U.S. patent application number 14/858660 was filed with the patent office on 2016-03-31 for heating element, process of producing heating element, heating device and image forming apparatus.
The applicant listed for this patent is Konica Minolta, Inc.. Invention is credited to Izumi MUKOYAMA, Junji UJIHARA.
Application Number | 20160091847 14/858660 |
Document ID | / |
Family ID | 55584270 |
Filed Date | 2016-03-31 |
United States Patent
Application |
20160091847 |
Kind Code |
A1 |
MUKOYAMA; Izumi ; et
al. |
March 31, 2016 |
HEATING ELEMENT, PROCESS OF PRODUCING HEATING ELEMENT, HEATING
DEVICE AND IMAGE FORMING APPARATUS
Abstract
An endless-belt shaped heating element made of a heat resisting
resin in which stainless-steel fibers subjected to annealing
treatment is dispersed is prepared. The heating element is adopted
as a heating belt of a fixing device of an image forming
apparatus.
Inventors: |
MUKOYAMA; Izumi; (Tokyo,
JP) ; UJIHARA; Junji; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Konica Minolta, Inc. |
Tokyo |
|
JP |
|
|
Family ID: |
55584270 |
Appl. No.: |
14/858660 |
Filed: |
September 18, 2015 |
Current U.S.
Class: |
399/329 ;
219/544; 219/549 |
Current CPC
Class: |
B29C 70/882 20130101;
B29K 2995/0016 20130101; B29C 70/20 20130101; B29L 2031/779
20130101; H05B 3/565 20130101; B29K 2105/08 20130101; G03G 15/2057
20130101; H05B 3/34 20130101; G03G 2215/2025 20130101 |
International
Class: |
G03G 15/20 20060101
G03G015/20; H05B 3/54 20060101 H05B003/54; H05B 3/44 20060101
H05B003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2014 |
JP |
2014-195014 |
Claims
1. A heating element comprising: an article comprising a
heat-resistant resin; and annealed stainless-steel fibers dispersed
in the article.
2. The heating element according to claim 1, wherein the heating
element satisfies Expression (1): {(L1-L0)/L0}.ltoreq.|0.0002| (1)
where L0 represents a size of the heating element in an initial
state, and L1 represents a size of the heating element which is
left under an environment of 200.degree. C. for one week.
3. The heating element according to claim 1, wherein the heating
element comprises 10 to 60 volume percent of the annealed
stainless-steel fibers.
4. The heating element according to claim 1, wherein the heating
element has a volume resistivity of 0.08.times.10.sup.-4 to
10.00.times.10.sup.-4 .OMEGA.cm.
5. The heating element according to claim 1, wherein the heating
element satisfies Expression (2):
1.ltoreq.(.rho.s1/.rho.s0).ltoreq.1.03 (2) where .rho.s0 represents
a resistance value (.OMEGA.) of the heating element in an initial
state, and psi represents a resistance value (.OMEGA.) of the
heating element which is left under an environment of 180.degree.
C. and 50 RH % for one week.
6. A heating device comprising: a heat generation member having a
sheet shape or an endless shape; a fixing roller disposed inside
the heat generation member, and configured to make contact with a
portion of an inner periphery surface of the heat generation
member; a pressure roller disposed outside the heat generation
member, and configured to press an outer peripheral surface of the
heat generation member toward the fixing roller; and a power supply
device configured to supply electricity to the heat generation
member, wherein the heat generation member is the heating element
according to claim 1 which has a sheet shape or an endless
shape.
7. An image forming apparatus comprising a fixing device for
applying heat and pressure to a recording medium to fix an unfixed
toner image formed on the recording medium by an
electrophotographic process on the recording medium, wherein the
fixing device is the heating device according to claim 6.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to and claims the benefit of
Japanese Patent Application No.2014-195014, filed on Sep. 25, 2014,
the disclosure of which including the specification, drawings and
abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a heating element, a
process of producing the heating element, a heating device and an
image forming apparatus.
[0004] 2. Description of Related Art
[0005] Thermal-film fixation type fixing devices are known as
fixing devices employed in image forming apparatuses such as
copiers and laser beam printers. Such fixing devices can shorten a
time from turn-on to copy start (warming-up time), and are
advantageous in terms of energy saving.
[0006] The fixing devices include a heating belt (heating element)
that generates heat in response to supply of electricity to the
heating belt. The heating belt is, for example, a seamless belt
including a film made of a heat-resistant resin such as polyimide
and a releasing layer made of fluororesin or the like that covers
the outer peripheral surface of the film. As such a heating belt, a
belt is known in which a belt-shaped substrate comprising the
heat-resistant resin contains conductive fibrous fillers that
satisfy a certain condition for the purpose of reducing the
resistance of the heating belt or increasing the stability of the
resistance (see, for example, Japanese Patent Application Laid-Open
Nos. 2012-8299 and 2013-25120).
[0007] The heating belt disclosed in Japanese Patent Application
Laid-Open No. 2012-8299 can sufficiently reduce the initial
resistance value thereof. In addition, the heating belt disclosed
in Japanese Patent Application Laid-Open No. 2013-25120 can provide
a high resistance stability in comparison with conventional belts.
However, the resistance value may increase with time even when
these heating belts are used, and utilization of the heating belts
in the fixing device of an image forming apparatus may result in
uneven fixing due to changes in resistance value in the heating
belt.
SUMMARY OF THE INVENTION
[0008] A first object of the present invention is to provide a
heating element whose resistance value is stable for a long period
of time.
[0009] A second object of the present invention is to provide an
image forming apparatus which can suppress uneven fixing.
[0010] At least to achieve the first object, the present invention
provides a heating element which includes: an article including a
heat-resistant resin; and annealed stainless-steel fibers dispersed
in the article.
[0011] At least to achieve the first object, the present invention
provides a process for producing a heating element which includes:
dispersing a stainless-steel fiber subjected to annealing treatment
in a heat-resistant resin or a precursor of the heat-resistant
resin; and producing a molded article of the heat-resistant resin
in which the stainless-steel fiber is dispersed.
[0012] At least to achieve the first object, the present invention
provides a heating device which includes: a heat generation member
having a sheet shape or an endless shape; a fixing roller disposed
inside the heat generation member, and configured to make contact
with a portion of an inner periphery surface of the heat generation
member; a pressure roller disposed outside the heat generation
member, and configured to press an outer peripheral surface of the
heat generation member toward the fixing roller; and a power supply
device configured to supply electricity to the heat generation
member, wherein the heat generation member is the heating element
according to claim 1 which has a sheet shape or an endless
shape.
[0013] To achieve at least one of the objects, an image forming
apparatus includes a fixing device configured to apply heat and
pressure to a recording medium to fix an unfixed toner image formed
on the recording medium by an electrophotographic process on the
recording medium, wherein the fixing device is the heating
device.
BRIEF DESCRIPTION OF DRAWINGS
[0014] The present invention will become more fully understood from
the detailed description given hereinbelow and the appended
drawings which are given by way of illustration only, and thus are
not intended as a definition of the limits of the present
invention, and wherein:
[0015] FIG. 1 schematically illustrates an example of a heating
element according to an embodiment of the present invention;
[0016] FIG. 2 schematically illustrates another example of the
heating element according to the embodiment of the present
invention;
[0017] FIGS. 3A and 3B are a front view and a side view,
respectively, each schematically illustrating a configuration of a
fixing device serving as an example of a heating device according
to the embodiment of the present invention; and
[0018] FIG. 4 schematically illustrates an exemplary configuration
of an image forming apparatus according to the embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] In the following, an embodiment of the present invention is
described.
[Heating Element]
[0020] A heating element according to the present embodiment
includes an article comprising a heat-resistant resin, and annealed
stainless-steel fibers dispersed in the article. The "heating
element" generates heat in response to electrification. The
configuration of the heating element (article) is not limited, and
for example, the heating element is a sheet, an endless belt, or
the like. The heating value of the heating element can be set by
the amount of electrification, the content of the annealed
stainless-steel fibers or the like, and can be increased by
increasing the amount of electrification, the content of the
annealed stainless-steel fibers or the like.
[0021] Examples of the heat-resistant resin include polyphenylene
sulfide, polyarylate, polysulfone, polyethersulfone,
polyetherimide, polyimide, polyamideimide and polyetheretherketone,
and these resins may be used alone or in combination. Among them,
polyimide is preferable in view of heat-resistance.
[0022] Polyimide can be obtained by proceeding
dehydration-cyclization (imidization) reaction of polyamic acid
that is a precursor of polyimide by heating at 200.degree. C. or
above or by using a catalyst. In view of this, when polyimide is
used as a heat-resistant resin, it is preferable that polyamic acid
and a stainless-steel fiber be mixed and thereafter heated at a
temperature of 200.degree. C. or above, for example. Polyamic acid
may be produced through a polycondensation reaction caused by
mixing and heating a solvent in which tetracarboxylic dianhydride
and a diamine compound are dissolved. Alternatively, a commercially
available polyamic acid may be used. Examples of the diamine
compound and tetra carboxylic dianhydride include the compounds
disclosed in Japanese Patent Application Laid-Open No. 2013-25120
(paragraphs 0123 to 0130).
[0023] The content of the heat-resistant resin in the heating
element is preferably 40 to 90 vol. % in view of formability and
the like.
[0024] One or more different annealed stainless steel fibers may be
used. Examples of the stainless steel of the stainless-steel fibers
include austenitic stainless steels, martensitic stainless steels,
ferritic stainless steels, austeniteferritic stainless steels, and
precipitation-hardening type stainless steels.
[0025] Examples of the austenitic stainless steels include SUS201,
SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS316 and SUS317.
Examples of the martensitic stainless steels include SUS403 and
SUS420. Examples of the ferritic stainless steels include SUS405,
SUS430 and SUS430LX. Examples of the austeniteferritic stainless
steels include SUS329J1. Examples of the precipitation-hardening
type stainless steels include SUS630. Among them, in view of
preventing oxidation, austenitic stainless steels and ferritic
stainless steels are preferable.
[0026] The ratio (l/L) of the minor axis (fiber sectional size; l)
to the major axis (fiber length; L) of the stainless-steel fibers
is 0.25 or smaller, for example. More preferably, the ratio 1/L is
0.025 to 0.25. Preferably, major axis L of the stainless-steel
fibers is 5 to 1000 .mu.m, more preferably, 10 to 200 .mu.m.
Preferably, minor axis 1 of the stainless-steel fibers is 0.5 to 30
.mu.m, more preferably, 1 to 10 .mu.m. It is to be noted that the
"fiber sectional size" means the major axis of the fiber as viewed
in cross section, and when the fiber has a circular shape as viewed
in cross section, the "fiber sectional size" is the diameter of the
circular shape.
[0027] The major axis and the minor axis of the stainless-steel
fibers are each an average value of the values that are measured
from an image such as a microphotograph. For example, the major
axis and the minor axis are measured in the following manner.
Specifically, first, the stainless-steel fibers are imaged at
.times.500 magnification by scanning-electron microphotography, and
an image thus obtained is taken into a scanner. Then the major axes
and the minor axes of 500 samples of the stainless-steel fibers
extracted from image data obtained by the manner are measured to
calculate the average value thereof.
[0028] The stainless-steel fibers may be produced stainless-steel
fibers, or commercially available stainless-steel fibers. For
example, the stainless-steel fibers are produced by publicly known
manufacturing methods. The stainless-steel fibers are produced in
the following manner. Specifically, a stainless steel is pulled out
from nozzles into a fibrous form, and then further extended and/or
heated as necessary. Thus, stainless-steel fibers having a desired
minor axis are produced, and then the fibers are cut into a desired
length.
[0029] The annealed stainless-steel fibers are stainless-steel
fibers that have been subjected to annealing treatment. "Annealing
treatment" is thermal treatment for removing internal strain of the
stainless-steel fibers resulting from processing and hardening.
With the annealing treatment, the texture of each of the
stainless-steel fibers is hardened, and the ductility of each of
the stainless-steel fibers is improved. During the annealing
treatment, for example, the stainless-steel fibers are heated for 4
to 10 hours under a nitrogen atmosphere such that the
stainless-steel fibers have a temperature (treatment temperature)
of 500 to 600.degree. C. When the treatment temperature is lower
than 500.degree. C., the internal strain may not be sufficiently
removed, and when the treatment temperature is higher than
600.degree. C., a passivation film, which will be described later,
on the surface of each of the stainless-steel fibers may be
destroyed.
[0030] The annealed stainless-steel fibers can be distinguished by
detecting characteristic changes caused by annealing. For example,
when a stainless-steel fiber is subjected to annealing, the lattice
defects of the metal texture of the stainless-steel fiber are
reduced, recrystallization is caused, and the texture is
uniformized, and as a result, the internal strain is substantially
removed, thus substantially eliminating the internal stress
(residual stress). This change in the stainless-steel fiber caused
by annealing is irreversible. Therefore, it is possible to
determine whether stainless-steel fibers dispersed in the article
of the heat-resistant resin are the annealed stainless-steel
fibers, by observing the texture of the stainless-steel fibers with
a metal microscope, or by observing their uniformity and
characteristic changes resulting from annealing in cross section,
or, by observing changes of the texture before and after the
annealing treatment of a sample of the stainless-steel fiber in the
heating element, for example.
[0031] The stainless-steel fibers may further include a coating.
Preferably, the coating is an oxidation-preventing coating that
prevents oxidation. For example, in view of providing the heating
element with a stable resistance at high temperatures, the coating
is preferably a film comprising an oxide of at least one of Cr, Mo,
Cu, and Si, or a composite oxide of Cr, Mo, Cu, and Si. More
preferably, the coating is a chromium oxide coating. While the
oxidation-preventing coating may cover substantially the entire
stainless-steel fiber or a part of the stainless-steel fiber, the
oxidation-preventing coating preferably covers substantially the
entire stainless-steel fiber.
[0032] The oxidation-preventing coating can be produced by a method
(1) in which the stainless-steel fibers are immersed in a solution
of a material of the oxidation-preventing coating; a method (2) in
which the stainless-steel fibers are heated at low temperatures in
oxygen or clean air; or a method (3) in which the stainless-steel
fibers are anode-polarized in a solution of an oxidant. In view of
uniformity of the resultant oxidation-preventing coating, the
method (1) is preferable.
[0033] The material of the oxidation-preventing coating is a
commonly-used oxidant, for example, and examples of such a material
include nitric acid, sulfuric acid, phosphoric acid, chromic acid
and dichromic acid. The method (1) can produce a coating comprising
various oxides (composite oxide) of Cr, Ni, Ti, Mo, Al, Si and the
like.
[0034] In view of providing the heating element with an appropriate
strength, toughness, conductivity and the like, the content of the
annealed stainless-steel fibers in the heating element is
preferably 10 to 60 volume %, more preferably 15 to 45 volume
%.
[0035] The heating element may further include other components in
addition to the heat-resistant resin and the annealed
stainless-steel fibers as long as the effect of the present
embodiment can be achieved. Examples of the other components
include conductive materials other than the annealed
stainless-steel fiber dispersed in the article of the
heat-resistant resin, electrodes, and other layers such as a
releasing layer.
[0036] The conductive materials may be used alone or in
combination. Examples of the conductive material include pure
metals such as gold, silver, iron, and aluminum, alloys such as
stainless steel (SUS) and Nichrome, and non-metals such as carbon
and graphite. The form of the conductive material is not limited,
and for example, the conductive material may be provided in a form
of spherical powder, unshaped powder, flat powder or fiber.
[0037] As the electrode, two or more electrodes are disposed in the
heating element. In view of efficiently supplying electricity for
desired heat generation, a pair of electrodes is disposed at
opposite end portions (both end edges) of the heating element.
Examples of the electrode include a metal thin plate, a ring formed
of a rounded metal thin plate, and a solidified material of a
conductive paste. The electrode formed of a metal thin plate is
bonded on the surface of the heating element with a conductive
adhesive agent for example. Examples of the electrode material
include iron, nickel, and stainless steels such as SUS430. Examples
of the conductive adhesive agent include a composition containing a
bonding preform such as epoxy resin and the above-described
conductive material, and silane coupling agent. Example of the
silane coupling agent includes alkylaminotrialkoxysilane.
[0038] Examples of the other layers include a releasing layer, an
elastic layer and a reinforcement layer. The releasing layer is a
layer having releasability, which is disposed on the surface of the
article of the heating element. Examples of the material of the
releasing layer include polyethylene, polypropylene, polystyrene,
polyisobutylene, polyester, polyurethane, polyamide, polyimide,
polyamide imide, alcohol-soluble nylon, polycarbonate, polyarylate,
phenol, polyoxymethylene, polyetheretherketone, polyphosphazene,
polysulfone, polyether sulfide, polyphenylene oxide, polyphenylene
ether, polyparabanic acid, polyallylphenol, fluororesin, polyurea,
ionomer, silicone, and mixture or copolymer thereof. The releasing
layer has a thickness of 5 to 20 .mu.m, for example.
[0039] The elastic layer is a layer having elasticity, and is
disposed between the article and the releasing layer for example.
Examples of the material of the elastic layer include silicone
rubber, thermoplastic elastomer and rubber materials. In view of
sufficiently ensuring thermal conductivity and elasticity, the
thickness of the elastic layer is set to 5 to 300 .mu.m, for
example.
[0040] The reinforcement layer is a layer intended to increase the
mechanical strength of the heating element, and is disposed on the
surface opposite to the releasing layer and the elastic layer in
the article. The reinforcement layer may be formed of the
above-described heat-resistant resin, and may have any
thickness.
[0041] The heating element has a configuration in which the
annealed stainless-steel fibers are dispersed in the article of the
heat-resistant resin, and thus the heating element can provide
excellent dimensional stability under high temperature
environments. The dimensional stability is appropriately set in
accordance with the use of the heating element. Preferably, the
heating element satisfies Expression (1) in view of limiting uneven
fixing of a formed image in the case where the heating element is
used as the heating belt of a fixing device of an
electrophotographic image forming apparatus, for example:
{(L1-L0)/L0}.ltoreq.|0.0002| (1)
[0042] where L0 represents the size of the heating element in the
initial state and L1 represents the size of the heating element
left at a temperature of 200.degree. C. for one week.
[0043] When the absolute value of the {(L1-L0)/L0} is greater than
0.0002, visually-recognizable uneven fixing may occur in an image
such as a solid image. The absolute value of the {(L1-L0)/L0} can
be set to 0.0002 or smaller by sufficiently subjecting the
stainless-steel fibers to annealing treatment under the
above-described condition, for example.
[0044] The heating value of the heating element may be
appropriately set in accordance with its use, and in view of this,
its resistance value may be appropriately set (in further
consideration of the amount of electrification in the use, for
example). For example, the heating element preferably has a volume
resistivity of 0.08.times.10.sup.-4 to 10.00.times.10.sup.-4
.OMEGA.cm, in view of ensuring efficient heat generation of the
heating belt. The volume resistivity is determined from, in the
case where a current is caused to flow through a portion between
two electrodes disposed in the heating element, the cross-sectional
area of the portion, the amount of the current, and the potential
difference between the two electrodes.
[0045] In addition, the heating element is excellent in dimensional
stability at high temperatures, and is therefore excellent in
stability of the resistivity at high temperatures. The stability of
the resistivity is appropriately set in accordance with the use of
the heating element. Preferably, the heating element satisfies
Expression (2) in view of limiting the uneven fixing, for
example:
1.ltoreq.(.rho.s1/.rho.s0).ltoreq.1.03 (2)
[0046] where .rho.s0 represents the resistance value (.OMEGA.) of
the heating element in the initial state, and .rho.s1 represents
the resistance value (.OMEGA.) of the heating element left under an
environment of 180.degree. C. and 50 RH % for one week.
[0047] When the ratio .rho.s1/.rho.s0 falls outside the range,
visually-recognizable uneven fixing may occur in a solid image. The
ratio .rho.s1/.rho.s0 can be adjusted to fall within the range by
sufficiently subjecting the stainless-steel fibers to annealing
treatment under the above-described condition, for example.
[0048] Except that the annealed stainless-steel fibers are used as
a conductive material, the heating element may be produced using
typical methods for producing the heating belt. For example, the
heating element may be produced by a method including a step of
dispersing the annealed stainless-steel fibers in the
heat-resistant resin or their precursor, and a step of producing a
molded article of the heat-resistant resin in which the annealed
stainless-steel fibers are dispersed. The molded article of the
heat-resistant resin may be produced by deposition (drying) of the
heat-resistant resin from the solution, or production of a
heat-resistant resin through the reaction of the precursor, or
both.
[0049] An example of the heating element is illustrated in FIG.
1.
[0050] As illustrated in FIG. 1, heating element 10 includes heat
generation layer 12 and electrodes 14. Heat generation layer 12 is
a polyimide film containing the annealed stainless-steel fibers.
Heat generation layer 12 has an endless-belt shape. Each electrode
14 is a ring composed of a metal thin plate. Each electrode 14 is
disposed on the outer peripheral surface of each end portion of
heat generation layer 12.
[0051] Heating element 10 is produced by the following method.
First, a varnish of polyamic acid containing the annealed
stainless-steel fibers is applied on the surface of a base (not
illustrated) to produce a coating film of the varnish, and this
coating film is dried and solidified. Next, the coating film is
thermally cured (imidized) in a heating furnace having a
temperature of 350 to 450.degree. C. to obtain heat generation
layer 12. Next, a conductive adhesive agent is applied at both ends
of heat generation layer 12, and rings each composed of a metal
thin plate are fitted and bonded on respective end portions of heat
generation layer 12 to obtain electrodes 14.
[0052] Another example of the heating element is illustrated in
FIG. 2.
[0053] As illustrated in FIG. 2, heating element 20 includes, in
addition to heat generation layer 12 and electrode 14, elastic
layer 16 disposed on the outer peripheral surface of heat
generation layer 12, and releasing layer 18 disposed on the outer
peripheral surface of elastic layer 16. As described above, elastic
layer 16 is a silicone rubber layer, for example. Releasing layer
18 is a fluororesin layer, for example.
[0054] Heating element 20 is produced by applying a coating
material of the silicone rubber material on the surface of heat
generation layer 12, housing heat generation layer 12 in a
fluororesin tube serving as releasing layer 18, and then curing the
coating material to produce a silicone rubber layer (elastic layer
16) that bonds heat generation layer 12 and the tube together. The
tube serves as releasing layer 18 disposed on elastic layer 16.
[0055] The heating element has a good dimensional stability, and
the resistance value of the heating element is stabilized for a
long period. The reasons for this are considered below.
[0056] In general, when a load such as a thermal load is applied to
a heating element, the resistance value of the heating element may
be changed because of dimensional change of the heating element due
to heat. However, normally, dimensional changes due to the
heat-resistant resin are not caused at a temperature of the heating
element in operation. For this reason, it can be said that the
dimensional change of the heating element is caused by deformation
of the stainless-steel fibers by a temporal thermal load.
[0057] Specifically, in general, when processing such as cutting is
performed on a metal, stress caused by the processing remains in
the metal as strain. Such a stress is released by heating. A
temperature environment of approximately 200.degree. C. is required
for a fixation process of an electrophotographic process, and when
the heating element is applied on the fixation process, the
stainless-steel fibers in which the stress remains are inevitably
deformed in the article of the heat-resistant resin at the
temperature. Consequently, the stainless-steel fibers in the
article are deformed, thus changing the distances between the
stainless-steel fibers in the article. Accordingly, it can be said
that the resistance value of the heating element is thus
changed.
[0058] In contrast, the heating element according to the present
embodiment contains an article of the heat-resistant resin, and the
annealed stainless-steel fibers dispersed in the article. That is,
the heating element contains stainless-steel fibers in which the
stress is removed before they are dispersed in the article. With
this configuration, even when the heating element generates heat
(for example, when it generates heat during the fixation process),
deformation of the stainless-steel fibers is not caused, and
therefore dimensional change of the heating element is not caused.
Thus, in the heating element, its resistance value is not changed
by heat generation.
[0059] As is obvious from the above descriptions, since the heating
element contains the article comprising the heat-resistant resin
and the annealed stainless-steel fibers dispersed in the
heat-resistant resin, the annealed stainless-steel fiber having
been subjected to the annealing treatment before the use of the
heating element, the resistance value of the heating element is
stabilized for a long period.
[0060] In addition, when the heating element satisfies the
above-mentioned Expression (1), the above-described uneven fixing
can be more effectively limited.
[0061] In addition, when the content of the annealed
stainless-steel fibers in the heating element is 10 to 60 volume %,
favorable mechanical and electrical properties of the heating
element can be more effectively achieved.
[0062] In addition, when the volume resistivity of the heating
element is 0.08.times.10.sup.-4 to 10.00.times.10.sup.-4 .OMEGA.m,
favorable heat generation as the heating belt can be more
effectively achieved.
[0063] In addition, when the heating element satisfies the
above-mentioned Expression (2), the uneven fixing can be more
effectively limited when it is used as the heating belt.
[0064] In addition, the process for producing the heating element
includes the steps of: dispersing the annealed stainless-steel
fibers in the heat-resistant resin or their precursor; and
producing a molded article of the heat-resistant resin in which the
annealed stainless-steel fibers are dispersed, and thus can provide
a heating element whose resistance value is stable for a long
period.
[Heating Device]
[0065] A heating device according to the present embodiment
includes: a sheet-shaped or endless-belt shaped heat generation
member; a fixing roller disposed inside the heat generation member
and configured to make contact with a part of the inner peripheral
surface of the heat generation member; a pressure roller disposed
outside the heat generation member and configured to press the
outer peripheral surface of the heat generation member toward the
fixing roller; and a power supply device configured to supply
electricity to the heat generation member. The heat generation
member is the sheet-shaped or endless-belt shaped heating
element.
[0066] The heating device includes a sheet-shaped or endless-belt
shaped heat generation section. The heating device is suitable for
surface-heating. Examples of the use of the heating device include
a fixing device of an electrophotographic image forming apparatus.
In the following, a fixing device as an example of the heating
device is described.
[0067] As illustrated in FIG. 3A and FIG. 3B, fixing device 70
includes fixing roller 72, heating belt 73, pressure roller 74 and
power supply device 75. Heating belt 73 has an endless-belt shape.
Heating belt 73 corresponds to the above-described heating element
10.
[0068] Fixing roller 72 includes mandrel 721 having a columnar
shape and resin layer 722 disposed on the peripheral surface of
mandrel 721. The outer diameter of resin layer 722 is smaller than
the internal diameter of heating belt 73. Fixing roller 72 is
disposed inside heating belt 73. Fixing roller 72 makes contact
with a portion of the inner peripheral surface of heating belt 73
in the circumferential direction of heating belt 73.
[0069] Pressure roller 74 includes mandrel 741 having a columnar
shape and resin layer 742 disposed on the peripheral surface of
mandrel 741. Pressure roller 74 is disposed to face fixing roller
72 with heating belt 73 therebetween. Pressure roller 74 is
disposed such that pressure roller 74 can press the outer
peripheral surface of heating belt 73 toward fixing roller 72.
Normally, pressure roller 74 is separated from heating belt 73.
[0070] Resin layers 722 and 742 are each a layer formed of publicly
known resin or a layer formed by foaming of publicly known resin.
Examples of the resins include silicone rubber and fluorine rubber.
At least one of resin layers 722 and 742 has elasticity that allows
the layer to be deformed when pressure roller 74 presses fixing
roller 72.
[0071] Pressure roller 74 may further include on resin layer 742 a
releasing layer having releasability to a recording medium such as
a plain sheet and toner. An example of the material of the
releasing layer includes fluororesin, and the releasing layer is
formed by a fluorinated tube, a fluorinated coating or the like.
The releasing layer has a thickness of 5 to 100 .mu.m, for
example.
[0072] Power supply device 75 includes alternating-current power
source 751, power supply member 752 configured to make contact with
electrode 14, and connecting wire 753 configured to connect
alternating-current power source 751 and power supply member 752
together. Power supply member 752 is biased toward electrode 14 by
an elastic member (not illustrated) such as a leaf spring and a
coil spring. Power supply member 752 may be a member that slides or
rotates with respect to electrode 14. Examples of power supply
member 752 include a carbon brush made of carbon material such as
graphite or copper-graphite composite material.
[0073] Heating belt 73, fixing roller 72 and pressure roller 74 are
rotatably provided. Each of heating belt 73, fixing roller 72 and
pressure roller 74 may be rotatably provided, or one of them may be
rotatably driven while the others following the rotation.
[0074] When pressure roller 74 presses the outer peripheral surface
of heating belt 73 toward fixing roller 72, a contacting part (nip
part) between heating belt 73 and pressure roller 74 is formed. The
nip part may be configured by depression of fixing roller 72, or by
depression of pressure roller 74.
[0075] Rotation of each roller and heating belt 73, supply of power
to heating belt 73 and formation of the nip part at the time of
fixation of a toner image may be performed as in publicly known
fixing devices. As long as the effect of the present embodiment can
be achieved, fixing device 70 may further include other
configurations of publicly known fixing devices.
[0076] Since heating belt 73 is heating element 10, dimensional
change of heating belt 73 can be suppressed even with the heat
generated by fixing device 70 in operation, and the resistance
value is not substantially changed. For example, when the heating
element is caused to generate heat by electrification under a
condition as a fixing device of an electrophotographic image
forming apparatus, the temporal resistance change rate (dynamic
resistance change rate described later) of the heating element can
be limited to 5% or lower.
[Image Forming Apparatus]
[0077] The image forming apparatus according to the present
embodiment includes a fixing device that fixes an unfixed toner
image, which is formed on a recording medium by an
electrophotographic process, onto the recording medium by heating
and pressing, and the fixing device is the above-mentioned heating
device. The image forming apparatus may have a configuration
similar to that of a publicly known image forming apparatus except
that the heating device is provided as the fixing device. In the
following, an example of the image forming apparatus according to
the present embodiment is described with reference to FIG. 4.
[0078] Image forming apparatus 50 includes an image forming
section, an intermediate transfer section, fixing device 70, an
image reading section and a recording medium conveyance
section.
[0079] The image forming section includes four image forming units
corresponding to colors of yellow, magenta, cyan and black. As
illustrated in FIG. 4, the image forming unit includes:
photoconductor drum 51; charging device 52 configured to charge
photoconductor drum 51; exposing device 53 configured to irradiate
charged photoconductor drum 51 with light to form an electrostatic
latent image; developing device 54 configured to supply toner to
photoconductor drum 51 on which an electrostatic latent image is
formed to form a toner image corresponding to the electrostatic
latent image; and cleaning device 55 configured to remove residual
toner on photoconductor drum 51.
[0080] Photoconductor drum 51 is a negative charge type organic
photoconductor having photoconductivity, for example. Charging
device 52 is a corona charger, for example. Charging device 52 may
be a contacting charger that brought a contact charging member such
as a charging roller, a charging brush, a charging blade into
contact with photoconductor drum 51 for charging. Exposing device
53 is composed of a semiconductor laser, for example. Developing
device 54 is a publicly known developing device in an
electrophotographic image forming apparatus, for example. The
"toner image" corresponds to a state where toner particles are
combined to form an image.
[0081] The intermediate transfer section includes a primary
transfer unit and a secondary transfer unit. The primary transfer
unit includes intermediate transfer belt 61, primary transfer
roller 62, backup roller 63, a plurality of support rollers 64 and
cleaning device 65. Intermediate transfer belt 61 is an endless
belt. Intermediate transfer belt 61 is installed in a stretched
state in a loop form by backup roller 63 and support rollers 64.
When at least one of backup roller 63 and support rollers 64 is
driven to rotate, intermediate transfer belt 61 travels along an
endless track in one direction, at a constant speed.
[0082] The secondary transfer unit includes secondary transfer belt
66, secondary transfer roller 67 and a plurality of support rollers
68. Secondary transfer belt 66 is also an endless belt. Secondary
transfer belt 66 is installed in a stretched state in a loop form
by secondary transfer roller 67 and support rollers 68.
[0083] For example, fixing device 70 is one illustrated in FIG. 3A
and FIG. 3B. Sheet S corresponds to a recording medium.
[0084] The image reading section includes sheet feeding device 81,
scanner 82, CCD sensor 83 and image processing section 84. The
recording medium conveyance section includes three sheet feed tray
units 91 and a plurality of registration roller pairs 92. Sheet
feed tray unit 91 stores therein sheets S (such as standard paper
and special paper) that are preliminarily discriminated and
separated based on their basis weights and sizes. Registration
roller pairs 92 are disposed in such a manner as to form a desired
conveyance path.
[0085] Image forming apparatus 50 forms an image as follows.
[0086] Scanner 82 optically scans and reads document D on the
contact glass that is sent from sheet feeding device 81. Light
reflected from document D is read by CCD sensor 83 to be converted
into input image data. The input image data is subjected to a
predetermined image processing at image processing section 84, and
sent to exposing device 53.
[0087] Meanwhile, photoconductor drum 51 rotates at a constant
circumferential velocity. Charging device 52 evenly and negatively
charges the surface of photoconductor drum 51. Exposing device 53
irradiates photoconductor drum 51 with laser beams corresponding to
input image data of respective color components. Thus, an
electrostatic latent image is formed on the surface of
photoconductor drum 51. Developing device 54 attaches toner on the
surface of photoconductor drum 51 to thereby visualize the
electrostatic latent image. Thus a toner image corresponding to the
electrostatic latent image is formed on the surface of
photoconductor drum 51. The toner image on the surface of
photoconductor drum 51 is transferred to intermediate transfer belt
61. The transfer residual toner of photoconductor drum 51 is
removed by cleaning device 55. Color toner images formed on
respective photoconductor drums 51 are sequentially transferred on
one another to intermediate transfer belt 61.
[0088] Meanwhile, secondary transfer belt 66 is pushed by secondary
transfer roller 67 toward backup roller 63, and thus brought into
pressure contact with intermediate transfer belt 61. In this
manner, a secondary transfer nip part is formed. In the meantime,
sheet S is conveyed to the secondary transfer nip part from sheet
feed tray unit 91 through registration roller pairs 92.
Registration roller pairs 92 correct skew of sheet S and adjust the
conveyance timing.
[0089] When sheet S is conveyed to the secondary transfer nip, a
transfer voltage is applied to secondary transfer roller 67, and
the toner image on intermediate transfer belt 61 is transferred to
sheet S. Sheet S on which the toner image has been transferred is
conveyed by secondary transfer belt 66 to fixing device 70. The
transfer residual toner on intermediate transfer belt 61 is removed
by cleaning device 65.
[0090] In fixing device 70, at the time of conveyance of sheet S,
pressure roller 74 is biased toward fixing roller 72 and heating
belt 73, and a fixing nip part is formed, for example. Heat and
pressure are applied on sheet S at the fixing nip part, for
example. Consequently, the toner image on sheet S is fixed on sheet
S. Sheet S on which the toner image is formed is ejected out of the
apparatus.
[0091] As described above, image forming apparatus 50 includes
fixing device 70. This prevents fixation problems such as uneven
fixing associated with dimensional change of heating belt 73 for a
long period of time in fixing device 70. Accordingly, image forming
apparatus 50 can stably form high quality images for a long period
of time.
[0092] As is obvious from the above descriptions, the present
embodiment can provide a heating element whose resistance value is
stable for a long period of time, and can provide an image forming
apparatus which can suppress the occurrence of uneven fixing.
EXAMPLES
[0093] The present invention will be described in detail based on
examples and comparative examples. In the following, unless
otherwise noted, operations are conducted at room temperature
(25.degree. C.). It is to be noted that the present invention is
not limited to the following Examples and so forth.
Example 1
[0094] First, annealed stainless-steel fibers are prepared. The
annealed stainless-steel fibers are fibers of SUS430, each of the
fibers having a minor axis of 8 .mu.m, a major axis of 35 .mu.m, an
aspect ratio (minor axis/major axis) of 0.229, and the annealing
treatment is conducted under a condition of a nitrogen atmosphere,
treatment time of 10 hours, and a treatment temperature of
500.degree. C.
[0095] 12 g of annealed stainless-steel fibers are put in a 100 g
of a polyamic acid solution (Ube Industries, Ltd. U-varnish S301,
solvent: N-methyl-2-pyrrolidone) which is a polyimide resin
precursor, and mixed with a rotation-revolution disperser for
agitation and defoaming to prepare a polyamic acid dope liquid.
[0096] The polyamic acid dope liquid is cylindrically applied on
the outer peripheral surface of a cylindrical metal mold by spiral
application such that the film obtained by baking has a thickness
of 100 .mu.m to form a coating film of the dope liquid, and the
coating film is dried at 120.degree. C. for 60 minutes. Thereafter,
the coating film is baked at 450.degree. C. for 20 minutes and thus
a cylindrical conductive belt is produced. The content of the
annealed stainless-steel fibers in the conductive belt is 20 volume
%.
[0097] Thereafter, one turn of a conductive tape CU-35C (available
from 3M), which has a width of 10 mm and a thickness of 2 mm and
serves as the electrode, is bonded on the outer peripheral surface
of each of the both end portions of the conductive belt and thus
heating element 1 is produced. The distance between the conductive
tapes (the distance between their edges nearer to each other) is
300 mm.
[Evaluation]
[0098] Dimensional change DL of heating element 1 is 0.0001. From
the following expression, the dimensional change DL is determined
by measuring, with a vernier caliper, distance L0 between the
electrodes of heating element 1 before heating element 1 is left
under a high temperature environment and distance L1 between the
electrodes after heating element 1 is left under a high temperature
environment for one week. The high temperature environment is an
environment of 200.degree. C. and 50 RH %.
DL=|(L1-L0)/L0|
[0099] In addition, heating element 1 has a volume resistivity
.rho. of 0.10.times.10.sup.-5 .OMEGA.cm. The volume resistivity is
determined from the following expression:
volume resistivity .rho.(.OMEGA.cm)=(R.times.d.times.W)/L
[0100] where R represents a resistance value when a voltage is
applied to the electrodes at both ends of heating element 1 and
measured using a resistance tester (LORESTA GP, Mitsubishi Chemical
Analytech Co.,Ltd), d is a thickness (cm) of heating element 1, W
represents a length (cm) of heating element 1 in the
circumferential direction, and L represents a distance between the
electrodes of heating element 1.
[0101] In addition, resistance change rate (static resistance
change rate) .rho.s of heating element 1 under a high temperature
environment is 1.03. The static resistance change rate .rho.s is
determined as the ratio .rho.s1/.rho.s0, that is, a ratio of volume
resistivity .rho.s1 of heating element 1 after it is left under the
high temperature environment for one week, to volume resistivity
.rho.s0 (the above-mentioned .rho.) of heating element 1 before it
is left under the high temperature environment. The high
temperature environment is an environment of 180.degree. C. and 50
RH %.
[0102] In addition, resistance change rate (dynamic resistance
change rate) .rho.d under a condition of electrification heat
generation of heating element 1 is 5% or lower. The dynamic
resistance change rate is determined from the following expression
by measuring volume resistivity .rho.d0 (the above-mentioned p) of
heating element 1 before electrification, and volume resistivity
.rho.d1 of heating element 1 after electrification. The
electrification is conducted in an electrification cycle
corresponding to the image formation for 600,000 A4-sheets, and one
cycle of the electrification cycle involves electrification between
the electrodes of heating element 1 for one minute and suspension
of the electrification for one minute. In addition, the temperature
of heating element 1 is maintained at 180.degree. C. by the
electrification.
.rho.d (%)=|{(.rho.1-.rho.d0)/.rho.d0}|.times.100
[0103] It is to be noted that the result of the measurement in
heating element 1 is an average value of measured values at five
points which are obtained from single heating element 1 or a
plurality of heating elements 1.
[0104] In addition, heating element 1 after the measurement of the
dynamic resistance change rate is installed as a fixing belt in an
image forming apparatus such as that illustrated in FIG. 4, and red
solid images (R solid images) are formed on 600,000 recording
media, and then, solid images of every 10,000 recording media are
visually observed to evaluate presence/absence of uneven fixing
based on the following criteria. It is to be noted that the "uneven
fixing" is a portion where toner fixation defect is observed, and
when the maximum length of the portion is 1 mm or longer, it is
determined that "uneven fixing is clearly found." The evaluation on
heating element 1 for uneven fixing is "A."
[0105] A: Uneven fixing is not found
[0106] B: Uneven fixing is clearly found
Example 2 and Comparative Example 1
[0107] Heating element 2 is produced in the same manner as in
Example 1 except that the temperature at which the stainless-steel
fibers are annealed is changed to 550.degree. C. In addition,
heating element C1 is produced in the same manner as in Example 1
except that stainless-steel fibers which are not subjected to the
annealing treatment are used.
Comparative Examples 2 to 4
[0108] Heating element C1 produced in the manner is subjected to
thermal treatment in the same condition of annealing treatment as
that of Example 1 except that treatment temperature is 400.degree.
C. to thereby produce heating element C2. In addition, in the same
manner as that for heating element C2 except that the treatment
temperature is changed to 450.degree. C., heating element C3 is
produced. Further, in the same manner as that for heating element
C2 except that the treatment temperature is changed to 500.degree.
C., heating element C4 is produced.
[0109] Heating elements 2 and C1 to C4 are measured and evaluated
in the same manner as that for heating element 1. Results of the
measurement and evaluation on heating elements 1, 2 and C1 to C4
are shown in table 1.
TABLE-US-00001 TABLE 1 Annealing treatment Resistance Temperature
DL .rho. .rho.s .rho.d Uneven Heater Timing (.degree. C.) (-)
(.OMEGA. cm) (-) (%) fixing 1 Before mixing 500 0.0001 1.0 .times.
10.sup.-5 1.03 .ltoreq.5 A 2 Before mixing 550 0.00008 1.0 .times.
10.sup.-5 1.02 .ltoreq.5 A C1 -- -- 0.0010 1.0 .times. 10.sup.-5
1.10 >10 B C2 After formation 400 0.0008 1.0 .times. 10.sup.-5
1.09 >10 B C3 After formation 450 0.0006 1.0 .times. 10.sup.-5
1.08 >10 B C4 After formation 500 0.0006 1.0 .times. 10.sup.-5
1.05 >10 B
[0110] As is obvious from the above descriptions, heating elements
1 and 2 having the annealed stainless-steel fibers are both have
desired heat generation characteristics, and are excellent in
dimensional stability.
[0111] In contrast, although heating elements C1 to C4 each have
desired heat generation characteristics, they are inferior to
heating elements 1 and 2 in dimensional stability. In heating
elements C1 to C4, although dimensional change is slightly caused
when they are heated as heating elements, they cause uneven fixing
in the image forming apparatus. One possible reason for the uneven
fixing is that the resistance value of the entire heating element
is changed due to the dimensional change of the heating
element.
[0112] From the results, one possible reason for the dimensional
change of the heating element is the dimensional change of the
stainless-steel fibers. Specifically, in the annealed
stainless-steel fibers, the internal strain of the fibers which is
left by processing is removed. Meanwhile, in the stainless-steel
fibers which are not subjected to annealing treatment, the internal
strain still remains, and the dimensional change of the heating
element is caused by the presence of the internal strain.
[0113] In addition, when the stainless-steel fibers are in
polyimide, the internal strain cannot be sufficiently removed even
when heating is conducted under an effective condition of annealing
treatment. For example, it can be said from dimensional change DL
shown in Table 1 that heat treatment on heating elements C2 to C4
conducted after formation does not substantially alter the physical
property of polyimide, and it can be said from resistance change
rates .rho.s and .rho.d shown in Table 1 that the treatment is
insufficient to sufficiently reduce the resistance change rate.
INDUSTRIAL APPLICABILITY
[0114] According to the present invention, it is possible to
provide an image forming apparatus in which uneven fixing is not
caused by dimensional change of the heating belt. Therefore,
according to the present invention, it is possible to expect
enhancement in performance and power saving in an
electrophotographic image forming apparatus, and further
popularization of the image forming apparatus.
* * * * *