U.S. patent application number 10/811867 was filed with the patent office on 2004-09-16 for multilayer pigments based on coated metal platelets.
Invention is credited to Andes, Stephanie, Dietz, Johann, George, Sabine, Herbski, Margarete, Kniess, Helge, Reynders, Peter, Steudel, Elke, Vogt, Reiner.
Application Number | 20040180010 10/811867 |
Document ID | / |
Family ID | 29403768 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040180010 |
Kind Code |
A1 |
Andes, Stephanie ; et
al. |
September 16, 2004 |
Multilayer pigments based on coated metal platelets
Abstract
The present invention relates to multilayer pigments based on
platelet-shaped metal substrates coated with two or more metal
oxide layers by a one-pot process in an exclusively aqueous medium.
The invention further relates to the use of the multilayer pigments
in paints, varnishes, printing inks, including security printing
inks, plastics, ceramic materials and cosmetic and for the laser
formulations marking of plastics.
Inventors: |
Andes, Stephanie; (Hanau,
DE) ; George, Sabine; (Bensheim, DE) ;
Herbski, Margarete; (Gross-Bieberau, DE) ; Reynders,
Peter; (Griesheim, DE) ; Vogt, Reiner;
(Kranichstein, DE) ; Dietz, Johann; (Dietzenbach,
DE) ; Kniess, Helge; (Weiterstadt, DE) ;
Steudel, Elke; (Darmstadt, DE) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Family ID: |
29403768 |
Appl. No.: |
10/811867 |
Filed: |
March 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10811867 |
Mar 30, 2004 |
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10453479 |
Jun 4, 2003 |
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10453479 |
Jun 4, 2003 |
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09762766 |
Feb 13, 2001 |
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09762766 |
Feb 13, 2001 |
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PCT/EP99/05915 |
Aug 11, 1999 |
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Current U.S.
Class: |
424/63 ; 106/430;
106/436 |
Current CPC
Class: |
C09C 2200/1054 20130101;
C09C 2200/1058 20130101; C09C 1/0015 20130101; C09C 1/0021
20130101; C09C 2200/306 20130101; C09C 2210/60 20130101; C01P
2004/20 20130101; C01P 2004/82 20130101; C09C 2220/106 20130101;
C09C 1/642 20130101; C01P 2006/60 20130101; C09C 1/0039 20130101;
C01P 2004/61 20130101; C09C 1/0051 20130101; C09C 1/0066 20130101;
C09C 2200/302 20130101; C09C 2200/303 20130101; C01P 2004/86
20130101; C01P 2006/12 20130101; C09C 1/0024 20130101; C01P 2004/62
20130101; C09C 2200/301 20130101 |
Class at
Publication: |
424/063 ;
106/430; 106/436 |
International
Class: |
A61K 007/021; C09C
001/04; C09C 001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 1998 |
DE |
198 36 810.0 |
Claims
1. A multilayer pigment based on platelet-shaped metal pigments and
produced by the exclusive wet-chemical coating of the metal
pigments in a one-pot process wherein the metal pigments,
optionally after prior passivation, are initially suspended in
water and coated with an amorphous glassy layer at pH 6-11 and then
with one or more metal oxides or metal oxide mixtures at a
pH<4.
2. A multilayer pigment according to claim 1, wherein the amorphous
glassy layer comprises SiO.sub.2, B.sub.2O.sub.3, phosphate, or a
mixture thereof.
3. A multilayer pigment according to claim 1, wherein the metal
oxide layer or the layer comprising a metal oxide mixture comprises
titanium dioxide, iron oxide, silicon dioxide, bismuth oxychloride,
zirconium oxide, tin oxide, zinc oxide, titanium suboxide, iron
oxyhydrate and/or chromium oxide.
4. A multilayer pigment according to claim 1, wherein up to 12
layers of metal oxide or metal oxide mixtures have been applied to
the metal pigment.
5. A multilayer pigment according to claim 1, wherein the metal
pigments are aluminum platelets.
6. A multilayer pigment according to claim 5, wherein the aluminum
platelets have been coated with an amorphous SiO.sub.2 layer and
then with a TiO.sub.2 and/or Fe.sub.2O.sub.3 layer.
7. A multilayer pigment according to claim 1, wherein the metal
pigments have been coated with an amorphous SiO.sub.2 layer and
then with an SnO.sub.2, TiO.sub.2 and/or Fe.sub.2O.sub.3 layer.
8. A multilayer pigment according to claim 1, wherein the metal
pigments have been coated with an amorphous SiO.sub.2 layer and
then with an SnO.sub.2, TiO.sub.2, SiO.sub.2, SnO.sub.2 and
TiO.sub.2 layer in alternating fashion.
9. A multilayer pigment according to claim 1, wherein the metal
pigments have been coated with an amorphous SiO.sub.2 layer and
then with an SnO.sub.2, Fe.sub.2O.sub.3, SiO.sub.2, SnO.sub.2 and
Fe.sub.2O.sub.3 layer in alternating fashion.
10. A paint, varnish, printing ink, plastic, ceramic material or
cosmetic formulation comprising a multilayer pigment according to
claim 1.
11. A laser marked plastic or a pigment blend comprising multilayer
pigments according to claim 1.
Description
[0001] The present invention relates to multilayer pigments based
on platelet-shaped metal substrates coated with two or more metal
oxide layers by a one-pot process in an exclusively aqueous medium.
The invention further relates to the use of the multilayer pigments
in paints, varnishes, printing inks, including security printing
inks, plastics, ceramic materials and in cosmetic formulations.
[0002] Effect pigments are used in many sectors of industry, for
example in automotive coatings, varnishes, inks, including printing
inks, especially security printing inks, paints, plastics, glasses,
ceramic products and cosmetic preparations.
[0003] Their optical effect is based on the directed reflection of
light at predominantly sheetlike, mutually parallel-oriented,
metallic or strongly refractive pigment particles. The latter are
platelet-shaped and their optical properties are determined by
reflection and interference.
[0004] Effect pigments providing an angle-dependent change of
colour between a plurality of interference colours are by virtue of
their colour play of particular interest for automotive coatings
and for application in forge proof security documents. Such
pigments based on multiply coated platelet-shaped metal substrates,
especially aluminium platelets, are known.
[0005] U.S. Pat. No. 3,438,796 first described multilayer pigments
based on a central highly reflective metal layer. Alternating
SiO.sub.2 and aluminium layers were deposited in a high vacuum
deposition process, separated from the base film, ground and
classified. The production process is such, however, that the
chemical resistance of the pigment powders thus produced is very
low, since the metal used is open to chemical attack at the edges.
The coated aluminium pigments thus obtained are costly and the
process is extremely unsuitable for practice on a large industrial
scale.
[0006] U.S. Pat. No. 4,879,140 discloses a further process for
producing aluminium pigments, which comprises vaporizing metal
compounds in a microwave plasma in such a way that they form a film
on predetermined surfaces in the chamber. This film can be
mechanically removed, ground and suitably classified. This process
is likewise subject to the cost and dimension disadvantages
mentioned.
[0007] EP 0 668 329 A2 discloses polychromatic pigments comprising
an aluminium substrate which is coated with silicon dioxide in a
neutral, aqueous medium. The wet-chemical coating of the substrates
is effected through hydrolytic decomposition of organic silicon
compounds in an ammonia solution without a change in the pH.
Thereafter, the CVD process can be used to apply further layers of,
for example, metals to the SiO.sub.2 coated aluminium
substrates.
[0008] The patent applications EP 0 686 675 A1, EP 0 708 154 A2 and
EP 0 741 170 A1 likewise each have aluminium pigments coated with
metal oxide layers by means of the CVD process.
[0009] EP 0 826 745 A2 discloses aluminium-based metal pigments
which are prepared by physical vapour deposition (PVD) and which
are distinguished by the fact that all metal surfaces which are
exposed following the comminution of a metal film produced by PVD,
especially the fracture surfaces, are coated with a passivating
protective layer.
[0010] The great disadvantage of all vapour deposition processes is
the associated high cost.
[0011] EP 0 768 343 A2 claims lustre pigments produced by applying
SiO.sub.2 layers to metal substrates by hydrolytic decomposition of
organic silicon compounds. The decomposition is supported by the
presence of an organic solvent in which the organometallic starting
components have a certain solubility. Owing to the use of
organometallic components and of organic solvents, this process is
not very economical and also necessitates high safety
precautions.
[0012] U.S. Pat. No. 2,885,366 discloses the coating of aluminium
platelets with silicon dioxide from water-glass solutions. Here,
however, the oxide layer is applied only for the purpose of
passivating the aluminium surface.
[0013] It is an object of the present invention to provide a
multilayer pigment which is based on metal platelets and for which
the base substrate is coated neither by CVD nor by PVD processes,
but exclusively wet-chemically and without the use of flammable
compounds. At the same time, the pigment shall be notable for its
optical properties and/or the strong angle dependence of the
interference colours and its advantageous application
properties.
[0014] Surprisingly, there has now been found a multilayer pigment
based on multiply coated platelet-shaped metal substrates where the
substrate is coated with dielectrics in an aqueous medium by a
one-pot process. The wet-chemically coated metal substrate is
especially notable for its colour strength. Metal platelets such as
aluminium, which react in water at various pH values with the
evolution of hydrogen, can be converted into chemically inert
multilayer pigments through suitable choice of the coating
parameters.
[0015] The present invention accordingly provides multilayer
pigments based on platelet-shaped metal pigments and produced by
the exclusive wet-chemical coating of the metal pigments in a
one-pot -process wherein the metal pigments are initially suspended
in water and coated with an amorphous glassy layer at pH 6-11 and
then with one or more metal oxides or metal oxide mixtures at a
pH<4.
[0016] The invention further provides for the use of the thus
produced multilayer pigments in paints, varnishes, printing inks,
including security printing inks, plastics, ceramic materials and
cosmetic formulations. The invention likewise provides for the use
of pigments of the invention as dopants in the laser marking of
plastics.
[0017] Suitable base substrates for the multilayer pigments of the
invention are platelets composed of metal or metal alloys, for
example, iron, aluminium, tin, zinc, silver, copper, titanium,
lanthanides, cobalt, nickel, and all commercially available metal
powders known to the person skilled in the art which are
substantially stable in water. It is further possible to use
mixtures of the metals and metal alloys mentioned as base
substrates. Preferred base substrates are aluminium platelets and
also aluminium alloys.
[0018] The size of the base substrates is not critical per se and
can be adapted to the particular intended application. In general,
the platelet-shaped metal substrates will have a thickness between
0.1 and 5 .mu.m, especially between 0.2 and 4.5 .mu.m. The extent
in the other two dimensions is customarily between 1 and 250 .mu.m,
preferably between 2 and 200 .mu.m, especially between 5 and 50
.mu.m.
[0019] The thickness of the individual metal oxide layers on the
metal substrate is essential for the optical properties of the
multilayer pigment. For a pigment to have intensive interference
colours, the individual layers have to be accurately adjusted with
regard to one another in thickness.
[0020] The colour variation with increasing film thickness is a
consequence of the intensification or attenuation of certain
wavelengths of the light through interference. When two or more
layers in a multilayer pigment possess the same optical thickness,
the colour of the reflected light intensifies with an increasing
number of layers. In addition, suitable choice of the layer
thicknesses is a way of obtaining particularly strong variation in
colour as a function of the viewing angle. A pronounced colour flop
develops. The thickness of the individual metal oxide layers
depends on the field of application and is generally 10 to 1000 nm,
preferably 15 to 800 nm, especially 20-600 nm, regardless of their
refractive index.
[0021] The multilayer pigments of the invention generally comprise
at least two metal oxide layers. Preferably, a layer of low
refractive index is present in combination with a coloured or
colourless metal oxide layer of high refractive index. The pigments
may comprise up to 12 layers, with the proviso that the thickness
of all the layers on the metal substrate should not exceed 3 um.
Preferably, the multilayer pigments of the invention contain not
more than 7, especially not more than 5, metal oxide layers.
Particular preference is given to pigments coated on the metal
substrate initially with an amorphous glassy layer, preferably an
amorphous SiO.sub.2 layer, and then with TiO.sub.2 and/or
Fe.sub.2O.sub.3.
[0022] The amorphous glass layer on the metal substrate consists
preferably of SiO.sub.2, Al.sub.2O.sub.3, AlO(OH), B.sub.2O.sub.3
or of the mixtures of the metal oxides mentioned. The thickness of
the layer is 10-1000 nm, preferably 20-800 nm, especially 30-600
nm.
[0023] The amorphous glassy layer, for example an SiO.sub.2 layer,
on the substrate has an inertizing effect, so that the metal
substrates thus treated can be stored in an aqueous medium for a
prolonged period, whereas the untreated metal powders will have
reacted, frequently before the day is out, to form the adequate
oxyhydrates. Even acidic pH ranges are survived intact by the metal
powders treated as well as alkaline pH ranges. The stability of the
metal substrates in aqueous media may usually be increased through
aftertreatment with known surface-active substances. Frequently it
is advisable to passivate the metal platelets prior to coating.
Passivation is effected by treating the metal powder in aqueous
solution with an oxidizing agent, preferably with hydrogen peroxide
or HNO.sub.3. The metal substrate thus passivated is subsequently
coated with the amorphous glassy layer.
[0024] The amorphous glassy layer preferably has one or more
coloured or colourless highly refractive metal oxide layers applied
to it. Suitable highly refractive layer materials include all
highly refractive materials known to the person skilled in the art
which are simple to apply to the substrate materials in filmlike
fashion. Particular suitability is possessed by metal oxides or
metal oxide mixtures, for example TiO.sub.2, Fe.sub.2O.sub.3,
ZrO.sub.2, ZnO, SnO.sub.2, BiOCl, pseudobrookite or compounds
having a high refractive index, for example -iron oxyhydrates,
titanium suboxides, chromium oxides and also mixtures or mixed
phases between the compounds mentioned or with other metal oxides.
The thickness of this layer is 10-1550 nm, preferably 15-400 nm,
especially 20-350 nm.
[0025] Suitable colourless coating materials of low refractive
index are preferably metal oxides or the corresponding oxyhydrates,
for example SiO.sub.2, Al.sub.2O.sub.3, AlO(OH), B.sub.2O.sub.3 or
a mixture of the metal oxides mentioned. The thickness of the layer
of low refractive index is 10-1000 nm, preferably 20-800 nm,
especially 30-600 nm
[0026] The multilayer pigments of the invention are produced by
depositing high and low refractive index interference layers of
precisely defined thickness and having smooth surfaces on the
inertized and optionally passivated metal substrate by hydrolytic
decomposition of metal salts. A particularly important requirement
is that the pH has to be readjusted for each coating step.
[0027] The initial step of producing the pigments is to suspend the
metal substrates, freed of any adherent organic constituents prior
to the coating operation, in water, and coat them with an amorphous
glassy layer at a pH of 6-11. This amorphous layer is preferably
created by precipitating SiO.sub.2 from sodium or potassium
silicate solutions or by hydrolytic decomposition of aluminium,
tin, zinc or boron salts and of their solutions in alkaline and
cationic form. Suitable materials for inertizing the metal
substrates are likewise phosphates, for example zinc, tin(II),
tin(IV), aluminium or zirconium phosphates.
[0028] After coating with the amorphous layer, the pH is reduced to
<4 with a mineral acid. One or more hydrolysable metal salts are
added to precipitate the metal oxides or metal oxyhydrates directly
onto the amorphous glassy layer without secondary precipitations.
The pH is customarily kept constant by the simultaneous metered
addition of a base and/or acid. Lastly, the coated pigments are
separated off, washed and dried and optionally calcined, the
calcination, temperature varying with regard to the substrate used
and the particular coating present. In general, calcination
temperatures are between 250 and 1000.degree. C., preferably
between 350 and 900.degree. C.
[0029] Preferably, the metal pigments, especially aluminium
platelets, are initially coated with an amorphous SiO.sub.2 layer
at pH 6-8. The amorphous SiO.sub.2 layer then has an a TiO.sub.2
layer and/or Fe.sub.2O.sub.3 layer applied to it wet-chemically in
a strongly acidic medium. Preference is further given to multilayer
pigments comprising a layer sequence of SiO.sub.2, SnO.sub.2,
TiO.sub.2 and/or Fe.sub.2O.sub.3 or of SiO.sub.2, SnO.sub.2,
TiO.sub.2, SiO.sub.2, SnO.sub.2 and TiO.sub.2 or of SiO.sub.2,
SnO.sub.2, Fe.sub.2O.sub.3, SiO.sub.2, SnO.sub.2 and
Fe.sub.2O.sub.3.
[0030] The amorphous silicon dioxide layer can be applied as
follows, for example. A potassium or sodium silicate solution is
metered at pH 6-11 into a hot suspension at about 50-100.degree. C.
of the metal substrate to be coated. A dilute mineral acid such as,
for example, HCl, HNO.sub.3 or H.sub.2SO.sub.4 is added
simultaneously to keep the pH constant. As soon as the desired
layer thickness is obtained with regard to SiO.sub.2, the addition
of the silicate solution is stopped. The batch is subsequently
stirred for about 0.5 h.
[0031] Titanium dioxide layers are preferably applied by the
process described in U.S. Pat. No. 3,553,001. An aqueous titanium
salt solution is gradually added to a hot suspension at about
50-100.degree. C. of the material to be coated, while at the same
time a base, for example an aqueous ammonia solution or aqueous
alkali metal hydroxide solution, is metered in to maintain a
substantially constant pH of about 0.5-3. As soon as the desired
layer thickness is obtained with regard to TiO.sub.2, the addition
of the titanium salt solution and of the base is stopped. This
process, also known as the titration process, is notable for
-avoiding an excess of titanium salt. This is achieved by supplying
to the hydrolysis only that quantity per unit time which is
necessary for uniform coating with the hydrated TiO.sub.2 and which
can be received per unit time by the available surface area of the
substrates to be coated. There is therefore no production of
hydrated titanium dioxide particles which are not precipitated on
the surface to be coated.
[0032] The metal substrates can also be coated using the
wet-chemical coating processes developed for producing pearl lustre
pigments, described for example in the German patents and patent
applications 14 67 468, 19 59 998, 20 09 566, 22 14 454, 22 15 191,
22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343,
31 51 354, 31 51 355, 32 11 602 and 32 35 017.
[0033] To enhance the light and weather stability it is frequently
advisable, depending on the field of application, to subject the
multilayer pigment to an aftercoating or aftertreatment. Useful
aftercoatings and aftertreatments include for example the processes
described in DE-C 22 15 191, DE-A 31 51 354, DE-A 32 35 017 or DE-A
33 34 598. This aftercoating further enhances the chemical
stability of the pigments and/or facilitates the handling of the
pigment, especially its incorporation into various application
media.
[0034] The pigments of the invention are compatible with a
multiplicity of colour systems, preferably from the sector of
varnishes, paints and printing inks. Owing to the uncopyable
effects, the multilayer pigments of the invention are particularly
useful in security printing inks for the production of forgeproof
security documents, for example banknotes, cheques, cheque cards,
credit cards, identity cards, passes, tax stamps, postage stamps,
rail and air tickets, telephone cards, lottery tickets, gift
vouchers, etc.
[0035] The layer pigments are also useful for functional
applications in corrosion protection and in the conductivity
sector.
[0036] The pigments of the invention are likewise useful as
dopants--alone or combined with other known dopants--in the laser
marking of plastics. Adding the pigments in concentrations of 0.1
to 4% by weight based on the plastics system, preferably 0.5 to
2.5% by weight, especially 0.3 to 2.0% by weight, provides laser
marking of high contrast. However, the concentration of the
pigments in the plastic is dependent on the plastics system used.
The low pigment content has little effect on the plastics system
and does not affect its processibility.
[0037] All known thermoplastic polymers, as described for example
in Ullmann, vol. 15, p. 0.457 ff., Verlag VCH, can be used for
laser marking. Examples of suitable plastics are polyethylene,
polypropylene, polyamides, polyesters, polyesteresters,
polyetheresters, polyphenylene ethers, polyacetate, polybutylene
terephthalate, polymethyl methacrylate, polyvinyl acetate,
polystyrene, acrylonitrile-butadiene-styrene (ABS),
acrylonitrile-styrene-acrylate (ASA), polycarbonate,
polyethersulfones, polyetherketones and their copolymers and/or
blends. Thermoplastic polyurethanes (TPUs) are particularly useful
owing to their superior mechanical properties and the economical
methods of processing. Thermoplastic polyurethanes are well-known
from numerous literature publications and patents, for example GB 1
057 018 or EP 0 594 931.
[0038] The coated metal pigments are incorporated in the
thermoplastic polymer by mixing the polymeric pellets with the
pigment and then forming the mixture at elevated temperature. In
the process of incorporating the pigments into the polymeric
pellets, adhesion promoters, organic polymer compatible solvents,
stabilizers and/or surfactants which are thermally stable under the
operating conditions can be added, if desired. The polymer
pellet/pigment mixture is generally prepared by charging a suitable
mixer with the pellets, adding any additives to wet the pellets and
thereafter adding the pigment and mixing it in. The plastic is
generally pigmented via a colour concentrate (masterbatch) or
compound. The mixture thus obtained can then be processed directly
in an extruder or an injection moulding machine. The moulded
articles formed in the course of the processing exhibit very
homogeneous disbursement of the pigments. This is followed by the
laser marking.
[0039] To mark the specimen by laser, it is introduced into the
path of a pulsed laser, preferably of an Nd-YAG laser (1064 or 532
nm) or CO.sub.2 laser (10.6 .mu.m). It is also possible to mark it
with an excimer laser, for example via a mask technique. However,
the desired results are also obtainable with other conventional
laser types which have a wavelength within a high absorption region
of the pigment used. The marking obtained is determined by the
irradiation time (or the number of pulses in the case of pulsed
lasers) and irradiative power of the laser and of the plastics
system used. The power of the laser used depends on the particular
application and can in the individual case be readily determined by
a person skilled in the art.
[0040] The present invention accordingly also provides for the use
of the pigments in formulations such as paints, printing inks,
including security printing inks, automotive finishes, varnishes,
plastics, ceramic materials and cosmetic formulations, and for the
laser marking of plastics.
[0041] It will be appreciated that, for the various applications,
the multilayer pigments of the invention may also advantageously be
used blended with other pigments, for example transparent and
hiding white, colour and black pigments and with platelet-shaped
iron oxides, organic pigments, holographic pigments, LCPs (liquid
crystal polymers), and conventional transparent, coloured and black
lustre pigments based on metal oxide-coated mica and SiO.sub.2
platelets, etc. The multilayer pigments can be mixed with
commercially available pigments and extenders in any
proportion.
[0042] The Examples hereinbelow are intended to describe the
invention more particularly without, however, limiting it.
EXAMPLES
Example 1
[0043] 100 g of aluminium powder having an average particle
diameter of -20 .mu.m (Resist 501 from Eckart Werke) and thermally
freed of the organic surface treatment at 400.degree. C. are
suspended in 2 l of completely ion-free water. After 0.5 h, the
addition is commenced at a metering rate of 2 ml/min, of the sodium
silicate solution at pH 7.5. Altogether, 1230 g of a sodium
silicate solution having an SiO.sub.2, content of 13.5% are added
while the pH is kept constant at 7.5 by means of hydrochloric acid.
The titration is continued until the desired layer thickness
(inertization) is obtained. The metered addition is then terminated
and the reaction completed by stirring at 90.degree. C. for 0.5 h.
The pH is then adjusted to 3.0 and the metered addition commenced
at 75.degree. C. of a 3% iron(III) chloride solution. The pH is
kept constant at 3.0 using 32% sodium hydroxide solution. Once the
desired layer thickness has been obtained with regard to iron(III)
oxide, the batch is stirred for a further 0.5 h and filtered to
collect the product. It is dried, classified and heat-treated at
400.degree. C.
[0044] The product consists of 32.5% of aluminium, 57.5% of
SiO.sub.2 and 10.0% of Fe.sub.2O.sub.3 and has a characteristic red
metallic lustre.
Example 2
[0045] Example 1 is repeated to coat 100 g of aluminium powder with
an SiO.sub.2 layer. After heating to 90.degree. C. for 0.5 h, a
titanium tetrachloride solution (400 g/l) is added at pH 1.8 at 4
ml/min until the desired layer thickness is obtained, maintained
using sodium hydroxide solution. After the coating has been
completed, the batch is stirred for 15 min. The product is filtered
off, washed, dried and heat-treated at 400.degree. C.
[0046] The product consists of 32.5% of aluminium, 57.5% of
SiO.sub.2 and 10.0% of TiO.sub.2 and has a characteristic silvery
lustre.
Example 3.
[0047] 100 g of aluminium powder are suspended in 400 ml of 10%
hydrogen peroxide solution and passivated by boiling for 10
minutes. The passivated aluminium powder is suspended in 2 l of
completely ion-free water and the suspension is stirred for 0.5 h.
The sodium silicate solution is added at a rate of 2 ml/min at a pH
of 6.5. Altogether, 1230 g of a silicate solution having an
SiO.sub.2 content of 13.5% are added while the pH is maintained at
6.5 using hydrochloric acid. The titration is continued until the
desired layer thickness is obtained. The suspension is subsequently
stirred for 0.5 h and then admixed with a tin solution (11.6 g of
SnCl.sub.4.5H.sub.2O dissolved in 40 ml of 37% hydrochloric acid
and made up to 400 ml with completely ion-free water) at a rate of
4 ml/min until the pH has dropped to 1.8. The pH is maintained at
1.8 using sodium hydroxide solution. On completion of the addition
of the tin salt solution, the batch is stirred for 0.5 h.
Thereafter, titanium tetrachloride solution (400 g/l) is added at 4
ml/min and pH 1.8 until the desired layer thickness is obtained.
The pH of 1.8 is maintained using sodium hydroxide solution.
Following a subsequent stirring time of 15 min, the product is
filtered off, washed, dried and heat-treated at 400.degree. C. The
product consists of 33.3% of aluminium, 55.6% of SiO.sub.2, 1.5% of
SnO.sub.2 and 9.6% of TiO.sub.2 and has a characteristic silvery
lustre.
Example 4
[0048] In a repeat of Example 3, 100 g of aluminium powder are
initially passivated with 400 ml of 10% hydrogen peroxide solution
and then coated with SiO.sub.2 at pH 6.5. The suspension is
subsequently stirred for 0.5 h at 90.degree. C. and then admixed
with a tin solution (11.6 g of SnCl.sub.4 5H.sub.2O dissolved in 40
ml of 37% hydrochloric acid and made up to 400 ml with completely
ion-free water) at a rate of 4 ml/min until the pH has dropped to
1.8. The pH is maintained at 1.8 using sodium hydroxide solution.
On completion of the addition of the tin salt solution, the batch
is stirred for 0.5 h. The pH is then adjusted to 3.0 and the
metered addition commenced at 0.75.degree. C. of a 3% iron(III)
chloride solution. The pH is kept constant at 3.0 using 32% sodium
hydroxide solution. Once the desired layer thickness has been
obtained with regard to iron(III) oxide, the batch is stirred for a
further 0.5 h to complete precipitation. The product is filtered
off, dried, classified and heat-treated at 400.degree. C. The
product consists of 31.7% of aluminium, 52.0% of SiO.sub.2, 2.0% of
SnO.sub.2 and 14.3% of Fe.sub.2O.sub.3 and has a characteristic
light golden lustre.
Example 5
[0049] In a repeat of Example 3, 100 g of aluminium powder are
initially passivated with 400 ml of 10% hydrogen peroxide solution
and then coated with SiO.sub.2 at pH 6.5. The suspension is
subsequently stirred for 0.5 h at 90.degree. C. and then admixed
with a tin salt solution (11.6 g of SnCl.sub.4.5H.sub.2O dissolved
in 40 ml of 37% hydrochloric acid and made up to 400 ml with
completely ion-free water) at a rate of 4 ml/min until the pH has
dropped to 1.8. The pH is maintained at 1.8 using sodium hydroxide
solution. On completion of the addition of the tin solution, the
batch is stirred for 0.5 h. Thereafter, titanium tetrachloride
solution (400 g/l) is added at 4 ml/min and pH 1.8 until the
desired layer thickness is obtained. The pH of 1.8 is maintained
during coating using sodium hydroxide solution. 15 min after
completion of the titanium dioxide coating, the pH is adjusted to
6.5 with sodium hydroxide solution. The addition of the sodium
silicate solution takes place at a rate of 2 ml/min. Altogether,
1230 g of a silicate solution having an SiO.sub.2 content of 13.5%
are added while the pH is maintained at 6.5 using hydrochloric
acid. The titration is continued until the desired layer thickness
is obtained. The suspension is subsequently stirred for 0.5 h and
then admixed with a tin salt solution (11.6 g of
SnCl.sub.4.5H.sub.2O dissolved in 40 ml of 37% hydrochloric acid
and made up to 400 ml with completely ion-free water) at a rate of
4 ml/min until the pH has dropped to 1.8. On completion of the
addition of the tin salt solution, the batch is stirred for 0.5 h.
Thereafter, a titanium tetrachloride solution (400 g/l) is metered
in at 4 ml/min and pH 1.8 until the desired layer thickness is
obtained. The pH of 1.8 is maintained using sodium hydroxide
solution. Following coating and a subsequent stirring time of 15
min, the product is finally filtered off, washed, dried and
heat-treated at 400.degree. C. The product consists of 19.9% of
aluminium, 66.3% of SiO.sub.2, 1.8% of SnO.sub.2 and 12.0% of
TiO.sub.2 and has a characteristic golden lustre.
Example 6
[0050] 100 g of gold-coloured brass powder having an average
particle diameter of 28 um (Resist CT from Eckart Werke) and
thermally freed of the organic surface treatment at 400.degree. C.
are suspended in 2 l of completely ion-free water. After 0.5 h, the
addition is commenced at a metering rate of 2 ml/min, of the sodium
silicate solution at pH 7.5. Altogether, 1230 g of a sodium
silicate solution having an SiO.sub.2 content of 13.5% are added
while the pH is kept constant at 7.5 by means of hydrochloric acid.
The titration is continued until the desired layer thickness is
obtained. The metered addition is then terminated and the reaction
completed by stirring at 90.degree. C. for 0.5 h. The pH is then
adjusted to 3.0 and the metered addition commenced at 75.degree. C.
of a 3% iron(III) chloride solution. The pH is kept constant at 3.0
using 32% sodium hydroxide solution. Once the desired layer
thickness has been obtained with regard to iron(III) oxide, the
batch is stirred for a further 0.5 h and filtered to collect the
product. It is dried, classified and heat-treated at 400.degree.
C.
[0051] The product consists of 32.3% of brass, 53.7% of SiO.sub.2
and 14.0% of Fe.sub.2O.sub.3 and has a characteristic copper-golden
metallic lustre.
Example 7
[0052] 100 g of aluminium powder thermally freed of the organic
surface treatment at 400.degree. C. are suspended in 2 l of
completely ion-free water. The pH is then adjusted to 6.0. At
75.degree. C., the aluminium flake suspension is simultaneously but
separately titrated with a solution of 20 g of SnSO.sub.4 in 100 ml
of completely ion-free water and a solution of 40 ml of
H.sub.3PO.sub.4 (orthophosphoric acid of density 1.75 g/cm.sup.3 in
80 ml of completely ion-free water). On completion of the addition,
the batch is stirred for 0.5 h to complete the reaction. The pH is
then adjusted to 3.0 and the metered addition commenced at
75.degree. C. of a 3% iron(III) chloride solution. The pH is kept
constant at pH=3.0 using 32% sodium hydroxide solution. On
obtainment of the desired layer thickness with regard to iron(III)
oxide., the batch is stirred for a further 0.5 h and filtered to
collect the product. It is dried, classified and heat-treated at
400.degree. C. The product consists of 71.8% of aluminium, 13.8% of
phosphate and 14.4% of Fe.sub.2O.sub.3 and has a characteristic red
metallic lustre.
Example 8
[0053] Red-brown injection mouldings are produced in a
polypropylene (Stamylan PPH, DSM), containing 0.5% of aluminium
pigment of Example 1.
[0054] The marking with an Nd-YAG laser (12 ampere, 10 kHz pulse
frequency and 200 mm/s) is high in contrast (dark marking) and
abrasion-resistant.
[0055] The marking with a CO.sub.2 laser (energy density 73
J/cm.sup.2) leads to a pale grey marking.
* * * * *