Title: Color image forming apparatus
Abstract: A multiple number of image forming stations are provided for multiple development colors including black. Each station having a photoreceptor. Each one of the photoreceptors has a charge transport layer including a binder resin that is a blend of at least two kinds of resins. The blended ration of at least two kinds of binder resins for the photoreceptor for black is made different from that of the binder resins for the photoreceptors for the other development colors. The photoreceptor for black presents a greater abrasion resistance than the photoreceptors for the other development colors. This structure makes it possible to use all the photoreceptors for back and colors, for and within, a concurrent period.
Patent Number: 7,010,245 Issued on 03/07/2006 to Shindoh, et al.
| Inventors:
|
Shindoh; Yuriko (Yamatokoriyama, JP);
Morita; Kazushige (Nara, JP);
Ishibashi; Hiroko (Ikoma, JP);
Shimoda; Yoshihide (Nara, JP);
Matsumoto; Masanori (Kashihara, JP)
|
| Assignee:
|
Sharp Kabushiki Kaisha (Osaka, JP)
|
| Appl. No.:
|
417162 |
| Filed:
|
April 17, 2003 |
Foreign Application Priority Data
| Apr 24, 2002[JP] | 2002-122637 |
| Current U.S. Class: |
399/159; 430/59.6; 430/46; 430/96 |
| Current Intern'l Class: |
G03G 15/01 (20060101) |
| Field of Search: |
430/596,96,46
399/159,179,299
|
References Cited [Referenced By]
U.S. Patent Documents
| 4030923 | Jun., 1977 | Krause et al.
| |
| 4840860 | Jun., 1989 | Staudenmayer et al.
| |
| 5122429 | Jun., 1992 | Sundararajan et al.
| |
| 5382489 | Jan., 1995 | Ojima et al.
| |
| 6146800 | Nov., 2000 | Yoshida et al.
| |
| 6461781 | Oct., 2002 | Srinivasan.
| |
| 2003/0206754 | Nov., 2003 | Morita et al.
| |
| Foreign Patent Documents |
| 10-333393 | Dec., 1998 | JP.
| |
| 11-24358 | Jan., 1999 | JP.
| |
| 11-52599 | Feb., 1999 | JP.
| |
| 2000/-242056 | Sep., 2000 | JP.
| |
| 2000/-242057 | Sep., 2000 | JP.
| |
| 2000/-330303 | Nov., 2000 | JP.
| |
| 2001-51467 | Feb., 2001 | JP.
| |
Primary Examiner: Rodee; Christopher
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch, LLP
Claims
What is claimed is:
1. An image forming apparatus comprising:
a multiple number of electrophotographic image forming stations for multiple
development colors including black, arranged in line in the paper feed direction,
each image forming station having a photoreceptor, a charger, an exposure device,
a developing device, a transfer device and a cleaning device,
each of the photoreceptors has a charge transport layer which is formed of a
charge transport material and a blend of, at least, two kinds of binder resins,
the blended ratio of at least two kinds of binder resins for the photoreceptor
for black is made different from that of the binder resins for the photoreceptors
for the other development colors so that the photoreceptor for black presents a
greater abrasion resistance than the photoreceptors for the other development colors.
2. The image forming apparatus according to claim 1, wherein the mass ratio of
the binder resin to the charge transport material in each photoreceptor is specified
to range from 10/14 to 10/20, and the blended ratio (%) of the principal component
binder resin (S) in the whole binder resin in the photoreceptor for black is made
greater by 20% or more than the blended ratio (%) of the same binder resin (S)
in the whole binder resin in the photoreceptors for other development colors.
3. The image forming apparatus according to claim 2, wherein at least one of
the binder resins for photoreceptors is a polycarbonate polymer having a structural
unit represented by the following general formula (1):
##STR16##
wherein R
1, R
2, R
3, R
4, R
5,
R
6, R
7 and R
8 individually represent a hydrogen
atom, halogen atom, substituted or unsubstituted alkyl of 1 to 6 carbon atoms,
C
4-C
10 cyclic hydrocarbon residual group, substituted or
unsubstituted aryl, and Z represents a group of atoms required to constitute a
substituted or unsubstituted carbocycle or substituted or unsubstituted heterocycle,
m being an integer.
4. The image forming apparatus according to claim 2, wherein the film thickness
of the charge transport layer ranges from 18 μm to 27 μm.
5. The image forming apparatus according to claim 1, wherein at least one of
the binder resins for photoreceptors is a polycarbonate polymer having a structural
unit represented by the following general formula (1):
##STR17##
wherein R
1, R
2, R
3, R
4, R
5,
R
6, R
7 and R
8 individually represent a hydrogen
atom, halogen atom, substituted or unsubstituted alkyl of 1 to 6 carbon atoms,
C
4-C
10 cyclic hydrocarbon residual group, substituted or
unsubstituted aryl, and Z represents a group of atoms required to constitute a
substituted or unsubstituted carbocycle or substituted or unsubstituted heterocycle,
m being an integer.
6. The image forming apparatus according to claim 5, wherein the film thickness
of the charge transport layer ranges from 18 μm to 27 μm.
7. The image forming apparatus according to claim 1, wherein the film thickness
of the charge transport layer ranges from 18 μm to 27 μm.
8. The image forming apparatus according to claim 1, wherein the shape and/or
appearance of the photoreceptor for black development or its part is made different
from the shape and/or appearance of the photoreceptors or their parts for the other
development colors.
Description
FIELD OF THE INVENTION
The present invention relates to a color image forming apparatus such as a color
printer, etc., and relates to a so-called tandem type color image forming apparatus
wherein a multiple number of photoreceptors are charged so as to develop color
images by developing devices holding different color toners.
DESCRIPTION OF THE PRIOR ART
Recently, in the field of color electrophotographic processing, tandem
type color image forming apparatuses in which a multiple number of photoreceptor
drums for multiple colors of toner are arranged in line to obtain a color image
have been used in order to enhance the printing speed. This tandem type configuration
lends itself to color image forming apparatuses and multi-color image forming apparatuses
for outputting image formed articles of reproduction and composition of color images
and multi-color images by successively transferring a plurality of color separation
images for color image data or multi-color image data, in a layered manner, as
well as image forming apparatuses including a color image forming function or multi-color
image forming function. It is essential for these image forming apparatuses that
all the photoreceptors arranged therein should always have the same level of quality
in order to provide images without color imbalance between the color components.
Even if uniform images free from unevenness can be obtained when all the photoreceptors
are unused, the problem may take place that the image quality becomes degraded
as the photoreceptors are worn down as they are used. Despite of its name, a color
image forming apparatus in practice is often used for monochrome (black/white)
printing other than color printing. There are cases where monochrome printing is
implemented more often than color printing, hence there is a drawback that the
photoreceptor for black images becomes worn away earlier than the other color photoreceptors.
Usually, the processing system is designed so that the four photoreceptors
for the four colors Y, M, C and K(Bk) toners will not present inharmonious wear
characteristics. If, however, the photoreceptors for individual toners are worn
away in different manners, there occurs color unevenness and color imbalance as
the number of copies increases. In such cases, all the drums, instead of the drum
which, alone, has been heavily degraded, should be replaced. Particularly, if hard
papers such as post cards are used, large wear takes place locally, causing large influences.
Further, when a contact-type chargers which will impose heavier burdens
on the photoreceptors are used, the amounts of wear of the drums become large.
If the wear of the photoreceptor is made small and uniform, it is possible to make
the interval for replacement of the drum longer. Further, if all the drums reach
the end of their life at almost the same time, concurrent replacement of all the
drums will never produce any loss. However, if the wear and degradation rates of
the drums differ between different colors of developing devices, degradation of
only one of them requires replacement of all the drums. Otherwise, color imbalance
between the new drum and the other drums, which have not been replaced, takes place,
resulting in failure to obtain good image quality. In other words, the interval
of drum replacement is determined by the most intensively degraded drum among the
four. This results in being wasteful and uneconomical.
As countermeasures, Japanese Patent Application Laid-open Hei 10 No.333393, Japanese
Patent Application Laid-open Hei 11 No.24358 and Japanese Patent Application Laid-open
Hei 11 No. 52599, disclose configurations in which an α-Si or α-SiC
photoreceptor is used for that for black development so as to enhance the photoreceptor
life while OPCs (organic photoreceptors) are used for those other than that for
black development. There is, however, a problem that α-Si and α-SiC
photoreceptors used in the above publications are less chargeable. As a solution
to this drawback, Japanese Patent Application Laid-open Hei 10 No.333393 specifies
the thickness of the photoreceptor to be 30 μm or more and its difference
in surface potential from the other organic photoreceptors to be equal to or lower
than 200 V. Japanese Patent Application Laid-open Hei 11 No.24358 proposes that
the applied voltage to the α-Si photoreceptor should be 1.05 to 2.50 times
the application voltage to the organic photoreceptors. Further, Japanese Patent
Application Laid-open Hei 11 No.52599 is aimed at increasing the chargeability
by adding an α-SiC surface layer.
In the above way, in order to extend the life of the photoreceptor for black
development
while making up for the low chargeability of the α-Si or α-SiC photoreceptor,
it is necessary to make complicated charge control for black development, resulting
in the need of extra cost. Further, since, other than the charge control, there
are differences in light sensitivity and susceptivity to temperature/humidity,
between the α-Si or α-SiC photoreceptor and the organic photoreceptor,
light exposure, transfer conditions and other factors differ between the α-Si
or α-SiC photoreceptor for black development and the organic photoreceptors
for development other than black. Therefore, a different control method of the
photoreceptor for black development from that for the photoreceptors for the other
colors should be used, thus again resulting in the need of extra cost. The α-Si
or α-SiC photoreceptors disclosed in Japanese Patent Application Laid-open
Hei 10 No.333393, Japanese Patent Application Laid-open Hei 11 No.24358 and Japanese
Patent Application Laid-open Hei 11 No.52599, have the problem that their production
cost is obviously high compared to the organic photoreceptors. Further, as another
problem, they consume large amounts of black toner, as is well known.
As the countermeasures against the above problems, Japanese Patent Application
Laid-open 2000 Nos.242056 and 242057 propose configurations where the drum for
black development alone is increased in diameter or increased in film thickness.
Japanese Patent Application Laid-open 2001 No.51467 refers to use of a non-contact
type charging means only for black development, increase in film thickness and
use of a resin having a large viscosity-average molecular weight. Further Japanese
Patent Application Laid-open 2000 No.330303 discloses a polycarbonate copolymer
resin as the resin for tandem photoreceptors. Further, provision of a protective
layer on only the photoreceptor for black development has been also investigated
as an optional method.
Increase of the drum diameter for black development alone as in Japanese
Patent Application Laid-open 2000 Nos.242056 and 242057 results in enlargement
of the machine body. Increase in thickness of the coating film may cause reduction
in the amount of charge or degrade dot reproducibility and/or line reproducibility
in the image. Further, use of a resin having a large viscosity-average molecular
weight produces an air entrapment problem when it is applied and causes difficulties
in application. Japanese Patent Application Laid-open 2000 No.330303 also discloses
use of various copolymer polycarbonate resins as the resin for tandem photoreceptors.
However, the discussed photoreceptors for black and other color development use
an identical configuration, hence it is impossible to lengthen the life of the
photoreceptor for black development in a general environment in which monochrome
copy mode is used often.
SUMMARY OF THE INVENTION
The present invention is aimed at solving the above conventional problems and
attaining the following object. It is therefore an object of the present invention
to provide a low-cost, color image forming apparatus in which the photoreceptors
for all colors can be used for and within, a concurrent period.
One aspect of the present invention resides in an image forming apparatus, comprising
a multiple number of electrophotographic image forming stations for multiple development
colors including black, arranged in line in the paper feed direction, each image
forming station having a photoreceptor, a charger, an exposure device, a developing
device, a transfer device and a cleaning device and characterized in that each
of the photoreceptors has a charge transport layer which is formed of a charge
transport material and a blend of, at least, two kinds of binder resins, the blended
ratio of at least two kinds of binder resins for the photoreceptor for black is
made different from that of the binder resins for the photoreceptors for the other
development colors so that the photoreceptor for black presents a greater abrasion
resistance than the photoreceptors for the other development colors.
In this case, the abrasion resistance of the drum for black development can be
improved without making a significant change of the characteristics as a photoreceptor,
such as sensitivity, resistance against ozone-induced damage, surface characteristic
and other characteristics such as coatability, by varying the blended ratio of
at least two kinds of resins being different in functions (resistance to abrasion,
etc.). Thereby, it is possible to extend the life of the photoreceptor drum for
black development, which is much used, longer than the photoreceptors used for
the other development colors, whereby it is possible to replace the black drum
and the color drums, all at once and hence produce good images free from imbalance
in color. Further, blending of resins makes it possible to provide multiple characteristics
as an electrophotographic photoreceptor. Blending of two or more kinds of resins
having different viscosity-average molecular weights makes it possible to adjust
the viscosity of the coating liquid to the coatable range, hence facilitates control
of the application performance of the coating liquid. Thus, function-oriented design
becomes possible.
The image forming apparatus of the present invention is characterized in that
the mass ratio of the binder resin to the charge transport material in each photoreceptor
is specified to range from 10/14 to 10/20, and the blended ratio (%) of the principal
component binder resin (S) in the whole binder resin in the photoreceptor for black
is made greater by 20% or more than the blended ratio (%) of the same binder resin
(S) in the whole binder resin in the photoreceptors for other development colors.
In this case, specifying the weight ratio of the binder resin to the charge transport
material to range from 10/14 to 10/20 makes it possible to provide a photoreceptor
which is excellent in electric characteristics and also in image stability against
ozone, NOx and the like. Here, when the charge transport substance is contained
in a ratio greater than 10/14, good sensitivity is obtained while the charging
characteristics, the mechanical strength of the coating and the image stability
against ozone, NOx and the like, generated during the charging process degrade
(resulting in occurrence of image deletion of halftones and generation of black
stripes). When the binder resin is contained in a ratio greater than 10/20, the
charging characteristics, the mechanical strength and the image stability are good
while the sensitivity markedly lowers.
Further, the difference in the blended ratio (%) of the principal component
binder resin (S) in the photoreceptor for black, between the photoreceptor for
black and the photoreceptors for the other development colors is made to be 20%
or greater, preferably 30% or greater, whereby it is possible to positively enhance
the abrasion resistance of the photoreceptor for black, thus achieving the intended
result. When the difference of the blended ratio is less than 20%, the difference
in abrasion resistance is so small that distinct difference in reduction of film
thickness cannot be found. Here, it is preferred that a resin having excellent
abrasion resistance is chosen as the principal component of the binder resin for
the photoreceptor for black.
Further, the image forming apparatus of the present invention is characterized
in that at least one of the binder resins for photoreceptors is a polycarbonate
polymer having a structural unit represented by the following general formula (1):
##STR1##
wherein R
1, R
2, R
3, R
4, R
5,
R
6, R
7 and R
8 individually represent a hydrogen
atom, halogen atom, substituted or unsubstituted alkyl of 1 to 6 carbon atoms,
C
4-C
10 cyclic hydrocarbon residual group, substituted or
unsubstituted aryl, and Z represents a group of atoms required to constitute a
substituted or unsubstituted carbocycle or substituted or unsubstituted heterocycle,
m being an integer.
Accordingly, when the present invention is realized, it is possible
to improve and control the image stability against ozone, NOx and the like and
abrasion resistance.
According to the present invention, the image forming apparatus is characterized
in that the charge transport layer is formed with a thickness of 18 to 27 μm.
In this case, it is possible to produce good images without any reduction in
the
amount of charge due to thinness of the film of the photoreceptor and without any
loss of dot reproducibility or line reproducibility in the images due to too much thickness.
In the present invention, the image forming apparatus is characterized in that
the photoreceptors other than that for black development are stopped operating
in monochrome (black and white) copy mode.
In this case, rotation of the unnecessary photoreceptors can be obviated so that
it is possible to reduce the film abrasion of the photoreceptors other than that
for black development.
In the present invention, the image forming apparatus is characterized in that
the photoreceptors other than that for black development are separated from the
paper feed line, in monochrome (black and white) copy mode.
In this case, since the photoreceptors other than that for black development
are
separated when the monochrome (black and white) copy mode is selected, it is possible
to avoid the chance of the coating films of the photoreceptors being abraded by
recording media and/or the recording media conveyer belt or the like, hence lengthen
the life of the photoreceptors.
The photoreceptors or their parts in the image forming apparatus are characterized
in that the shape and/or appearance of the photoreceptor for black development
or its part is made different from the shape and/or appearance of the photoreceptors
or their parts for the other development colors.
There are cases where the photoreceptors of different colors cannot be differentiated
only from their appearances. Designing them so as to be incompatible to each other
obviates misplacement of the photoreceptors into the wrong places, hence intended
result can be positively be achieved.
The photoreceptors used in the above image forming apparatus, both the photoreceptor
that is much used and the photoreceptors that are less used can be replaced at
the same time, whereby it is possible to realize a low-cost configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic front sectional view showing the configuration of a digital
color copier as an image forming apparatus of the present invention;
FIG. 2 is a flowchart showing the operational control in accordance with the
output image mode designation;
FIG. 3 is a CuKα characteristic X-ray diffraction chart of titanyl phthalocyanine
used in the embodiment; and
FIG. 4 is a schematic sectional view of a layered photoreceptor according to
the embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiment of the present invention will hereinafter be described in detail
with reference to the accompanying drawings.
To begin with, the constituent materials in the schematic sectional view of a
layered photoreceptor shown in FIG. 4 as one embodiment of the photoreceptor of
the present invention will be described. In FIG. 4,
1 designates a conductive
substrate,
2 a charge generation layer,
3 a charge transport layer,
4 a photosensitive layer of the photoreceptor consisting of an undercoat
layer, charge generation layer and charge transport layer, and
5 an undercoat
layer provided between the conductive substrate and the charge generation layer.
As conductive substrate
1, metals such as aluminum, copper, brass, zinc,
nickel, stainless steel, chromium, molybdenum, vanadium, indium, titanium, gold
and platinum and alloys of these can be used. Other than these, polyester film,
paper and metal film on which aluminum, aluminum alloy, tin oxide, gold, indium
oxide or the like is deposited or applied, plastic and paper containing conductive
particles, and plastics containing conductive polymers or the like can be used.
These materials are shaped and used in a cylindrical, columnar form or in a film
sheet form.
Undercoat layer (intermediate layer)
5 may be provided between conductive
substrate
1 and charge generation layer
2. As the undercoat layer
5, an inorganic layer such as an anodic oxide thin film formed on aluminum,
aluminum oxide, aluminum hydroxide and the like, an organic layer such as polyvinyl
alcohol, casein, polyvinyl pyrolidone, polyacrylic acid, celluloses, gelatin, starch,
polyurethane, polyimide, polyamide and the like and an organic layer containing
as inorganic pigments, conductive or semi-conductive particles, of metal such as
aluminum, copper, tin, zinc, titanium or the like or of metal oxide such as zinc
oxide, aluminum oxide, titanium oxide or the like, can be used. As to crystalline
types of titanium oxide, there are various types such as the anatase form, rutile
form and amorphous type, and any of these can be used alone or in combination.
Titanium oxide particles covered with Al
2O
3, ZrO
2
or the like or a combination of these can be preferably used.
As the binder resin contained in undercoat layer
5, polyvinyl alcohol,
casein, polyvinyl pyrolidone, polyacrylic acid, celluloses, gelatin, starch, polyurethane,
polyimide, polyamide and other resins can be used. Among these, polyimide resin
is preferably used. This is because the binder resin of the undercoat layer is
demanded to be insoluble and non-swelling in the solvent used for forming the photoconductive
layers over undercoat layer
5, and to present excellent adhesiveness to
conductive substrate
1 and enough flexibility. Among polyimide resins, alcohol-soluble
nylon resins can be more preferably used. Specific examples of the resin include
so-called copolymer nylons having 6-nylon, 66-nylon, 610-nylon, 11-nylon, 12-nylon
and others compolymerized, and chemically modified nylons such as N-alkoxymethyl
denatured nylon.
In the present invention, general solvents can be used as the organic solvent
for the application liquid of undercoat layer
5, but it is preferred that,
when alcohol-soluble nylon resin, which is more preferable, is used as the binder
resin, a pure or mixture type organic solvent selected from the lower alcohol group
having 1 to 4 carbon atoms and another group of organic solvents including dichloromethane,
chloroform, 1,2-dichloroethane, 1,2-dichloropropane, toluene, tetrahydrofuran and
1,3-dioxolane be preferably used. In this case, mixing the pure alcohol solvent
with the above organic solvent improves dispersibility of titanium oxide in the
solvent compared to that in the pure alcohol solvent, so that it is possible to
make the stability under storage long-lasting and reuse the application liquid.
This also prevents coating defects and uneven coating of undercoating layer
5 when the conductive substrate is dip coated in the application liquid
for undercoat layers to form undercoat layer
5, whereby it is possible to
achieve uniform application of the photoconductive layer thereon, which leads to
provision of an electrophotographic photoreceptor excellent in imaging characteristics
and free from film defects.
Production of undercoat layer
5 can be carried out using an undercoat
layer application liquid that has been prepared by blending the above inorganic
pigment with a solvent and binder resin and dispersing the mixture by means of
a ball mill, Dyno-mill, supersonic oscillator or other dispersing machines. For
a sheet-like substrate, a baker applicator, bar coater, casting, spin coating or
other methods can be used. For a drum substrate, a spray method, vertical ring
method, dip coating or other methods can be used.
Charge generation layer
2 is mainly composed of a charge generating
material which generates electric charges by illumination of light, and contains
publicly known binder, plasticizer and sensitizer, as necessary. Examples of the
charge generation material include: perylene pigments such as peryleneimide, perylenic
anhydride; polycyclic quinone pigments such as quinacridone, anthraquinone; phthalocyanine
pigments such as metal and metal-free phthalocyanines, halogenated metal-free phthalocyanine;
squarium dyes; azulenium dyes; thiapyrilium dyes; and azo pigments having a carbazole
skeleton, styryl stilbene skeleton, triphenylamine skeleton, dibenzothiophene skeleton,
oxadiazole skeleton, fluorenone skeleton, bis-stilbene skeleton, distyryl oxadiazole
skeleton or distyryl carbazole skeleton.
In particular, metal-free phthalocyanine pigments, oxotitanyl phthalocyanine
pigments,
bisazo pigments containing a fluoren ring or fluorenone ring, bisazo pigments consisting
of aromatic amines and triazo pigments can present especially high charge generation
power, so that use of these provides a high sensitive photoreceptor. Further, with
concern to oxotitanyl phthalocyanines, a crystalline type which presents a diffraction
peak at a Bragg angle (2θ±0.2°) of 27.3° in the X-ray diffraction
spectrum can provide a further high sensitivity and so is more preferred.
Production of charge generation layer
2 can be carried out using
an application liquid that has been prepared by blending the fine particles of
the above charge generation material with an organic solvent and pluverizing and
dispersing the particles by means of a ball mill, sand grinder, paint shaker, supersonic
dispersing machine or the like. For a sheet-like substrate, a baker applicator,
bar coater, casting, spin coating or other methods can be used. For a drum substrate,
a spray method, vertical ring method, dip coating or other methods can be used.
In order to enhance the binding property, binder resins as follows may be added,
for example: polyester resin, polyvinyl acetate, polyacrylic ester, polycarbonate,
polyarylate, polyvinyl acetoacetal, polyvinyl propynal, polyvinyl butyral, phenoxy
resin, epoxy resin, urethane resin, melamine resin, silicone resin, acrylic resin,
cellulose ester, cellulose ether, vinylchloride-vinyl acetate copolymer resin.
The film thickness is preferably 0.05 to 5 μm, more preferably 0.1 to 1 μm.
The charge generation layer may contain various additives such as a leveling agent
for improving application performance, antioxidant and sensitizer, as required.
Charge transport layer
3 provided over charge generation layer
2
essentially consists of a charge transport material for accepting charges generated
within the charge generation material, and transporting them, and a binder (binder
resin). As the charge transport material, the following electron donative materials
can be used: poly-N-vinyl carbazole and its derivatives, poly-g-carbazolyl ethylglutamate
and its derivatives, pyrene-formaldehyde condensate and its derivatives, polyvinyl
pyrene, polyvinyl phenanthrene, oxazole derivatives, oxadiazole derivatives, imidazole
derivatives, 9-(p-diethylamine styryl) anthracene, 1,1-bis (4-dibenzyl aminophenyl)
propane, styryl anthracene, styryl pyrazoline, pyrazoline derivatives, phenylhydrazones,
hydrazone derivatives, triphenylamine compounds, tetraphenyl diamine compounds,
triphenylmethane compounds, stilbene compounds, azine compounds having a 3-methyl-2-benzothiazoline
ring, etc.
Alternatively, the following electron acceptable substances can be
used: fluorenone derivatives, dibenzothiophene derivatives, indeno thiophene derivatives,
phenanthrene quinone derivatives, indeno pyridine derivatives, thioxanthone derivatives,
benzo[c]cinnoline derivatives, phenazine oxide derivatives, tetracyanoethylene,
tetracyanoquinodimethane, bromanil, chloranil, benzoquinone, etc. Of these, particular
types of butadiene compounds, styryl compounds and amine compounds, having the
following structure are more preferable in the present invention since they show
high hole transporting properties so that a high sensitivity can be maintained
even when the resin ratio is high. One example is shown below.
##STR2##
(wherein Ar
1, Ar
2, Ar
3 and Ar
4 each
represent an aryl which may have a substituent, at least one of Ar
1 to
Ar
r being an aryl having an amino-substituent as its substituent and
n being 0 or 1.)
As the specific examples of the general formula (2), the following compounds
(2-1)
to (2-12) can be mentioned.
##STR3##
##STR4##
##STR5##
As styryl compounds, the compounds having the following general form (3) can
be
mentioned.
##STR6##
(wherein Ar
5 represents an aryl which may have a substituent,
Ar
6 represents a phenylene, naphthylene, biphenylene or anthrylene which
may have a substituent, R
9 represents a hydrogen atom or lower alkyl
or lower alkoxyl, X represents a hydrogen atom or an alkyl which may have a substituent,
or an aryl which may have a substituent, and Y represents an aryl which may have
a substituent).
As the specific examples of the general formula (3), the following compounds
(3-1)
to (3-16) can be mentioned.
##STR7##
##STR8##
##STR9##
##STR10##
As amine compounds, the compounds having the following general formula (4) can
be mentioned.
##STR11##
(wherein R
10 to R
15 each represent a hydrogen atom,
halogen atom, alkyl, alkoxyl, p, q, r, s, t and u indicating an integer 1 to 5).
As specific examples of the general formula (4), the following compounds (4-1)
to (4-6) can be mentioned.
##STR12##
Charge transport layer
3 is given in the form of the above-mentioned
charge transport material bound by a binder resin. The binder resin used for charge
transport layer
3 is selected from those which are compatible with the charge
transport material. Examples include vinyl polymers such as polymethylmethacrylate,
polystyrene and polyvinyl chloride, polycarbonate resin, polyester resin, polyester
carbonate resin, polysulfone resin, phenoxy resin, epoxy resin, silicone resin,
polyarylate resin, polyamide resin, polyurethane resin, polyacrylamide resin and
phenol resin.
In particular, polystyrene, polycarbonate, polyarylate and polyphenylene oxide
resins have a volume resistivity of 10
13 Ω or greater and are
excellent in coating performance and electric characteristics.
These resins can be used alone or may be partially cross-linked so to present
thermosetting properties. In the present invention, a blend of two or more kinds
of resins is used. The resins selected as the blend of two or more kinds may be
resins which have different polymer structural units, one from another, or resins
which have the same polymer structural unit but are different in viscosity-average
molecular weight or the like. Resins which are substantially different in functions
such as abrading performance, etc., maybe preferably used. Blending, at least,
two or more kinds makes it possible to provide multiple characteristics as an electrophotographic
photoreceptor, that is, the necessary abrasion resistance, surface characteristic,
resistance against ozone-induced damage, sensitivity and others. Blending of resins
having different viscosity-average molecular weights makes it possible to adjust
the viscosity of the coating liquid to the coatable range, hence facilitates control
of the application performance of the coating liquid, whereby function-oriented
design becomes possible. Though a blend of two kinds of resins is used as the binder
resin in the present embodiment, the invention should not be limited to two kinds
and three or more kinds of resins may be blended.
As the binder resin used here, polycarbonate polymers having repeat units of
the
following general form (5) are preferably used.
##STR13##
(wherein each R
2′ individually represents a halogen atom,
vinyl, allyl, substituted or unsubstituted alkyl of 1 to 10 carbon atoms, substituted
or unsubstituted aryl of 6 to 12 carbon atoms, substituted or unsubstituted cycloalkyl
of 3 to 12 carbon atoms, substituted or unsubstituted alkoxyl of 1 to 6 carbon
atoms, or substituted or unsubstituted aryloxyl of 6 to 12 carbon atoms, 'a' being
an independent integer of 0 to 4, Y representing single bond, —O—,
—CO—, —S—, —SO—, SO
2—, —CR
3′R
4′—,
substituted or unsubstituted cycloalkylidene of 5 to 11 carbon atoms, substituted
or unsubstituted α, ω-alkylene of 2 to 12 carbon atoms, 9,9-fluorenylidene,
1,8-menthane diyl, 2,8-menthane diyl, substituted or unsubstituted pyrazilidene,
or substituted or unsubstituted arylene of 6 to 24 carbon atoms. Here, R
3
and R
4 individually represent a hydrogen atom, or substituted
or unsubstituted alkyl of 1 to 10 carbon atoms, or substituted or unsubstituted
aryl of 6 to 12 carbon atoms.)
The polycarbonate polymer used in the present invention may have one or more
types of repeat units having the general form (5). Further, the polycarbonate polymer
may contain repeat units other than that having the general form (5), as long as
no obstruction to the achievement of the object of the present invention occurs.
In the general representation (5), specific examples of R
2′,
Y, R
3′ and R
4′ are as follows.
Examples of a halogen atom represented by R
2′ include
fluorine, chlorine, bromine and iodine. Of these, fluorine, chlorine and bromine
are preferred.
Examples of the unsubstituted alkyl of 1 to 10 carbon atoms, represented
by R
2′, R
3′ and R
4′, include
methyl, ethyl, propyl, isopropyl, butyl, 2-butyl, tert-butyl, isobutyl, pentyl,
hexyl, heptyl, octyl, nonyl and decyl. Of these, methyl, ethyl, propyl, isopropyl,
butyl, 2-butyl and tert-butyl are preferred.
Examples of the unsubstituted aryl of 6 to 12 carbon atoms, represented
by R
2′, R
3′ and R
4′, include
phenyl, naphthyl and biphenylyl, and phenyl is preferred. Examples of the unsubstituted
cycloalkyl of 3 to 12 carbon atoms, represented by R
2′, include
cyclopentyl, cyclohexyl and cycloheptyl. Of these cyclopentyl and cyclohexyl are preferred.
Examples of the unsubstituted alkoxyl of 1 to 6 carbon atoms, represented
by R
2′, include methyl oxyl, ethyl oxyl, propyl oxyl, isopropyl
oxyl, butyl oxyl, 2-butyl oxyl, tert-butyl oxyl, isobutyl oxyl, pentyl oxyl and
hexyl oxyl. Of these, methyl oxyl, ethyl oxyl, propyl oxyl and isopropyl oxyl are preferred.
Examples of the unsubstituted aryloxyl of 6 to 12 carbon atoms, represented
by R
2′, include phenyl oxyl, naphthyl oxyl and biphenylyl oxyl.
Of these, phenyl oxyl is preferred. Examples of the unsubstituted arylene of 6
to 24 carbon atoms, represented by Y, include phenylene, naphthylene, biphenylylene,
terphenylylene and quaterphenylylene. Of these, phenylene is preferred.
Examples of the unsubstituted cycloalkylidene of 5 to 11 carbon atoms, represented
by Y, include cyclopentylidene, cyclohexylidene, cycloheptylidene, cyclooctylidene,
cyclononylidene, cyclodecylidene and cycloundecylidene of these, cyclohexylidene
is preferred.
Examples of the unsubstituted α, ω-alkylene of 2 to 12 carbon
atoms, represented by Y, include ethylene, trimethylene, tetramethylene, pentamethylene,
hexamethylene, heptamethylene, octamethylene, nonamethylene, decamethylene, undecamethylene
and dodecamethylene. Of these, ethylene and trimethylene are preferred. As the
1,8-menthane diyl, represented by Y, 1,8-p-menthane diyl is preferred. As the 2,8-menthane
diyl, represented by Y, 2,8-p-menthane diyl is preferred.
The substituted alkyl, substituted aryl, substituted alkoxyl, substituted aryloxyl,
substituted cycloalkyl, substituted arylene, substituted α, ω-alkylene,
substituted cycloalkylidene and substituted pyraziridene indicate the aforementioned
unsubstituted alkyl, unsubstituted aryl, unsubstituted alkoxyl, unsubstituted aryloxyl,
unsubstituted cycloalkyl, unsubstituted arylene, unsubstituted α, ω-alkylene,
unsubstituted cycloalkylidene and unsubstituted pyraziridene, of which one of hydrogen
atoms is substituted by a substituent.
Examples of the substituents of the substituted alkyl and substituted alkoxyl
include halogen atoms (fluorine, chlorine, bromine, iodine), aryls of 6 to 12 carbon
atoms (phenyl, naphthyl, biphenylyl), alkoxyls of 1 to 4 carbon atoms (methoxy,
etoxy, propoxy, isopropoxy, butoxy, sec-butoxy, tert-butoxy, isobutoxy), alkylthiols
of 1 to 4 carbon atoms (methylthio, etc.) and arylthiols of 6 to 12 carbon atoms
(phenylthio, etc.).
Examples of the substituentional groups of the substituted aryl, substituted
aryloxyl and substituted arylene include halogen atoms (fluorine, chlorine, bromine,
iodine), alkyls of 1 to 4 carbon atoms (methyl, ethyl, propyl, isopropyl, butyl,
sec-butyl, tert-butyl, isobutyl), alkoxyls of 1 to 4 carbon atoms (methoxy, etoxy,
propoxy, isopropoxy, butoxy, sec-butoxy, tert-butoxy, isobutoxy), alkylthiols of
1 to 4 carbon atoms (methylthio, etc.) and arylthiols of 6 to 12 carbon atoms (phenylthio, etc.).
Examples of the substituents of the substituted α, ω-alkylene,
substituted cycloalkyl, substituted cycloalkylidene and substituted pyraziridene
include halogen atoms (fluorine, chlorine, bromine, iodine), alkyls of 1 to 4 carbon
atoms (methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, isobutyl),
aryls of 6 to 12 carbon atoms (phenyl, naphthyl, biphenylyl), alkoxyls of 1 to
4 carbon atoms (methoxy, etoxy, propoxy, isopropoxy, butoxy, sec-butoxy, tert-butoxy,
isobutoxy), alkylthiols of 1 to 4 carbon atoms (methylthio, etc.) and arylthiols
of 6 to 12 carbon atoms (phenylthio, etc.). As a preferred examples of the substituted
alkyls of 1 to 10 carbon atoms, substituted by halogen atoms for R
2′,
R
3′ and R
4′, trifluoromethyl with the three
hydrogen atoms of the methyl substituted with fluorine atoms can be mentioned.
When the polycarbonate polymer having the above general form (5) is used alone,
the polymer preferably has a viscosity-average molecular weight of 20,000 to 70,000.
When it is less than 20,000, the plate wear is markedly reduced. When greater than
70,000, the solution viscosity increases while the plate wear is improved to some
degree, hence it takes long time to mix it with the charge transport material and
uneven application of coating tends to occur, resulting in a reduced productivity.
In particular, it is preferred in the present invention, that at least one of
the binder resins includes a polycarbonate polymer having, at least, one structural
unit represented by the following general form (1).
##STR14##
(wherein R
1, R
2, R
3, R
4, R
5,
R
6, R
7 and R
8 individually represent a hydrogen
atom, halogen atom, substituted or unsubstituted alkyl of 1 to 6 carbon atoms,
C
4-C
10 cyclic hydrocarbon residual group, substituted or
unsubstituted aryl. Z represents a group of atoms required to constitute a substituted
or unsubstituted cycle or substituted or unsubstituted heterocycle, m being an integer).
As the specific examples of general form (1), the following compounds (1-1) to
(1-4) can be mentioned.
##STR15##
Since the binder resins represented by the above general formula (1) present
low permeability to gas, it is possible to prevent infiltration of gases such as
ozone, NOx and the like which will degrade photoreceptor characteristics. These
resins present excellent compatibility with the charge transport material and also
have excellent durability. Blends of these resins also present excellent compatibility
with the charge transport material and have excellent durability.
The polycarbonate resin having the above general form (1) preferably has a viscosity-average
molecular weight of about 20,000 to 50,000. When it is less than 20,000, while
the image stability (against image deletion of halftones and occurrence of black
stripes) against ozone, NOx, etc., generated by the charging process, improves,
the plate wear is markedly reduced. When greater than 50,000, lowering of the initial
sensitivity, increase in remaining potential when used repeatedly and lowering
of the image stability become augmented while the plate wear is improved to some degree.
Examples of solvents for dissolving (dispersing) these materials include
ketones such as acetone, methylethylketone, cyclohexanone, etc., ethers such as
ethylether, tetrahydrofuran, etc., aliphatics such as chloroform, dichloroethane,
dichloromethane, etc., halogenated hydrocarbons, aromatics such as benzene, chlorobenzene,
toluene, etc. Of these, tetrahydrofuran is especially preferred.
The ratio between the charge transport material and binder resin in the charge
transport layer in each photoreceptor is usually set at about 10/6 to 10/15, however,
in the present invention, it is preferably set at 10/14 to 10/20, in view of improving
abrasion resistance. When the charge transport substance is contained in a ratio
greater than 10/14, good sensitivity is obtained, while the charging characteristics,
the mechanical strength of the coating and the image stability (occurrence of image
deletion of halftones and black stripes) against ozone, NOx and the like, generated
during the charging process, degrade. In contrast, when the binder resin is contained
in a ratio greater than 10/20, the charging characteristics, the mechanical strength
and the image stability are good while the sensitivity markedly lowers. The charge
transport layer is preferably formed with a thickness of 15 to 30 μm, more
preferably 18 to 27 μm.
The application liquid for charge transport layers of the present invention may
contain additives such as plasticizer, antioxidant, ultraviolet absorbent, leveling
agent and the like, in order to improve film forming performance, flexibility,
application performance and the like. As the antioxidant, typical antioxidants
which are added to resins can be used as is. For example, vitamin E, hydroquinone,
hindered amine, hindered phenol, p-phenylenediamine, arylalkane and their derivatives,
organosulfur compounds, organophosphorous compounds and others can be blended.
As a leveling agent, silicone oils, polymers or origomers having perfluoroalkyl
side chains can be used. The proper usage of the leveling agent is 0 to 20 parts
by weight relative to 100 parts by weight of the binder resin.
The application liquid for charge transport layers can be prepared without any
problem by a typical method in which the charge transport substance, binder resin
and additives are measured and then dissolved altogether into a predetermined amount
of organic solvent. However, it is preferred that the binder resin has been dissolved
first into the solvent and then, the carrier transport substance is added and dissolved
therein. This method improves dispersibility of the carrier transport substance
in the binder resin and inhibits possible and local crystallization of the carrier
transport agent in the film, whereby it is possible to improve the initial sensitivity
and potential stability after repeated usage and provide good image characteristics
and the like.
For application, the same method as used for the undercoat layer and charge generation
layer can be used.
For attachment of the photoreceptors into a copier or printer, rotational mechanisms
are needed. Specifically, a drive transmission part called 'flange' is assembled
for each photoreceptor. These flanges usually have the same shape and appearance.
In the present invention, the photoreceptor for black development and the photoreceptors
for the other development colors or their parts (transmission parts such as flanges,
etc.,) should be made different in shape and/or appearance. If their shapes are
indistinguishable, the flanges can be made different in color so as to obviate
misplacement. Since full performance cannot be obtained if the photoreceptors are
set in the wrong places, it is preferred that the flange for the photoreceptor
for black should be formed with a different shape from that of the other photoreceptors
so it will be incompatible with the others. In this case, misplacement such as
of the photoreceptor having a lower durability being attached for black development,
will never take place, hence it is possible to obtain the intended effect.
Next, the image forming apparatus of the present invention will be described
with reference to the accompanying drawing. FIG. 1 is a schematic front sectional
view showing the configuration of a digital color copier as an image forming apparatus
in accordance with the embodiment of the present invention. The copier body
1
has an original table
111 and a control panel on the top thereof and has
an image reading portion
110 and an image forming unit
210 within.
A reversing automatic document feeder (RADF)
112 is arranged on the top
surface of original table
111 in a predetermined position with reset to
the original table
111 surface whilst being supported so as to be opened
and closed relative to original table
111.
RADF
112, first, conveys an original so that one side of the original
opposes image reading portion
110 at the predetermined position on original
table
111. After the image scanning of this side is completed, the original
is inverted and conveyed to original table
111 so that the other side opposes
image reading portion
110 at the predetermined position on original table
111. Then, when RADF
112 completes image scanning of both sides of
one original, the original is discharged and the duplex copy conveying operation
for a next document is implemented. The operation of the conveyance and face inversion
of the original is controlled in association with the whole copier operation.
Image reading portion
110 is disposed below original table
111
in order to read the image of the original conveyed onto original table
111
by means of RADF
112. Image reading portion
110 includes original
scanning portion
113 and
114 which reciprocates along, and in parallel
to, the undersurface of original table
111, an optical lens
115 and
a CCD line sensor
116 as a photoelectric converting device. This original
scanning portion
113 and
114 is composed of first and second scanner
units
113 and
114. First scanner unit
113 has an exposure
lamp for illuminating the original image surface and a first mirror for deflecting
the reflection image of light from the original toward the predetermined direction
and moves at the predetermined speed in a reciprocating manner in parallel with,
whilst being kept a certain distance away from, the undersurface of original table
111.
Second scanner unit
114 has second and third mirrors which deflect
the reflected light image from the original, deflected by first mirror of first
scanner unit
113 toward the predetermined direction and moves in a reciprocating
manner at a speed related to that of first scanner unit
113 and in parallel thereto.
Optical lens
115 reduces the reflected light image from the original,
thus deflected by third mirror of the second scanner unit, so that the reduced
light image will be focused on the predetermined position on CCD line sensor
116.
CCD line sensor
116 implements sequential photoelectric conversion of
the focused light image into electric signals and outputs them. CCD line sensor
116 is a three-line color CCD which reads monochrome or color images and
outputs line data as to color separation components R(red), G(green) and B(blue).
The original image in formation thus obtained in the electric signal form from
this CCD line sensor
116 is further transferred to an after mentioned image
processor where predetermined image data processes are performed.
Next, the configuration of image forming unit
210 and the configuration
of the components related to image forming unit
210 will be described. Provided
below image forming unit
210 is a paper feeding mechanism
211 which
separates a sheet of paper (recording medium) P, one by one, from a stack of paper
held in a paper tray and feeds it toward image forming unit
210. The paper
P thus separated is delivered into image forming unit
210 with its timing
controlled by a pair of registration rollers
212 located before image forming
unit
210. The paper P with an image formed on its one side is conveyed and
re-fed to image forming unit
210 in time with image forming of image forming
unit
210.
Arranged under image forming unit
210 is a conveyer and transfer
belt mechanism
213. A conveyer and transfer belt
216 of conveyer
and transfer belt mechanism
213 is wound and tensioned between a driving
roller
214 and an idle roller
215 so that the upper and lower parts
of the belt extend approximately parallel to each other. The conveyer and transfer
belt
216 electrostatically attracts paper P to itself to convey it. Further,
a pattern image detecting unit is provided under and in proximity to conveyer and
transfer belt
216.
Arranged in the paper conveyance path, downstream of conveyer and transfer
belt mechanism
213 is a fixing unit
217. This fixing unit
217
fixes the transferred toner image onto paper P. The paper P having passed through
the nip between a pair of fixing rollers of fixing unit
217 passes through
a conveyance direction switching gate
218 and is discharged by discharge
rollers
219 to a paper output tray
220 attached to the outer wall
of copier body
1.
This switching gate
218 selectively connects the conveyance path of paper
P after fixing with either the path to discharge paper P to the outside of copier
body
1 or the path to recirculate paper P toward image forming unit
210.
The paper P which is designated to be conveyed again to image forming unit
210
by means of switching gate
218 is inverted by means of a switch-back conveyance
path
221 and then re-fed to image forming unit
210.
Arranged above, and in proximity to, conveyer and transfer belt
216
in image forming unit
210 are the first image forming station Pa, the second
image forming station Pb, the third image forming station Pc and the fourth image
forming station Pd, in the above mentioned order from the upstream side of the
paper conveyance path.
Conveyer and transfer belt
216 is frictionally driven by driving
roller
214 in the direction indicated by arrow Z in FIG. 1, and carries
paper P which is fed by paper feeding mechanism
211 as stated above and
sequentially conveys it through image forming stations Pa to Pd.
All the image forming stations Pa to Pd are of a substantially identical configuration.
Each image forming station Pa, Pb, Pc and Pd has a photoreceptor drum
222a,
222b,
222c and
222d, which is driven
in the rotational direction indicated by arrow F in FIG. 1. Provided around each
photoreceptor drum
222a-
222d, are a primary charger
223a,
223b,
223c and
223d for
uniformly charging photoreceptor drum
222a-
222d, a
developing unit
224a,
224b,
224c and
224d for developing the static latent image formed on photoreceptor
drum
222a-
222d, a transfer charger
225a,
225b,
225c and
225d for transferring
the developed toner image on photoreceptor drum
222a-
222d
to paper P, and a cleaning unit
226a,
226b,
226c
and
226d for removing the leftover toner from photoreceptor drum
222a-
222d, in this order with respect to the rotational
direction of each photoreceptor drum
222a-
222d.
Arranged above photoreceptor drums
222a-
222d are
laser beam scanner units
227a,
227b,
227c
and
227d, respectively. Each laser beam scanner unit
227a-
227d
includes: a semiconductor laser element (not shown) for emitting a spot beam
modulated in accordance with the image data; a polygon mirror (deflecting device)
240 for deflecting the laser beam from the semiconductor laser element,
in the main scan direction; an f-theta lens
241 for focusing the laser beam
deflected by polygon mirror
240 onto the surface of photoreceptor drum
222a-
222d;
and mirrors
242 and
243.
The pixel signal corresponding to the black component image of a color original
image is supplied to laser beam scanner unit
227a; the pixel signal
corresponding to the cyan color component image of a color original image is supplied
to laser beam scanner unit
227b; the pixel signal corresponding to
the magenta color component image of a color original image is supplied to laser
beam scanner unit
227c; and the pixel signal corresponding to the
yellow color component image of a color original image is supplied to laser beam
scanner unit
227d.
In this arrangement, the static latent images corresponding to the color separations
of the original image information are formed on photoreceptor drums
222a
to
222d. Developing units
224a,
224b,
224c and
224d hold black toner, cyan color toner, magenta
color toner and yellow color toner, respectively. The static latent image on photoreceptor
drum
222a-
222d is developed by the toner of a corresponding
color. Thus, the color separations of the original image information are reproduced
in image forming unit
210 as toner images of different colors.
Provided between the first image forming station Pa and paper feeding mechanism
211 is a paper-attraction charger
228, which electrifies the conveyer
and transfer belt
216 surface so that paper P fed from paper feeding mechanism
