JP2004302488A - Belt fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a release temperature width by preventing a fixing belt from being entangled around a recording material. <P>SOLUTION: The belt fixing device is equipped with the endless fixing belt 15 which is stretched between a plurality of belt conveyor rollers 12 and 13 and rotates, a pressure roller 14 which is pressed against a portion of the fixing belt which is wound around one fixing roller 12 between the plurality of belt conveyor rollers 12 and 13, and heat sources 28 and 26 which add heat to toner T on the recording material passing through a nip N where the pressure roller 14 is pressed against the fixing belt 15 via at least the fixing belt, and is characterized in that the width of the nip N is ≥25° in circumferential angle α viewed from the center of the fixing roller 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a belt fixing device for fixing a toner image on a recording material in an image forming apparatus such as an electrophotographic copying machine or a printer, and more particularly, to a nip where a pressure roller is pressed against a fixing roller around which a fixing belt is wound. The present invention relates to a belt fixing device configured to fix a toner image on a recording material by passing the recording material.

  Conventionally, in an electrophotographic image forming apparatus, a document image is first read by a document reading unit, and then the document image read by the document reading unit on an electrostatic latent image carrier such as a photosensitive drum of the image forming unit. Image exposure is performed correspondingly to form an electrostatic latent image. Further, the electrostatic latent image is developed into a visible toner image, the toner image is transferred onto a recording paper or the like conveyed from a recording material supply unit, fixed, and discharged to a paper discharge unit. Take the configuration.

  As a fixing device used in the image forming section of the image forming apparatus, a so-called heat roller type fixing device has been conventionally used in many cases. This fixing device presses and rotates a fixing roller having a heat source therein and a pressure roller, and heat-presses and fixes an unfixed toner image on recording paper passing through a nip forming a pressure contact portion between the two rollers. The length of the elastic body provided on the surface of the fixing roller cannot be increased beyond a certain value because it is necessary to suppress the increase of the ab time. If the thickness of the elastic body on the surface of the fixing roller cannot be sufficiently ensured in this manner, the nip width cannot be increased beyond a certain width, and the release temperature range at which good fixing can be performed becomes narrow. Note that the release temperature range is defined as a cold offset at which the fixing temperature is low and the toner adheres to the fixing roller or the belt or is not sufficiently fixed on the recording material, and a fixing temperature is too high and the attraction force between the toners is weakened. This is referred to as a fixing temperature range in a good fixing region between the hot offset where toner adheres to the fixing roller and the belt again.

  Here, a belt fixing device has been developed in which a heat source is provided at a portion other than the fixing roller so that the warm-up time can be reduced, and an example thereof is disclosed in JP-A-8-339133 (Patent Document 1). .

  In this belt fixing device, as shown in FIG. 13, an endless fixing belt 100 is wound around a fixing roller 101 and a heating roller 102 and rotated, and a pressure roller 103 is applied to the fixing roller 101 via the fixing belt 100. It is pressed. Further, a pre-fixing guide 105 is provided on the upstream side in the recording material conveying direction Y of the nip 104, which is a portion where the fixing belt 100 and the pressing roller 103 are in pressure contact with each other. Here, when the fixing roller 101 is driven to rotate and the fixing belt 100 rotates in the same direction, the heating roller 102 and the pressure roller 103 also follow. In this case, each part of the fixing belt 100 is heated by the heating roller 102 before reaching the nip 104, and the heated part is guided by the pre-fixing guide 105 to heat the toner image on the recording material s conveyed in advance. After the recording material s is softened, the toner image is fixed by passing the recording material s through the nip 104.

The belt contact roller 106 is brought into contact with the fixing belt 100 by receiving the elastic force of a spring (not shown). The belt contact roller 106 is a cleaning means for removing dirt due to paper dust, toner or the like adhering to the fixing belt 100, or is provided on the belt surface in order to suppress a so-called offset phenomenon in which toner transfers from the recording material s to the fixing belt 100. It is configured as an application roller that applies an offset suppressing release agent such as silicone oil.
The fixing device of the belt fixing method can set the fixing temperature to a relatively low temperature by dispersing the time and place where the toner on the recording material is heated by heating the belt having a certain area, thereby fixing the toner in the fixing device. This has the advantages of shortening the time required for warming up (warm-up time) and saving energy.

  The above-mentioned belt fixing device is, for example, a heat fixing device for a recording material carrying an unfixed toner image to be fixed in an image forming apparatus such as a copying machine, a laser beam printer (LBP), an electrostatic printer, and a recording carrying an image. It is effectively used as a means or a device for heat-treating a material to be heated, such as a device for modifying the surface property by heating the material, a device for temporarily attaching the material, and the like.

JP-A-8-339133

  By the way, in the fixing device A adopting the belt fixing method, the angle θ between the recording material s entering the nip 104 and the fixing belt 100 is set to be small, and the releasing temperature width is to be widened by the residual heat effect. However, in the case of this conventional apparatus, depending on the type of the recording material s, a new problem occurs such that the unfixed toner image rubs against the fixing belt 100 before entering the nip portion, causing image disturbance, and the like. It is not enough to expand the range. In addition, this method has a problem that the recording material is liable to be wound around the fixing belt unless the nip width is larger than a certain width. Furthermore, in order to suppress the offset phenomenon in order to solve the problem that the release temperature width is narrow, an offset suppression release agent (oil) is applied to the belt surface using a belt contact roller 106 or the like. To apply the coating material, the releasing agent remains on the fixed recording material, the releasing agent adheres to the user's hand, or the fixed image is damaged due to uneven application of the releasing agent. There is a problem that it is not suitable for maintenance by a user because an oil tank to be held is required.

A first object of the present invention is to suppress the winding of a recording material around a fixing belt and improve the release temperature range.
Further, a second object is to particularly prevent the recording material from winding around the fixing belt and toner offset.
Further, a third object is to facilitate the reduction of the radius of the fixing roller and the fixing belt immediately downstream of the nip, to improve the release temperature range, to prevent the recording material from wrapping around the fixing belt, and to reduce the driving torque. It is in.

A fourth object of the present invention is to provide a heat source at a portion other than the fixing roller to shorten a warm-up time.
A fifth object of the present invention is to promote a small R shape immediately downstream of the nip between the fixing roller and the fixing belt, prevent the recording material from being wound around the fixing belt, and reduce the driving torque.
Further, a sixth object is to make the pressure roller and the fixing roller form a downward nip shape, thereby preventing the recording material from winding around the fixing belt.
Further, a seventh object is to prevent the recording material from winding around the pressure roller by coating with a high release material, for example, PFA.

Further, an eighth object is to stabilize the recording material conveyance performance by causing the fixing roller to rotate the fixing belt.
Further, a ninth object is to drive the fixing roller and the pressure roller together to prevent the fixing belt and the fixing roller from being damaged by friction with the pressure roller, and to prevent the fixing belt and the pressure roller from being damaged. An object of the present invention is to prevent wrinkles and the like of a recording material from occurring due to a peripheral speed difference.
Further, a tenth object is to reduce the variation in the linear speed at which the recording material is conveyed by setting the pressure roller on the driving side.
Further, an eleventh object is to drive the pressure roller and the fixing roller together to prevent the fixing belt and the fixing roller from being damaged by friction with the pressure roller, and to prevent the fixing belt and the pressure roller from being damaged. An object of the present invention is to prevent wrinkles and the like of a recording material from occurring due to a peripheral speed difference.

According to the first aspect of the invention, an endless fixing belt that is wound around and rotates between a plurality of belt transport rollers, and is wound around one of the plurality of belt transport rollers on the fixing belt. A belt fixing device comprising: a pressing roller that presses against a portion; and a heat source that applies heat to toner on a recording material that passes through a nip where the fixing belt and the pressing roller press against each other. It is characterized in that the circumferential angle as viewed from the center is 25 ° or more.
With the above configuration, when the nip width formed by the fixing belt and the pressure roller exceeds 25 ° in the circumferential angle as viewed from the center of the fixing roller, the nip width relatively increases, and the fixing roller and the fixing roller are located immediately downstream of the nip. The fixing belt wound therearound forms a small R-shaped portion. For this reason, this small R-shaped portion prevents the recording material from wrapping around the fixing belt, expands the fixing release temperature range, prevents toner offset, and requires a very small amount of release agent. Alternatively, oil-less operation is possible, and an effect that maintenance by the user himself is also possible is obtained.

According to a second aspect of the present invention, in the belt fixing device according to the first aspect, the surface of the fixing belt is coated with a release agent.
With the above configuration, the recording material after passing through the nip formed by the fixing belt and the pressure roller can be reliably separated from the fixing belt by the action of the release agent, and the winding of the recording material around the fixing belt can be more reliably prevented. Thus, toner offset can be more reliably prevented.

According to a third aspect of the present invention, in the belt fixing device according to the first or second aspect, the surface layer of the fixing roller is covered with a sponge-like heat insulating material, and the thickness thereof is 17 to the diameter of the fixing roller. % Or more.
As described above, the configuration in which the sponge-like elastic body is coated on the fixing roller significantly forms a small R-shaped portion immediately downstream of the nip, which is a factor for improving the release temperature range. Is maintained at 17% or more of the diameter of the fixing roller, it is possible to more reliably obtain the effect of improving the release temperature width by the small R-shaped portion formed by the fixing roller and the fixing belt. Also, the torque required to drive the belt fixing device is reduced.

According to a fourth aspect of the present invention, in the belt fixing device according to any one of the first to third aspects, the heat source is provided at a portion other than inside the fixing roller.
With the configuration described above, since no heat source is provided inside the fixing roller, it is possible to prevent the warm-up time from being lengthened even if the thickness of the elastic body covering the surface of the fixing roller is increased.

According to a fifth aspect of the present invention, in the belt fixing device according to any one of the third to fourth aspects, the hardness of the sponge-like heat insulating material on the surface of the fixing roller is 30 ° or less in Asker hardness. I do.
According to the above configuration, since the sponge-like heat insulating material has a low hardness, the small R-shaped portion is reliably formed at a position immediately downstream of the nip between the fixing roller and the fixing belt wound around the fixing roller, and the diameter thereof is further reduced. For this reason, the winding of the recording material around the fixing belt is more reliably prevented, the torque required to drive the belt fixing device is reduced, and the motor can be further downsized.

According to a sixth aspect of the present invention, in the belt fixing device according to any one of the first to fifth aspects, a surface layer of the pressure roller is formed of an elastic body and has a thickness of 2 mm or less, and has a hardness of 40 mm or less according to JISA. ° or more.
With this configuration, the pressure roller is a rigid body as compared with the fixing roller, and as a result, the nip shape is convex upward, that is, a downward nip shape. Therefore, it is possible to more reliably prevent the recording material after fixing from being wound around the fixing belt.

According to a seventh aspect of the present invention, in the belt fixing device according to any one of the first to sixth aspects, the surface layer of the pressure roller is coated with a high release material.
With this configuration, it is possible to more reliably prevent the recording material from being wound around the pressure roller by coating with a high release material, for example, PFA.

According to an eighth aspect of the present invention, in the belt fixing device according to any one of the first to seventh aspects, the fixing roller is provided with a driving force for rotationally driving the fixing belt. .
With the above configuration, the recording material conveyance performance can be stabilized.

According to a ninth aspect of the present invention, in the belt fixing device according to the eighth aspect, the driving force is applied to the pressure roller via a one-way clutch.
With the above configuration, since the pressure roller and the fixing belt are driven together, it is possible to prevent the fixing belt and the fixing roller from being damaged by friction with the pressure roller without slipping. Further, since the one-way clutch is interposed, the peripheral speed difference between the fixing belt and the pressure roller can be absorbed, and the generation of wrinkles or the like on the conveyed recording material can be prevented.

According to a tenth aspect of the present invention, in the belt fixing device according to any one of the first to seventh aspects, a driving force is applied to the pressure roller.
With the above configuration, the pressure roller is closer to the rigid body than the fixing roller, so that the variation in the linear velocity at which the recording material is conveyed can be reduced, and the conveyance performance of the recording material can be stabilized.

An eleventh aspect of the present invention is the belt fixing device according to the tenth aspect, wherein the driving force is applied to the fixing roller via a one-way clutch.
With the above configuration, since the pressure roller and the fixing belt are driven together, it is possible to prevent the fixing belt and the fixing roller from being damaged by friction with the pressure roller without slipping. Further, since the one-way clutch is interposed, the peripheral speed difference between the fixing belt and the pressure roller can be absorbed, and the generation of wrinkles or the like on the conveyed recording material can be prevented.

  According to the first aspect of the present invention, the nip width is set to be equal to or more than 25 ° in the circumferential angle as viewed from the center of the fixing roller, so that the nip width formed by the fixing belt and the pressure roller is relatively increased, and immediately after the nip downstream. The fixing roller and the fixing belt wound around it can form a small round shape. For this reason, this small R-shaped portion prevents the recording material from wrapping around the fixing belt, expands the fixing release temperature range, prevents toner offset, and requires a very small amount of release agent. Alternatively, oil-less operation is possible, and an effect that maintenance by the user himself is also possible is obtained.

  According to the second aspect of the present invention, since the surface of the fixing belt is covered with the release agent, the recording material after passing through the nip formed by the fixing belt can be reliably separated from the fixing belt by the action of the release agent. Can be more reliably prevented from being wound around the fixing belt, and toner offset can be more reliably prevented.

  According to a third aspect of the present invention, the surface of the fixing roller is covered with a sponge-like heat insulating material, and the thickness thereof is 17% or more of the diameter of the fixing roller. The small round shape is remarkably formed immediately downstream, and the effect of improving the release temperature width by the small round shape can be more reliably obtained. Also, the torque required to drive the belt fixing device is reduced.

According to the fourth aspect of the present invention, since the heat source is provided in a portion other than the inside of the fixing roller and the heat source is not provided inside the fixing roller, the warm-up can be performed even if the thickness of the elastic body covering the surface of the fixing roller is increased. It is possible to prevent the time from becoming long.
According to the invention of claim 5, the hardness of the sponge-like heat insulating material on the surface of the fixing roller is set to 30 ° or less in Asker hardness, and the hardness of the sponge-like heat insulating material becomes soft. The small round shape is reliably formed, and its diameter becomes smaller. For this reason, the winding of the recording material around the fixing belt is more reliably prevented, the torque required to drive the belt fixing device is reduced, and the motor can be further downsized.

  According to a sixth aspect of the present invention, the surface of the pressure roller is made of an elastic material and has a thickness of 2 mm or less, its hardness is 40 ° or more according to JISA, and the pressure roller is a rigid body as compared with the fixing roller, and has a nip shape. Is convex upward, that is, a downward nip shape. Therefore, it is possible to more reliably prevent the recording material after fixing from being wound around the fixing belt.

According to the seventh aspect of the present invention, since the surface layer of the pressure roller is coated with the high release material, the winding of the recording material around the pressure roller can be more reliably prevented.
According to the eighth aspect of the present invention, since the fixing roller is provided with a driving force for rotationally driving the fixing belt, the recording material conveyance performance can be stabilized.
According to the ninth aspect of the present invention, since the driving force is applied to the pressure roller via the one-way clutch and the pressure roller and the fixing belt are driven together, there is no slippage between the two and the fixing belt and the fixing roller are applied. It is possible to prevent pain due to friction with the pressure roller. Further, since the one-way clutch is interposed, the peripheral speed difference between the fixing belt and the pressure roller can be absorbed, and the generation of wrinkles or the like on the conveyed recording material can be prevented.

According to the tenth aspect of the present invention, the driving force is applied to the pressing roller. In this case, since the pressing roller is closer to a rigid body than the fixing roller, the linear velocity of conveying the recording material is reduced. The recording material can be made smaller and the recording material conveyance performance can be stabilized.
According to the eleventh aspect of the present invention, the driving force is applied to the fixing roller via the one-way clutch, and the pressure roller and the fixing belt are driven together. The pain caused by friction with the rollers can be prevented. Further, since the one-way clutch is interposed, the peripheral speed difference between the fixing belt and the pressure roller can be absorbed, and the generation of wrinkles or the like on the conveyed recording material can be prevented.

  FIG. 1 shows a belt fixing device to which the present invention is applied, and the belt fixing device is provided in an image forming section in charge of an image forming process of a color copying machine (not shown). Here, an unillustrated color copier (hereinafter simply referred to as a copier) reads a document image by a document reading unit, forms a toner image corresponding to the document image by an image forming unit, and is supplied from a paper feeding unit. A schematic configuration is adopted in which the image is transferred onto a recording sheet, fixed, and an image-formed recording sheet from the image forming unit is discharged to a sheet discharging unit.

  As shown in FIG. 2, the image forming unit here includes a photosensitive drum 1 having a photosensitive layer forming an electrostatic latent image carrier on the surface of an aluminum base, and the photosensitive drum 1 is driven by a driving unit (not shown). The photoconductor is driven in the rotation direction n at a linear speed of the photoconductor in accordance with a predetermined mode. A charging device 2, a laser diode (LD) 3 forming an optical writing device, a developing unit 4, a transfer belt 5, a belt fixing device 6, a cleaning device and a static elimination device (not shown) are arranged in this order in the vicinity of the peripheral edge of the photoconductor. Is done. The charging device 2 can control the amount of charge by controlling the potential applied to the grid 2a, and the laser diode (LD) 3 emits a laser beam having a light intensity corresponding to image data from a scanner (not shown) to correspond to an image. The formed electrostatic latent image is formed on the photosensitive layer of the photosensitive drum 1. The developing unit 4 is a rotatable container having a revolver shape, and has four developing tanks therein, each of which is provided with a yellow (Y), a magenta (M), a cyan (C), and a black (K). ), A developer consisting of four colors. A developing bias is applied to a developing sleeve (not shown) in each developing tank, and toner is supplied onto the image carrier of the photosensitive drum 1 to develop a toner corresponding to a latent image potential to visualize the image. .

  The toner image formed on the image carrier of the photosensitive drum 1 is transferred onto the transfer belt 5. At this time, the transfer amount can be properly controlled by applying an appropriate bias to the primary transfer roller 7. By repeating the above charging, exposing, developing, and transferring steps in the order of black (K), cyan (C), magenta (M), and yellow (Y), a superimposed image of the four-color toner is formed on the transfer belt 5. Created. The superimposed image of the four color toners transferred onto the transfer belt 5 is transferred onto the recording paper 9 at once by applying an appropriate bias to the secondary transfer roller 8. Here, the recording paper 9 to which the superimposed image of the four-color toner has been transferred is sent to the belt fixing device 6 by the guide unit 10, and after the toner image is fixed in the belt fixing device 6, The sheets are discharged and stacked. Here, the recording paper 9 has been described as the recording material, but the recording material may be a sheet made of another material.

Here, the configuration of the belt fixing device 6 is shown in FIGS.
The belt fixing device 6 shown in FIG. 1 includes a frame 11 fixed to a base frame of a copying machine (not shown), in which a fixing roller 12, a heating roller 13, a pressure roller 14, a fixing roller A fixing belt 15 wound and stretched between the fixing roller 12 and the heating roller 13 and an oil application roller 16 for applying silicone oil, which is an offset suppressing release agent, to the outer surface of the fixing belt 15 are provided.
The frame 11 has a rectangular frame shape with the longitudinal direction X (see FIG. 3) in the direction perpendicular to the paper surface of FIG. 1, and end plates 111 provided at left and right ends thereof (shown by a two-dot chain line in FIG. 3). ), And a plurality of bar-shaped members 112 (only one is shown in FIG. 3) that are long in the longitudinal direction X and that integrally connect both end plates 111 to each other.

The fixing belt 15 is wound around the fixing roller 12 and the heating roller 13. The base of the fixing belt 15 is a thin film of nickel having a thickness of 100 μm and a release layer of 200 μm silicone rubber on the surface. It is formed so as to have good thermal responsiveness. The base of the fixing belt 15 may be made of polyimide, and the thickness may be about 30 to 150 μm in consideration of flexibility.
The fixing roller 12 is rotatably supported on the left and right end plates 111 via a pair of bearings (not shown) at the left and right ends of the center shaft 121. The fixing roller 12 is formed by covering a core metal with a heat-resistant porous elastic body having a small heat conductivity and a heat insulating action. Here, in particular, a sponge-like heat insulating material is employed as a material of the surface layer of the fixing roller 12, and its thickness is set so as to exceed 17% of the diameter of the fixing roller 12. The formation of the R shape r is facilitated. Moreover, the sponge-like heat insulating material has a hardness of 30 ° or less in Asker hardness, thereby facilitating the formation of a small R shape r described later and reducing the driving torque on the fixing roller 12 side. I have.

  The input gear 17 is integrally attached to one end of the center shaft 121 of the fixing roller 12, and a fixing roller driving system D is connected thereto. The fixing roller driving system D includes an input gear 17, a driving gear 20 meshing with the input gear 17, and a motor 18 connected to the other end of a driving shaft 19 integrally connected to the driving gear 20. A part of the drive shaft 19 is pivotally supported by an end plate 111 via a bearing (not shown), and the motor 18 at the other end of the drive shaft 19 is also supported by a bracket (not shown) extending from the end plate 111. Here, the motor 18 supported by the end plate 111 can transmit its rotation from the driving gear 20 to the fixing roller 12 via the input gear 17, and when the fixing roller 12 rotates, the fixing belt wound around the roller is rotated. 15 rotates, and the heating roller 13 and the pressure roller 14 can be driven to rotate. As shown in FIG. 6, one end of the motor 18 is connected to a DC power supply 33 and the other end is connected to a controller 36 as control means via a switch transistor 34 and a motor driver 35, and on / off control is performed.

  As shown in FIG. 5B, the pressing roller 14 is rotatably supported by the pressing roller slider 23 via bearings b (only one of which is shown in FIG. 5B) at the left and right ends of its central shaft 141. The pressure roller slider 23 is slidably fitted in a vertically long guide groove 24 of the end plate 111. In addition, the slider 23 receives a pressing force from a compression spring 25 that abuts one end on the lower edge side of the guide long groove 24, and applies the pressing force to the fixing belt 15 and the fixing roller 12 via the pressing roller 14, and the toner image 9 can be heated and pressed. Further, a heater 26 (see FIG. 5B) is built in the center shaft 141 of the pressure roller 14, and the heater 26 is supported via a heater bracket 27 extending from the pressure roller slider 23 side. . A thermistor S1 (see FIG. 6) is provided for the pressure roller 14, and the heater 26 controls the triac 42 and the heater so that the temperature of the pressure roller approaches the set temperature in accordance with the detected temperature. It is controlled by the controller 36 via the driver 45.

  The pressure roller 14 is formed of a rigid aluminum pipe having a high rigidity and a high thermal conductivity by using a thick-walled aluminum pipe. The thickness of the elastic body of the surface layer is set to a value of 2 mm or less, and its hardness is 40 ° in JISA. What can hold the above is adopted.

  Accordingly, when the pressure roller 14 is pressed against the fixing roller 12 around which the fixing belt 15 is wound, an upwardly convex, that is, a downward nip N can be formed with a predetermined nip width L in the transport direction Y. The toner image is fixed on the recording paper 9 with N, and the recording paper 9 after fixing is prevented from wrapping around the fixing belt 15 so as to be smoothly discharged. The nip width L can be expressed as the circumferential angle α of the fixing roller 12, and the circumferential angle α of the fixing roller 12 and the pressing roller 14 with respect to the fixing belt 15 is set so as to secure 25 ° or more. The pressure is adjusted by the compression spring 25, and the surface material of each member is adjusted as described above.

The surface layer of the pressure roller 14 is coated with a high release material such as PFA, PTFE, or FEP, which has good releasability, thereby preventing the recording paper 9 from wrapping around the pressure roller 14, The fusing to the fixing belt 15 is prevented. On the other hand, at a predetermined position on the outer surface of the fixing belt 15, an oil application roller 16 supported by roller support means (not shown) is elastically pressed against the outer surface of the fixing belt 15 to fix the offset suppressing release agent (oil). A very small amount is applied to the outer surface of the belt 15, which also prevents the recording paper and toner from adhering to the fixing belt 15. Note that the oil application roller 16 and an oil tank (not shown) may be eliminated to simplify the apparatus.
Below the fixing belt 15, a pre-fixing guide 21 is provided so that the recording paper 9 supporting the toner image T can advance to the nip N between the belt 15 and the pressure roller 14 without touching the fixing belt 15, After the nip N, a paper discharge guide 22 is provided.

  As shown in FIG. 1, the heating roller 13 is supported at its left and right ends by a slider 29 via a heating roller bearing b (only one is shown in FIG. 5A). The slider 29 is slidably fitted in a guide elongated groove 30 extending obliquely upward of the end plate 111, and the slider 29 is pressed by a spring 31 having one end supported by a spring receiver 301 formed on the end plate 111. Then, the toner is pressed in a direction away from the fixing roller 12 along the guide long groove 30. Therefore, a tension corresponding to the pressing force of the spring 31 is applied to the fixing belt 15 wound between the fixing roller 12 and the heating roller 13.

  The heating roller 13 is formed by using an aluminum pipe and having a large thermal conductivity. As shown in FIG. 5A, a heater 28 is built in a central hole 131 of the heating roller 13, and the heater 28 is supported via a heater bracket 32 extending from a slider 29. A thermistor S2 (see FIG. 6) is provided for the belt portion on the heating roller 13, and the heater 28 causes the triac 43 and the heater to move the belt temperature closer to the set temperature in accordance with the detected temperature. Is controlled by the controller 36 via the driver 46.

  The controller 36 is a well-known microcomputer whose main part is constituted by an input / output circuit 361 connected to the drivers 45 and 46, the motor driver 35 and the thermistors S1 and S2, and a RAM (random number) capable of writing various data. (Access memory) 362, a ROM (read only memory) 363 storing and processing control programs for image forming, setting values, and the like, and a CPU 364 forming a control circuit. The controller 36 drives and controls the heaters 28 and 26 of the heating roller 13 and the pressure roller 14 in accordance with a predetermined heater control program. Moreover, the copy control is performed by operating the motor driver 35 of the motor 18 for the fixing roller 12, the other image forming means, and the motor drivers of the respective image forming means.

Next, the operation of the belt fixing device of FIG. 1 will be described.
It is assumed that the image forming unit shown in FIG. 2 operates according to a known image forming process of a color copying machine. At this time, after the main switch (not shown) is turned on, the controller 36 controls each movable portion according to the warm-up mode, the standby mode, and the copy mode, and simultaneously drives the motor 18 of the belt fixing device, the heaters 26 and 28, and the like.
In this case, the controller 36 turns on and off the respective triacs 42 and 43 in accordance with the pressure roller temperature and the fixing belt temperature detected by the thermistors S1 and S2 of the belt fixing device, and interrupts the current from the AC power supply 44, The on / off of the heaters 26 and 28 is controlled, and the fixing belt temperature and the pressure roller temperature are controlled to target values. When the belt fixing device is driven, the heating roller 13 always applies a tensile force corresponding to the pressing force of the spring 31 to the fixing belt 15 to suppress the generation of belt noise. Always applied to suppress toner offset.

In such a driving state, the pressing roller 14 receives the pressing force of the spring 25 and presses against the fixing belt 15 so as to always form the nip N at a circumferential angle α of the fixing roller 12 exceeding 25 °. The toner image T on the recording paper 9 is heated and pressed when passing through the nip N to thereby fix the toner image T on the recording paper 9.
In this case, the reason why the circumferential angle α of the nip N at which the fixing roller 12 around which the fixing belt 15 is wound and the pressure roller 14 are pressed against each other is set to 25 ° or more will be described below.

  As described above, the temperature range between the cold offset and the hot offset is referred to as a release temperature range in which a good fixing area is obtained. The release temperature range is determined by the fixing roller 12 around which the fixing belt 15 is wound and the pressure roller 14. Are presumed to increase with an increase in the circumferential angle α of the nip N with which the nip N is pressed, and the characteristics are shown in FIG. In FIG. 4, when the circumferential angle α of the nip N exceeds 25 °, the release temperature width sharply increases, and this is considered to be a factor other than the increase in the nip width. That is, in the press-contact shape of the pressure roller 14 against the fixing roller 12 and the fixing belt 15, a small R shape indicated by a symbol r in FIG. 1 is formed at a position immediately downstream in the transport direction Y of the nip N generated at this time. In the small R shape r, the amount of separation from the surface of the recording paper 9 with respect to the rotational angular displacement of the fixing belt 15 is particularly large as compared with other portions.

For this reason, if the circumferential angle α is set to 25 ° or more so that the small R shape r can be formed, the recording paper 9 can be prevented from being displaced following the fixing belt 15, and the recording paper 9 can be prevented from being displaced. Winding around the fixing belt 15 can be prevented, and toner offset can be reliably prevented. In addition, since the release temperature range is expanded, the release agent is also very small, and the release agent remains on the fixed recording material at this point, and the release agent adheres to the user's hand, This can prevent the occurrence of defects in the fixed image due to uneven coating.
Although the belt fixing device of FIG. 1 applies a relatively small amount of the release agent to the fixing belt 15 by the oil application roller 16, an oil tank (not shown) holding the oil application roller 16 and the release agent may be used in some cases. And an oil-less belt fixing device may be configured. In this case, there is an advantage that the device can be reduced in size and maintenance by the user can be performed.

  Here, in order to easily form the small R shape immediately after the fixing belt 15 is located at the position immediately downstream of the nip, as described above, the surface layer of the fixing roller 12 is formed of a sponge-like heat insulating material, and the thickness thereof is set to the fixing roller 12. Is set to be greater than 17% with respect to the diameter of the nip N so that the nip N can be easily secured at a circumferential angle α of 25 ° or more. For this reason, the small round shape r can be formed more reliably, and since the surface layer of the fixing roller 12 is formed of a sponge-like heat insulating material, the driving torque of the motor 18 for driving this belt fixing device can be relatively small. In this respect, there is an effect that the size of the motor 18 can be reduced.

Further, in the belt fixing device shown in FIG. 1, heaters 26 and 28 are dispersedly disposed on the pressing roller 14 and the heating roller 13 which are parts other than the fixing roller 12. As a result, it is possible to prevent the warm-up time from being prolonged despite the fact that the surface layer of the fixing roller 12 is formed of a relatively thick sponge-like heat-insulating layer that exceeds 17% of the diameter of the fixing roller 12. This sponge-like heat insulating layer can suppress the heat of the fixing belt 15 from being dissipated to the fixing roller 12 side. In this regard, the warm-up time can be shortened, and unnecessary driving of the heater 28 and the like can be reduced.
Further, since the hardness of the sponge-like heat insulating material forming the surface layer of the fixing roller 12 is 30 ° or less in Asker hardness, the small R shape r can be easily formed at the position immediately downstream of the nip N on the downstream side of the conveyance path. Accordingly, the driving torque on the fixing roller 12 side can be reduced and the size of the motor 18 can be reduced.

As described above, in the belt fixing device of FIG. 1, the fixing roller 12 directly receives the driving force of the motor 18, and the fixing belt 15 wound around the fixing roller 12 and the pressing roller 14 pressed against the fixing roller 12 are driven to rotate. The fixing drive system D1 shown in FIGS. 7 and 8 may be used instead.
The fixing drive system D2 has an input gear 17a integrally attached to one end of the center shaft 121 of the fixing roller 12, and a drive gear 20a meshed with the input gear 17a, similarly to the fixing drive system D1 of FIG. A motor 18a connected to the other end of a drive shaft 19a integrally connected to the drive gear 20a is provided similarly to the fixing drive system D1 in FIG. Further, in addition to these, the fixing drive system D2 includes a one-way clutch 38 and a driven gear 37 externally fitted to an end of the center axis 141 of the pressure roller 14 outside the portion facing the pressure roller slider 23.

Here, the driven gear 37 meshes with the input gear 17a and is fitted around the center shaft 141 so as to be relatively rotatable. The one-way clutch 38 has an inner shell portion integrally connected to the center shaft 141 and an outer shell portion fixed to the driven gear 37. Here, the one-way clutch 38 allows transmission of the torque from the input gear 17a to the driven gear 37, and cuts the transmission of the torque from the driven gear 37 to the input gear 17a.
For this reason, it is possible to prevent the pressure roller 14 from slipping with respect to the fixing roller 12 and to rotate both rollers synchronously.

When the identification driving system D2 is used instead of the fixing driving system D1 of FIG. 1, the same operation and effect as those of the belt fixing device of FIG. 1 can be obtained, and in particular, the fixing roller 12 and the pressure roller 14 are synchronized. Because of the rotation, the fixing belt 15 and the fixing roller 12 can be prevented from being damaged by friction with the pressure roller 14, and the durability thereof can be improved. In addition, through the one-way clutch 38, the peripheral speed difference between the fixing belt 15 and the pressure roller 14 can be absorbed, and wrinkles or the like can be prevented from being generated on the recording paper 9 being conveyed.
In the above description, the fixing driving system D1 is employed in the belt fixing device of FIG. 1, but instead, the fixing driving system D3 illustrated in FIGS. 9 and 10 may be employed.

The fixing drive system D3 is integrally provided with an input gear 37b at one end of a center shaft 141 of the pressure roller 14 which is pressed against the fixing roller 12 around which the fixing belt 15 is wound, and a drive gear 20b meshed with the input gear 37b. And a motor 18b connected to the other end of the drive shaft 19b integrally connected to the drive gear 20b.
One end of the central shaft 141 is pivotally supported by an end plate 111 via a bearing (not shown), and an input gear 37b is attached to an outer end thereof. The end plate 111 extends outside the bracket (not shown), and the drive shaft 19b is pivotally supported on the bracket via a bearing (not shown) to support the motor 18b. Here, the rotation of the motor 18b can be transmitted from the driving gear 20b to the pressure roller 14 via the input gear 37b, and the rotation of the pressure roller 14 allows the fixing roller 12 around which the fixing belt 15 is wound to rotate. Here, since the pressure roller 14 is closer to a rigid body than the fixing roller 12, the pressure roller 14 directly receiving the driving force of the motor 18b rotates the fixing roller 12 around which the fixing belt 15 is wound. Variations in the linear velocity at which the recording paper 9 is transported in the transport direction Y are reduced, and at this point, the recording paper 9 can be stably transported in the transport direction Y while fixing the recording paper 9 under pressure.

In the above description, the fixing driving system D1 is employed in the belt fixing device of FIG. 1, but instead, the fixing driving system D4 illustrated in FIGS. 11 and 12 may be employed.
This fixing drive system D4 has an input gear 37c integrally attached to one end of a center shaft 141 of the pressure roller 14 which presses against the fixing roller 12, similarly to the fixing drive system D3 of FIG. A drive gear 20c to be meshed and a motor 18c connected to the other end of a drive shaft 19c integrally connected to the drive gear 20c are provided. Further, in addition to these, the fixing drive system D4 includes a one-way clutch 39 and a one-way clutch 39 at an outer end of a portion of the center shaft 121 of the fixing roller 12 around which the fixing belt 15 is wound with an end plate 111 facing a bearing (not shown). An externally fitted driven gear 17c is provided.

Here, the driven gear 17c meshes with the input gear 37c and is fitted around the center shaft 121 so as to be relatively rotatable. The one-way clutch 39 has an inner shell portion integrally connected to the center shaft 121 and an outer shell portion fixed to the driven gear 17c. Here, the one-way clutch 39 allows the transmission of the rotational force from the driven gear 17c meshing with the input gear 37c to the fixing roller 12 side, and the rotational force from the fixing roller 12 side to the input gear 37c meshing with the driven gear 17c. Cut the transmission. That is, it is possible to prevent the fixing roller 12 from slipping with respect to the pressure roller 14, and to rotate both rollers and the fixing belt 15 synchronously.
When the fixing driving system D4 is used in place of the fixing driving system D1 of FIG. 1, the same operation and effect as those of the belt fixing device of FIG. 1 can be obtained, and especially, the pressure roller 14 and the fixing belt 15 slide. Therefore, the fixing belt 15 and the fixing roller 12 can be prevented from being damaged by friction with the pressure roller 14. Further, through the one-way clutch 39, the peripheral speed difference between the fixing belt 15 and the pressure roller 14 can be absorbed, and wrinkles and the like can be prevented from being generated on the recording paper 9 being conveyed.

As described above, the belt fixing device incorporates heaters 26 and 28 in the pressure roller 14 and the heating roller 13, and transfers the heat of these heaters to the recording paper 9 via the pressure roller 14, the heating roller 13, and the fixing belt 15. However, instead of this, the heater 26 of the pressure roller 14 may be eliminated, and the heater 28 may be incorporated only in the heating roller 13. In such a case, in particular, FIGS. Each of the 11 belt fixing devices is very effective in simplifying the device. Further, a fixing belt (not shown) may be configured to generate heat itself. In this case, the same operation and effect as those of the belt fixing device of FIG. 1 can be obtained.
Further, the above-described belt fixing device has been applied to an electrophotographic color copying machine, but instead of this, it is used as a belt fixing device used in other image forming apparatuses such as a single-color copying machine (not shown) and a printer. The same operation and effects as those of the belt fixing device of FIG. 1 can be obtained in these cases.

1 is a schematic side view of a belt fixing device to which the present invention is applied. FIG. 2 is a schematic diagram of an image forming unit of an electrophotographic copying machine equipped with the belt fixing device of FIG. 1. FIG. 2 is an enlarged perspective view of a main part of the belt fixing device of FIG. 1. FIG. 2 is a characteristic diagram of a circumferential angle α of a nip formed by a fixing roller and a pressure roller around a fixing belt of the belt fixing device of FIG. 1 and a release temperature width. FIG. 2 is a schematic cross-sectional view of a main part of the belt fixing device of FIG. 1, in which (a) illustrates one end of a heating roller and (b) illustrates one end of a pressure roller. FIG. 2 is a power supply circuit diagram of the belt fixing device of FIG. 1. FIG. 9 is a schematic side view when the belt fixing device of FIG. 1 is equipped with a fixing driving system D2 as a modification. FIG. 8 is a partially cutaway perspective view of the belt fixing device of FIG. 7. FIG. 9 is a schematic side view when the belt fixing device of FIG. 1 is equipped with a fixing driving system D3 as a modification. FIG. 10 is a partially cutaway perspective view of the belt fixing device of FIG. 9. FIG. 11 is a schematic side view when the belt fixing device of FIG. 1 is equipped with a fixing driving system D4 as a modification. FIG. 12 is a partially cutaway perspective view of the belt fixing device of FIG. 11. FIG. 9 is a schematic side view of a conventional belt fixing device.

Explanation of reference numerals

12 Fixing Roller 13 Heating Roller 14 Pressure Roller 15 Fixing Belt 16 Oil Application Roller 17, 17a, 37b, 37c
Input gear 17c, 37 Follower gear 18, 18a, 18b, 18c
Motor 20, 20a, 20b, 20c
Drive gear 26, 28 Heater 38, 39 One-way clutch r Small R shape α Circumference angle D1, D2, D3, D4
Fixing drive system N nip T Toner image

Claims (11)

An endless fixing belt that is wound around and rotates between a plurality of belt conveyance rollers, and a pressure roller that presses against a portion of the plurality of belt conveyance rollers that is wound around one of the plurality of belt conveyance rollers on the fixing belt. And a heat source for applying heat to the toner on the recording material passing through the nip where the fixing belt and the pressure roller are pressed against each other via at least the fixing belt.
A belt fixing device, wherein a width of the nip is equal to or greater than 25 degrees in a circumferential angle as viewed from a center of the fixing roller. The belt fixing device according to claim 1,
A belt fixing device, wherein the surface of the fixing belt is coated with a release agent. The belt fixing device according to claim 1 or 2,
A belt fixing device, wherein a sponge-like heat insulating material is coated on a surface layer of the fixing roller, and a thickness thereof is 17% or more of a diameter of the fixing roller. The belt fixing device according to any one of claims 1 to 3,
The belt fixing device according to claim 1, wherein the heat source is provided in a portion other than the inside of the fixing roller. The belt fixing device according to any one of claims 3 to 4,
A belt fixing device, wherein the hardness of the sponge-like heat insulating material on the surface of the fixing roller is 30 ° or less in Asker hardness. The belt fixing device according to any one of claims 1 to 5,
A belt fixing device, wherein a surface layer of the pressure roller is formed of an elastic body and has a thickness of 2 mm or less, and has a hardness of 40 ° or more according to JISA. The belt fixing device according to any one of claims 1 to 6,
A belt fixing device, wherein a surface of the pressure roller is coated with a high release material. The belt fixing device according to any one of claims 1 to 7,
A belt fixing device, wherein a driving force for rotating the fixing belt is applied to the fixing roller. The belt fixing device according to claim 8,
A belt fixing device, wherein the driving force is applied to the pressure roller via a one-way clutch. The belt fixing device according to any one of claims 1 to 7,
A belt fixing device, wherein a driving force is applied to the pressure roller. The belt fixing device according to claim 10,
A belt fixing device, wherein the driving force is applied to the fixing roller via a one-way clutch.

Images