Titanium dioxide pigments

There are provided titanium dioxide pigments characterized by improved gloss developing and dispersibility properties in surface coating vehicles and reduced dispersant requirements. Said titanium dioxide pigments comprise pigmentary titanium dioxide particles having deposited thereon a treating agent comprising at least one amine salt of a monoprotic.

FIELD OF THE INVENTION 
The present invention relates to titanium dioxide pigments characterized by 
their improved gloss developing and dispersibility properties in surface 
coating vehicles and by their reduced dispersant requirements. More 
specifically, the present invention relates to pigmentary titanium dioxide 
particles having adsorbed on the surfaces thereof a treating agent 
comprising an amine salt of a monoprotic acid. 
BACKGROUND OF THE INVENTION 
Pigmentary titanium dioxide is the most widely used white pigment in 
commerce today. Its pre-eminence is due, in the main, to its extraordinary 
combination of properties including little or no adsorption of visible 
light, high refractive index, high opacity and the ability to confer 
durability to coatings containing this pigment. However, regardless of the 
pre-eminence of this pigment much effort has been and continues to be 
expended to further improve its performance. This particularly is true 
with regard to efforts to reduce the pigment's dispersant requirements to 
improve its gloss developing and dispersibility characteristics. 
Many proposals have been made in the art for improving the gloss developing 
and dispersibility characteristics of pigmentary titanium dioxide. In 
general, these proposals have involved the treatment of the pigment with a 
diversity of organic substances of various descriptions. For example, U.S. 
Pat. No. 3,015,573 discloses the treatment of dry titanium dioxide 
pigments with amine salts prepared from water soluble tertiary amines such 
as triethanolamine with sparingly water soluble organic acids such as 
adipic acid. According to this patent, the use of sparingly water soluble 
organic acids, i.e., acids having water solubilities in the range of from 
0.05 to 2.0 weight percent, to prepare the amine salt treating agents is 
essential if pigments that are more readily dispersible in both organic 
and aqueous media are to be obtained, a major objective of the invention 
of this patent. In addition to being more readily dispersible, the 
pigments described in this patent are said to exhibit a greater tendency 
to dry flow and to form as few as 20 percent of the oversize aggregates 
which said pigment would otherwise form. The other principal physical 
properties, e.g., oil adsorption, color, gloss and the like are 
substantially unaffected and remain substantially those of the 
corresponding pigments without the amine salt. 
In a similar manner, U.S. Pat. No. 3,506,466 discloses the chemical 
treatment of pigmentary titanium dioxide to improve its dispersibility. 
According to this patent, amine salts prepared from alkanolamines such as 
triethanolamine, triisopropanolamine, and the like and oxycarboxylic acids 
such as citric acid, tartaric acid, and the like are capable of improving 
the dispersibility of pigmentary titanium dioxide as well as other 
properties thereof including tinting strength and scattering coefficient. 
The amine salts are applied either in pure form or dissolved in water and 
added to an aqueous slurry of the pigment. The slurry then is dried and 
the dried pigment subjected to fluid energy milling. 
U.S. Pat. No. 3,825,438 discloses the coating of titanium dioxide pigment 
with one or more hydrous metal oxides in the presence of a polyhydric 
alcohol and/or a carboxylic acid. The alcohols and/or the acids useful in 
the practice of the invention of this patent are those that contain at 
least two hydroxyl groups, which term is defined to include the hydroxyl 
groups present in the carboxyl groups of the acids. In accordance with the 
teachings of this patent, while the alcohols and/or acids can be added to 
the titanium dioxide pigment at any convenient stage, it is essential that 
such addition be accomplished prior to completion of the deposition of the 
hydrous metal coating. The resulting pigment is said to have improved 
dispersibility when compared with a pigment coated in the absence of these 
alcohols and/or acids. In addition, such treatment is said to further 
improve one or more of the gloss, hiding power, stoving color and drying 
time of the pigment produced using this treatment. 
A treatment specifically directed to improving the gloss developing 
properties of titanium dioxide pigment is disclosed in U.S. Pat. No. 
3,173,722. According to the disclosure of this patent, the gloss 
developing properties of titanium dioxide pigments are improved by 
treating a wet milled hydrous metal oxide coated titanium dioxide pigment 
with a combination of either benzoic or para-aminobenzoic acid and an 
amine such as triethanolamine. The treatment merely comprises adding the 
acid and amine to the pigment and, without removing these materials from 
the pigment, milling the pigment to produce a finely divided, high tinting 
strength material having greatly improved gloss developing properties. 
It is evident from the above art disclosure that many different chemical 
treatments have been proposed to improve various physical properties of 
titanium dioxide pigments. This is particularly true with respect to 
improving the dispersibility and dry flow characteristics of titanium 
dioxide pigment. However, many of the chemical treatments proposed would 
appear to be specific for improving only that property of the pigment 
which it is desired to improve. At best, other properties remain 
substantially the same as the corresponding untreated pigment or, at 
worst, are adversely affected by the treatment. 
The present invention is directed principally to the chemical treatment of 
titanium dioxide pigments to improve the dispersibility of the pigment in 
surface coating vehicles. Surprisingly, however, the pigments so treated 
further exhibit significantly improved gloss developing properties and 
lower dispersant demands. 
SUMMARY OF THE INVENTION 
The present invention relates to titanium dioxide pigments having improved 
dispersibility and gloss developing properties in surface coating vehicles 
and reduced dispersant requirements. Particularly, the titanium dioxide 
pigments of this invention comprise pigmentary titanium dioxide particles 
having adsorbed on the surface thereof, a treating agent comprising an 
amine salt of a monoprotic acid. 
The invention further relates to a method for treating titanium dioxide 
pigments with said amine salts to provide the improved titanium dioxide 
pigments of the invention. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention arises from the discovery that amine salts described 
below will, when applied to the surface of a titanium dioxide pigment, 
impart to said pigment improvements in certain of the physical properties 
thereof. These improvements include an increase in the dispersibility of 
said pigment in a surface coating vehicle, an increase in the gloss 
developing properties of said pigment and a reduction in the dispersant 
requirement. These improvements are obtained whether the pigment 
undergoing treatment is a bare or noncoated pigment or a coated pigment, 
i.e., a pigment having one or more materials such as the known hydrous 
oxides of the metals aluminum, titanium, zirconium, cerium, silicon, zinc, 
and the like deposited thereon. 
The preferred amine salts which can be used to prepare the improved 
titanium dioxide pigments of this invention are dimethylolpropionic acid 
(DMPA)+triisopropanolamine (TIPA), DMPA+TIPA+trimethylolethane (TME), and 
DMPA+TIPA+trimethylolpropane (TMP), dimethylolbutanoic acid (DMBA)+TIPA, 
DMBA+TIPA+TME, and DMBA+TIPA+TMP. 
Advantageously, the amine salts employed to produce the titanium dioxide 
pigments of this invention contain a molar ratio of from about 1:1::1:2, 
preferably from about 1:1::1:1.1, dimethylolpropionic acid or 
dimethylolbutanoic acid to triisopropanolamine, thus producing a neutral 
salt with or without excess alkanolamine. Preferably such amine salts 
contain a ratio of from about 95:5::1:1 amine salts to trimethylolethane. 
The amine salts of this invention also preferably contain a ratio of from 
about 95:5::1:1 amine salts to trimethylolpropane. 
Known alkanolamines useful in preparing the amine salts of the present 
invention are disclosed in U.S. Pat. No. 4,752,340. It has been discovered 
that triisopropanolamine (TIPA) is preferred in this application. 
The amine salts employed to produce the improved titanium dioxide pigments 
of the present invention can be used as preformed solutions or they can be 
formed in situ in the presence of the pigment to be treated. When this 
latter procedure is employed, one more convenient means for accomplishing 
the formation of the acid or amine salt and its adsorption by the pigment 
is by metering the pigment and the desired acid and amine into a grinding 
apparatus known as a fluid energy mill. Examples of such mills are 
disclosed in U.S. Pat. No. 2,032,827 and U.S. Pat. No. 2,219,011. In using 
such mills, the pigment is introduced as a jet into a stream of 
superheated steam circulating through the mill at extremely high 
velocities whereby the pigment particles are entrained in said steam and 
caused to collide with each other with great force. The small amounts of 
the acid and amine required to produce the amine salt either can be 
metered directly into the mill or into the pigment stream as said stream 
enters the mill. The collisions which occur between the pigment particles 
within the mill spread the acid or amine salt uniformly over the surface 
of the colliding particles. 
Generally, the amine salts disclosed hereinabove and used to prepare the 
improved titanium dioxide pigments of this invention will be employed in 
the form of preformed solutions. A preformed solution is prepared simply 
by adding the desired quantity of the acid or amine to a suitable solvent. 
Such solvent can be any organic liquid or, preferably, water. This 
preformed solution then is added to the pigment in any convenient manner 
including adding the solution to a slurry of the pigment, spraying the 
solution onto the pigment or metering the preformed solution into a fluid 
energy mill for treatment of the pigment therein in a manner similar to 
that discussed above. 
Whether employed as a preformed solution or formed in situ during the 
milling of the pigment to be treated with the amine salt, the amounts of 
amine salt will be amounts sufficient to result in an essentially neutral 
condition (i.e., having a pH of from about 6.0 to about 8/0). 
The amount of the amine salt added to or formed in situ and deposited on 
the surface of the titanium dioxide pigment will range from about 0.01 to 
about 3.0 weight percent based on the weight of the pigment. Preferred 
amounts range from about 0.2 to about 0.5 weight percent. 
In a preferred embodiment of this invention, the titanium dioxide pigments 
to which the amine salts described hereinabove can be applied will be 
those pigments upon which has been deposited one or more coatings of a 
hydrous oxide of a metal selected from the group consisting of aluminum, 
titanium, zirconium, cerium, silicon, zinc, and the like. Methods for 
depositing such hydrous metal oxide coatings upon bare titanium dioxide 
pigments are well known. While such methods may vary with respect to the 
particular processing conditions employed, most of these methods utilize 
similar procedures for forming the coating of the hydrous metal oxide on 
the pigment particles. Thus, in general, a water soluble salt or compound 
of aluminum, titanium, zirconium, cerium, silicon, zinc, and the like is 
first mixed with an aqueous dispersion or solution of the titanium dioxide 
pigment to be coated. After addition of the water soluble salt or compound 
the pH of the aqueous dispersion or solution is altered to effect the 
precipitation of the desired hydrous metal oxide onto the pigment. When 
the added water soluble salt or compound produces an acid pH condition in 
the aqueous dispersion or solution of the pigment, then it is necessary to 
alter this pH by the addition of an alkali to effect precipitation of the 
hydrous metal oxide. When the added water soluble salts or compounds 
produce an alkaline pH then it is necessary to add an acid to produce the 
desired precipitation. However, in these methods it is possible to employ 
acid reacting and basic reacting water soluble salts or compounds to 
effect the desired precipitation thereby eliminating the need for any 
separate addition of acids or alkali. 
Generally, in applying a coating of a hydrous metal oxide to the titanium 
dioxide pigment any water soluble hydrolysable salt may be used to provide 
the coating of the hydrous metal oxide. Thus, salts such as aluminum 
sulfate, aluminum nitrate, titanium sulfate, titanium tetrachloride, 
zirconium sulfate, cerium sulfate and zinc sulfate can be employed. Alkali 
metal aluminates may be employed in place of the water soluble aluminum 
salts. Generally, hydrous silicon oxide or silica coatings are provided 
through the use of water soluble silicates such as the alkali metal 
silicates as represented by sodium silicate. 
The above described general methods for applying hydrous metal coatings to 
the titanium dioxide pigment, and which methods do not form any part of 
the present invention, can be carried out either in a batchwise manner or 
continuously. In a continuous operation, the water soluble salts or 
compounds of one or more of the metals of aluminum, titanium, zirconium, 
cerium, silicon, zinc, and the like will be added to a continuous flowing 
stream of the aqueous dispersion of the titanium dioxide pigment. 
The amount of the hydrous metal oxide or oxides deposited onto the titanium 
dioxide pigment can vary over a wide range, but usually will be at least 
about 0.05 weight percent and can be up to about 15 weight percent. A more 
preferred range for the amounts of the hydrous metal oxide or oxides 
deposited on the pigment will range from about 0.5 weight percent to about 
10 weight percent based on the weight of the pigment. 
Most preferred titanium dioxide pigments for use in preparing the improved 
titanium dioxide pigments of this invention are those titanium dioxide 
pigments having deposited thereon one or more hydrous metal oxides 
selected from the group consisting of alumina, silica and titanium oxides. 
As noted throughout this disclosure, the amine salts described hereinabove 
are capable of providing titanium dioxide pigments characterized by 
increased dispersibility and gloss developing properties in surface 
coating vehicles and lower dispersant requirements in water base coatings. 
The magnitude of the increases in dispersibility and gloss developing 
properties and reduction in dispersant demand is significant, particularly 
when compared to untreated pigment or pigment treated with more 
conventional materials, e.g., polyols such as trimethylolethane, or other 
amine salts such as those described in U.S. Pat. No. 4,752,340. However, 
the greatest benefit provided by the titanium dioxide pigments of this 
invention is in their significantly improved dispersant requirement in 
water based coatings when compared to other amine salts. 
The invention is further described and illustrated by the examples which 
follow. The examples represent specific embodiments of the invention and 
are not to be construed as limitations thereon.

EXAMPLES 1-14 
Examples 1-14 are finished pigment samples representative of the improved 
titanium dioxide pigment of the present invention. In general, each of 
Examples 1-14 was prepared by first blending a particular amine salt 
solution as disclosed herein with a particular commercially produced 
titanium dioxide base pigment, i.e., a pigment having deposited thereon 
coatings of one or more hydrous metal oxides and requiring final dry 
milling and classification. Each of the resulting pigment/amine salt 
blends was subjected to milling to provide the finished pigments 
comprising Examples 1-14. 
In order to determine the gloss, scatter, tint strength, and dispersant 
demand improvements using the present invention, a set of experimental 
pigments were produced. Base pigments were sandmilled to approximately 
98%&lt;0.49.mu. and micronized at 1.8 steam/pigment. The milling aids used 
and results are given in Table 1. 
TABLE 1 
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RESULTS FROM MILLING AID STUDY 
Excess Tint Dispersant 
Example 
Base 
Milling Aid 
TIPA 
Gloss 
Scatter 
Strength 
Demand 
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1 1 other amine salt 
64 6.16 
713 0.84 
2 1 TME 61 6.03 
693 0.67 
3 1 RMP 62 6.10 
701 0.71 
4 1 DMPA/TIPA 
N 64 6.14 
733 0.61 
5 1 DMPA/TIPA 
Y 64 6.07 
722 0.64 
6 1 DMPA/TIPA 
Y 63 6.20 
711 0.64 
7 1 DMPA Y 63 6.14 
696 0.58 
8 2 other amine salt 
61 6.18 
670 0.93 
9 2 TME 59 6.15 
627 0.53 
10 2 TMP 58 6.10 
635 0.67 
11 2 DMPA/TIPA 
N 61 6.16 
635 0.55 
12 2 DMPA/TIPA 
N 61 6.21 
645 0.60 
13 2 DMPA/TIPA 
Y 60 6.27 
676 0.65 
14 2 DMPA Y 61 6.19 
670 0.65 
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As can be seen the Polyols (TME and TMP) gave good dispersant demand, but 
lower gloss and tint strength. The other amine salts gave higher (worse) 
dispersant demand, but good gloss and tint strength. The amine salt of the 
present invention resulted in both low dispersant demand and good gloss 
and tint strength. 
While this invention has been described and illustrated by the Examples 
shown, other variations may be employed within the scope of the following 
claims.