JPH1152767A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure satisfactory fixing even in the case a toner image transferred on a transfer material has ununiform toner-layer-thickness. SOLUTION: An elastic body 13 is provided downstream from a heating body 12 in the direction of the carrying of a transfer material P so as to be close to or in contact with the heating body 12. In the area N1 where the heating body 12 and a pressure roller 11 are in contact by pressing with each other, the toner image Ta on the transfer material P is melted under heat, and in the area N2 where the elastic body 13 and the pressure roller 11 are in contact by pressing each other, the toner image Ta melted under heat is pressed under heat. Thus, because the elastic body 13 follows the shape of the toner image Ta, colors an sufficiently be mixed even in the case the toner image Ta is multicolor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing a developer image transferred onto a recording medium, for example, a transfer material by heating and pressing, and an electrophotographic process provided with the fixing device. The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that forms an image.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic process, a surface of a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image bearing member is uniformly charged by a charging device during image formation. The processed and charged photosensitive drum surface is exposed by an exposure device to form an electrostatic latent image.
The electrostatic latent image is developed by a developing device to form a toner image, the toner image is transferred to a transfer material such as paper as a recording medium by a transfer device, and the toner image is transferred onto the transfer material by a fixing device. Is fixed as a permanently fixed image.

[0003] As the fixing device, recently, a fixedly supported heating element (thermal heater, hereinafter referred to as a heater) has been used.
A heat-resistant film (fixing film) conveyed while being pressed against the heater; and a pressure member for bringing the transfer material into close contact with the heater via the fixing film. A fixing device (film heating method) in which an unfixed toner image formed and supported on the transfer material is heated and fixed on the transfer material by applying to the transfer material.
Has been devised.

Such a film heating type fixing device has a low heat capacity heating as a heater in comparison with other heat fixing type devices such as a heat roller type, a hot plate type, a belt type, a flash fixing type, and an open fixing type. A body can be used, and the temperature of the heater, which is a heating body, can be relatively low, so that power can be saved and the time from power-on to image output can be shortened (quick start property).

[0005] A heater as a heating element is an insulating substrate (base material) having low heat capacity, such as heat resistance and good thermal conductivity, such as ceramics.
A low-heat-capacity heat-generating resistor having a low heat capacity is formed by coating the heat-generating resistor with a low heat capacity in a linear or band shape, and the heater has a smaller heat capacity of the resistor and the substrate than the current supplied to the resistor. Therefore, the surface rapidly rises to a required fixing temperature (for example, about 200 ° C.).

The fixing film in contact with the heater also has a small heat capacity, and the heat energy of the heater side is effectively transmitted to the transfer material side in pressure contact with the fixing film via the fixing film to heat and fix the toner image. Is executed.

In the temperature control of the heater, the temperature of the heater is detected by a temperature detecting element, and the energization to the energized heating resistor is controlled based on the temperature detection information to control the temperature of the heater to a predetermined fixing temperature. An energization control configuration is adopted.

[0008]

By the way, in the above-mentioned fixing device of the conventional film heating system, the fixing film is rubbed while applying a high pressure to the heating film made of ceramic such as glass. There is a problem that the fixing film is worn and the life is shortened. In particular, in an image composed of multiple toner layers, such as a full-color image, it is necessary to apply high pressure when the toner is in a melt-softened state to sufficiently mix colors, and it has been difficult to improve the life.

In addition, when the unfixed toner image has a portion where the thickness of the toner layer is high and a portion where the thickness of the toner layer is low, if the surface of the heating body is rigid, sufficient pressure is not applied to the toner where the thickness of the toner layer is low. In some cases, the fixability was insufficient or offset occurred.

Further, when a color image is formed on a transparency sheet for OHP, if the toner in a portion where the toner thickness is small is not sufficiently melted, light transmittance is poor at the time of projection and the image becomes blackish. There was a point.
Generally, such a phenomenon is likely to occur in the contour portion of the toner image.

As a method of solving these problems, a method of providing a rubber elastic layer on the surface of a heating element or a fixing film has been proposed. However, these methods are required to transfer heat through the elastic layer. However, when this elastic layer is made thicker, the heating efficiency is lowered, so that it cannot be made too thick, and a sufficient effect cannot be obtained.

Further, there has been proposed an apparatus provided with a means for mutually pressing a fixing film and a transfer material by a pressurizing rotator after a toner image is heated and melted by a heater.
In the method of applying pressure by another pressurizing rotary body after passing through the heat fixing nip, the pressurizing step and the heating step are separated, and the heat capacity of the pressurizing rotary body is large, so that the pressurizing rotary body is hard to warm.

For this reason, it is difficult to apply pressure when the toner is in a melt-softened state, and it has been necessary to provide another heating means for the pressing member. Further, after passing through the heating nip, the fixing film and the transfer material may be separated or shifted.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device and an image forming apparatus capable of improving the life of the apparatus and performing satisfactory fixing.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been made in consideration of the above circumstances. An endless heat-resistant fixing film rotatably in contact with the heating member; and a rotatable pressure member for contacting the object to be heated with the heating member via the fixing film. In the fixing device that heats the object to be heated by the fixing film and the object to be heated being nipped and conveyed together in the press-contact nip portion formed by An elastic member is provided which comes into contact with or comes into contact with the pressure member via the fixing film.

Further, the pressure between the elastic member and the pressing member is set to be larger than the pressure between the heating element and the pressing member.

Further, the apparatus has a temperature detecting means for detecting a temperature near a sliding surface of the elastic member with the fixing film, and based on temperature information of the elastic member detected by the temperature detecting means, the heating element It is characterized in that temperature control is performed.

Further, a thin film layer having good slidability is provided on at least a sliding surface of the elastic member with the fixing film.

Further, the image forming apparatus according to the present invention comprises an image carrier for carrying an image, a transfer means for transferring a toner image formed on the image carrier to a transfer material, and a transfer device for transferring the toner image onto the transfer material. A fixing device according to any one of claims 1 to 4, wherein the fixing device fixes the formed toner image by heating and pressing.

(Operation) According to the structure of the present invention, the elastic member is provided which comes into contact with or comes into contact with the pressing member via the fixing film in the vicinity of or in contact with the downstream side of the heating member in the conveying direction of the heated member. By this, a heated body, for example, a transfer material carrying an unfixed toner image, which is sandwiched and conveyed together with the fixing film between the heating body and the pressing member, is heated and pressed by the heating body, and the toner image is melted and softened. To be. When the toner image in the melt-softened state is heated and pressed between the elastic member and the pressing member, the elastic member conforms to the shape of the toner image. Fixing can be performed.

Further, by making the pressing force between the heating element and the pressing member smaller than the pressing force between the elastic member and the pressing member, the generation and abrasion of the fixing film sliding on the heating element can be reduced. be able to.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic configuration diagram showing an image forming apparatus (a laser beam printer in the present embodiment) provided with a fixing device according to the present embodiment.

This image forming apparatus includes a photosensitive drum 1 as an image carrier, a charging roller 2, an exposing device 3, a developing device 4,
A transfer roller 5 and a fixing device 6 are provided.

The photosensitive drum 1 is a negatively charged OPC photosensitive drum, has a photosensitive layer or the like on a drum base made of aluminum, and is driven to rotate at a predetermined process speed in the direction of arrow a.

The charging roller 2 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force, is rotated by the rotation of the photosensitive drum 1, and is rotated by a charging bias power supply (not shown) with respect to the charging roller 2. A charging bias is applied to charge the photosensitive drum 1 to a predetermined polarity and potential.

The exposure device 3 forms an electrostatic latent image by performing exposure with laser light on the charged photosensitive drum 1 via a reflection mirror 3a in accordance with input image information.

In the present embodiment, the developing device 4 is a reversal developing device having a developing sleeve 4a.
A predetermined developing bias is applied to a from a developing bias power supply (not shown).

The transfer roller 5 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force, and a predetermined developing bias is applied from a transfer bias power supply (not shown).

The fixing device 6 has a fixing film 10 and a pressure roller 11. The fixing film 10 is disposed in the fixing film 10 facing the pressure roller 11 with the fixing film 10 interposed therebetween along the longitudinal direction of the fixing film 10. (The detailed configuration and operation of the fixing device 6 will be described later.)

Next, an image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is rotated at a predetermined process speed in the direction of arrow a by a driving means (not shown), and a uniform charging process of negative polarity is performed by the charging roller 2 to which a charging bias is applied. receive.

Then, the surface of the charged photosensitive drum 1 is exposed to laser light from the exposure device 3 via the reflection mirror 3a to form an electrostatic latent image corresponding to input image information. Then, the electrostatic latent image is developed by the developing sleeve 4a to which the developing bias is applied, and is visualized as a toner image.

When the toner image on the surface of the photosensitive drum 1 reaches the transfer nip between the transfer roller 5 and the photosensitive drum 1, the transfer material P is transported to the transfer nip at this timing, and a transfer bias is applied. Transfer roller 5
The toner image is transferred. The transfer material P on which the toner image has been transferred is fixed to the fixing film 10 of the fixing device 6 and the pressure roller 1.
The toner image is heated and welded onto the transfer material P and output.

Next, the configuration of the fixing device 6 will be described.

FIG. 2 is an enlarged sectional view of the fixing device 6.

The fixing device 6 includes a heater unit 14 having a heating body 12 and an elastic body 13, an endless film-like heat-resistant fixing film 10 that slides in contact with the heater unit 14 on one surface, and a fixing film 10. A pressure roller 11 having a rubber elastic layer for bringing the transfer material P into contact with the heating body 12 and the elastic body 13 of the heater unit 14 is provided.

The fixing film 10 is stretched around a driving roller 15, a tension roller 16, and a heater unit 14. The heating body 12 adhered to a heat insulating holder 17 made of a heat-resistant resin such as PPS and the elastic body 13 made of silicone rubber are fixed to a support 18 made of SUS. On the surface of the heating element 12, a temperature detecting element 19 is provided. The elastic body 13 is a transfer material P of the heating body 12.
It is installed in contact with the downstream side in the transport direction.

The pressure roller 11 is brought into contact with the heater unit 14 with a total pressure of 5 to 50 kg by a biasing means (not shown). The pressing force between the elastic body 13 and the pressing roller 11 is smaller than the pressing force between the heating body 12 and the pressing roller 11. Is also configured to be large.

The fixing film 10 is rotationally driven at a predetermined peripheral speed in the direction of arrow b without wrinkles, meandering, and speed uniformity as the driving roller 15 is driven to rotate clockwise. The pressure roller 11 rotates in the direction of arrow c following the running of the fixing film 10.

The rotatingly driven fixing film 10 is repeatedly subjected to heat fixing of a toner image, and therefore has excellent heat resistance, release properties and durability, and generally has a total thickness of 100 μm or less.
Preferably, a thin material having a thickness of 40 μm or less is used. For example, polyimide (PI) / polyetherimide (PEI)
A single-layer film or a composite layer film of a heat-resistant resin such as PES / PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin), for example, 20 μm
At least on the image contacting surface side of the thick film, a releasable coating layer obtained by adding a conductive material to a fluororesin such as PTFE (tetrafluoroethylene resin), PAE, or FEP is applied to a thickness of 10 μm.

The heating element 12 is a low-heat-capacity linear heating element having a longitudinal direction extending in a direction intersecting with the surface movement direction of the fixing film 10, and includes a heater substrate 12a, a current-generating heating element (heating element) 1
2b and a protective layer 12c. The heater substrate 12a is a member having heat resistance, insulation, and low heat capacity, and is, for example, an alumina substrate having a thickness of 1 mm, a width of 10 mm, and a length of 240 mm.

The heating element 12b is formed along a longitudinal portion of the lower surface of the heater substrate 12a (on the side facing the fixing film 10) close to the elastic body 13, for example, Ag / Pd (silver / palladium), Ta ₂ N, or the like. Is applied by screen printing or the like to a thickness of about 10 μm and a width of 1 to 3 mm, and heat-resistant glass is coated thereon as a protective layer 12c by about 10 μm.

The elastic body 13 has an Asker C hardness of 40.
2.5 mm thick silicone rubber of ５０50 ° was used.
In order to make the toner image follow the height of the toner image, a silicone sponge having an Asker C hardness of 20 to 40 °, a heat-resistant nonwoven fabric such as Nomex (trade name) or a felt is preferable.

The temperature detecting element 19 is, for example, a Pt film or the like which is provided by coating the substantially central portion of the upper surface of the heater substrate 12a (the surface opposite to the surface on which the heating element 12b is provided) by screen printing or the like. Is a low heat capacity resistance thermometer. As the temperature detecting element 19, a thermistor or the like having a low heat capacity may be arranged so as to be in contact with the heater substrate 12a.

The heating element 12 is heated by heat generated by energization of the heating element 12b, and is controlled to a predetermined fixing temperature by a temperature control circuit (not shown) including a temperature detecting element 19.

Next, the fixing operation by the fixing device 6 will be described.

The fixing device 6 is operated by the above-described image forming operation.
The transfer material P carrying the unfixed toner image Ta conveyed to the upper surface thereof is pressed into a pressure contact portion N between the heating body 12 and the pressure roller 11.
1 enters between the fixing film 10 and the pressure roller 11.

The heating element 2 is energized and heated at a predetermined timing according to an image formation start signal.
a shows the fixing film 1 formed by the heating element 12 at the press contact portion N1.
0 to heat and melt.

The transfer material P that has passed through the pressure contact portion N 1 passes through the pressure contact portion N 2 between the elastic body 13 and the pressure roller 11 while keeping the transfer material P in close contact with the fixing film 10.

At the press contact portion N2, the toner image Ta on the transfer material P heated and melted at the press contact portion N1 is transferred to the press contact portion N1.
By receiving a large pressing force by the elastic body 13 together with the fixing film 10 heated in step (1), color mixing can be sufficiently performed even in a color image including a multilayer toner image. At this time, the elastic body 13 is deformed following the height of the toner image, so that the thin fixing film 10 is brought into close contact with the high and low portions of the toner image and pressed, so that the toner image contour is sufficiently melted, Mixed colors.

Further, even when a color image is formed on the OHP sheet, it is possible to prevent the occurrence of black false contours in the transmission image.

After passing through the pressure contact portion N2, the fixing film 1
The transfer material P on which the toner image is fixed is discharged after the curvature of the transfer material P is sequentially separated from 0.

As described above, in the present embodiment, the pressure contact portion N
By reducing the pressing force in 1, abrasion of the inner surface of the fixing film 10 caused by sliding of the protective layer 12 c made of glass or the like and the fixing film 10 was reduced, and the life of the apparatus was improved.

Further, since the pressing force at the press contact portion N2 can be made larger than that at the press contact portion N1, satisfactory results can be obtained even when a color image composed of a multi-layer toner image or a color image is formed on an OHP sheet as described above. Fixing can be performed.

Further, in the press-contact portion N2 where the pressing step is performed, it is possible to lower the temperature of the heating body 12 if the heat does not escape from the elastic body 13 to the support member 18 side. Is a material having a high heat insulating property, for example, a material having bubbles such as a foam or felt is preferable.

(Second Embodiment) FIG. 3 is an enlarged sectional view showing a fixing device of an image forming apparatus according to the present embodiment.

The fixing device according to the present embodiment uses felt (Nomex (trade name in this embodiment)) 13 as the elastic body 13 of the heater unit 14, and uses the elastic body 1.
3, a second temperature detecting element 20 is arranged at a substantially central portion in the longitudinal direction inside the sliding surface side with the fixing film 10, and the elastic body 1
No. 3 has a configuration in which the sliding surface with the fixing film 10 is covered with a 20 μm-thick sheet 21 made of Teflon over the entire longitudinal area. Other configurations and operations are the same as those of the first embodiment.

If the fixing process is continuously performed during the above-described image forming operation, the temperature of the elastic body 13 becomes too high, and the melt viscosity of the toner image when the fixing film 10 and the transfer material P are separated is too low. Hot offset may occur.

When the fixing process is started from a state where the fixing device 6 is sufficiently cooled, the temperature of the elastic body 13 is not sufficiently increased when the fixing process of the first transfer material P is performed. Pressing portion N2 between body 13 and pressure roller 11
In some cases, the toner image cools instantaneously even if pressure is applied, resulting in insufficient fixing.

For this reason, in the present embodiment, during the fixing operation, the temperature of the elastic body 13 during the fixing process is detected by the second temperature detecting element 20 and the temperature of the elastic body 13 becomes too high. For example, when the temperature exceeds 150 ° C., energization control is performed on the heating element 2 b by control of a control device (not shown) so that the temperature of the heating element 12 detected by the temperature detecting element 19 becomes 160 ° C.

When the temperature of the elastic body 13 is low, for example, 100 ° C. or lower, the heating element 2b is controlled by a control device (not shown) so that the temperature of the heating body 12 becomes about 200 ° C. Energization control is performed.

Usually, the temperature of the heating element 12 is 180 ° C.
By controlling the power supply to the heating element 2b under the control of a control device (not shown), a sufficient fixing property can be obtained without always causing a high-temperature offset.

Further, by covering the sliding surface of the elastic body 13 with the fixing film 10 with a sheet 21 having good slidability such as Teflon, the driving torque of the fixing film 10 can be reduced, and Fixing film 1 of elastic body 13
It is possible to prevent a foreign substance such as abrasion powder from adhering to the sliding surface with zero, thereby causing uneven gloss and scratching the fixing film 10.

As described above, also in the present embodiment, the wear of the fixing film 10 can be reduced, the life of the apparatus can be improved, and good fixing can be performed.

[0066]

As described above, according to the present invention,
By providing an elastic member that comes into contact with or is in contact with the downstream side of the heated body in the conveying direction of the heated body, the fixing member is in contact with the pressing member via the fixing film. An object to be heated, for example, a transfer material carrying an unfixed toner image, which is nipped and conveyed together, is heated and pressed by the heating element, so that the toner image is melted and softened. When the toner image in the melt-softened state is heated and pressed between the elastic member and the pressing member, the elastic member conforms to the shape of the toner image. In this case, it is possible to perform satisfactory fixing even on a contour portion where the toner thickness is small, and it is possible to prevent the occurrence of uneven transparency even when a toner image is formed on an OHP sheet.

Further, by making the pressing force between the heating element and the pressing member smaller than the pressing force between the elastic member and the pressing member, it is possible to reduce the occurrence of scratches and abrasion of the fixing film sliding on the heating element. Thus, the life of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus including a fixing device according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing the fixing device according to the first embodiment of the present invention.

FIG. 3 is an enlarged sectional view showing a fixing device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier) 2 Charging roller 3 Exposure device 4 Developing device 5 Transfer roller 6 Fixing device 10 Fixing film 11 Pressure roller (Pressing member) 12 Heating body 13 Elastic body (Elastic member) 14 Heater unit 19 Temperature Sensing element 20 Second temperature sensing element 21 Sheet (thin film layer)

Claims (5)

[Claims] 1. A heating body, a rotatable endless heat-resistant fixing film that slides in contact with one side of the heating body and comes into contact with a body to be heated on the other side, and via the fixing film. A rotatable pressure member for bringing the heated body into contact with the heated body, and the fixing film and the heated body are put together in a press-contact nip formed by the heated body and the pressing member. A fixing device that heats the object to be heated by being nipped and conveyed, wherein the heating member approaches or comes into contact with a downstream side of the object to be heated in a conveying direction of the object to be heated, and abuts the pressure member via the fixing film. A fixing device provided with an elastic member. 2. The fixing device according to claim 1, wherein a pressing force between the elastic member and the pressing member is set to be larger than a pressing force between the heating member and the pressing member. . 3. A temperature detecting means for detecting a temperature near a sliding surface of the elastic member with the fixing film, wherein the heating element is detected based on temperature information of the elastic member detected by the temperature detecting means. The fixing device according to claim 1, wherein temperature control is performed. 4. The fixing device according to claim 1, wherein a thin film layer having good slidability is provided on at least a sliding surface of the elastic member with the fixing film. 5. An image carrier for carrying an image, transfer means for transferring a toner image formed on the image carrier to a transfer material, and heating and pressurizing the toner image transferred on the transfer material. The fixing device according to any one of claims 1 to 4, wherein the fixing device performs fixing.