JP2013101239A - Heat-generating fixation belt and fixation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-generating fixation belt and a fixation device that have superior mechanical strength against pressing force applied in an axial direction, is free from end cracking in spite of long-period use, and suppresses generation of image unevenness in a fixed image.SOLUTION: The heat-generating fixation belt is an endless heat-generating fixation belt having a resistance heat generating layer and a pair of electrodes for supplying electric power to the resistance heat-generating layer, and characterized in that the resistance heat-generating layer has graphite fiber of 30-150 μm dispersed in heat-resistant resin while oriented to extend in a peripheral direction of the heat generating fixation belt.

Description

  The present invention relates to a heat generating fixing belt for thermally fixing a toner image formed by an electrophotographic image forming method onto an image support, and a fixing device including the heat generating fixing belt.

  Conventionally, in an image forming apparatus such as a copying machine or a laser beam printer, as a method for fixing an unfixed toner image transferred onto an image support such as plain paper after toner development, contact heating fixing is performed using a heat roller method. Many methods have been used.

  However, the heat roller type fixing device has a problem that it takes time to raise the temperature to a fixable temperature and requires a large amount of heat energy, and the time from power-on to copy start (warming up time). In recent years, it has become the mainstream to adopt a thermal film fixing method from the viewpoint of shortening the length and saving energy.

In this thermal film fixing type fixing device, a seamless fixing belt in which a release layer such as a fluororesin is laminated on the outer surface of a heat resistant film made of polyimide or the like is used.
In such a heat film fixing type fixing device, for example, the heat resistant film is heated via a ceramic heater, and the toner image is fixed on the surface of the heat resistant film. Therefore, the heat conductivity of the heat resistant film is important. The point is that if the heat resistance film is made thin to improve the thermal conductivity, the mechanical strength decreases, and it is difficult to rotate at high speed, so it is difficult to adopt it for medium to high speed machines. In addition, there is a problem that ceramic heaters are easily damaged.

In order to solve such problems, in recent years, a fixing heating layer having a heating element is incorporated in the fixing belt itself, and the fixing belt is directly heated by supplying power to the resistance heating layer to fix the toner image. A device has been proposed. An image forming apparatus equipped with this type of fixing device has a short warm-up time, consumes less power than the thermal film fixing method, and is excellent in terms of energy saving and high speed.
As the resistance heating layer of such a fixing belt, a layer in which a conductive substance is dispersed in a heat resistant resin such as a polyimide resin is used.

  However, since such a heat generating fixing belt is thinly configured to save energy, there is a problem that the mechanical strength is not sufficient. Specifically, for example, contact between a heat generating fixing belt and a member that restricts movement of the heat generating fixing belt in the axial direction during driving causes an end crack such as a crack or a chip at the end of the heat generating fixing belt. Sometimes.

  As a technique for improving the mechanical strength of the heat-generating fixing belt, for example, in a resistance heat-generating layer, graphite fibers are oriented and dispersed in a certain direction in a heat-resistant resin (see Patent Document 1), carbon It has been proposed that nanomaterials are axially oriented and dispersed in a heat-resistant resin (see Patent Document 2).

However, the exothermic fixing belt disclosed in Patent Document 1 uses extremely long graphite fibers of several hundred μm to several mm, and such extremely long graphite fibers can be easily oriented in a certain direction. However, there is a problem in that the heat-generating fixing belt obtained is inferior in film forming property and image unevenness occurs in the fixed image.
Further, in the heat fixing belt disclosed in Patent Document 2, since the carbon nanomaterial is oriented in the axial direction, the effect of improving the mechanical strength against the pressing force applied in the axial direction is hardly obtained.

JP 59-77467 A JP 2009-109997 A

Conventionally, heat-fixing belts using short graphite fibers have excellent film-forming properties, but the short graphite fibers are oriented in a certain direction because they have a higher degree of fluidity than long graphite fibers. It was difficult to do.
In the present invention, a heat generating fixing belt in which short graphite fibers are oriented in the circumferential direction is obtained by forming a resistance heat generating layer by a specific method.

  The present invention has been made on the basis of the above circumstances, and its purpose is excellent in mechanical strength against a pressing force applied in the axial direction, and does not cause end cracks even after long-term use. Another object of the present invention is to provide a heat-generating fixing belt and a fixing device in which occurrence of image unevenness in a fixed image is suppressed.

The heat-generating fixing belt of the present invention is an endless heat-generating fixing belt including a resistance heat-generating layer and a pair of electrodes for supplying power to the resistance heat-generating layer,
The resistance heating layer is characterized in that graphite fibers having a length of 30 to 150 μm are dispersed in a heat resistant resin in an oriented state so as to extend along the circumferential direction of the heat generating fixing belt.

  In the heat-generating fixing belt of the present invention, the heat-resistant resin is preferably a polyimide resin.

  In the heat-generating fixing belt of the present invention, it is preferable that an elastic layer and a release layer are laminated on the resistance heat-generating layer, and the surface layer of the heat-generating fixing belt is composed of the release layer.

A fixing device of the present invention is a fixing device provided in an electrophotographic image forming apparatus,
A fixing rotating body having the heat generating fixing belt and the nip forming roller, and a pressure roller;
The heat fixing belt is provided so as to be sandwiched between a nip forming roller disposed inside the heat fixing belt and a pressure roller disposed outside the heat fixing belt,
A movement restricting member is provided at each of both ends of the rotation shaft of the nip forming roller so as to restrict the movement of the heat-generating fixing belt in the axial direction.

  According to the heat fixing belt of the present invention, the specific short graphite fiber is dispersed in the heat resistant resin so as to be oriented along the circumferential direction of the heat fixing belt. It has excellent mechanical strength against the pressing force applied to it, does not cause end cracks even after long-term use, and suppresses occurrence of image unevenness in a fixed image.

2A and 2B are schematic views showing an example of the configuration of the fixing device of the present invention, in which FIG. 1A is a perspective view showing a state in which a bearing material related to a nip forming roller is removed, and FIG. FIG. 2 is a longitudinal sectional view showing the fixing device of FIG. 1 in a state having a bearing material related to a nip forming roller. FIG. 2 is a perspective view showing a part of a heat generating fixing belt in the fixing device of FIG. It is a perspective view which shows the orientation state of the graphite fiber in the resistance heating layer of a heat-generating fixing belt. It is a top view which expands and shows the resistance heating layer of a heat-generating fixing belt partially.

  Hereinafter, the present invention will be specifically described.

[Fixing device]
1A and 1B are schematic views showing an example of the configuration of a fixing device according to the present invention, in which FIG. 1A is a perspective view showing a state in which a bearing material related to a nip forming roller is removed, and FIG. FIG. 2 is a longitudinal sectional view showing the fixing device of FIG. 1 in a state having a bearing material related to the nip forming roller.
The fixing device of the present invention is provided in an electrophotographic image forming apparatus, and includes, for example, one fixing rotator 22 in contact with one surface on which a toner image is formed on an image support P, and the other fixing rotator. A pressure roller 26 is brought into pressure contact with each other, and a nip portion N is formed by the pressure contact portion between the fixing rotating body 22 and the pressure roller 26.
One fixing rotator 22 in contact with one surface of the image support P on which the toner image is formed is an endless heat generating fixing belt 10 of the present invention and a nip forming roller disposed inside the heat generating fixing belt 10. The heat fixing belt 10 is provided so as to be sandwiched between the nip forming roller 22a and a pressure roller 26 disposed outside the heat fixing belt 10.
In the fixing rotator 22, the nip portion forming roller 22a is supported on a machine frame (not shown) of the fixing device by bearing members 22d provided at both ends of the rotating shaft 22b. The bearing member 22d also functions as a movement restricting member that restricts the movement of the heat generating fixing belt 10 in the axial direction.
1 and 2, reference numeral 26b denotes a rotating shaft of the pressure roller 26. In FIG. 2, 22c denotes a drive gear.

  In the fixing device 20 of this example, the axial length of the pressure roller 26 is configured to be shorter than the nip portion forming roller 22a, and the axial length of the heat generating fixing belt 10 and the nip portion forming roller 22a. The axial lengths are substantially equal, and only the central portion of the heat generating fixing belt 10 where the resistance heat generating layer 15 (see FIG. 3) is formed is in contact with the pressure roller 26 and is in pressure contact therewith. A pair of electrodes 12, 12 are provided at both ends of the heat-generating fixing belt 10 that is not in contact with the pressure roller 26, and these electrodes 12 are connected to a high-frequency power source 29 via a power supply member 12 b and a lead wire 12 a. It becomes.

  In this fixing device 20, the heat generating fixing belt 10 is rotated in accordance with the rotational driving of the nip portion forming roller 22a and the pressure roller 26 is driven to rotate, and an image support P on which a toner image is formed on one surface thereof. However, the toner image is fixed on the image support P by being conveyed while being pressed by the nip portion N.

[Heat fixing belt]
As shown in FIGS. 3 and 4, the heat-generating fixing belt 10 of the present invention is composed of graphite fibers (hereinafter also referred to as “graphite short fibers”) G having a long diameter (L) of 30 to 150 μm. A resistance heating layer 15 made of a resin dispersed in an oriented state extending along the circumferential direction of 10, an elastic layer 13, and a release layer 17 are laminated, and a pair for supplying power to the resistance heating layer 15. The electrode 12 is provided.
Specifically, the reinforcing layer 11 is formed on the endless resistance heating layer 15, the elastic layer 13 is formed on the reinforcing layer 11, and the release layer 17 is formed on the elastic layer 13. The electrode 12 is formed over the entire circumference in the circumferential direction so as to be in contact with both ends of the resistance heating layer 15.
The reinforcing layer 11 is provided as necessary, and the heat-generating fixing belt 10 of the present invention can be provided with other functional layers as necessary.

In the present invention, the circumferential direction of the heat fixing belt 10 refers to a direction (indicated by α in FIG. 4) that is substantially perpendicular to the axis of the heat fixing belt 10 on the peripheral surface of the heat fixing belt 10.
In the present invention, “the state in which the graphite short fibers G are oriented so as to extend along the circumferential direction of the heat-generating fixing belt 10” means that when observed with an optical microscope at a magnification of 100 times, as shown in FIG. Of 100 arbitrary graphite short fibers G, 90% by number or more are oriented with an inclination θ within ± 20 ° about a line c1 perpendicular to the longitudinal direction of the heat generating fixing belt 10.
In the present invention, the axial direction of the heat-generating fixing belt 10 refers to a direction substantially horizontal to the axis of the heat-fixing belt 10, and the short graphite fibers are oriented so as to extend along the axial direction of the heat-fixing belt. The state means that for 100 arbitrary short graphite fibers when observed in the same manner, 90% by number or more are oriented with an inclination within ± 20 ° C. around a line c2 parallel to the longitudinal direction of the heat generating fixing belt. The state that is.

  More than 90% by number of the short graphite fibers G are oriented with an inclination θ within ± 20 ° about the line c1 perpendicular to the longitudinal direction of the heat-generating fixing belt 10, so that the end portions of the heat-generating fixing belt move. It has a high stress against strain caused by the collision of the regulating member (bearing member 22d), and a sufficient resistance against cracking can be obtained.

The arrangement direction of the short graphite fibers in the resistance heating layer 15 of the heat fixing belt 10 can be observed with an optical microscope.
Specifically, after peeling off the release layer 17, the elastic layer 13, and the reinforcing layer 11 laminated on the resistance heating layer 15, the surface of the resistance heating layer 15 is observed at a magnification of 100 using an optical microscope. can do.

(Resistance heating layer)
(resin)
The resin constituting the resistance heating layer 15 according to the heat fixing belt 10 of the present invention includes a polyimide resin, and may also include other resins.
The other resin is preferably a heat-resistant resin having a short-term heat resistance of 200 ° C. or more and a long-term heat resistance of 150 ° C. or more. Examples of such a heat-resistant resin include polyphenylene sulfide resin (PPS), Examples include polyarylate resin (PAR), polysulfone resin (PSF), polyethersulfone resin (PES), polyetherimide resin (PEI), polyamideimide (PAI), and polyetheretherketone resin (PEEK).
Further, as the other resin, a non-heat-resistant resin other than the above-mentioned heat-resistant resin may be included, but the content ratio of the non-heat-resistant resin is less than 40% by volume of the entire resin constituting the resistance heating layer 15. It is very preferable.

  The content ratio of the polyimide resin in the resin constituting the resistance heating layer 15 is preferably 50% by volume or more, and particularly preferably 100% by volume.

(Graphite short fiber)
The graphite short fiber G dispersed in the resistance heating layer 15 is a conductive substance and is fibrous graphite.
Here, the term “fibrous” means that the major axis (L) is at least four times the minor axis (l).

The long diameter (L) of the graphite short fiber G is 30 to 150 μm, preferably 30 to 80 μm.
Moreover, it is preferable that the short diameter (l) of the graphite short fiber G is 3-15 micrometers, More preferably, it is 5-10 micrometers.
When the major axis is less than 30 μm, end cracks or the like occur when used over a long period of time. This is presumably because the mechanical strength against the pressing force applied in the axial direction cannot be sufficiently obtained. When the major axis exceeds 150 μm, image unevenness such as a fiber pattern appearing in the fixed image occurs. This is presumably because the obtained resistance heating layer has a rough surface.
When the short diameter is less than 3 μm, the contact resistance becomes excessively large when the graphite short fibers dispersed in the resistance heating layer 15 come into contact with each other, and the resistance value of the resistance heating layer 15 as a whole is sufficiently increased. When the short diameter exceeds 15 μm, the dispersibility of the graphite short fiber in the resistance heating layer 15 may be low, and there may be a local variation in the conduction resistance.

  In the above, the long diameter (L) and the short diameter (l) of the graphite short fiber G are obtained by taking a photograph magnified 500 times using a scanning electron micrograph, and from an image captured by a scanner, The average value is calculated by measuring the major axis and minor axis for 500 samples, respectively.

  As a method for producing the graphite short fiber G, a known production method can be employed. That is, first, when it is necessary to make the graphite drawn out from the nozzle into a fiber shape further thin, it is stretched while being heated as necessary, and then carbonized by steaming at a temperature of 200 to 300 degrees C. A strong yarn is then made, and then steamed at a high heat of 1000 to 3000 degrees. By passing through such a process, impurities other than carbon contained in the yarn are lost, and a carbon framework (molecular structure) with very high strength is obtained. Through such a process, first, a yarn having a short diameter (l) of a desired short graphite fiber G is obtained, and this is cut into a predetermined length (long diameter (L)) to obtain a target graphite short fiber. Fiber G can be produced.

The volume resistivity of the graphite short fiber G is preferably 1 × 10 ⁻¹ Ω · m or less.
When the volume resistivity of the graphite short fiber G is fibrous, a constant current I (A) is passed through the graphite short fiber G, and a potential difference V (V) between electrodes separated by a distance L is measured. It is calculated from the following formula (1).
Formula (1): Volume resistivity ρv = (V · Wt) / IL
[Wt is the cross-sectional area of the graphite short fiber G. ]

  The content of the short graphite fiber G in the resistance heating layer 15 is 5 to 60% by mass.

  The thickness of the resistance heating layer 15 is preferably 10 to 300 μm, more preferably 30 to 200 μm, and particularly preferably 80 to 160 μm.

The volume resistivity of the resistance heating layer 15 is preferably 8 × 10 ⁻⁶ to 1 × 10 ⁻² Ω · m.

The volume resistivity of the resistance heating layer 15 is calculated by the following formula (2) by providing electrodes with conductive tape at both ends of the entire circumference in the circumferential direction of the heat fixing belt 10 and measuring resistance values at both ends.
Formula (2): Volume resistivity ρ = (R · d · W) / L
[Where R is the resistance value (Ω), d is the thickness (m) of the resistance heating layer 15, W is the circumferential length (m) of the heating fixing belt 10, and L is the length between the electrodes (m). It is. ]

〔electrode〕
The electrode 12 provided on the heat-generating fixing belt 10 of the present invention is a layered material, specifically, a ring-shaped electrode member formed by electroforming, spatula drawing, press drawing or the like, or metal An electrode member obtained by processing a sheet into a ring shape by laser welding or the like is fitted into a rotating core body before applying a polyamic acid dope solution for generating a polyimide resin in the process of forming the resistance heating layer 15, and the polyimide resin is baked. Can be formed by adhering to the resistance heating layer 15.
The electrode member for forming the electrode 12 may have a hole formed by etching, laser drilling, or the like at the contact point with the resistance heating layer 15 in order to improve adhesion to the resistance heating layer 15. Good. Although there is only one point of contact between the electrode member and the resistance heating layer 15, it is preferable that the electrode member and the resistance heating layer 15 are formed so as to be in contact with each other in the circumferential direction over the entire circumference.

  Although it does not specifically limit as an electrode member for forming the electrode 12, It is preferable to use what consists of material with low electrical resistivity, such as Ni, SUS, and Al, and excellent in heat resistance and oxidation resistance.

  As the thickness of the electrode member for forming the electrode 12 increases, the rigidity becomes higher, so that the fracture resistance is excellent. However, due to the difficulty of deformation, the nip portion N is formed by the pressure contact portion with the pressure roller 26. In view of the balance with flexibility, the thickness is preferably 10 to 100 μm, more preferably 30 to 60 μm.

  As the power supply member 12b, various carbon brushes made of, for example, copper graphite or carbon graphite can be used.

Power is supplied to the resistance heating layer 15 from, for example, a high-frequency power supply 29 via a power supply member 12b and the electrode 12 via a bundled wire and a harness.
Power supply from the power supply member 12b to the electrode 12 is performed, for example, by bringing the power supply member 12b into contact with only the electrode 12. Specific contact methods include a sliding contact method and a rotating contact method using a roller.
The contact load between the power supply member 12 b and the electrode 12 may be a load that ensures conduction and does not cause excessive stress in driving the heat-generating fixing belt 10.

[Elastic layer]
The elastic layer 13 constituting the heat generating and fixing belt 10 of the present invention is made of, for example, a heat resistant resin having elasticity.
Examples of the heat resistant resin having elasticity include silicone rubber, natural rubber (NR), butadiene rubber (BR), acrylonitrile butadiene rubber (NBR), hydrogenated NBR (H-NBR), styrene butadiene rubber (SBR), and isoprene rubber. (IR), urethane rubber, chloroprene rubber (CR), chlorinated polyethylene (Cl-PE), epihalohydrin rubber (ECO, CO), butyl rubber (IIR), ethylene propylene diene polymer (EPDM), fluoro rubber, acrylic rubber (ACM) And the like. Among these, it is preferable to use CR, ECO, silicone rubber, butyl rubber, acrylic rubber, and urethane rubber.

  The elastic layer 13 preferably has a thickness of 50 to 300 μm, more preferably 100 to 200 μm.

[Release layer]
The release layer 17 constituting the heat-generating fixing belt 10 of the present invention is made of polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer ( FEP).

  The thickness of the release layer 17 is preferably 1 to 20 μm, more preferably 2 to 10 μm.

(Reinforcement layer)
The reinforcing layer 11 constituting the heat-generating fixing belt 10 of the present invention is provided as necessary, and the reinforcing layer 11 is made of a heat resistant resin.
Examples of the heat-resistant resin constituting the reinforcing layer 11 include those listed as the resin constituting the resistance heating layer 15 described above.

  The thickness of the reinforcing layer 11 is preferably 20 to 100 μm, more preferably 30 to 80 μm.

  According to the heat-generating fixing belt 10 as described above, the short graphite fibers G are dispersed in the heat-resistant resin in an oriented state so as to extend along the circumferential direction of the heat-generating fixing belt 10. It has excellent mechanical strength against the applied pressing force, does not cause edge cracks even after long-term use, and suppresses occurrence of image unevenness in a fixed image.

[Method of forming heat-generating fixing belt]
The heat-generating fixing belt 10 as described above can be formed by using various known methods. For example, the resistance heat-generating layer 15 is preferably formed as follows.

In particular,
(1) A polyamic acid dope preparation step for preparing a polyamic acid dope solution in which graphite short fibers G are added and dispersed in polyamic acid as a coating solution for forming the resistance heating layer 15;
(2) A belt-shaped precursor preparation step of applying a polyamic acid dope solution on the rotating core so that the graphite short fibers G are oriented in the circumferential direction and drying to obtain a belt-shaped precursor;
(3) It is comprised from the imidation reaction process of baking a belt-shaped precursor and producing | generating a polyimide resin.
The reinforcing layer 11, the electrode 12, the elastic layer 13, and the release layer 17 can each be formed by an appropriate method.

(1) Polyamic acid dope preparation step In this polyamic acid dope preparation step, polyamic acid is synthesized by polycondensation of aromatic tetracarboxylic acid and aromatic diamine, and graphite short fiber G is dispersed in this. It is a process.
Specifically, polycondensation is performed in a solvent composed of a good solvent for polyamic acid to obtain a polyamic acid solution in which the polyamic acid is dissolved.

The good solvent for polyamic acid refers to a solvent capable of uniformly dissolving the polyamic acid at a concentration of 20% by mass or more at 25 ° C. Examples of such good solvents include N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone, and hexamethylsulfol. Examples include amides such as amides; sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide; and organic polar solvents such as sulfones such as dimethyl sulfone and diethyl sulfone. These may be used alone or in combination of two or more.
As the good solvent, N-methylpyrrolidone is preferably used.

  The amount of the good solvent to be used may be an amount such that the concentration of the polyamic acid in the polyamic acid solution obtained after the condensation polymerization is in the range of 2 to 50% by mass, for example.

  Various known methods can be employed as a method for polycondensing the aromatic tetracarboxylic acid and the aromatic diamine. Specifically, for example, the aromatic tetracarboxylic acid and the aromatic diamine are used in approximately equimolar amounts, and the solvent is reduced in a temperature range of 100 ° C. or lower, preferably 0 to 80 ° C. for 0.1 to 60 hours. The method of superposing | polymerizing is mentioned.

[Aromatic tetracarboxylic acid]
The aromatic tetracarboxylic acid used for the synthesis of the polyamic acid is not particularly limited, and examples thereof include aromatic tetracarboxylic acid, acid anhydrides, salts and esterified products thereof, and mixtures thereof. It is preferable to use an acid dianhydride of an aromatic tetracarboxylic acid.
Specific examples of the acid dianhydride of aromatic tetracarboxylic acid include, for example, pyromellitic dianhydride (PMDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,3,3 ′ , 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2 ′, 3,3′-benzophenone tetracarboxylic acid dihydrate 2,3,3 ′, 4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA), bis (3,4-dicarboxyphenyl) Sulfone dianhydride, bis ( , 3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1- Bis (3,4-dicarboxyphenyl) ethane dianhydride, 2,2-bis [3,4- (dicarboxyphenoxy) phenyl] propane dianhydride (BPADA), 4,4 ′-(hexafluoroisopropylidene) ) Diphthalic anhydride, oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyphenyl) sulfoxide dianhydride, thiodiphthalic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bis (3 - and the like dicarboxyphenyl) fluorene dianhydride and 9,9-bis [4- (3,4'-dicarboxyphenoxy) phenyl] fluorene dianhydride. Among these, pyromellitic dianhydride (PMDA), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3 ′, 4,4′-benzophenonetetracarboxylic acid Preferred are dianhydride (BTDA), 2,2-bis [3,4- (dicarboxyphenoxy) phenyl] propane dianhydride (BPADA), oxydiphthalic anhydride (ODPA), and the like.
These may be used alone or in combination of two or more.

  The amount of the aromatic tetracarboxylic acid used is preferably such that the aromatic tetracarboxylic acid: aromatic diamine has a molar ratio of 0.85: 1 to 1.2: 1.

  The polyamic acid preferably has a number average molecular weight of 1,000 or more, more preferably 2,000 to 500,000, and particularly preferably 5,000 to 150,000.

The number average molecular weight of the polyamic acid is measured by gel permeation chromatography (GPC) soluble in tetrahydrofuran (THF). Specifically, using an apparatus “HLC-8220” (manufactured by Tosoh Corporation) and a column “TSKguardcolumn + TSKgelSuperHZM-M3 series” (manufactured by Tosoh Corporation), while maintaining the column temperature at 40 ° C., tetrahydrofuran (THF) was used as a carrier solvent. The sample was flowed at a flow rate of 0.2 ml / min, and the sample was dissolved in tetrahydrofuran to a concentration of 1 mg / ml under a dissolution condition in which treatment was performed at room temperature using an ultrasonic disperser for 5 minutes, and then a membrane having a pore size of 0.2 μm. A sample solution is obtained by processing with a filter, and 10 μL of this sample solution is injected into the apparatus together with the above carrier solvent, detected using a refractive index detector (RI detector), and the molecular weight distribution of the measurement sample is monodispersed. This is calculated using a calibration curve measured using polystyrene standard particles. As a standard polystyrene sample for calibration curve measurement, the molecular weights manufactured by Pressure Chemical are 6 × 10 ² , 2.1 × 10 ³ , 4 × 10 ³ , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ , 1 .1 x 10 ⁵ , 3.9 x 10 ⁵ , 8.6 x 10 ⁵ , 2 x 10 ⁶ , 4.48 x 10 ⁶ It was created. A refractive index detector was used as the detector.

[Aromatic diamine]
The aromatic diamine used for the synthesis of the polyamic acid is not particularly limited. For example, paraphenylenediamine (PPD), metaphenylenediamine (MPDA), 2,5-diaminotoluene, 2,6-diaminotoluene, 4, 4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-biphenyl, 3,3'-dimethoxy-4,4'-biphenyl, 2,2-bis (trifluoromethyl) -4, 4'- Diaminobiphenyl, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane (MDA), 2,2-bis- (4-aminophenyl) propane, 3,3′-diaminodiphenylsulfone (33DDS), 4, 4'-diaminodiphenyl sulfone (44DDS), 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl Rufide, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether (34 ODA), 4,4′-diaminodiphenyl ether (ODA), 1,5-diaminonaphthalene, 4,4′-diaminodiphenyldiethylsilane, 4 , 4′-diaminodiphenylsilane, 4,4′-diaminodiphenylethylphosphine oxide, 1,3-bis (3-aminophenoxy) benzene (133APB), 1,3-bis (4-aminophenoxy) benzene (134APB) 1,4-bis (4-aminophenoxy) benzene, bis [4- (3-aminophenoxy) phenyl] sulfone (BAPSM), bis [4- (4-aminophenoxy) phenyl] sulfone (BAPS), 2, 2-Bis [4- (4-aminophenoxy) phenyl] propaprop (BAPP), 2,2-bis (3-aminophenyl) 1,1,1,3,3,3-hexafluoropropane, 2,2-bis (4-aminophenyl) 1,1,1,3 Examples include 3,3-hexafluoropropane and 9,9-bis (4-aminophenyl) fluorene. Among these, paraphenylenediamine (PPD), metaphenylenediamine (MPDA), 4,4′-diaminodiphenylmethane (MDA), 3,3′-diaminodiphenylsulfone (33DDS), 4,4′-diaminodiphenyl, among others Sulfone (44DDS), 3,4'-diaminodiphenyl ether (34ODA), 4,4'-diaminodiphenylether (ODA), 1,3-bis (3-aminophenoxy) benzene (133APB), 1,3-bis (4 -Aminophenoxy) benzene (134APB), bis [4- (3-aminophenoxy) phenyl] sulfone (BAPSM), bis [4- (4-aminophenoxy) phenyl] sulfone (BAPS), 2,2-bis [4 -(4-Aminophenoxy) phenyl] propane (BAPP) Etc. are preferred.
These may be used alone or in combination of two or more.

  The polyamic acid dope solution needs to dissolve or disperse the graphite short fiber G in the polyamic acid solution obtained as described above, and contain additives such as a conductive agent, a surfactant, and a viscosity modifier as necessary. Depending on the condition, it is prepared by adjusting the concentration and viscosity by adding a solvent for dilution.

  The amount of the total solvent in the polyamic acid dope solution is preferably 20 to 90% by mass, and more preferably 40 to 70% by mass.

  Further, the viscosity of the polyamic acid dope solution is not particularly limited as long as the resistance heating layer 15 having a desired thickness is obtained, and is set to, for example, 10 cp to 10,000 cp.

  Additives such as surfactants and viscosity modifiers are described in the latest polyimides—Basics and Applications— (edited by Nippon Polyimide Research Group (NTS Publishing) and the latest polyimide materials and applied technologies (supervised by Masaaki Enomoto, CMC Publishing). Substance can be used.

  When the graphite short fibers G and / or additives that are not dissolved in the polyamic acid dope solution are contained, it is preferable to use means for achieving uniform dispersion in the polyamic acid dope solution. For example, mixing and dispersion may be performed using a known mixer such as mixing with a stirring blade, mixing with a static mixer, mixing with a single-screw kneader or a twin-screw kneader, mixing with a homogenizer, or mixing with an ultrasonic disperser.

(2) Belt-like precursor preparation step In this belt-like precursor preparation step, the polyamic acid dope solution is applied onto an appropriate rotating core, and then the solvent is evaporated to remove the belt-like precursor. It is a process.
As the rotating core body, for example, a stainless steel pipe or the like can be used.

As a method of applying the polyamic acid dope solution on the rotating core, a spiral coating method can be used.
The spiral coating method uses a liquid feeding pump such as a MONO pump or gear pump, a coating device consisting of piping and nozzles such as Teflon (registered trademark) tubes, and the rotating core is held horizontally with respect to the rotating core. And rotating the nozzle in the axial direction of the rotating core while discharging the polyamic acid dope solution from the nozzle while bringing the nozzle close to the peripheral surface of the rotating core in the coating apparatus. In this method, a polyamic acid dope solution is applied in a spiral shape over the entire peripheral surface of the core.

Specific examples of specific application conditions will be given.
・ Rotating core size: φ30mm, length 450mm
-Temperature of the polyamic acid dope solution: 25 ° C
・ Nozzle shape: Conical nozzle ・ Nozzle diameter: 4 mm
・ Distance between the nozzle tip and the peripheral surface of the rotating core: 5 to 20 mm
・ Discharge rate from nozzle: 3cc / min
・ Axis movement speed of nozzle core: 45mm / min
-Rotational speed (circumferential speed) of the rotating core: 3500-4500 mm / min

The graphite short fiber G can be dispersed in the resistance heating layer 15 in a state of being oriented so as to extend along the circumferential direction of the heat generating fixing belt 10 by applying it on the rotating core by a spiral coating method.
This is because the graphite short fibers dispersed in the polyamic acid dope liquid are usually difficult to orient in a certain direction because of the freedom of fluidity. This is because the short graphite fibers G are oriented in the direction in which the nozzles extend, and the state in which the short graphite fibers G are oriented in the moving direction of the nozzles, that is, in the circumferential direction of the rotating core body, is maintained.

The drying temperature for evaporating the solvent is not particularly limited as long as it is a temperature lower than the imidization start temperature described later and can evaporate the solvent, and is, for example, 40 to 280 ° C, preferably 80 to 260 ° C. More preferably, it is 120-240 degreeC, Most preferably, it is 120-220 degreeC.
This drying may be performed until the solvent content of the belt-shaped precursor after drying reaches a level suitable for forming the belt-shaped precursor.

(3) Imidization reaction step In this imidation reaction step, the belt-like precursor is calcined at a specific calcining temperature for a predetermined time to imidize polyamic acid to form a resistance heating layer 15 made of polyimide resin and an electrode. In this step, 12 is bonded to the resistance heating layer 15.

The specific firing temperature related to the imidization reaction is an imidization start temperature, and is usually 280 ° C. or higher, preferably 280 to 400 ° C., more preferably 300 to 380 ° C., and particularly preferably 330 to 380 ° C.
Moreover, baking time is 10 minutes or more normally, Preferably it is 30 to 240 minutes.

[Image forming apparatus]
The fixing device of the present invention can be mounted on an image forming apparatus having various known configurations.

(Image support)
In the image forming method using the fixing device of the present invention, as the image support P for fixing the toner image, coated paper such as plain paper, fine paper, art paper or coated paper from thin paper to thick paper, Various examples of commercially available Japanese paper, postcard paper, OHP plastic film, cloth, and the like can be given, but the invention is not limited to these.

As mentioned above, although embodiment of this invention was described concretely, embodiment of this invention is not limited to said example, A various change can be added.
For example, a primer layer can be formed between the resistance heating layer 15 and the elastic layer 13 constituting the heat fixing belt 10 for the purpose of stabilizing the adhesiveness. The primer layer has a thickness of 2 to 5 μm, for example.

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

[Example 1]
(1) Production of electrode A rotating core body [1] with an electrode is formed by fitting an electrode ring member having a width of 20 mm and a thickness of 50 μm into a region of 5 cm on each end of a stainless steel pipe having an outer diameter of 30 mm and a total length of 450 mm. did.

(2) Preparation of polyamic acid dope for producing resistance heating layer 80 g of polyamic acid obtained from biphenyltetracarboxylic dianhydride and paraphenylenediamine, and 18 g of graphite fiber (diameter 8 μm, length 32 μm) The polyamic acid dope solution [1] was obtained by sufficiently stirring and defoaming with a planetary mixer.

(3) Production of resistance heating layer and reinforcing layer While rotating the rotating core with electrode [1] while holding the rotating shaft horizontally, using a coating device equipped with a MONO pump, a Teflon (registered trademark) tube and a nozzle, The nozzle is moved in the axial direction of the rotating core [1] with electrode while the nozzle is brought close to the rotating core [1] with electrode and the polyamic acid dope solution [1] is discharged from the nozzle. Thus, the polyamic acid dope solution [1] is spirally applied to the entire central region of the stainless steel tube without the electrode ring so as to slightly overlap the inner side in the axial direction of the electrode ring of the rotary core with electrode [1], and By flattening, a coating film having a film thickness of 600 μm is formed, and then the rotating shaft is held horizontally while rotating at a rotation speed (circumferential speed) of 50 mm / min. The laminated structure [a] was obtained by drying at 0 ° C. for 1 hour to remove the solvent, and then the polyamic acid “U-varnish S301” (manufactured by Ube Industries) was deposited on the laminated structure [a] to a thickness of 500 μm. Then, the coated product is dried at 120 ° C. for 20 minutes to obtain a belt-shaped precursor, which is heated from room temperature to 400 ° C. over 3 hours in a nitrogen atmosphere and baked to be imidized. Then, the resistance heating layer was formed so as to be bonded to the electrode ring, and the reinforcing layer was formed to produce a laminated structure [A1] composed of an endless polyimide resin belt.
When this laminated structure [A1] was observed with an optical microscope, it was confirmed that the graphite fibers were oriented in the circumferential direction.
-Application conditions-
-Temperature of the polyamic acid dope solution: 25 ° C
・ Nozzle shape: Conical nozzle ・ Nozzle diameter: 4 mm
・ Distance from the nozzle tip to the peripheral surface of the rotating core [1]: 20 mm
・ Discharge rate from nozzle: 3cc / min
-Moving speed of the nozzle rotation core [1] in the axial direction: 45 mm / min
-Rotational speed (circumferential speed) of the rotating core [1]: 4000 mm / min

(4) Preparation of elastic layer On the above laminated structure [A1], a primer “X331565” (manufactured by Shin-Etsu Chemical Co., Ltd.) is brushed, dried at room temperature for 30 minutes to form a primer layer, and then a silicone rubber A composition prepared by mixing a liquid rubber of “KE1379” (manufactured by Shin-Etsu Chemical Co., Ltd.) and two liquids of silicone rubber “DY356013” (manufactured by Toray Dow Corning Silicone Co., Ltd.) in a ratio of 2: 1 was formed on the primer layer with a thickness of 200 μm. And then heated at 150 ° C. for 30 minutes for primary vulcanization, and further heated at 200 ° C. for 4 hours to perform post vulcanization to form an elastic layer on the primer layer. A laminated structure [A2] provided with an elastic layer thereon was formed. The hardness of this elastic layer was 26 degrees.

(5) Production of release layer After the surface of the elastic layer of the laminated structure [A2] is washed, the PTFE resin dispersion “30J” (manufactured by DuPont) is used as the fluororesin (B) in the laminated structure [ A2] is rotated for 3 minutes while rotating, taken out, dried at room temperature for 20 minutes, and then the fluororesin on the surface of the elastic layer is wiped with a cloth, and further PTFE resin and PFA resin are used as fluororesin (A). A fluororesin dispersion “855-510” (manufactured by DuPont) mixed at a ratio of 7: 3 and adjusted to a solid content concentration of 45% and a viscosity of 110 mPa · s was applied onto the layer made of fluororesin (B). The film was coated to a thickness of 15 μm, dried at room temperature for 30 minutes, and then heated at 230 ° C. for 30 minutes. Thereafter, the tube is passed through a tubular furnace having an inner diameter of 100 mm and the furnace temperature set at 270 ° C. in about 10 minutes, the fluororesin is formed by firing, cooled, and separated on the elastic layer of the laminated structure [A2]. A mold layer was formed to obtain an exothermic fixing belt [1]. Thereafter, the heat fixing belt [1] was separated from the stainless steel tube.

[Examples 2 to 5, Comparative Examples 1 to 4]
In Example 1, exothermic fixing belts [2] to [9] were obtained in the same manner except that graphite fibers having the lengths shown in Table 1 were used.
When the resistance heating layer of the heat fixing belts [2] to [9] was observed with an optical microscope, the graphite fibers of the heat fixing belts [2] to [5] and [9] were oriented in the circumferential direction. Further, it was confirmed that the graphite fibers were randomly oriented in the heat fixing belts [6] and [7].

[Comparative Example 5]
In Example 1, application of the polyamic acid dope liquid [1] to the rotating core body is performed by immersing the rotating core body in the polyamic acid dope liquid so that the axial direction is vertical, and pulling it up at a predetermined speed. Except for the formation, a heat-generating fixing belt [10] was obtained in the same manner.
When the resistance heating layer of the heat-generating fixing belt [10] was observed with an optical microscope, it was confirmed that the graphite fibers were oriented in the axial direction.

<Performance evaluation>
Using the heat generating fixing belts [1] to [10] described above, evaluations were made on edge cracks, film forming properties, and image unevenness.

(1) Cracks at the end Using the fixing device of the copier “bizhub C280” (manufactured by Konica Minolta Business Technologies), an external power supply, drive unit and temperature control unit can be connected to this, and a heat generating fixing belt can be attached. At the same time, attach a heat generating fixing belt to the fixing device idle rotation jig that has been modified to break the pressure balance by applying different pressures at both ends of the pressure roller. A forced durability test was performed in which an image support such as paper was driven for 1000 hours (equivalent to about 1 million sheets of actual paper) while applying voltage and controlling at a temperature controlled temperature of 180 ° C. . In addition, since the pressure balance at both ends of the pressure roller is broken, the heat-generating fixing belt easily comes into contact with the bearing material of the nip portion forming roller.
-Configuration conditions of the fixing device idle rotation jig-
・ Rotating speed of heat fixing belt: 130mm / sec
・ Applying pressure on the drive transmission side: 6kgf
・ Pressure force on the non-drive transmission side: 9kgf

Ten heat-generating fixing belts [1] to [10] are prepared for each, a forced endurance test is performed with a fixing device idling jig, the state of the end of the heat-generating fixing belt is visually confirmed, and the following evaluation is performed. Evaluation was made according to criteria. The results are shown in Table 1.
-Evaluation criteria-
A: For all 10 pieces, no deformation was observed at the end even after 1,000 hours of endurance, and there was no problem at all.
○: For all 10 pieces, there was no deformation at the end when 600 hours endured, and there was no problem in practical use.
(Triangle | delta): At the time of enduring 600 hours, some deformation | transformation was seen in the edge part about some of 10 pieces, and there is a problem level.
X: About all 10 pieces, damage such as losing, cracking and cracking was seen before 600 hours endurance, and there was a problem level.

(2) Film-forming property For each of the heat-generating fixing belts [1] to [10], an evaluation belt in which only the resistance heat-generating layer is formed is prepared, and for this evaluation belt, an eddy current film thickness manufactured by Fischer is used. The film thickness deviation was measured using a meter and evaluated according to the following evaluation criteria. The results are shown in Table 1.
-Evaluation criteria-
A: The film thickness deviation in the belt axis direction is a level of 10 μm or less.
◯: The film thickness deviation in the belt axis direction is greater than 10 μm and 20 μm or less.
(Triangle | delta): The film thickness deviation of a belt axis direction is a level larger than 20 micrometers and 30 micrometers or less.
X: The film thickness deviation in the belt axis direction is greater than 40 μm.

(3) Image unevenness The fixing device of the copying machine “bizhub C280” (manufactured by Konica Minolta Business Technologies) is equipped with a heat-generating fixing belt with the pressure balance kept normal, and in a normal temperature and humidity environment (temperature 25 ° C., humidity) 50%), 50,000 test images were formed, and the obtained fixed images were evaluated according to the following evaluation criteria. The results are shown in Table 1.
-Evaluation criteria-
A: Image streaks and color unevenness are not seen in the 50,000th fixed image, and there is no problem at all.
○: Image streaks and color unevenness are not seen in the 40,000th fixed image, and there is no problem at all.
Δ: Some image streaks and color irregularities are seen in the 40,000th fixed image, and there is a problem.
X: A large amount of image streaks and color unevenness is observed in any fixed image, and there is a problem level.

DESCRIPTION OF SYMBOLS 10 Heat generation fixing belt 11 Reinforcement layer 12 Electrode 12a Lead wire 12b Power supply member 13 Elastic layer 15 Resistance heat generation layer 17 Release layer 20 Fixing device 22 Fixing rotating body 22a Nip portion forming roller 22b Rotating shaft 22c Drive gear 22d Bearing member 26 Pressure roller 26b Rotating shaft 29 High-frequency power supply G Graphite short fiber N Nip part P Image support

Claims (4)

An endless heat-generating fixing belt comprising a resistance heating layer and a pair of electrodes for supplying power to the resistance heating layer,
The heat generating fixing belt is characterized in that the resistance heat generating layer is formed by dispersing graphite fibers having a length of 30 to 150 μm in a heat resistant resin in an oriented state so as to extend along a circumferential direction of the heat generating fixing belt. .   The heat-fixing belt according to claim 1, wherein the heat-resistant resin is a polyimide resin.   3. The heat fixing according to claim 1, wherein an elastic layer and a release layer are laminated on the resistance heat generating layer, and a surface layer of the heat fixing belt is constituted by the release layer. belt. A fixing device provided in an electrophotographic image forming apparatus,
A fixing rotator having the heat generating fixing belt and the nip forming roller according to any one of claims 1 to 3, and a pressure roller.
The heat fixing belt is provided so as to be sandwiched between a nip forming roller disposed inside the heat fixing belt and a pressure roller disposed outside the heat fixing belt,
A fixing device, wherein a movement restricting member is provided at each of both ends of the rotation shaft of the nip forming roller so as to restrict the movement of the heat generating fixing belt in the axial direction.

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