U.S. patent application number 10/772070 was filed with the patent office on 2004-08-19 for method and apparatus for manufacturing developer, and developer.
This patent application is currently assigned to Sharp Kabushiki Kaisha. Invention is credited to Kikawa, Keiichi, Nakano, Shinichi, Shibai, Yasuhiro.
Application Number | 20040161686 10/772070 |
Document ID | / |
Family ID | 32844204 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040161686 |
Kind Code |
A1 |
Nakano, Shinichi ; et
al. |
August 19, 2004 |
Method and apparatus for manufacturing developer, and developer
Abstract
The invention provides a method and an apparatus for
manufacturing a developer, which can manufacture a developer having
a uniform and fine particle shape in a narrow particle size
distribution and having a coloring agent highly dispersed therein
at the primary particle level, the method and apparatus at the same
time enabling continuous and efficient production without opening
and closing a reactor. The method comprises the steps of:
dissolving a binding resin component in a supercritical or
subcritical fluid so that the binding resin component is blended
with a coloring agent component; and reducing the solubility of the
binding resin component in the supercritical or subcritical fluid
so that the binding resin component is precipitated in the form of
particles with the coloring agent component dispersed in the
interior thereof. In the aforementioned method and apparatus, the
reactor provided with at least a stirring mechanism and a mechanism
for discharging dissolved components has a developer material
carrier comprising a mesh that prevents the passage of treated
materials and allows the passage of the supercritical or
subcritical fluid.
Inventors: |
Nakano, Shinichi; (Nara,
JP) ; Shibai, Yasuhiro; (Nara, JP) ; Kikawa,
Keiichi; (Osaka, JP) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Assignee: |
Sharp Kabushiki Kaisha
|
Family ID: |
32844204 |
Appl. No.: |
10/772070 |
Filed: |
February 3, 2004 |
Current U.S.
Class: |
430/105 ;
430/137.1 |
Current CPC
Class: |
G03G 9/0804
20130101 |
Class at
Publication: |
430/105 ;
430/137.1 |
International
Class: |
G03G 009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2003 |
JP |
2003-28528 |
Claims
What is claimed is:
1. A developer manufacturing method, comprising the steps of:
dissolving a binding resin component in a supercritical or
subcritical fluid so that the binding resin component is blended
with a coloring agent component; and reducing the solubility of the
binding resin component in the supercritical or subcritical fluid
so that the binding resin component is precipitated in the form of
particles with the coloring agent component dispersed in the
interior of the binding resin component, wherein a reactor provided
with at least a stirring mechanism and a mechanism for discharging
the dissolved components has a developer material carrier
comprising a mesh that prevents the passage of treated materials
and allows the passage of the supercritical or subcritical
fluid.
2. A developer manufacturing apparatus comprising at least a
rector, a jet mechanism and a mechanism-connecting therebetween,
wherein a developer is manufactured by the steps of: dissolving a
binding resin component in a supercritical or subcritical fluid so
that the binding resin component is blended with a coloring agent
component; and reducing the solubility of the binding resin
component in the supercritical or subcritical fluid so that the
binding resin component is precipitated in the form of particles
with the coloring agent component dispersed in the interior of the
binding resin component, wherein the reactor provided with at least
a stirring mechanism and a mechanism for discharging the dissolved
components has a developer material carrier comprising a mesh that
prevents the passage of treated materials and allows the passage of
the supercritical or subcritical fluid.
3. The developer manufacturing apparatus according to claim 2,
wherein the developer material carrier comprises a plurality of
meshes.
4. The developer manufacturing apparatus according to claim 2,
wherein the developer material carrier has a stirring mechanism
incorporated therein.
5. The developer manufacturing apparatus according to claim 2,
wherein the developer material carrier rotates together with the
stirring mechanism.
6. The developer manufacturing apparatus according to claim 2,
wherein the developer material carrier rotates in reverse relative
to the rotation direction of the stirring mechanism.
7. The developer manufacturing apparatus according to claim 2,
wherein the developer material carrier also functions as a stirring
mechanism.
8. A developer manufactured by the method of claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a developer for developing
an electrostatic latent image formed on an image carrier by an
electrophotographic process or an ion-flow method, a manufacturing
method thereof, and a manufacturing apparatus thereof.
BACKGROUND OF THE INVENTION
[0002] Image forming apparatuses such as a laser printer, LED
(light emitting diode) printer, or a digital photocopying machine,
employ an electrophotographic method. These apparatuses electrify
the entire surface of a photoreceptor and create a desired
electrostatic latent image by irradiating the surface with light in
accordance with image information by use of a laser beam, LED or
the like. The electrostatic latent image is visualized with a
developer by a developing section to form a visible image, and the
visible image is fixed onto a recording medium, thereby obtaining
an image.
[0003] Recently, there has been an increasing demand for
size-reduced image forming apparatuses. In an image forming
apparatus employing the electrophotographic method, the developer
storage section is a significant part of the image forming
apparatus in terms of achieving size reduction because the space
occupied by the developer storage section is large. In particular,
in the recent networked environment, a single image forming
apparatus is used by a number of people for a great number of
printouts. Therefore, for users' convenience, a large quantity of
developer must be stored in the image forming apparatus.
[0004] Recently, there has also been an increasing demand for color
image output. Since a color image forming apparatus uses developers
of three or four colors, the space occupied by the developers in
the image forming apparatus becomes much larger. Further, when
color reproduction for color images is carried out by multi-color
overlapping, the amount of developer used on a recording medium
(e.g., paper and an OHP sheet) becomes large. For thermally fixing
such large amounts of developer, larger amounts of heat are
necessary compared with the case of monochrome images, thus
requiring a large fixing section.
[0005] In addition, there is a demand for a method for
manufacturing a developer that saves more energy and is more
environment-friendly. Developer manufacturing methods that are
currently available and mainly used include a conventional method
involving melting, kneading, and grinding processes, and recently
introduced polymerization methods (e.g., suspension method,
emulsion method, and dispersion method) in a liquid solvent.
[0006] For example, a developer used for a dry developing method
contains a thermoplastic resin (binding resin), a pigment (coloring
agent) and a mold release agent as main components. In addition,
magnetic powder, a charge control agent, a flow improver or the
like may be added, if necessary, for the production of the
developer. Then, a method for manufacturing such developer is
generally adopted wherein all the raw materials are mixed at one
time, and heated, melted and dispersed by a kneading machine, etc.
to obtain homogeneous composition. Then the obtained composition is
cooled, crushed, and classified to obtain a developer having a
volume average particle diameter of approximately 10 .mu.m.
[0007] In particular, a color developer for electrophotography used
for the formation of color images is generally manufactured by
dispersing various chromatic color pigments in a binding resin. For
such cases, performances required for the developer that is used
are higher than those in the case of obtaining black images. In
other words, as a developer, proper color development (color
degree) or optical transparency (transparency), when the developer
is used for a sheet for an overhead projector (OHP), is required,
in addition to mechanical and electronic stability with respect to
extrinsic factors such as mechanical shocks or humidity.
[0008] A developer that contains a pigment as a coloring agent is
exemplified by JP Patent Publication (Kokai) No. 49-46951 A (1974)
stated below. However, a pigment-containing color developer
exhibits poor pigment dispersibility in a binding resin, resulting
in inferior color degree (color development) and transparency,
although it has excellent light resistance.
[0009] As methods for improving the dispersibility of a pigment in
a binding resin, the following technologies are proposed.
[0010] (1) A technology for obtaining a color developer by using a
polyester resin (resin A) as a binding resin, coating a pigment in
advance with a polyester resin (resin B) with a molecular weight
higher than resin A, and dispersing the coated pigment in resin A
(JP Patent Publication (Kokai) No. 62-280755 A (1987)).
[0011] (2) A color developer characterized in that a processed
pigment obtained by melting and kneading a pigment and a resin for
the pigment is dispersed and contained in a binding resin, the
resin for pigment has a smaller weight average molecular weight
than the binding resin, and the binding resin has a weight average
molecular weight of 100,000 or more (JP Patent Publication (Kokai)
No. 2-66561 A (1990)).
[0012] (3) A technology for obtaining a color developer by the
following steps. In a first step, a mixture of a binding resin and
a pigment is kneaded with an organic solvent at a temperature lower
than the melting point of the binding resin. In a second step, the
binding resin and a charge control agent are further added, and
melted and kneaded by heat (JP Patent Publication (Kokai) No.
9-101632 A (1997)).
[0013] (4) A pigment used for a developer has a low molecular
weight material absorbed therein, the low molecular weight material
having a lower melting point and a lower melt viscosity than a
binding resin as a principal constituent component of the
developer. The oil absorption of the low molecular weight material
is 50 g or more (per 100 g of pigment) and the oil absorption ratio
of the low molecular weight material to the pigment is 100% to 300%
of the saturation oil absorption. The melt viscosity of the low
molecular weight material is 0.1 Pa.cndot.s or less at 20.degree.
C. (the melting point of the low molecular weight material). In
addition, a pretreatment method of developer pigment, a developer
and a manufacturing method of the developer are also proposed in JP
Patent Publication (Kokai) No. 2000-81736 A.
[0014] However, none of the methods disclosed in these patent
documents can provide sufficient pigment dispersion, thus currently
resulting in inferior color degree and transparency. Further, in
the case of a black developer for monochrome images, carbon is
commonly used as a black coloring agent in an amount of 7 to 15
parts by weight. For manufacturing such black developer, a method
is commonly used wherein carbon powder is mixed with other raw
materials before kneading and then the mixture is melted and
kneaded. Unlike a color developer, transparency is not required for
a black developer, and therefore the amount of carbon is increased
to enhance color degree. However, the increase of conductive carbon
is not preferable in terms of the stability of electrical charge
because it reduces the volume resistivity of the developer. It is
thus necessary that the carbon should be thoroughly dispersed to
increase the volume resistivity of a developer.
[0015] A two-step kneading method for the above color developer has
not been adopted as a method for improving carbon dispersion due to
its high cost, and in general (5) a method for reducing the
treatment capacity in the kneading step is adopted. In addition,
(6) a method for lowering resin temperature in the kneading step or
(7) a method in which a rolling and cooling method is prescribed
after kneading is proposed. However, the treatment capacity
according to methods (5) to (7) is small, resulting in increased
costs.
[0016] JP Patent Publication (Kokai) No. 8-141306 A (1996)
discloses a technique regarding a method and a device for
extraction of a fluid flowing in a radial direction whereby a
predetermined material is extracted from a solid material (e.g.,
naturally occurring material and ceramics) using a supercritical
fluid or a liquid. However, the technique disclosed therein is
insufficient for reducing extraction period, and further, it is
expensive since the treatment capacity is small.
SUMMARY OF THE INVENTION
[0017] In view of the above circumstances, the present invention
has an object to provide a fluid extraction method and an apparatus
therefor, which enable easy operations for inserting and removing
treated materials and reduce dead space and increase treatment
capacity.
[0018] As a result of intensive researches, the present inventors
have found that the above object can be achieved by providing a
specific developer material carrier in a reactor used in the method
and apparatus for manufacturing a developer using a supercritical
fluid or a subcritical fluid.
[0019] According to a first aspect of the present invention, a
method for manufacturing a developer is provided. The method
comprises the steps of: dissolving a binding resin component in a
supercritical or subcritical fluid so that the binding resin
component is blended with a coloring agent component, and reducing
the solubility of the binding resin component in the supercritical
or subcritical fluid so that the binding resin component is
precipitated in the form of particles with the coloring agent
component dispersed in the interior of the binding resin component.
In the method, the reactor provided with at least a stirring
mechanism and a mechanism for discharging dissolved components has
a developer material carrier comprising a mesh that allows the
passage of the supercritical or subcritical fluid and prevents the
passage of the treated materials.
[0020] The main technology of the present invention involves at
least a method for manufacturing a developer by: dissolving a
binding resin component in a supercritical or subcritical fluid so
that the binding resin component is blended with a coloring agent
component; and reducing the solubility of the binding resin
component so as to precipitate the binding resin component in the
form of particles, so that a developer in which the coloring agent
component is dispersed in the binding resin component precipitated
in the form of particles is manufactured. When a developer is
manufactured by dissolving a binding resin component in a
supercritical or subcritical fluid and blending it with a coloring
agent component without appropriate supply of developer materials,
reducing the solubility of the binding resin component in the
supercritical or subcritical fluid, and precipitating the binding
resin component in the form of particles while the coloring agent
component is dispersed in the binding resin component, a developer
with a nonuniform composition may be produced. Namely, there is a
case wherein some developers have excessive amounts of resin
component but others have small amounts thereof. Therefore, uniform
input amounts of the developer components are required.
[0021] In contrast, the present invention produces the following
actions and effects. Namely, a developer material carrier is
provided in a reactor having at least a stirring mechanism and a
mechanism for discharging dissolved components. The developer
material carrier comprises a filter that prevents the passage of
treated materials and allows the passage of the supercritical or
subcritical fluid, and thereby insoluble components are captured.
This enables only the dissolved components to be dispersed in the
supercritical or subcritical fluid in the reactor, thereby
preventing the generation of coarse particles and enabling the
generation of particles having a desired shape.
[0022] According to a second aspect of the present invention, there
is provided an apparatus for manufacturing a developer comprising
at least a reactor, a jet mechanism and a mechanism for connecting
therebetween. The developer is manufactured by the apparatus
through the steps of dissolving a binding resin component in a
supercritical or subcritical fluid so that the binding resin
component is blended with a coloring agent component, and reducing
the solubility of the binding resin component in the supercritical
or subcritical fluid so that the binding resin component is
precipitated in the form of particles while the coloring agent
component is dispersed in the interior of the binding resin
component. In the apparatus, the reactor provided with at least a
stirring mechanism and a mechanism for discharging dissolved
components has a developer material carrier comprising a mesh that
prevents the passage of treated materials and allows the passage of
the supercritical or subcritical fluid.
[0023] The developer material carrier preferably comprises a
plurality of meshes. Since the carrier comprises meshes, elution is
more uniformly carried out, thereby enabling the obtainment of a
developer having a desired particle diameter.
[0024] The developer material carrier preferably has a structure
with a stirring mechanism incorporated thereinto. When the
developer material carrier has such structure, the solubility speed
of the developer material in the supercritical fluid or the
subcritical fluid is increased, resulting in improved production
efficiency.
[0025] The developer material carrier preferably rotates together
with the stirring mechanism. The rotation of the developer material
carrier together with the stirring mechanism activates the
convection of the supercritical or subcritical fluid to improve the
solubility speed of the developer material in the supercritical or
subcritical fluid, and to prevent the passage of coarse
particles.
[0026] The developer material carrier preferably rotates in reverse
relative to the rotation direction of the stirring mechanism. The
reverse rotation of the developer material carrier relative to the
rotation direction of the stirring mechanism increases the
frequency of contact between the supercritical fluid and the
developer material, thereby enabling the increase of the solubility
speed.
[0027] The developer material carrier preferably also functions as
a stirring mechanism. When the developer material carrier also
works as the stirring mechanism, the number of parts in the reactor
is reduced, so that influences such as contaminations can be
prevented.
[0028] According to a third aspect of the present invention, there
is provided a developer for electrostatic development that is
manufactured by the above manufacturing method or apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a diagram showing an apparatus used for
manufacturing a developer according to the present invention.
[0030] FIGS. 2A and 2B are internal diagrams of a high pressure
cell of the developer manufacturing apparatus according to the
present invention.
[0031] FIG. 3 is a graph showing the comparison in particle
diameter distribution of developers produced according to the
present invention and according to a crushing method.
[0032] FIGS. 4A and 4B are schematic views showing the results of
observation by a TEM (transmission electron microscope) of
developers described in Example 3 of the present invention. FIG. 4A
shows the results when the developer was manufactured by a crushing
method. FIG. 4B shows the results when the developer was
manufactured by a supercritical method.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0033] The method of the present invention involves the steps of
dissolving a binding resin component in a supercritical fluid or a
subcritical fluid so that the binding resin component is blended
with a coloring agent component, and lowering the solubility of the
binding resin component in the supercritical or subcritical fluid
so that the binding resin component is precipitated in particle
form while the coloring agent component is dispersed in the
interior of the binding resin component.
[0034] A substance will be in a fluid form with equal densities in
gaseous and liquid phases when the temperature and the pressure of
the substance are set to certain conditions (the supercritical
point or higher). A fluid at a temperature and a pressure above the
vicinity of the critical point is referred to as a supercritical
fluid. Moreover, a substance will have a state close to that of a
supercritical fluid when the conditions are below but close to
those of a supercritical point. The substance in such fluid form is
referred to as a subcritical fluid.
[0035] Supercritical or subcritical fluids (hereinafter, the term
"supercritical fluid" includes a subcritical fluid unless otherwise
specified) show the properties of both gases and liquids. For
example, a supercritical fluid is made to have a density close to
that of a liquid (100 times greater than that of a gas), a
viscosity similar to that of a gas (about 10 to 100 times smaller
than that of a liquid), a diffusion coefficient about 10 to 100
times smaller than that of a liquid, and a heat conductivity
coefficient close to that of a liquid (about 100 times greater than
that of a gas).
[0036] A supercritical fluid generally has a great dissolving power
and properties such that the dissolving power largely varies in
accordance with changes in temperature and pressure. The properties
of a supercritical fluid make it excellent as a reaction solvent or
an extraction solvent. In recent years, application of a
supercritical fluid has been thus actively studied in the fields of
separation, extraction, purification, and the like of substances,
such as caffeine extraction from coffee and separation and
extraction of wastes.
[0037] Further, a desired substance is dissolved in a supercritical
fluid, and the solubility of the substance in the supercritical
fluid is significantly decreased by rapid expansion of
supercritical solution (RESS method) or by addition of a poor
solvent or a surfactant, thereby precipitating the dissolved
substance. By taking advantage of this feature, particulate
production, for example, is carried out.
[0038] Methods for producing particulates by using a supercritical
fluid are disclosed in, for example, JP Patent Publication (Kokai)
No. 10-13341 A (1998). These are methods for producing particulates
used for coating a developer, but the document includes no
description of a production method of the developer itself.
[0039] The present inventors focused attention on the
aforementioned properties concerning supercritical fluid, and
attempted various applications of these properties for producing a
developer. As discussed previously, it is important to enhance
coloring power of a developer in order to achieve the
miniaturization of an electrophotographic image forming apparatus
using the developer. For this case, the dispersibility of the
coloring agent component must be improved for increasing the amount
of the coloring agent component in the developer.
[0040] In a process employing a developer material supply system
after pressure reduction, features of the supercritical or
subcritical fluid, that is, a great dissolving power and a large
diffusion coefficient, are exhibited by blending a coloring agent
component and a binding resin component of the developer in the
supercritical fluid in a reactor. These features allow the
dissolved substance (the coloring agent component) or the mixed-in
substance (particulates of the coloring agent component) to be
uniformly dispersed while preventing agglomeration. This produces a
good dispersion of the coloring agent component in the
supercritical fluid.
[0041] Subsequently, the dissolved solute components are
precipitated, for example, by depressurizing the supercritical
fluid in the reactor. At this time, when the solubility of the
solutes in the supercritical fluid is rapidly reduced by RESS
method or the like, the dissolved binding resin component is
precipitated in the form of particulate. Since pigment is well
dispersed in the supercritical fluid at this stage, a developer in
the form of particulates can be obtained with the coloring agent
component uniformly dispersed in the particulates of the binding
resin component.
[0042] Examples of the substances that can be used as the
supercritical fluid include CO.sub.2, N.sub.2, CH.sub.4,
C.sub.2H.sub.6, CF.sub.3H, NH.sub.3, CF.sub.3Cl, CH.sub.3OH,
C.sub.2H.sub.5OH, and H.sub.2O.
[0043] The binding resin component is not particularly limited as
long as it is a resin used for a developer. However, examples
thereof include styrene resins, such as polystyrene,
styrene-butadiene copolymer and styrene-acrylic copolymer, ethylene
resins, such as polyethylene, polyethylene-vinyl acetate copolymer,
and polyethylene-vinyl alcohol copolymer, acrylate resins, such as
polymethyl methacrylate, phenolic resins, epoxy resins, allyl
phthalate resins, polyamide resins, polyester resins, and maleic
acid resins. The binding resin component preferably has a
weight-average molecular weight of 1.times.10.sup.3 to
1.times.10.sup.6.
[0044] The coloring agent component includes organic pigments and
inorganic pigments. Examples of these pigments include Carbon
Black, Aniline Blue, Chalco Oil Blue, Chrome Yellow, Ultramarine
Yellow, Methylene Blue, duPont Oil Red, Quinoline Yellow, Methylene
Blue Chloride, Phtharocyanin Blue, Rose Bengal, Disazo Yellow,
Carmin 6B, and Quinacridone. The particle diameter of the pigment
(primary particle) is from 40 nm to 400 nm, and is preferably 100
nm to 200 nm.
[0045] In addition to the binding resin component and coloring
agent component to be mixed in the supercritical fluid, a
supplement additive (an entrainer) may be added for enhancing the
affinity between the supercritical or subcritical fluid and the
solutes.
[0046] Examples of the supplement additives, though depending on
the combination of a supercritical fluid substance to be used and a
solute to be blended therewith, include: alcohols such as methanol,
ethanol, isopropanol, and butanol; ketones, such as methyl ethyl
ketone, acetone, and cyclohexanone; ethers such as diethyl ether
and tetrahydrofuran; hydrocarbons, such as toluene, benzene, and
cyclohexane; esters, such as ethyl acetate, butyl acetate, methyl
acetate, and alkyl carbonic ester; halogenated hydrocarbons, such
as chlorobenzene and dichloromethane; water; and ammonia. It should
be noted that water or ammonia can be used as supplement additives,
only when they are not used as the supercritical or subcritical
fluid.
[0047] Next, in a reactor having at least a stirring mechanism and
a mechanism for discharging dissolved components, a mechanism that
carries a developer material and allows only the dissolved
components to be dissolved and dispersed in the supercritical or
subcritical fluid in the reactor will be described.
[0048] An example for the above operation method and an apparatus
according to the present invention will be explained. As an
apparatus for manufacturing the developer of the present invention,
an apparatus having a configuration as shown in FIG. 1 is
exemplified. First, a gas is supplied to a reactor 7 from a gas
cylinder 1 filled with a substance to be used as a supercritical
fluid. Pressure is applied to the gas by a pressurizing pump 2 so
that the gas has a desired pressure. Further, the pressure of an
entrainer 3 (supplement additive) is increased to a desired level
by a pressurizing pump 4 in the same manner. The high-pressure gas
and the entrainer 3 are transferred to a reactor 7 via valves 5 and
6. During this process, the temperature of the high-pressure gas
may be adjusted to be close to a desired level by a preheating coil
or the like, which is not shown in the figure. Further, the
supercritical gas and the entrainer 3 may be blended together in
advance in another vessel (not shown) before being introduced into
the reactor 7.
[0049] A binding resin component and a coloring agent component as
developer materials are enclosed in the reactor 7. The reactor 7 is
provided with, for example, a heater 10 or a constant-temperature
water tank (not shown) to result in a desired temperature. Further,
the pressure in the reactor 7 is adjusted to a desired level by the
valves 5 and 6. The temperature and the pressure are monitored by a
thermometer 9 and a pressure gauge 11.
[0050] In this way, a supercritical fluid having a supercritical
state, the entrainer, the binding resin component, and the coloring
agent component are blended together in the reactor 7. Here, a
stirring device (e.g., a stirring device with impeller blades),
though not shown in the figure, may be used to stir the contents of
the reactor 7, if necessary.
[0051] A connecting mechanism from the reactor 7 to a nozzle 15 and
the nozzle 15 itself can adjust the temperature of the
high-pressure gas to close to a desired level by a preheating coil,
for example. Further, a thermometer is installed in the vicinity of
an outlet of the nozzle 15, thereby enabling the monitoring of the
temperature of the high-pressure gas.
[0052] While maintaining the above state, a pressure-reducing valve
12 shown in FIG. 1 is opened for rapidly expanding the
supercritical fluid in the reactor 7. This remarkably reduces the
solubility of each solute dissolved in the supercritical fluid. As
a result, each solute is precipitated in the form of
particulate.
[0053] In this process, the affinities between the coloring agent
component and binding resin component, and that between the
entrainer and the supercritical fluid are properly determined and
the pressure adjustment conditions for the reactor 7 are properly
determined. Developer particulates can thereby be obtained having a
state wherein the coloring agent component is almost uniformly
dispersed and embedded in the binding resin component precipitated
in the form of particulate. These developer particulates, having a
volume average particle diameter of 3 .mu.m to 7 .mu.m, are
colleted via the nozzle 15 in a particle collecting box 17.
[0054] Thereafter, for adjusting the fluidity of the obtained
developer, if necessary, a fine powder of silica, for example, may
be applied on the surface of the developer by publicly known
methods (e.g., use of a dry mixer), thereby manufacturing final
developers.
[0055] Hereinafter, the embodiment, and the actions and effects
obtained by the invention of each claim, will be explained.
[0056] (Claim 1)
[0057] According to conventional developer manufacturing methods,
insoluble materials of developer composition are discharged and
thereby an agglomeration is generated. Further, shear force is
applied in the precipitation process, so that fibrous products are
precipitated.
[0058] A method of the present invention is characterized in that a
reactor provided with at least a stirring mechanism and a mechanism
for discharging dissolved components has a developer material
carrier comprising a mesh that prevents the passage of treated
materials and allows the passage of a supercritical or subcritical
fluid. The method produces the following actions and effects: only
the dissolved components are dispersed in the supercritical or
subcritical fluid in the reactor because of capturing of the
insoluble components, so that the generation of coarse particles
can be prevented and particles having a desired particle shape can
be produced.
[0059] (Claim 2)
[0060] An apparatus of the present invention is characterized in
the same manner as claim 1 in that a reactor provided with at least
a stirring mechanism and a mechanism for discharging dissolved
components has a developer material carrier comprising a mesh that
prevents the passage of treated materials and allows the passage of
a supercritical or subcritical fluid. The apparatus produces the
following actions and effects: only the dissolved components are
dispersed in the supercritical or subcritical fluid in the reactor
because of capturing of the insoluble components, so that the
generation of coarse particles can be prevented and particles
having a desired particle shape can be produced.
[0061] (Claim 3)
[0062] A mechanism for storing developer materials cannot remove
insoluble components when materials having uneven particle sizes
are used, finally causing the generation of coarse particles.
However, according to the present invention, the developer material
carrier comprises a plurality of meshes, thereby producing the
following actions and effects: the use of the meshes enables more
uniform elution, so that a developer having a desired particle
diameter can be obtained.
[0063] (Claim 4)
[0064] It takes much time to dissolve developer materials in a
supercritical or subcritical fluid, thus posing an obstacle to the
enhancement of the production efficiency. However, the developer
material carrier of the present invention has a configuration such
that a stirring mechanism is incorporated thereinto. Such
configuration produces the following actions and effects: the
incorporation of the stirring mechanism in the developer material
carrier increases the solubility speed of the developer materials
in the supercritical or subcritical fluid, so that the production
efficiency can be improved.
[0065] (Claim 5)
[0066] It takes much time to dissolve a developer material in a
supercritical or subcritical fluid, thus posing an obstacle to the
enhancement of the production efficiency. According to the present
invention, the developer material carrier rotates together with the
stirring mechanism. Such configuration produces the following
actions and effects: the solubility speed of the developer material
in the supercritical or subcritical fluid is increased, so that the
production efficiency can be improved.
[0067] (Claim 6)
[0068] When the developer material carrier rotates in the same
direction as the stirring mechanism, the fluid flows in one
direction, so that sometimes little stirring effect can be
obtained. According to the present invention, the developer
material carrier rotates in reverse relative to the rotation
direction of the stirring mechanism. Such configuration produces
the following actions and effects: the reverse rotation increases
the frequency of contacts between the supercritical fluid and the
developer materials, so that the solubility speed can be
increased.
[0069] (Claim 7)
[0070] When a developer material carrier and a stirring mechanism
are separately provided, dead space is generated. Therefore, when
the stirring mechanism is washed, developer materials may remain as
contaminants in the mechanism. According to the present invention,
the developer material carrier is used as a stirring mechanism.
Such configuration produces the following actions and effects: the
developer material carrier has a combined function of the stirring
mechanism, and thereby the number of the parts in the reactor is
decreased, so that the influences such as contaminations can be
prevented.
EXAMPLES AND COMPARATIVE EXAMPLES
[0071] The present invention will hereinafter be described in
accordance with concrete examples and comparative examples.
However, it should be noted that the scope of the present invention
is not limited to these examples.
[0072] (Example for Manufacturing Developer)
[0073] A developer manufacturing apparatus as shown in FIG. 1 was
used for manufacturing a developer of the present invention. A
reactor 7 had a volumetric capacity of, for example, 1000 cm.sup.3,
and contained a developer material carrier 8 therein. In the
present example, the gas used as a supercritical fluid was carbon
dioxide. In addition, ethanol (commercially available as a common
reagent) was used as an entrainer.
[0074] 50 g of polyester resin (Sanyo Chemical Industries Co.,
Ltd.; Product Name: EP208) as a binding resin component and 20
parts by weight of carbon black (Mitsubishi Chemical Co., Ltd.,
Product Name: MA100) as a pigment based on 100 parts by weight of
the polyester resin were inputted in the reactor in advance. It
should be noted that the entrainer was incompatible with the
binding resin component at ordinary temperature and ordinary
pressure
[0075] The carbon dioxide gas supplied from a gas cylinder 1 was
pressurized by a pressure pump 2 and introduced into the reactor 7
via a valve 6. 200 ml of ethanol as the entrainer 3 was also
introduced into the reactor 7 via a pressure pump 4.
[0076] At this stage, a pressure-reducing valve 12 for discharging
remained closed, and the pressure inside the reactor 7 increased
through the introduction of pressurized carbon dioxide. Further,
heaters 10, 13, and 14 were used for adjusting the temperature in
the reactor 7, the temperature of a connecting mechanism, and the
temperatures of a jet mechanism and in the vicinity of an outlet
thereof.
[0077] When the reactor 7 has an internal pressure of 7.3 MPa or
more, the inside of the reactor 7 becomes supercritical. Carbon
dioxide has a critical temperature of 304.6 K, and thus carbon
dioxide becomes supercritical by setting the temperature to 304.6 K
or more.
[0078] After keeping this state for, for example, 20 minutes, the
pressure-reducing valve 12 was opened to discharge the mixed
solution in the reactor 7 from the nozzle 15 into a particle
collecting box 17. Rapid expansion was caused thereby, and
developer particulates that contained the pigment uniformly
dispersed in the binding resin component precipitated in a
generally spherical shape were deposited and collected in the
particle colleting box 17.
[0079] Here, the carbon dioxide as the supercritical fluid and the
ethanol as the entrainer contained in the mixed solution were
separated from each other by a recovery mechanism (not shown) for
recycling purposes.
[0080] In the present example, since the entrainer incompatible
with the binding resin component was used at ordinary temperature
and ordinary pressure, the agglomeration (that is, the bonding
between themselves) of the obtained developer particulates can be
prevented even if a trace amount of the entrainer adheres to the
surface of the developer particulates. Thus, developer particulates
can be obtained having a fine particle shape. Subsequently, 0.1
parts by weight of silica (Nihon Aerosil Co., Ltd.; Product Name:
R742) was added to cover the developer particulates by a well-known
method (e.g., by a dry mixer) for adjusting fluidity or the like,
and then final developers were obtained.
[0081] FIGS. 2A and 2B illustrate the inside of the reactor 7. FIG.
2A shows a reactor having stirrers 18 and FIG. 2B shows a reactor
having a developer material carrier 19 that incorporates stirrers
therein.
Example 1
[0082] A developer was manufactured in the same manner as the
manufacturing example except that the developer material carrier
was composed of one sheet of 400 mesh.
[0083] When the reactor 7 has an internal pressure of 7.3 MPa or
more, the reactor 7 has a supercritical state inside. In Example 1,
the internal pressure of the reactor 7 was set to 20 MPa by
adjusting valves 5 and 6 so that at least the binding resin
component in the reactor 7 was dissolved.
[0084] The thus-manufactured developer had a high content of
pigment and excellent pigment dispersibility, and therefore a
desired printing density could be obtained even with a small amount
of the developer. The amount of developer necessary for obtaining a
predetermined number of printouts was several times smaller than in
a case where a conventional developer (e.g., developer obtained by
a publicly known method involving melting, kneading, and grinding
processes) is used. Therefore, a user-friendly and miniaturized
image forming apparatus can be provided without shortening the
exchange cycle of developer.
[0085] In the case of a developer manufactured by a conventional
method (e.g., a publicly known method involving melting, kneading,
and grinding processes) so as to contain a high concentration of
pigment as in the present example, the formation of good images is
hindered as the image quality becomes deteriorated due to fog
generation or increased instability in the degree of developer
charge depending on the environment in which the developer is
used.
[0086] Moreover, according to conventional methods, developer
particles become crushed after long usage, and thus fine powders
are generated or the particle diameter distribution is changed,
causing problems such as deterioration in image quality. However,
the developer of the present invention can prevent the above
problems, thus stably enabling the formation of good images.
Example 2
[0087] A developer was manufactured in the same manner as the above
manufacturing example except that the developer material carrier 8
was composed of three sheets of 400 mesh.
Example 3
[0088] A developer was manufactured in the same manner as the above
manufacturing example except that the developer material carrier 8
had a configuration wherein stirrers 18 were incorporated
therein.
Example 4
[0089] A developer was manufactured in the same manner as the above
manufacturing example except that the developer material carrier 8
rotated together with stirrers 18.
Example 5
[0090] A developer was manufactured in the same manner as the above
manufacturing example except that the developer material carrier 8
rotated in reverse relative to the rotation direction of stirrers
18.
Example 6
[0091] A developer was manufactured in the same manner as the above
manufacturing example except that the developer material carrier 8
has a configuration 19 whereby it also functions as a stirring
mechanism.
[0092] [Recovery and Evaluation of Developers]
[0093] The recovery of each developer manufactured in the above
examples 1 to 6 was proportionally calculated relative to the
amount inputted into the reactor 7.
[0094] Ferrite carrier having an average diameter of 80 .mu.m was
mixed with 100 parts by mass of each developer prepared in Examples
1 to 6 so that a two-component developer with a developer
concentration of 4% was prepared. Using the obtained developer,
solid images with a dimension of 50 mm.times.50 mm were printed out
at the initial stage and after 10,000 copies were continuously made
with a printing density of 6% by an electrophotographic copier
(Model No. AR-450M manufactured by Sharp). Thereafter, the
densities of the image parts and the non-image parts thereof were
measured by a densitometer (Model No. RD-918, Macbeth Co.). In
addition, the developers were sampled from a developing device of
the electrophotographic copier at the initial stage and after
continuous printing of 10,000 copies, and the charge amount of each
sample was measured by a blow-off method. Here, charge stability is
defined as the existence of a small charge amount difference
between that at the initial stage and that resulting after
continuous printing of 10,000 copies.
[0095] Image density was evaluated based on three levels: excellent
(1.4 or more), good (less than 1.4 to 1.2), and poor (less than
1.2).
[0096] Further, fogging was evaluated based on three levels:
excellent (0.8 or less), good (1.2 to more than 0.8), and poor
(more than 1.2).
[0097] Moreover, charge stability was evaluated based on three
levels. When the charge after 10,000 copies is 80% to 100% of that
present at the initial stage, the charge stability is considered
"excellent." When the percentage is 60% to less than 80%, it is
considered "good." When the percentage is less than 60%, it is
considered "poor."
[0098] The relationships between developer manufacturing methods,
and the recovery and the image quality are summarized in Tables 1
and 2.
1TABLE 1 Relationship between developer manufacturing methods, and
recovery and image quality Image density Fogging After After
Recovery 10,000 10,000 Charge Total (%) Initial copies Initial
copies stability evaluation Example 1 42 Excellent Poor Excellent
Poor Excellent Good Example 2 20 Excellent Poor Excellent Good
Excellent Good
[0099]
2TABLE 2 Relationship between developer manufacturing methods, and
recovery and image quality Image density Fogging After After
Recovery 10,000 10,000 Charge Total (%) Initial copies Initial
copies stability evaluation Example 1 42 Excellent Poor Excellent
Poor Excellent Good Example 3 31 Excellent Good Excellent Good
Excellent Good Example 4 53 Excellent Good Excellent Excellent
Excellent Good Example 5 60 Excellent Excellent Excellent Good
Excellent Good Example 6 65 Excellent Excellent Excellent Excellent
Excellent Excellent
[0100] As shown in FIG. 1, when the elution of the insoluble
components is controlled, good results were obtained in terms of
image density, fogging, and charge stability. Further, as shown in
FIG. 2, excellent results were obtained in terms of image density,
fogging, and charge stability by efficiently eluting the dissolved
components.
[0101] The present invention can provide a developer having a
uniform and fine particle shape in a narrow particle size
distribution, in which a coloring agent in the developer is highly
dispersed at the primary particle level. At the same time, the
present invention provides a method and an apparatus for
manufacturing such developer, which enable continuous and efficient
production without opening and closing a reactor.
* * * * *