U.S. patent application number 10/352222 was filed with the patent office on 2003-07-17 for process for making particulate compositions.
Invention is credited to Bedells, Alison Dawn, Morris, Daniel Patrick.
Application Number | 20030134218 10/352222 |
Document ID | / |
Family ID | 10829640 |
Filed Date | 2003-07-17 |
United States Patent
Application |
20030134218 |
Kind Code |
A1 |
Bedells, Alison Dawn ; et
al. |
July 17, 2003 |
Process for making particulate compositions
Abstract
There is described a process for producing a particulate
composition comprising the steps of: (a) forming a first dispersion
comprising first particles stabilized in a first fluid by first
species; (b) optionally the step of forming a second dispersion
comprising second particles stabilized in a second fluid, miscible
with the first fluid, by second species; (c) after (or
simultaneously with) the optional step of mixing the first and
second dispersions together if the second dispersion was formed
from step b); inducing association between the dispersed particles
to form clusters; and (d) binding together the particles within the
clusters; characterized in that the first and/or second particles
comprise at least one polar functional group to facilitate the
binding of the particles in step (d). Preferably the polar group is
other than an acid group, more preferably comprises at least one
hydroxy group, non-acidic polar group and/or non-basic polar group,
most preferably comprises one or more hydroxy and/or ether groups
(e.g. an optionally polymeric alkylene glycol alkyl ether). A
preferred embodiment of the process comprises mixing together two
aqueous dispersions of particles (e.g. pigment particles and
particles of hydroxy functional latex polymer). The dispersions are
stabilized with surfactants. Association of the particles into
clusters is induced by known means (e.g. heating and stirring) and
the clusters are grown by aggregation into loose matrices which are
more fused together to form particles which can be used in
electroreprographic toners.
Inventors: |
Bedells, Alison Dawn;
(Whalley Range Manchester, GB) ; Morris, Daniel
Patrick; (Blackley, GB) |
Correspondence
Address: |
PILLSBURY WINTHROP, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Family ID: |
10829640 |
Appl. No.: |
10/352222 |
Filed: |
January 28, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10352222 |
Jan 28, 2003 |
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09647548 |
Oct 2, 2000 |
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6531254 |
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09647548 |
Oct 2, 2000 |
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PCT/GB99/00917 |
Mar 23, 1999 |
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Current U.S.
Class: |
430/109.1 ;
430/137.14 |
Current CPC
Class: |
G03G 9/08791 20130101;
C08J 3/215 20130101; G03G 9/0819 20130101; G03G 9/0806 20130101;
C08J 2325/04 20130101 |
Class at
Publication: |
430/109.1 ;
430/137.14 |
International
Class: |
G03G 009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 1998 |
GB |
9806934.7 |
Claims
1. A process for producing a particulate composition comprising the
steps of: (a) forming a first dispersion comprising first particles
stabilised in a first fluid; (b) forming a second dispersion
comprising second particles which comprise hydroxy groups directly
bonded to the surface by forming part of a polymer from which the
particles are formed which particles do not contain acidic or basic
polar groups and are stabilised in a fluid, miscible with the first
fluid; (c) mixing the first and second dispersions together; (d)
inducing association between the dispersed particles to form
clusters; and (e) binding together the particles within the dusters
by raising their temperature to effect fusion.
2. A process as claimed in claim 1 in which the first particles are
pigmentary particles.
3. A process as claimed in claim 1 or 2 in which step (e) takes
place whilst the particles are in dispersion in a fluid.
4. A process for producing an electroreprographically effective
toner and/or developer composition which process comprises a
process as claimed in any preceding claim.
5. An electroreprographically effective toner and/or developer
composition produced by a process as claimed in claim 4.
6. An electroreprographic toner composition comprising particles
produced by a process as claimed in any one of claims 1 to 4 in
which 80% of the toner particles have a diameter in the range 2 to
20 micrometers.
7. A developer composition comprising an electroreprographic toner
composition as claimed in claim 5, and an electroreprographically
effective, inert carrier and/or diluent.
8. An electroreprographic device, a component for said device or a
consumable useable with said device each of which comprises a
composition as claimed in claim 5, 6 or 7.
9. Use of a composition as claimed in claim 5, 6 or 7 as a
consumable in an electroreprographic device.
10. A process for producing a coloured toner composition which
comprises: (a) forming an aqueous dispersion comprising pigmentary
particles; (b) forming a second aqueous dispersion comprising
polymer particles, the polymer comprising hydroxy functional
groups; (c) mixing the first and second dispersions to obtain a
substantially homogeneous mixture in the absence of substantial
association; (d) forming clusters by inducing the particles to
associate; (e) inducing growth of the clusters into dispersed
matrices of loosely associated clusters; (f) heating the mixture
from step (e) at a temperature above the glass transition
temperature of the constituent hydroxy functional polymer to fuse
together the clustered particles to form internally coalesced
particles of a coloured toner, and (g) collecting the coloured
particulate toner obtained in step (f) and producing optionally
after washing, drying and/or blending with other suitable
ingredients, a coloured toner composition.
Description
[0001] The present invention relates to a process for making
particulate compositions. Such compositions have particular utility
in the field of electroreprography. Preferred aspects of the
invention relates to processes for making toner compositions for
use in electroreprography.
[0002] Electroreprography is any process in which an image is
reproduced by means of electricity and incident radiation, usually
electromagnetic radiation more usually visible light.
Electroreprography comprises the technology of electrophotography
which encompasses photocopying and laser printing technologies. In
both these technologies a latent electrostatic image in charge is
produced by exposure of a photoconductive drum to light. This can
be either reflected light from an illuminated image (photocopying)
or by scanning the drum with a laser usually under instruction from
a computer (laser printing). Once a latent image has been produced
in charge it must be developed to form a visible image on the drum
which can then be transferred onto a suitable substrate so a hard
copy of the image is obtained (e.g. by printing onto paper).
[0003] Suitable developers, which may be liquid or dry
compositions, comprise particles of a toner which are
electrostatically attracted to the latent image. Liquid developers
comprise a toner dispersed in a suitable insulating liquid. Dry
developers may comprise single component systems comprising a
toner, or two component systems which comprise a mixture of a toner
and a carrier. A toner may comprise particles of a polymeric
component, a colouring agent and optionally other internal and/or
external additives such as charge control agents and/or surface
additives to improve the flowability of the toner particles. The
polymeric component of the toner is electrically insulating to
enable the toner to be electrostatically charged during the
electroreprographic process and also acts to fix the toner to the
printed substrate, usually by fusion of the polymer onto the
substrate by heating. The colouring agent, which is usually a
pigment, imparts the required colour to the toner.
[0004] During use in an electroreprographic device, friction
between particles of toner with their carrier and/or with parts of
the device in which the toner is used cause the toner particles to
become charged with an electrostatic charge (tribocharge). The
exact mechanism to produce the toner image will then vary according
to the specific device used. For example in a conventional
photocopier the toner composition may be formulated so that
tribocharged toner particles will be opposite in sign to the latent
image on the drum and toner will be attracted to the latent image
on the drum to develop an image in toner on the drum which
corresponds to the original document. The developed image is then
transferred to a substrate such as paper (e.g. by a pressure roller
and/or voltage). The transferred image is fixed to the substrate
(e.g. by heat, pressure and/or suitable solvents) to produce a hard
copy of the image. The image drum is then cleaned and the device is
ready to produce the next copy. Thus developer compositions are
used both to develop the latent image on the drum and to produce
the final hard copy.
[0005] There are a number of methods for making toners. The most
common method is to mix the polymer and optional other ingredients
(e.g. colorant) together by kneading in a ball mill above the
melting point of the resin. The optional ingredients may be added
simultaneously or sequentially to the resin before or after melting
the resin, but are generally added to the resin when molten.
Generally, this involves mixing the molten composition for several
hours at temperatures from 120.degree. C. to 200.degree. C., in
order to uniformly distribute any optional ingredients (if present)
throughout the toner resin. The resultant melt may then be cooled,
extruded and then formed into particles with a mean diameter of
typically below 20 .mu.m. The particle formation is achieved by
physical processes such as crushing, grinding, milling, and/or
pulverising the extrudate. The fine powder of colour toner or
toner-resin so obtained is either used directly, is diluted with an
inert solid as carrier and/or is coated with surface additives such
as silica by mixing for example in a suitable blending machine.
[0006] As well as being extremely energy intensive, such physical
processes result in a wide distribution of particle sizes within
the toner. This leads to significant disadvantages. A wide particle
size range generates more uneven tribocharge within the toner which
leads to an uneven print density in the final image. The fine dust
within such toner compositions leads to fogging of the image
produced and more readily contaminates the interior of the device
in which the toner is used. The larger particles reduce the
resolution of images developed with the toner. Methods for
classifying this wide particle size (such as air classification or
sieving) are wasteful as material outside the required size range
is recycled which adds to the cost.
[0007] Modern electroreprographic devices require toners which
avoid some or all of the preceding disadvantages and have some or
all of the following properties: low temperature at which the toner
image fixes onto the printed substrate; wide temperature range over
which fusion of the toner occurs; low contamination of the device
in which it is used; ability to generate tribocharge at a
controlled level, which is stable with time and which is reasonably
independent of either temperature or humidity; small particle size
(preferably <7 .mu.m) with narrow size distribution to provide
good image resolution; cheap to produce in large volumes; uniform
dispersion of colorant(s) and other additives [e.g. charge control
agents (CCAs) and waxes]; ability to produce matt or gloss images
as required; high optical density; wide colour gamut; and/or
resistance to smudging and smearing in the final image. These
properties are strongly influenced by the choice of toner resins.
It is not feasible or cost effective to produce a toner having
these parameters using the conventional extrusion and milling
processes described above.
[0008] Therefore to overcome these disadvantages, methods for
chemically producing toners have been developed in which the toner
particles are prepared by chemical processes such as aggregation or
suspension rather than abraded from much larger sized material by
physical processes. Chemically produced toners made by prior art
suspension methods are less satisfactory as it is difficult to
control particle shape or obtain a narrow distribution of particle
size using such methods. Aggregation processes are preferred as
they provide a greater degree of control of the properties of
resultant toner particles such as size distribution, particle shape
and/or particle composition.
[0009] Certain prior art applications (for example JP 2-259770, JP
2-259771, JP 2-11968, JP 2-061650 and JP 2-093659 [Kokai] and U.S.
Pat. No. 4,983,488, U.S. Pat. No. 5,066,560 and EP 0162577 all to
Hitachi) disclose methods for chemical production of toners using
an irreversible coagulation method for particle growth. JP 2-061650
is typical of these and describes mixing aqueous dispersions of
latex and a pigment followed by a coagulation step. These Hitachi
patents all describe use of coagulating agents, such as suitable
salts, which reduce the stability of the colloid irreversibly.
[0010] The mechanism of the Hitachi processes is as follows. In a
colloid stabilised by charged surfactants, surrounding each
dispersed particle in the continuous (typically aqueous) phase
there will be a so called `double layer` where counter ions (of
opposite charge to the net charge on the particle) will be in
excess. The degree to which the counter ions are in excess will
decrease with increasing distance from the dispersed particle. The
thickness of this double layer will be determined by the rate at
which the net charge decreases with distance from the particle
which is dependent on inter alia the ionic strength of the colloid.
The colloid will only be stable whilst the ionic repulsion between
these double layers keeps the dispersed particles a sufficient
distance apart for short range attractive forces (such as van der
Waals forces) not to be significant. If the double layer is too
thin the dispersed particles can approach sufficiently closely for
these attractive forces to predominate. Thus altering the ionic
strength of the colloid will effect the thickness of the double
layer and hence the stability of the colloid. When the ionic
strength is raised to a particular amount the double layer is so
thin there is effectively no ionic repulsion between particles and
the forces between the particles are purely attractive which leads
to the formation of a large solid mass. Hence adding a suitable
ionic salt to a colloid (so called salting out) at a certain
concentration will suddenly produce an irreversible, collapse of
the dispersed particles into a distinct mass.
[0011] EP 0225476, EP 0609443, EP 0302939, all in the name of
Nippon Carbide, describe various processes for chemically producing
toners in which aggregation is induced (for example by
heating).
[0012] Various patent applications all in the name of Xerox (e.g.
EP 0631196, EP 0631057, EP 0631197, EP 0631194, EP 0671664, EP
0631195, GB 2279464, GB 2279465 and GB 2269179) describe
modifications of a process for chemically producing toners in which
dispersions stabilised with opposite charged surfactants are mixed
together to start aggregation. Typical of these applications is EP
0631196 (Xerox) which describes a process for preparing a toner by
aggregation of a mixture of an aqueous suspension of a pigment
stabilised with ionic surfactant and an aqueous suspension of a
latex stabilised with an ionic surfactant of opposite charge to
that stabilising the pigment. The oppositely charged surfactants
cause the pigment and latex particles to associate into clusters of
particles immediately the dispersions are mixed. The clusters are
grown by heating. Once the desired cluster size has been reached
further aggregation is minimised by adding additional surfactant to
stabilise the suspension of clusters. Then the particle clusters
are fused together by heating the mixture above the glass
transition temperature (T.sub.g) of the latex to form irregularly
shaped toner particles comprising pigment and latex which can be
collected.
[0013] In these processes the different dispersed particles begin
to associate as soon as the dispersions mix. The amount of
association is controlled by the ratio of cationic to anionic
functionality between the two surfactants which must be balanced
with the required ratio of the two different particle components.
The ratio of the two surfactants must be chosen carefully to ensure
that the correct amount of mixing of the ingredients can occur.
[0014] In the prior art processes after the dispersed particles are
associated and grown into clusters; the clusters of particles must
be bound internally to from fused irregularly shaped matrices
(which are suitable for use as toners). The binding step is often
difficult and energy intensive in the prior art methods. It is an
object of the present invention to provide an improved process for
chemically producing particulate compositions, such as toners.
[0015] The present invention relates to improved processes for
producing particulate compositions (such as chemically produced
toners) in which fusion of the associated particles is more readily
achieved. Surprisingly the applicant has discovered that if the
particles comprise a polar functional group, especially a hydroxy
functional group the fusion step can be achieved more readily.
[0016] Therefore broadly in accordance with one aspect of the
present invention there is provided a process for producing a
particulate composition comprising the steps of:
[0017] (a) forming a first dispersion comprising first particles
stabilised in a first fluid;
[0018] (b) optionally the step of forming a second dispersion
comprising second particles stabilised in a second fluid, miscible
with the first fluid;
[0019] (c) after (or simultaneously with) the optional step of
mixing the first and second dispersions together if the second
dispersion was formed from step b); inducing association between
the dispersed particles to form clusters; and
[0020] (d) binding together the particles within the clusters;
[0021] characterised in that the first and/or second particles
comprise at least one polar functional group.
[0022] The applicant has discovered that when the particles from
steps (a) and/or (b) comprise a polar functional group this
facilitates the binding of the particles in step (d). (for example
by controlling fusion e.g. by heating). Preferably the polar group
comprises other than an acid and/or basic polar group, more
preferably comprises at least one hydroxy group, non-acidic polar
group and/or non-basic polar group, most preferably comprises one
or more hydroxy and/or ether groups (e.g. PEG functionality and/or
alkylene glycol alkyl ether).
[0023] If the particles from steps (a) and/or (b) comprises one or
more polymers it is advantageous if at least one of such polymers
comprise polar groups (preferably those described above) to control
the particle binding in step (d). In particular the polymer which
may be a homo or co polymer may comprise hydroxy or other polar
functional groups. A preferred hydroxy-functional polymer is an
hydroxy functional latex copolymer optionally prepared by emulsion
polymerisation. Preferred polar-functional polymers, which do not
comprise an hydroxy group, yet which are also suitable for
controlling fusion comprise: polymeric alkylene glycol alkyl
ethers: for example poly(ethylene glycol) monomethyl ether acrylate
and/or methacrylate; and/or poly(propylene glycol) monomethyl ether
acrylate and/or methacrylate.
[0024] Copolymers may be prepared by copolymerising (e.g. by
emulsion polymerisation) an hydroxy-functional and/or other
polar-functional polymer precursor (preferably a monomer) with
other polymer precursors (e.g. other monomers) to form particles of
copolymer (e.g. copolymers of stryene, butyl acrylate and an
hydroxy functional monomer). Preferably the hydroxy functional
monomer is present in the copolymer in an amount from about 0.1% to
about 10% w/w, preferably from about 1 to about 5% w/w to be useful
for controlling the fusion process. Suitable hydroxy-functional
polymers and/or polymer percursors for making them comprise:
2-hydroxyethyl acrylate and/or methacrylate; hydroxypropyl and/or
hydroxybutyl acrylates and/or methacrylates; poly(ethylene glycol)
mono acrylates and/or methacrylates; and/or poly (propylene glycol)
mono acrylates and/or methacrylates.
[0025] The advantage of using polar functional particles
(preferably hydroxy-functional copolymers) in the process of the
present invention is to control the fusion process. In step (c)
particles of non-functional polymers associate and grow well. They
also fuse easily, in the sense that coalescence occurs readily.
However with such polymers it is more difficult to maintain the
particle size distribution, as "gritting" occurs. Very high levels
of polar functionality (e.g. >10%) give good particle size
stability, but the coalescence rate may be low. Intermediate levels
of such functionality (from about 2% to about 10%) are found to
give good particle size control and adequate coalescence rates.
[0026] Unless the context clearly indicates otherwise, as used
herein plural forms of the terms herein are to be construed as
including the singular form and vice versa.
[0027] Preferably the particulate composition produced by the above
method is electroreprographically effective. More preferably the
above process produces a composition which (optionally after
further finishing steps) can be used as a toner and/or developer
composition for an electroreprographic imaging device. The term
`electroreprographically effective` (for example with reference to
the toners, compositions, ingredients and/or processes described
herein) will be understood to mean effective for use in an
electroreprographic method by for example: providing the required
properties to a toner and/or developer, being compatible with any
inert carriers and/or diluents suitable for formulating such toners
and/or developers (for example those described herein), being
compatible with electroreprographic devices (such as photo-copiers
and/or laser printers) and/or being capable of being printed in
such devices. Preferably to be acceptable for use in
electroreprography ingredients are Ames negative.
[0028] Although the particulate compositions produced by the
process of the invention have particular utility as toners for use
in electroreprography, they may also be useful where compositions
comprising small particles of narrow size distribution and known
chemical composition would also be advantageous, for example in
catalysis.
[0029] In step c) optionally, after association has occurred for a
selected period, further association between the particles may be
substantially inhibited. Preferably the association in step (c)
comprises aggregation, flocculation and/or coagulation.
[0030] Optionally the processes of the present invention may also
comprise the following additional growth process in step c):
[0031] (i) inducing, optionally by heating and/or agitation, growth
of the clusters formed by association into dispersed matrices of
loosely associated clusters; and
[0032] (ii) optionally once the desired matrix size has been
achieved, substantially reducing further growth by suitable means,
for example by adding non-ionic and/or ionic surfactant and/or
changing pH.
[0033] Preferably the polar group forms part of the particles'
surface. The polar group may be directly bonded to the surface
(e.g. by forming part of the material [such as a polymer] from
which the particle is formed. The polar group may also be more
loosely associated with the particle surface (e.g. by absorption,
adsorption, physisorption and/or chemisorption to the surface such
as a suitable surfactant.
[0034] Preferably in the process of the present invention (the
steps labelled as above) preferred features comprise:
[0035] (a) forming a first dispersion comprising first particles
stabilised in a first fluid;
[0036] (b) optionally forming a second dispersion comprising second
particles stabilised in a second fluid, miscible with the first
fluid;
[0037] (c) substantially inducing association between the particles
to form clusters;
[0038] (d) heating the mixture at a temperature which causes the
particles within each cluster substantially to fuse together; and
the additional step of
[0039] (e) collecting the fused clusters to form a particulate
composition.
[0040] Thus in this preferred aspect of the present invention the
particles may be stabilised by surfactant.
[0041] A further optional step between steps b) and c) above
comprises mixing the first and optionally second dispersions to
obtain a substantially homogeneous mixture without substantial
association in which the first and second particles are
substantially inhibited from associating (e.g. by surfactant).
[0042] A still further optional feature after mixing the dispersion
from steps a) and b) is that the resultant mixture may be heated to
a higher temperature to aid homogeneous dispersion of the mixture.
In such a case growth may occur in step (c) without further heating
but simply by mixing of the particle dispersion. If the dispersed
particles comprise polymers the mixing temperature may be
substantially about or above the glass transition temperature
(T.sub.g) of any constituent polymers. Thus for example in the
preferred methods described below the first and second dispersions
(e.g. pigment and latex dispersions) are mixed after having been
heated to the growth temperature, or just below. Preferably this
mixture in step `c)` is stirred and heated at a temperature in a
range from about 30.degree. C. below to about 30.degree. C. above
(preferably about .+-.20.degree. C., more preferably about
.+-.10.degree. C.) the T.sub.g of any constituent polymers (e.g.
the latex) substantially to induce growth of the pigment/polymer
clusters particles to form matrices. The temperature of the mixture
in step (c) will preferably be in the range from about 30.degree.
C. to about 80.degree. C.
[0043] The advantage of heating is that the viscosity of the
associated mixture never reaches too a high level. The reasons for
this are not known. However, without wishing to be bound by theory,
it may be because at a higher mixing-temperature some cluster
growth occurs during association; and/or perhaps because the
viscosity of the gel is lower at higher temperature.
[0044] A further preferred aspect of the present invention (the
steps labelled as above) comprises:
[0045] (a) forming a first dispersion comprising first particles
dispersed in a first fluid, stabilised by a first surfactant;
[0046] (b) optionally forming a second dispersion comprising second
particles dispersed in a second fluid, miscible with the first
fluid, stabilised by a second surfactant;
[0047] (c) mixing the first and optionally second dispersions to
obtain a substantially homogeneous mixture without substantial
association; and reducing the stability of the dispersed particles
in the homogenised mixture, substantially to induce association
between the particles to form clusters.
[0048] A preferred process of the present invention uses hydroxy
functional polymers to produce a coloured toner composition. Thus
this process (the steps labelled as above) further comprises:
[0049] (a) forming a first aqueous dispersion comprising pigmentary
particles;
[0050] (b) forming a second aqueous dispersion comprising polymer
particles, the polymer comprising an hydroxy functional group;
[0051] (c) mixing the first and second dispersions to obtain a
substantially homogeneous mixture in the absence of substantial
association; forming clusters by inducing the particles to
associate; and then inducing growth of the clusters into dispersed
matrices of loosely associated clusters;
[0052] (d) heating the reaction mixture from step `c)` at a
temperature above the glass transition temperature of the
constituent hydroxy functional polymer to fuse together the
clustered particles to form internally coalesced particles of a
coloured toner; and
[0053] (e) collecting the coloured particulate toner obtained from
step `f)` to produce, after optional washing, drying and/or
blending with other suitable ingredients, a coloured toner
composition.
[0054] The first and second surfactants may optionally be the
same.
[0055] The processes of the present invention produces particulate
compositions having particles with a size distribution which is
readily controllable and lies within a narrow range. The present
processes avoid the need for further energy intensive milling or
classification steps. The processes allow precise control over the
final particle size and produce small particles, economically in
good yield with a low level of fines. Such small particles are
ideal for use in toners where small particles are desirable for
producing images of improved resolution. Toner compositions
produced by the processes of the present invention may be any
colour including black.
[0056] An optional step between step c) [growth of the particles
into clusters] and step d) [fusion of the particle clusters] is
stabilising the particle size distribution before raising the
temperature to effect fusion. One method is to add extra surfactant
which may be ionic or non-ionic.
[0057] It is desirable to remove any surfactant which may remain on
the particles as otherwise the tribocharge level of the resultant
toner is likely to be humidity dependant.
[0058] Preferably the process of the present invention directly
produces toner particles substantially having a diameter from about
2 .mu.m to about 20 .mu.m, more preferably from about 3 .mu.m to
about 15 .mu.m, most preferably from about 5 .mu.m to about 10
.mu.m. Preferably 80% of the particles fall within the preceding
size ranges, more preferably 90%, most preferably 95%. Toner with a
mean particle size of 5 .mu.m or below may have particular utility
for high resolution printing.
[0059] The particle size given herein is a linear dimension
corresponding to the diameter of a sphere approximately of same
volume as the particular particle of interest which may be
substantially irregular in shape.
[0060] It can be seen therefore that the process of the present
invention provides a high degree of flexibility in the choice of
resin components and colorants as a wide variety of combinations of
surfactants can be used. The present invention can use any suitable
method to induce and inhibit particle association, for example
those aggregation, flocculation and/or coagulation methods taught
in the prior art described herein. The particle dispersants can be
stabilised and de-stabilised by any suitable means for example by
surfactants (which may be non-ionic or ionic). This provides a
means for more exactly controlling the particle size distribution,
which can be readily and inexpensively optimised for the
ingredients used and the properties desired in the final toner
product. A preferred method is that described in the applicant's
co-pending British application GB 9708815.7.
[0061] The dispersion of pigmentary particles in step `a)` may
consist only of a dispersion of pigment; or may comprise a mixture
of pigment and polymer for example as produced by one of more of
the following methods. The colorant comprising the pigmentary
particles may be any colour including black, and may comprise
dye(s) [which are substantially soluble in the medium to which they
are added] and/or pigment(s) [which are substantially insoluble in
the medium to which they are added].
[0062] An aqueous dispersion of pigmentary particles may be
produced by a solution dispersion process in the following way. A
polymer (e.g. polyester) is dissolved in an organic solvent. Any
solvent which is immiscible with water, which will dissolve the
polymer and which can be removed by distillation relatively easily
could be utilised. Suitable solvents comprise xylene, ethyl acetate
and/or methylene chloride. To this solution is added a colorant
either a pigment or a dye. If a dye is used this is simply
dissolved in the polymer solution to produce a coloured liquid
solution. If a pigment is used it may be added, preferably with one
or more suitable pigment dispersants (which may be ionic or
non-ionic) and the pigment is milled in the polymer solution to
produce a coloured liquid dispersion. Other optional additives such
as charge control agents and waxes may be added to the liquid
(either dissolved or dispersed in the solvent).
[0063] Where transparency is desirable, for example where the toner
is used to produce an optionally coloured image on a clear
substrate through which light is projected (such as in printing
onto transparencies for use on an overhead projector) it is
desirable that the toner comprises small sized particles of pigment
within the toner. Therefore to produce such transparent toners the
particles in the pigment dispersion may be of low particle size
(preferably with a mean particle size diameter of less than about
300 nm).
[0064] The coloured liquid is added to an aqueous solution
comprising the surfactant and is mixed thoroughly (e.g. under high
shear) to generate an emulsion. It will be appreciated that the
surfactant may be supplemented by further optional stabilising
species. The emulsion comprises a dispersed phase comprising
droplets of the coloured organic liquid (e.g. particles of solid
pigment dispersed in the polymer solution) dispersed within the
continuous aqueous phase of the emulsion. Preferably the droplets
formed have a diameter of particle size from about 0.1 .mu.m to
about 3.0 .mu.m. The droplets of coloured organic liquid are
stabilised in the aqueous phase by the first ionic species.
[0065] The organic solvent is then removed from the dispersed phase
by distillation to leave an aqueous dispersion of pigmentary
particles containing the colorant dispersed or dissolved within the
solid polymer, the dispersed phase being stabilised in the aqueous
phase by the first ionic surfactant. The dispersed pigmentary
particles can be used as the raw material in step a) and preferably
have a particle diameter of from about 60 nm to about 2 .mu.m, more
preferably from about 100 nm to about 2 .mu.m. The size of the
pigmentary particles may be controlled by the amount of ionic
species and the degree of mixing of the emulsion.
[0066] The dispersion of pigmentary particles in step `a)` may also
be prepared by emulsion polymerisation to form a latex (e.g. using
a mixture of stryene and acrylic monomers). The colorant may be
incorporated into the latex in various ways, for example by any of
the following and/or combinations thereof. An aqueous dispersion of
pure pigment and/or pigmented or dyed polymer (produced by the
solution/dispersion process described above) may be used as the
seed for polymerisation. Alternatively a dye (optionally dissolved
in a solvent) may be added to the latex followed by heating.
Another method is to perform the emulsion polymerisation in the
presence of a dye which preferably is co-polymerisable with the
monomers used to form the latex.
[0067] Optionally any of the coloured polymer particles made as
described above can be self agglomerated alone without the polymer
dispersion in step `b)`.
[0068] Preferably the polymer dispersion in step `b)` comprises an
hydroxy functional latex, which may be colourless, formed by a
conventional emulsion polymerisation process (e.g. using a mixture
of stryene and acrylic monomers). Several emulsion polymers can be
made, for example those with different molecular weight
distributions, and these can then be blended prior to use of the
blend in the aggregation process of the invention.
[0069] One advantage of the mixing two dispersions and then
associating is that toner particle can be obtained with a wider
range of polymeric and other ingredients prepared in each
dispersion, that may otherwise be incompatible or difficult to
formulate in the same toner resin. For example polymers prepared by
the solution/dispersion method preferred for step a) [described
herein] may not be readily prepared by the emulsion polymerisation
method preferred in step b) and vice versa. Using a mixture of
polymers also gives greater opportunity to adjust the properties of
the final toner, which are strongly influenced by the choice of
polymer(s).
[0070] The particles may be collected in step g) by any convenient
conventional method for example centrifugation, micro-filtration,
freeze drying or spray drying.
[0071] In principle the association step c) could be carried out in
the same vessel in which dispersions from steps a) and b) are
initially mixed, provided the vessel is equipped with both a high
shear mixer and a bulk agitator. In practice, two methods are
preferred, the "circulation" system and the "single pass"
system.
[0072] In the "circulation" system the mixture of the dispersions
from steps a) and b) (optionally heated to around the polymer
T.sub.g, see below) are pumped in a loop from the stirred tank past
an external high shear mixer and back into the reaction vessel.
Particle association is effected by adjusting the pH by adding acid
(or base) into the stream just before the high shear head and/or
reaction vessel.
[0073] In the "single pass" method the mixture of the dispersions
from steps a) and b) are pumped from one (optionally heated)
reaction vessel to another reaction vessel past the high shear
head. The pH is adjusted by adding acid (or base) simultaneously at
the required rate, again just before the shear head and/or reaction
vessel.
[0074] A further aspect of the present invention comprises
particles obtained and/or obtainable by any of the processes of the
present invention as described herein. Preferably particulate
compositions of the present invention comprise those which are
electroreprographically effective (e.g. toner and/or developer
compositions). Preferred toners exhibit the particles sizes
described herein. Preferred developers further comprise an
electroreprographically effective, inert carrier and/or diluent
(for example those described herein). The carrier and/or diluent
may comprise particles of a size substantially in the range from
about 20 .mu.m to about 100 .mu.m.
[0075] A still further aspect of the present invention provides an
electroreprographic device (e.g. a device for colour and/or black
and white printing such as a photocopier, laser printer and/or fax
machine), a component for said device and/or a consumable useable
with said device; any of which comprise a composition obtainable by
any of the processes of the invention as described herein.
[0076] Compositions of the present invention may exist sealed
within an electroreprographic device and/or any component thereof
(e.g. spare part and/or replaceable mechanical element) which may
or may not be sold separately from the whole device. More commonly,
compositions of the present invention are sold separately from the
devices and other components thereof as a consumable for use in the
device. Consumables useable with these devices may comprise
cartridges comprising toners and/or developers of the present
invention which may be liquid and/or solid. The cartridges may be
sealed, disposable cartridges (which are pre-filled and used once)
or may be re-fillable, re-cyclable cartridges (which can be emptied
and/or filled by the user and/or sent to the manufacturer of the
device or a third party for re-filling). The cartridges may be
removable (wholly or in part) from the device; may be shaped to fit
in a particular device or a generic device; and may also comprise
other parts of the mechanism of the device in which they are used.
The cartridges may comprise a single storage compartment for
dispensing monochrome toner (e.g. black) or may comprise a
plurality of storage compartments for use in devices which can
print partial or full colour images. Thus a cartridge with four
compartments may dispense a three colour trichomat plus black. Less
commonly a cartridge with three compartments may suffice if the
black is to be formed by combining the three colours of the
trichromat.
[0077] A yet further aspect of the present invention provides use
of a composition obtainable as described herein, in the manufacture
of a electroreprographic device, as a component for said device
and/or as consumable for use with said device.
[0078] Toners of the present invention preferably comprise a resin
as a binder. The terms resin and polymer are used herein
interchangeably as there is no technical difference between them.
Other ingredients which optionally may be added to a toner
compositions comprise one or more of the following and any suitable
mixtures thereof: colorant(s), magnetic additive(s), charge control
agent(s), wax(es) and/or additive(s) to improve the flow, charge,
fusing and/or transfer properties of the toner and/or to aid
cleaning of the device (e.g. image drum) in which the toner is
used.
[0079] In addition to the hydroxy functionalised resin used herein
the toner resin may comprise any other thermoplastic resin suitable
for use in the preparation of toner compositions. Preferably the
toner resin comprises one or more of the following: a styrene
and/or substituted styrene polymer, (such as homopolymer [for
example polystyrene] and/or copolymer [for example
styrene-butadiene copolymer and/or styrene-acrylic copolymer {e.g.
a styrene-butyl methacrylate copolymer and/or polymers made from
stryene-butyl acrylate and other acrylic monomers such as hydroxy
acrylates or hydroxy methacylates}]); polyesters (such as specially
alkoxylated bis-phenol based polyester resins [for example those
described in U.S. Pat. No. 5,143,809]), polyvinyl acetate,
polyalkenes, poly(vinyl chloride), polyurethanes, polyamides,
silicones, epoxy resins and resins. The toner resins may be
optionally cross-linked (e.g. to provide the required melt
rheology). Therefore multi-functional monomers may be added (e.g.
during polymerisation) to the toner resin to make cross-linked
polymer particles (e.g. monomers such as di- or tri-functional
acrylates or methacrylates and/or divinylbenzene can be added to a
styrene-acrylic copolymer). Chain transfer agents may be added to
the toner resin to reduce the molecular weight (e.g. thiols can be
added to stryene-acrylic resins). The toner resins may also be
modified (e.g. at any suitable time before, during and/or after
polymerisation) by other conventional methods well-known to a
polymer chemist to achieve particularly desired properties. Further
examples of the aforementioned resins and other resins also
effective for use in toners are given in the book
"Electrophotography" by R. M. Shafert (Focal Press) and in the
following patents or patent applications: GB 2,090,008, U.S. Pat.
No. 4,206,064 and U.S. Pat. No. 4,407,924. It is especially
preferred that the toner resin is compatible with any optional
colorant used so it is easier to formulate in such resins and
produce clear, durable and bright reprographic images. Preferably,
the resin has a melting temperature between about 120.degree. C.
and about 220.degree. C. and more preferably between about
140.degree. C. and about 180.degree. C. However certain resins
(e.g. some resins used for coloured toners) may have a lower
melting temperature.
[0080] The term colorant as used herein encompasses both dyes
(which are substantially soluble in the medium to which they are
added) and pigments (which are substantially insoluble in the
medium to which they are added). A colorant comprises any material
which is imparts colour to a medium by any mechanism, for example
by attenuation, absorption, reflection and/or scattering of
radiation in the region of the electromagnetic spectrum visible to
the human eye. Colour as used herein encompasses black, white and
greys as well as hues such as red green and blue. For example
colour can arise by chemical processes (e.g. absorption,
re-radiation, phosphorescence and/or fluorescence), physical
processes (e.g. scattering of radiation by particles similar in
size to the wavelength of the incident radiation) and/or by any
other processes. The terms colorant and colour as used herein
unless the context indicates differently also includes materials
which have their effect in the region of the electromagnetic
spectrum which is non-visible to the human eye (such as infra red
or ultra-violet radiation) and which might have application in the
electroreprographic area such as for optionally invisible markers
in security applications (e.g. currency and security marking).
[0081] The colorant may where appropriate [e.g. within the
pigmentary particles of step `a)`] comprise a dye (soluble in the
medium to which it is added) and/or a pigment (insoluble in the
medium to which it is added). Dyes may comprise disperse dyes which
are dispersible in one solvent (e.g. water) but which become
soluble in another (e.g. the resin on fusion of the toner
particle). For toner applications either dyes or pigments may be
used, each having different advantages. Some of the advantages of
using dyes over pigments to provide colour in toners comprise any
of the following: less quantities of dye are required; there is
less likely to be a negative influence on tribocharging efficiency;
more brilliant colours can be obtained leading to better colour
mixing and a wide colour gamut; a typical absorbance/reflectance
spectra of a dye comprises sharp narrow peaks; the images produced
are less grainy; the melting point and/or viscosity of toners may
be lower; dyes may be chemically modified to alter toner
properties; and dyes may be easily purified. Some of the advantages
of using pigments over dyes to provide colour in toners comprise
any of the following: little bleeding or blooming problems in the
image; improved light and solvent fastness; higher thermal
stability; high extinction coefficients especially for particles
below 100 nm in diameter; and greater chemical inertness. One of
the advantages of the process of the present invention is that
toner particles can be readily produced which comprise both dye(s)
and pigment(s) with the advantages of both colorants. Alternatively
as a greater variety of different colorants can be used in the
present process the specific colorant(s) chosen can be selected to
optimise more exactly the properties of a toner for a specific
use.
[0082] Preferably toners comprise suitable colorants, such as
pigments, for example if the toner is black (for producing black
and white images) a suitable colorant may comprise carbon back.
Coloured toners (e.g. for use in colour copies and colour laser
printers) may comprise a trichromatic set of toners, each toner in
the trichromatic toner set preferably comprising a toner resin and
respectively a cyan colorant, a magenta colorant and a yellow
colorant. Conventional colorants for colour toners are described,
for example, in U.S. Pat. No. 5,102,764; U.S. Pat. No. 5,032,483
and EP 0,159,166. Other suitable colorants for use in toner
compositions may be selected from one or more of the following and
any suitable mixtures thereof: ferrite, magnetite, metallised
phthalocyanines (e.g. copper or nickel phthalocyanines, also known
as Pc, which are blue), quinacridone, perylene, benzidine,
nigrosine, aniline, quinoline, anthraquinone, azo disperse dye
(e.g. azo pyridones, also known as AP, which are yellow),
benzodifuranones (also known as BDF, e.g. those which are red),
metallised lake pigments;. water insoluble or soluble basic dyes
(especially the water soluble triphenylmethane dyestuff);
xanthenes; monoazo and/or diazo pigments; diarylides;
benzimidazolones; isolindolines; isoindolinones; and any mixtures
thereof. The toner composition may contain up to 20% colorant,
preferably from about 0.1% to about 10%, more preferably from about
0.5% to about 10% and most preferably from about 1% to about 8% by
weight of the toner composition.
[0083] Colorants for use in toner compositions generally have good
heat and light fastness together with low bleed characteristics in
the substrate to which they are applied. Preferably the colorant is
tinctorially strong, easy to use and is available in a wide variety
of derivatives to expand the shade gamut. More preferably the
colorant is stable in the processing conditions encountered on
formulation, exhibits good stability and fastness when applied to a
substrate and has a disposition in colour space which provides a
wide and useful gamut of shades from a small number of colorants.
Generally the colorant comprises a pigment, however the colorant
may also comprise a dye, preferably disperse dyestuffs or
solvent-soluble dyestuffs.
[0084] The colorant may comprise a magnetic additive (e.g. ferrite
and/or magnetite) optionally mixed with a coloured pigment, in
which case the colorant is preferably present from 5% to 70% and
more preferably from 10% to 50% by weight of the toner composition.
Mixtures of carbon black and magnetite are available commercially
and those containing from about 1% to 15% are preferred, especially
those containing from 2% to 6% carbon black based on the weight of
carbon black and magnetite.
[0085] Toners comprising a magnetic additive may be useful to print
items for use in methods such as magnetic ink character recognition
(MICR). MICR is used to machine process large volumes of printed
data (e.g. cheques). Chemically produced toners of the present
invention which also magnetic are particularly useful in MICR as
the controlled particle size leads to sharper printed images and
less tendency for the machine to detect incorrectly or fail to read
the original image. Thus MICR toners of the present invention
reduce the error rate in high volume applications. For certain
applications (e.g. cheques) security may also be an issue. The
magnetic properties of an item printed using a magnetic toner are
not readily detectable to the user. Thus a person who attempts to
make an illicit copy will use a conventional (non-magnetic) toner
and the magnetic properties of original will not be readily
reproduced by conventional copying methods. Therefore MICR can also
be used to distinguish between originals and illicit copies.
[0086] Coloured toners are of use in colour electroreprography for
producing colour images on sheet or film material, especially paper
and transparencies (e.g. those made from plastics materials such as
polyester and acetate for example for use as overhead
transparencies). Particularly useful colour toners are those which
exhibit bright and intense colours and produce images with good
fastness properties, these are especially useful for laser printing
on paper.
[0087] It can been seen that it is desirable for toner compositions
to comprise particles which can possess readily an electrostatic
charge (tribocharge) so they can be attracted to the latent image
on the drum to develop the latent image. Toners which readily
tribocharge may also have the further advantage of facilitating
rapid and more complete removal of any residual toner from the
image drum (e.g. by electrostatic repulsion). This may improve
image quality (by reducing ghost images from previous copies) and
may reduce the cycle time between copies and thus increase the
speed of copying.
[0088] It has been found that the addition of certain charge
control agents (hereinafter known as CCAs) to toner compositions
helps the production and stability of tribocharge within the toner.
Use of CCAs may also lead to improved image quality when the latent
image is transferred to the paper. The mechanism for the action of
CCAs is unclear, but the industry continues to seek compounds with
improved abilities as CCAs. Properties desired in ideal CCAs; toner
compositions to which they are added; and/or the hard copies they
produce are well known to those skilled in the art. Such properties
might comprise any or all of the following: ability to stabilise
larger tribocharge; improved tribocharge distribution and/or
uniformity of charge within an individual toner particle and/or
across the population of toner particles within a toner
composition; reduced cost, reduced toxicity or non-toxicity,
greater stability under conditions of use, good compatibility with
the binder resin in a toner, improved image resolution, greater
speed of image production, reduction in print bleed in the hard
copy and/or improved colorant properties.
[0089] CCAs may be coloured or substantially colourless. Coloured
CCAs have utility as the colorant in the toner for example as dyes
or pigments depending on the substrate in which they are used.
Colourless CCAs have particular utility in non-black coloured
toners (such as for colours which have weak shades) where adding
colourless CCAs would not substantially alter the colour of the
toner to which they are added.
[0090] A CCA may be capable of stabilising a positive electrostatic
charge (positive charging) and/or negative electrostatic charge
(negative charging). Preferred positive charging CCAs comprise
amine derivatives, more preferably alkoxylated amines and/or
quaternary ammonium compounds, such as cetyl pyridinium chloride or
bromide. Preferred negative charging CCAs comprise metal complexes
or salts, preferably comprising an aryl moiety, for example a bis
azo aryl moiety, more preferably a 2:1 metal complex or salt of a
hydroxynaphthoic acid and/or napthenic acid. Complexes of Zn or Cr
may also be effective colourless negative charging CCAs (e.g. di
tert-butyl salicylate complexes). CCAs may also comprise suitable
electron donating dyes (e.g. nigrosine).
[0091] The substituents on a CCA may be selected to improve the
compatibility of the CCA with the toner resins with which they are
formulated. Thus, the size and length of the substituents may be
selected to optimise the physical entanglement or interlocation
with the resin or they may contain reactive entities capable of
chemically reacting with the resin.
[0092] The amount of CCA in the toner is preferably at least about
0.1%, more preferably at least about 0.5% and most preferably at
least about 1% by weight of the toner. The amount of CCA in the
toner is desirably up to about 12%, preferably up to about 10% more
preferably up to about 5% and especially up to about 3% by weight
of the toner. Preferably toners comprise suitable agents to control
particle flow such as one or more of the following: alumina,
silica, benzoguanine-formaldehyde resin, hydroxyapatite,
fluroresin, acrylic polymer beads, titania and/or any suitable
mixtures thereof.
[0093] It will be understood that one or more of ingredient(s)
listed herein may be added to the toner compositions of the present
invention to serve more than one function. For example magnetite
may act as both colorant and magnetic material.
[0094] The invention is now further illustrated by the following
non-limiting example in which all references to amounts (such as
w/w) are to percentages by mass of ingredient to the total mass of
the composition to which they are added unless indicated to the
contrary.
EXAMPLE 1
[0095] (a) Aqueous pigment dispersion
[0096] A dispersion of Heliogen Blue L7080 (Pigment Blue 15:3,
BASF) in water (27.3% solids) was made in a similar manner to the
dispersion made in Example 1a) above, using an Eiger bead mill, and
the dispersants Akypo RLM100 (10% w/w on the pigment, available
commercially from Kao Corporation) and Solsperse 27000 (10% w/w on
the pigment).
[0097] (b) Latex
[0098] An hydroxy functional polymer latex was made by emulsion
polymerisation, the polymer being made from styrene (82.5%),
acrylic ester monomers (15.2%) and 2-hydroxyethyl methacrylate
(2.5%). Ammonium persulphate (0.5% w/w of monomers) was used as the
initiator and a mixture of thiol chain transfer agents (2.5%) used.
The surfactant used in the polymerisation was Akypo RLM100 (3% w/w
of monomers). The latex had a solids level of 40%. The Tg of the
polymer was 61.degree. C., and a GPC analysis against polystyrene
standards determined its Mn as 7,500 and Mw as 23,700
[0099] (c1) Mixing the dispersions
[0100] The latex (677 g), the pigment dispersion (52.2 g) and water
(1050 g) were mixed in a stirred tank and heated to 57.degree. C.
The stirring speed was 550 rpm. The mixture was then pumped using a
peristaltic pump from the tank through a flow cell equipped with an
Ultra Turrax T50 high shear mixer operating at 10,000 rpm, and back
into the stirred tank.
[0101] (c2) Inducing association
[0102] During the circulation a 2% solution of sulphuric acid (120
g) was added over 12 minutes close to the high shear head. The
final pH of the associated mixture was 2.1. After 3 minutes further
circulation the high shear mixing was stopped and the associated
material present in the flow cell pumped back into the stirred
tank.
[0103] (c3) Cluster growth
[0104] The temperature of the mixture in the tank from step (c2)
was raised to 66.degree. C. and the mixture stirred for one hour.
The pH was then adjusted to 7.9 with the addition of a 1% solution
of sodium hydroxide in water, and the mixture stirred for a further
5 minutes.
[0105] (d) Fusion
[0106] The temperature of the mixture from (c3) was raised to
92.degree. C. and maintained there for two hours, before cooling to
room temperature. Sodium dodecylbenzenesulphonate (2% w/w of toner,
added as a 10% solution in water) was then added to a small sample.
The mixture was heated at 110.degree. C. for 2 hours under pressure
and the sample was subjected to continuous agitation. The resulting
blue toner particles had a smooth but non-spherical appearance.
Analysis with the Coulter Counter showed a mean volume particle
size of 7.2 .mu.m, with a GSD of 1.34. A separate sample was mixed
with 2% sodium dodecylbenzenesulphonate as above and fused at
120.degree. C. under pressure for 30 minutes. The resulting toner
was spherical in shape. Analysis with the Coulter Counter showed a
mean volume particle size of 7.0 .mu.m, with a GSD of 1.30.
EXAMPLE 2
[0107] (a) Aqueous pigment dispersion
[0108] A dispersion of Monolite Rubine 3B (Pigment Red 122, Zeneca)
in water (24.6% solids) was made in a similar manner to Example 1a)
above, using an Eiger bead mill, and the dispersants Akypo RLM100
(10% w/w of pigment) and Solsperse 27000 (10% w/w/ of pigment).
[0109] (b) Latex
[0110] The latex was the same as that used in Example 1
[0111] (c1) Mixing the dispersions
[0112] The latex (451 g), the pigment dispersion (38.6 g) and water
(1310 g) were mixed in a stirred tank and heated to 66.degree. C.
The stirring speed was 510 rpm. The mixture was then pumped using a
peristaltic pump from the tank through a flow cell equipped with an
Ultra Turrax T50 high shear mixer operating at 10,000 rpm, and back
into the stirred tank.
[0113] (c2) Inducing association
[0114] During the circulation a 2% solution of sulphuric acid (85
g) was added over 10 minutes into the stirred tank. The final pH of
the associated mixture was 2.1. The high shear mixing was stopped
and the associated material present in the flow cell pumped back
into the stirred tank.
[0115] (c3) Cluster growth
[0116] The mixture was stirred at 66.degree. C. for one hour, and
the pH was then adjusted to 7.7 with the addition of a 1% solution
of sodium hydroxide in water.
[0117] (d) Fusion
[0118] The temperature of the mixture from (c3) was raised to
92.degree. C. and maintained there for two hours, before cooling to
room temperature. To a small sample was then added sodium
dodecylbenzenesulphonate (2% w/w of toner, added as a 10% solution
in water) The mixture was heated at 120.degree. C. for 30 minutes
under pressure and the sample was subjected to continuous
agitation. The resulting magenta toner particles had a smooth but
non-spherical appearance. Analysis with the Coulter Counter showed
a mean volume particle size of 8.6 .mu.m, with a GSD of 1.22.
EXAMPLE 3
[0119] (a) Aqueous pigment dispersion
[0120] A dispersion of Pigment Yellow 3G (the pigment Yellow 17
available commercially from Tennants) in water (25.7% solids) was
made in a similar manner to Example (1a) above, using an Eiger bead
mill, and the dispersants Akypo RLM100 (10% w/w of pigment) and
Solsperse 27000 (10% w/w of pigment).
[0121] (b) Latex
[0122] The latex was the same as that used in Examples 1 and 2.
[0123] (c1) Mixing the dispersions
[0124] The latex (890 g), the pigment dispersion (73 g) and water
(1386 g) were mixed in a stirred tank and heated to 66.degree.
C.
[0125] (c2) Inducing association
[0126] The mixture was then pumped using a peristaltic pump from
the tank through a flow cell equipped with an Ultra Turrax T50 high
shear mixer operating at 10,000 rpm, and into a separate stirred
tank. Simultaneously with this a 2% solution of sulphuric acid (150
g) was injected over 3.5 minutes into the flow cell, close to the
high shear head, to mix with the latex and pigment mixture.
[0127] (c3) Cluster growth
[0128] The associated mixture was then stirred at 66.degree. C. for
one hour and then sodium dodecylbenzenesulphonate (5% w/w of the
toner, added as a 10% solution in water) was added.
[0129] (d) Fusion
[0130] The temperature was then raised to approximately 100.degree.
C. and maintained at this temperature for 6 hours, before cooling
to room temperature. The resulting yellow toner particles had a
smooth but non-spherical appearance. Analysis with the Coulter
Counter showed a mean volume particle size of 6.4 .mu.m, with a GSD
of 1.25.
EXAMPLE 4
[0131] (a) Aqueous pigment dispersion
[0132] A dispersion of Heliogen Blue L7080 (Pigment Blue 15:3 from
BASF) in water (24.2% solids) was made in a similar manner to the
above, using an Eiger bead mill, and the dispersants Akypo RLM100
(10% w/w of pigment) and Solsperse 27000 (10% w/w of pigment).
[0133] (b) Latex
[0134] The latex was the same as that used in Examples 1, 2 and
3.
[0135] (c1) Mixing the dispersions
[0136] The latex (891 g), the pigment dispersion (77.5 g) and water
(1382 g) were mixed in a stirred tank and heated to 62.degree.
C.
[0137] (c2) Inducing association
[0138] The mixture was then pumped using a peristaltic pump from
the tank through a flow cell equipped with an Ultra Turrax T50 high
shear mixer operating at 10,000 rpm, and into a separate stirred
tank. Simultaneously with this a 2% solution of sulphuric acid (150
g) was injected over 3.5 minutes into the flow cell, close to the
high shear head, to mix with the latex and pigment mixture.
[0139] (c3) Cluster growth
[0140] The associated mixture was stirred at 550 rpm and the
temperature raised to 68.degree. C. After one hour the pH was
raised to 9 with the addition of sodium hydroxide solution.
[0141] (d) Fusion
[0142] The temperature of the mixture from step (c3) was raised to
100.degree. C. and stirred for 4 hours. The dispersion was then
cooled and transferred to a stirred pressure vessel and the
temperature raised to 120.degree. C. The dispersion was stirred at
this temperature for one hour, before cooling to room temperature.
After 30 minutes the resulting blue toner particles had a smooth,
but irregular appearance. Analysis with the Coulter Counter showed
a mean volume particle size of 7.4 .mu.m, with a GSD of 1.25. After
one hour the toner particles were nearly spherical, with a mean
volume particle size of 7.4 .mu.m and a GSD of 1.26.
* * * * *