Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-04-23
2003-09-16
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S415000, C106S418000, C106S439000, C106S456000
Reexamination Certificate
active
06620233
ABSTRACT:
The present invention relates to novel goniochromatic luster pigments based on titanium dioxide-coated silicatic platelets which have been heated in a reducing atmosphere and which comprise at least one layer packet comprising
A) a colorless coating having a refractive index n≦1.8 and
B) a coating which has a refractive index n≧2.0, which includes iron(III) oxide and which selectively absorbs visible light.
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 or 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 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 goniochromatic luster pigments based on metallic substrates or on nonmetallic substrates which are at least partially transparent to visible light, both the metallic and the nonmetallic substrates being coated with a combination of low refractive and high refractive or reflecting coatings.
An important group of known goniochromatic luster pigments are the goniochromatic luster pigments wherein the platelet-shaped substrate has been repeatedly coated with low refractive metal oxide (especially silicon dioxide) and high refractive metal oxide (especially iron(III) oxide or titanium dioxide).
For instance, EP-A-708 154 and 753 545 describe goniochromatic luster pigments which are based on respectively aluminum and iron oxide platelets which have first been coated with a silicon dioxide layer and then with an iron(III) oxide layer. The interference colors of these pigments are predominantly in the red hue region.
DE-A-196 18 569 discloses a luster pigment which is based on mica platelets coated successively with titanium dioxide, silicon dioxide and iron(III) oxide. This luster pigment has a brownish orange masstone color and a coppery interference color. Luster pigments having a blue interference color and high transparency are obtainable according to DE-A-196 18 569 when the outer iron oxide layer is replaced with a further titanium dioxide layer.
According to EP-A-933 403 luster pigments having a blue masstone color are obtainable by successive coating of mica platelets with titanium dioxide, silicon dioxide and cobalt aluminate.
Finally, EP-A-753 545 and prior German Patent Application 198 22 046.4 disclose goniochromatic pigments based on mica platelets which comprise an inner titanium dioxide layer reduced in the presence of ammonia. The pigment described in EP-A-753 545 is additionally coated with silicon dioxide and molybdenum and has a vigorous blue interference color which flops toward violet at comparatively steep viewing angles. However, this pigment presents problems with regard to waterfastness. In prior German
Patent Application 198 22 046.4 the substrate particles are additionally coated with silicon dioxide and titanium dioxide. The luster pigments obtained are intensively blue and have high lightness values.
It is an object of the present invention to provide further goniochromatic luster pigments for the blue to green hue region which have 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) independently of each other to said titanium dioxide-coated silicatic platelets which have been heated in a reducing atmosphere 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 finally provides for the use of the luster pigments of the present 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 titanium dioxide-coated silicatic platelets which have been heated in a reducing atmosphere and which comprise multiple coating.
Suitable silicatic platelets include especially light-colored or white micas, particular preference being given to flakes of preferably wet-ground muscovite. It will be appreciated that the range of useful starting materials further includes other natural micas, such as phlogopite or biotite, artificial micas, talcum or glass flakes or silicon dioxide platelets.
The silicatic platelets sent for reduction are coated with a layer which consists essentially of titanium dioxide and which may include further, preferably colorless metal oxides such as tin dioxide, zirconium dioxide, aluminum oxide and silicon dioxide as minor constituents (generally <5% by weight).
The size of the silicate 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 200 &mgr;m, especially from about 5 to 100 &mgr;m, and thicknesses from about 0.1 to 1 &mgr;m, especially around about 0.5 &mgr;m. Their specific free surface area (BET) is customarily within the range from 1 to 15 m
2
/g, especially within the range from 3 to 12 m
2
/g.
The thickness of the TiO
2
layer determines the reflection color of the platelets and is preferably within the range from 50 to 100 nm (silver) or within the range from 300 to 340 nm (blue; optical layer thicknesses).
To produce the luster pigments of the invention, the titanium dioxide-coated silicate platelets have been heated in a reducing gas atmosphere.
Examples of suitable reducing gases include ammonia gas, hydrogen, volatile hydrocarbons (especially C
1
-C
4
-alkanes) and mixtures thereof. These gases are preferably used mixed with inert gases such as nitrogen (cf. EP-A-735 115 and the references cited therein, which include EP-A-332 071).
Preferred reducing gases are ammonia gas and mixtures of ammonia gas with volatile hydrocarbons such as methane, ethane and/or propane, for which a volume ratio of from about 95:5 to 70:30 is advisable. The proportion of the particularly preferred reducing gas/inert gas mixtures which is accounted for by nitrogen is preferably, respectively, up to 90% by volume and within the range from 10 to 60% by volume.
Suitable temperatures for the reduction are generally within the range from 400 to 900° C. and preferably within the range from 750 to 850° C. when ammonia gas is used and >800 to 900° C. when ammonia gas/hydrocarbon mixtures are used.
The reduction leads to the formation of blue, reduced titanium species having oxidation states <4 to 2 (lower titanium oxides such as Ti
3
O
5
, Ti
2
O
3
to TiO, titanium oxynitrides and also titanium nitride). It is customary for from 5 to 100% b
Adel Jörg
Mronga Norbert
Schmid Raimund
Seeger Oliver
BASF - Aktiengesellschaft
Koslow C. Melissa
Manlove Shalie
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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