Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-09-22
2002-10-01
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S419000, C106S430000, C106S431000, C428S688000, C428S689000, C428S697000, C428S702000, C428S704000
Reexamination Certificate
active
06458197
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field
The present invention relates to a pigment based on bismuth vanadate, the behavior of which with respect to heat is greatly improved.
The invention also relates to the process for producing this pigment and to the application of the latter, in particular in the coloring of plastics, paints or lacquers.
2. Related Art
Bismuth vanadate is used, inter alia, as a yellow inorganic pigment. It is employed in coloring plastics and paints, also as a catalyst in the oxidation of olefins, as a contrast-enhancing pigment for television screens and as a reversible temperature indicator. It is a well known chemical compound (DE 422 947, U.S. Pat. Nos. 3,843,554, 4,115,142, JP 62277485 and DE 19733584).
Pure or modified pigments based on bismuth vanadate are nontoxic, have a vivid yellow color, have a high coloring strength and have excellent opaqueness, they are readily dispersed in their medium of use. However, their resistance, especially towards heat, is insufficient; this restricts their use in plastics or in formulations prepared or machined under hot conditions.
A large number of materials are colored with pigments: paints, lacquers, inks or plastics. In particular, compounds treated at high temperature, such as polyethylene, polystyrene, polycarbonate, polypropylene or Acrylnitril-Butadiene-Styrene (ABS-resin), are obtained by extrusion or injection molding of the colored mass softened with the heat. The use of a fairly high temperature results in an undesired change in the starting color (generally a darkening).
Numerous known processes attempt to improve the stability of pigments to light, to heat or to chemicals. These stabilization processes consist of a coating, a doping or a modification of the pigment crystal.
Patent Application EP 239 526 discloses a process for coating with a layer based on aluminum, on titanium, on cerium, on antimony, on zirconium, on silicon, on phosphorus or on zinc, in a proportion of 2 to 40%. According to Patent Application DE 4 037 878, the resistance of pigments to acids and especially to hydrochloric acid can be improved by coating with phosphates of metals, such as calcium, magnesium, aluminum, zinc, zirconium or titanium, in a proportion of 2 to 20%. Mentioned is made, in Patent Application WO 9211205, for pigments based on bismuth silicovanadate and/or phosphovanadate, of coatings of inorganic oxide, hydrate, silicate, phosphate and carbonate.
According to U.S. Pat. No. 4,063,956, the resistance to heat of thermoplastics and the resistance to chemicals is increased by coating with an inorganic precoat and subsequently with a thick layer of silicon oxide; thus, first a layer of hydrated oxides of aluminum, of silicon, of titanium, of boron, of tantalum, of molybdenum, of zinc, of manganese, of tin, of hafnium, of thorium, of niobium, of barium, of strontium, of nickel and/or of antimony is applied, with a preference for aluminum, silicon, titanium and boron. This precoat serves to increase the adhesion of the second layer, composed of amorphous and dense silicon oxide; the silica layer acts mainly to improve the resistance to heat and to acids.
A calcined pigment can also be coated in a bead mill; a first layer of silica is deposited in a basic medium and subsequently a second layer of silica is deposited, optionally in the presence of magnesium fluosilicate, of silanes or of an emulsion formed of polyethylene waxes (EP 271 813).
According to Patent Application DE 3,135,281, coating can also be carried out with layers of zirconium and silicon oxides in order to improve the resistance to light and resistance to beat in U.S. Pat. No. 4,115,142, the resistance of pigments is improved by coating with a layer of silica or of aluminum phosphate.
In Patent EP 723 998, the stability of bismuth vanadate pigments is improved by coating with compounds based on aluminum and zinc phosphates or on silicon and aluminum oxides.
In general, it may be said that any coating system recommended for improving pure or modified pigments based on bismuth vanadate resembles the well known and proven processes applied to various inorganic pigments: for example, titanium dioxides, chromium yellows, molybdenum oranges or iron oxides.
It is well known that powdered pigments, dried at more than 100° C., exhibit a less reactive surface due to the loss of hydroxyl groups. In point of fact, it is precisely these OH groups which Tnake possible good attachment of the coating layers. Consequently, it is difficult to obtain, by coating, sufficiently reliable stabilization of the pigments, in particular those based on bismuth vanadate, which allows them to be used in plastics or paints and resins treated at high temperatures.
It is the same with doping processes. Thus, according to U.S. Pat. No. 4,026,722, a pigment based on bismuth vanadate possessing improved resistance is obtained by virtue of crystallization with silicon and aluminum oxides. The amounts used are very large and even exceed the amount of bismuth vanadate.
According to Patent GB 2,034,342, mixtures of bismuth phosphate, of vanadium pentoxide and of zinc, calcium, barium and magnesium oxides can be calcined.
Patent U.S. Pat. No. 4,781,761 discloses stabilization of a pigment based on titanium, oxide by a first layer of amorphous and dense silica, doped with 10% of boron oxide, and by a second layer of aluminum oxide (2 to 8%).
According to Patent Application DE 3,926,870, the phototropism of pigments based on bismuth vanadate is reduced by providing them with a fine layer of trivalent iron oxide or hydrate (0.001 to 2%).
According to Patent Application DE 3,906,670, the resistance to heat of preparations comprising inorganic and organic pigments can be increased by doping with boron (3 to 10% of boric acid); the sole boron derivative with a truly effective action is boric acid; sodium tetraborate (borax) is not suitable, moreover.
In Patents DE 3,136,279 and DE 3,409,722, a mixture of zinc and iron oxides is treated, before calcination, with boron compounds (H
3
BO
3
, BPO
4
) in a proportion of 0.1 to 1% or with compounds forming alumina phosphates (Al2O
3
, P
2
O
5
, and the like), in order to obtain highly crystalline pigments with a very low content of chloride.
It was already known tat chemical compounds based on aluminum, antimony, ammonium and zinc hydroxides, oxides, phosphates or borates can render organic plastics more resistant to heat and can even slow down their combustion (U.S. Pat. No. 5,248,337, BE 769,799 and GB 2,262,518). The addition of these products to the pigment itself and not to the thermoplastic makes it possible to improve the resistance to heat to a slight extent (Patent EP 370 082).
The preparation of masterbatches with pigments treated with boric acid is generally difficult (undispersed residues, nonhomogeneity, and the like). However, the compound H
3
BO
3
is necessary in order to obtain a degree of resistance to heat. These processes do not make it possible to obtain pigments based on bismuth vanadate which are simultaneously easy to use and highly resistant to heat (300° C.).
SUMMARY
The present invention is targeted essentially at obtaining bismuth-based pigments which correspond to high resistance requirements, in particular to excellent resistance to heat.
Another aim of the present invention is targeted at providing a bismuth-based pigment which can be easily used in materials subjected to high temperatures.
An additional aim of the present invention consists in providing a process which makes possible reliable and efficient attachment of the coating layers to a bismuth-based pigment crystal.
The invention relates to a pigment based on bismuth vanadate which exhibits an improved resistance to heat, characterized in that it is coated with several layers of inorganic compounds m several successive stages, the last of these layers being based on a zinc and boron compound.
Preferably, the pigment is precoated with at least one first layer of inorganic compounds selected from the group consisting of hydrates, oxides, silicates, carbonates, phospha
Buyse Emile Joseph
Vermoortele Frank
Gebroeders Cappelle N.V.
Green Anthony J.
Knobbe Martens Olson & Bear LLP
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