JP2003084597A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of eliminating all the trouble such as fixing irregularity, wrinkles and hot-offset by nearly uniformizing the temperature distribution in the longitudinal direction of a fixing roller being the cause of the fixing irregularity, the wrinkles and further the hot-offset. SOLUTION: This fixing device 11 is equipped with a belt 12 laid around a plurality of rollers, and a pressure roller 17 opposed to one roller 14 of the rollers while putting a sheet S in between in a state where at least one roller 14 of the rollers round which the belt 12 is laid is opposed to the sheet S carrying toner being a fixing object, and has constitution that the toner is heated and pressured while holding and carrying the sheet S between one roller 14 of the rollers and the roller 17. In the device 11, the roller 15 other than the roller 14 opposed to the sheet out of the rollers round which the belt 12 is laid is used as a means for uniformizing the temperature distribution in all the area in the width direction of the sheet S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device and an image forming apparatus using the same, and more particularly to a structure for uniforming temperature distribution during fixing.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine, it is possible to prevent a toner image after development transferred from a photosensitive member forming a latent image carrier from falling off from a transfer medium. In order to do so, the fixing step is executed. In the fixing step, for example, an operation is employed in which the toner used in the developing process is melted by heating and pressurizing, and then the toner is permeated into the sheet or the like serving as an image carrier to be fused.

As the fixing method, there are a contact fixing method in which a heat source side member and a toner as an object to be fixed are in direct contact, and a non-contact method using atmospheric heating. A heat roller fixing method is a typical contact fixing method. The heat roller fixing method includes a pair of rollers that are in contact with each other, and one roller is used as a heating roller that comes into direct contact with toner, and the other roller is used as a pressure roller. A nip portion for sandwiching and conveying the sheet is formed at a position where both rollers come into contact with each other, and when the sheet passes through the nip portion, heating and pressurization are performed and the toner melts and permeates into the sheet.

The heating roller is called a fixing roller because it has a heat source such as a halogen lamp or a nichrome wire inside and can directly fix the toner in contact with the toner. As the configuration of the fixing roller, in addition to the configuration in which the heat source is built in, there is also a configuration in which the surface has a heating layer and is a heating element capable of self-heating. The fixing roller is designed so that the heat source is maintained and controlled by the temperature sensor provided on the peripheral surface so that the surface temperature becomes a predetermined temperature, thereby stabilizing the amount of heat supplied to the sheet passing through the nip portion. I am letting you. The heat quantity is set corresponding to the heating time based on the moving speed of the sheet in the nip portion, and the electric power control for the heat source is performed so that the heat source temperature corresponding to the heat quantity is obtained.

In recent years, energy saving has been advocated, and a fixing device which is a target of power consumption is no exception. For this reason, in the fixing device, a method has been adopted in which the power consumed during standby is reduced by lowering the temperature during standby.

However, if the standby temperature is lowered, the time required for the fixing device to rise to a temperature at which fixing can be performed, that is, the so-called warm-up time, becomes long, and the efficiency at the time of copying, printing out, or printing becomes poor. . To shorten the warm-up time, there is a method of reducing the heat capacity by reducing the thickness of the fixing roller. When the heat capacity of the fixing roller is reduced, the temperature on the surface of the fixing roller reacts sensitively.
That is, the temperature is lowered at the location where the heat is easily released due to the low heat capacity and the temperature is lowered, and the temperature difference from the location at which the heat is not advanced significantly becomes remarkable. Therefore, the temperature tends to be non-uniform in the axial direction of the fixing roller, that is, in the width direction of the sheet. As a result, depending on the size of the member to be heated including the sheet passing through the nip portion and the state of conveyance, the temperature distribution in the longitudinal direction of the member may change, and thus the fixability may deteriorate.

The member to be heated includes not only the sheet but also the toner carried on the sheet. The size of the sheet carrying the toner is, for example, when the image forming apparatus using the fixing device is a copying machine. And A3 portrait, A4 portrait,
There are A4 landscape, B4 portrait, B4 landscape, B5 portrait, B5 landscape and the like.
Of these sizes, setting the short axis direction of the sheet (corresponding to the width direction that is a direction perpendicular to the length direction of the sheet) in a state parallel to the axial direction of the fixing roller is in the vertically long state, that is, When the conveyance direction and the longitudinal direction of the sheet are the same, and the longitudinal direction of the sheet (the length direction of the sheet) is set in a state parallel to the axial direction of the fixing roller, the laterally long state, that is, the conveyance direction This is a state in which the width direction of the sheet matches.

When the heated member passes through the nip portion, the following problems occur due to the difference in the area facing the longitudinal direction of the fixing roller. When a small-sized member to be heated is passed through the nip portion, heat is consumed in the region where the member to be heated is opposed, while the fixing roller and the pressure roller are not in the region where the member to be heated is not opposed. The direct contact causes heat to be stored in the member to be heated and the temperature rises.

In the region where the temperature rises, the temperature rise becomes more remarkable than when the temperature is controlled to the predetermined temperature, and as a result, the temperature may reach the predetermined temperature or higher. Therefore, for example, when fixing a sheet of A4 size and then fixing a sheet of A3 size, when a small-sized heated member is passed and then a large-sized heated member is passed,
The temperature distribution in the longitudinal direction of the fixing roller in a large-sized member to be heated is not uniform, which may cause uneven fixing and wrinkles in the member to be heated. Further, in an abnormally high temperature region, the toner newly carried by the large-sized member to be heated is excessively melted, and its viscoelasticity causes reverse transfer to the surface of the fixing roller, causing a so-called hot offset phenomenon. It may happen.

Conventionally, as a method of solving such a problem, two or more heaters having different light distribution characteristics are provided as heating sources, and the lighting ratio of the heaters at start-up and passage of a heated member The way I changed it, or
A method has been proposed in which the lighting ratio of the heater is changed according to the size of the heated member and the number of times of continuous fixing (for example, JP-A-5-165372 and JP-A-5-281).
877, JP 6-11999, JP 6
No. 19362, No. 6-19363, No. 8-220932, No. 11-16730.
7 publication).

[0011]

In general, when a plurality of heaters are used, there is a problem that if the light distributions of the heaters overlap, the light distribution at that portion becomes too strong. That is, when the light emitting areas corresponding to the light distribution are overlapped with each other, the light emission amounts in the areas are overlapped with each other and the temperature is increased. Therefore, in the method disclosed in the above publication in which a plurality of heaters are used, the lighting ratio of the heaters is only switched based on the rising time and the normal fixing operation, and an abnormal temperature rise during lighting, As a result, no measures have been taken against the uneven temperature distribution in the longitudinal direction of the fixing roller.
As a result, when the temperature distribution in the axial direction of the fixing roller is not uniformly maintained, wrinkles are likely to occur due to uneven fixing due to occurrence of hot offset and peripheral speed difference due to difference in thermal expansion amount in the axial direction of the roller. Become. Moreover, when a plurality of heaters are provided in order to make the light emission ratios different, it is undeniable that the configuration including the control becomes complicated.

On the other hand, as a fixing method, there is a belt fixing method using a thin belt as a heating member, instead of the above heat roller fixing method. This method has a smaller heat capacity of the belt than that of the roller, so that the temperature rises quickly, the warm-up time is shortened, and it is also useful for energy saving measures. However, even when the belt is used instead of the roller, the problem due to the difference in sheet size when the roller is used still remains.

In view of the problems in the above-described conventional fixing device and image forming apparatus, an object of the present invention is to substantially uniformize the temperature distribution in the longitudinal direction of the fixing roller which causes fixing unevenness, wrinkles, and hot offset. Accordingly, it is an object of the present invention to provide a fixing device and an image forming apparatus that can solve all the above problems.

[0014]

The invention according to claim 1 is
A belt that is wound around a plurality of rollers, and at least one of the rollers around which the belt is wound faces a sheet carrying a toner to be fixed, and a sheet that sandwiches the sheet and faces one of the rollers. In a fixing device having a pressure roller, and heating and pressing the toner while nipping and transporting the sheet by one of the rollers and the pressure roller, among the rollers around which the belt is wound. Then, except for the rollers other than the roller facing the above sheet,
It is characterized in that it is used as a means for uniforming the temperature distribution in the entire width direction of the sheet.

According to a second aspect of the invention, the rollers other than the roller facing the sheet are tension rollers of the belt.

The invention according to claim 3 is characterized in that the rollers other than the roller facing the sheet are constituted by heat pipes.

The invention according to claim 4 is characterized in that the fixing device according to any one of claims 1 to 3 is used for an image forming apparatus.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram showing an example of an image forming apparatus to which a developing device according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 also has a copying function capable of forming an electrostatic latent image on a photoconductor, which is a latent image carrier, based on image information obtained by reading a document and image information from a host computer or the like. The printer is a full-color printer that can perform visible image processing of an electrostatic latent image using a plurality of colors.

In FIG. 1, a photoconductor 2 which is a latent image carrier on the drum is arranged inside the image forming apparatus 1. Around the photoconductor 2, a charging device 3, a writing device 4, which performs an image forming process along the rotation direction of the photoconductor.
A developing device 5, a transfer device 6, and a cleaning device 7 are arranged respectively.

The writing device 4 used in the image forming apparatus 1 in this embodiment is provided with a laser light source capable of emitting a laser beam in accordance with an image signal from a control unit (not shown). Although not shown, the writing light is emitted not only by the output signal from the computer but also by the image signal based on the original image read by the scanner 8 provided in the image forming apparatus 1. That is, the image forming apparatus 1 is provided with the original placing table 1A on the upper surface of the housing so that the original can be placed, and the scanner 8 for reading the original image is provided below the original placing table 1A. It is provided. The scanner 8 includes a reading optical system having a known structure and a reading element, and the image information obtained by the reading element is output to the control unit.

Although no reference numeral is attached to the writing device 4,
In addition to a laser light source (not shown), polygon mirrors 4A, f
The θ lens 4B, the BTL lens 4C, and the writing mirror 4D are provided, and the scanner 8 is provided with a scanning light source and a reflecting mirror and is movable in parallel with the document table, and is for optical path conversion. A second scanner unit 8B that includes a pair of mirrors and is movable, and a substrate 8D that includes a lens 8C and a CD element that is an optical reading element are provided.

The transfer device 6 in this embodiment is the photosensitive member 2
A primary transfer device 6A for primary-transferring a visible image from the secondary transfer device 6B and a secondary transfer device 6B for secondary-transferring the visible image from the primary transfer device 6A to a sheet such as a recording sheet are provided. The primary transfer device 6A includes an intermediate transfer belt 6A1 wound around a plurality of rollers, and a primary transfer charger 6A2 disposed at a position where the intermediate transfer belt 6A1 and the photoconductor 2 face each other.
The visible image on the photoconductor 2 can be transferred onto the intermediate transfer belt 6A1. An image of a color having a complementary color relationship with the color separation can be superimposedly transferred onto the intermediate transfer belt 6A1 by a developing device 5 described later.
The images that have been superimposed and transferred are collectively transferred to a sheet (hereinafter, referred to as a sheet) such as a recording sheet by the secondary transfer device 6B. The secondary transfer device 6B is
The primary transfer device 6A includes a charging roller that can be brought into contact with and separated from the intermediate transfer belt 6A1 with a sheet conveyance path interposed therebetween. While sandwiching and conveying a moving sheet, a superimposed image on the intermediate transfer belt 6A1 is formed. It can be electrostatically transferred to a sheet. The secondary charging device 6B can be brought into contact with the intermediate transfer belt 6A1 only when transferring a single color or when collectively transferring the superimposed images, and when the images of each color are transferred to the intermediate transfer belt 6A1. 6A
The image is not disturbed without coming into contact with 1.

Intermediate transfer belt 6A1 and secondary transfer device 6B
The sheet is fed by the sheet feeding device 9 to the secondary transfer position corresponding to the position opposite to. The sheet feeding device 9 includes a sheet feeding cassette 9A that can store recording sheets and a sheet feeding cassette 9A.
A feeding roller 9B for feeding the sheet in A, a separation roller pair 9C, a conveying roller 9D and a registration roller 9
E equipped with a paper feed cassette 9A toward the secondary transfer position
The sheet separated from the inside is fed after the registration timing is set by the registration roller 9E.

In this embodiment, it is also possible to feed sheets of different sizes or different sizes from the inside of the paper feed cassette. For this reason, the casing of the image forming apparatus is provided with a manual feed tray 9F, a part of which can be raised and lowered.
A conveyance roller 9D is arranged at a position where the movement path of the sheet fed from the paper feed tray 9A merges between the manual feed tray 9F and the registration roller 9E, and a feeding roller 9B is arranged at the manual feed tray 9F. There is.

In the above structure, the electrostatic latent image formed on the photoconductor 2 is subjected to visible image processing by the developing device 5 and transferred to the intermediate transfer belt 6A1 by the primary transfer device 6A. When the image has a single color, the transferred image on the intermediate transfer belt 6A1 is secondarily transferred to the sheet fed from the paper feeding device 9 by the secondary transfer device 6B as it is, and when the image has a plurality of colors, the intermediate transfer is performed. After being superimposedly transferred onto the belt 6A1, it is collectively transferred onto the sheet by the secondary transfer device 6B. The sheet after the secondary transfer is separated from the secondary transfer position and is transported to the fixing device 11 via the transport device 10, where the image is fixed and the sheet is discharged.

Details of the fixing device 11 according to the embodiment of the present invention are shown in FIG. In FIG. 2, the fixing device 11
Is provided with a fixing belt 12 wound around a plurality of rollers. The fixing belt 12 is made of polyimide resin, which is one of the heat-resistant materials, and has a thickness of about 0.05 to 0.2 mm. The surface of the fixing belt 12 is a silicone rubber layer as a release layer. It is coated with a thickness of about 1 to 0.2 mm.

As the material of the fixing belt 12, it is possible to use stainless steel, nickel, or other metal materials other than resin. Although not shown, offset belt ring portions formed of convex portions are provided on both ends of the fixing belt 12 in the width direction, and the offset ring portions are opposed to the end surface of the roller, so that the offset in the width direction is regulated. It is like this. Although not shown, a release agent for offset prevention, such as silicone oil, is applied to the surface that comes into contact with the toner.

In FIG. 2, the rollers around which the fixing belt 12 is wound are a heating roller 13, a fixing roller 14 and a tension roller 15. The heating roller 13 is a member for heating the fixing belt 12 that is wound around. For this reason, the heating roller 13 is provided with a halogen lamp LP1 having an output of 650 W capable of uniform light emission in the axial direction corresponding to the maximum width of the sheet passing at the center of the cross section, and the thermistor 16 facing the surface is used. By outputting the temperature detection information to a temperature control unit (not shown), the surface temperature is controlled to 170 ° C.

As the heating roller 13, an aluminum cylinder having a thickness of 2 mm and good thermal conductivity is used to prevent temperature unevenness in the axial direction. Further, the surface is anodized to prevent the belt 12 from being worn.

The fixing roller 14 forms a nip portion of the sheet S in cooperation with the pressure roller 17 that faces the fixing belt 12 with the fixing belt 12 interposed therebetween, and heats the sheet S while nipping and conveying the sheet S at the nip portion. Therefore, the fixing roller 14
Is made of a metal cylinder such as steel having a rubber layer having a thickness of about 5 mm on its surface, and emits light uniformly over the maximum width of the sheet S along the axial direction inside the cylinder. Halogen lamp LP with 150W output
Equipped with 2. The halogen lamps LP1 and LP2 are designed to be temperature-controlled by simultaneous control.

The pressure roller 17, which faces the fixing roller 14 with the fixing belt 12 interposed therebetween, is composed of a metal cylinder such as steel having a rubber layer having a thickness of 2 mm provided on the surface thereof. It is equipped with a halogen lamp LP3 having a similar construction to that in 14. Halogen lamp L
The surface temperature of P3 is controlled to 150 ° C. by the thermistor 19 facing the surface.

The pressure roller 17 is pressed by the pressure member 18 toward the fixing roller 14 with the fixing belt 12 interposed therebetween, and has a shape that follows the peripheral surface of the fixing roller 14 by elastically deforming the rubber layer. A nip area where the sheet S can be nipped and conveyed can be formed. In particular, by setting the angle of tolerance between the straight line connecting the heating roller 13 and the fixing roller 14 and the straight line connecting the fixing roller 14 and the pressing roller 17 to each other, the angle is set to 90 to 270 °. The length of the nip region between the fixing roller 14 and the pressure roller 17 can be set, and the heating range in which the heating efficiency for the sheet S is maximized can be set.

The tension roller 15 is the heating roller 13
And the fixing belt 1 wound around the fixing roller 14.
2 is a member for preventing looseness, and in this embodiment,
It corresponds to one of the rollers other than the fixing roller 14 which is a roller facing the sheet S.

The tension roller 15 is composed of a heat pipe which can be displaced by the pressure member 20 in a direction in which tension is applied to the fixing belt 12. The heat pipe constituting the tension roller 15 has a structure in which a heat medium capable of repeating a liquefied state and a vaporized state by heat circulation is enclosed in a vacuum state, and heat generated in a portion heated in the axial direction is It is possible to move instantly with respect to the unheated part.

Since this embodiment has the above-mentioned configuration,
The sheet S after the secondary transfer is separated from the secondary transfer position and is transported to the fixing device 11 via the transport device 10, where the image is fixed and discharged.

In the fixing device 11, the heating roller 13
And halogen lamps LP1 and LP in the fixing roller 14
2 is emitted, its temperature is maintained at 170 ° C. by temperature control using thermistors 16 and 19, and the fixing belt 12 wound around the roller 13 is heated to a predetermined temperature. The fixing device 11 via the transport device 10.
When the sheet S conveyed toward the sheet is nipped and conveyed in a nip region formed by the fixing roller 14 and the pressure roller 17, the sheet S comes into contact with the fixing belt 12 to carry the toner T carried on the surface. Is melted by heating and pressurizing action, penetrates into the sheet S and is fixed.

In the fixing device 11, the temperature drops in the width corresponding to the size of the sheet S passing through the nip portion.
FIG. 3 is a diagram showing a temperature distribution when sheets S having different widths pass through the fixing device 11. In FIG. 3, when a sheet S of A4 size passes through the fixing device 11, it is set in advance on the fixing belt 12. The temperature on the fixing belt 12 decreases to T1 with respect to the fixing temperature T0. Therefore, when the A3 size sheet S having a width larger than the A4 size reaches the fixing device 11, the fixing temperature for the A3 size sheet S is not at a predetermined temperature in the range where the A4 size sheet S has passed, and therefore, it is necessary for fixing. It becomes impossible to obtain a sufficient amount of heat. Therefore, uneven temperature distribution in the width direction of the A3 size sheet S causes uneven fixing on the A3 size sheet S, and wrinkles occur due to change in thermal expansion amount of the roller at the nip portion.

In the present embodiment, the temperature of the fixing belt 12 in the widthwise contact range with the sheet S reaches the predetermined fixing temperature or lower, but the temperature generated in the fixing belt 12 when passing through the tension roller 15. The temperature gradient is eliminated by the movement of heat in the tension roller 15 according to the gradient, and the temperature distribution in the width direction is made uniform. Therefore, when the nip portion between the fixing roller 14 and the pressure roller 17 is reached again, the new sheet S can be contacted in a state where the temperature distribution in the width direction is balanced, so that the sheet can be continuously contacted. Therefore, when the sheets S of the same size pass through the nip portion, or when the sheet S of a different size from the preceding sheet S, in particular, the sheet S of a size larger than the preceding sheet S passes through the nip portion, the temperature distribution imbalance is eliminated. Will be there. As a result, the fixing roller 1 that contacts the fixing belt 12
No change in the surface temperature of the pressure roller 17 and the pressure roller 17 causes no change in the amount of thermal expansion in the axial direction on the roller side. Occurrence can be prevented in advance. In addition, since the amount of heat received in the width direction of the sheet S does not change, the fixing state in the width direction of the sheet S does not change regardless of the size, and uneven fixing is reliably prevented. Become.

[0039]

According to the inventions of claims 1 and 3,
Since the temperature distribution can be kept uniform over the width direction of the sheet regardless of the size of the sheet passing through, it is possible to use a simple structure without providing multiple heat sources with different light emission ratios or one roller. Offset It is possible to prevent uneven fixing and wrinkles due to the occurrence of offset. Particularly, in the invention according to claim 3, since the rollers other than the roller facing the sheet are constituted by the heat pipes, temperature circulation can be instantaneously performed and the temperature gradient in the width direction of the sheet can be eliminated. .

According to the second aspect of the invention, since the roller used as the temperature distribution uniforming means is a tension roller other than the roller facing the sheet, that is, a member that is pressed against the sheet to apply tension to the sheet, The temperature control can be performed most easily, and the temperature distribution in the width direction of the sheet can be easily kept uniform.

According to the invention described in claim 4, since the temperature distribution in the heating region for the sheet is kept uniform irrespective of the sheet size, wrinkles are generated in a part of the sheet or overheating is caused in a part of the sheet. It is possible to prevent occurrence of an abnormal image due to hot offset or the like due to occurrence of a state.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an example of an image forming apparatus in which a fixing device according to an embodiment of the present invention is used.

FIG. 2 is a schematic diagram for explaining a configuration of a fixing device according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining a change in temperature distribution depending on the size of a sheet passing through a fixing device.

[Explanation of symbols]

1 Laser printer which is one of image forming apparatuses 2 Photoconductor 11 which is a latent image carrier 11 Fixing device 12 Fixing belt 13 Heating roller 14 Fixing roller 15 corresponding to a roller facing a sheet To a roller other than a roller facing a sheet Equivalent tension roller S Sheet T Toner

Claims (4)

[Claims] 1. A belt wound around a plurality of rollers, and at least one of the rollers wound around the belt faces a sheet carrying a toner to be fixed, and the rollers are sandwiched with the sheet sandwiched therebetween. In a fixing device having one pressure roller facing each other, and heating and pressing the toner while nipping and transporting the sheet with one of the rollers and the pressure roller, the belt is wound around. In the fixing device, a roller other than the roller facing the sheet is used as the temperature distribution uniformizing means in the entire width direction of the sheet. 2. The fixing device according to claim 1, wherein the rollers other than the roller facing the sheet are tension rollers of the belt. 3. The fixing device according to claim 1, wherein the rollers other than the roller facing the sheet are heat pipes. 4. An image forming apparatus using the fixing device according to any one of claims 1 to 3.