Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2161816
Production of coatings having three-dimensional optical effects
The present invention relates to a novel process for the produc-
5 tion of coatings having three-dimensional optical effects by ori-
enting magnetically orientable, lamellar pigments.
Prints or finishes which exhibit three-dimensional optical fea-
tures are suitable not only for decorative purposes but are also
10 of interest in particular for the production of forgery-proof ma-
terials, in particular for security printing, so they cannot be
photocopied and therefore enable the original to be easily dis-
tinguished from forgeries.
15 Such three-~ nsional optical effects can advantageously be pro-
duced by orienting magnetic, lamellar pigments in the still liq-
uid application medium by the influence of a magnetic field and
can be fixed by subsequent curing of the application medium.
20 US-A-2 570 856 describes the magnetic orientation of ferromag-
netic metal pigments, but no feasible process for the controlled
production of three-dimensional effects is disclosed here.
DE-A-39 38 055 discloses various methods for producing three-
25 dimensional patterns by orientation of magnetizable, lamellar
pigments, in particular of mica and aluminum lamellae, which are
coated with a magnetic layer or mixed with magnetic material.
In one of these methods, the desired pattern is applied to a mu-
30 metal foil by punching or cutting out, the layer to be oriented
is placed on this foil and a magnetic field of suitable magnitude
is generated under the foil, with the result that orientation of
the magnetic pigment particles corresponding to the desired pat-
tern should take place. However, the disadvantage here is that an
35 optimum, ie. complete, field configuration of the magnetic par-
ticles is not achieved above the mu-metal foil, and a new mu-
metal foil must be prepared for each pattern.
In a second method, a character is written directly into a moist
40 print by moving a permanent magnet along it. However, for perma-
nent orientation of the pigment particles, the magnetic filed has
to act for a certain time, ie. the magnet has to be moved slowly,
and it is for this reason that the layer is partially dry even
before the end of the write process.
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In a third method, a treatment in a magnetic field is combined
with treatment with UV light in order to cure the layer. In this
complicated variant, the moist layer is exposed through a photo-
mask, the pigment particles are then magnetically oriented in the
5 still moist parts and the entire layer is then cured by UV light.
It is an object of the present invention to remedy the stated de-
ficiencies and to provide a feasible orientation method.
10 We have found that this object is achieved by a process for the
production of coatings having three-dimensional optical effects
by orientation of magnetically orientable, lamellar pigments,
which comprises orienting the pigments in the still liquid coat-
ing by means of the magnetic field of a previously magnetically
15 configured sheet-like transfer medium.
Suitable magnetizing sheet-like transfer media for the novel pro-
cess are in particular plastics films in which magnetically hard
particles are incorporated, but other sheet-like magnet designs
20 could also be used.
The plastics films may be applied to a thin substrate, for exam-
ple an adhesive film, but are preferably substrate-free materi-
als, especially magnetic foils or adhesive magnetic foils or mag-
25 netic tapes, such as those which are generally available commer-
cially. The thickness of these materials is as a rule from 0.1 to
5 mm.
The magnetically hard particles contained in the plastics films
30 may consist, for example, of the following magnetically hard
materials:
hard ferrites, such as barium ferrite and strontium ferrite; rare
earth alloys, such as samarium/cobalt alloys; the AlNiCo group;
35 metal oxides which are used for magnetic information storage,
such as cobalt-containing y-iron(III) oxide, chromium dioxide or
pure iron particles.
Typical dimensions of the magnetically hard particles are in gen-
40 eral from a few 10 ~m down to 10-20 nm.
The magnetic particles can be prepared in a conventional manner,
for example by sintering or rapid quenching and subsequent com-
minution.
21 61 81 6
The magnetic properties of the transfer medium need not meet any
special requirements, but materials having high saturation magne-
tization are generally advantageous. It is also advantagoeus if
the coercive force is roughly of the same magnitude as the magne-
5 tization of the total transfer medium, but this is not essential.
The thickness of the transfer medium corresponds preferably to0.3-3 times the resolution desired in the final special-effect
coating.
In the novel process, the desired three-dimensional optical ef-
fects are transferred by means of the magnetic field of the pre-
viously correspondingly configured transfer medium to the magnet-
ically orientable lamellar pigments in the still moist coating
15 (for example print or finish.
It is advisable first uniformly to magnetize the transfer medium,
ie. uniformly to orient all magnetic particles in the transfer
medium (preferably perpendicular to the surface of the transfer
20 medium) and thus to remove existing magnetization patterns. This
is advantageously effected with the aid of a strong, large-area
permanent magnet, for example based on neodymium/iron/boron al-
loys, such as Nd2Fel4B.
25 The subsequent configuration of the transfer medium, ie. the con-
trolled remagnetization of the part-magnets, for recording the
desired information or the three-dimensional pattern, can be par-
ticularly advantageously effected by movement of the transfer me-
dium relative either to (between) the pole pieces of a double-en-
- 30 ded electromagnet or to the pole piece of a one-ended pin-like
electromagnet equipped with a pole piece only on one side.
Preferred embodiments of the double-ended and of the one-ended
version are shown schematically in Fig. 1 and Fig. 2.
Fig. 1 shows the preferred perpendicular arrangement of the mov-
able transfer medium (T) in the gap of an electromagnet equipped
with pole pieces (p) at both ends.
40 Fig. 2 shows the preferred perpendicular arrangement of the
transfer medium (T), which is once again movable, relative to the
pole piece (p) of the one-ended, pin-like electromagnet. In order
to make the magnetic circuit more effective, it is advisable in
the case of the one-ended version to generate a partial magnetic
45 yoke by placing a magnetically soft plate (W), for example of
iron, underneath.
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of course, the coils (S) may in both cases be oriented at other
points in the magnetic circuit or may be completely or partly re-
placed by permanent magnets.
5 In order to achieve good resolution during recording, it is ad-
visable, as indicated in Fig. 1 and Fig. 2, to use tapering pole
pieces. The diameter at the tip of the pole piece depends on the
desired local resolution in the special effect coating and is as
a rule from about 0.3 to 3 times this resolution.
The field strength in the gap of the double-ended electromagnet
or the field strength in front of the pole of the one-ended elec-
tromagnet (pin) preferably corresponds to the coercive force of
the transfer medium.
The double-ended version of the electromagnet is, as a rule, a
better resolution of the recorded three-dimensional pattern. How-
ever, the one-ended, pin-like version is easier to handle. De-
pending on the requirements, one or other version will therefore
20 be given preference.
The recording process (ie. configuration of the transfer medium)
may also be automatic with the aid of a plotter. Depending on the
geometry, it is more advantageous to arrange the transfer medium
25 or the magnet (or both) in such a way that it is or they are
movable. This makes it possible to transfer characters or graph-
ics directly from a computer to the transfer medium.
The subsequent transfer of the three-dimensional patterns to the
30 coating contA;n;ng magnetic pigment or to the material (eg. film,
paper, cardboard or (preferably nonmagnetic) metal) coated with
magnetic pigments (and printed, lacquered or coated by the con-
ventional methods), the configured transfer medium is brought
into contact as completely and uniformly as possible with the
35 still moist coating (print or finish) in which the pigment par-
ticles are still mobile. Preferably, the coating material is sim-
ply placed on the transfer medium.
With the aid of the novel process, all magnetically orientable,
40 lamellar pigments can be oriented easily and in a controlled man-
ner. Examples are the ferromagnetic metal lamellae mentioned in
US-A-2 570 856 and the mica and aluminum lamellae which are men-
tioned in DE-A-39 38 055 and are coated with magnetite, and the
aluminum lamellae which are described in DE-A-43 13 541 and in
45 DE-A-43 40 141, which is not a prior publication, and are coated
with an inner layer cont~;n;ng iron, cobalt, nickel and
y-iron(III) oxide (maghemite) and with a further nonferromagnetic
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metal oxide layer and/or an outer passivating layer containing
phosphate, chromate andtor vanadate.
The aluminum lamellae which are described in DE-A-44 19 173,
5 which is not a prior publication, and have a multiple coating
comprising (A) iron, cobalt, nickel, magnetite and/or y-Fe2O3, (B)
silica and/or alumina and (C) metal and/or nonselectively
absorbing metal oxide are particularly noteworthy. In the case of
finishes or prints which contain these pigments, the
10 three-dimensional effects are accompanied not only by the usual
light/dark flop but also by a color change between the
interference colors.
As a rule, the action times for the orientation of pigment par-
15 ticles are only from 1 to 100 seconds, regardless of the complex-
ity of the patterns.
Depending on the type of coating medium (for example, reference
may be made here to DE-A-39 38 055), the subsequent drying pro-
20 cess by which the pigment particles and hence the three-dimen-
sional optical effects are fixed can be accelerated by additional
UV irradiation.
With the aid of the novel process, three-dimensional optical
25 effects can advantageously be produced reliably and with the
desired (good1 resolution, ie. with the desired contrast and the
desired strength, in coatings, such as prints or finishes,
containing magnetically orientable, lamellar pigments, advanta-
geously by simple adaptation of the process diameters (pole piece
30 diameter and field strength of the magnet, contact time, thick-
ness and coercive force of the transfer medium. The present
process is in particular cost-efficient, owing to the short time
it requires (short recording times and short transfer times), the
reusability of the transfer medium, which can be uniformly
35 magnetized again at any time with the aid of a strong permanent
magnet and is then available for further recording processes, and
the possibility of automation by computer control.
Examples
A commercial, 1 mm thick barium ferrite-containing adhesive mag-
netic film (from IBS, Berlin) was completely magnetized in each
case with a powerful permanent magnet (Nd2Fe14B), after which a
zigzag pattern was repeatedly recorded on said film with movement
45 at a speed of about 1 cm/sec, with the aid of an electromagnet
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equipped with pole pieces at both ends (pole piece spacing about
1 mm, 2 coils with 480 windings each).
The pole piece diameter and current were varied as stated in the
5 table.
A still moist screen print was then placed on the recorded-on
magnetic film for 60 seconds in each case.
lO The screen prints used for this purpose were each applied to pa-
per or film by printing (49-line screen) a screen printing ink
which contained 20 g of magnetizable pigment (Example 1 of
DE-A-43 13 541) in 80 g of a commercial binder solution
(copolymer based on vinyl chloride and vinyl isobutyl ether
15 _ Laroflex~ MP45-/-acetate/aliphatic).
In all cases, the zigzag pattern was clearly visible in the dried
print and could not be copied unchanged.
20 Further details of these experiments and the results thereof are
shown in the table below.
Table
Example Pole piece diameter Current Result in the print
[mm] [A]
1 l 0.4 contrast and resolution
excellent; coat thickness
1 mm
2 0.5 0.4 Contrast and resolution
good; coat thickness
slightly less than 1 mm
3 0.5 0.8 Contrast and resolution
good; coat thickness 1.5 mm
4 2 0.4 Contrast and resolution
good; coat thickness 2 mm
