[0001] The present invention relates to particulate toner material for developing electrostatic
charge patterns or images.
[0002] In electrostatography a latent electrostatic charge image is made visible, i.e. developed,
by charged toner particles.
[0003] In electrophotography an electrostatic latent charge image is obtained with an electrophotographic
material typically comprising a coating of a photoconductive insulating material on
a conductive support. Said coating is given a uniform surface charge in the dark and
is then exposed to an image pattern of activating electromagnetic radiation such as
light or X-rays. The charge on the photoconductive element is dissipated in the irradiated
area to form an electrostatic charge pattern which is then developed with an electroscopic
marking material. The marking material or toner, as it is also called, whether carried
in an insulating liquid or in the form of a dry powder deposits on the exposed surface
in accordance with either the charge pattern or the discharge pattern as desired.
If the photoconductive element is of the reusable type, e.g. a selenium coated drum,
the toner image is transferred to another surface such as paper and then fixed to
provide a copy of the original.
[0004] A variety of electrostatic developers are available for use in developing electrostatic
charge patterns. A distinction is made between dry and liquid developers. According
to a known embodiment in dry developers carrier particles are mixed with toner particles
electrostatically adhering thereto. The carrier may comprise various materials and
as the name implies, serves as a medium for carrying the electrostatically responsive
marking particles to the charge pattern to be developed. Among the more common types
of carrier-toner developers are dry developers known for use in cascade development
as described e.g. in U.S.Patent Specification No. 2,618,552 and for use in magnetic
brush development as described e.g. in U.S.Patent Specification No. 3,003,462.
[0005] The cascade development technique is carried out by rolling or cascading across the
electrostatic latent image bearing surface, a developing mixture composed of relatively
large carrier particles, each having a number of electrostatically adhering toner
particles on its surface. As this mixture rolls across the image-bearing surface,
the toner particles are electrostatically deposited on the charged portions of the
image.
[0006] The magnetic brush development technique involves the use of magnetic means associated
with a developing mixture composed of magnetic carrier particles carrying a number
of smaller electrostatically adhering toner particles. In this technique the developer
composition is maintained during the development cycle in a loose, brushlike orientation
by a magnetic field surrounding, for example, a rotatable non-magnetic cylinder having
a means with magnetic poles mounted inside. The magnetic carrier particles are attracted
to the cylinder by the described magnetic field, and the toner particles are held
to the carrier particles by virtue of their opposite electrostatic polarity. Before
and during development, the toner acquires an electrostatic charge of a sign opposite
to that of the carrier material due to triboelectric charging derived from their mutual
frictional interaction. When this brushlike mass of magnetic carrier with adhering
toner particles is drawn across the surface bearing the electrostatic image, the toner
particles are electrostatically attracted to an oppositely charged latent image and
form a visible toner image corresponding to the electrostatic image. Since electrostatic
charge remains in the non-exposed areas of a photoconductive surface electrophotography
is inherently a direct positive process. In some instances, however, photocopying
requires the production of positive prints from photographic negatives.
[0007] Such is possible with line negatives as original due to the fringe effect. By the
fringe effect negative charges will be induced in the exposed areas which carried
originally positive charges but leaked off by the photoexposure. So, if a photoconductor
coating being originally overall charged positively has lost its positive charge in
correspondence with the line pattern of the original negative, charges of negative
sign will be induced in the exposed line pattern by the fringe effect of the still
surrounding positive charge pattern. Such makes that positively charged toner will
become attracted by said negative charges and a positive image will be developed with
respect to the original negative.
[0008] Reversal development of large image area will likewise be possible by applying a
bias voltage to a magnetic brush applicator which acting as a development electrode
induces when positively charged, through the conductive carrier particles a negative
charge in the discharged area of the previously positively charged photoconductor
coating (ref. R.M.Schaffert "Electrophotography" The Focal Press - London, New York
enlarged and revised edition 1975 p. 50-51 and T.P.Maclean "Electronic Imaging" Academic
Press - London, 1979 p.231).
[0009] In dry toner development systems the toner is normally a fine powder of natural or
synthetic resins having a colorant and a charge controlling agent dissolved or dispersed
therein.
[0010] Known positive charge controlling compounds for use in dry toners are dye bases and
salts thereof such as nigrosine dye base and salts described in GB-P 1,253,573. Such
charge controlling agents are usually added to the thermoplastic resin to be dispersed
in the resin in molten state. Upon cooling the mixture is micropulverized and the
particles with desired particle size separated e.g. by wind sifter.
[0011] Coloured charge controlling substances have the disadvantage that their colour interferes
with the colour intensionally given to the toner mass. For the obtaining of neutral
black or spectrally pure colours required in multicolour reproduction the inherent
colour of the charge controlling substance may form a serious obstacle. Therefore
preference is given to the use of colourless charge controlling substances.
[0012] According to the published unexamined Japanese patent application (Kokai) 6 0188-959
an electrostatic image developing toner contains as charge controlling agent a piperidine
compound corresponding to the following general formula (I) :

wherein : R₁, R₂, R₃ and R₄ are each 1-6C alkyl, R₅ is hydrogen or 1-5C alkyl, R₆
is hydrogen or 1-12C alkyl or 3-12C alkenyl, or 7-12C aralkyl; n is an integer of
1-4 and R₇ is acyl or N-substituted carbamoyl where n is 1, diacyl, dicarbamoyl or
carbonyl where n is 2, triacyl where n is 3 and tetraacyl where n is 4.
[0013] It is an object of the present invention to provide a particulate toner material
for developing electrostatic charge images which toner material contains a colourless
transparent charge controlling agent that does not interfere with the colouring agent
of the toner material and also acts as stabilizing agent protecting organic dyes against
discolouration by the action of light, ultraviolet radiation and the heat applied
in thermal fixing of the toner image.
[0014] It is a further object of the present invention to provide such toner material wherein
the charge controlling agent yields a particularly high positive charge to the toner
particles and has a good miscibility or compatibility with the polymeric binder material
present in the toner material.
[0015] Other objects and advantages of the present invention will become clear from the
further description.
[0016] In accordance with the present invention there is provided particulate toner material
for use in the development of latent electrostatic images, wherein said particulate
toner material is capable of acquiring by triboelectric contact electrification a
net positive charge and contains thermoplastic resin(s) as binder in combination with
a colorant and a colourless compound capable of imparting a positive charge to the
particulate toner material when in frictional contact with said carrier particles,
characterized in that said colourless compound contains in its molecular structure
at least one polyalkyl substituted piperidine group and a sterically hindered phenol
group.
[0017] In the particulate toner material according to the present invention said colourless
compound is used preferably in an amount in the range of 0.5 to 5 % by weight with
respect to the total toner composition.
[0018] Preferred compounds for use according to the present invention correspond to the
following general formula (A) :

wherein :
R¹ is hydrogen or alkyl having 1 to 4 carbon atoms,
R² is alkyl or hydroxyalkyl, each having 1 to 12 carbon atoms, alkenyl or alkynyl
each having 3 or 4 carbon atoms or aralkyl such as benzyl,
R³ is hydrogen or methyl,
R⁴ and R⁵ are each alkyl having 1 to 5 carbon atoms or cycloalkyl having 5 to 8 carbon
atoms,
X is oxygen or NH,
Y is hydrogen, alkyl having 1 to 12 carbon atoms or -C
nH
nCOOR⁷, in which n is 0 or an integer from 1 to 10 and R⁷ is hydrogen, alkyl having
1 to 18 carbon atoms, especially methyl or ethyl, or the Y is a substituent of the
formula :

wherein :
R¹ and R² are as defined above, or
Y is a substituent of the formula :

wherein :
R¹ and R² are as defined above, and R⁹ is hydrogen or alkyl having 1 to 4 carbon atoms,
especially methyl or ethyl,
m is 1 or 2, and
p is 0 or 1.
[0019] Typical representatives of compounds according to said general formula (A) wherein
X is oxygen are described in US-P 4,268,593 relating to recording material for colour
photography wherein said compounds are used as light stabilizers.
[0020] The synthesis methods for preparing said compounds can be found in US-P 4,198,334
and 4,268,593 and in German Offenlegungsschriften (DE-OS) Nos. 2,456,364, 2,647,452,
2,654,058 and 2,656,769.
[0021] For illustrative purposes the preparation of an ester compound according to the above
general formula (A) having the following structural formula (Z) is given hereinafter.

[0022] 23.3 g of butylmalonic acid bis(1,2,2,2,6,6-pentamethyl-4-piperidinyl) ester and
13.2 g of N-(3,5-di-tert-butyl-4-hydroxybenzyl)dimethylamine were dissolved in 200
ml toluene. After addition of 0.25 g of LiNH ₂, the mixture was refluxed for 15 minutes
to give butyl(3,5-di-tert-butyl-4-hydroxybenzyl)malonic acid bis(1,2,2,6,6-pentamethyl-4-piperidinyl)
ester. Melting point : 147 °C.
[0023] Particularly high triboelectric positive charging of toner particles according to
the present invention is obtained with the compound according to the above structural
formula (Z).
[0024] The toner particle material according to the present invention may be used as so-called
mono-component toner or in admixture with carrier particles.
[0025] The toner material can be prepared by any conventional technique such as spray drying
a solution in a suitable volatile solvent or grinding a solidified composition of
homogeneously mixed ingredients including a thermoplastic binder, colorant and a colourless
positive charge-imparting polymeric amino compound(s) according to said general formula
(A).
[0026] The toner particles have preferably a particle size in the range of 3 to 30 µm, and
more preferably in the range of 5 to 20 µm.
[0027] It has been established experimentally that when the basic ring nitrogen atom of
the piperidine nucleus or nuclei according to the above general formula (A) is transformed
into a salt form by reaction with an acid or by quaternization the positive charge
controlling properties are maintained.
[0028] Although the colourless charge controlling substances are preferably present in dissolved
state in the thermoplastic resin binder of the toner, such is not strictly necessary.
When said substances are present in dispersed state the colour of the colorant is
not that vivid by the opalescent character of the dispersion. A "colloidal" dispersion
is mostly obtained when amino-salts and quaternary derivatives of the compounds according
general formula (A) are used.
[0029] When amino-salts or quaternary ammonium salts derived from the amines according to
the above general formula (A) are used the anion(s) of these salts may be of any type
known in the art. Suitable anions are e.g. hydroxyl (OH⁻), chloride, iodide, sulfate,
ZnCl⁻⁴, and tolusulfonate. The affinity of the anion with respect to the carrier particle
surface may play a role in the triboelectric charging [ref. the book "Electrophotography"
by R.M. Schaffert, The Focal Press - London and New York (1975), p. 559-560].
[0030] For lowering the Coulomb attraction of the anions and cations, which may be in favour
of the transfer of the anions of the toner particles to the carrier particles whereby
triboelectric charging is improved, preferably anions of relatively large size are
used, e.g. PF

and other large size anions such as the tetraphenylboride anion described for use
in liquid electrophoretic developers in US-P 4,525,446.
[0031] For obtaining a hard toner which is in favour of a longer developer lifetime because
"smearing" of the toner particles on the carrier particles becomes less, preference
is given to thermoplastic resins having a melting point in the range of 100 to 120°C,
glass transition temperature (Tg) larger than 60 °C, with in their structure a major
part by weight of aromatic groups, e.g. phenyl groups. Said polymers may contain a
minor part by weight of electron donating groups, e.g. alkylamino or arylamino groups
to further improve the positive chargeability of the toner.
[0032] The charge imparting compounds applied according to the present invention yield particularly
high positive charging when dissolved or dispersed in a thermoplastic binder being
a resin selected from the group consisting of a homopolymer and copolymer of styrene
wherein the styrene content is preferably at least 50 mole %. Preferred copolymers
of styrene for use in toner material according to the present invention are copolymers
of styrene-(meth)acrylic acid esters such as styrene-methyl acrylate copolymer, styrene-ethyl
acrylate copolymer, styrene-n-butyl acrylate copolymer, styrene-n-octyl acrylate copolymer,
styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-n-butyl
methacrylate copolymer, styrene-isobutyl methacrylate copolymer, styrene-n-octyl methacrylate
copolymer, styrene-heptadecyl methacrylate copolymer, copoly(styrene-butadiene), and
a copolymer of styrene including up to 25 % by weight of monomer units comprising
a dialkylamino group.
[0033] Preferred copolymers containing said group have the following structural formula
(B) :

wherein :
x is 83-87 % by weight
y is 0-4 % by weight
z is 13-17 % by weight,
and have a melting point (ring and ball method) in the range of 106 to 115°C.
[0034] Said copolymers which may be used separately or in combination can be prepared by
common addition polymerisation starting with the monomers involved.
[0035] In the particulate toner material according to the present invention the colorant
being a dye or pigment may be soluble or dispersable in the polymeric resin binder.
[0036] In order to obtain toner particles with sufficient optical density in the spectral
absorption region of the colorant, the colorant is used preferably in an amount of
at least 2 % by weight with respect to the total toner composition, more preferably
in an amount in the range of 5 to 15 % by weight.
[0037] For black toners preference is given to carbon black as a colorant.
[0038] Examples of carbon black and analogous forms therefor are lamp black, channel black,
and furnace black e.g. SPEZIALSCHWARZ IV (trade-name of Degussa Frankfurt/M, W.Germany)
and VULCAN XC 72 and CABOT REGAL 400 (trade-names of Cabot Corp. High Street 125,
Boston, U.S.A.).
[0039] The characteristics of preferred carbon blacks are listed in the following table
1.
TABLE 1
|
SPEZIALSCHWARZ |
CABOT REGAL 400 |
origin |
channel black |
furnace black |
density |
1.8 g x cm⁻³ |
1.8 g x cm⁻³ |
grain size before entering the toner |
25 nm |
25 nm |
oil number (g of linseed oil adsorbed by 100 g of pigment |
300 |
70 |
specific surface (sq.m per g) |
120 |
96 |
volatile material (% by weight) |
12 |
2.5 |
pH |
3 |
4.5 |
colour |
brown-black |
black |
[0040] Toners for the production of colour images may contain organic dyes or pigments of
the group of phthalocyanine dyes, quinacridone dyes, triaryl methane dyes, sulphur
dyes, acridine dyes, azo dyes and fluoresceine dyes. A review of these dyes can be
found in "Organic Chemistry" by Paul Karrer, Elsevier Publishing Company, Inc. New
York (1950).
[0041] Typical inorganic pigments include black iron(III) oxide, copper(II) oxide and chromium(III)
oxide powder, milori blue, ultramarine cobalt blue and barium permanganate.
[0042] In order to obtain toner particles having magnetic properties a magnetic or magnetizable
material may be added during the toner production.
[0043] Magnetic materials suitable for said use are magnetic or magnetizable metals including
iron, cobalt, nickel and various magnetizable oxides including (hematite) Fe₂O₃, (magnetite)
Fe₃O₄, CrO₂ and magnetic ferrites, e.g. these derived from zinc, cadmium, barium and
manganese. Likewise may be used various magnetic alloys, e.g. permalloys and alloys
of cobalt-phosphors, cobalt-nickel and the like or mixtures of any of these. Good
results can be obtained with about 30 % to about 80 % by weight of magnetic material
with respect to the resin binder of the toner.
[0044] In the preparation of the toner the colorant and optionally magnetic material may
be added in finely divided state to the mixture of molten resin binder while stirring
until a mixture of homogeneously dispersed or dissolved material in the resin melt
is obtained. The mixing temperature is e.g. in the range of 100 to 150°C.
[0045] After cooling, the solid mass obtained is crushed and ground e.g. in a hammer mill
followed by a jet-mill to an average particle size of 1 to 50 microns. The fraction
having a particle size between 3-30 µm separated e.g. by air sifter is used. The resulting
powder may not be tacky below 50°C.
[0046] For a given charge density of the charge-carrying surface the maximum development
density attainable with toner particles of a given size is determined by the charge/toner
particle mass ratio, which is determined substantially by the triboelectric charge
obtained by friction-contact with the carrier particles.
[0047] In a particular embodiment the toner according to the present invention is applied
in a carrier-toner mixture wherein the toner acquires a positive charge by frictional
contact with the carrier. The carrier-toner mixture is preferably applied to the surface
carrying a latent electrostatic image by cascade-, or magnetic brush development which
techniques are described in detail by Thomas L. Thourson in his article "Xerographic
Development Processes : A Review", IEEE Transactions on Electron Devices, Vol. ED-19,
No. 4, April 1972 p. 497-504.
[0048] Suitable carrier particles for use in cascade and for magnetic brush development
are described in GB-P 1,438,110.
[0049] The carrier particles are preferably at least 3 times larger in size than the toner
particles. For use in cascade development their particle size is preferably in the
range of 50 to 1000 microns.
[0050] The carrier particles may be made of iron or steel optionally provided with an oxide
skin. Other types of carriers are on the basis of magnetic material such as ferrites
or magnetite finely dispersed in a resin binder material, so-called composite type
carriers, examples of which are given in US-P 4,600,675 and published European patent
application 0 289 663. Iron or steel carrier beads may be subjected to special pretreatments
to enhance the triboelectric charging of the toner. Suitable coating-treatments of
carrier beads are described e.g. in said last mentioned GB-P 1,438,110.
[0051] In magnetic brush development the carrier particles are magnetically attractable.
Particularly suited are the iron bead carrier particles according to United States
Patent Specification 2,786,440, which particles have been washed free from grease
and other impurities and have a diameter of 1.52x10⁻¹ to 2.03x10⁻¹ mm.
[0052] In a preferred embodiment of the present invention the toner particles are mixed
with iron carrier beads of a diameter in the range of 50 to 200 microns having a thin
iron oxide skin. These carrier beads have almost a spherical shape and are prepared
e.g. by a process as described in GB-P 1,174,571.
[0053] The developer composition may for example contain 1 to 5 parts by weight of toner
particles per 100 parts by weight of carrier particles.
[0054] According to a particular embodiment the flowing properties of the developer are
improved by mixing the toner particles with a flow improving substance such as colloidal
silica particles and/or microbeads of a fluorinated polymer. The flow improving substance
is used e.g. in an amount of 0.05 to 1 % by weight with respect to the toner.
[0055] Colloidal silica has been described for that purpose in the GB-P 1,438,110. Particularly
useful is AEROSIL 300 [trade mark of Degussa, Frankfurt (M) W.Germany] for colloidal
silica having a specific surface area of 300 sq.m/g. The specific surface area can
be measured by a method described by Nelsen and Eggertsen in "Determination of Surface
Area Adsorption Measurements by Continuous Flow Method", Analytical Chemistry, Vol.
30, No. 8 (1958) 1387-1390.
[0056] Suitable fluorinated polymer beads for improving the flowing properties of the toner
as well as of the carrier particles are described in the United States Patent Specification
4,187,329. A preferred fluorinated polymer for said use is poly(tetrafluoroethylene)
having a particle size of 3 to 4 µm and melting point of 325-329°C Such poly(tetrafluoroethylene)
is sold under the trade name HOSTAFLON TF-VP-9202 by Farbwerke Hoechst A.G. W.Germany.
[0057] An other fluorinated polymer useful for that purpose is polyvinylidene fluoride having
an average particle size of 5 µm sold under the trade name KYNAR RESIN 301 by Pennwalt
Corp. - Plastic div. England.
[0058] The colloidal silica and/or said fluorinated polymer particles are mixed preferably
with the toner in a proportion of 0.15 % to 0.075 % by weight. The toner becomes thereby
non-tacky and obtains a reduced tendency to form a film on the xerographic plates
or drums e.g. having a vapour-deposited coating of a photoconductive Se-As alloy on
a conductive substrate e.g. aluminium.
[0059] The following comparative example illustrates the present invention without, however,
limiting it thereto. All parts, ratios and percentages are by weight unless otherwise
stated.
Comparative Example
Toner preparation without colouring agent
[0060] A pseudo toner was prepared without colouring agent to check whether or not the incorporated
charge controlling agent yielded a clear mixture on melting with the elected resin
binder.
[0061] Two comparable colourless pseudo toners were prepared by mixing in the melt 5 parts
of a furtheron identified charge controlling substance with 95 parts of copolymer
of (styrene-n-butylmethacrylate)(65/35) having a ring and ball softening point : 123
°C which copolymer serves as thermplastic binder. The mixture was melt-kneaded at
130°C for 30 minutes. Thereupon the mixture was cooled down to room temperature, crushed
and then pulverised by milling in a jet mill.
[0062] By wind sifter a toner particle fraction having an average particle size of 13 µm
was separated.
Developer preparation
[0063] An electroscopic developer was prepared by mixing 3% of the separated toner particles
with iron bead carrier particles having an iron oxide skin and average grain size
of 80 µm. The triboelectric charging of the resulting powder mixture was realized
by a 30 minutes agitation in a metal cylinder having a diameter of 6 cm, being filled
for approximately 30% by volume with said mixture and revolving at a speed of 60 rpm.
Measurement.
[0064] Different triboelectric charge measurement techniques are available all being based
on the separation of the toner particles from the admixed carrier particles and the
determination of the charge of the separated toner particles directly or indirectly.
Depending on the applied technique somewhat differing charge to mass ratio (Q/M) values
are obtained expressed in coulomb/gram (C/g). For obtaining comparable results the
same separation and measuring technique should be used with toner of the same average
particle size since the triboelectric charging is a surface phenomenon.
[0065] In the present example the separation of the toner from the carrier particles was
realized in a commercially available blow-off type powder charge measuring device.
By calculating the surface area of the pseudo toner for a given mass and using the
Q/M data from the resulting blow-off separation the charge density was calculated,
and expressed in C/cm ².
[0066] The results obtained with a charge controlling substance according to the structural
formula (Z) applied in the present invention and charge controlling compound No. 14
of the already mentioned published unexamined Japanese patent application (Kokai)
6 0188-959 having the following structure are mentioned in Table 2.
TABLE 2
Charge controlling agent |
10⁻¹⁰ C/cm² |
Compound (Z) |
+ 27.4 |
Compound (Z).2 HCl |
+ 22.5 |
No. 14 |
+ 8.1 |
[0067] The pseudo toners obtained with said both charge controlling agents were perfectly
optically clear which proves their good compatibility with the applied resin binder.
1. Particulate toner material for use in the development of latent electrostatic images,
wherein said particulate toner material is capable of acquiring by triboelectric contact
electrification a net positive charge and contains thermoplastic resin(s) as binder
in combination with a colorant and a colourless compound capable of imparting a positive
charge to the particulate toner material when in frictional contact with said carrier
particles, characterized in that said colourless compound contains in its molecular
structure at least one polyalkyl substituted piperidine group and a sterically hindered
phenol group.
2. Particulate toner material according to claim 1, wherein said colourless compound
corresponds to the following general formula (A) :

wherein :
R¹ is hydrogen or alkyl having 1 to 4 carbon atoms,
R² is alkyl or hydroxyalkyl, each having 1 to 12 carbon atoms, alkenyl or alkynyl
each having 3 or 4 carbon atoms or aralkyl,
R³ is hydrogen or methyl,
R⁴ and R⁵ are each alkyl having 1 to 5 carbon atoms or cycloalkyl having 5 to 8 carbon
atoms,
X is oxygen or NH,
Y is hydrogen, alkyl having 1 to 12 carbon atoms or -C
nH
nCOOR⁷, in which n is 0 or an integer from 1 to 10 and R⁷ is hydrogen, alkyl having
1 to 18 carbon atoms or the Y is a substituent of the formula :

wherein :
R¹ and R² are as defined above, or
Y is a substituent of the formula :

wherein :
R¹ and R² are as defined above, and R⁹ is hydrogen or alkyl having 1 to 4 carbon atoms,
m is 1 or 2, and
p is 0 or 1.
3. Particulate toner material according to claim 1 or 2, wherein said colourless compound
is used in amount in the range of 0.5 to 5 % by weight with respect to the total toner
composition.
4. Particulate toner material according to any of the preceding claims, wherein said
colourless compound is dissolved or dispersed in a thermoplastic binder being a resin
selected from the group consisting of a homo- and copolymer of styrene wherein the
styrene content is at least 50 mole %.
5. Particulate toner material according to claim 4, wherein said copolymer is selected
from the group consisting of styrene-methyl acrylate copolymer, styrene-ethyl acrylate
copolymer, styrene-n-butyl acrylate copolymer, styrene-n-octyl acrylate copolymer,
styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-n-butyl
methacrylate copolymer, styrene-isobutyl methacrylate copolymer, styrene-n-octyl methacrylate
copolymer, styrene-heptadecyl methacrylate copolymer, copoly(styrene-butadiene), and
a copolymer of styrene including up to 25 % by weight of monomer units comprising
a dialkylamino group.
6. Particulate toner material according to any of claims 1 to 5, wherein the colorant
is carbon black.
7. Particulate toner material according to any of claims 1 to 5, wherein the colorant
is an organic dye or pigment selected from the group consisting of phthalocyanine
dyes, quinacridone dyes, triaryl methane dyes, sulphur dyes, acridine dyes, azo dyes
and fluoresceine dyes.
8. Particulate toner material according to any of the preceding claims, wherein the
toner particles incorporate a magnetic or magnetizable material.
9. Particulate toner material according to any of the preceding claims, wherein said
material is present in admixture with carrier particles suited for use in cascade-,
or magnetic brush development of latent electrostatic charge images.
10. Particulate toner material according to claim 9, wherein said carrier particles
are at least 3 times larger in size than the toner particles and have an average grain
size in the range of 50 to 1000 microns.
11. Particulate toner material according to claim 9 or 10, wherein the carrier particles
are made of iron or steel provided with an oxide skin.