JP2002162849A - Fixing device - Google Patents

Abstract

[PROBLEMS] To provide a fixing device capable of suppressing heat conduction from a heat fixing roller and shortening a warm-up time and a first copy time. A heat-fixing roller system having a heat-fixing roller, and configured to heat and pressurize a transfer sheet carrying a toner image to melt the toner and fix the toner on the transfer sheet. In the fixing device, the fixing device is a belt that presses the transfer sheet against the heat fixing roller,
A pressure belt supporting means comprising a plurality of belt support members, and an inner peripheral surface of the pressure belt for narrowing the pressure belt and the transfer sheet between the heat fixing roller and an outer peripheral surface of the pressure belt. A pressure assisting means which is detachable from the pressure belt in accordance with the surface temperature of the heat fixing roller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device of a heat fixing roller type using a pressure belt provided in an image forming apparatus such as a laser printer, a copying machine, and a facsimile.

[0002]

2. Description of the Related Art Generally, a fixing device provided in an image forming apparatus comprises a heat fixing roller having a built-in heater therein, and a pressure roller which presses against the heat fixing roller. Then, the transfer sheet (paper) on which the toner image has been transferred is pressed against the heat fixing roller by a pressure roller,
The toner image is fixed on the transfer sheet by the heat of the heater and the pressure at the time of pressing. That is, as shown in FIG.
The fixing device 1 is mainly composed of a heat fixing roller 2 and a pressure roller 3, and the surface of the heat fixing roller 2 formed of a cylindrical body is subjected to a fluororesin process so that the toner is kept releasable from the toner. ing. A heater 4 as a heating member is provided inside the heat fixing roller 2. The heater 4 is a rod-shaped heater having a heating wire inside, and both ends are fixed to a side plate (not shown) of the fixing device 1, and the energization thereof is controlled by control means (not shown). In the vicinity of the outer peripheral surface of the heat fixing roller 2, a thermistor (not shown) for detecting the temperature of the outer peripheral surface of the heat fixing roller 2 and a peeling claw are provided. The thermistor outputs the detected temperature signal to the control unit, and the control unit controls the energization of the heater 4 in response to the temperature signal.

[0003] The exfoliation claw, which is swingably supported, has its tip end in contact with the outer peripheral surface of the heat-fixing roller 2, and a transfer sheet 7 to which toner 6 conveyed from a printing unit is adhered. When the heat-fixing roller 2 is adhered to the outer peripheral surface of the heat-fixing roller 2, the heat-fixing roller 2 and the transfer sheet 7 are separated from each other by the leading end. The pressure roller 3 disposed below the heat fixing roller 2 is rotatably supported by a support shaft (not shown) having both ends fixed to a side plate (not shown) of the fixing device 1. The outer peripheral surface of the heat fixing roller 2 is pressed against the outer peripheral surface of the heat fixing roller 2. Guide plates (not shown) for guiding the transfer of the transfer sheet 7 are provided in the vicinity of the pressure contact portion between the heat fixing roller 2 and the pressure roller 3, respectively.
Each guide plate is fixed to a side plate (not shown) of the fixing device 1. Then, the transfer sheet 7 sent from the printing unit
Is guided by a guide plate to a pressure contact portion between the heat fixing roller 2 and the pressure roller 3, and the toner 6 is fixed on the surface thereof by the heating by the heater 4 and the pressure contact force of the pressure roller 3.

Here, as described above, the heat fixing roller 2
Is applied with high pressure by the pressure roller 3,
The heat fixing roller 2 is formed of a relatively thick member in order to prevent its deformation. However, when the heat-fixing roller 2 is formed of a thick member as described above, the amount of heat of the heater 4 provided therein must be increased, so that power consumption may increase. Further, there is a problem that it takes time for the heat from the heater 4 provided inside to reach the outer peripheral surface of the heat-fixing roller 2, and the warm-up time of the fixing device 1 itself is delayed. Therefore, in order to solve the above-described problems, the heating / fixing roller 2 is formed of a thin cylindrical body, and by taking measures to reduce the heat capacity of the heating / fixing roller 2, it is possible to speed up warming-up. On the other hand, if the heat-fixing roller 2 is formed of a thin cylindrical body, the heat-fixing roller 2 is crushed in the radial direction or bent in an arc shape, thereby causing a gap between the heat-fixing roller 2 and the pressure roller 3. However, there is a problem that a fixing failure occurs due to the generation of a gap in the sheet.

Therefore, in order to solve the above problem, the diameter of the heat fixing roller 2 is formed to be constant in the length direction, while the pressure roller 3 is formed in the length direction more than both ends in the length direction. The center of the heat fixing roller 2 is formed in a regular crown shape with a larger diameter, and the heat fixing roller 2 is crushed in the radial direction by the load or bent in an arc shape, so that the pressing roller 3 A conventional technique is disclosed in which the pressure is constant over the length direction. That is, it is generally widely known that wrinkles are likely to occur when the pressure roller 3 has a regular crown shape. However, since the rotation speed of the heat fixing roller 2 is constant over the length direction, the transfer sheet 7 No wrinkles are likely to occur. However, such a technique for preventing the generation of wrinkles by keeping the rotation speed constant, on the other hand, causes wrinkles due to trivial factors, and also causes a rise in cost because high precision is required in manufacturing. There's a problem.

To prevent the occurrence of wrinkles due to the heat-fixing roller 2 having the regular crown shape as described above, when the heat-fixing roller 2 has the regular crown shape, the heat-fixing roller 2 and the pressure roller are used. A technique is disclosed in which the shape of the nip formed between the nip portion and the nip portion 3 is uniform and the nip speed is kept constant to prevent wrinkles. However, similarly, in the case of this technique, wrinkles are caused by trivial factors, and high precision is required in manufacturing, which may increase costs.

As described above, the conventional heating / pressing type fixing device using the heat fixing roller 2 and the pressure roller 3 has a large heat capacity in addition to the above-described problems. Therefore, there is a fundamental problem that heat of the heat fixing roller 2 is taken away and a loss occurs in a warm-up time. Also, during the initial rotation of the heat fixing roller 2, heat is taken from the heat fixing roller 2, causing a large temperature drop, and a fixing failure occurs until recovery to a set temperature is obtained, so that the transfer sheet 7 cannot be passed. There is a problem.

Therefore, in recent years, a fixing device using a so-called belt fixing system in which the pressure roller 2 is replaced with a belt having a small heat capacity has been receiving attention. A fixing device using the belt fixing method will be described with reference to FIG. That is, as shown in FIG. 8, a fixing device 1a using the belt fixing method includes a heat fixing roller 2 having a heater 4 built therein, and a heat resistant pressure belt 11 pressed against the heat fixing roller 2. And a belt driving means (not shown) for moving the pressure belt 11. The pressure belt 11 is moved in the same direction as the transfer sheet 7 carrying the unfixed image, and The heating and fixing roller 2 is configured to be heated while narrowing the pressure, and to pass through the heating fixing roller 2 to heat and fix an unfixed image on the transfer sheet 7.

That is, as shown in FIG.
Is mainly composed of a heat-fixing roller 2 and a pressure belt 11, and the surface of the heat-fixing roller 2 formed of a cylindrical body is subjected to a fluororesin processing so that the toner has a releasability from the toner. I have. Inside the heating and fixing roller 2, a heater 4 is provided as a heating member. The heater 4 is a rod-shaped heater having a heating wire inside, and both ends are fixed to side plates (not shown) of the fixing device 1a, and are controlled by control means (not shown). A thermistor (not shown) for detecting the temperature of the outer peripheral surface of the heat fixing roller 2 and a peeling claw (not shown) are disposed near the outer peripheral surface of the heat fixing roller 2. The thermistor outputs the detected temperature signal to the control means, and the control means controls the heater 4 in response to the temperature signal. The exfoliation claw has its tip end abutting on the outer peripheral surface of the heat fixing roller 2, and the transfer sheet 7 to which the toner 6 conveyed from the printing unit is attached is applied to the outer peripheral surface of the heat fixing roller 2. At the time of sticking, the heat fixing roller 2 and the transfer sheet 7 are separated by the leading end.

A pressure belt 11 disposed below the heat fixing roller 2 is rotatably supported by two support member rollers 12, 13 fixed to a side plate (not shown) of the fixing device 1a. The support member roller 15 is urged downward by a spring 14 as an urging means, and a pressure belt is
Reference numeral 11 denotes a nip portion (A portion) which is pressed against the outer peripheral surface of the heat fixing roller 2. Further, guide plates (not shown) for guiding the transfer of the transfer sheet 7 are provided in the vicinity of the pressure contact portion between the heat fixing roller 2 and the pressure belt 11, respectively. Each guide plate is fixed to a side plate (not shown) of the fixing device 1a. Then, the transfer sheet 7 sent from the printing unit is guided by the guide plate and
The toner 6 is fixed to the surface by the heating by the heater 4 and the pressing force with the pressure belt 11.

That is, in this belt system, since the pressing belt 11 is used on the pressing side, the heat capacity is small, so that the heat transfer to the pressing portion is small. As a result, the warming-up time can be improved, and the temperature drop of the heat-fixing roller 2 can be suppressed to be small for the same reason at the time of initial roller rotation.

[0012]

However, in the case of the fixing device using the conventional belt fixing method as described above, the fixing device to the nip portion A is only urged downward by the support member roller 15 (FIG. 8). Since the pressure applied by the pressure belt 11 is lower than the required pressure, sufficient pressure cannot be generally obtained in the fixing nip portion by this belt method, and there is a problem that the fixing property is reduced. As another conventional example, a fixing device 1b shown in FIG. 9 has been proposed in order to eliminate such a fixing defect. In the case of the fixing device 1b, a pressing auxiliary member 30 is provided which can contact the inner peripheral surface of the pressure belt 11 at the nip portion A and press the heating fixing roller 2 with a predetermined pressure. However, such a pressing auxiliary member 30 enables accurate pressurization at the nip portion A, so that insufficient fixing can be eliminated. On the other hand, however, the fixing heat from the heat fixing roller 2 to the pressing auxiliary member 30 is reduced. , The warm-up time of the heat fixing roller 2 itself is delayed, and the surface temperature during initial rotation is greatly reduced. Similarly, as a conventional example, Japanese Patent Publication No. 2527670 discloses a technique of arranging a guide plate for assisting pressing in the nip portion A. In this case, the fixing property can be improved, but the guide plate can be used. The heat capacity at the press contact increases,
As a result, there is a problem that the above advantages are lost.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional fixing device, suppress the heat conduction from the heat fixing roller, and shorten the warm-up time and the first copy time. It is an object of the present invention to provide a fixing device.

[0014]

In order to achieve the above object, the present invention has a heating and fixing roller, and performs heating and pressing on a transfer sheet carrying a toner image. In a fixing device of a heat fixing roller type configured to fuse toner and fix the transfer sheet, the fixing device includes a pressing belt that presses the transfer sheet against the heat fixing roller, and a pressing belt that presses the transfer sheet. And a pressure belt for narrowing the pressure belt and the transfer sheet between the pressure fixing belt supporting means including a plurality of belt support members and the outer peripheral surface of the heat fixing roller and the pressure belt. A pressure assisting means capable of coming and going on the inner peripheral surface, the pressure assisting means being capable of coming into contact with and separating from the pressure belt in accordance with the surface temperature of the heat fixing roller. A. In this case, when the pressure belt is a heat-resistant endless film, the heat capacity of the pressure belt can be further reduced, so that the warm-up time and the first copy time can be reduced.

[0015]

FIG. 1 is a schematic longitudinal sectional view showing the structure of an image forming apparatus A to which the present invention is applied. That is,
As shown in FIG. 1, the apparatus main body is provided with paper feeding means 19, 19 having a plurality of paper feeding cassettes 17 and paper feeding rollers 18, and the paper 20 fed by each of these paper feeding means 19, 19 is registered. The toner is conveyed to the photoconductor 22 that is rotationally driven (clockwise) by a roller 21 at a certain timing. This photoconductor 22
During rotation, the surface is uniformly charged by the charging charger 23. On the other hand, the scanner section 24 reads the original reflected light from the exposure lamp 25, processes the read data, and transmits the read data to the laser optical system 26.
Then, the laser beam is irradiated to the charged photoconductor 22 by the laser optical system 26, and a desired electrostatic latent image is formed. This electrostatic latent image is visualized by a developer (toner) when passing through a developing device 27, and this visible image is transferred to a sheet 20 conveyed to a photoreceptor 22.
By 28, the sheet is transported to the fixing device 1c (FIG. 2). Here, the residual toner on the photoconductor 22 is removed by the cleaning device 30.

Here, a feature of the present invention is that a warming-up time is provided by providing a pressing auxiliary member for pressing the nip portion A in order to prevent a decrease in the fixing property in the fixing device, and allowing the pressing auxiliary member to be able to contact and separate. And to reduce the decrease in surface temperature during the initial rotation. That is, as shown in FIG. 2, in the present invention, the fixing device 1c mainly includes a heat fixing roller 2 and a pressure belt 11, and the surface of the cylindrical heat fixing roller 2 is processed with a fluororesin. The release property is maintained for the toner. Inside the heating and fixing roller 2, a heater 4 is provided as a heating member. The heater 4 is a rod-shaped heater having a heating wire inside, and both ends are fixed to side plates (not shown) of the fixing device 1a, and are controlled by control means (not shown). A thermistor (not shown) for detecting the temperature of the outer peripheral surface of the heat fixing roller 2 and a peeling claw (not shown) are provided near the outer peripheral surface of the heat fixing roller 2. The thermistor outputs the detected temperature signal to the control means, and the control means receives the temperature signal and controls the heater 4. The exfoliation claw has its tip end in contact with the outer peripheral surface of the heat-fixing roller 2, and the transfer sheet 7 to which the toner 6 conveyed from the printing unit (not shown) is attached is transferred to the heat-fixing roller 2. When the heat fixing roller 2 is adhered to the outer peripheral surface of the transfer sheet 2, the heat fixing roller 2 and the transfer sheet 7 are separated from each other by the leading end.

A pressure belt 11 disposed below the heat fixing roller 2 is rotatably supported by two support member rollers 12, 13 fixed to a side plate (not shown) of the fixing device 1c. The support member roller 15 is urged downward by a spring 14 as urging means, and the pressure belt 11 is pressed against the outer peripheral surface of the heat fixing roller 2 at the nip portion (A portion). The pressing auxiliary member 30 is, for example, a pressing belt.
The roller 11 rotates together with the roller 11, but may be a leaf spring made of a material such as stainless steel instead of the roller.

In the fixing device 1c of the present invention, as compared with the above-described fixing device 1b, a pressing auxiliary member 31 for pressing a nip portion A formed by the pressing belt 11 and the heat fixing roller 2 is provided by a solenoid 32. The difference is that the pressure belt 11 can be brought into contact with and separated from the pressure belt 11. FIG. 3 shows a second embodiment of the present invention, in which a cam 36 is used as the contacting / separating means instead of the above-described solenoid. That is, as shown in FIG. 3, the contact / separation mechanism is constituted by a cam plate 35 fixed to the support member roller 34 and a pair of cams 36, 36. The pressure of the pressure belt 11 can be freely adjusted.

In the present invention, the contact / separation mechanism described above is characterized in that it is controlled by the surface temperature of the heat fixing roller 2 as shown in FIG. That is, when the pressing auxiliary members 31, 34 are in the separated state, when the surface temperature of the heat fixing roller 2 reaches the temperature α, the contact / separation mechanism operates, and the pressing auxiliary members 31, 34 come into contact with the pressure belt 11, and The heat fixing roller 2 is pressed. On the other hand, when the surface temperature of the heat fixing roller 2 is lower than the temperature β, the contact / separation mechanism is released and the pressing auxiliary roller 3 pressing the heat fixing roller 2 is released.
1 and 34 are separated from the pressure belt 11. Thereby, the heat fixing roller 2 can be heated without loss of heat at the time of warm-up or recovery, which requires heat. In addition, the surface temperature drop at the time of the initial rotation can be a problem in the related art as compared with the conventional example (dotted line diagram) because the heat of the overshoot after the heating and fixing roller 2 reaches the set temperature can be utilized. It is possible to reduce the heat propagation from the heat fixing roller 2 which has been performed.

FIG. 5 shows the structure of a pressure belt according to a third embodiment of the present invention. That is, FIG. 5 is an enlarged view of the pressing belt 11, in which a polyimide resin film, for example, having a thickness of 75 μm is used as the base 11b, and its contact surface with the outer peripheral surface of the heat fixing roller is used. For example, a fluorine resin 11a coated with a thickness of 30 μm is used. Thus, the heat capacity of the conventional rubber-based material can be greatly reduced, and the heat transfer from the heat fixing roller 2 to the pressure belt 11 can be further suppressed. Therefore, the temperature drop of the heat-fixing roller 2 which has conventionally been caused by the rotation of the roller when the fixing device starts up can be reduced, so that the first copy time and the warm-up time can be reduced.

FIG. 6 shows the structure of a fixing device according to a fourth embodiment of the present invention. That is, the fixing device 1
"e" differs from the fixing device 1c of the first embodiment in the thickness of the heat fixing roller itself. For example, the heat-fixing roller 2a is made of an iron material having a diameter of φ50 mm and a thickness of 1.0 mm or less, and an aluminum material uses a thin member having a diameter of φ50 mm and a thickness of 1.5 mm or less. Thus, the core of the heat fixing roller 2a can be made thinner and the weight of the core can be reduced, so that the temperature rising speed of the heat fixing roller 2a can be further shortened in combination with the operation and effect of the first embodiment. It becomes possible.

[0022]

According to the present invention, as described above, in order to achieve the above object, the invention according to claim 1 has a transfer sheet having a heat fixing roller and carrying a toner image. A fixing device of a heat-fixing roller type configured to heat and pressurize the toner to fuse the toner and fix the toner onto the transfer sheet. Pressurizing belt, and pressurizing belt, and pressurizing belt support means including a plurality of belt supporting members, and the pressing belt between the heat fixing roller and the outer peripheral surface of the pressing belt. And a pressing auxiliary means capable of coming into contact with and separating from the inner peripheral surface of the pressure belt for narrowing the transfer sheet, and the pressing auxiliary means contacts the pressing belt in accordance with the surface temperature of the heat fixing roller. Detachable Since the pressing auxiliary member is separated from the pressing belt, it is possible to prevent an increase in heat capacity at the pressing portion, thereby preventing a loss of warm-up time and a decrease in temperature during initial rotation. effective. Further, the invention according to claim 2 is the same as the invention according to claim 1.
In the invention described in (1), the pressure belt is a heat-resistant endless film, so that the pressure belt can be made thinner, and the heat capacity of the pressure belt can be made smaller, so that the warming-up time is improved and the fixing temperature drops. There is an effect that reduction of the amount can be achieved.

The invention described in claim 3 is the first invention.
In the invention described in Item 2 or 2, since the heat fixing roller is formed of a thin member, the volume of the heat fixing roller can be reduced, the heat capacity can be reduced, and the warm-up time can be further reduced. effective.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view showing an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram illustrating a schematic configuration of a fixing device according to the first embodiment.

FIG. 3 is a diagram illustrating a schematic configuration of a fixing device according to a second embodiment.

FIG. 4 is an explanatory diagram showing a control method in the contact / separation mechanism according to the present invention.

FIG. 5 is a diagram illustrating a schematic configuration of a fixing device according to a third embodiment.

FIG. 6 is a diagram illustrating a schematic configuration of a fixing device according to a fourth embodiment.

FIG. 7 is a diagram showing a schematic configuration of a conventional fixing device (first example).

FIG. 8 is a diagram showing a schematic configuration of a conventional fixing device (second example).

FIG. 9 is a diagram showing a schematic configuration of a conventional fixing device (third example).

[Explanation of symbols]

 A Image Forming Apparatus 1, 1a-e Fixing Device 2, 2a Heat Fixing Roller 3 Pressure Roller 5, 14 Spring 12, 13, 15 Support Member Roller 17 Paper Cassette 18 Paper Feed Roller 19 Paper Feeding Means 21 Registration Roller 22 Photosensitive Body 23 Charger 24 Scanner 30, 31, 34 Pressing assisting member 32 Solenoid 35 Cam plate 36 Cam

Claims (3)

[Claims] 1. A heat-fixing roller having a heat-fixing roller and configured to apply heat and pressure to a transfer sheet carrying a toner image to melt the toner and fix the toner on the transfer sheet. In a fixing device of a system, the fixing device is configured to press the transfer sheet against the heat fixing roller, and to hang the pressure belt,
A pressure belt supporting means comprising a plurality of belt support members, and an inner peripheral surface of the pressure belt for narrowing the pressure belt and the transfer sheet between the heat fixing roller and an outer peripheral surface of the pressure belt. A fixing device, comprising: a detachable pressing assisting means, wherein the pressing assisting means is freely movable toward and away from the pressure belt in accordance with the surface temperature of the heat fixing roller. 2. The fixing device according to claim 1, wherein the pressure belt is a heat-resistant endless film. 3. The fixing device according to claim 1, wherein the heat fixing roller is formed of a thin member.