Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02294235 1999-12-17
;'~E, PAN-FPI THIS Ai~9ED
THEfi-TRANSLATION
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- Laser-markable plastics
The present invention relates to laser-markable
plastics of which a feature is that a plastic which is
difficult to laser-treat comprises as absorber material
one or more intrinsically laser-markable polymers in
the form of micromilled particles having a particle
size of 0.1 - 100 Vim.
The labelling of production goods is becoming
increasingly important in almost all sectors of
industry. For example, it is frequently necessary to
apply production dates, expiry dates, barcodes, company
logos, serial numbers, etc. At present, these marks are
predominantly made using conventional techniques such
as printing, embossing, stamping and labelling.
However, the importance of contactless, high-speed and
flexible marking using lasers is increasing, especially
in the case of plastics. This technique makes it
possible to apply graphic inscriptions, for example
barcodes, at high speed even on a non-planar surface.
Since the inscription is within the plastics article
itself, it is durable and resistant to abrasion.
Many plastics, for example polyethylene (PE),
polypropylene (PP), polyamide (PA), polymethyl meth
acrylate (PMMA), polyoxymethylene (POM), polyurethane
(PUR), polyesters have hitherto proved to be very
difficult or even impossible to mark by means of the
laser. A COZ laser which emits light in the infrared
region at' 10.6 ~m produces only a faint, barely legible
mark on polyolefins, even at very high output levels,
since the absorpt~.on coefficient of the plastics to be
processed is not high enough at these wavelengths to
induce a colour change in the polymeric material. The
plastic must not completely reflect or transmit the
laser light, since if it did there would be no
interaction. However, there must also not be strong
absorption, since in that case the plastic evaporates.
to leave only an engraving. The absorption of the laser
beams and hence the interaction with the material
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- depends on the chemical structure of the plastic and on
the laser wavelength employed. In many cases it is
necessary to add appropriate additives, for example
absorbers, in order to render plastics laser
s inscribable.
The article "Pearl Lustre Pigments -
Characteristics and Functional Effects" in Speciality
Chemicals, May 1982, Vol.2, No. 2 discloses the use of
pearl lustre pigments for laser marking. Pearl lustre
.10 pigments, however, have the disadvantage that they
severely alter the colour properties of the plastic, an
effect which is often unwanted.
DE-A 29 36 926 discloses that the inscription
of a polymeric material by means of laser light can be
15 achieved by adding to the plastic a filler, such as
carbon black or graphite, which discolours on exposure
to energetic radiation.
EP 0 190 997 A prepares laser-inscribable
moulding compounds, including PE, ~.~ or PS, by
20 adding at least one inorganic pigment to the high
molecular mass organic material.
In EP 0 330 869, Ti02 and carbon black are added
to PBT and PET. The inscription is dark on a light
background. The use of carbon black and/or graphite as
25 absorbers in connection with the laser marking of
polyesters is known from EP 0 485 181.
However, the fillers known for laser marking
have the disadvantage either that they permanently
colour the plastic that is to be inscribed, and hence
30 the laser inscription, which is usually a dark script
on a lighter background, then lacks sufficient
contrast, i . a . legibility, or that as in the case, for
example, of kaolin the mark is very faint and becomes
readily visible only when large amounts of the additive
35 are employed.
DE 195 36 047 describes the use of
polycarbonate, which itself is difficult to laser-mark
owing to its amorphous structure, in a polymer matrix
of a polyalkylene terephthalate. Through absorption of
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laser energy it is possible for dark characters to be
achieved on a light background in the polymer matrix of
a polyalkylene terephthalate.
In addition to the abovementioned plastics,
however, there are also polymers which can be marked by
means of a laser with darkness and great contrast
without the addition of additives. Examples of such
polymers include PET, butadiene-styrene (ABS),
polystyrene, polyphenyl ether (PPO), liquid crystal
polymers (LCP), polyphenylene sulfide, polyarylates,
'polyaryl sulfides, polyaryl sulfones, polyaryl ether
ketones, and blends thereof.
The object of the present invention, therefore,
was to find laser-markable plastics which permit high
contrast laser marking on exposure to laser light. In
this context, the filler or successful absorber should
have a very pale, neutral inherent colour and should
possess the properties of the precoloured plastic that
is to be marked or should have little or no effect on
these properties.
It has surprisingly been found that a plastic
which is difficult to laser-treat can be marked very
effectively if, for example, one of the abovementioned
intrinsically markable polymers is added in fine
distribution to the plastic. The intrinsic markability
of the polymer is thus transferred to the plastic which
shows little if any such behaviour. Following laser
bombardment, a plastic doped in this way shows high
contrast'and crisply contoured markings even at low
laser intensities.
The invention therefore provides laser-markable
plastics, characterized in that plastics which are
difficult to laser-treat comprise one or more
intrinsically markable polymers having a particle size
of from 0.1 to 100 Vim. .
Through the addition of micromilled,
intrinsically markable polymers as absorbers in
concentrations of 0.1 to loo by weight, preferably 0.1
to 5°s by weight and, in particular, 0.1 to 2% by
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- weight, based on the plastics system, a high contrast
is obtained in connection with laser marking. The
concentration of the intrinsically markable polymers in
the plastic, however, is dependent on the plastics
system employed and on the laser used.
Suitable polymers or polymer mixtures are all
known readily laser-treatable plastics, such as PET,
ABS, polystyrene, PPO, polyphenylene sulfide,
polyphenylene sulfone, polyimidosulfone and LCPs, for
example.
Micromilled thermoplastics having a very high
melting range of >300°C are particularly suitable. The
crispness of the contours of the mark is determined in
particular by the particle size of the micromilled
polymers. The polymers preferably have particle sizes
in the range from 0.1 to 50 Vim, in particular from 1 to
2 0 ~.m .
The resulting mark is positively influenced if
the intrinsically markable polymer comprises as further
absorber, a light-sensitive pigment, such as a filler,
for example, a conductive pigment and/or a special-
effect pigment. The addition of a further absorber
intensifies the contrast as a function of the plastics
system used. The amount of light-sensitive pigment
added should be between 0.1 and 90%
Particularly suitable light-sensitive pigments
are fillers, such as Ti02 and Si02, for example, and
phyllosilicates. Suitable silicatic platelets here are,
in particular, light-coloured or white micas. It is of
course also possible to use other natural micas, such
as phlogopite and,biotite, synthetic mica, talc flakes
and glass flakes. By special-effect pigments are meant
all known lustre, metallic and pearl lustre~pigments,
as marketed, for example, by the companies Mearl,
Eckart-Werken and Merck KGaA. Examples of suitable
conductive pigments are the pigments marketed under the
tradename Minatec~ by Merck KGaA. These are platelet-
shaped TiOz/ mica pigments comprising an external
tin/antimony oxide layer as conductive coat. Other
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suitable light-sensitive pigments are the oxides,
hydroxides, sulfides, sulfates and phosphates of metals
such as copper, bismuth, tin, zinc, silver, antimony,
manganese, iron, nickel and chromium, for example.
5 Particular mention should be made in this case of the
use of antimony, bismuth oxychloride and basic
copper(II) hydroxide phosphate. Particular preference
in this context is given to a product as formed by
heating blue Cu ( I I ) orthophosphate ( Cu3 ( POQ ) 2~3 Hz0) by
heating lto from 100 to 200°C, and which has the
empirical chemical formula 4 CuO~PZO5~H20 or
Cu, (PO,) 2~Cu (OH) 2. Other suitable copper phosphates are 6
CuO~PZ05~3 HzO, Cu3 (P04) z~3 Cu (OH) Z, 5 CuO~P205~3 H20,
Cu3 (P04) y2 Cu (OH) Z~H20, 4 CuO~Pz05, 4 CuO~P205~3Hz0, 4
CuO~Pz05- 1.5 HzO, 4 Cu0-PZOS~ 1.2 H20.
An improvement in laser markability is also
achieved if, in addition to the intrinsically marking
polymer, one or more abovementioned light-sensitive
pigments are added as a further component to the
plastic. In this case the proportion by weight of all
absorbers in the plastic, in combination with the
micromilled polymers, should not exceed a total of l00
by weight, based on the plastics system. The plastic
preferably contains 0-5% by weight of light-sensitive
pigments, especially 0-to by weight. In this context,
there is no restriction on the proportion in which the
light-sensitive pigments are mixed with the micromilled
polymers.
It is also possible to add, to the plastic that
is difficult to laser-treat, colour pigments, which
permit colour variations of any type and at the same
time ensure that the laser marking is retained.
The light-sensitive pigments and/or colour
pigments are added preferably together with the
polymers, although separate addition is also possible
in principle. A mixture of different light-sensitive
pigments can also be added to the plastic.
Marking is preferably carried out using high-
energy radiation, generally in the wavelength range
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from 150 nm to 10,600 nm, in particular in the range
from 150 nm to 1100 nm. Mention may be made here, for
example, of COz lasers (10,600 nm), Nd:YAG lasers
(1064 nm or 532 nm) or pulsed UV lasers (excimer
lasers). Particular preference is given to the use of
Nd:YAG lasers (1064 nm and 532 nm) and COz lasers
(10,600 nm). The energy densities of the lasers
employed are generally in the range from 0.3 mJ/cmz to
50 J/cmz, preferably in the range from 0.3 mJ/cm~ to
10 J/cmz .
All known plastics which can only be laser-
marked with great difficulty, as are described, for
example, in Ullmann, Vol. 15, p. 457 ff.,
-, Verlag VCH or Saechtling Kunststoff Taschenbuch,
can be employed for laser marking through addition of
the polymers of the invention. Examples of such
plastics are thermosets, polyethylene (PE-HD, PE-LD,
PE-LLD), polypropylene (PP), polyesters, polyacetal,
polyamides (PA), polyurethanes (PUR), polybutylene
terephthalate, polymethyl methacrylate (PMMA),
polyvinyl acetal, polystyrene, butadiene-styrene (ABS),
acrylonitrile-styrene-acrylate (ASA), and their
copolymers and/or mixtures thereof. In particular,
polyolefins, polyurethanes, polyoxymethylenes and
polyamides, owing to their mechanical properties, the
cost-effective processing methods and their poor laser-
markability, are suitable for doping with the polymers
of the invention.
The incorporation of the micromilled polymer
into the plastic takes place by the techniques known
for pigments and fillers. Subsequently, the pigmented
plastic is then deformed under the action of heat. When
choosing the intrinsically markable polymer to be
milled it should be borne in mind that the particle
structure is retained following the incorporation; in
other words, the particles should not be soluble in the
melt, and should not melt as well. This is achieved by
appropriate tailoring of the melting ranges of the
plastics system to that of the micromilled polymer.
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When the micromilled polymer is incorporated
into the plastics granules it is possible, if desired,
to add coupling agents, organic, polymer-compatible
solvents, stabilizers, optical brighteners, colour
pigments, dyes, fillers, reinforcing agents,
flameproofing additives, antistatics and/or surfactants
which are temperature-stable under the operating
conditions. In addition to the auxiliaries customarily
employed it is possible to add further additives, not
mentioned here, to the plastic. The presence of further
'additives in the existing plastics systems, however,
may exert an effect on the marking result.
The plastics granule/polymer mixture is
generally prepared by charging an appropriate mixer
with the plastics granules, wetting them with any
additives, and then adding the micromilled polymers and
mixing them in. The mixture obtained in this way can
then be processed directly in an extruder or an
injection moulding machine. The mouldings formed in the
course of processing usually exhibit a very homogeneous
distribution of the polymers or of the polymer mixture.
Finally, laser marking takes place, preferably with a
Nd:YAG laser.
Inscription with the laser is carried out by
introducing the sample into the beam path of a pulsed
laser, preferably a Nd:YAG laser. Inscription with a COZ
laser or an excimer laser is also possible. However,
the desired results can also be achieved with other
types ofwlaser featuring a wavelength in a range of
high absorption by the intrinsically marking polymer.
The resulting shade and depth of colour are determined
by the laser parameters, such as the irradiation time
and irradiation output. The output of the lasers used
depends on the particular application and can be
determined regularly in each individual case by the
skilled worker.
The plastic doped in accordance with the
invention can be used in all sectors where customary
printing processes have hitherto been employed for the
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inscription of plastics. For example, mouldings of the
plastic of the invention can be employed in the
electrical, electronic and motor vehicle industry. The
labelling and inscription of, for example, housings,
lines, keycaps, transcripts or functional parts in the
heating, ventilation and cooling sectors, or switches,
plugs, levers and handles which consist of the plastic
of the invention, can be marked with the aid of
laser light, even at difficult-to-reach points. Owing
to its low heavy-metal content, the plastics system of
the invention can also be employed in packaging in the
foodstuffs sector or in the toy sector. The markings on
packaging are notable for their resistance to wiping
and scratching, for their stability during subsequent
sterilization processes, and for the fact that they can
be applied in a hygienically pure manner in the marking
. process. Complete label motifs can be applied durably
to the packaging for a reusable system. Another
important area of application for laser inscription is
that of identity cards and plastic tags for the
individual identification of animals: so-called cattle
tags or earmarks. The laser marking of plastics
articles or mouldings which consist of the plastic of
the invention is hence possible.
The examples which follow are intended to
illustrate the invention without, however, restricting
it.
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Examples
Example 1
_ g _
99 parts of polypropylene (Stamylan PPH 10 from DSM)
1 part of polyphenylene sulfide milled to a particle
size < 25 ~m
The components are physically mixed and by
means of an injection moulding machine are homogenized
and shaped to form platelets. The inscription with a
Nd:YAG laser at 532 and 1064 nm wavelengths shows a
high-contrast black marking with a smooth surface over
a wide range of settings.
Example 2
99.5 parts of polypropylene (Stamylan PPH 10)
0.5 part of polyphenylene sulfone milled to a
particle size < 10 ~m
The components are mixed and by means of an
injection mou 'n machine are homogenized and shaped
to form The inscription with a Nd:YAG ~~~~,~~
laser shows a high-contrast black marking with a smooth
surface over a wide range of settings.
Example 3
99 parts of polyamide 6 (Ultramid B3K from BASF)
1 part of polyimidosulfone milled to a particle size
3 0 < 15 ~.m
The components are mixed and by means of an
injection moulding machine are homogenized and shaped
to form platelets . The inscription with a Nd: YAG laser
shows a high-contrast deep-black marking with a smooth
surface over a wide range of settings.
Example 4
99.6 parts of polyamide 6 (Ultramid B3K)
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0.4 part of polyphenylene sulfide milled to a
particle size < 10 ~m
The components are mixed and by means of an
injection moulding machine are homogenized and shaped
to form platelets. The inscription with a Nd:YAG laser
shows a high-contrast black marking with a smooth
surface over a wide range of settings.
Example 5
99 parts of polyoxymethylene (Delrin from Du Pont)
1 part of polyphenylene sulfide milled to a particle
size < 5 ~m
The components are mixed and by means of an
injection mou~~~ machine are homogenized and shaped
to form . The inscription with a Nd:YAG
laser shows a high-contrast black marking with a smooth
surface over a wide range of settings.
Example 6
99 parts of unsaturated polyester resin (Palatal from
BAS F )
1 part of polyphenylene sulfide milled to a particle
size < 10 ~.m
The polyphenylene sulfide is incorporated
homogeneously into the liquid polyester casting resin
by stirring. Following the addition of accelerator (Co
octoate) and hardener (cyclohexanone peroxide), the
mixture is poured into a mould. After curing has taken
place, a moulding is obtained which can be given a
high-contrast black marking by means of Nd:YAG lasers.
Example 7
99 parts of polysulfone (Ultrason from BASF)
are compounded on an extruder together with 1 part of
mica. The compound is micromilled to a particle size of
< 10 Vim. 0.50 of the powder thus obtained are added to
a PMMA. This mixture is processed on an extruder to
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give sheets which can be given a black and high-
contrast marking with a Nd:YAG laser at a wavelength of
S32 and 1,064 nm.
Example 8
96 parts of polyphenylene sulfide are
compounded by the method of Example 7 with 4 parts of
basic copper phosphate. An addition of just 0.40 of the
micromilled powder of this mixture to commonly non-
laser-markable plastics, such as.
(a) polyethylene (PE)
(b) polypropylene (PP)
(c) olyamide (PA)
(d) thyl methacrylate (PMMA)
(e) polyurethane (PU)
. (f) polyoxymethylene (POM)
gives deep-black, high-contrast markings with crisp
contours using a Nd:YAG laser.
