JP2004138949A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents paper from being wrapped round a roller on the toner side even when a large amount of toner is transferred to thin paper or a full-color image is formed, thereby hindering the occurrence of paper separation failure or curling. <P>SOLUTION: A fixing roller 51 has a metal core 57a and a first elastic layer 58a formed round the metal core 57a. A pressure roller 52 has a metal core 57b and a second elastic layer 58b formed round the metal core 57b. The relationship between the stiffness c1 of the first elastic layer 58a and the stiffness c2 of the second elastic layer 58b is c1<c2. The thickness n1 of the first elastic layer 58a and the thickness n2 of the second elastic layer 58b are substantially the same. The outside diameter h1 of the fixing roller 51 and the outside diameter h2 of the pressure roller 52 are also substantially the same. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus including a fixing device that passes a sheet carrying an unfixed toner image through a nip formed between a pair of heated rollers, heats and melts the unfixed toner on the sheet, and fixes the unfixed toner on the sheet. Equipment related.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, usually, unfixed toner on a sheet is fixed by a heat roller fixing method. That is, at least one roller of the roller pair forming the nip is heated by a built-in heat source, and the unfixed toner is heated and melted through the paper carrying the unfixed toner image in the nip between the pair of rollers to be fixed on the paper. Things.
[0003]
In a full-color image forming apparatus, it is necessary to fix a large amount of toner with high image quality, and it is required that both the fixing roller and the pressure roller have flexible roller surfaces. Therefore, both the fixing roller and the pressure roller have a configuration in which an elastic rubber layer having a certain thickness is wound around the cored bar.
[0004]
In such a heat roller fixing method, the heat capacity of the roller is large, and it takes a long time until heat is propagated from a heat source such as a halogen lamp built in the roller and the surface of the roller reaches a temperature required for fixing. Therefore, even if the power switch of the image forming apparatus is turned on, it is necessary to wait until the roller surface reaches a fixing temperature (fixing temperature). This warm-up period of several minutes significantly reduces the efficiency of office work.
[0005]
One of the techniques for reducing the warm-up time and the power consumption of the heat roller fixing method is an external heat fixing method. In this method, a heat source is not built in the fixing roller or the pressure roller, but a heat source is built in the external heating roller.The external heating roller is pressed against the surface of the fixing roller or the pressure roller, and the fixing roller or the pressure roller is pressed. Is heated from the surface.
[0006]
For example, in the fixing device described in Patent Document 1, as shown in FIG. 5, fixing is performed by passing a sheet on which toner has been transferred between a pair of rollers 207 having the same configuration. The roller 207 does not have a heat source inside, but is provided with a heating roller 201 that rotates in contact with the outer peripheral surface of the roller 207 instead. The roller 207 is provided with a heat-resistant and heat-insulating foamed elastic material layer 210 such as a silicon sponge around the cored bar 211, and a good heat conductive elastic material such as alumina or silica in rubber. A thin layer 209 of a material filled with a high thermal conductive filler is provided, and a release resin layer 208 such as a PFA (tetrafluoroethylene-per-fluoroalkylvinyl ether copolymer) tube is provided on the surface layer.
[0007]
The heating roller 201 pressed against each roller 207 is composed of a metal roller 205 provided with a heater 206 at the center. If the heater 206 is energized to generate heat, the temperature of the metal roller 205 rises, and heat is transmitted to the good heat conductive elastic layer 209 on the surface of the roller 207 with which the metal roller 205 contacts, and the temperature of the roller 207 increases. . However, since the foamed elastic layer 210 on the inside has heat insulating properties, heat is not transmitted to the back, that is, to the core metal 211. This not only improves the thermal efficiency and shortens the rise time until fixing becomes possible, but also reduces the temperature difference at the boundary between the cored bar 211 and the foamed elastic layer 210. There is no risk of damage. The roller 207 has a structure in which a foamed elastic layer 210, a good heat conductive elastic layer 209, and a release resin layer 208 are laminated on a cored bar 211, that is, since the outer layer is formed of an elastic body, the roller 207 has a small pressure contact. A large nip can be obtained by elastic deformation even with force. Since a pair of rollers 207 having the same structure is pressed against each other, the nip formed therebetween is substantially flat.
[0008]
Since the fixing roller is in direct contact with the unfixed toner on the paper, the paper is more likely to adhere than the pressure roller. That is, there is a tendency that the separating property of the sheet after passing through the nip is inferior. As a countermeasure, a separation claw may be provided on the surface of the fixing roller. However, problems such as a trace of peeling by the claw and an increase in curl degree are likely to occur. In particular, since a full-color image generally has a high toner area ratio on paper, there is a problem that unfixed toner adheres to the fixing roller and the paper is wrapped around the fixing roller, and poor separation of the paper is likely to occur. Even if the image is not a full-color image, the same problem occurs when a large amount of toner is transferred to thin paper.
[0009]
[Patent Document 1]
JP-A-4-116677
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems of the related art, and prevents a sheet from being wound around a roller (fixing roller) on a toner surface side even when a large amount of toner is transferred to a thin sheet. It is a first object of the present invention to provide an image forming apparatus capable of suppressing occurrence of paper separation failure and curling.
Further, it is a second object of the present invention to provide an image forming apparatus capable of suppressing occurrence of paper separation failure and curling even in the case of a full-color image in which the toner area ratio on paper tends to be high.
[0011]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 is a fixing roller for fixing unfixed toner on a sheet, and a first roller for externally heating the fixing roller. An image forming apparatus provided with a fixing device having an external heating unit, a pressing roller that forms a nip that abuts the fixing roller to insert a sheet, and a second external heating unit that externally heats the pressing roller. The fixing roller has a core and a first elastic layer formed around the core, and the pressing roller has a core and a second elastic layer formed around the core. In addition, a relationship of c1 <c2 is established between the hardness c1 of the first elastic layer and the hardness c2 of the second elastic layer.
[0012]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the thickness n1 of the first elastic layer and the second elastic layer n2 are substantially the same. And
[0013]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, an outer diameter h1 of the fixing roller and an outer diameter h2 of the pressure roller are substantially the same.
[0014]
According to the first to third aspects of the present invention, since the pressing roller includes the elastic layer having a higher hardness than the fixing roller, the pressing roller bites into the fixing roller, and the nip is upwardly convex along the pressing roller. Curved into a shape. As a result, the sheet passes through the nip with the leading end deflected to the pressure roller side, and is discharged, so that curling of the sheet to the fixing roller side due to contraction of the image surface of the sheet is suppressed, and the sheet The separation property between the image surface side and the fixing roller is improved. Therefore, it is not necessary to dispose a sheet separating claw on the surface of the fixing roller.
[0015]
The invention according to claim 4 forms a fixing roller for fixing unfixed toner on the paper, a first external heating means for heating the fixing roller from outside, and a nip for abutting the fixing roller and passing the paper through. An image forming apparatus comprising: a fixing device having a pressure roller for heating and a second external heating means for externally heating the pressure roller, wherein the fixing roller includes a core metal and a first metal member formed around the core metal. The pressure roller has a core metal and a second elastic layer formed around the core metal, and has a layer thickness n1 of the first elastic layer and a second elastic layer. The relationship of n1> n2 is established between the thickness of the body layer and the thickness n2.
[0016]
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, an outer diameter h1 of the fixing roller and an outer diameter h2 of the pressure roller are substantially the same.
[0017]
According to the fourth and fifth aspects of the present invention, since the pressure roller has a smaller thickness of the elastic layer than the fixing roller, the pressure roller bites into the fixing roller and the nip faces upward along the pressure roller. Curved in a convex shape. As a result, the sheet passes through the nip with the leading end deflected to the pressure roller side, and is discharged, so that curling of the sheet to the fixing roller side due to contraction of the image surface of the sheet is suppressed, and the sheet The separation property between the image surface side and the fixing roller is improved. Therefore, it is not necessary to dispose a sheet separating claw on the surface of the fixing roller.
[0018]
According to a sixth aspect of the present invention, there is provided a fixing roller for fixing unfixed toner on a sheet, a first external heating means for heating the fixing roller from outside, and a nip for abutting the fixing roller to insert the sheet. An image forming apparatus comprising: a fixing device having a pressure roller for heating and a second external heating means for externally heating the pressure roller, wherein the fixing roller includes a core metal and a first metal member formed around the core metal. The pressure roller has an elastic layer, and the pressure roller has a core metal and a second elastic layer formed around the core metal, and has an outer diameter h1 of the fixing roller and an outer diameter h2 of the pressure roller. , A relationship h1 <h2 is established.
[0019]
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, a layer thickness n1 of the first elastic layer and a layer thickness n2 of the second elastic layer are substantially the same. It is characterized by the following.
[0020]
According to the sixth and seventh aspects of the present invention, since the outer diameter of the fixing roller is smaller than the outer diameter of the pressure roller, the sheet after passing through the nip is easily separated from the fixing roller due to the curvature. Accordingly, the separation property between the image surface side of the sheet and the fixing roller is improved, and it is not necessary to dispose a sheet separation claw on the surface of the fixing roller.
[0021]
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the first external heating means includes a heat source therein and comes into contact with the surface of the fixing roller. A second heating roller for heating the pressure roller by heating the fixing roller by contacting the surface of the pressure roller with the heat source therein. It is characterized by being.
[0022]
According to the invention described in claim 8, since the fixing roller and the pressure roller can be directly heated by the external heating roller, the warm-up time can be reduced.
[0023]
As described above, according to the first to eighth aspects of the present invention, it is possible to omit the paper separating means such as the separation claw and the decurling means for preventing or reducing the curl of the paper, thereby making it possible to reduce the number of parts and cost. .
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[0025]
FIG. 1 shows a model cross section of a tandem type color printer 1 which is an example of an xerographic type image forming apparatus. FIG. 2 shows a model cross section of the image forming unit.
[0026]
In the printer 1, either full-color image output or monochrome image output is selected according to the color information of the document image data from the external computer. The image output speed is set to 20 sheets / minute in A4 size in both full color and monochrome. In this specification, specific numerical values such as dimensions, ratios, speeds, voltages, and temperatures appear in addition to the image output speed. However, these numerical values are examples of one preferred example and limit the scope of the invention. It does not do.
[0027]
A paper transport belt 8 is disposed inside the housing 2 of the printer 1. The paper transport belt 8 is wound around the pulleys 10 and 11, and transports the paper horizontally from right to left in FIG. On the paper receiving side of the paper transport belt 8, a paper feed device 12 and a paper transport path 13 are arranged. A fixing device 50, a sheet conveyance path 15, and a discharge unit 16 are disposed on the sheet discharge side of the sheet conveyance belt 8. The discharge section 16 is provided on the upper surface of the housing 2.
[0028]
A total of four image forming units are arranged in series on the paper transport belt 8 from the upstream side to the downstream side in the paper transport direction. The four image forming units are, in order from the upstream side, a black image forming unit 30B, a yellow image forming unit 30Y, a cyan image forming unit 30C, and a magenta image forming unit 30M.
[0029]
FIG. 2 shows the structure of the image forming units 30B, 30Y, 30C, and 30M. Since the image forming units have the same structure, the identification symbols “B”, “Y”, “C”, and “M” are omitted, and only the reference numeral “30” is provided.
[0030]
The core of the image forming unit 30 is a photosensitive drum 4 using amorphous silicon as a photosensitive member, around which a main charger 5, an LED print head unit 6, a developing device 3, and a cleaning device 20 are arranged. I have. Also, as shown in FIG. 1, the transfer roller 9 faces the photosensitive drum 4 with the paper transport belt 8 interposed therebetween. The transfer roller 9 also has a role of supporting the sheet conveying belt 8 and bringing it into contact with the photosensitive drum 4. A voltage of -1.5 kV is applied to the transfer roller 9.
[0031]
The developing device 3 contains a developer in which toners of each color of black, yellow, cyan, and magenta and a ferrite carrier are mixed at a weight ratio of 5:95. The toner has a median diameter (by volume) of 9 μm as measured by a Coulter counter, and the ferrite carrier has an average particle diameter of 70 μm. The developing device 3 is provided with a developing sleeve 3a containing a fixed magnet (not shown).
[0032]
The photoreceptor drum 4 and the developing sleeve 3a face each other with a gap of 0.5 mm therebetween, and rotate so that the opposing surfaces move in the same direction. The peripheral speed of the photosensitive drum 4 is 100 mm / sec, and the peripheral speed of the developing sleeve 3a is 200 mm / sec. A magnetic brush is formed on the surface of the developing sleeve 3a by a developer. Further, the toner is positively charged by friction with the carrier. An uncut plate (not shown) is provided for the developing sleeve 3a. The gap between the cutting board and the developing sleeve 3a is 0.5 mm. A developing bias voltage of +300 V is applied to the developing sleeve 3a.
[0033]
The developer in the developing device 3 is consumed by the development. In order to supplement the consumed developer, toner supply containers 7B, 7Y, 7C, and 7M are provided corresponding to the image forming units 30B, 30Y, 30C, and 30M, and the developer is supplied by a conveying unit (not shown). As a result, the developing device 3 always holds an appropriate amount of the developer therein.
[0034]
The cleaning device 20 includes a rubber cleaning roller 21 that contacts the photosensitive drum 4, a cleaning blade 22 that scrapes toner not transferred onto the paper from the photosensitive drum 4, and a discharge spiral 23 that discharges the toner to a collection container (not shown). Having. The cover of the cleaning device 20 is not shown in FIG.
[0035]
The printer 1 performs an image output operation as follows.
[0036]
The surface of the photosensitive drum 4 is uniformly charged to +400 V by the main charger 5. When document image data is input from an external computer or the like, the LED print head 6 irradiates the surface of the photosensitive drum 4 with LED light corresponding to the document image data. On the surface of the photosensitive drum 4, the voltage of the exposed portion irradiated with the LED light is attenuated to +25 V, and an electrostatic latent image is formed together with the +400 V portion of the non-exposed portion. With the developing bias voltage of +300 V applied to the developing sleeve 3a, the positively charged toner in the developer adheres to the exposed portion, and the electrostatic latent image is visualized by the toner.
[0037]
The paper transport belt 8 carries the paper supplied from the paper feeding device 12 and travels in the same direction as the moving direction of the surface of the photosensitive drum 4 at the same peripheral speed of the photosensitive drum 4 at 100 mm / sec. The exposure timing of the photosensitive drum 4 by the LED print head 6 is set so that the transfer of the toner is started from a predetermined position on the sheet.
[0038]
When the paper on the paper transport belt 8 passes below the photosensitive drum 4, the toner attached to the photosensitive drum 4 is attracted to the paper by the voltage of -1.5 KV applied to the transfer roller 9. As a result, the toner is transferred to the paper.
[0039]
The toner not transferred to the paper is scraped off by the cleaning blade 22 and discharged to a collection container (not shown) by the discharge spiral 23. The cleaning roller 21 adjusts the surface of the photosensitive drum 4 after the toner transfer.
[0040]
The toner of each color of black, yellow, cyan, and magenta is sequentially transferred in the image forming units 30B, 30Y, 30C, and 30M. It is drawn into the device 50. Then, after the toner is fixed by the heat roller inside the fixing device 50, the toner is discharged to the discharge unit 16 via the paper conveyance path 15.
[0041]
FIG. 3 is a schematic cross-sectional view illustrating a roller configuration of the fixing device 50. A fixing roller 51 and a pressure roller 52 that press against each other to form a nip for fixing, a first heating roller 53 that contacts the fixing roller 51, and a second heating roller 54 that contacts the pressure roller 52; A total of four rollers are arranged.
[0042]
Heaters 55 and 56 as heat sources are disposed inside the first heating roller 53 and the second heating roller 54. When one of the fixing roller 51 and the first heating roller 53 rotates, the other rotates accordingly, and the heat of the first heating roller 53 uniformly heats the outer peripheral portion of the fixing roller 51. Similarly, if one of the pressure roller 52 and the second heating roller 54 rotates, the other rotates accordingly, and the heat of the second heating roller 54 uniformly heats the outer peripheral portion of the pressure roller 52.
[0043]
The fixing roller 51 and the pressure roller 52 have metal cores 57a and 57b at the center, respectively. In the fixing roller 51, a first elastic layer 58a is formed around a core bar 57a, and in the pressing roller 52, a second elastic layer 58b is formed around a core bar 57b. . The fixing roller 51 and the pressure roller 52 are configured such that the following relationship occurs between them.
[0044]
First, the following relationship is established between the hardness (Asuka C hardness) c1 of the first elastic layer 58a and the hardness (Asuka C hardness) c2 of the second elastic layer 58b.
c1 <c2
[0045]
The thickness n1 of the first elastic layer 58a is substantially the same as the thickness n2 of the second elastic layer 58b.
[0046]
Further, the outer diameter h1 of the fixing roller 51 and the outer diameter h2 of the pressure roller 52 are substantially the same.
[0047]
By setting the hardness and thickness of the elastic layer of the fixing roller 51 and the pressing roller 52 and the outer diameter of the roller as described above, the pressing roller 52 having an elastic layer having a higher hardness than the fixing roller 51 is provided. Bites into the fixing roller 51, and the nip is curved in an upwardly convex shape along the pressure roller 52. As a result, the sheet passes through the nip with the leading end deflected to the pressure roller 52 side and is discharged, and curling of the sheet toward the fixing roller 51 due to contraction of the image surface of the sheet is suppressed. In addition, the separability between the image surface side of the sheet and the fixing roller 51 is improved.
[0048]
The fixing roller 51 and the pressure roller 52 may be configured so that the following relationship occurs between them.
[0049]
First, the following relationship is established between the layer thickness n1 of the first elastic layer 58a and the layer thickness n2 of the second elastic layer 58b.
n1> n2
[0050]
The outer diameter h1 of the fixing roller 51 and the outer diameter h2 of the pressure roller 52 are substantially the same.
[0051]
According to this configuration, since the pressure roller 52 has a thinner elastic layer than the fixing roller 51, the pressure roller 52 bites into the fixing roller 51, and the nip faces upward along the pressure roller 52. Curved in a convex shape. As a result, the sheet passes through the nip with the leading end deflected to the pressure roller side, and is discharged, so that curling of the sheet to the fixing roller side due to contraction of the image surface of the sheet is suppressed, and the sheet The separation property between the image surface side and the fixing roller is improved.
[0052]
The fixing roller 51 and the pressure roller 52 may be configured so that the following relationship occurs between them.
[0053]
First, the following relationship is established between the outer diameter h1 of the fixing roller 51 and the outer diameter h2 of the pressure roller 52.
h1 <h2
[0054]
The layer thickness n1 of the first elastic layer 58a is substantially equal to the layer thickness n2 of the second elastic layer 58b.
[0055]
According to this configuration, since the outer diameter of the fixing roller 51 is smaller than the outer diameter of the pressing roller 52, the sheet after passing through the nip is easily separated from the fixing roller 51 due to the curvature. Accordingly, the separation property between the image surface side of the sheet and the fixing roller 51 is improved, and it is not necessary to dispose a sheet separation claw on the surface of the fixing roller 51.
[0056]
Preferably, the fixing roller 51 and the pressure roller 52 are configured as follows. That is, the elastic layers 58a and 58b are formed of sponge, and the release layers 59a and 59b are provided outside thereof. The elastic layers 58a and 58b may be formed of low heat capacity rubber. Rubber containing metal may be provided outside the elastic layers 58a and 58b made of sponge, and the release layers 59a and 59b may be provided outside the rubber.
[0057]
【Example】
Hereinafter, embodiments of the present invention will be described.
[0058]
The paper feed speed (process speed) of the image forming apparatus 1 is set to 120 mm / sec. Generally, a metal (practically, aluminum or iron) is used for the heat roller from the viewpoint of thermal conductivity and strength, and a heat-resistant release material such as PEA or PTEE is applied to the surface as needed. In this embodiment, an aluminum hollow shaft having a diameter of 20 mm and a wall pressure of 0.5 mm was used.
[0059]
The fixing roller only needs to have a heat capacity enough to fix the toner on the paper on the roller surface. The heat roller is a low heat capacity rubber, a foamed sponge, or a low heat capacity rubber or a foamed sponge + a high heat conductive thin layer and a heat release layer. Can be used. When it is desired to transmit high heat, high heat conductive silicon rubber, metal, or a material obtained by dispersing a heat conductive filler (metal or the like) in silicon rubber can be used.
[0060]
The fixing roller and the pressure roller are formed by molding a layer of foamed silicone rubber on the surface of a metal shaft as a metal core, and covering the surface with a 50 μm-thick PFA tube. The pressure was set so that the nip width between the heating roller and the fixing roller was about 6 mm, and the nip width between the fixing roller and the pressure roller was about 6 to 7 mm.
[0061]
FIG. 4 is a table showing conditions of each embodiment. In the first embodiment, the outer shape of the core is 12 mm for both the fixing roller and the pressure roller. The roller outer diameter was 26 mm on the fixing roller side and 29 mm on the pressure roller side. The thickness of the elastic layer was 7 mm for both the fixing roller and the pressure roller. The hardness (Asuka C hardness) of the elastic layer was 40 degrees on the fixing roller side and 60 degrees on the pressure roller side.
[0062]
In the case of Example 1, the nip was slightly convex upward, and even when a large amount of toner-transferred paper passed, the paper did not wind around the fixing roller, and good separability was obtained.
[0063]
In Example 2, the outer shape of the core of the fixing roller was 12 mm, and the outer shape of the core of the pressure roller was 16 mm. The outer diameter of the roller is 26 mm for both the fixing roller and the pressure roller. The layer thickness of the elastic layer was 7 mm on the fixing roller side and 5 mm on the pressure roller side. The hardness (Asuka C hardness) of the elastic layer was 40 degrees for both the fixing roller and the pressure roller.
[0064]
In the case of Example 2, the nip was slightly convex upward, and even when a large amount of toner-transferred paper passed, the paper did not wind around the fixing roller, and good separability was obtained.
[0065]
In Example 3, the outer shape of the core of the fixing roller was 6 mm, and the outer shape of the core of the pressure roller was 12 mm. The outer diameter of the roller is 20 mm on the fixing roller side and 26 mm on the pressure roller side. The thickness of the elastic layer was 7 mm for both the fixing roller and the pressure roller. The hardness (Asuka C hardness) of the elastic layer was 40 degrees for both the fixing roller and the pressure roller.
[0066]
In the case of Example 3, even when the paper on which a large amount of toner was transferred passed, the paper was not wrapped around the fixing roller, and good separability was obtained.
[0067]
【The invention's effect】
According to the present invention, the hardness of the elastic layer of the pressure roller is made higher than the hardness of the elastic layer of the fixing roller, and the thickness of the elastic layer of the pressure roller is made smaller than the thickness of the elastic layer of the fixing roller. By adopting a configuration in which the outer diameter of the fixing roller is made smaller than the outer diameter of the pressure roller, curling of the sheet toward the fixing roller is suppressed, or the sheet is easily separated from the fixing roller, and The separability between the image surface side and the fixing roller is improved. Therefore, it is not necessary to dispose a sheet separating claw on the surface of the fixing roller.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a printer according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an image forming unit of the printer. FIG. 3 is a schematic cross-sectional view showing a roller configuration of a fixing unit of the printer. FIG. 4 is a table showing conditions and results of the embodiment. FIG. 5 is a schematic cross-sectional view showing a roller configuration of a conventional fixing unit.
Reference Signs List 50 fixing device 51 fixing roller 52 pressure roller 53 first heating roller 54 second heating roller 55, 56 heating heater 57a, 57b cored bar 58a first elastic layer 58b second elastic layer 59a, 59b Release layer

Claims (8)

A fixing roller for fixing the unfixed toner on the paper, a first external heating means for externally heating the fixing roller,
A pressure roller that forms a nip that abuts the fixing roller and allows paper to pass through;
An image forming apparatus comprising: a fixing device having a second external heating unit that externally heats a pressure roller;
The fixing roller has a cored bar and a first elastic layer formed around the cored bar,
The pressure roller has a cored bar and a second elastic layer formed around the cored bar,
An image forming apparatus, wherein a relationship of c1 <c2 is established between the hardness c1 of the first elastic layer and the hardness c2 of the second elastic layer. 2. The image forming apparatus according to claim 1, wherein a thickness n1 of the first elastic layer and a thickness of the second elastic layer n2 are substantially the same. 3. The image forming apparatus according to claim 2, wherein an outer diameter h1 of the fixing roller is substantially equal to an outer diameter h2 of the pressure roller. A fixing roller for fixing unfixed toner on paper,
First external heating means for externally heating the fixing roller;
A pressure roller that forms a nip that abuts the fixing roller and allows paper to pass through;
An image forming apparatus comprising: a fixing device having a second external heating unit that externally heats a pressure roller;
The fixing roller has a cored bar and a first elastic layer formed around the cored bar,
The pressure roller has a cored bar and a second elastic layer formed around the cored bar,
An image forming apparatus, wherein a relationship of n1> n2 is established between a layer thickness n1 of the first elastic layer and a layer thickness n2 of the second elastic layer. The image forming apparatus according to claim 4, wherein an outer diameter h1 of the fixing roller is substantially the same as an outer diameter h2 of the pressure roller. A fixing roller for fixing unfixed toner on paper,
First external heating means for externally heating the fixing roller;
A pressure roller that forms a nip that abuts the fixing roller and allows paper to pass through;
An image forming apparatus comprising: a fixing device having a second external heating unit that externally heats a pressure roller;
The fixing roller has a cored bar and a first elastic layer formed around the cored bar,
The pressure roller has a cored bar and a second elastic layer formed around the cored bar,
An image forming apparatus, wherein a relationship h1 <h2 is established between an outer diameter h1 of a fixing roller and an outer diameter h2 of a pressure roller. 7. The image forming apparatus according to claim 6, wherein a thickness n1 of the first elastic layer and a thickness n2 of the second elastic layer are substantially the same. The first external heating unit is a first heating roller that includes a heat source therein and heats the fixing roller by contacting the surface of the fixing roller.
8. The apparatus according to claim 1, wherein the second external heating means includes a heat source therein, and is a second heating roller for heating the pressure roller by contacting the surface of the pressure roller. An image forming apparatus according to any one of the above.

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