Rare earth-transition metal oxide pigments

Details Rare earth-transition metal oxide pigments Rare earth-transition metal oxide pigments

2001-06-14

2003-06-24

Le, H. Thi (Department: 1773)

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C106S001230, C106S001250, C106S001260, C106S419000, C106S436000, C106S453000, C106S456000, C106S459000, C106S479000, C106S480000, C423S021100, C423S023000, C423S049000, C423S053000, C423S062000, C423S069000, C423S099000, C423S138000, C428S402000, C501S134000, C501S152000

Reexamination Certificate

active

06582814

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to compositions that produce novel inorganic pigments with various advantages over traditional pigment formulations. More specifically, the present invention relates to the use of compositions containing transition metals combined with rare earth metals used in pigmentary applications. The pigments may be used in plastics, paints, coatings, glass enamels and other materials.
BACKGROUND INFORMATION
Inorganic pigments are widely used in various applications such as paints, inks, plastics, rubbers, ceramics, enamels and glasses. These pigments may impart coloristic properties, and protect the coating from the effects of visible as well as ultraviolet and infrared light. These properties depend on both their visible as well as UV and IR reflectance spectrums. In addition to absorbing light, their ability to scatter or reflect light also contributes to their functionality. In order to be suitable in a wide variety of applications, they need to demonstrate a high degree of light fastness and their high temperature stability. A summary of the large number of inorganic pigments produced and some of their applications can be found in Volume 18 of the fourth edition of the Kirk-Othmer Encyclopedia of Chemical Technology, 1996. A systematic list of mixed metal oxide inorganic colored pigments is also given in the publication “DCMA: Classification and Chemical Description of the Mixed Metal Oxide Inorganic Colored Pigments”, Second Edition, January 1982.
Black or dark colored colorants for the coatings and plastics industry are typically based on either carbon black, Cr—Fe based hematite blacks, or blacks formulated from various elements, but typically containing two or more of the elements Ni—Mn—Cu—Fe—Cr, arranged in a spinel type structure. Although carbon black is often the least expensive pigment to produce a black color, the Cu—Cr oxide spinel pigment is often chosen due to its ease of dispersibility as well as its temperature and weathering stability in certain resin systems.
Transition metals are used as a chromophore in a vast number of mixed metal oxide pigments. These light transition metal elements, containing titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc are listed in a large number of DCMA (Dry Color Manufacturers Association) pigment compositions.
In contrast, rare earths are used quite sparingly in inorganic pigments. A notable exception is praseodymium in praseodymium zircon yellow (DCMA 14-43-4). U.S. Pat. No. 5,911,921 describes the use of ytterbium phosphate as an IR absorbing material. U.S. Pat. No. 5,560,772 describes the use of rare earths such as terbium, cerium and praseodymium in combination with each other and zirconium oxide to form red shade compounds. U.S. Pat. Nos. 5,423,912, 5,149,369, and 4,239,548 relate to the use of a cerium as a coating layer in inorganic pigments.
SUMMARY OF THE INVENTION
The present invention provides pigments with enhanced color, composition, and performance characteristics. The pigments can be represented by the formula (Re
x
Tm)O
y
, where Re represents at least one rare earth element selected from yttrium, lanthanum and elements in the Lanthanide Series of the Periodic Table, Tm represents at least one transition metal selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, x ranges from 0.01 to 99, and y designates the number of oxygen atoms required to maintain electroneutrality. Preferably, x ranges from 0.08 to 12, more preferably from 0.25 to 4, most preferably from 0.5 to 2, and y ranges from x+1 to 2x+2. These colorants can be used to form colored objects or coatings through their use in applications such as paints, inks, plastics, glasses, ceramics and the like.
The present invention also relates to the production of rare earth-transition metal oxide pigments, substitution of other elements into these pigments, and the use of protective or functional coatings on these pigments in order to enhance their properties.
The present pigments have been found to be stable with respect to temperature and light, providing lightfast pigments. In addition, these materials tend to have a low solubility which leads to a high degree of resistance to attack from solvents, acids or bases. The pigments exhibit higher strengths than provided by typical pigments in plastics and coating applications.
Another advantage of the present pigments is that when colored ceramic or glass objects containing the pigments are recycled, less objectionable coloration is passed on to the recycled glass than with conventional black colorants which may contain cobalt, chromium, nickel, and other elements.
Another property of these pigments is their ability to change to a different color when exposed to very high temperatures. For example, when surfaces containing these materials are subjected to high temperatures by laser marking, the reactions initiated by these high temperatures allow legible marks to be obtained.
Another aspect of the present invention is to provide a method of making rare earth transition metal oxide pigments. One method includes the steps of mixing powders capable of yielding such metal oxides, and calcining the mixture.
These and other aspects of the present invention will be more apparent from the following description.
DETAILED DESCRIPTION
This invention relates to the use of rare earth oxides combined with transition metal oxides as pigments. These pigments are of the formula (Re
x
Tm)O
y
, where Re represents at least one rare earth element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, preferably at least one metal selected from Y, La, Ce, Pr, Nd, Pm and Sm. The transition metal (Tm) represents at least one metal selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, and x ranges from 0.01 to 99, and y designates the number of oxygen atoms required to maintain electroneutrality. Preferably, x ranges from 0.08 to 12, more preferably from 0.25 to 4, most preferably from 0.5 to 2, and y ranges from x+1 to 2x+2.
Rare earth-transition metal oxide materials of the above-noted formula have been found to possess favorable colorant properties. The pigments are useful in many applications, including organic chemical compositions such as plastics, rubbers, and the like, coating compositions such as paints, printing inks, and the like, and inorganic chemical compositions such as glass enamels, porcelain enamels, ceramics and the like.
Preferred pigment compositions include (Y
x
Mn)O
y
, (Y
x
Co)O
y
, (Y
x
Cu)O
y
, (Y
x
Cr)O
y
, (La
x
Mn)O
y
, (La
x
Co)O
y
, (La
x
Cu)O
y
, (La
x
Cr)O
y
, (La
x
Ni)O
y
, (Ce
x
V)O
y
, (Pr
x
V)O
y
, (Pr
x
Mn)O
y
, (Pr
x
Co)O
y
, (Pr
x
Cu)O
y
, (Pr
x
Cr)O
y
, (Nd
x
V)O
y
, (Nd
x
Mn)O
y
, (Nd
x
Co)O
y
, (Nd
x
Cu)O
y
, (Nd
x
Cr)O
y
, (Nd
x
Ni)O
y
, (Sm
x
V)O
y
, (Sm
x
Mn)O
y
, (Sm
x
Co)O
y
, (Sm
x
Cu)O
y
and (Sm
x
Cr)O
y
.
The present pigments may include at least one dopant selected from Groups I-A, II-A, III-A, IV-A, V-A, VI-A, VII-A, VIII-A, I-B, II-B, III-B, IV-B, V-B, VIII-B, the Actinide elements and the Lanthanide elements in a total amount of up to 50 mol percent.
In one embodiment of the invention, the rare earth-transition metal pigments comprise PrMnO
3
. Iron, cobalt and other metal atoms may fully or partially substitute for the manganese constituents of such a Pr-Mn oxide pigment, and lanthanum and other rare earths may fully or partially substitute for the praseodymium. Some other preferred compositions include PrCoO
3
, LaCoO
3
, YMnO
3
, LaMnO
3.15
, La(NiMn)O
3
, Nd
2
NiO
4
, Nd
2
CuO
4
and Y
2
Cu
2
O
5
.
The present rare earth-transition metal oxide pigments typically have average particle sizes of from about 0.1 to about 20 microns, preferably from about 0.2 to about 10 microns, and more preferably from about 0.5 to about 5 microns. In some embodiments, the morphology of the pigment particles is substantially equiaxed. However, other morphologies may be possible, such as platelets and elongated shapes.
The rare earth-transition metal oxide pigments of the present

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