FIELD OF THE INVENTION
[0001] This invention relates to dry non-magnetic toner particles comprising a white pigment,
especially to dry non-magnetic toner particles comprising rutile type TiO
2. It further relates to a method for printing images on a transparent wherein the
images contain a white background.
BACKGROUND OF THE INVENTION
[0002] White toner particles and their use is known in the art, especially for printing
on a black background or for printing techniques wherein black and white toners are
used for printing different grey levels.
[0003] In
EP-A-253 560, an electrophotographic copying method is disclosed, comprising the use of a copying
apparatus having a positive-image copying system, wherein toner images with a coloured
toner are formed and transferred to a coloured insulating paper of a colour different
to that of said toner while selecting the colours of the paper and the toner so as
to form reverse images. In an example a white toner with 100 parts by weight of a
styrene-acrylic resin and 20 parts by weight of rutile type TiO
2 is disclosed.
[0004] In
EP-A-280 378 a white toner is disclosed comprising a fixing resin and dispersed therein, a titanium
dioxide pigment of high purity containing at least 99 % by weight of TiO
2, not more than 0.1 % by weight of Al
2O
3 and not more than 0.05 % by weight of SiO
2 as a white pigment, said titanium dioxide having an average particle diameter of
not less than 0.05 µm. In this disclosure it is stressed that good charging quality
of the toner particles can not be reached when the TiO
2 is not that pure. It is said that maximum 50 parts by weight, preferably maximum
30 parts by weight, of the TiO
2 can be used for 100 parts by weight of toner resin because toner with higher amounts
of TiO
2 can not be fixed.
[0005] In
JP-A-01 048067 a white toner is disclosed wherein between 5 and 20 % by weight of TiO
2 is present, preferably there is between 8 and 10 % by weight of TiO
2.
[0006] In
US-A-4,943,506 a white toner is disclosed comprising binder resin and titanium dioxide with 0.20-0.35
µm in mean particle size at the content of 15-60 parts by weight on the basis of 100
parts by weight of the binder resin.
[0007] In
US-A-5,077,158, a process for toning an image is disclosed, which comprises developing an electrostatic
latent image with a grey toner, wherein a mixture of a white toner and a black toner
is used as the grey toner. The white toner comprises preferably TiO
2 in the rutile crystal structure and for at most 50 parts by weight for 100 parts
by weight of toner resin.
[0008] Nowadays a well accepted way of printing labels is printing them with digital electrostatographic
printing means, e.g. the CHROMAPRESS (trade name of Agfa-Gevaert NV, Mortsel, Belgium)
or the DCP1 (trade name of Xeikon NV, Mortsel, Belgium). Also transparent labels are
printed with such printing devices, and when opaque white images on a transparent
support, it is preferred to have toner particles giving a high opacity, i.e. the hiding
power of a layer of white toner must be very high. When a transparent self-adhesive
label for application on a coloured, e.g. red, background is printed with white lettering,
it is desired that the lettering really shows white and not white with a faint red
hue. Also when on a transparent label a bar-code has to be printed, it is desired
for better readability of the bar-code that it is printed on a white background and
then the white must be very opaque. The known toner particles are well suited for
printing white images, but for printing for the printing of white images on transparent
substrates, the hiding power has to be still higher.
OBJECTS AND SUMMARY OF THE INVENTION
[0009] It is an object of the invention to provide white non-magnetic toner particles with
high hiding power, wherein TiO
2 particles are present and well mixed with the toner resin, that have good fixing
properties and that give stable printing results in long time printing runs.
[0010] It is also an object of the invention to provide an electrostatographic method for
printing white images with high hiding power on a transparent substrate.
[0011] Further objects and advantages of the invention will become clear from the detailed
description hereinafter.
[0012] The object of the invention is realised by providing non-magnetic toner particles
comprising 100 parts by weight of toner resin, wherein at least 50 parts by weight
of said toner resin is a polyester resin and between 65 and 180 parts by weight of
rutile type TiO
2 for 100 parts by weight of said toner resin .
[0013] The further object of the invention is realised by providing an electrostatographic
printing method for white toner images with an opacity, OP, of at least 60 % comprising
the steps of :
- image-wise applying between 7.5 g/m2 and 15 g/m2 of white non-magnetic toner particles containing a toner resin and a white pigment
on a substrate and
- fixing said non-magnetic toner particles on said substrate, characterised in that,
said non-magnetic toner particles comprise 100 parts by weight of toner resin, wherein
at least 50 parts by weight of said toner resin is a polyester resin and between 65
and 180 parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin .
DETAILED DESCRIPTION OF THE INVENTION
[0014] It was, surprisingly, found that it was possible to prepare non-magnetic toner particles
with from 65 to 180 parts by weight of rutile type TiO
2 for 100 parts by weight of toner resin, when said toner resin comprised at least
50 parts by weight of a polyester resin, although the prior art teachings indicate
that not more than 60 parts by weight of rutile type TiO
2 for 100 parts by weight of toner resin could be incorporated in toner particles.
No problems were with respect to stability of the toner charge, to the fixing properties
were observed, even not when the rutile type TiO
2 was only between 95 and 98 % pure. Both in fixing system where the fixing proceeded
by hot-roller fixing as in a system where the fixing proceeds by non-contact means,
especially by infra-red radiation, the fixing quality of the toner image was good
despite the high pigment to resin ratio.
[0015] This finding opens the way to the possibility of producing non-magnetic toner particles
that can be used for producing white image with high opacity or high hiding power
(i.e. an opacity of at least 60 %) even when only between 0.75 mg and 1.5 mg/cm
2 (7.5 g/m
2 and 15 g/m
2) non-magnetic toner particles are deposited. It showed possible to produce white
non-magnetic toner particles according to this invention, giving an opacity of at
least 60 % when between 0.9 mg and 1.1 mg/cm
2 (9 g/m
2 and 11 g/m
2) of toner particles were deposited.
[0016] Opacity or hiding power of a white image was measured by applying the white toner
particles on a transparent support forming an image of even patch of white density,
placing said image on a light trap and measuring, in reflectance mode, the opacity
, the opacity being the ratio of the reflected light intensity over the intensity
of the light irradiated on the white image. Then the same white image is placed over
a white tile and again in reflectance mode, the opacity
is measured. In both measurements I
0 is the same. The opacity or in fact the hiding power of the white image is determined
by the ratio
. The larger OP the higher the hiding power.
[0017] It was found that the toner resin could be any resin know in the art as long as for
100 parts (wt/wt) of toner resin at least 50 parts (wt/wt) of a polyester was present.
Preferably the toner resin in non-magnetic toner particles according to this invention
contains a least 50 parts (wt/wt) of a polyester with acid or hydroxyl value between
10 and 30 mg KOH/g. More preferably the toner resin in non-magnetic toner particles
according to this invention is a polyester or a mixture of different polyesters. In
that case, it is preferred to use a polyester with acid or hydroxyl value between
10 and 30 mg KOH/g or when a mixture of different polyesters is used to include in
that mixture at least 50 % (wt/wt) of a polyester with acid or hydroxyl value between
10 and 30 mg KOH/g. Very useful polyester resins for use in non-magnetic toner particles
according to this invention are tabulated in table 1.
Table 1
Chemical structure |
AV* |
HV** |
Tg °C |
Mn+ |
Mw† |
1. Polyester resin of terephthalic acid, ethyleneglycol and DIANOL 22 |
3 |
31.1 |
62 |
3.6 |
10 |
2. Polyester resin of fumaric acid and DIANOL 33 |
17 |
5.2 |
55 |
4.4 |
12 |
3. Polyester resin of terephthalic acid, isophthalic acid and DIANOL 22 and ethyleneglycol |
18 |
20.9 |
60 |
4 |
18 |
4. Polyester resin of DIANOL 33/DIANOL 22, terephthalic acid and trimellitic acid |
30 |
50 |
65 |
2.0 |
14 |
5. Polyester resin of DIANOL 33, iosphthalic acid and adipic acid |
16 |
na |
58 |
4.1 |
9.7 |
* AV : acid value in mg KOH/g resin |
** HV : hydroxyl value in mg KOH/g resin |
+ Mn : numerical average molecular weight (x 1000) |
† Mw : weight average molecular weight (x 1000) |
DIANOL 22 is a trade name of AKZO CHEMIE of the Netherlands for bis-ethoxylated 2,2-bis(4-hydroxyphenyl)propane.
DIANOL 33 is a trade name of AKZO CHEMIE of the Netherlands for bis-propoxylated 2,2-bis(4-hydroxyphenyl)propane.
|
na : not available |
[0018] It proved that from the white pigments known in the art, (e.g. BaSO
4, ZnO, TiO
2, etc), TiO
2 in rutile crystal configuration was the most efficient. The titanium dioxide useful
in this invention does not need to be for at least 99 % pure, although rutile type
TiO
2 with a purity of 99 % and up can be used in this invention, it is also possible to
use TiO
2 with a purity between 94 % and 98 %, this means that TiO
2 wherein Al
2O
3 and/or SiO
2 are present in a relative high amount is also useful in non-magnetic toner particles
according to this invention. This has the advantage that for producing non-magnetic
toner particles of this invention also less pure and thus less expensive TiO
2 can be used. The non-magnetic toner particles according to this invention comprising
TiO
2 in rutile crystal configuration can further comprise SiO
2 or Al
2O
3 that is deliberately added to the TiO
2. These compounds can be added to the mixture of toner resin and TiO
2, during the melt kneading step in the production of the non-magnetic toner particles,
or can first be mixed to fix the SiO
2 or Al
2O
3 on the surface of the TiO
2. Such treatments of the TiO
2 have been described in US-A-4 943 506.
[0019] The surface of the TiO
2 for use in toner particles according to this invention can also, before adding it
to the bulk of the toner particles, be treated by an organic compounds selected from
the group of silicone oils, silane coupling agent, titanium coupling agents aluminium
coupling agents and zirco-aluminium coupling agents.
[0020] Typical useful silane coupling agents are, e.g., vinyl triacetoxy silane, methyl
trimethoxy silane, vinyl tris(methoxyethoxysilane), methyl triethoxysilane, etc..
Useful titane coupling agents are, e.g., isopropyl triisostearoyl titanate, isopropyl
trioctanoyl titanate, etc.. A typical useful aluminium coupling agent is, e.g., acetoalkoxy
aluminium di-isopropylate. Examples of rutile type TiO
2 commercially available and useful in non-magnetic toner particles of this invention
are, e.g., BAYERTITAN RKB2 and BAYERTITAN RDFI (trade names of Bayer AG, Leverkusen,
Germany) or RHODITAN RL60 and RHODITAN RL67 (trade names of Rhone-Poulenc, France).
From these commercial available rutile type TiO
2 it is preferred to use BAYERTITAN RDFI.
[0021] Toner particles according to this invention can also comprise fluorescent brightening
agents, that fluoresce under UV-light. By adding such fluorescent brightening agents,
the whiteness of an image printed with white non-magnetic toner particles of this
invention is enhanced. Typical useful fluorescent brightening agents are, e.g.,
sold by Ciba-Geigy, Switserland under trade name UVITEX OKF,
sold by Ciba-Geigy, Switserland under trade name UVITEX OB, or derivatives of stilbene.
[0022] The addition of fluorescent brightening agents to enhance the whiteness of a toner
according to this invention has advantages over the addition of blue colouring agents.
A image made with white toner of this invention with a fluorescent brightening agent
does not show a bluish hue and can thus be used in relative high concentration, i.e.
up to 10 parts (wt/wt) for 100 parts (wt/wt) of toner resin. Preferably an amount
between 1 and 5 parts (wt/wt) for 100 parts (wt/wt) of toner resin is used.
[0023] White toner particles comprising a fluorescent brightening agent are very useful
in security printing. With such toners an image can be printed on white paper, white
polymeric image receiving sheets without fluorescent brightening agent. Such an image
is almost invisible under normal ambient lightening conditions, but becomes clearly
visible under UV-light. It is also possible to print a first white image on a coloured
background with toner particles of this invention that do not contain a fluorescent
brightening agent and another image (near to said first image or on top of it) with
non-magnetic toner particles of this invention that do contain a fluorescent brightening
agent. In this case the first image is visible under normal ambient lightening conditions
and the second becomes visible under UV-illumination. Thus it is possible to add in
the print a kind of "ghost image" that is only visible under UV (ultraviolet) illumination.
Such a feature adds to the security of, e.g., identity documents.
[0024] Toner particles according to this invention can, even without the presence of a fluorescent
brightening agent, be used for including security features in printed matter. It is
possible to print on a transparent support (mostly a polymeric support) an even white
background with toner particles according to this invention wherein a white image
with different opacity (from slightly, i.e. less than 1 % different up to 25 % different)
is present. The image of different density can be printed by applying a higher or
lower amount of toner particles than the amount of toner particles used to print the
background density. In this case the same toner particles can be used. The image of
different density can be printed by applying toner particles containing a lower amount
of TiO
2 than the amount of TiO
2 present in the toner particles used to print the background density. In reflection
mode such a white background looks as having an even density, but in transmission
the image with lower white opacity is easily seen such that a kind of "watermark"
is introduced. The white background can then be used for printing any image by any
other printing means. It is evident that the methods of including security features
as described above using white toner particles not having a fluorescent brightening
agent can be combined with methods wherein white toner particles having a fluorescent
brightening agent are used.
[0025] Toner particles according to this invention can further comprise waxes, especially
useful waxes are monohydroxy compounds with formula CH
3(CH
2)
nOH wherein n is an integer between 21 and 360 or monocarboxy compounds with formula
CH
3(CH
2)
nCOOH wherein n is an integer between 21 and 360. Such compounds are available under
trade name UNICID for the monocarboxy compounds and UNILIN for the monohydroxy compounds
from PETROLITE, 6910 East 14th street, TULSA, Oklahoma 74112, USA. Also onium compounds
having an alkylgroup of at least 12 C-atoms and at most 25 C-atoms can be added to
the non-magnetic toner particles of this invention. Such an onium compound is beneficial
as charge control agent and, as disclosed in US-A-5 622 803 and US-A-5 532 097 for
giving the toner particles a narrow charge distribution. A typical member of the class
of useful onium compounds for incorporation in toner particles of this invention is
(CH
3)
3N
+C
16H
33 Br
- It was moreover found that, although the TiO
2 could be well dispersed in a toner resin as long as for 100 parts (wt/wt) of toner
resin at least 50 parts (wt/wt) of a polyester was present, the dispersion of the
TiO
2 was still better when either a monohydroxy compound with formula CH
3(CH
2)
nOH wherein n is an integer between 21 and 360, a monocarboxy compound with formula
CH
3(CH
2)
nCOOH wherein n is an integer between 21 and 360 or an onium compound having an alkylgroup
of at least 12 C-atoms and at most 25 C-atoms was present.
[0026] Toner particles according to this invention are preferably used in a non-magnetic
mono-component developer or in a two component developer wherein the non-magnetic
toner particles are used together with magnetic carrier particles. The use of the
non-magnetic toner particles of this invention in a two-component developer is most
preferred and the non-magnetic toner particles comprise at least one resistivity lowering
substance compound having a volume resistivity lower than the volume resistivity of
said resin, wherein said substance is capable of lowering the volume resistivity of
said resin by a factor of at least 3.3 when present in said resin in a concentration
of 5 % by weight relative to the weight of said resin. The non-magnetic toner particles
have preferably an absolute median |q/d| charge/diameter value lower than 10 fC/10
µm but not lower than 1 fC/10 µm, the distribution of the charge/diameter values of
the individual non-magnetic toner particles is has by a coefficient of variation η
≤ 0.33.
[0027] Although the white toner particles of this invention can be used with any kind of
magnetic carrier particles known in the art, e.g. iron beads, composite carriers,
etc, with an average particles diameter from 10 to 200 µm, it is preferred to use
the white non-magnetic toner particles of this invention in a developer comprising
magnetic carrier particles said carrier particles having :
- a saturation magnetisation value, Msat, expressed in Tesla (T) such that Msat > 0.30 T
- a volume average particle size (Cavg) such that 30 µm < Cavg < 60 µm
- a volume based particle size distribution so that at least 90 % of the particles having
a particle diameter C such that 0.5Cavg < C < 2Cavg
- a volume based particles size distribution having less than b % particles smaller
than 25 mm wherein b = 0.35 x (Msat)2 x P wherein Msat = saturation magnetisation value expressed in T and P = the maximal field strength
of the magnetic developing pole expressed in kA/m
- a core particle coated with a silicone resin coating in an amount (RC) such that 0.2
% wt/wt < RC < 2 % wt/wt.
[0028] The present invention also encompasses a method for producing white toner images
with an opacity, OP, of at least 60 % comprising the steps of :
- image-wise applying between 7.5 g/m2 and 15 g/m2 of white non-magnetic toner particles containing a toner resin and a white pigment
on a substrate and
- fixing said non-magnetic toner particles on said substrate, characterised in that,
said toner particles comprise 100 parts by weight of toner resin, wherein at least
50 parts by weight of said toner resin is a polyester resin and between 65 and 180
parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin .
[0029] The present invention also encompasses a method for including security features to
a toner image comprising the steps of
- applying a toner image to a white, non fluorescent, substrate,
- applying an image of white non-magnetic toner particles comprising 100 parts by weight
of toner resin, wherein at least 50 parts by weight of said toner resin is a polyester
resin and between 65 and 180 parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin and between 0.5 and 5 parts (wt/wt) for
100 parts by weight of said toner resin of a fluorescent brightening agent and
- fixing the images to said substrate.
[0030] The invention also comprises a method for including security features to a toner
image comprising the steps of
- applying on a substrate an image of white non-magnetic toner particles comprising
100 parts by weight of toner resin, wherein at least 50 parts by weight of said toner
resin is a polyester resin and between 65 and 180 parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin and wherein no fluorescent brightening
agent is present,
- applying on said substrate an image of white non-magnetic toner particles comprising
100 parts by weight of toner resin, wherein at least 50 parts by weight of said toner
resin is a polyester resin and between 65 and 180 parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin and between 0.5 and 5 parts (wt/wt) for
100 parts by weight of said toner resin of a fluorescent brightening agent and
- fixing said toner image to said substrate.
[0031] The invention further encompasses a method for including security features to a toner
image comprising the steps of
- applying in a single step on a transparent support a white image with opacity (OP3)
by depositing an amount, A g/m2, of white toner particles according to this invention not containing a fluorescent
brightener,
- applying an even white background with opacity (OP4) around said image by depositing
an amount ,B g/m2, of white toner particles according to this invention not containing a fluorescent
brightener, so that the amount B is different from said amount A, for forming an image
that is invisible in reflection mode and visible in transmission mode and
- fixing said image to said support.
[0032] The invention further encompasses a method for including security features to a toner
image comprising the steps of
- applying on a transparent support a white image with opacity (OP3) by depositing an
amount, A g/m2, of white toner particles according to this invention not containing a fluorescent
brightener and containing an amount C parts of TiO2 per 100 parts of toner resin,
- applying an even white background with opacity (OP4) around said image by depositing
an amount ,A g/m2, of white toner particles according to this invention not containing a fluorescent
brightener, and containing an amount D parts of TiO2 per 100 parts of toner resin, so that the amount D is different from said amount
C, for forming an image that is invisible in reflection mode and visible in transmission
mode and
- fixing said image to said support.
EXAMPLES
PREPARATION OF THE TONER PARTICLES
[0033] 50 parts of resin No. 3 of Table 1 and 50 parts of resin No. 5 of Table 1 as were
melt-blended for 30 minutes at 110 °C in a laboratory kneader with various amounts
of TiO
2.
[0034] After cooling the solidified mass was pulverised and milled using an ALPINE Fliessbettgegenstrahlmühle
type 100AFG (trade name) and further classified using an ALPINE multiplex zig-zag
classifier type 100MZR (trade name). The average particle size of the separated toner
was measured by COULTER COUNTER MODEL MULTISIZER (trade name) was found to be 8.0
µm by volume.
[0035] To improve the flowability of the toner mass the toner particles were mixed with
0.5 % of hydrophobic colloidal silica particles (BET-value 130 m
2/g) to give a toner composition.
[0036] Twelve different types of toner particles (T1 to T12) were prepared, the amount,
the nature and the manufacturer of TiO
2 added to the toner particles are tabulated in table 2.
DEVELOPERS
[0037] A Cu-Zn ferrite based coated carrier was prepared by coating a Cu-Zn ferrite core
with 1 % of dimethylsilicone using a solution spraying technique in a fluidized bed
and post curing the coating. The carrier showed a saturation magnetisation (M
sat) of 0.41 T. The particle size distribution was characterised by :
d
v50% = 52.5 µm, d
v10 % = 32 µm and d
v90 % = 65 µm.
The amount of particles < 25 µm was 4.9 % wt/wt.
[0038] A developer was prepared by adding 7,5 % of the toner compositions to the carrier
particles.
PRINTING EXAMPLES
[0039] The thus obtained developers were used separately in an X-35 (trade name of Agfa-Gevaert
N.V.) electrophotographic copier wherein the photoconductive drum was evenly exposed
forming a latent image, the latent image was developed with one of the developers
containing the toner particles described above and wherein the image was transferred
on one side of a transparent support PROPYLUX type 60064 (trade name) a label material
available from Jackstädt GmbH, Wuppertal, Germany.
[0040] From said X-35 copier the standard hot roller fuser was removed, and the toner of
the unfixed copy was non-contact fused by radiation using an infra-red black body
radiant element placed at a distance of 10 mm from the transparent support carrying
the toner image. The support passed by the radiant element at a speed of 5 cm per
second. The average power provided to the radiant heating element was 375 W making
the element operate at a temperature of 600 °C using reflectors to concentrate the
radiant heat onto the support.
[0041] With each of the developers four different patches of even white density, but with
differing opacity, were printed by applying different amounts of toner particles,
ranging from 5 g/m
2 to 15 g/m
2. For each of these patches the opacity was measured as described above. By interpolation
the opacity reached by applying 10 g/m2 (1 mg/cm
2) of white toner particles were determined. The values are also tabulated in table
2.
Table 2
# |
Parts (wt/wt) TiO2 for 100 parts of toner resin |
Type* |
Trade name |
Opacity in % for 10g/m2 deposited toner particles |
1 |
25 |
A |
KRONOS A |
48 |
2 |
67 |
A |
KRONOS A |
56 |
3 |
150 |
A |
RHODITAN AT1 |
51 |
4 |
67 |
R |
BAYERTITAN RKB2 |
60 |
5 |
150 |
R |
BAYERTITAN RKB2 |
62 |
6 |
150 |
R |
RHODITAN RL60 |
61 |
7 |
150 |
R |
RHODITAN RL67 |
61 |
8 |
67 |
R |
BAYERTITAN RDFI |
62 |
9 |
83 |
R |
BAYERTITAN RDFI |
65 |
10 |
150 |
R |
BAYERTITAN RDFI |
68 |
11 |
25 |
R |
BAYERTITAN RDFI |
44 |
12 |
60 |
R |
BAYERTITAN RDFI |
57 |
* Type : A = anataas, R = rutile |
KRONOS A : trade name of Kronos NV, Brussel, Belgium
RHODITAN : trade name of Rhone-Poulenc, France
BAYERTITAN : trade name of Bayer AG, Leverkusen Germany |
1. Dry non-magnetic toner particles comprising
a toner resin, wherein at least 50 parts by weight of said toner resin is a polyester
resin and
between 65 and 180 parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin .
2. Dry non-magnetic toner particles according to claim 1, wherein said toner resin is
a polyester.
3. Dry non-magnetic toner particles according to claim 1 or 2 wherein said polyester
is a polyester having an acid value between 10 and 30 mg KOH/g of polyester.
4. Dry non-magnetic toner particles according to any of claims 1 to 3, wherein said rutile
type TiO2 has a purity between 94 and 98 %.
5. Dry non-magnetic toner particles according to any of claims 1 to 4, further comprising
a fluorescent brightening agent.
6. Dry non-magnetic toner particles according to any of claims 1 to 5, further comprising
a compound selected from the group consisting of monohydroxy compounds with formula
CH3(CH2)nOH wherein n is an integer between 21 and 360, monocarboxy compounds with formula
CH3(CH2)nCOOH wherein n is an integer between 21 and 360 and onium compounds having an alkylgroup
of at least 12 C-atoms and at most 25 C-atoms.
7. Use of dry non-magnetic toner particles according to any of claims 1 to 6 in a two
component developer containing magnetic carrier particles.
8. Use of dry non-magnetic toner particles according to any of claims 1 to 6, for including
security features in printed matter.
9. An electrostatographic printing method for white toner images with an opacity, OP,
of at least 60 % comprising the steps of :
- image-wise applying between 7.5 g/m2 and 15 g/m2 of white non-magnetic toner particles containing a toner resin and a white pigment
on a substrate and
- fixing said non-magnetic toner particles on said substrate,
characterised in that, said toner particles comprise
a toner resin, wherein at least 50 parts by weight of said toner resin is a polyester
resin and
between 65 and 180 parts by weight of rutile type TiO2 for 100 parts by weight of said toner resin .
10. A method according to claim 9, wherein said toner particles are deposited in an amount
9 g/m2 and 11 g/m2.