1. Field of the invention.
[0001] The present invention relates to a method for producing toner images, wherein the
toner images are highly resistant to wear, using UV-radiation curable resin particles.
2. Background of the Invention
[0002] In imaging methods as e.g. electro(photo)graphy, magnetography, ionography, etc.
a latent image is formed that is developed by attraction of so called toner particles.
Afterwards the developed latent image (toner image) is transferred to a final substrate
and fused to this substrate. In DEP the so called toner particles are imagewise deposited
directly on a final substrate and fused to this substrate.
[0003] Toner particles are basically polymeric particles comprising a polymeric resin as
main component and various ingredients mixed with said toner resin. Apart from colourless
toners, which are used e.g. for finishing function, the toner particles comprise at
least one black and/or colouring substances, e.g., coloured pigment.
[0004] In the different imaging methods, described above, the toner particles can be present
in a liquid or in a dry developer composition.
[0005] In most cases the use of dry developer compositions is preferred. The main advantage
of using a dry developer composition resides in the absence of the need to eliminate
the liquid phase after development. The avoidance of the-need to evacuate (mainly
organic) liquids is desirable both from an economical standpoint and from an ecological
standpoint.
[0006] However, in all techniques using dry particulate material to form an image, the images
are built up by application of particulate marking elements in multiple, superimposed
layers onto the substrate. The problems associated with multiple, superimposed layers
of particulate marking particles that are in one way or another fixed on a substrate
are manifold, not only with respect to image quality but also with respect to image
stability and with respect to mechanical issues.
[0007] In, e.g. EP-A 471 894, EP-A 554 981, US 4,828,950 and US 4,885,603, it has been disclosed
to apply a layer of transparent toner particles on top of the toner image to provide
better resistance to physical damage.
[0008] In, e.g., US 3,723,114 the problem of storage properties of fused toner images is
addressed, the main problem being the fact that the toner images can, depending on
the storage conditions, become tacky after storage. The problem is solved by using
in the toner resin a substantial portion of thermosetting polymers.
[0009] The use of photo-curable toners has been suggested in, e.g., US 5,470,683 to produce
toner images having better weather resistance. In that application, a capsule toner
is provided having a core comprising a polymerizable compound, a polymerization initiator
and other normal toner ingredients. The core is surrounded by a hard shell that breaks
during the fixing step. After the fixing step the polymerizable compound is polymerized,
in this particular disclosure, by low energy visible light. Although following the
teachings of these disclosures leads to the production of toner layers that are not
easily damaged, the nature of the solutions itself limits the variety of resins that
can be used in the manufacturing of the toner. Therefore further improvements along
the lines of the disclosures referred to above are desirable.
3. Objects and Summary of the Invention
[0010] It is an object of the invention to provide a method for producing toner images that
are very resistant to external physical influences.
[0011] It is a further object of the invention to provide a method for forming toner images
wherein said toner image is very resistant to the influence of common organic solvents.
[0012] It is a further object of the invention to provide a method for producing toner images
that are very weather resistant.
[0013] It is a still further object of the invention to provide a method for producing toner
images that are very resistant to external physical influences and that exhibit an
even gloss.
[0014] Further objects and advantages of the present invention will become evident from
the detailed description hereinafter.
[0015] The objects of this invention are realized by providing a method for forming toner
images using particles comprising a radiation curable compound, said radiation curable
resin having a Tg ≥ 35 °C, as claimed in claim 1.
4. Detailed Description of the Invention.
[0016] Since toner particles to be used in electrostatographic printing apparatus have preferably
a quite high mechanical strength in order to be able to withstand the mechanical influences
(pressure, friction, etc) in the printing apparatus before and during development,
it is important to preserve the mechanical strength of the toner particles.
[0017] Therefore it is preferred that the radiation curable compound comprises an oligomeric
or polymeric compound instead of only monomeric compounds. A monomeric compound may
be present in the mixture of radiation curable compounds, as long as the mixture of
radiation curable compounds (i.e. a radiation curable composition) itself has a Tg
≥ 35 °C. The oligomeric or polymeric radiation curable compounds have a Tg ≥ 35 °C,
preferably the Tg is larger than 40 °C.
[0018] The radiation curable composition or compound can be added to the toner particles
in addition to a toner resin and other toner ingredients. Due to the oligomeric or
polymeric nature of the radiation curable compounds these compounds can also be used
as sole toner resin. Although toner particles according to the present invention can
be coloured (i.e. comprise a pigment or a dye) the toner particles of the present
invention are especially useful when they are intended to form a clear finish layer
on top of a toner image. When the clear toner particles according to the present invention
are used to provide a clear finish layer on top of the image, an image with very even
gloss is obtained. The word "clear" means herein not giving, in a wavelength range
extending from 400 to 700 nm, a visible diffuse density, said visible diffuse density
being defined as less than 15 % light reduction integrated over that wavelength range.
An "image on a substrate" is, in the context of this invention, meant to include a
substrate carrying human readable or/and machine readable text, a substrate carrying
figures, a substrate carrying pictures (both coloured and monochromatic) as well as
a substrate carrying a combination of at least two of the above.
A clear finish layer can be useful on any toner image, but is especially useful when
it is applied on top of a toner image showing different thickness in the image are
mostly toner images made up by the overlay of several layers of different types of
toner particles (e.g. in full colour toner images or in a black and white (monochrome)
image with extended tonal range as disclosed in European Application 95202768, filed
on October 13, 1995). In such images a relief structure is present. Said clear finish
layer can be produced by depositing said clear toner particles by an image-wise depositing
step, a non-image-wise depositing step or a counter-image-wise depositing step. It
is preferred that said clear toner particles are deposited either non-image wise (i.e.
in a uniform layer over the whole surface of the substrate, having toner particles
or not) or counter-image-wise. Counter-image-wise means that a thicker fixed clear
finish layer is present in the lower thickness areas of the image and a thinner fixed
clear finish layer is present in the higher thickness areas of the image.
[0019] When the image comprises both text and e.g. full-colour pictures, it may be beneficial
to deposit said clear toner particles, according to this invention and comprising
a radiation curable compound, only on the surface of the full-colour pictures and
not over the text portions. In such a way glossy pictures are combined with less glossy
text.
[0020] The radiation curable groups are curable by UV-light.
[0021] Very useful radiation curable polymeric compounds, in toner particles for use in
the present invention are UV curable solid epoxy resins with Tg ≥ 35 °C as disclosed
in EP-A 667 381. In this application solid compositions (I) are described containing
(a) a solid, oligomeric, cationically polymerisable polyglycidyl ether or ester (II),
or a mixture of (II) with a liquid or crystalline monomeric mono-, di- or poly-epoxy
resin, or a mixture of (II) with a cyclic acetal, where (II) have a Tg of above 35
deg.C,
(b) a multifunctional nucleophilic chain transfer agent,
(c) 0.05-3 wt.% photoinitiator for cationic polymerisation (with respect to the amount
of a), and
(d) optionally normal additives for coating powders.
These compositions (I) are melted together and the cooled mixture is milled. The
exemplified compositions have a Tg between 65 and more than 115 °C.
[0022] Other useful UV curable resins for incorporation in toner particles, according to
this invention, are powders based on unsaturated polyesters and polyurethaneacrylates,
a typical example of such a polymeric UV curable system is available through Hoechts
High Chem, Hoechts-Sara Pero (Mi) Italy. Such a system comprises a solid unsaturated
polyester resin under trade name ALFTALAT VAN 1743, having a Tg ≥ 52 °C and an urethane
adduct with acrylic functional groups under trade name ADDITOL 03546, having a Tg
≥ 47 °C. The properties of this system have be described in European Coating Journal
n° 9/95 606-608 (1995). Also non-acrylate binder systems are useful in the present
invention, e.g. a powder composed of a mixture of an unsaturated polyester resin in
which maleic acid or fumaric acid is incorporated and a polyurethane containing a
vinylether. Such a binder system has been developed by DSM resins of the Netherlands
and the properties thereof have been described in European Coating Journal n° 3/96
115-117 (1996).
For the UV curing to proceed it is necessary that a photoinitiator is present. Very
useful initiators are sulphonium salts as e.g. triarylsulphonium salts, triarylsulphoniumhexafluorophosphate,
benzophenones, etc. Typical very useful photoinitiators in the context of this invention,
are, e.g., 2-hydroxy-2-methyl-1-phenyl-propan-1-one, compound I, a mixture of compound
I and compound II and compound III :
[0023] The initiator (photoinitiator) is preferably incorporated in the toner particles
together with the UV curable system.
It is, however, also possible, within the scope of the invention, to have the pair
radiation curable compound and initiator in various combinations :
i) both a UV-curable compound (or a mixture of UV-curable compounds) and a photoinitiator
(or mixture of photoinitiators) are only incorporated in the toner particles, not
in the substrate,
ii) both a UV-curable compound (or a mixture of UV-curable compounds) and a photoinitiator
(or mixture of photoinitiators) are in incorporated in the toner particles, and a
UV-curable compound (or a mixture of UV-curable compounds) is incorporated in the
substrate,
iii) a UV curable compound (or a mixture of UV-curable compounds) is incorporated
in the toner particles and both a UV-curable compound (or a mixture of UV-curable
compounds) and a photoinitiator (or mixture of photoinitiators) are incorporated in
the substrate,
iv) a UV curable compound (or a mixture of UV-curable compounds) is incorporated in
the toner particles and a photoinitiator (or mixture of photoinitiators) is incorporated
in the substrate.
When the photoinitiator and/or the UV curable compound are incorporated in the substrate,
it is preferred that the substrate comprises a toner receiving layer.
[0024] The toner particles according to the present invention may comprise the radiation
curable resins (radiation curable compounds or compositions) that are UV-curable resins
as sole toner resin, or the radiation curable resins may be mixed with other toner
resins. In that case all toner resins, known in the art are useful for the production
of toner particles according to this invention. The resins mixed with the radiation
curable resins can be polycondensation polymers (e.g. polyesters, polyamides, co(polyester/polyamides),
etc), epoxy resins, addition polymers or mixtures thereof.
[0025] It may be beneficial that the toner particles not only comprise a compound carrying
a radiation curable group, but further comprise a reactive group RGA being a member
selected from the group consisting of epoxy groups, aldehyde groups, hydroxyl groups,
carboxyl groups, mercapto groups, amino groups and amide groups. In this case the
toner particles can comprise e.g. a toner resin selected from the group described
in table 1 or an epoxy resin and a UV curable solid resin (composition) with Tg ≥
35 °C.
TABLE 1
Chemical structure |
AV* |
HV** |
Tg |
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. Copoly(styrene-butylacrylate-butylmethacrylate-stearylmethacrylate-methacrylic
acid) (65/5/21/5/4) |
12 |
0 |
58 |
6 |
108 |
5. Copoly(styrene-butylmethacrylate-acrylic acid) (80/15/5). |
5 |
0 |
63 |
5.5 |
180 |
6. Polyester resin of DIANOL 33/DIANOL 22, terephthalic acid and trimellitic acid |
30 |
50 |
65 |
2.0 |
14 |
7. Co(Styrene/n-butylmethacrylate), diCOOH terminated (65/35) |
15 |
0 |
48 |
2.1 |
10 |
* 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. |
[0026] In this embodiment of the invention, where the toner particles comprise further reactive
groups RGA, it is preferred to use a substrate comprising a reactive group RGB, being
a member selected from the group consisting of epoxy groups, aldehyde groups, hydroxyl
groups, carboxyl groups, mercapto groups, amino groups and amide groups and being
chosen such as to form a reaction pair with said reactive groups RGA. This embodiment
has the advantage that the resins comprised in the fixed image can be not only radiation
cured but also thermally cross-linked and chemically attached to the substrate by
chemical bonds.
[0027] In the embodiment wherein the substrate comprises reactive groups RGB and the toner
particles comprise not only radiation curable compounds having a Tg ≥ 35 °C, but also
reactive groups RGA, it is preferred to add catalysers, speeding up the reaction between
reactive groups RGA and RGB, to either the toner particle, the substrate or to both.
These catalysers are e.g. acids (both organic and anorganic) and tertiary amines.
Very suitable catalysers are p-toluenesulfonic acid, trimethylamine and triethylamine.
[0028] Toner particles according to the present invention can be prepared by any method
known in the art. These toner particles can be prepared by melt kneading the toner
ingredients (e.g. toner resin, charge control agent, pigment, etc) and said radiation
curable compounds. After the melt kneading the mixture is cooled and the solidified
mass is pulverized and milled and the resulting particles classified. Also the "emulsion
polymerisation" and "polymer emulsion" techniques for toner preparation can be used
to prepare toner particles according to this invention. In the "emulsion polymerization"
technique a water-immiscible polymerizable liquid is sheared to form small droplets
emulsified in an aqueous solution, and the polymerization of the monomer droplets
takes place in the presence of an emulsifying agent; such a technique is described
e.g. in US P 2,932,629, US P 4,148,741, US P 4,314,932 and EP-A 255 716. In the "polymer
emulsion" technique, a pre-formed polymer is dissolved in an appropriate organic solvent
that is immiscible with water, the resulting solution is dispersed in an aqueous medium
that contains a stabilizer, the organic solvent is evaporated and the resulting particles
are dried; such a technique is described in, e.g., US P 4,833,060.
[0029] Toner particles useful in this invention can have an average volume diameter between
1 and 50 µm, preferably between 3 and 20 µm. When the toner particles are intended
for use in colour imaging, it is preferred that the volume average diameter is between
3 and 10 µm, most preferred between 3 and 8 µm. The particle size distribution of
said toner particles can be of any type. It is however preferred to have an essentially
(some negative or positive skewness can be tolerated, although a positive skewness,
giving less smaller particles than an unskewed distribution, is preferred) Gaussian
or normal particle size distribution, either by number or volume, with a coefficient
of variability (standard deviation divided by the average) (ν) smaller than 0.5, more
preferably of 0.3.
[0030] Toner particles, useful in this invention, can comprise any normal toner ingredient
e.g. charge control agents, pigments both coloured and black, anorganic fillers, anti-slip
agents, waxes, etc. A description of charge control agents, pigments and other additives
useful in toner particles, to be used in a toner composition according to the present
invention, can be found in e.g. EP-A 601 235.
[0031] The toner particles can be used as mono-component developers, both as a magnetic
and as a non-magnetic mono-component developer. The toner particles can be use din
a multi-component developer wherein both magnetic carrier particles and toner particles
are present. The toner particles can be negatively charged as well as positively charged.
[0032] The radiation curing can proceed on line, e.g, in the fusing station itself of an
electrostatographic apparatus or in a station immediately adjacent to said fusing
station.
[0033] The radiation curing can proceed off-line in a separate apparatus wherein the fused
layer of toner particles is heated again and irradiated with curing rays. It is important
that the radiation (UV-) curing proceeds on the molten toner particles and while the
toner receiving layer has some fluidity. Preferably said radiation curing proceeds
at a temperature that preferably is at most 150 °, most preferably at most 120 °C.
Therefore it is preferred to use toner particles, comprising a radiation curable compound
having a Tg ≥ 35 °C, that have a meltviscosity at 120 °C between 50 and 2000 Pas,
preferably between 100 and 1000 Pas. All meltviscosities mentioned herein are measured
in a RHEOMETRICS dynamic rheometer, RVEM-200 (One Possumtown Road, Piscataway, NJ
08854 USA). The viscosity measurement is carried out at a sample temperature of 120
°C. The sample having a weight of 0.75 g is applied in the measuring gap (about 1.5
mm) between two parallel plates of 20 mm diameter one of which is oscillating about
its vertical axis at 100 rad/sec and amplitude of 10
-3 radians. The fluidity of the toner receiving layer at the temperatures mentioned
above can be increased by incorporating waxes or "heat solvents" also called "thermal
solvents" or "thermosolvents"in the toner receiving layer on the substrate.
[0034] By the term "heat solvent" in this invention is meant a non-hydrolysable organic
material which is in solid state at temperatures below 50 °C but becomes on heating
above that temperature a plasticizer for the binder of the layer wherein they are
incorporated. Useful for that purpose are a polyethylene glycol having a mean molecular
weight in the range of 1,500 to 20,000 described in US-P 3,347,675. Further are mentioned
compounds such as urea, methyl sulfonamide and ethylene carbonate being heat solvents
described in US-P 3,667,959, and compounds such as tetrahydro-thiophene-1,1-dioxide,
methyl anisate and 1,10-decanediol being described as heat solvents in Research Disclosure,
December 1976, (item 15027) pages 26-28. Still other examples of heat solvents have
been described in US-P 3,438,776, and 4,740,446, and in published EP-A 0 119 615 and
0 122 512 and DE-A 3 339 810.
[0035] Said toner receiving layer may further comprise a binding agent or mixture of binding
agents, also stabilizers, toning agents, antistatic agents, spacing particles (both
polymeric or anorganic). In addition to said ingredients the toner receiving layer
may contain other additives such as free fatty acids, antistatic agents, e.g. non-ionic
antistatic agents including a fluorocarbon group as e.g. in F
3C(CF
2)
6CONH(CH
2CH
2O)-H, ultraviolet light absorbing compounds, white light reflecting and/or ultraviolet
radiation reflecting pigments, and/or optical brightening agents.
[0036] Said step of depositing said clear toner particles can be an image-wise depositing
step, a non-image-wise depositing step or a counter-image-wise depositing step, as
described above.
In a method of the invention, wherein additionally to the step of image-wise depositing
toner particles on a substrate, a step of depositing clear toner particles on the
image is included, only said clear toner particle comprise a radiation curable resin
with Tg ≥ 35 °C.
[0037] The present invention also includes an apparatus for forming toner images on a substrate
comprising :
i) means for image-wise depositing toner particles comprising a radiation curable
resin having a Tg ≥ 35 °C on a substrate,
ii) means for fusing said toner particles on said substrate characterised in that
it further comprises means for on-line radiation curing said fused toner particles.
[0038] The present invention further includes an apparatus for forming a toner image on
a substrate comprising the steps of :
i) means for image-wise depositing toner particles on said substrate,
ii) means for depositing clear toner particles, comprising a radiation curable resin
having a Tg ≥ 35 °C on top of said image-wise deposited toner particles,
iii) means for fusing said toner particles on said substrate characterised in that
it further comprises means for on-line radiation curing said fused toner particles.
[0039] Said means for fusing said toner particles to the substrate can be any means known
in the art, the means for fusing toner particles according to this invention can be
contact (e.g. hot-pressure rollers) or non-contact means. In an apparatus according
to the present invention, however, the fusing means it is preferred to be mainly,
preferably exclusively, non-contact means. Non-contact fusing means according to this
invention can include a variety of embodiments, such as : (1) an oven heating process
in which heat is applied to the toner image by hot air over a wide portion of the
support sheet, (2) a radiant heating process in which heat is supplied by infrared
and/or visible light absorbed in the toner, the light source being e.g. an infrared
lamp or flash lamp. According to a particular embodiment of "non-contact" fusing the
heat reaches the non-fixed toner image through its substrate by contacting the support
at its side remote from the toner image with a hot body, e.g., a hot metallic roller.
In the present invention, non-contact fusing by radiant heat, e.g., infrared radiation
(IR-radiation), is preferred.
[0040] In a apparatus according to the present invention the clear toner particles comprising
a UV-curable resin are used and thus the means for radiation curing the toner particles
comprise are means for UV-curing ( UV-light emitters as e.g. UV lamps). In an apparatus
according to the present invention, it is preferred that the radiation curing proceeds
on-line. Therefore it is preferred that said means for fusing said toner images emit
infrared radiation (are infra-red radiators) and said means for UV curing (e.g. one
or more UV emitting lamps as, e.g. high pressure mercury lamps) are installed immediately
after said fusing means so that the UV curing proceed on the still molten toner image.
A combination of infra-red radiators (the means for fusing the toner particles) and
UV emitting lamps (the means for radiation curing) in a single station (a fixing/curing
station), so that the fusing and the radiation curing proceed simultaneously, is also
a desirable design feature of an apparatus according to this invention. The apparatus
according to the present invention can comprise if so desired, more than one fixing/curing
station. The UV emitting means are preferably UV radiators with a capacity (an intensity)
between 20 W/cm and 150 W/cm.
[0041] The means for image-wise depositing toner particles can, in apparatus according to
this invention, be direct electrostatic printing means (DEP), wherein charged toner
particles are attracted to the substrate by an electrical field and the toner flow
modulated by a printhead structure comprising printing apertures and control electrodes.
Said means for image-wise depositing toner particles can also be toner depositing
means wherein first a latent image is formed. In such an apparatus, within the scope
of the present invention, said means for image-wise depositing toner particles) comprise
:
- means for producing a latent image on a latent image bearing member,
- means for developing said latent image by the deposition of said toner particles,
forming a developed image.
[0042] Said latent image may be a magnetic latent image that is developed by magnetic toner
particles (magnetography) or, preferably, an electrostatic latent image. Such an electrostatic
latent image is preferably an electrophotographic latent image and the means for producing
a latent image are in this invention preferably light emitting means, e.g., light
emitting diodes or lasers and said latent image bearing member comprises preferably
a photoconductor.
EXAMPLE
1. Preparation of the toner particles and the developers
Yellow toner (Y)
[0043] 49 parts of a polyester with acid value AV of 17 mg KOH/g (number 2 of Table 1) and
49 parts of a polyester with AV of 18 mg KOH/g (number 3 of Table 1) were melt-blended
for 30 minutes at 110 °C in a laboratory kneader with 2 parts of SICOECHTGELB D 1355
DD (Colour Index PY 13, trade name of BASF AG, Germany).
[0044] After cooling the solidified mass was pulverized and milled using an ALPINE Fliessbettgegenstrahlmühle
type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier
type 100MZR (tradename). The average particle size of the separated toner was measured
by Coulter Counter model Multisizer (tradename) was found to be 8.0 µm by volume.
[0045] 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).
Magenta Toner (M)
[0046] The preparation of the Yellow toner was repeated, but instead of 2 parts SICOECHTGELB
PY13, 2 parts of PERMANENT CARMIN FFB 02 (Colour Index PR146, tradename of Hoechst
AG, Germany) were used.
Cyan toner (C)
[0047] The preparation of the Yellow toner was repeated, but instead of 2 parts SICOECHTGELB
PY13, 2 parts of HELIOGEN BLAU D7072DD (Colour Index PB15:3, trade name of BASF AG,
Germany) were used.
Black toner (K)
[0048] The preparation of the Yellow toner was repeated, but instead of 2 parts SICOECHTGELB
PY13, 2 parts of CABOT REGAL 400 (carbon black, trade name of the Cabot Corp. High
Street 125, Boston, U.S.A.) were used.
[0049] The four toners, Y, M, C and K had a meltviscosity at 120 ° C of 250 Pas (measured
as described above at a frequency of 16 Hz.
Clear toner (CT)
[0050] 68 parts of solid unsaturated polyester resin having a Tg ≥ 45 °C available from
Hoechst High Chem, Hoechts-Sara, Pero (Mi) Italy under trade name ALFTALAT VAN 1743,
29 parts of an aliphatic urethane adduct with acrylic functional groups, having a
Tg ≥ 52 °C, available from Hoechst High Chem, Hoechts-Sara, Pero (Mi) Italy under
trade name ADDITOL 03546 and 3 parts of
available from Ciba-Geigy,
Basel, Switserland under tradename IRGACURE 651 were melt-blended for 30 minutes at
110 °C in a laboratory kneader.
[0051] After cooling the solidified mass was pulverized and milled using an ALPINE Fliessbettgegenstrahlmuhle
type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier
type 100MZR (tradename). The average particle size of the separated toner was measured
by Coulter Counter model Multisizer (tradename) was found to be 8.0 µm by volume.
The clear toner CT had a meltviscosity at 120 °C of 195 Pas.
[0052] To improve the flowability of the toner mass the toner particles were mixed with
0.3 % of hydrophobic colloidal silica particles (BET-value 130 m
2/g).
Developers
[0053] Each of the above prepared toners were used to form carrier-toner developers by mixing
said mixture of toner particles and colloidal silica in a 4 % ratio with silicone-coated
Cu-Zn ferrite carrier particles having an average diameter of 55 µm.
2. Printing Example
[0054] Full colour toner images were produced using a commercial CHROMAPRESS (a trade name
of Agfa-Gevaert NV, Mortsel, Belgium). The images were covered with a layer of clear
toner such that 0.9 mg/cm
2 clear toner was present.
The fusing took place with radiant heat (a IR-lamp) at 120 °C and the fused tone layer
was immediately, without cooling irradiated with a UV-lamp for 0.5 sec with a high
pressure mercury lamp and intensity of 80 W/cm.
A second image without UV-curing was also produced. The resistance of both images
against solvents was tested by rubbing the image 10 consecutive times with a cloth
soaked with MEK (methylethyleketone). The UV-cured image, whereas the non-cured image
disappeared after rubbing once.
[0055] The UV-cured image showed an even high gloss of more than 90 % when measured under
an angle of 60 ° with a gloss measuring device (MINOLTA MULTI-GLOSS 268, trade name
of Minolta, Osaka, Japan).