulting from their differing methods of production. These impurities can cause particle agglomeration, effect particle size distribution and ultimately pigment gloss and/or durability.
The prior art discloses adding different chemicals before or during titanium dioxide formation to prevent unwanted growth and agglomeration of titanium dioxide that may effect gloss and durability in the end product. For example, in the chloride process, titanium dioxide is made by reacting titanium tetrachloride (TiCl
4
) with oxygen. The prior art describes adding aluminum trichloride (AlCl
3
) with TiCl
4
to promote substantially rutile titanium dioxide formation. One way to reduce particle size and agglomerates is to add a silicon halide (i.e. silicon tetrachloride). The reaction between silicon tetrachloride (SiCl
4
) and oxygen results in the formation of silica that reduces the sintering rate of titania and results in smaller particles and fewer agglomerates. Unfortunately, SiCl
4
addition promotes unwanted anatase that may result in a less durable pigment.
Other prior art references disclose treating titanium dioxide after the pigment is produced. For example, the prior discloses improving gloss and durability of titanium dioxide pigment by coating or wet treating the pigment with inorganic compounds. Wet treatment processes are well known in the art and typically involve precipitating hydrous oxide coatings onto the titanium dioxide pigment from metal salt solutions. Some pigment coatings include oxides and hydroxides of alumina, silica, zirconium and phosphate. These wet treatment processes can result in a more durable pigment with improved gloss.
In general, inorganic coatings are known to improve durability, dispersibility and/or gloss of the titanium dioxide pigment. However, some coatings cause the formation of agglomerates that tend to cause difficulties in dispersing pigments into various compositions thereby reducing gloss and durability.
Based on the foregoing, there is still a need for titanium dioxide pigments that have improved gloss and/or durability. These pigments are useful in the manufacture of paints, plastics, and other coating systems.
SUMMARY OF THE INVENTION
The present invention provides titanium dioxide pigments with reduced particle size, improved gloss and/or durability and methods of making these pigments. Preferred titanium dioxide pigments of the present invention are substantially free from sulfate.
In one embodiment, the present invention provides a method for preparing titanium dioxide pigment having improved gloss and/or durability comprising: treating titanium dioxide with a plurality of metal salts under conditions suitable to form the titanium dioxide pigment having improved gloss and/or durability, wherein at least one of the plurality of metal salts is capable of providing a monovalent anion.
In another embodiment, the present invention provides a method for preparing titanium dioxide pigment, having improved gloss and/or durability comprising: wet treating titanium dioxide with an alumina compound, a zirconia compound capable of providing a monovalent anion and a phosphate compound under conditions suitable to form the titanium dioxide pigment having improved gloss and/or durability.
In still another embodiment, the present invention provides a method for preparing titanium dioxide pigment having improved gloss and/or durability, comprising: wet treating an aqueous slurry of titanium dioxide with an alumina compound, a zirconia compound capable of providing a monovalent anion and a phosphate compound under conditions suitable to form the titanium dioxide pigment having improved gloss and/or durability.
In one exemplary embodiment, the present invention provides a titanium dioxide pigment having improved gloss and/or durability produced by a method comprising: wet treating titanium dioxide with an alumina compound, a zirconia compound capable of providing a monovalent anion and a phosphate compound under conditions suitable to form the titanium dioxide pigment having improved gloss and/or durability.
In another exemplary embodiment, the present invention provides a titanium dioxide pigment having improved gloss and/or durability produced by a method comprising: wet treating an aqueous slurry of titanium dioxide with an alumina compound, a zirconia compound capable of providing a monovalent anion and a phosphate compound under conditions suitable to form the titanium dioxide pigment having improved gloss and/or durability.
In yet another exemplary embodiment, the present invention provides, a substantially sulfate-free titanium dioxide pigment having improved gloss and/or durability comprising: titanium dioxide base surface treated with an alumina compound, a zirconia compound and a phosphate compound.
For a better understanding of the present invention together with other and further embodiments, reference is made to the following description taken in conjunction with the examples, the scope of which is set forth in the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
In preparing the preferred embodiments of the present invention, various alternatives may be used to facilitate the objectives of the invention. These embodiments are presented to aid in an understanding of the invention and are not intended to, and should not be construed to, limit the invention in any way. All alternatives, modifications and equivalents that may become obvious to those of ordinary skill upon reading the present disclosure are included within the spirit and scope of the present invention.
This disclosure is not a primer on TiO
2
pigment production, basic concepts known to those skilled in the field of TiO
2
production have not been set forth in detail. Concepts such as choosing appropriate reactor, additives for TiO
2
pigment production, or suitable conditions for wet treatment (i.e., temperature, pH, residence times, etc) are readily determinable by those skilled in the industry and are generally described in the prior art. Attention is therefore directed to the appropriate texts and references known to those skilled in the art with regard to these matters.
The titanium dioxide pigments of the present invention are prepared starting with titanium dioxide base particles. Titanium dioxide base particles are produced commercially in two crystalline forms, namely the rutile form which is usually produced by the chloride and sulfate processes and the anatase form which is usually produced by the sulfate process. Both of these processes are well known to those skilled in the art. The present invention is applicable to both the rutile and anatase forms of TiO
2
pigment.
Preferably, the base titanium dioxide pigment is substantially free from metal salts capable of generating polyvalent anions i.e., sulfate anions (SO
4
2−
). Thus, the present invention contemplates treating titanium dioxide base with at least one metal salt capable of generating monovalent anions. Suitable metal salts capable of generating monovalent anions include silicon halides, such as SiBr
4
, SiF
4
, SiI
4
, SiCl
4
, alumina halides, i.e., AlCl
3
, AlBr
3
and AlI
3
, and zirconia halides, such as, ZrCl
4
. These metal salts can be introduced into the reactor before or during TiO
2
formation by methods known in the art.
As used herein, substantially sulfate-free means that the Ti
Burniston Robert
Stratton John
Tear Brian
Kalow David A.
Kalow & Springut LLP
Koslow C. Melissa
Manlove Shalie
Millennium Inorganic Chemicals, Inc.
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