JP5768725B2 - Endless heating element, heating belt and fixing device - Google Patents

Description

  The present invention relates to an endless heating element, a heating belt, and a fixing device.

  In electrophotographic printers and copiers, after a toner image is formed on a sheet, the sheet is generally fixed by heat and pressure by a fixing device. The fixing device includes a pair of fixing rollers each having a heat source therein, and the pair of fixing rollers press against each other to form a nip. The fixing roller rotates while sandwiching the sheet by the nip, and heats and pressurizes the sheet.

  Conventionally, a heat source such as a heater is built in the fixing roller and heated. Instead, a heat generating belt in which an endless heat generating element that generates heat when energized is formed as a heat generating layer is used. The fixing device provided with the heat generating belt has a shorter time and heat energy required for heating up to the fixing temperature than the case where the fixing roller has a built-in heat source, and has high thermal efficiency.

  As the conductive material for the endless heating element, carbon black having excellent thermal conductivity is often used. Carbon black is dispersed in a substrate such as polyimide resin to produce an endless heating element, but carbon has low dispersibility. Similar to the endless heating element, a dispersant such as polyvinyl pyrrolidone may be used in an intermediate transfer body produced by dispersing carbon black in a polyimide resin (see, for example, Patent Documents 1 and 2).

JP 2005-181750 A JP 2009-133969 A

  However, the conventional endless heating element has a problem that the resistance of the endless heating element changes with the voltage application time when it is heated by energization. Due to the change in resistance, the surface temperature of the heat generating belt becomes unstable when the endless heat generating element generates heat, and unevenness occurs in the finish of the fixing process, thereby degrading the image quality. In order to maintain a constant surface temperature, it is necessary to control the voltage applied to the endless heating element, and it is difficult to control the voltage in accordance with the resistance that changes constantly.

  An object of the present invention is to suppress a change in resistance of an endless heating element.

According to the invention of claim 1,
An endless heating element that disperses a fibrous conductive material in a polyimide resin and generates heat when energized,
There is provided an endless heating element containing polyvinyl pyrrolidone in a range of 0.1 to 10.0% by mass with respect to all components of the endless heating element.

According to invention of Claim 2,
The endless heating element according to claim 1, wherein the endless heating element has a volume resistivity in the range of 0.08 × 10 ^{−4 to} 10.00 × 10 ⁻⁴ (Ω · m). .

According to invention of Claim 3,
A heating belt in which the endless heating element according to claim 1 is formed as a heating layer is provided.

According to invention of Claim 4,
A fixing device provided with the heat generating belt according to claim 3 is provided.

  According to the present invention, it is possible to suppress a change in resistance of an endless heating element even when heat is generated by energization and a temperature change occurs.

It is an image figure of the fibrous graphite disperse | distributed in a polyimide resin. It is the schematic of the coating device of an endless heat generating body coating liquid. 1 is a schematic view of a fixing device including a heat generating belt in which an endless heat generating element is used as a heat generating layer. FIG. 4 is a cross-sectional view of the fixing device in FIG. 3. It is sectional drawing of a heat generating belt. It is a figure explaining the measuring method of resistance of an endless exothermic body.

Hereinafter, embodiments of an endless heating element, a heating belt, and a fixing device of the present invention will be described with reference to the drawings.
In addition, description of "-" which shows a numerical range represents that a lower limit and an upper limit are included in the numerical range.

<Endless heating element>
In the endless heating element according to the present invention, a heating element obtained by dispersing a fibrous conductive material in the polyimide resin using a polyimide resin as a base material is formed in an endless shape, and generates heat when energized.

  A polyimide resin is prepared by imidating a polyamic acid solution prepared by mixing and heating a tetracarboxylic dianhydride and a diamine compound in an approximately equimolar amount and heating and polycondensation reaction. be able to.

  Examples of the tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride. Anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride 2,2′-bis (3,4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, berylene-3,4,9,10-tetracarboxylic acid bis Anhydrides, bis (3,4-dicarboxyphenyl) ether dianhydride, ethylenetetracarboxylic dianhydride and the like can be mentioned. Alternatively, these derivatives can also be used.

  Examples of the diamine compound include p-phenylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane, 3,3′-dichlorobenzidine, 4,4′-diaminodiphenyl sulfide. 3,3′-diaminodiphenylsulfone, 1,5-diaminonaphthalene, m-phenylenediamine, p-phenylenediamine, 3,3′-dimethyl-4,4′-biphenyldiamine, benzidine, 3,3′-dimethyl Benzidine, 3,3′-dimethoxybenzidine, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylpropane, 2,4-bis (β-amino-tert-butyl) toluene, bis (p-β- Amino-tert-butylphenyl) ether, bis (p-β-methyl-6- Minophenyl) benzene, bis-p- (1,1-dimethyl-5-amino-pentyl) benzene, 1-isopropyl-2,4-m-phenylenediamine, m-xylylenediamine, p-xylylenediamine, di ( p-aminocyclohexyl) methane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, diaminopropyltetramethylene, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 2, 11-diaminododecane, 1,2-bis-3-aminopropoxyethane, 2,2-dimethylpropylenediamine, 3-methoxyhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine 3-methylheptamethylenediamine, 5-methylnonamethylenediamine, 2,17-diaminoeicosadecane, 1,4-diaminocyclohexane, 1,10-diamino-1,10-dimethyldecane, 1,12-diaminocyclohexane, Examples include 1,10-diamino-1,10-dimethyldecane, 1,12-diaminooctadecane, and 2,2-bis [4- (4-aminophenoxy) phenyl] propane.

  Any of the above tetracarboxylic dianhydrides and diamine compounds may be used alone or in combination of two or more.

The tetracarboxylic dianhydride and the diamine compound are mixed in an organic polar solvent.
Examples of the organic polar solvent include N, N-dialkylamides such as N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylformamide, N, N-diethylacetamide, N, N-dimethylmethoxyacetamide and the like. In addition to the above, dimethyl sulfoxide, hexamethyl phosphortriamide, N-methyl-2-pyrrolidone, pyridine, dimethyl sulfoxide, tetramethylene sulfone, dimethyl tetramethylene sulfone and the like can be mentioned. Any of these may be used alone or in combination of two or more.

  By heating the polyamic acid to about 200 to 450 ° C., the imidization reaction proceeds and the polyamic acid is converted to polyimide. However, by using a catalyst or a dehydrating agent, the imidization reaction may be advanced at a lower temperature. it can. The catalyst is not particularly limited as long as the imidization reaction is promoted, and examples thereof include imidazoles, secondary amines, and tertiary amines. Examples of the dehydrating agent include organic carboxylic acid anhydrides, N, N′-dialkylcarbodiimides, lower fatty acid halides, halogenated lower fatty acid anhydrides, arylphosphonic acid dihalides, thionyl halides, and the like.

  Examples of fibrous conductive materials include pure metal fibers made of gold, silver, iron, aluminum, etc., alloy fibers made of stainless nichrome, etc., non-metallic fibers made of carbon (also called carbon), graphite (also called graphite), etc. Can be mentioned. Graphite refers to artificial graphite obtained by graphitizing amorphous carbon (so-called carbon black) at a high temperature of 2000 degrees or more. Among these, fibrous graphite is preferable because of its good thermal conductivity.

  It is preferable that the volume ratio of the fibrous conductive material in the endless heating element is 60% by volume or less. As the content ratio of the fibrous conductive material in the endless heating element increases, the contact area between the fibrous conductive materials increases, so that the endless heating element has a low resistance.

FIG. 1 is an image diagram of a fibrous conductive material dispersed in a polyimide resin.
As shown in FIG. 1, fibrous conductive materials 232 overlap each other in the polyimide resin 231. When a voltage is applied to the endless heating element, free electrons move between the fibrous conductive materials 232. In FIG. 1, the arrows illustrate the movement of free electrons. During the movement, free electrons collide with molecules existing in the endless heat generating body, so that the molecules vibrate and heat is generated.

Polyimide resin is excellent in heat resistance, but expands and contracts depending on temperature. When the position of the fibrous conductive material changes due to expansion and contraction of the polyimide resin and the contact area between the fibrous conductive materials changes, the resistance of the endless heating element changes.
In order to suppress this change in resistance, the endless heating element according to the present invention contains polyvinylpyrrolidone.

  When polyvinyl pyrrolidone is contained, the mechanism of the effect of suppressing the resistance change of the endless heating element is not clear even when the temperature changes due to heat generation. However, in the endless heating element, polyvinyl pyrrolidone is a fiber. It is presumed that it covers the periphery of the conductive material. Even if the fibrous conductive materials are bound together by polyvinylpyrrolidone covering the periphery, and the polyimide resin expands and contracts due to temperature changes, there is no change in the positional relationship of the fibrous conductive materials, or there is a change. Is a small change. As a result, it is speculated that the change in resistance of the endless heating element can be suppressed.

The endless heating element has a content ratio of polyvinylpyrrolidone in the range of 0.1 to 10.0% by mass with respect to all components of the endless heating element. When the content mass ratio is less than 0.1% by mass, the function of polyvinylpyrrolidone as a binder is not exhibited, and the resistance change rate of the endless heating element increases. On the other hand, when the content mass ratio exceeds 10.0% by mass, the viscosity of the polyamic acid solution to which polyvinyl pyrrolidone is added increases, and the dispersibility of polyvinyl pyrrolidone significantly decreases. As a result, the function of polyvinylpyrrolidone as a binder is not exhibited.
If it is in the range of the said content mass ratio, it is preferable that a polyvinyl pyrrolidone exists in the range whose weight average molecular weight is 10,000-100,000.

The endless heating element has a volume resistivity (Ω · m) in the range of 0.08 × 10 ^{−4 to} 10.00 × 10 ⁻⁴ (Ω · m). This is preferable.

(Method for producing endless heating element)
As one embodiment of a method for producing an endless heating element according to the present invention, a production method including the following steps is exemplified.

(1) Step of preparing a polyamic acid solution Tetracarboxylic dianhydride and a diamine compound are dissolved in an organic polar solvent in equimolar amounts. The melt is mixed, heated, and subjected to a polycondensation reaction to prepare a polyamic acid solution.

(2) Step of preparing a dispersion of a fibrous conductive material A fibrous conductive material is dispersed in the polyamic acid solution prepared in the step (1) to prepare a dispersion of a fibrous conductive material. The dispersion method is not particularly limited, and for example, the dispersion can be performed using a nanomizer, ultrasonic wave, ball mill, sand mill, basket mill, homogenizer, or the like.
The content (volume%) of the fibrous conductive material in the polyamic acid solution is preferably in the range of 15 to 60 volume% from the viewpoint of the strength of the endless heating element.
In addition, the viscosity of the obtained dispersion is generally in the range of 1 to 100 Pa · s, which is optimal in terms of coating. The viscosity is a value measured at a temperature of 25 ° C. using a measuring instrument TVB10 (manufactured by Toki Sangyo Co., Ltd.).

(3) Step of preparing endless heating element coating solution (2) Polyvinylpyrrolidone is added and dispersed in the dispersion prepared in step (2) to obtain an endless heating element coating solution. The dispersion method is not particularly limited, and the method exemplified as the dispersion method of the fibrous conductive material can be used.
As described above, the addition amount of polyvinyl pyrrolidone is preferably such that the content mass ratio with respect to the endless heating element is in the range of 0.1 to 10.0% by mass.

(4) Production process of endless heating element The coating film of the endless heating element coating solution prepared in the step (3) is formed endlessly. The endless heating element coating liquid coating method is not particularly limited, but from the viewpoint of uniformity of film thickness, ease of control, etc., a spiral that is coated on the surface of the mold while rotating the cylindrical mold A coating method is preferred. For example, as shown in FIG. 2, a cylindrical mold a1 is set in the coating apparatus, and the endless heating element is discharged uniformly from the nozzle a2 of the coating apparatus while rotating the mold a1 at a constant rotational speed. Apply to. After drying this and removing the organic polar solvent, the imidization reaction proceeds to produce an endless heating element. The imidization reaction may proceed by baking at a high temperature of about 300 to 450 ° C., or may proceed by low temperature heating using a catalyst and a dehydrating agent.

The endless heating element according to the present invention can be suitably used as a heating layer of a heating belt provided in a fixing device or the like.
Hereinafter, an embodiment of an endless heating element according to the present invention will be described as a heating belt used as a heating layer and a fixing device provided with the heating belt.

<Fixing device>
FIG. 3 is a schematic diagram of the fixing device according to the present embodiment. 4 is a cross-sectional view of the fixing device taken along line XX in FIG.
As shown in FIGS. 3 and 4, the fixing device includes a pair of fixing rollers 1 </ b> A and 1 </ b> B and a heat generating belt 2. The fixing roller 1 </ b> A is disposed inside the heat generating belt 2, and the fixing rollers 1 </ b> A and 1 </ b> B are in contact with each other through the heat generating belt 2. The sheet P conveyed to the fixing rollers 1A and 1B is sandwiched between nips N formed by the pressure contact of the fixing rollers 1A and 1B, and is subjected to a fixing process by heating with the heating belt 2 and pressing with the fixing rollers 1A and 1B. Is done.

The fixing rollers 1A and 1B are configured substantially the same, and include a cored bar 11, an elastic layer 12, and the like as shown in FIG.
As the metal core 11, aluminum having good thermal conductivity is mainly used, but nonmagnetic stainless steel materials, heat resistant glass, and the like can also be used.
The elastic layer 12 is made of synthetic rubber such as silicone rubber or fluorine rubber.
In addition, you may provide the coating layer which coat | covers the surface of the elastic layer 12 with fluororesins, such as PFA.

During the fixing process, both ends of the core metal 11 of the fixing roller 1B are urged by an urging means (not shown), and the fixing roller 1B comes into pressure contact with the fixing roller 1A via the heat generating belt 2.
Further, the fixing rollers 1A and 1B are rotated by a driving unit (not shown) and rotate around the cored bar 11 as a rotation axis. By the rotation of the fixing rollers 1A and 1B, the sheet is conveyed while being fixed.

<Heat belt>
FIG. 5 is a cross-sectional view of the heat generating belt 2 taken along the line XX of FIG.
As shown in FIG. 5, the heat generating belt 2 is formed with a reinforcing layer 21, a heat generating layer 22, an elastic layer 23, and a release layer 24 in this order from the side in contact with the fixing roller 1B.

The reinforcing layer 21 is provided to maintain strength. As the reinforcing layer 21, it is preferable to use the same material as the base material used for the heat generating layer 22, that is, a polyimide resin.
The reinforcing layer 21 preferably has a layer thickness in the range of 20 to 80 μm.

As the heat generating layer 22, the endless heat generating element described above is used, and the heat generating layer 22 is formed by dispersing a fibrous conductive material in a polyimide resin as a base material.
The heat generating layer 22 preferably has a layer thickness of 50 to 200 μm.

  The heat generating layer 22 generates heat when energized. As shown in FIG. 5, at both ends of the heat generating belt 2, a power receiving unit 25 is provided instead of the elastic layer 23 and the release layer 24. The power receiving unit 25 is an electrode, a conductor, or the like. The power feeding unit 3 is provided adjacent to the power receiving unit 25, and the power feeding unit 3 is urged by the urging unit 4 and contacts the power receiving unit 25 during the fixing process. The power receiving unit 25 supplies the current supplied from the power source 6 via the power supply unit 3 to the heat generating layer 22. The solid arrows in FIG. 5 indicate the flow of current supplied to the heat generating layer 22.

As the elastic layer 23, an elastic body having heat resistance is used. Examples of such an elastic body include silicone rubber and fluorine rubber, and specific examples include silicone rubber KE1379 (manufactured by Shin-Etsu Chemical Co., Ltd.), silicone rubber DY356013 (manufactured by Toray Dow Corning), and the like.
The thickness of the elastic layer 23 is preferably about 20 to 200 μm in order to improve the thermal conductivity of heat generated by the heat generating layer 22.

  The release layer 24 is provided so that the toner T on the paper P in contact with the heat generating belt 2 is easily separated from the heat generating belt 2. As the release layer 24, for example, a fluororesin is used, and examples thereof include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether polymer, and tetrafluoroethylene-hexafluoropropylene. The layer thickness of the release layer 24 is preferably about 5 to 30 μm.

(Method for manufacturing heat generating belt)
The heat generating belt 2 can be manufactured by the following method, but the manufacturing method is not limited to this (formation of reinforcing layer and heat generating layer).
A polyamic acid solution and an endless heating element coating solution are prepared in the same manner as in the method for manufacturing an endless heating element described above.
As shown in FIG. 2, a cylindrical mold a1 is set in the coating apparatus, and the polyamic acid solution is discharged from the nozzle a2 of the coating apparatus and uniformly coated while rotating the mold a1 at a constant rotational speed. . Thereafter, it is heated to 120 ° C. and dried for 40 minutes.
An endless heating element coating solution is uniformly coated on the dried polyamic acid solution coating film. The application method is the same as for the polyamic acid solution. This is heated to 120 ° C. and dried for 40 minutes. Thereafter, the reinforcing layer 21 and the heat generating layer 22 are formed by baking at 400 ° C. for 20 minutes.
(Formation of elastic layer and release layer)
An elastic layer coating solution prepared in advance is applied onto the heat generating layer 22. Next, after heating at 150 ° C. for 30 minutes for primary vulcanization, heating is performed at 200 ° C. for 4 hours for secondary vulcanization to form the elastic layer 23.
A release layer coating solution is applied onto the elastic layer 23 to form the release layer 24. Finally, after cooling to room temperature, the heat generating belt 2 is obtained by releasing from the mold a1.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these.

[Example 1]
<Preparation of endless heating element 11>
680 parts by mass of N-methyl-2-pyrrolidone as a solvent is put into a container. Thereto, the following polyamic acid composition was charged and dissolved in a solvent, and then mixed and heated to cause a polycondensation reaction to prepare a polyamic acid solution.
(Polyamide acid composition)
Tetracarboxylic dianhydride (3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride; manufactured by Mitsubishi Kasei Co., Ltd.) 0.42 mol diamine compound (p-phenylenediamine; manufactured by Tokyo Chemical Industry Co., Ltd.) 0. 42 moles

  To 100 parts by mass of the prepared polyamic acid solution, 90 parts by mass of fibrous graphite (milled fiber XN-100, manufactured by Nippon Graphite Co., Ltd.) having an average fiber length of 18 (μm) is added, and Robomix (manufactured by PRIMIX). To prepare an endless heating element coating solution s1. The volume ratio of fibrous graphite in the endless heating element coating solution s1 was 25% by mass.

  A stainless steel cylindrical mold was attached to the coating apparatus, and the prepared endless heating element coating liquid s1 was uniformly applied to the mold surface by the coating apparatus. As shown in FIG. 2, the coating apparatus discharges the coating liquid from the nozzle a2 while rotating the mold a1, and applies the coating liquid to the peripheral surface of the mold a1. The nozzle a2 moves in the direction of the rotation axis of the mold a1 while discharging the coating liquid.

The coating conditions by the coating device are as follows.
Polyamic acid solution temperature: 25 ° C
Nozzle discharge port shape: conical Nozzle discharge port diameter: 2 mm
Distance from nozzle outlet to mold surface: 5mm
Discharge rate of coating liquid from nozzle: 5 ml / min
The moving speed of the nozzle mold in the direction of the rotation axis: 1 mm / sec
Mold rotation speed: 40rpm
The rotational speed of the mold was measured with HT-4200 (manufactured by Ono Sokki Co., Ltd.).

  After coating, the mold a1 was rotated at a rotation speed of 40 rpm, and heated at a temperature of 120 degrees for 40 minutes and dried to remove the solvent. Then, when it baked for 20 minutes at the temperature of 400 degreeC and it was made to cool to room temperature, the metal mold a1 was removed and the endless heating element 1 was obtained.

<Preparation of endless heating elements 21, 31, 41, 51, 61>
In the production of the endless heating element 11, the endless heating element was changed except that the addition amount of fibrous graphite was changed and the content (volume%) of the fibrous graphite was changed to the content as shown in Tables 1 and 2. In the same manner as in Example 11, endless heating elements 21, 31, 41, 51 and 61 were produced.

<Preparation of endless heating element 12>
In the same manner as the endless heating element 1, a polyamic acid solution and a dispersion of fibrous graphite were prepared. To this dispersion, 0.1 part by mass of polyvinyl pyrrolidone (polyvinyl pyrrolidone K90, manufactured by Tokyo Chemical Industry Co., Ltd.) having a weight average molecular weight of 630000 is added and dispersed with Robomix (manufactured by PRIMIX) to prepare an endless heating element coating liquid s2. Obtained.

A stainless steel cylindrical mold was mounted on the coating device, and the prepared endless heating element coating solution s2 was uniformly applied by the coating device. The application method and application conditions are the same as the application method and application conditions in the endless heating element 11.
After coating, the mold was rotated at a rotational speed of 40 rpm, and heated at a temperature of 120 degrees for 40 minutes and dried to remove the solvent. Then, it baked for 20 minutes at the temperature of 400 degreeC, and the endless heat generating body 12 was formed. The solid content of the polyimide resin in the endless heating element 12 was 20 parts by mass.

<Production of endless heating elements 13 to 16>
Endless heating elements 13 to 16 were prepared in the same manner as the endless heating element 12 except that the content (mass%) of polyvinylpyrrolidone was changed as shown in Table 1 in the preparation of the endless heating element 12. did.

<Production of Endless Heating Elements 22-26, 32-36, 42-46, 52-56, 62-66>
In the production of the endless heating element 12, the endless heating element 12 was changed except that the content (volume%) of fibrous graphite and the content (mass%) of polyvinylpyrrolidone were changed as shown in Tables 1 and 2. In the same manner, endless heating elements 22 to 26, 32 to 36, 42 to 46, 52 to 56, and 62 to 66 were produced.

<Evaluation>
About the produced endless heat generating elements 11-16, 21-26, 31-36, 41-46, 51-56, 61-66, the following item was evaluated.

(1) Volume resistivity (Ω · m)
As shown in FIG. 6, copper tape b2 (CU-35C, manufactured by Sumitomo 3M) was attached to both ends of the endless heating element b1 to form electrodes.
A power source b3 (PCR2000L, manufactured by Kikusui Electronics Co., Ltd.) and an LCR meter b4 (3532-80, manufactured by Hioki Electric Co., Ltd.) were connected between the electrodes. An AC voltage was applied by the power source b3, and the resistance (Ω) between the electrodes was measured by the LCR meter b4. The applied voltage was set so that the surface temperature of the endless heating element b1 was 180 ° C. The surface temperature is a value measured by a digital radiation temperature sensor FT-H20 (manufactured by Keyence Corporation).
The volume resistivity (Ω · m) was calculated from the measured resistance (Ω), the distance z (mm) between the electrodes, and the thickness (μm) of the endless heating element b1.

(2) Resistance change rate (%)
Similarly to the volume resistivity, the resistance (Ω) was measured at 0 hours and 300 hours by applying an AC voltage. From the measured value when the application time of the alternating voltage was 0 hour and the measured value when the alternating voltage was 300 hours, the resistance change rate was obtained by the following equation.
Resistance change rate (%) = (measured value at 300 hours−measured value at 0 hour) / measured value at 0 hour

(3) Image quality level Heating belts having endless heating elements 11-16, 21-26, 31-36, 41-46, 51-56, 61-66 as heating layers are prepared, and each heating belt is provided. The image quality level of the toner image when the fixing process was performed by the fixing device was evaluated.

(Production of heat generating belt)
In the same manner as the production of the endless heating element 11, a polyamic acid solution and an endless heating element coating solution s1 were prepared.
As shown in FIG. 2, the polyamic acid solution was discharged by a coating apparatus and uniformly applied around the cylindrical mold. Then, it heated at 120 degreeC and dried for 40 minutes. The prepared endless heating element coating solution s1 was uniformly coated on the dried polyamic acid solution coating film by a coating apparatus and dried at 120 ° C. for 40 minutes. Then, it baked at 400 degreeC for 20 minutes.
After cooling, a mixed liquid in which silicone rubber KE1379 (manufactured by Shin-Etsu Chemical Co., Ltd.) and silicone rubber DY356013 (manufactured by Toray Dow Corning Co., Ltd.) were mixed at a content ratio of 2: 1 was discharged and applied by a coating apparatus. Next, primary vulcanization was performed by heating at 150 ° C. for 30 minutes, and then secondary vulcanization was performed by heating at 200 ° C. for 4 hours.
Further, when a release layer coating liquid (Teflon (registered trademark) 350-J: manufactured by Mitsui / Dupont Fluoro Chemical Co., Ltd.) is applied and cooled to room temperature, the endless heating element 11 generates heat by being released from the mold. A heat generating belt formed as a layer was obtained.

  In the same manner as the endless heating element 11, a heating belt in which each endless heating element 12-16, 21-26, 31-36, 41-46, 51-56, 61-66 was formed as a heating layer was produced. .

The produced heating belts are mounted on bizhubC550 (made by Konica Minolta Business Technologies), respectively, and the printing test is performed at a printing rate of 5%, and the toner image density after initial printing and after printing 900,000 sheets is measured by a density sensor. The image quality level was evaluated from the difference as follows.
A: There is no density difference or almost no density unevenness.
B: Although there is a density difference and density unevenness can be confirmed, it is within an allowable range.
C: There is a large density difference, and density unevenness can be clearly confirmed.
Among A to C, A and B are assumed to be acceptable levels.

Tables 1 and 2 below show the evaluation results of each item.

As shown in Tables 1 and 2, the endless heating elements according to the examples have a resistance change rate of 5.0% or less, and all the image quality is also acceptable. It can be seen that the rate of change in resistance decreases in proportion to the content of polyvinylpyrrolidone, but the rate of change in resistance increases outside the range of 0.1 to 10% by mass and the image quality decreases.
On the other hand, the endless heating elements according to the comparative examples all have a resistance change rate of 6% or more, and the image quality is degraded.
Moreover, according to the comparative example, when the volume resistivity is out of the range of 0.08 × 10 −4 to 10.00 × 10 −4 (Ω · m), the resistance change rate is increased to 10% or more, It can be seen that the image quality is significantly reduced.

[Example 2]
<Preparation of endless heating element 71>
The endless heating element 53 of Example 1 was manufactured in the same manner as the endless heating element 53 except that granular graphite (UP-5; manufactured by Nippon Graphite Co., Ltd.) was used instead of fibrous graphite. 71 was produced.

<Preparation of endless heating element 72>
An endless heating element 72 was prepared in the same manner as the endless heating element 71 except that an endless heating element coating solution without addition of polyvinylpyrrolidone was used in the preparation of the endless heating element 71.

<Evaluation>
The resistance change rate (%) was determined and evaluated for the endless heating element 53 manufactured in Example 1 and the endless heating elements 71 and 72 manufactured in Example 2.
The resistance change rate (%) was obtained by the same method as the resistance change rate of Example 1.

Table 3 below shows the resistance change rate (%) of the endless heating elements 53, 71 and 72.

  As shown in Table 3, the endless heating element 53 using fibrous graphite and added with polyvinylpyrrolidone has a resistance change rate of only 2.0%. This figure shows that there is virtually no change in resistance. On the other hand, the endless heating elements 71 and 72 using granular graphite have a resistance change rate close to 10%. In addition, the endless heating elements 71 and 72 using granular graphite show almost no difference in resistance change rate depending on whether or not polyvinylpyrrolidone is added.

1A, 1B Fixing roller 2 Heat generating belt 21 Reinforcing layer 22 Heat generating layer 23 Elastic layer 24 Release layer 25 Power receiving unit 3 Power feeding unit P Paper T Toner

Claims (4)

An endless heating element that disperses a fibrous conductive material in a polyimide resin and generates heat when energized,
An endless heating element containing polyvinylpyrrolidone in a range of 0.1 to 10.0% by mass with respect to all components of the endless heating element. 2. The endless heating element according to claim 1, wherein a volume resistivity of the endless heating element is in a range of 0.08 × 10 ^{−4 to} 10.00 × 10 ⁻⁴ (Ω · m).   A heating belt in which the endless heating element according to claim 1 or 2 is formed as a heating layer.   A fixing device comprising the heat generating belt according to claim 3.

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