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The present invention relates to platelet-shaped pigments that comprise a layer obtained by calcining Ti02/SiOy or Ti02/metal, especially Ti, Zr, Cr, or Zn, more especially Al 5 (0.03 =y= 1.95), and to the use thereof in paints, textiles, ink-jet printing, cosmetics, coatings, plastics, printing inks, in glazes for ceramics and glass, and in security printing.
The pigments according to the invention are distinguished by a high gloss and a very uniform thickness, as a result of 10 which very high colour purity and colour strength are obtained.
The known titanium dioxide reducing pigments are based on the use of mica or titanium dioxide platelets as the base substrate. The titanium dioxide is applied to the coated or 15 non-coated base substrates by precipitation and is subsequently reduced to titanium suboxides. Gaseous reducing agents, such as hydrogen or ammonia, or metals, such as, for example, silicon or titanium, are generally used as the reducing agents. 20
U.S. Pat. No. 4,948,631 discloses a process for the preparation of particularly bluish pearl lustre pigments by reduction of mica pigments coated with titanium dioxide with ammonia at temperatures of from 750 to 850° C.
JP H4-20031 describes a process for the preparation of a 25 coloured mica pigment by mixing a mica pigment coated with titanium dioxide with titanium and reducing the resuming mixture in vacuo at from 500 to 1000° C.
DE-A-19618562 discloses a titanium dioxide reducing
pigment consisting of titanium dioxide, titanium suboxides and, where appropriate, a further metal dioxide or titanium oxynitrite. That pigment is obtained by solidifying an aqueous solution of a thermally hydrolysable titanium compound on an endless belt, detaching the resulting layer, coating the 35 resulting titanium dioxide platelets with further titanium dioxide by the wet process, drying and, where appropriate, calcining and treating in a non-oxidising gas atmosphere.
A disadvantage of the known pigments, however, is that they have a too low hiding power and/or do not exhibit colour 4Q flop.
A high-gloss, platelet-shaped titanium reducing pigment based on Si02 platelets is described in DE-A-19843014. The titanium reducing pigment is obtained by mixing Si02 platelets coated with Ti02 and, where applicable, with at least one 45 further metal oxide, with at least one solid reducing agent in a ratio of from 100:1 to 5:1, and calcining the mixtures in a non-oxidising gas atmosphere at a temperature of more than 600° C.
Surprisingly, it has now been found that pigments based on 50 SiOj, or metal platelets, especially Ti, Zr, Cr, or Zn platelets, more especially Al platelets with high gloss and colour flop, can also be obtained when Ti02-coated SiOy platelets, wherein 0.03£=y=1.95, or Ti02-coated metal platelets, in particular Al platelets, are first calcined in a non-oxidising gas 55 atmosphere at a temperature of more than 600° C, and particularly the Ti02-coated SiOy platelets are then treated, where appropriate, at a temperature of more than 200° C, preferably more than 400° C. and especially from 500 to 1000° C, with air or another oxygen-containing gas. 60
BRIEF DESCRIPTION OF THE DRAWIFIG
FIG. 1 shows the reflection spectra at 10 degrees 65 degrees of Samples 1 and 2. 65
The present invention accordingly relates to a plateletshaped pigment comprising a layer obtained by calining
Ti02/SiOj, wherein 0.03SyS 1.95, especially 0.03SyS 1.80, more especially 0.70£=y=1.80, or Ti02/metal, in particular Ti02/Al.
The particles of the platelike pigments generally have a length of from 1 urn to 5 mm, a width of from 1 urn to 2 mm, and a thickness of from 20 nm to 2 urn, and a ratio of length to thickness of at least 2:1, the particles having two substantially parallel faces, the distance between which is the shortest axis of the core.
The flakes of the present invention are not of a uniform shape. Nevertheless, for purposes of brevity, the flakes will be referred to as having a "diameter." The flakes have a high plane-parallelism and a defined thickness in the range of ±30%, especially ±10%, most preferred +/-5% of the average thickness. They have a thickness of from 20 to 2000 nm, especially from 100 to 350 nm. It is presently preferred that the diameter of the flakes be in a preferred range of about 1-60 um with a more preferred range of about 5-40 urn.
The term "SiOy with 0.03 =y = 1.95" means that the molar ratio of oxygen to silicon at the average value of the silicon oxide layer is from 0.03 to 1.95. The composition of the silicon oxide layer can be determined by ESCA (electron spectroscopy for chemical analysis). SiOx, SiOxl, SiOx2, SiO 1; and SiOz are defined accordingly.
According to the present invention the term "aluminum" comprises aluminum and alloys of aluminum. Alloys of aluminum are, for example described in G. Wassermann in Ullmanns Enzyklopadie der Industriellen Chemie, 4. Auflage, Verlag Chemie, Weinheim, Band 7, S. 281 to 292. Especially suitable are the corrosion stable aluminum alloys described on page lOto 12 of WO00/12634, which comprise besides of aluminum silicon, magnesium, manganese, copper, zinc, nickel, vanadium, lead, antimony, tin, cadmium, bismuth, titanium, chromium and/or iron in amounts of less than 20% by weight, preferably less than 10% by weight.
Preference is given to pigments comprising
(a) a substrate layer of SiOz, wherein 0.03SzS2.0,
(b) an intermediate layer obtained by calcining Ti02/SiOj„ wherein 0.03£=y=1.8, in a non-oxidising atmosphere and
(c) a Ti02 layer, or
to pigments comprising
(a) a substrate layer of Al,
(b) an intermediate layer obtained by calcining Ti02/Al in a non-oxidising atmosphere and
(c) a Ti02 layer,
special preference being given to pigments based on SiOz platelets or Al platelets the entire surface of which is coated with Ti02 and which are then calcined in a non-oxidising atmosphere.
Depending on the layer thicknesses of the Ti02 and the SiOj, layer and on the process parameters selected in the calcining process, the entire Ti02 or SiOy layer may become incorporated in the intermediate layer, producing in that case platelet-shapedpigments having only a substrate layer (a) and an intermediate layer (b) or an intermediate layer (b) and a Ti02 layer (c).
In that embodiment, the invention accordingly relates to platelet-shaped pigments the particles of which generally have a length of from 2 um to 5 mm, a width of from 2 um to 2 mm and a thickness of from 20 nm to 1.5 um, and a length to thickness ratio of at least 2:1, the particles having a core of SiOz or Al with two substantially parallel faces, the distance between which faces is the shortest axis of the core, and having a Ti02 layer applied to the parallel faces, and preferably to the entire surface, of the core, there being arranged between the SiOz or Al substrate and the Ti02 layer an inter3
mediate layer obtained by calcining Ti02/SiOj„ wherein 0.03£=y=1.8. The pigments may, where appropriate, have further layers on top of the Ti02 layer.
The thickness of the SiOz layer is generally from 20 to 1000 nm, preferably from 50 to 500 nm, and that of the Ti02 layer 5 is generally from 1 to 200 nm, especially 10 to 100 nm, more especially from 20 to 50 nm.
The invention also relates to the use of the pigments according to the invention in paints, textiles (EP02405889.3), ink-jet printing (EP02405888.5), cosmetics (WO/03076520), 10 printing inks, plastics, coatings (WO03/068868), especially in automotive finishes, in glazes for ceramics and glass, and in security printing.
The pigments based on SiOz or Al platelets are obtained by calcining Ti02-coated SiOy or Al platelets, wherein 15 0.03£=y=1.95, especially 0.03£=y=1.80, more especially 0.70£=y=1.80, in a non-oxidising gas atmosphere at a temperature of more than 600° C. (below 600° C. with Al), preferably in the range from 700 to 1100° C, for more than 10 minutes, preferably for from 15 to 120 minutes. Particularly 20 the pigments based on the SiOy platelets can then be treated, at a temperature of more than 200° C, preferably more than 400° C. and especially from 500 to 1000° C, with air or another oxygen-containing gas.
The Ti02-coated SiOy or metal platelets, in particular Al 25 platelets, can basically be obtained by means of a process comprising the following steps (WO03/068868):
a) vapour-deposition of a Ti02 layer onto a carrier,
b) vapour-deposition of an SiOy layer or a metal layer, in 3Q particular an aluminium layer, onto the Ti02 layer obtained
in step a), and
c) vapour-deposition of a Ti02 layer onto the SiOy layer or metal layer obtained in step b).
Preferably, a separating agent is vapour-deposited onto the 35 carrier before step a), to produce a separating agent layer which facilitates separation of the flakes from the carrier.
Preferably, however, first SiOy or Al flakes are produced which are then coated with Ti02 by wet-chemical application.
The invention is illustrated below in more detail with ref- 40 erence to Al as metal layer without limiting the scope thereof.
There may be used as Al substrate Al platelets punched from Al foil or Al pigments produced by known atomising and grinding techniques. Preferably, Al flakes produced by means of physical vapour deposition are used (see, for example, U.S. Pat. No. 4,321,087, WO00/24946). Such a process comprises the following steps:
a) vapour-deposition of a separating agent onto a carrier to produce a separating agent layer, 50
b) vapour-deposition of an Al layer onto the separating agent layer,
c) dissolution of the separating agent layer in a solvent and
d) separation of the Al flakes from the solvent
The aluminium pigments may then be coated with titanium 55 dioxide by the chemical vapour deposition (CVD) process, for example in accordance with EP-A-38428. In that process, TiCl4 vapour is allowed to react in low concentration with H20 vapour in a fluidised bed in the presence of warmed moving Al particles. 60
TiCl4+2 H20+A1 pigment^Ti02/Al pigment+4 HC1
The titanium-dioxide-coated Al flakes are then calcined in a non-oxidising gas atmosphere at a temperature below 600° C, for more than 10 minutes, preferably for from 15 to 120 65 minutes. The reduction reaction takes place in a non-oxidising gas atmosphere, such as, for example, N2, Ar, He, C02, H2
or NH3, preference being given to N2 or Ar. In the case of N2 or NH3, TiN or TiON may be produced in addition to Ti02_x.
2 Al+6 Ti02^Al203x3 Ti203
2 Al+3 Ti02^Al203x3 TiO
The titanium-dioxide-coated reducing pigments may then be coated with further inorganic coatings, such as, for example, a Fe203, chromium oxide, or CrOOH, Si02, A1203 or Zr02 coating.
It is especially advantageous to use SiOy flakes as starting material. Platelet-shaped SiOy substrates wherein 0.95£=y=1.95, preferably wherein 1.0£=y=1.80, can be obtained by means of a process comprising the following steps (see WO03/068868):
a) vapour-deposition of a separating agent onto a carrier to produce a separating agent layer,
b) vapour-deposition of an SiOy layer onto the separating agent layer,
c) dissolution of the separating agent layer in a solvent and
d) separation of the SiOy flakes from the solvent.
The process mentioned above makes available SiOz substrates that, compared with natural mica platelets and with platelets produced in wet procedures, have a high degree of plane parallelism and a defined thickness in the region of ±30%, preferably ±10%, most preferred +/-5%, of the average thickness.
SiOj, substrates or layers, wherein 0.70£=y=0.99, are formed preferably by evaporating silicon monoxide containing silicon in an amount up to 20% by weight at temperatures of more than 1300° C. If, under industrial vacuums of a few 10~2 Pa, Si is vaporised (instead of Si/Si02 or SiO/Si) silicon oxides can be obtained which have an oxygen content of less than 0.95, that is to say SiOx, wherein 0.03SxS0.95, especially 0.05SxS0.50, very especially 0.10SxS0.30 (WO03/ 076520).
The SiOj, layer wherein 0.95£=y=1.95, preferably 1.0£=y=1.80, in step b) is preferably vapour-deposited from a vaporiser containing a charge comprising a mixture of Si and Si02, SiOy, or a mixture thereof. The SiOy layer is obtained by heating a preferably stoichiometric mixture of fine silicon and quartz (Si02) powder in a vaporiser described, for example, in DE-C-4342574 and in U.S. Pat. No. 6,202,591 to more than 1300° C. under a high vacuum. The reaction product is silicon monoxide gas, which under vacuum is directed directly onto the passing carrier, where it condenses as SiO. Non-stoichiometric mixtures may also be used. The vaporiser contains a charge comprising a mixture of Si and Si02, SiOy, or a mixture thereof, the particle size of the substances that react with one another (Si and Si02) being advantageously less than 0.3 mm. The weight ratio of Si to Si02 is advantageously in the range from 0.15:1 to 0.75:1 (parts by weight); preferably, a stoichiometric mixture is present SiOy present in the vaporiser vaporises directly. Si and Si02 react at a temperature of more than 1300° C. to form silicon monoxide vapour. The separating agent condensed onto the carrier may be a lacquer, a polymer, such as, for example, those described in U.S. Pat. No. 6,398,999 (thermoplastic polymers), especially acrylic or styrene polymers or mixtures thereof, an organic substance soluble in organic solvents or water and vaporisable in vacuo, such as anthracene, anthraquinone, acetamidophenol, acetylsalicylic acid, camphoric anhydride, benzimidazole, benzene-1,2,4tricarboxylic acid, biphenyl-2,2-dicarboxylic acid, bis(4-hydroxyphenyl)sulfone, dihydroxyanthraquinone, hydantoin, 3-hydroxybenzoic acid, 8-hydroxyquinoline-5-sulfonic acid monohydrate, 4-hydroxy coumarin, 7-hydroxycoumarin,