Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-03-02
2001-02-27
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S419000, C106S420000, C106S425000, C106S426000, C106S428000, C106S430000, C106S431000, C106S436000, C106S438000, C106S439000, C106S441000, C106S442000, C106S446000, C106S450000, C106S456000, C106S457000, C106S459000, C106S481000, C106S482000, C106S483000, C428S403000, C428S404000, C427S215000, C427S218000, C427S219000
Reexamination Certificate
active
06193794
ABSTRACT:
The present invention relates to novel goniochromatic luster pigments based on multiply coated iron oxide platelets comprising at least one layer packet comprising
A) a colorless coating having a refractive index n≦1.8, and
B) a colorless coating having a refractive index n≧2.0.
This invention further relates to the production of these luster pigments and to their use for coloring coatings, inks, including printing inks, plastics, glasses, ceramic products and decorative cosmetic preparations.
Luster effect pigments are used in many sectors of industry, for example in automotive coatings, decorative coating, plastics pigmentation, paints, printing inks, especially security printing inks, and cosmetics.
Their optical effect is based on the directed reflection of light at predominantly sheetlike, mutually parallel-oriented, metallic or strongly refractive pigment particles. Depending on the composition of the pigment platelets, interference, reflection and absorption phenomena create angle-dependent color and lightness effects.
Owing to their uncopiable optical effects, these pigments are increasingly gaining in importance for the production of forgeryproof security documents, such as banknotes, checks, check cards, credit cards, tax stamps, postage stamps, rail and air tickets, telephone cards, lottery tickets, gift vouchers, passes and identity cards.
Markings prepared with the luster effect pigments and the absence of these markings or their alteration, for example in a color copy (disappearance of color flops and luster effects), are reliably discernible by the unaided, naked eye and so make it easy to distinguish the copy from the original.
Particular interest pertains to goniochromatic luster pigments which exhibit an angle-dependent color change between two or more intensive interference colors and hence an attractive color play.
The prior art discloses a number of metallic-based goniochromatic luster pigments, which are produced via physical vapor deposition techniques (U.S. Pat. Nos. 3,438,796 and 5,135,812) or by coating of metal platelets by means of gas phase decomposition of volatile precursors (CVD=Chemical Vapor Deposition) or by wet-chemical coating of the metal platelets (EP-A-668 329, EP-A-708 154 and WO-A-96/34917).
Goniochromatic luster pigments based on transparent, silicatic substrates or coated iron(III) oxide platelets are described in DE-A-196 18 569 and EP-A-753 545, respectively.
Prior art luster pigments differ from the pigments of the present invention in the type of substrate material and/or of the applied coatings.
It is an object of the present invention to provide further goniochromatic luster pigments having advantageous application properties.
We have found that this object is achieved by the goniochromatic luster pigments defined at the beginning.
The present invention further provides a process for producing these luster pigments, which comprises applying said coatings (A) and (B) to said iron oxide platelets independently of each other either wet-chemically by hydrolytic decomposition of organic or inorganic metal compounds or by gas phase decomposition of volatile, organic or inorganic metal compounds.
The present invention further provides a process for producing inventive luster pigments based on magnetite platelets, which comprises
a) coating iron(III) oxide platelets initially with said coatings (A) and (B) and subsequently treating the coated platelets with hydrogen at from 150 to 600° C., or
b) initially treating said iron(III) oxide platelets with a reducing gas at from 150 to 600° C. and subsequently coating the magnetite platelets obtained with said coatings (A) and (B).
The present invention finally provides for the use of the luster pigments of this invention for coloring coatings, inks, including printing inks, plastics, glasses, ceramic products and decorative cosmetic preparations.
The goniochromatic luster pigments of the present invention are based on multiply coated iron oxide platelets.
Examples of preferred substrate materials are platelet-shaped &agr;-iron(III) oxide (&agr;-Fe
2
O
3
, hematite), which may be doped with silicon (EP-A-14 382), aluminum (EP-A-68 311) or aluminum and manganese (EP-A-265 820), and platelet-shaped iron(II/III) oxide (Fe
3
O
4
, magnetite), which may likewise be doped with the metals mentioned.
The iron oxide platelets of the present invention are highly refractive. Their refractive index n is generally ≧2.0, preferably ≧2.4. The doped or undoped iron(III) oxide platelets are essentially transparent to virtually nontransparent for visible light depending on the contemplated wavelength, whereas the magnetite platelets are essentially opaque.
The size of the iron oxide platelets is not critical per se and can be adapted to the particular application intended. In general, the platelets have mean largest diameters from about 1 to 50 &mgr;m, preferably from 5 to 20 &mgr;m. The thickness of the platelets is generally within the rang e from 0.1 to 1 &mgr;m, preferably around about 0.3 &mgr;m. Their specific free surface area (BET) is customarily within the range from 0.5 to 15 m
2
/g, especially within the range from 1 to 12 m
2
/g.
The luster pigments of the present invention combine a colorless low refractive coating (A) with a colorless high refractive coating (B). They may comprise a plurality of identical or different combinations (layer packets) of (A)+(B), but coating with just one layer packet (A)+(B) is preferred.
The colorless low refractive coating (A) has a refractive index n ≦1.8, preferably ≦1.6, and an absorption constant k=0 in the visible wavelength range.
The layer material (A) is suitably any low refractive colorless substance which can be applied to the iron oxide platelets in the form of a durable film, inorganic materials being preferred.
Particularly suitable materials include for example metal oxides and metal oxide hydrates such as silicon oxide, silicon oxide hydrate, aluminum oxide, aluminum oxide hydrate and mixtures thereof, preference being given to silicon oxide (hydrate).
The geometric layer thickness of the coating (A) is generally within the range from 50 to 800 nm, preferably within the range from 100 to 600 nm. Since the layer (A) essentially determines the interference colors of the pigments of the present invention, it has a minimum layer thickness of about 200 nm for luster pigments which have just one layer packet (A)+(B) and which exhibit a particularly pronounced color play and hence are also preferred. If a plurality (e.g., 2, 3 or 4) of layer packets (A)+(B) are present, the layer thickness of (A) is preferably within the range from 50 to 200 nm.
As the layer thickness of (A) increases, the dry pigment powder is observed in plan view to pass repeatedly in succession through the interference colors of blue-green-gold-red-violet, the angle dependence of the hue increasing starting with the second order blue. However, the interference colors are visible only in the dry state and disappear completely in the moist state or in varnish. The additional coating with (B) renders the optically variable layer visible in varnishes, too.
The colorless high refractive coating (B) has a refractive index n≧2.0, especially ≧2.4, and an absorption constant k=0 in the visible wavelength range.
The layer material (B) is suitably any high refractive colorless substance which can be applied to the (A)-coated iron oxide platelets in the form of a durable film.
Particularly suitable layer materials (B) include not only metal sulfides such as zinc sulfide but especially metal oxides and metal oxide hydrates, for example titanium dioxide, titanium oxide hydrate, zirconium dioxide, zirconium oxide hydrate, tin dioxide, tin oxide hydrate, zinc oxide, zinc oxide hydrate and mixtures thereof, preference being given to titanium dioxide and titanium oxide hydrate and their mixtures with up to about 5% by weight of the other metal oxides, especially tin dioxide. Titanium dioxide can also be used together with low refractive co
Mronga Norbert
Schmid Raimund
Seeger Oliver
BASF - Aktiengesellschaft
Green Anthony
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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