U.S. patent application number 12/181789 was filed with the patent office on 2008-12-18 for method of manufacturing an intermediate transfer belt.
Invention is credited to Minoru Matsuo, Yuuji Natori.
Application Number | 20080308962 12/181789 |
Document ID | / |
Family ID | 35239559 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080308962 |
Kind Code |
A1 |
Natori; Yuuji ; et
al. |
December 18, 2008 |
METHOD OF MANUFACTURING AN INTERMEDIATE TRANSFER BELT
Abstract
A method for making an intermediate transfer belt includes
transferring a mixture of a solution of a thermosetting resin and a
particulate electroconductive material into a centrifugal mold;
rotating the centrifugal mold to form a film attached to an inner
periphery thereof; thermally imidizing the film to have an
imidization ratio not greater than 98%; and drawing the film to
entirely harden the film and to form the intermediate transfer
belt.
Inventors: |
Natori; Yuuji; (Numazu-shi,
JP) ; Matsuo; Minoru; (Sagamihara-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
35239559 |
Appl. No.: |
12/181789 |
Filed: |
July 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11114026 |
Apr 26, 2005 |
7424256 |
|
|
12181789 |
|
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Current U.S.
Class: |
264/114 |
Current CPC
Class: |
G03G 2215/1623 20130101;
G03G 15/1685 20130101 |
Class at
Publication: |
264/114 |
International
Class: |
B22F 3/00 20060101
B22F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2004 |
JP |
2004-130354 |
Apr 14, 2005 |
JP |
2005-117179 |
Claims
1. A method of manufacturing an intermediate transfer belt,
comprising: transferring a mixture of a solution of a thermosetting
resin and a particulate electroconductive material into a
centrifugal mold; rotating the centrifugal mold to form a film
attached to an inner periphery thereof; thermally imidizing the
film to have an imidization ratio not greater than 98%; and drawing
the film to entirely harden the film and to form the intermediate
transfer belt, wherein the intermediate transfer belt is used in an
electrophotographic image forming process in which a toner image of
each color formed on plurality of image bearing members is
overlappingly transferred to the intermediate transfer belt to form
a multi-colored image thereon, which is transferred to a transfer
material.
2. The method according to claim 1, wherein the intermediate
transfer belt is formed with an elasticity modulus of from 7,000 to
15,000 MPa.
3. The method according to claim 1, wherein the intermediate
transfer belt is formed with a surface resistivity .rho.s of from
1.0.times.10.sup.10 to 1.0.times.10.sup.13.OMEGA..
4. The method according to claim 1, wherein the intermediate
transfer belt is formed with a volume resistivity .rho.v of from
1.0.times.10.sup.5 to 1.0.times.10.sup.11 .OMEGA.cm.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/114,026, filed Apr. 26, 2005, and is based upon and claims
the benefit of priority from the prior Japanese Patent Application
Nos. 2004-130354 filed on Apr. 26, 2004 and 2005-117179 filed on
Apr. 14, 2005, the entire contents of each of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an endless intermediate
transfer belt to which multiple toner images formed of a single
color on multiple image forming members are overlappingly
transferred. The toner images form a multi-colored image which is
transferred to a transfer material. An image forming apparatus
including the intermediate transfer belt, an image forming method
using the intermediate transfer belt and a method of manufacturing
the intermediate transfer belt are also described.
[0004] 2. Description of the Background
[0005] To obtain multi-colored images by using an image forming
apparatus such as a photocopier and a printer, the following
processes are typically used: [0006] (1) Forming images of a single
color on image bearing members; [0007] (2) Sequentially
overlappingly transferring each color image to an intermediate
transfer belt serving as intermediate transfer medium; and [0008]
(3) Electrostatically transferring the image on the intermediate
transfer belt to a transfer material simultaneously.
[0009] The image forming apparatus mentioned above has been
improved with regard to the speed of photocopying and the image
quality and is now expected to have the same image quality as that
of printing machines with regard to multiple-color overlapped
images.
[0010] Published unexamined Japanese Patent Application No.
(hereinafter referred to as JOP) 2002-244391 discloses an image
forming apparatus which can prevent registration shift during
intermediate transfer by controlling the rotation speed of multiple
image bearing members and the surface speed of an image transfer
belt to form images with good quality without color shift.
[0011] In addition, JOP 11-109761 discloses an intermediate
transfer belt for use in forming electrophotographic images which
is flow-cast to form an endless belt by centrifugal-molding
single-layer structured materials formed of thermosetting resins
having a high temperature resistivity such as polyimides,
polyamideimides and electroconductive carbon which is dispersed in
the resin.
[0012] Further, JOP 2003-145561 discloses a technology by which
aromatic polyimides having an inflexible structure are highly drawn
to orient molecules.
[0013] However, the inventions mentioned above have the following
drawbacks.
[0014] It is practically impossible to eliminate the difference
between the rotation speed of multiple image bearing members and
the surface speed of an intermediate transfer belt, even after
these speeds are controlled. Registration shifts of color images on
an intermediate transfer belt thus tend to occur, especially when
the belt has a low elasticity modulus. As a result, good image
quality is not obtained.
[0015] In recent years, more and more photocopiers and printers
include a four-tandem engine system (significantly increasing
speed), in which a color image is formed in one pass, instead of a
single engine system (printing speed is slow), in which a transfer
drum must rotate four times to form one color image.
[0016] However, since a four color toner image is formed on an
intermediate transfer belt in one pass, there is a color shift in
the image finally obtained because of slackening between the right
hand side portion and the left hand side portion of the
intermediate transfer belt, and flexure of the belt between each
transfer drum. These problems are caused by transient decrease in
the speed of the intermediate transfer belt due to the contact
between the intermediate transfer belt and transfer drums for each
color.
[0017] In addition, in JOP 2003-145561, the technology disclosed
therein is not applied to an intermediate transfer belt using a
polyimide resin to which an electroconductive agent such as carbon
black is added. When this disclosed technology is applied to such
an intermediate transfer belt, since a filler represented by black
carbon, etc., is mixed in the polyimide film as an
electroconductive agent and imparts semi-conductive properties.
Thus charged toner particles can be transferred from a transfer
drum to an intermediate transfer belt because of this filler. This
is true for the case of transfer to a printing paper.
SUMMARY OF THE INVENTION
[0018] The present inventors recognized a need exists for an
endless intermediate transfer belt for use in forming
electrophotographic images which can prevent slackening of the
intermediate transfer belt and a registration shift of color images
formed thereon, an image forming apparatus having the intermediate
transfer belt, and an image forming method using the intermediate
transfer belt.
[0019] Accordingly, an object of the present invention is to
provide an endless intermediate transfer belt for use in forming
electrophotographic color images which can prevent slackening of
the intermediate transfer belt and a registration shift of images
formed thereon to improve the quality of color images formed by
using a tandem engine system. In addition, the present invention
has another object of providing an image forming apparatus having
the intermediate transfer belt mentioned above and an image forming
method using the intermediate transfer belt mentioned above.
[0020] Briefly these objects and other objects of the present
invention as hereinafter will become more readily apparent and can
be attained by an intermediate transfer belt including a drawn
component not greater than 98% of which is imidized. The
intermediate transfer belt is used in an electrophotographic image
forming process in which a toner image of each color formed on
plurality of image bearing members is overlappingly transferred to
the intermediate transfer belt to form a multi-colored image
thereon and then the multi-colored image is transferred to a
transfer material.
[0021] As another aspect of the present invention, an intermediate
transfer belt is provided which is prepared by a process including
the steps of transferring a mixture of a solution of a
thermosetting resin and a particulate electroconductive material
into a centrifugal mold, rotating the centrifugal mold to form a
film attached to an inner periphery thereof, thermally imidizing
the film to have an imidization ratio not greater than 98%; and
drawing the film to entirely harden the film and to form the
intermediate transfer belt. The intermediate transfer belt is used
in an electrophotographic image forming process in which a toner
image of each color formed on plurality of image bearing members is
overlappingly transferred to the intermediate transfer belt to form
a multi-colored image thereon, which is transferred to a transfer
material.
[0022] It is preferred that the drawing is performed in the
circumferential direction of the film.
[0023] It is still further preferred that the drawing is performed
in the circumferential direction of the film to a drawing
magnification power of 1.01 to 1.10.
[0024] It is still further preferred that the film is drawn by a
drawing base at a constant drawing speed in the circumferential
direction thereof while the film is rotated.
[0025] It is still further preferred that the drawing is performed
in the axial direction of the film.
[0026] It is still further preferred that the drawing is performed
in the axial direction of the film to a drawing magnification power
of 1.01 to 1.20.
[0027] It is still further preferred that the drawing is performed
in the circumferential direction and the axial direction of the
film.
[0028] It is still further preferred that the drawing is performed
in the circumferential direction and the axial direction of the
film to a drawing magnification power of from 1.01 to 1.15.
[0029] It is still further preferred that, while the film is
rotated, the film is drawn by a chucking portion of a drawing
device in a direction different from the rotation direction of the
film.
[0030] It is still further preferred that the mixture for forming
the endless intermediate transfer belt is a polyamic acid
solution.
[0031] It is still further preferred that the thermal imidizing is
performed at a temperature range of from 25 to 220.degree. C.
[0032] It is still further preferred that the drawing is performed
in a temperature range of from 25 to 220.degree. C.
[0033] It is still further preferred that the intermediate transfer
belt has an elasticity modulus of from 7,000 to 15,000 MPa.
[0034] It is still further preferred that the intermediate transfer
belt has a surface resistivity .rho.s of from 1.0.times.10.sup.10
to 1.0.times.10.sup.13.OMEGA..
[0035] It is still further preferred that the intermediate transfer
belt has a volume resistivity .rho.v of from 1.0.times.10.sup.5 to
1.0.times.10.sup.11 .OMEGA.cm.
[0036] As another aspect of the present invention, an image forming
apparatus is provided which includes the following: an image
bearing member configured to bear a latent electrostatic image; a
charging device configured to charge a surface of the image bearing
member; a developing device configured to develop the latent
electrostatic image with a toner; a cleaning device configured to
remove residual toner on the image bearing member; an intermediate
transfer belt configured to transfer the toner image on the image
bearing member to form an image thereon and to transfer the toner
image onto a recording material, the intermediate transfer belt, a
fixing device configured to fix the toner image on the recording
material. The intermediate transfer belt is prepared by the
following: transferring a mixture of a solution of a thermosetting
resin and a particulate electroconductive material into a
centrifugal mold; rotating the centrifugal mold to form a film
attached to an inner periphery thereof; thermally imidizing the
film to have an imidization ratio not greater than 98%; and drawing
the film to entirely harden the film and to form the intermediate
transfer belt.
[0037] As another aspect of the present invention, an image forming
method is provided which includes the following steps; irradiating
an image bearing member with a laser beam to form a latent
electrostatic image on the image bearing member; developing the
latent electrostatic image with a toner; removing residual toner on
the image bearing member; first transferring the toner image to an
intermediate transfer belt; second transferring the toner image on
the intermediate transfer belt to a recording material; and fixing
the toner image on the intermediate transfer belt upon application
of heat and pressure. The intermediate transfer belt is prepared by
the following process: transferring a mixture of a solution of a
thermosetting resin and a particulate electroconductive material
into a centrifugal mold; rotating the centrifugal mold to form a
film attached to an inner periphery thereof; thermally imidizing
the film to have an imidization ratio not greater than 98%; and
drawing the film to entirely harden the film and to form the
intermediate transfer belt.
[0038] As another aspect of the present invention, a method of
manufacturing an intermediate transfer belt is provided which
includes the following steps: transferring a mixture of a solution
of a thermosetting resin and a particulate electroconductive
material into a centrifugal mold; rotating the centrifugal mold to
form a film attached to an inner periphery thereof; thermally
imidizing the film to have an imidization ratio not greater than
98%; and drawing the film to entirely harden the film and to form
the intermediate transfer belt. The intermediate transfer belt is
used in an electrophotographic image forming process in which a
toner image of each color formed on plurality of image bearing
members is overlappingly transferred to the intermediate transfer
belt to form a multi-colored image thereon, which is transferred to
a transfer material.
[0039] These and other objects, features and advantages of the
present invention will become apparent upon consideration of the
following description of the preferred embodiments of the present
invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] Various other objects, features and attendant advantages of
the present invention will be more fully appreciated as the same
becomes better understood from the detailed description when
considered in connection with the accompanying drawings in which
like reference characters designate like corresponding parts
throughout and wherein:
[0041] FIG. 1 is a schematic perspective diagram illustrating an
example of a method of drawing the endless intermediate transfer
belt of the present invention for use in electrophotography in its
circumferential direction;
[0042] FIG. 2 is a perspective diagram illustrating an example of
the drawing device which draws the intermediate transfer belt of
the present invention having an endless form for use in
electrophotography in its circumferential direction;
[0043] FIG. 3 is a schematic perspective diagram illustrating an
example of a method of drawing the endless intermediate transfer
belt of the present invention for use in electrophotography in its
axial direction;
[0044] FIG. 4 is a perspective diagram illustrating an example of
the drawing device which draws the endless intermediate transfer
belt of the present invention for use in electrophotography in its
axial direction;
[0045] FIGS. 5A to 5F are diagrams illustrating a preparation
method of the endless intermediate transfer belt of the present
invention for use in electrophotography;
[0046] FIG. 6A is a plan view illustrating an electrode for
measuring;
[0047] FIG. 6B is a longitudinal section illustrating a surrounding
of an electrode portion;
[0048] FIG. 7 is a schematic lateral view illustrating an example
of the image forming apparatus using the endless intermediate
transfer belt of the present invention for use in
electrophotography; and
[0049] FIG. 8 is a diagram illustrating an example of an image
printed by the image forming apparatus using the endless
intermediate transfer belt of the present invention for use in
electrophotography.
DETAILED DESCRIPTION OF THE INVENTION
[0050] The present invention will be described below in detail with
reference to several embodiments and accompanying drawings, wherein
like reference numerals designate identical or corresponding parts
throughout the several views.
[0051] Polymers for use in an intermediate transfer belt for use in
electrophotography process performed by a color photocopier are
required to have good flame resistance, strength and electric
stability. Polyimide resins are excellent materials in terms of
strength, thermal resistance and friction chargeability. In
embodiments of the present invention, an endless intermediate
transfer belt for use in electrophotography may be manufactured
using polyimide resins.
[0052] Polyimide resins are synthesized from its precursor, i.e.,
polyamide acids. Polyamide acids have a characteristic in that a
polyamide acid change to a polyimide upon application of heat or by
a catalyst through imide ring closure and is dissolved in a
particular solvent.
[0053] In the present invention, various kinds of electroconductive
particulate materials or particulate materials having a low
electric resistance are used as materials to control the resistance
of the intermediate transfer belt. For example, metal powder and
metal suboxide powder of tin oxide and indium oxide, and preferably
carbon black powder can be used. Also these can be used in
combination and nonvolatile liquid having a low electric resistance
can be also mixed therewith. In one embodiment, carbon is dispersed
in a polyamide acid solution (hereinafter referred to as mixed
polyamic acid solution).
[0054] Carbon can be typified into acetylene black, oil furnace
black, thermal black, channel black, etc. Acetylene black is
obtained by thermal decomposition in a furnace where acetylene has
been preliminary heated. Oil furnace black can be prepared by
blowing oil into a furnace to perform incomplete combustion by
controlling the amount of air, and subsequent to cooling down,
capturing the carbon with a cyclone, etc. Thermal black can be
obtained by alternately heat reserving and heat decomposing natural
gas in a regenerative heater in a temperature range of from 200 to
1,700.degree. C. Channel black can be obtained by blowing natural
gas flame onto a long strip iron plate and attaching carbon
thereto. Materials having a specific gravity close to that of
polyamic acid and not much different from that of a resin may be
used as electroconductive materials.
[0055] There is no specific limitation to the selection of carbons
for use in the endless intermediate transfer belt for use in
forming electrophotographic images. However, when an intermediate
transfer belt having a high surface resistance is desired, carbon
providing a high electroconductivity when added in a small amount,
such as acetylene black (manufactured by Denki Kagaku Kogyo
Kabushiki Kaisha) and ketchen black EC (manufactured by Lion
Corporation), may be avoided.
[0056] Carbon may be dispersed by supersonic dispersion methods,
ballmill dispersion methods, sandmill dispersion methods, etc.
Typically, instead of directly dispersing carbon in a polyamide
acid solution, carbon is dispersed in N-methyl pyrrolidone
(hereinafter referred to as NMP) and the resultant carbon
dispersion solution is mixed with a polyamide acid solution. A
carbon solution in which carbon having a particular particle
diameter is dispersed is thus prepared.
[0057] FIG. 5 illustrates a manufacturing method of an endless
intermediate transfer belt of the present invention for use in
forming electrophotographic images. As illustrated in FIGS. 5A and
5B, a predetermined amount of a polyamide acid solution 31, which
is a mixture of a polyamide acid solution 29 and a carbon
dispersion solution 30, is first poured into a centrifugal mold.
The mixture is poured while the centrifugal mold is slowly rotated.
When pouring the mixture is complete, the rotation speed of the
centrifugal mold is gradually increased to a predetermined rotation
speed. The centrifugal mold is rotated at the predetermined speed
for a predetermined period of time.
[0058] In one embodiment, as illustrated in FIG. 5C, the polyamide
acid mixture solution 31 is poured into a cylinder mold 33 serving
as a centrifugal mold by way of a pouring tube 32. The cylinder
mold 33 has an inner diameter of 100 mm and a length of 250 mm. The
cylinder mold is rotated at 10 rpm while the polyamide acid mixture
solution 31 is poured until the mixture is completely poured.
[0059] Next, as illustrated in FIG. 5D, when pouring is finished,
the rate of rotation of the cylinder mold 33 is increased to 400
rpm. Thereafter, the cylinder mold 33 is gradually heated to
100.degree. C. by a heater having a sheet form 34. The temperature
is kept near 100.degree. C. to volatilize the solvent from a
polyamide acid mixture solution layer 31a, which is applied to the
inner circumference of the cylinder mold 33. In one embodiment, the
cylinder mold 33 is not heated by a heater having a sheet form 34,
and can be heated by a heating furnace, etc.
[0060] The organic solvent evaporates while the centrifugal mold is
rotated so that the polyamide acid is increasingly solidified,
resulting in formation of a film having a cylindrical form.
[0061] In one embodiment, two-axis roll drawing is performed in the
temperature range of from 25 to 220.degree. C. in which polyamide
acid solution is changed to polyimide through imide ring closure
(i.e. partially imidization). When this two-axis-roll drawing is
performed at too high a temperature, solidification occurs along
with partial imidization, which is not suitable for drawing. In
contrast, when this two-axis-roll drawing is performed at too low a
temperature, the obtained film does not sufficiently support itself
so that it is impossible to draw the obtained film.
[0062] In one embodiment, the drying temperature range for drawing
is from 80 to 170.degree. C. When the temperature is too high, the
surface which is partially imidized is not uniform. When the
temperature is too low, the film to be drawn does not have enough
strength to support itself.
[0063] Next, the device and the method for use in drawing are
concretely described.
[0064] After sufficiently volatilizing the solvent from the
polyamide acid mixture solution layer 31a, the belt 31b finished
with primary drying is removed from the cylinder mold 33. The film
finished with the primary drying is a partially imidized film
(i.e., in a partially solidified state) and also is in a rubber
state in which the solvent composition is still contained in a
large amount. The film in this rubber state can be subject to
swelling treatment using a solvent if necessary.
[0065] Next, drawing in the circumferential direction is performed.
The belt 31b removed from the cylinder mold 33 is set on a drawing
device for use in drawing in the circumferential direction. The
base of the drawing device is moved in the circumferential
direction at a particular drawing speed until the belt is drawn
while the belt is rotated.
[0066] In one embodiment, the drawing magnification power is from
1.01 to 1.10. When the drawing magnification power is too large,
the surface property of the belt deteriorates. When the drawing
magnification power is too small, the value of the elasticity
modulus is not improved by drawing.
[0067] While drawing, the partially imidized belt is rotated at a
constant speed by a rotation roller. The drawing device base is
moved at a speed as low as possible. The diameter of the rotation
roller contained in the drawing device may be as large as or less
than the diameter of a roller to which the intermediate transfer
belt is installed in an image forming apparatus.
[0068] The belt can be drawn to the axial direction. A film which
has finished with primary drying and achieved a partially imidized
state is set on a device for use in drawing in the axial direction
to a drawing magnification of from 1.01 to 1.20 as illustrated in
FIG. 4. In addition a partially imidized film which is finished
with the circumferential direction drawing can be also set on a
device for use in drawing in the axial direction to a drawing
magnification of from 1.01 to 1.15.
[0069] The partially imidized belt is drawn in the axial direction
by a chucking portion remodeled based on a manually-driven drawing
device while the partially imidized belt is rotated at a constant
speed by a rotation roller.
[0070] The method of drawing the belt is not limited to the method
mentioned above. The belt can be drawn by other methods such as a
tender method and a tube method. The belt can be drawn in a
direction different from the circumferential direction by a tender.
In one embodiment, the drawing temperature range for drawing is
from 25 to 220.degree. C. This drawing temperature can be
arbitrarily set depending on conditions.
[0071] In one embodiment, the diameter of the rotation roller
contained in the drawing device is as large as or less than the
diameter of a roller to which the intermediate transfer belt is
installed in an image forming apparatus. It is possible to control
the thickness of the belt by controlling the outer diameters of the
center portion and the end portion of the roller. Thereby, it is
possible to prevent deviation of the thicknesses of the center
portion and the end portion after drawing.
[0072] The physicality of the film can be improved by the drawing
treatment mentioned above. The reason why the mechanical strength
of the film is improved is that after sufficiently volatilizing the
solvent from the polyamide acid mixture solution layer 31a (i.e.,
after primary drying is finished), the arrangement of polyamic acid
molecules is aligned in one direction by drawing, resulting in
amelioration of the mechanical strength of the film.
[0073] The mechanical strength of a film can be controlled by
uniformly aligning the molecular orientation. Namely, the strength
of an endless intermediate transfer belt for use in forming
electrophotographic images can be controlled by controlling the
drawing magnification power and the drawing direction.
[0074] After the drawing treatment mentioned above, the polyamide
acid belt 31b is set on an imidization mold 37 as illustrated in
FIG. 5E. Next, as illustrated in FIG. 5F, the polyamide acid belt
31b set on the imidization mold 37 is set in a furnace 38, the
temperature of which is maintained to be 300.degree. C. and heated
for 20 minutes to obtain a wholly aromatic polyimide belt. The
polyamide acid film which has finished with drawing treatment may
be further heated for imide ring closure to further improve its
characteristics such as thermal resistance, chemical resistance and
mechanical strength. This imide ring closure is performed by
heating and the solvent remaining in the polyamide acid film is
thoroughly evaporated and removed.
[0075] The imide ring closure can be performed by heating the film
at the temperature mentioned above for the time mentioned above
while still rotating the film after the partial imidization
treatment and two-axis roll treatment. Also, the imide ring closure
can be performed by removing the polyamic acid film from the
centrifugal mold, coating the film on a cylindrical imidization
mold prepared separately and entirely heating the film and the mold
by way of a heating means such as hot air.
[0076] The polyimide film thus obtained is suitably processed to a
variety of applications. As in the present invention, when the
polyimide film is used as an endless intermediate transfer belt for
use in the electrophotographic process performed by, for example, a
color photocopier, the film is severed to a required length and a
member to prevent twisting of the film is set on both open ends
thereof if necessary.
[0077] In addition, the range of the surface resistivity of the
obtained intermediate transfer belt is from 1.0.times.10.sup.10 to
1.0.times.10.sup.13.OMEGA.. When the surface resistivity is too
high, electric charges are present only on the surface of the
intermediate transfer belt and do not move inside the intermediate
transfer belt so that the electric field is weak. When the surface
resistivity is too low, the electric charges tend to flow in the
lateral direction. The range of the volume resistivity of the
obtained intermediate transfer belt is from 1.0.times.10.sup.5 to
1.0.times.10.sup.11 .OMEGA.cm. When the volume resistivity is too
high, electric charges are present only on the surface of the
intermediate transfer belt and do not move inside the intermediate
transfer belt so that the electric field is weak. When the volume
resistivity is too low, the electric charges tend to flow in the
lateral direction.
[0078] Having generally described embodiments of this invention,
further understanding can be obtained by reference to certain
specific examples which are provided herein for the purpose of
illustration only and are not intended to be limiting.
EXAMPLES
[0079] The present invention is further concretely described with
reference to examples below. The examples below are with regard to
belts formed of a polyimide but belts formed of other resin
materials can be also used.
[0080] FIG. 8 is a diagram illustrating color shifts of color
images. Color shift occurring when two line images are formed is
described as an example.
[0081] In the case of a two-line image in which four colors are
overlapped, unless the distances between the two lines for each
color are the same, a color shift occurs in the two-line image.
[0082] It is not likely that the distance between the two lines
formed on a transfer drum for each color varies since the two lines
are written on the transfer device for each color with the same
writing device.
[0083] When the surface speed of each image forming member 1a, 1b,
1c and 1d matches the surface speed of an intermediate transfer
belt 10 (shown in FIG. 7) at the transfer portion (i.e., when
writing and transferring are synchronized), the images are
transferred and overlapped on the intermediate transfer belt 10
from each image bearing member while the distances illustrated in
FIG. 8 are maintained as the same, resulting in no occurrence of
color shift (shown in FIG. 8(b)).
[0084] However, when the surface speed of each image forming member
1a, 1b, 1c and 1d does not match the surface speed of an
intermediate transfer belt 10 at the transfer portion, the line
distances on each image bearing member 1a, 1b, 1c and 1d vary when
the image is transferred onto the intermediate transfer belt 10.
Therefore, a color shift occurs as illustrated in FIG. 8(a).
Example 1
[0085] As illustrated in FIG. 5A, a base material 29 and a solution
30 were prepared. In the base material 29, a polyamide acid was
dissolved in NMP such that the amount of the polyamide acid was 20
weight %. In the solution 30, ASAHI #60H (N-658) (furnace black
manufactured by Asahi Carbon Co., Ltd.) was dispersed in NMP.
Several kinds of solution can be mixed in each of the base material
29 and the solution 30.
[0086] Next, as illustrated in FIG. 5B, the base material 29 was
mixed with the solution 30 in which ASAHI #60H (N-568) was
dispersed (hereinafter this mixture is referred to as a polyamide
acid mixture solution 31). The composition was that ASAHI #60
(N-258) was 22 phr (solid portion) based on the solution portion of
the polyimide.
[0087] Next, as illustrated in FIG. 5C, the polyamide acid mixture
solution 31 was poured to the cylinder mold 33 contained in a
centrifugal mold through a pouring tube 32. The cylinder mold had
an inner diameter of 124 mm and a length of 250 mm. When the
polyamide acid mixture solution 31 was poured, the cylinder mold 33
was rotated at 10 rpm and this rotation speed was not changed until
the pouring was finished.
[0088] When the pouring was finished, the rotation speed of the
cylinder mold 33 was increased up to 400 rpm as illustrated in FIG.
5D. Thereafter, while the cylinder mold 33 was gradually heated up
to 100.degree. C. by a heater having a sheet form 34 and the
temperature was kept near 100.degree. C. to volatilize the solvent
of the polyamide acid solution layer 31a coated on the inner
circumference of the cylinder mold 33.
[0089] Next, after sufficiently volatilizing the solvent of the
polyamide acid mixture solvent layer 31a, a polyamide acid belt
(i.e., a partially imidized belt) 31b was removed from the cylinder
mold 33, set on a drawing device of drawing the belt in the
circumferential direction indicated by arrow A in FIG. 2, and
heated at 120.degree. C. Thereafter the belt was heated at
220.degree. C.
[0090] Then, the base of the drawing device was moved at a constant
drawing speed to a predetermined drawing magnification power while
the partially-imidized belt was rotated. The predetermined drawing
magnification power was 1.05 in this case.
[0091] After the polyamide acid belt 31 was drawn in its
circumferential direction, the polyamide acid belt 31 was set on a
device by which the belt was drawn to its axial direction indicated
by arrow B in FIG. 4. The polyamide acid belt 31b was drawn to a
predetermined drawing magnification power by a chucking portion
remodeled based on a manually-driven drawing device while the
polyamide acid belt 31b was rotated by a rotation roller. In this
example, the polyamide acid belt 31b was repetitively drawn until
the drawing magnification power reached 1.07.
[0092] As illustrated in FIG. 5E, the polyamide acid belt 31b was
set on an imidization mold 37. The imidization mold 37 was then put
into a furnace 38 the temperature of which was maintained at
300.degree. C. (as illustrated in FIG. 5F), and heated for 20
minutes to obtain an intermediate transfer belt.
[0093] The elasticity modulus of the intermediate transfer belt
manufactured by the processes mentioned above was measured based on
JIS-K7127 using a Shimadzu AGS-50A measurement device. The
measuring result was that the elasticity moduli in the
circumferential direction and in the axial direction were 8,100 MPa
and 8,200 MPa, respectively.
[0094] The surface resistivity and volume resistivity of the
intermediate transfer belt were measured based on JIS-K6911 using a
ring electrode 21 and a pillar electrode 22, as illustrated in FIG.
6A. Based on JIS-K6911, the surface resistivity and the volume
resistivity were calculated by using the following formulae:
.rho.v=.pi.d.sup.2/4t.times.R.sub.v
.rho.s=.pi.(D+d)/(D-d).times.R.sub.s
[0095] In these formulae, .rho.v represents volume resistivity
(M.OMEGA.cm), .rho.s represents surface resistivity (M.OMEGA.), d
represents the outer diameter of the pillar electrode (cm), t
represents the thickness of the target to be measured, Rv
represents volume resistivity (M.OMEGA.), D represents the inner
diameter of the ring electrode on the surface, Rs represents the
surface resistivity (M.OMEGA.), and .pi. represents the ratio of
the circumference of a circle to the diameter of the circle.
[0096] As illustrated in FIG. 6B, the ring electrode 21 and the
pillar 22 were concentrically located on the measuring side of the
insulation board 24. The resistance between the ring electrode 21
and the pillar electrode 22 was defined as Rs. When measuring the
resistance, an earth electrode 23 was provided on the side opposite
to the side to be measured. The surface resistivity of the
intermediate transfer belt has a surface resistivity .rho.s of
6.02.times.10.sup.11.OMEGA. when the surface resistivity was
measured by this measuring method. The resistance between the
pillar electrode and its facing electrode was defined as Rv. The
volume resistivity .rho.v of the intermediate transfer belt was
9.03.times.10.sup.9 .OMEGA.cm when the surface resistivity was
measured by this measuring method.
[0097] Imidization ratio of the intermediate transfer belt was
determined based on the peak intensity ratio measured by a
transmission method using FT/IR (ATR) SpectrumGX device (PERKIN
ELMER).
(Imidization ratio)=(A1780/A1500)/(Aimd1780/Aimd1500).times.100
In the relationship mentioned above, A1780 represents the
absorption intensity based on 1780 cm.sup.-1 imide linkage peak of
a sample before heat treatment, A1500 represents the absorption
intensity based on 1500 cm.sup.-1 benzene ring peak of a sample
before heat treatment, Aimd 1780 represents the absorption
intensity based on 720 cm.sup.-1 imide linkage peak of a heat
treatment film before drawing, and Aimd 1500 represents the
absorption intensity based on 1500 cm.sup.-1 benzene ring peak of a
heat treatment film before drawing.
[0098] The imidization ratio measured by this method was 90%.
[0099] An image forming apparatus illustrated in FIG. 7 include the
following: photoreceptor drums (1a, 1b, 1c and 1d), which are
charged substances functioning as image bearing members; chargers
(2a, 2b, 2c and 2d) to charge the photoreceptor drums; an
irradiation portion (not shown) to irradiate the charged
photoreceptor drums to form images thereon; developing devices (3a,
3b, 3c and 3d) to develop the irradiated images on the irradiated
photoreceptor drums with a toner; an intermediate transfer belt 10
to receive the transfer of the toner images developed by the
developing devices; photoreceptor cleaners (4a, 4b, 4c and 4d) to
clean the photoreceptor drums; primary transfer rollers (5a, 5b, 5c
and 5d); an intermediate transfer belt driving roller 6; an
intermediate transfer belt pressing roller 7; an intermediate
transfer belt opposing roller 8; a transfer roller 9; a transfer
belt cleaner (not shown) to clean the intermediate transfer belt
10; and a fixing device (not shown) to fix the toner images
transferred onto a transfer material from the intermediate transfer
belt 10.
[0100] The developing devices mentioned above have a developing
device 3a for black color, a developing device 3b for cyan color, a
developing device 3c for magenta color and a developing device 3d
for yellow color.
[0101] When the line images illustrated in FIG. 8 were photocopied
by the image forming apparatus mentioned above, since there was no
speed difference among the photoreceptor drums, the registration
shift of each color image did not occur and clear and good images
were obtained.
Example 2
[0102] The intermediate transfer belt of Example 2 was obtained in
the same manner as in Example 1 except that, after volatilizing the
solution from the polyamide acid mixture solution layer 31a, the
polyamide acid belt (i.e., partially imidized belt) 31b was removed
from the cylinder mold 33 and set on a drawing device illustrated
in FIG. 2 and the temperature was set to 80.degree. C. Imidization
ratio was not greater than 90%.
[0103] The obtained intermediate transfer belt showed good
self-support property. The elasticity modulus of the intermediate
transfer belt was measured. The elasticity modulus in the
circumferential direction was 7,100 MPa and the elasticity modulus
in the axial direction was 7,500 MPa. The intermediate transfer
belt had a surface resistivity .rho.s of
5.12.times.10.sup.11.OMEGA. and a volume resistivity .rho.v of
8.12.times.10.sup.9 .OMEGA.cm.
[0104] When the line images illustrated in FIG. 8 were photocopied
using the image forming apparatus, since there was no speed
difference among the photoreceptor drums, the registration shift of
each color toner image did not occur and good, clear images were
obtained.
Example 3
[0105] The intermediate transfer belt of Example 3 was obtained in
the same manner as in Example 1 except that, after sufficiently
volatilizing the solution of the polyamide acid mixture solution
layer 31a, the polyamide acid belt (i.e., partially imidized belt)
31b was removed from the cylinder mold 33 and set on a drawing
device illustrated in FIG. 2 and the temperature was set to
60.degree. C. The imidization ratio was not greater than 90%.
[0106] Although it took a relatively long time in comparison with
Example 2, the obtained intermediate transfer belt showed good
self-support characteristics. The elasticity modulus of the
intermediate transfer belt was measured. The elasticity modulus in
the circumferential direction was 7,000 MPa and the elasticity
modulus in the axial direction was 7,200 MPa. The volume
resistivity ratio of the belt was measured. The intermediate
transfer belt had a surface resistivity .rho.s of
7.12.times.10.sup.11.OMEGA. and a volume resistivity .rho.v of
8.92.times.10.sup.9 .OMEGA.cm.
[0107] When the line images illustrated in FIG. 8 were photocopied
using the image forming apparatus, since there was no speed
difference among the photoreceptor drums, the registration shift of
each color image did not occur and clear and good images were
obtained.
Example 4
[0108] The intermediate transfer belt of Example 4 was obtained in
the same manner as in Example 1 except that the drawing in the
circumferential direction was not performed. The elasticity modulus
of the intermediate transfer belt was measured. The elasticity
modulus in the circumferential direction was 7,200 MPa and the
elasticity modulus in the axial direction was 7,400 MPa. The
intermediate transfer belt had a surface resistivity .rho.s of
6.12.times.10.sup.11.OMEGA. and a volume resistivity .rho.v of
9.12.times.10.sup.9 .OMEGA.cm.
[0109] When the line images illustrated in FIG. 8 were photocopied
using the image forming apparatus, since there was no speed
difference among the photoreceptor drums, the registration shift of
each color image did not occur and good, clear images were
obtained.
[0110] The intermediate transfer belt of Example 5 was obtained in
the same manner as in Example 1 except that the drawing in the
axial direction was not performed. The elasticity modulus of the
intermediate transfer belt was measured. The elasticity modulus in
the circumferential direction was 7,500 MPa and the elasticity
modulus in the axial direction was 7,300 MPa. The intermediate
transfer belt had a surface resistivity .rho.s of
6.17.times.10.sup.11.OMEGA. and a volume resistivity .rho.v of
9.17.times.10.sup.9 .OMEGA.cm.
[0111] When the line images illustrated in FIG. 8 were photocopied
using the image forming apparatus, since there was no speed
difference among the photoreceptor drums, the registration shift of
each color image did not occur and good, clear images were
obtained.
Comparative Example 1
[0112] The sample belt of Comparative Example 1 was obtained in the
same manner as in Example 1 except that, after pouring the
polyimide acid solution, the film was imidized without drawing the
film after drying the film up to 100.degree. C. The elasticity
modulus of the intermediate transfer belt was measured. The
elasticity modulus in the circumferential direction was 3,500 MPa
and the elasticity modulus in the axial direction was 3,200
MPa.
[0113] When the line images illustrated in FIG. 8 were photocopied
using the image forming apparatus, primary transfer of each color
toner image was performed well, but each color toner image did not
overlap well with the other toner color images. That is, each color
toner image was not properly transferred. Therefore, color shifts
occurred in the color image on a transfer paper, resulting in
failure to obtain good color images.
Comparative Example 2
[0114] The sample belt of Comparative Example 2 was obtained in the
same manner as in Example 1 except that, after pouring the
polyimide acid solution, the drying temperature was up not to
100.degree. C. but to 180.degree. C. The elasticity modulus of the
intermediate transfer belt was measured. The elasticity modulus in
the circumferential direction was 2,550 MPa and the elasticity
modulus in the axial direction was 2,210 MPa.
[0115] When the line images illustrated in FIG. 8 were photocopied
using the image forming apparatus, primary transfer of each color
toner image was performed well, but each color toner image did not
overlap well with the other color toner images. That is, each color
toner image was not properly transferred. Therefore, color shifts
occurred in the color image on a transfer paper, resulting in
failure to obtain good color images.
Comparative Example 3
[0116] After pouring the polyamide acid mixture solution, drying
was performed not up to 100.degree. C. but at 23.degree. C. The
result was that a film was not formed. That is, the strength
necessary to be drawn was not obtained, i.e., drawing was not
performed.
[0117] According to the endless intermediate transfer belt obtained
in Examples mentioned above, uniform belts in which carbon is well
dispersed can be obtained by using a polyamic acid mixture as the
base material. As a result, endless belts having an excellent
elasticity modulus can be obtained.
[0118] In addition, by drying the polyamide acid belt in the
temperature range of from 25.degree. C. to 220.degree. C. to
imidize the belt, the strength of the belt is strong enough to have
good self-supporting characteristics and an imidized film having a
uniform surface can be obtained.
[0119] Further, by drawing the polyamide acid belt in the
temperature range of from 25.degree. C. to 220.degree. C., the film
can be optimally drawn without solidifying during drawing.
[0120] Furthermore, by limiting the drawing magnification power of
the polyamide acid belt in the circumferential direction to from
1.01 to 1.10, a belt having an excellent elasticity modulus can be
obtained. When forming an image by using this belt, registration
shift of each color toner image does not occur and thus good, clear
images can be obtained.
[0121] Also, by limiting the drawing magnification power for the
polyamide acid belt in the axial direction to from 1.01 to 1.10, a
belt having an excellent elasticity modulus was obtained. When
forming an image by using this belt, registration shift of each
color toner image did not occur and thus good, clear images were
obtained.
[0122] In addition, as for Examples mentioned above, since the belt
has an elasticity modulus of from 7,000 to 15,000 MPa, an
intermediate transfer belt having a high elasticity modulus and an
excellent mechanical strength can be obtained. Good images without
a registration shift in each toner image can be obtained by such an
intermediate transfer belt.
[0123] Further, since such a belt has a surface resistivity .rho.s
of from 1.0.times.10.sup.10 to 1.0.times.10.sup.13.OMEGA., a good
electrophotographic process, i.e., a good transfer process
irrespective of the difference in Q/M of a toner, can be performed
and thus a good image can be obtained.
[0124] Furthermore, since such a belt has a volume resistivity
.rho.v of from 1.0.times.10.sup.5 to 1.0.times.10.sup.11.OMEGA., a
good electrophotographic process, i.e., a good transfer process
irrespective of the difference in Q/M of a toner, can be performed
and thus a good image can be obtained.
[0125] This document claims priority and contains subject matter
related to Japanese Patent Applications No. 2004-130354 and
2005-117179, filed on Apr. 26, 2004, and Apr. 14, 2005,
respectively, each of which are incorporated herein by
reference.
[0126] Having now fully described the invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made thereto without departing from the spirit
and scope of the invention as set forth therein.
* * * * *