Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-02-07
2003-04-01
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S419000, C106S440000, C106S442000, C106S444000, C106S449000, C106S456000, C106S461000, C106S467000
Reexamination Certificate
active
06540824
ABSTRACT:
TECHNICAL FIELD
The present invention relates to titanium-iron complex oxide pigments producing a yellow color for use in coloring plastics, ceramics, coating compositions, etc. and processes for preparing the same.
BACKGROUND ART
Complex oxide pigments of the pseudo-brookite type are known as titanium-iron inorganic pigments which produce a yellow color.
The specification of U.S. Pat. No. 4,036,662 discloses pigments of pseudo-brookite and of pseudo-brookite and rutile in mixture which are represented by Fe
2
TiO
5
•xTiO
2
wherein x is 0 to 15. According to the disclosure, the color tone is adjustable by varying the mixing ratio of Fe
2
TiO
5
and TiO
2
. The specification states that fine particles, up to 1 &mgr;m in mean size, are obtained by mixing the materials in the form of aqueous suspensions, dehydrating the mixture and thereafter calcining the mixture at a temperature of 600 to 1100° C., and that a yellow pigment is available by making the calcining atmosphere reductive with use of carbon black or a like reducing agent. However, the pigment obtained by the above method still remains to be improved in saturation, tinting strength and covering power for use in coloring plastics and coating compositions of which high functions are required.
Fukuji Suzuki prepared Fe
2
TiO
5
of the pseudo-brookite type by mixing titanium oxide of the anatase type and alpha-iron oxide (hematite) and calcining the mixture of 1100 to 1200° C. in the atmosphere [“Shikizai (coloring materials),” 57(12)652-659, 1984]. Although this method starts to produce Fe
2
TiO
5
at a temperature of not lower than 800° C., the reaction mixture needs to be heated to 1200° C. for the completion of the reaction. The method therefore has the drawbacks of requiring a high calcining cost for preparing the product at such a high temperature and necessitating much time for pulverization since the reaction mixture has been calcined to a great extent. Additionally, the resulting product Fe
2
TiO
5
has the same composition as the product of the foregoing U.S. patent wherein x is 0, and is insofar in saturation, tinting strength and covering power.
JP-A No. 8-73224(1996) discloses a process for preparing complex oxide pigments of the pseudo-brookite type represented by Al
x
Fe
2-x
TiO
b
•yTiO
2
wherein 0<x≦1 and 0≦y. According to the disclosure, intensely yellow finely particulate complex oxide pigments having high saturation are prepared by dispersing or dissolving oxides, hydroxides or water-soluble salts of iron and aluminum in a hydrated titanium oxide slurry, causing the resulting slurry to produce a coprecipitate at a suitable pH, and washing the coprecipitate with water, followed by filtration, drying and calcining at a temperature of about 800 to about 1100° C. This process nevertheless involves limitations to starting materials, requires complex equipment and steps and is high in production cost.
Thus, titanium-iron complex oxide pigments of pseudo-brookite are produced by mixing titanium oxide or metatitanic acid with an iron oxide, iron hydroxide or water-soluble iron salt in a predetermined ratio in a dry or wet state, or causing an aqueous solution of water-soluble salts of titanium and iron to undergo coprecipitation and washing the precipitate, followed by drying to obtain a material mixture, and calcining the mixture in air or a reducing atmosphere at a temperature of 800 to 1200° C. In the calcining step, Ti, Fe or O from particles of one of the materials diffuse into those of the other, thereby giving rise of a reaction to form and grow pseudo-brookite crystals. To industrially manufacture a stabilized product, especially iron-containing complex oxides, by such a solid-phase reaction, the stability of the materials to be used, the stability of the materials as mixed together and the stability of calcining operation are of extreme importance.
The materials, especially iron compounds, such as iron oxides or iron hydroxides, are easily oxidized or reduced by a slight change in temperature and atmosphere. Accordingly, it is difficult to obtain materials which always exhibit constant reactivity during calcining, hence limitations of the materials usable. Further when materials are mixed together which are different in specific gravity, particle size or bulkiness, segregation is liable to occur in the mixture being prepared by mixing or as prepared by mixing owing to the difference in specific gravity or particle size, presenting difficulty in affording a material mixture of uniform composition.
Further since mass transfer between the particulate materials is a rete controlling factor of the reaction, low temperatures lead to a low reaction rate to result in low productivity, quantity manufacture of the desired product on an industrial scale requires a high temperature for calcining.
Because the iron oxide or iron hydroxide in the material mixture is easily oxidized or reduced by a slight change in the temperature or atmosphere, a product of uniform color is not available unless the calcining temperature and atmosphere are controlled closely.
It is known well that when iron-containing complex oxide pigments are to be manufactured with good stability and with uniform color produced, it is necessary to use materials of high quality as controlled strictly, to hold the materials as uniformly mixed at all times and to calcine the mixture with the temperature, time and atmosphere controlled strictly. These requirements make the equipment and process complex and result in an increased manufacturing cost.
In view of the foregoing problems, an object of the present invention is to provide a yellow pigment which contains a titanium-iron complex oxide of the pseudo-brookite type and produces a stabilized color more yellowish than conventionally and which is universally usable for coloring plastics, ceramics and coating compositions.
DISCLOSURE OF THE INVENTION
The present applicant previously proposed a process for producing a yellow pigment of the rutile type by mixing titanium oxide, oxide of one of Co, Cr and Ni and oxide of one of Sb, Nb and W, grinding the resulting composition by a dry method using a mill to prepare composite particles by utilizing a mechanochemical reaction, and calcining the particles [see JP-A No. 10-219134 (1988)]. The process is adapted for the production of complex oxide pigments of the rutile type such as Ti-Sb-Cr, Ti-Sb-Ni, Ti-Nb-Co or Ti-W-Ni.
The present inventors have subsequently conducted research for the production of yellow pigments and found that a pseudo-brookite complex oxide pigment of outstanding characteristics can be obtained by applying a mechanochemical reaction to titanium-iron material particles to prepare composite particles, followed by calcining.
Stated more specifically, the present invention provides a first complex oxide pigment, i.e., a titanium-iron complex oxide pigment which is characterized in that the pigment contains a pseudo-brookite complex oxide represented by:
the composition formula (M
1-x
•Fe
x
)O•TiO
2
or
the composition formula (Fe
1-y
•Al
y
)
2
O
3
•TiO
2
wherein M is one of the bivalent metals Mg, Sr and Z, the ratios of Fe, Al and M to Ti are in the respective ranges of 0.3≦Fe/Ti≦4.5, 0≦Al/Ti≦6.5, and 0≦M/Ti≦2.6, and x and y are in the respective ranges of 0≦x<1 and 0≦y<1.
The present invention further provides a process for producing the first complex oxide pigment. This process is characterized by mixing particulate starting materials for Ti, Fe, Al and M in specified proportions, grinding the resulting particulate composition in a dry state to give the composition energy sufficient to cause a mechanochemical reaction, join the particles to one another and prepare composite particles wherein the elements Ti, Fe, Al and M are present, and calcining the composite particles at 700 to 1200° C.
The present invention provides a second complex oxide pigment, i.e., a titanium-iron complex oxide pigment which is characterized in that the pigment contains a
Kataoka Koji
Suzuki Takayuki
Armstrong Westerman & Hattori, LLP
Bell Mark L.
Ferro Enamels (Japan) Limited
Manlove Shalie
LandOfFree
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