JP2003195669A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of realizing excellent fixing properties even in the case of an image requiring a large amount of toner put on a recording medium such as a color image without spoiling the shortening of rise time and small power which are the advantages of a film heating system. <P>SOLUTION: This fixing device is provided with a pair of roller members 71 and 72 forming a fixing nip (n) by coming into press-contact with each other, an endless belt 73 laid round one of the roller members 71, and a heating means 75 for heating the front surface side of the belt 73 at a position separate from the nip (n). The fixing device is so constituted to fix a toner image supported on the recording medium P on the medium P by bringing the image into contact with the belt 73 and making the image pass through the nip (n) together with the belt 73, thereby heating and pressuring it. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device that fuses color or monochrome toners on a recording medium using an electrophotographic system and fixes the toner to the recording medium, and an image forming apparatus equipped with this fixing device. .

[0002]

2. Description of the Related Art In an image output device using an electrophotographic system such as a copying machine or a laser beam printer, an electrostatic latent image is formed on a surface of a latent image carrier having a photosensitive layer by laser irradiation. A toner image is formed by attaching toner to the toner, and the toner image is transferred to a recording medium such as a recording sheet by electrostatic force to form an image. However, in this state, the toner is merely fixed on the recording medium and is not fixed, and hence it is necessary to perform a work of permanently fixing the toner on the recording medium thereafter. The most effective means for doing this is to apply heat to melt the powdery toner and then apply pressure so as to press the toner and the recording medium.

Generally, in an image forming apparatus using an electrophotographic method, two rollers called a fixing roller and a pressure roller are mainly constituted as means for permanently fixing toner on a recording medium. A so-called heat roller type fixing device is used. The surface of each of these rollers is made of elastic rubber, and the surface of the fixing roller, or the surface of the fixing roller and the pressure roller is 150 to 20 by a heater provided in the cavity of the cylindrical roller core metal.
It is heated to 0 ° C and controlled by a temperature detector.
Further, the fixing roller and the pressure roller are adapted to rotate at a constant speed while contacting each other by a constant pressure.
The recording medium on which the toner is transferred enters the nip portion between the fixing roller and the pressure roller with the toner bearing surface facing the fixing roller side, whereby heat and pressure are applied to the toner, and the toner on the recording medium is transferred. Fixing takes place.

In recent years, instead of the fixing roller, a ceramic heater is arranged through a thin film, and the recording medium on which the toner is transferred and the film material are fixed together by moving and passing through the heater position. Fixing devices are also widely used. Such a film heating type heating device is known in JP-A-63-313182, JP-A-2-157878, and the like, and has a lower heat capacity as a heating body than the above heat roller type fixing device. A linear heating element and a film material having a thickness of, for example, 40 μm
Since a thin heat resistant film material having a thickness of about m can be used, it is advantageous that the rise time to a predetermined fixing temperature can be shortened (quick start property) and power saving can be achieved.

FIG. 5 is a schematic diagram of an example of a film heating type fixing device using an endless film type film material.

Reference numeral 79 is an endless film type thin film heat-resistant film material (hereinafter, also simply referred to as a film), 78 is a film driving roller, 74 is a driven roller also serving as a film tension roller, and 75 is a heating body (thermal heater). Drive roller 78 and driven roller 7
4, the heating body 75 is arranged substantially parallel to each other in the axial direction, and the endless film 79 is composed of these three members 78, 74,
It is stretched between 75.

Both ends of the drive roller 78 and the driven roller 74 are rotatably supported by bearings between bearing members (not shown). The heating body 75 is a fixing member fixedly supported by a heater support serving as an immovable member. Drive roller 78
Is driven to rotate clockwise in the drawing by a drive system (not shown), and the endless film 79 is given a conveying force by the frictional force between the outer peripheral surface of the drive roller 78 and the inner surface of the film as the drive roller 78 is rotationally driven. While the inner surface of the film slides on the lower surface of the heating body 75, the inner surface of the film is rotationally moved between the drive roller 78, the driven roller 74 and the heating body 75 in the clockwise direction of arrow a in the drawing.

Reference numeral 72 denotes a pressure roller having a rubber elastic layer having a good releasability such as silicon rubber. A film 79 is sandwiched between the lower surface of the heating body 75 and an unillustrated urging means such as a total pressure. The endless film 79 is pressed against the lower surface of the heating body with a contact pressure of 4 to 8 kg, and rotates in the forward direction with respect to the rotation direction of the film at the same peripheral speed as the rotation speed of the film as the endless film 79 rotates.

The endless film 79 has a total thickness of 100 μm.
m, more preferably less than 40 μm, a single-layer or multi-layer film material having heat resistance, good thermal conductivity, low heat capacity, releasability, mechanical strength, durability and the like. As an example of the film structure, FIG. 6 shows the layer structure of the film 79. 79
Reference numeral 1 denotes polyimide (PI), which is a heat-resistant layer as a base layer (base film) of the film, and 792 is a release layer laminated on the outer surface (the surface facing the toner image) of the heat-resistant layer 791, which is made of a fluororesin. It

The heating element 75 is a linear heating element having a low heat capacity and having the longitudinal direction in the axial direction of the endless film 79 (the direction orthogonal to the rotational movement direction a of the endless film, hereinafter referred to as the film width direction) and generating heat when energized. . As an example, a heater substrate, and an energization heating element layer formed in a strip shape or a linear shape along the length in a substantially central portion of the lower surface of the substrate,
The lower surface of the substrate including the energization heating element layer is covered with a heat-resistant glass as a surface protection layer having a thickness of about 10 μm, and the temperature sensing element 76 provided on the upper surface of the substrate controls energization of the heating element layer. The temperature of the heating element is controlled to a predetermined temperature.

The heating element 75 has a small overall heat capacity, and the temperature of the heater at the pressure contact portion reaches the temperature at which the toner on the recording material P can be fixed in a short time (quick start property). (Standby temperature control) It is not necessary to keep it in advance, energy saving can be realized, and the temperature rise inside the machine can be prevented.

[0012]

However, the above-mentioned film heating type fixing device has the following problems.

1. Since the pressure is applied via the heater, the pressure cannot be increased from the strength of the heater, and fixing failure occurs due to insufficient pressure. Further, when fixing a color image in which a large amount of toner is loaded, the recording medium and toner are separated due to insufficient pressure.

2. Since a hard heater is contacted via a thin film, when an image with large unevenness such as a color image is fixed, defective fixing occurs in a portion with large unevenness of toner.

3. When a film having an increased thickness is used in order to improve the fixability of a color image, heat transfer is delayed, and it is difficult to shorten the rise time, which is an advantage.

Therefore, the present invention does not impair the shortening of the rise time and the reduction in power consumption, which are the advantages of the film heating method, and is good even in the case of an image such as a color image having a large amount of toner on the recording medium. It is an object of the present invention to provide a fixing device and an image forming apparatus that can realize fixability.

[0017]

According to a first aspect of the present invention, there is provided a pair of roller members which are in pressure contact with each other to form a fixing nip, an endless belt which is wound around the one roller member, and which is separated from the fixing nip. A heating means for heating the endless belt at a fixed position, and the toner image carried on the recording medium is brought into contact with the belt to pass through the fixing nip together with the endless belt to heat and press the toner image. A fixing device for fixing an image on the recording medium.

A second invention is characterized in that, in the above-mentioned first invention, the endless belt has thermal conductivity larger in a surface direction than in a thickness direction.

A third invention is characterized in that, in any one of the above inventions, the other roller member has a heat insulating property.

A fourth invention is characterized in that, in any one of the above inventions, the one roller member is a drive roller.

A fifth invention is characterized in that, in the above-mentioned fourth invention, the other roller member is driven by the one roller member by frictional contact with the belt.

A sixth invention is characterized in that, in any one of the above inventions, the endless belt is tensioned between the one roller member and a tension roller.

A seventh invention is characterized in that, in any one of the above inventions, the heating means directly contacts and heats the belt.

An eighth invention is the invention according to any one of the first to sixth inventions, characterized in that the heating means heats the belt in a non-contact manner.

A ninth invention is characterized in that, in any one of the above inventions, the heating means heats a surface side of the belt.

In a tenth aspect based on the eighth aspect, the heating means is disposed on the entrance side of the fixing nip and heats the toner image on the recording medium conveyed to the fixing nip in a non-contact manner. It is characterized by

An eleventh invention is an image forming means for forming a toner image on a latent image carrier and transferring the toner image onto a recording medium by a transfer means, and a recording medium on which the toner image is transferred by the transfer means. The image forming apparatus is characterized by including the fixing device according to any one of the above-mentioned inventions that conveys the unfixed toner image onto the recording medium.

In the above-described invention, the belt is warmed before the recording medium carrying the unfixed toner image enters the fixing nip, so that it is not necessary to install a heater in the fixing nip portion.
The pressure can be increased.

Further, by heating the belt on the surface side in contact with the recording medium, the thickness of the belt itself can be increased, and the followability to irregularities of the toner is improved.

Further, by setting the thermal conductivity of the belt in the relationship of surface direction> thickness direction, the heat of the heating means can be efficiently transmitted to the recording medium, and the rise time is increased even if a thick belt is used. Can be shortened and power can be saved.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

(First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 2 is a schematic configuration diagram showing an electrophotographic color copying machine which is an embodiment of the image forming apparatus according to the present invention.

In FIG. 2, reference numeral 1 denotes a photoconductor, which has a photo-semiconductive layer on the surface of a conductive substrate such as aluminum and rotates in the direction of arrow X. A primary charger 2 uniformly negatively charges the surface of the photoconductor 1 by using corona discharge. 3 is an exposure device, which exposes the surface of the uniformly charged photoconductor 1 imagewise,
Form an electrostatic latent image. Numeral 4 is a rotatably arranged developing device for each color, which develops the electrostatic latent image on the photoconductor 1 with toner to visualize it.

A transfer drum 5 winds a transfer paper P, which is a recording medium supplied from a paper cassette, and electrostatically transfers the toner image on the photoconductor 1 by a corona charger. 6 is a cleaning device, which is the photoconductor 1 after the toner image is transferred.
The toner remaining on the surface is scraped off, and the photoconductor 1 can be used again for image formation.

A fixing device 7 fixes the transfer paper P on which each color is transferred by heat and pressure, and fixes the toner on the transfer paper P. The fixing device 6 is a feature of the present invention and will be described in detail later.

The sequence of the entire apparatus of this embodiment will be briefly described below by taking the case of copying in the full color mode as an example.

When copying is started, first, the primary charger 2 uniformly charges the photoconductor 1. Then, the exposure device 3 exposes the image exposure, which is obtained by reading the original document on the original table 8 and performing color separation, to form a yellow electrostatic latent image of the first color on the photoconductor 1.

Next, in the developing section, the electrostatic latent image is visualized by the yellow developing device 4y set in advance at the developing position, and a yellow toner image is formed on the photoconductor 1.

On the other hand, the transfer paper P of a size matched to the original is transferred from the paper cassette 9 in time with this toner image.
Is sent to the conveyance roller 91 and is wound around the transfer drum 5 by the adsorption charger 51.

The toner image is discharged in advance by the corona charger 52 and electrostatically transferred onto the transfer paper P by the transfer charger 53 at the transfer portion.

Similarly, magenta, cyan, and black electrostatic latent images are formed in order, and the developing devices 4m, 4c, and 4k of the respective colors are formed.
To develop a full-color image on the transfer paper P and superimpose it. The transfer paper P on which the full-color image is formed is separated from the transfer drum 5 by the separation charger 54 and is conveyed to the fixing device 7.

In the fixing device 7, the toners of the respective colors superposed on the transfer paper P are mixed by heat and pressure to be bonded to the transfer paper P, and are discharged to the paper discharge tray 81 as a full color print.

Next, the fixing device, which is a feature of the present invention, will be described in detail.

FIG. 1 is a schematic diagram showing an example of a fixing device having the features of the present invention.

An endless belt member 73 conveys heat used for fixing, and is stretched between two rollers of a belt tension roller 74 also serving as a driving roller 71 and a driven roller.

Drive roller 71 and tension roller 74
Are arranged substantially parallel to each other in the axial direction, and both end shaft portions are rotatably supported between bearing members (not shown). The drive roller 71 is rotationally driven in the clockwise direction in the drawing by a drive system (not shown), and the endless belt 73 is given a conveying force by the frictional force between the outer peripheral surface of the drive roller 71 and the inner surface of the belt as the drive roller 71 is rotationally driven. Then, it is rotated between the drive roller 71 and the tension roller 74 in the clockwise direction of arrow b in the drawing.

The heating element 75 is the same as the heating element described in the conventional example of FIG. 5, and is fixedly supported by a heater support (not shown) as a stationary member and abuts against the endless belt 73 by the tension of the tension roller 74. Is supplied with heat energy. Similarly, reference numeral 76 is a temperature detecting element for controlling the heating element 75 at a predetermined temperature. The heating element 75 is provided between the drive roller 71 and the tension roller 74 on the upstream side of the endless belt 73 in the transport direction when viewed from the drive roller 71.

Reference numeral 72 denotes a pressure roller, which is a drive roller 71.
The tension roller 74 is arranged substantially parallel to the axial direction of the tension roller 74, and both ends of the tension roller 74 are rotatably supported. Further, since the endless belt 73 is sandwiched between the endless belt 73 and the endless belt 73, the endless belt 73 is elastically deformed to create the nip portion n necessary for fixing because the endless belt 73 is sandwiched between the endless belt 73 and the drive roller 71. Further, the pressure roller 72 itself is not provided with a drive means, and is rotated in the forward direction with respect to the belt rotational movement direction at substantially the same peripheral speed due to the frictional force with the rotationally moving endless belt 73.

A guide 77 smoothly guides the transfer paper P to the fixing nip portion n, and further guides the fixed transfer paper P coming out from the nip portion n to the paper discharge tray 81.

The endless belt 73 has a layer thickness of 200 μm, and at least the surface thereof is made of a material having excellent elasticity to improve the followability with respect to the unevenness of the toner layer on the transfer paper P. Furthermore, what is characteristic is the anisotropic thermal conductivity, and the thermal conductivity in the surface direction (belt rotation direction in the figure) is approximately 100 times higher than that in the thickness direction. .

Therefore, as shown in FIG. 3, the heat energy of the heating element 75 provided on the surface of the belt which comes into contact with the toner layer is greater than the heat energy (arrow group c) in the thickness direction of the belt 73 in the belt conveying direction. The thermal energy (arrow group d) heading for becomes larger, and the thermal energy can be efficiently transported to the fixing nip portion n in combination with the transportation of the belt 73.

Further, since the heat of the heater can be efficiently transmitted to the recording medium, the rise time can be shortened and the power consumption can be reduced even if a thick belt is used.

The driving roller 71 has a shape in which a foamed layer of silicon rubber having a good heat insulating property is provided around a cored bar, and the periphery thereof is coated with a silicon rubber having a strong frictional force.
This prevents heat from escaping from the endless belt 73, and further increases the frictional force with the belt to ensure reliable conveyance.

The foamed layer of the driving roller 71 has not only heat insulation but also elasticity for forming a fixing nip. However, if it is too soft, it may cause problems such as poor conveyance of the belt and wrinkling of the belt, so that it has an appropriate hardness. Need to choose.

The pressure roller 72 has a structure similar to that of the driving roller 71, and has a core metal provided with a foam layer and a surface layer. However, since the pressure roller 72 is in direct contact with the transfer paper P, the pressure roller 72 has a surface. It uses a material with releasability. Further, since there is no heating element in the nip n formed with the driving roller 71, it is possible to dramatically increase the pressing force as compared with the conventional film heating type fixing device, which is necessary for fixing a color image. It is possible to configure with a high contact pressure.

An example of actually performing the image forming property using the fixing device of the present embodiment will be shown.

For the endless belt 73, a carbon graphite sheet having anisotropic thermal conductivity is used. This thermal conductivity was 400 W / m · ° C. in the surface direction, and 4 W / m · ° C. in the thickness direction.

The drive roller 71 has a process speed of 12
It was driven at 0 mm / sec, and the endless belt 73 was also moving at substantially the same speed.

The heating element 75 has its control temperature set to 200 ° C. and generates heat a little earlier in time with the timing when the transfer sheet P enters the nip.

When the transfer paper on which the color image was transferred was fixed under the above conditions, good fixing properties were obtained, and the short rise time and power consumption were equivalent to those of the film heating type fixing device. Was obtained.

(Second Embodiment) FIG. 4 shows a second embodiment.

In FIG. 4, the same members as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, the film 7
Although the resistance heating element is used as the heating source of the heating element for heating 3, the halogen lamp 751 is used as the heating source in the second embodiment. This halogen lamp 7
Similar to the drive roller 71, 51 is arranged in the direction perpendicular to the paper surface to fill the width of the belt 73.

Reference numeral 752 denotes a reflecting plate for reflecting the heat light of the halogen lamp 751 toward the film 73, and efficiently transfers the heat light of the halogen lamp 751 onto the endless belt 73 and the guide 77. It is arranged to illuminate. Further, the temperature measuring element 76 is a reflection plate 752.
Is disposed on the back surface of the halogen lamp 751 and detects the temperature of the reflection plate to indirectly control the temperature of the halogen lamp 751.

By using such a heating element, the heat energy can be supplied to the endless belt 73 right before the nip portion, and the heat energy can be effectively used. Further, since the radiant heat can be applied to the transfer paper P on the guide 77 on the entrance side, the transfer paper P can be warmed before entering the fixing nip, and the fixing property can be further improved. .

Further, this is a secondary effect, but since the belt is warmed without contact, it is possible to reduce deterioration due to rubbing of the belt and temperature unevenness due to poor contact.

[0067]

As described above, according to the present invention, the following effects can be obtained.

1. By heating the belt before entering the fixing nip, it was not necessary to install a heater in the pressurizing portion, and the pressure could be increased.

2. By heating the belt on the surface side that contacts the recording medium, the thickness of the belt itself can be increased,
The conformability to the toner unevenness is improved.

3. By setting the thermal conductivity of the belt so that the surface direction> thickness direction, the heat of the heater can be efficiently transmitted to the recording medium, and even if a thick belt is used, the rise time is shortened and power consumption is saved. Was achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fixing device according to a first embodiment of the present invention.

2 is a schematic configuration diagram showing an electrophotographic color copying machine having the fixing device of FIG.

FIG. 3 is a schematic diagram showing a heat flow of the fixing device of FIG.

FIG. 4 is a schematic configuration diagram of a fixing device according to a second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a conventional film heating type fixing device.

6 is a structural diagram of the film of FIG.

[Explanation of symbols]

1 photoconductor 2 Primary charger 3 exposure equipment 4 developing device 5 transfer drum 6 cleaning device 7 Fixing device 71 drive roller 72 Pressure roller 73 Endless Belt 74 Tension roller 75 heating element 76 Temperature sensor 77 Guide 8 manuscript table 9 paper cassettes P transfer paper

Claims (11)

[Claims] 1. A pair of roller members that are in pressure contact with each other to form a fixing nip, an endless belt that is wound around the one roller member, and heating that heats the endless belt at a position distant from the fixing nip. And fixing the toner image on the recording medium by bringing the toner image carried on the recording medium into contact with the belt and passing the fixing nip together with the endless belt to heat and pressurize the toner image. Characterizing fixing device. 2. The endless belt has a thermal conductivity greater in the surface direction than in the thickness direction.
The fixing device described in 1. 3. The fixing device according to claim 1, wherein the other roller member has a heat insulating property. 4. The fixing device according to claim 1, wherein the one roller member is a driving roller. 5. The fixing device according to claim 4, wherein the other roller member is driven and driven by the one roller member by frictional contact with the belt. 6. The fixing device according to claim 1, wherein the endless belt is tensioned between the one roller member and a tension roller. 7. The fixing device according to claim 1, wherein the heating unit directly contacts and heats the belt. 8. The fixing device according to claim 1, wherein the heating unit heats the belt in a non-contact manner. 9. The fixing device according to claim 1, wherein the heating unit heats the surface side of the belt. 10. The heating device is arranged on the inlet side of the fixing nip and heats a toner image on a recording medium conveyed to the fixing nip in a non-contact manner. Fixing device. 11. A toner image is formed on a latent image carrier,
11. An image forming unit for transferring the toner image onto a recording medium by a transfer unit and a recording medium on which the toner image is transferred by the transfer unit are conveyed to fix an unfixed toner image on the recording medium. An image forming apparatus comprising the fixing device according to any one of claims.