U.S. patent application number 15/734741 was filed with the patent office on 2021-08-05 for polyolefin composition providing marking by fluorescence.
The applicant listed for this patent is BOREALIS AG. Invention is credited to Francis Costa, Bhawna Kulshreshtha, Denis Yalalov.
Application Number | 20210238385 15/734741 |
Document ID | / |
Family ID | 1000005580121 |
Filed Date | 2021-08-05 |
United States Patent
Application |
20210238385 |
Kind Code |
A1 |
Kulshreshtha; Bhawna ; et
al. |
August 5, 2021 |
POLYOLEFIN COMPOSITION PROVIDING MARKING BY FLUORESCENCE
Abstract
The present invention is directed to a polyolefin composition
comprising carbon black which shows fluorescence when irradiated
with UV light. The polyolefin composition of the present invention
comprises a polyolefin, carbon black in an amount of 0.25 to 1.0 wt
%, an optical brightener in an amount of 0.001 to 0.1 wt %, and a
UV agent. The present invention is further directed to a molded
article comprising the polyolefin composition of the present
invention. The present invention is further directed to a wire or
cable comprising an outer layer comprising the polyolefin
composition of the present invention. Finally, the present
invention is directed to a method for detection of a polyolefin
composition by UV light and to a method for detection of a molded
article or a wire or cable by UV light.
Inventors: |
Kulshreshtha; Bhawna;
(Vienna, AT) ; Yalalov; Denis; (Stenungsund,
SE) ; Costa; Francis; (Linz, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOREALIS AG |
Vienna |
|
AT |
|
|
Family ID: |
1000005580121 |
Appl. No.: |
15/734741 |
Filed: |
June 12, 2019 |
PCT Filed: |
June 12, 2019 |
PCT NO: |
PCT/EP2019/065364 |
371 Date: |
December 3, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/06 20130101;
C08L 23/06 20130101; C09K 2211/1051 20130101; C08L 2207/062
20130101; C08L 2203/202 20130101; C08L 2201/08 20130101; C08K
5/0041 20130101; C08K 3/04 20130101; C08K 5/45 20130101; B41M 5/267
20130101 |
International
Class: |
C08K 5/00 20060101
C08K005/00; C08L 23/06 20060101 C08L023/06; C08K 5/45 20060101
C08K005/45; C08K 3/04 20060101 C08K003/04; B41M 5/26 20060101
B41M005/26; C09K 11/06 20060101 C09K011/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2018 |
EP |
18178455.4 |
Claims
1. A polyolefin composition comprising (A) a polyolefin, (B) carbon
black in an amount of 0.25 to 1.0 wt % based on the weight of the
polyolefin composition, (C) an optical brightener in an amount of
0.001 to 0.1 wt % based on the weight of the polyolefin
composition, and (D) a UV agent.
2. The polyolefin composition according to claim 1, wherein the
polyolefin is selected from the group consisting of an ethylene
homopolymer, an ethylene copolymer, a propylene homopolymer, a
propylene copolymer, a blend of an ethylene homopolymer and an
ethylene copolymer, and a blend of a propylene homopolymer and a
propylene copolymer.
3. The polyolefin composition according to claim 1, wherein the
ethylene copolymer is a copolymer of ethylene and a
C.sub.3-C.sub.12-alpha-olefin.
4. The polyolefin composition according to claim 1, wherein the
propylene copolymer is a copolymer of propylene and ethylene and/or
a C.sub.4-C.sub.12-alpha-olefin.
5. The polyolefin composition according to claim 1, wherein the
polyolefin is high density polyethylene (HDPE).
6. The polyolefin composition according to claim 1, wherein the
polyolefin is polypropylene.
7. The polyolefin composition according to claim 1, wherein the
amount of carbon black is 0.25-0.75 wt %, preferably 0.25-0.5 wt %,
based on the weight of the polyolefin composition.
8. The polyolefin composition according to claim 1, wherein the
amount of the optical brightener is 0.001 to 0.05 wt %, preferably
0.003 to 0.03 wt %, based on the weight of the polyolefin
composition.
9. The polyolefin composition according to claim 1, wherein the
optical brightener is
2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole).
10. The polyolefin composition according to claim 1, wherein the
amount of the UV agent is 0.1 to 1.0 wt % based on the weight of
the polyolefin composition.
11. A molded article comprising, preferably consisting of, a
polyolefin composition according to claim 1.
12. The molded article according to claim 11, wherein the article
is an outer layer of a cable.
13. A cable comprising an outer layer comprising, preferably
consisting of, the polyolefin composition according to claim 1.
14. A method for detection of a polyolefin composition by UV light
comprising the following steps providing a polyolefin composition
according to claim 1, irradiating the polyolefin composition with
UV light, detecting fluorescence emitted from the polyolefin
composition.
15. A method for detection of a molded article or a cable by UV
light comprising the following steps providing a molded article or
a cable according to claim 11, irradiating the molded article or
the cable with UV light, detecting fluorescence emitted from the
molded article or the cable.
16. A method for detection of a molded article or a cable by UV
light comprising the following steps providing a molded article or
a cable according to claim 13, irradiating the molded article or
the cable with UV light, detecting fluorescence emitted from the
molded article or the cable.
Description
[0001] The present invention is directed to a polyolefin
composition comprising carbon black which shows fluorescence when
irradiated with UV light. It is suitable for many applications
where marking of a molded article made of a polyolefin composition
is required, e.g. as outer layer of a wire or cable or in
automotive applications. The present invention is further directed
to a molded article comprising the polyolefin composition of the
present invention. The present invention is further directed to a
wire or cable comprising an outer layer comprising the polyolefin
composition of the present invention. Finally, the present
invention is directed to a method for detection of a polyolefin
composition by UV light and to a method for detection of a molded
article or wire or cable by UV light.
[0002] Marking of molded articles is a continued need to indicate
serial numbers and further information thereon. The skilled person
knows suitable methods for marking of molded articles made of
polyolefin compositions like those based on polyethylene or
polypropylene, e.g. conventional printing techniques like ink jet,
embossing etc. In the area of communication and power cables,
marking is necessary in order to provide information to the
installer, such that the installation is done correctly and
efficiently. Similarly, in the automotive field, marking is
necessary to provide information about the manufacturer of the
molded article since often a particular molded article to be used
in e.g. a car is received from more than one supplier. Also several
further data is often required on a molded article, e.g.
productions dates, expiry dates, bar codes, and company logos.
[0003] For many applications, however, conventional printing
techniques like ink jet, embossing etc. are not suitable, since the
outer surface of the molded article is not sufficient for providing
a print using the conventional techniques, or since the shape of
the molded article does not allow printing with conventional
techniques, e.g. since the relevant part of the surface of the
molded article is non-planar.
[0004] Therefore, use of laser printing techniques is gaining more
importance. In particular for fiber optic micro cables (FOC),
conventional printing techniques are not suitable, given the very
small outer surface of such micro cables. The increased need for
micro cables has accordingly also increased the use of laser
printing. One of the advantages of laser printing is that such
printing can be performed at higher line speed compared to the
alternatives, thus increasing cost-efficiency. Another advantage is
that a laser-induced print cannot be erased so easily by rubbing or
friction as opposed to ink jet print.
[0005] EP 0 924 095 A1 discloses a method for marking a polyolefin
composition comprising irradiating with a YAG laser a polyolefin
composition containing 0.1 to 1.0 part by weight of carbon black
per 100 parts by weight of the polyolefin composition, wherein the
carbon black has an average secondary particle size of not smaller
than 150 nm.
[0006] Apart from the importance of marking of the surface of a
molded article with e.g. text and labels, which may provide
important information about the type and/or origin of the molded
article, it would be also desirable to have a marking which is
typical for the particular molded article or for the underlying
polyolefin composition and which marking cannot be seen at first
glance but is visible under particular conditions. For example, it
would be desirable if an individual wire or cable, or a certain
type of wire or cable, could be easily identified amongst other
wires or cables. This could be interesting in case of malfunction
and help to identify the particular wire or cable which shall be
advantageously disconnected or replaced, e.g. in a cable funnel
with several different cables.
[0007] Amongst the possibilities of further marking is in general
the addition of agents which cause fluorescence upon irradiation
with UV light, so-called optical brighteners or fluorescent agents.
However, in case of outer layers of wires or cables the high load
of carbon black usually prevents any visible detection of
fluorescence. Similar considerations apply of course for molded
articles containing carbon black used in different fields of
applications, e.g. automotive.
[0008] There is accordingly still a need for providing a polyolefin
composition comprising carbon black which shows fluorescence when
irradiated with UV light.
[0009] The present invention is based on the finding that the
object can be solved by provision of a polyolefin composition
comprising an ethylene or propylene homo- or copolymer, carbon
black, an optical brightener and a UV agent. The polyolefin
composition is suitable for many applications, e.g. in the field of
automotive, or for a cable jacketing layer, i.e. an outer layer of
a wire or cable, and provides good results in laser printing,
too.
[0010] The polyolefin composition according to the present
invention has the advantage of showing fluorescence upon
irradiation with UV light.
[0011] Accordingly, the present invention is in one aspect directed
to a polyolefin composition comprising [0012] (A) a polyolefin,
[0013] (B) carbon black in an amount of 0.25 to 1.0 wt % based on
the weight of the polyolefin composition, [0014] (C) an optical
brightener in an amount of 0.001 to 0.1 wt % based on the weight of
the polyolefin composition, and [0015] (D) a UV agent.
[0016] It should be noted that in polyolefin compositions of the
prior art used as jacketing (outer layer) of fiber optic micro
cables (FOC), the amount of carbon black is at least 2.5 wt %. This
amount of carbon black is normally necessary in order to provide
sufficient UV stability to the jacketing layer.
[0017] The polyolefin composition according to the present
invention further comprises a UV agent to compensate the lack of
carbon black, i.e. the relatively low amount of carbon black, and
accordingly provide sufficient protection against UV light.
[0018] It is believed that the reduced amount of carbon black
allows the visible detection of fluorescence.
Polyolefin (A)
[0019] The polyolefin (A) is preferably selected from the group
consisting of an ethylene homopolymer, an ethylene copolymer, a
propylene homopolymer, a propylene copolymer, a blend of an
ethylene homopolymer and an ethylene copolymer, and a blend of a
propylene homopolymer and a propylene copolymer.
[0020] The ethylene homopolymer, the ethylene copolymer, the
propylene homopolymer, and the propylene copolymer may consist of
more than one homopolymer or copolymer, respectively, i.e. two
homopolymers differing in the molecular weight distribution, two
copolymers differing in the molecular weight distribution and/or
differing in the content and/or type of comonomer. The same counts
for the homopolymer and the copolymer in the blends. Further on, in
these blends also the homopolymer and the copolymer may differ in
the molecular weight distribution.
[0021] The terms "ethylene homopolymer" and "propylene homopolymer"
as used herein relate to a polyethylene or polypropylene,
respectively, that consists substantially, i.e. of at least 99.5 wt
%, more preferably of at least 99.8 wt %, of ethylene or propylene
units, respectively. In a preferred embodiment only ethylene or
propylene units, respectively, are used in polymerization. In a
preferred embodiment only ethylene or propylene units,
respectively, are detectable in the ethylene homopolymer or
propylene homopolymer, respectively. The comonomer content can be
determined with .sup.13C NMR spectroscopy.
[0022] The term "copolymer" as used herein covers polymers obtained
from co-polymerisation of at least two, i.e. two, three or more
different monomers, i.e. the term "copolymer" as used herein does
e.g. not exclude so-called terpolymers obtained from
co-polymerisation of three different monomers.
[0023] The content of the polyolefin (A) in the polyolefin
composition of the present invention is usually at least 90 wt %,
preferably at least 95 wt %, more preferably at least 98 wt %, and
still more preferably at least 98.5 wt %. The content of the
polyolefin (A) in the polyolefin composition of the present
invention is usually not higher than 99.5 wt %.
[0024] Suitable ethylene homopolymers are low density polyethylene
(LDPE, density of 0.910-0.940 g/cm.sup.3) and high density
polyethylene (HDPE, density of at least 0.941 g/cm.sup.3). The
latter is preferred for cable applications.
[0025] The melt flow rate of suitable ethylene homopolymers is
preferably 0.2 to 3.0 g/10 min, more preferably 0.2 to 2.0 g/10
min.
[0026] Suitable ethylene copolymers are linear low density
polyethylene (LLDPE, density of 0.915-0.925 g/cm.sup.3) and very
low density polyethlylene (VLDPE, density of 0.880-0.915
g/cm.sup.3). Suitable comonomers are
C.sub.3-C.sub.12-alpha-olefins, preferably 1-butene, 1-hexene,
4-methyl-1-pentene, and/or 1-octene.
[0027] Suitable propylene homopolymers are high isotactic propylene
homopolymers.
[0028] Suitable propylene copolymers are copolymers, i.e. random
and block copolymers, with ethylene and/or a
C.sub.4-C.sub.12-alpha-oelfin, preferably with ethylene, 1-butene,
1-hexene, 4-methyl-1-pentene, and/or 1-octene. Suitable propylene
copolymers include impact copolymers having a matrix which is a
propylene homopolymer or a propylene random copolymer having
dispersed therein an ethylene-propylene rubber (EPR).
[0029] The polyolefin (A) may be unimodal or bimodal.
[0030] Preferably, the polyolefin (A) of the present invention is
bimodal, more preferably the polyolefin of the present invention is
multimodal polyethylene consisting of a low-molecular weight
ethylene homopolymer mixed with a high-molecular weight copolymer
of ethylene and butene, 4-methyl-1-pentene, 1-hexene, or
1-octene.
[0031] A suitable polyolefin (A) according to the present invention
is a polyolefin having properties required in the technical area of
jacketing, i.e. a polyolefin providing low shrinkage, high
Environmental Stress Crack Resistance (ESCR) and low Flexural
Modulus. Thus, the polyolefin (A) of the present invention
preferably has the following ESCR properties: F10>1500 h, more
preferably >8000 h; F1>700 h, more preferably >3000 h. In
this regard, the polyolefin (A) according to the present invention
may be high density polyethylene (HDPE) or polypropylene.
Carbon Black (B)
[0032] The skilled person knows carbon black as additive in
polyolefin compositions.
[0033] Together with the UV agent it provides protection against UV
light.
[0034] The polyolefin composition according to the present
invention comprising 0.25-1.0 wt % carbon black is suitable for
laser printing and provides a light-coloured visible marking with
good contrast towards dark background of black colour. It is
believed that the irradiation from the laser beam decomposes the
carbon black into volatile components. These volatile components as
well as the absorption of heat from the laser beam foam the
surface, which scatters light and leaves a light-colored
impression. The polyolefin composition according to the present
invention comprising carbon black in the range varying from 0.25 to
1.0 wt % exhibits a good performance for laser marking. In the
presence of a higher amount of carbon black, laser marking
efficiency deteriorates, and when the amount of carbon black is
above 1.0 wt %, poor contrast is achieved. The particular selected
range of amount of carbon black allows the visible detection of
fluorescence.
[0035] Preferably, the amount of carbon black in the polyolefin
composition is 0.25-0.75 wt %, more preferably 0.25-0.5 wt %.
[0036] According to the present invention, carbon black may be
added in the form of a masterbatch, wherein carbon black is
dispersed in a suitable matrix, such as a polyolefin matrix.
Alternatively, carbon black may be added directly.
UV Agent (D)
[0037] As mentioned above, it has been noted that at rather low
carbon black loadings, e.g. loadings below 2.5 wt %, degradation of
the base resin (polyolefin) caused by UV irradiation may occur. The
UV agent provides additional protection against UV light.
[0038] The amount of UV agent is preferably 0.1-1.0 wt %, more
preferably 0.2-0.5 wt %, and still more preferably 0.2-0.3 wt %,
based on the weight of the polyolefin composition.
[0039] Suitable UV agents are benzoates, triazoles, triazines or
hindered amines. Particularly, a mixture of equal amounts of
dimethyl succinate polymer with
4-hydroxy-2,2,6,6,-tetramethyl-1-piperidineethanol and
poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6-
,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4--
piperidinyl)imino]]) (Tinuvin 783 FDL, commercially available from
BASF) may be used as UV-agent.
Optical Brightener (C)
[0040] Optical brighteners are known to the skilled person and are
chemical compounds that absorb light in the ultraviolet and violet
region of the electromagnetic spectrum, i.e. around 300-430 nm, and
re-emit light in the violet and blue region by fluorescence, i.e.
around 400-500 nm.
[0041] Optical brighteners which are usable according to the
present invention are e.g. those which belong to the class
represented by 4,4'-bis(2-benzoxazolyl)stilbene and its
derivatives, like those having alkyl substituents on the aromatic
rings, and those which belong to the class represented by
2,5-bis(benzoxazol-2-yl)thiophene and its derivatives, like those
having alkyl substituents on the aromatic rings. Further optical
brighteners are disclosed in paragraph [0004] of US 2009/0137445
A1. A particular preferred optical brightener is
2,5-bis(5-tent-butyl-benzoxazol-2-yl)thiophene which is also known
as 2,5-thiophenediylbis(5-tent-butyl-1,3-benzoxazole) (CAS-Nr.
7128-64-5).
[0042] Other known optical brighteners which may be used
alternatively or additionally are those disclosed in US
2009/0137445 A1, i.e. inorganic optical brighteners based on
so-called inorganic phosphors, i.e. synthetically produced
crytalline compounds preferably having a particle size distribution
of from 0.01 to 20 .mu.m, wherein said inorganic phosphors are
preferably selected from the group consisting of sulfides and
selenides, oxysulfides, oxygen-dominant phosphors and halide
phosphors, more preferably selected from the group consisting of
BaMgAl.sub.10O.sub.17:Eu, BaMg.sub.2Al.sub.16O.sub.27:Eu,
Sr.sub.3Ca.sub.2(PO.sub.4).sub.3Cl:Eu and
(SrBaCa).sub.5(PO.sub.4).sub.3Cl:Eu, wherein the content of
europium is from 0.1 to 0,5 mole %.
[0043] As indicated above, the optical brightener is present in an
amount of 0.001 to 0.1 wt % based on the weight of the polyolefin
composition, preferably 0.001 to 0.05 wt %, more preferably 0.003
to 0.03 wt %.
Polyolefin Composition
[0044] The polyolefin composition of the present invention may have
a density of 0.915 to 0.955 g/cm.sup.3, preferably 0.920 to 0.950
g/cm.sup.3.
[0045] The polyolefin composition of the present invention may
comprise further usual additives, preferably in a total amount of
not more than 5 wt % in total, i.e. the sum of the contents of
polyolefin (A), carbon black (B), optical brightener (C), and UV
agent (D), is preferably at least 95 wt % based on the weight of
the polyolefin composition of the present invention.
[0046] The polyolefin composition according to the present
invention may further comprise an antioxidant, such as sterically
hindered phenol, phosphorus-based antioxidant, sulphur-based
antioxidant, nitrogen-based antioxidant, or mixtures thereof. In
particular, a mixture of equal amounts of pentaerythritol
tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and
tris(2,4-di-tert-butylphenyl)phosphite (Irganox B225) may be used
as antioxidant.
[0047] The polyolefin composition according to the present
invention may further comprise an antistatic agent, such as calcium
stearate, sodium stearate or zinc stearate.
[0048] Molded Article
[0049] The present invention is in a further aspect directed to a
molded article comprising, preferably consisting of, the polyolefin
composition of the present invention as described above including
all preferred embodiments.
[0050] Suitable molded articles are e.g. automotive parts or outer
layers of a wire or cable, e.g. of a power or communication wire or
cable.
[0051] According to a particular preferred embodiment, the molded
article according to the present invention is an outer layer of a
wire or cable, in particular of a fiber optic micro cable (FOC),
i.e. a cable jacket.
[0052] The present invention is in a further aspect directed to a
cable comprising an outer layer comprising, preferably consisting
of, the polyolefin composition of the present invention as
described above including all preferred embodiments.
Detection by UV Light
[0053] The present invention is in a further aspect directed to a
method for detection of a polyolefin composition by UV light
comprising the following steps [0054] providing a polyolefin
composition of the present invention as described above including
all preferred embodiments, [0055] irradiating the polyolefin
composition with UV light, [0056] detecting fluorescence emitted
from the polyolefin composition.
[0057] The present invention is in a further aspect directed to a
method for detection of a molded article or a cable by UV light
comprising the following steps [0058] providing a molded article or
a cable as described above including all preferred embodiments,
[0059] irradiating the molded article or the cable with UV light,
[0060] detecting fluorescence emitted from the molded article or
the cable.
[0061] The UV light may have any suitable wavelength. The
wavelength of the UV light is suitably 250-400 nm.
[0062] The fluorescence emitted from the polyolefin composition,
the molded article, or the cable according to the present
invention, respectively, may be detected by usual methods known to
the skilled person. One possible and easy way of detecting the
emitted fluorescence is by visual inspection.
[0063] In the following the present invention is further
illustrated by means of examples.
EXAMPLES
1. Definitions/Measuring Methods
[0064] The following definitions of terms and determination methods
apply for the above general description of the invention as well as
to the below examples unless otherwise defined.
Density
[0065] Density is measured according to ISO 1183-1--method A
(2004). Sample preparation is done by compression moulding in
accordance with ISO 1872-2:2007.
Flexural Modulus
[0066] Flexural modulus was determined according to ISO
178:2010/Amd.1:2013.
Melt Flow Rate Melt flow rate MFR.sub.2 of polyethylene was
determined according to ISO 1133 at 190.degree. C. under a load of
2.16 kg. Melt flow rate MFR.sub.2 of polypropylene was determined
according to ISO 1133 at 230.degree. C. under a load of 2.16
kg.
2. Examples
[0067] The following materials and compounds are used in the
Examples.
TABLE-US-00001 PE1 poly(ethylene-co-(1-butene)) copolymer having a
density of 963 kg/m.sup.3, an MFR.sub.2 of 12 g/10 min, mixed with
39 wt % of carbon black (CB) PE2 bimodal high density polyethylene
(HDPE) having a density of 944 kg/m.sup.3, an MFR.sub.2 of 1.7 g/10
min, a flexural modulus of 850 MPa, commercially available as
Borstar HE6068 from Borealis AG Optical
2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole), brightener
commercially available as Tinopal OB CO from BASF SE UV agent
Tinuvin 783 FDL commercially available from BASF SE Antioxidant
Irganox B225 commercially available from BASF SE Antistatic calcium
stearate commercially available as Ceasit SW from agent Baerlocher
GmbH
[0068] PE2 is used as base resin and contains already 0.2 wt % of
the antioxidant, 0.15 wt % of the antistatic agent and 0.3 wt % of
the UV agent.
[0069] Three samples were prepared using PE1 as the carbon black
masterbatch (MB), wherein PE1 was compounded with the base resin
PE2 in an amount such that the amount of carbon black in the final
composition is 0.5 wt % for each of the three samples (see Table
1). In the sample of the comparative example CE1 no optical
brightener is added. In the samples of the inventive examples IE1
and 1E2 optical brightener is added.
[0070] Compounding was implemented on ZSK 18 MEGAlab laboratory
twin screw extruder under the following conditions: speed 200 rpm;
melt temperature 175-190.degree. C.; pressure 45-50 bar; output 5
kg/h. Plaques of size 150.times.80.times.3 mm were produced from
the resulting composition using injection moulding on Engel ES
700H/80V/700H/250 3K machine under following conditions: injection
speed 11 mm/s; injection time 3.4 sec; switching pressure 66 bar;
holding time during backpressure 15 sec; cooling time 20 sec; cycle
time 45 sec; melt temperature 150.degree. C.; mould temperature
50.degree. C.
TABLE-US-00002 TABLE 1 Compositions of examples wt % CE1 IE1 IE2
Constituents Sample 1 Sample 2 Sample 4 PE2 98.75 98.74 98.745 PE1
1.25 1.25 1.25 Optical brightener -- 0.01 0.005 UV agent + + +
Antioxidant + + + Antistatic agent + + + "+" indicates the presence
of these compounds in PE2
[0071] Laser marking was carried out using Laser machine,
"SpeedMarker 700, 20 W Fiber laser". For marking, a frequency range
of 20-100 kHz and a power varying between 5-70% of 20 W was used.
Speed was kept constant at 2000 mm/s.
[0072] FIG. 1 shows the laser printed samples as indicated in Table
1 above, wherein these samples are irradiated with UV light, here
250-400 nm.
[0073] Each square represents a combination of frequency to power
of the ranges indicated above.
[0074] The laser printed samples were irradiated with UV light
(wavelength 250-400 nm). As can be seen from FIG. 1, the inventive
samples containing the optical brightener show fluorescence when
irradiated with UV light.
* * * * *