JP6848371B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to an image forming apparatus including a fixing device and a fixing device.

In recent years, there has been an increasing market demand for energy saving and high speed for image forming devices such as copiers, printers, facsimiles, and multifunction devices having at least two functions thereof.

Among the image forming devices, the fixing device consumes a large amount of power and has a lot of room for energy saving. Therefore, various proposals have been made. There is known a fixing device that is configured to heat directly without using a conductor and can obtain good fixing property even when mounted on a high-production image forming device (see, for example, Patent Document 1). In this fixing device, the pressure roller arranged on the outer peripheral side of the endless fixing belt and the nip forming member fixedly arranged inside the fixing belt (inside the loop) are pressed against each other via the fixing belt to obtain a fixing nip. Is forming.

On the other hand, in the image forming apparatus, recording materials of various sizes are used. In order to support recording materials of various sizes, if the length of the fixing heat source (heater) of the fixing device is adjusted to the maximum size of the recording material, the fixing belt, which is a non-passing part when fixing small size recording materials, is used. / The temperature at the end of the roller rises. Since the end portion becomes overheated during continuous paper passing, for example, it is necessary to slow down the transport speed of the recording material to reduce the productivity.

In order to deal with this problem, a fixing device having a halogen heater having a dense light distribution in the center and a halogen heater having a dense light distribution near the ends is known inside the fixing belt / roller. .. In the case of a small size recording material, this fixing device lights only the halogen heater with a dense light distribution in the center, and in the case of a recording material larger than the small size, both halogen heaters are turned on for fixing. ..

However, unlike the inkjet recording method, in image formation using toner, printing is performed by providing a non-printing area. Therefore, although the frequency of use is very low, when image formation is performed with the full standard paper size, A recording material that is one size larger than the standard paper size is used (for example, an A3 size that is one size larger than the A3 size), or a 13-inch size material may be used. Therefore, further improvement was desired in order to cope with these special size recording materials.

In response to such a problem, Patent Document 2 provides a plurality of halogen heaters having different light distributions in the width direction of the belt (paper width direction) inside the endless belt, and also provides a plurality of halogen heaters in the longitudinal direction of the belt member. It has been proposed to provide end heaters in contact with the inner or outer surface of the belt at both ends, at positions upstream of the nip in the direction of rotation of the belt.

However, in the fixing device disclosed in Patent Document 2, when the contact pressure of the end heater with respect to the fixing belt is increased in order to increase the heat transfer efficiency from the end heater to the fixing belt, the contact pressure between the end heater and the fixing belt is increased. The frictional force increases. This may lead to poor running of the fixing belt, resulting in a decrease in reliability.

On the other hand, if the contact pressure of the end heater with respect to the fixing belt is reduced in order to avoid poor running of the fixing belt, heat transfer to the fixing belt becomes insufficient. This may lead to excessive temperature rise of the end heater, resulting in a decrease in reliability.

Further, there is also a problem of quality deterioration that the residual toner on the fixing belt that has not been fixed to the recording material at the fixing nip portion is remelted at the position of the end heater and remains as the fixed toner.

Further, in recent years, the fixing device is required to further shorten the first print time, and the following problems have become apparent.

Since the nip forming member slides on the inner surface of the belt member, a lubricant such as fluorine grease or silicone oil is applied to the sliding surface to reduce the sliding torque. In particular, fluorine grease has good retention in the nip forming member, and is advantageous for an increase in torque of the fixing device over time.

However, fluorine grease has the property that its viscosity changes with temperature. In order to shorten the first print time, it is necessary to start the fixing device quickly, but especially when it is cold, the viscosity becomes large and the starting torque of the fixing device becomes large. Therefore, a drive motor with a high torque output is required, which leads to an increase in cost.

Further, when the fixing belt is rotated with such a high torque, a large load is applied not only to the fixing belt but also to the gears that drive the fixing device. Therefore, the mechanical life of the fixing belt, the fixing device, and the image forming device may be shortened.

An object of the present invention is to provide a fixing device capable of dealing with a special size recording material such as A3 novi without impairing reliability and quality, and capable of reducing starting torque even in a cold state.

The tasks are a flexible, endless belt, a pressure member provided on the outside of the belt and facing the belt, a radiant heat source provided on the inside of the belt, and the inside of the belt. A nip forming member provided in the above to form a fixing nip between the belt and the pressurizing member, and a plurality of nip forming members provided at the respective ends of the nip forming member to heat the longitudinal end portions of the belt. A contact heat transfer type heat source and a heat transfer assisting member that covers the surfaces of the nip forming member and the plurality of contact heat transfer type heat sources facing each other and transfers heat in the longitudinal direction of the belt. The inside of the belt is coated with a lubricant, and the problem is solved by a fixing device that operates in the order of heat generation of the plurality of contact heat transfer type heat sources, rotation of the belt, and heat generation of the radiant heat source. ..

Since the fixing device of the present invention is provided with a plurality of contact heat transfer type heat sources for heating the longitudinal end of the belt at each end of the nip forming member, the reliability and quality of the recording material of a special size are impaired. Can be dealt with without. Further, since the operation is started in the order of heat generation of the contact heat transfer type heat source, belt rotation, and heat generation of the radiant heat source, the starting torque can be reduced even in the cold state.

It is a schematic diagram which shows the image forming apparatus which concerns on one Embodiment of this invention. It is a schematic cross-sectional block diagram which shows one Embodiment of a fixing device. It is a perspective view which shows the basic structure of the nip formation unit. It is a perspective view which shows the structure of the nip formation unit and the halogen heater. It is a schematic diagram which shows the arrangement of the heating part of a halogen heater and an end heater. It is a schematic diagram which shows the positional relationship of each heat generating part of a halogen heater and an end heater. It is a graph (first pattern) which shows the heating output of the 2nd halogen heater. It is a graph which shows the state of each heating output of the halogen heater which has a heat generating part near the center, and the halogen heater which has a heat generating part near an end part. It is a graph (second pattern) which shows the heating output of the 1st and 2nd halogen heaters. It is a graph (third pattern) which shows another example of the heating output of the 1st and 2nd halogen heaters. It is a figure explaining the position of the temperature detection part provided for the end heater. It is a flowchart which shows the operation of the fixing device which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the temperature near the fixing nip part and a unit torque in a fixing device.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 is a color laser printer, and four image forming portions 4Y, 4C, 4M, and 4K are juxtaposed in the center of the printer body along the spreading direction of the intermediate transfer belt 30. There is. Each image forming unit 4Y, 4C, 4M, 4K accommodates developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, it has the same configuration.

Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 for charging the surface of the photoconductor 5. A developing device 7 that supplies toner to the surface of the photoconductor 5 and a cleaning device 8 that cleans the surface of the photoconductor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4K are assigned color codes, and the other image forming units 4Y, 4C, and 4M have a color code. The code is omitted.

An exposure device 9 that exposes the surface of the photoconductor 5 is arranged below the image forming portions 4Y, 4C, 4M, and 4K. The exposure device 9 includes a light source, a polygon mirror, an f−θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

A transfer device 3 is arranged above the image forming portions 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

The intermediate transfer belt 30 is an endless belt, and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, the secondary transfer backup roller 32 is rotationally driven so that the intermediate transfer belt 30 orbits (rotates) in the direction indicated by the arrow in the figure.

Each of the four primary transfer rollers 31 forms an intermediate transfer nip by sandwiching an intermediate transfer belt 30 with each photoconductor 5. Further, a power supply of the printer main body is connected to each primary transfer roller 31, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. ..

The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, similarly to the primary transfer roller 31, the power supply of the printer main body is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It is supposed to be done.

The belt cleaning device 35 has a cleaning brush and a cleaning blade arranged so as to come into contact with the intermediate transfer belt 30.
A bottle accommodating portion 2 is provided on the upper portion of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K accommodating replenishing toner are detachably attached to the bottle accommodating portion 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development is performed from each toner bottle 2Y, 2C, 2M, 2K via this replenishment path. Toner is replenished to the device 7.

On the other hand, at the lower part of the printer main body, a paper feed tray 10 containing the paper P as a recording material, a paper feed roller 11 for carrying out the paper P from the paper feed tray 10, and the like are provided. Here, the recording material includes, in addition to plain paper, thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

A transport path R for passing the paper P from the paper feed tray 10 through the secondary transfer nip and discharging the paper P to the outside of the apparatus is provided in the printer main body. In the transport path R, a pair of resist rollers 12 as transport means for transporting the paper P to the secondary transfer nip are arranged on the upstream side in the paper transport direction from the position of the secondary transfer roller 36.

Further, a fixing device 20 for fixing the unfixed image transferred to the paper P is arranged on the downstream side in the paper transport direction from the position of the secondary transfer roller 36. Further, a pair of paper ejection rollers 13 for ejecting the paper to the outside of the apparatus are provided on the downstream side of the transport path R in the paper transport direction with respect to the fixing device 20. Further, a paper ejection tray 14 for stocking the paper ejected outside the apparatus is provided on the upper surface of the printer main body.

The basic operation of the printer according to this embodiment is as follows. When the image-drawing operation is started, each of the photoconductors 5 in each image-forming unit 4Y, 4C, 4M, and 4K is rotationally driven clockwise in the figure, and the surface of each photoconductor 5 is brought to a predetermined polarity by the charging device 6. It is uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9, and an electrostatic latent image is formed on the surface of each photoconductor 5. At this time, the image information to be exposed to each photoconductor 5 is monochromatic image information obtained by decomposing a desired full-color image into yellow, cyan, magenta, and black color information. By supplying toner to the electrostatic latent image formed on each photoconductor 5 in this way by each developing device 7, the electrostatic latent image is visualized (visualized) as a toner image. ..

Further, when the image-drawing operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the drawing to rotate the intermediate transfer belt 30 in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

After that, when the toner image of each color on the photoconductor 5 reaches the primary transfer nip with the rotation of each photoconductor 5, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. The intermediate transfer belt 30 is sequentially superposed on the intermediate transfer belt 30 and transferred. Thus, a full-color toner image is supported on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be completely transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. The surface of each photoconductor 5 is then statically eliminated to initialize the surface potential.

At the lower part of the image forming apparatus, the paper feed roller 11 starts rotational driving, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent out to the transport path R is timed by the resist roller 12 and sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip.

After that, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 orbits travel, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed at the nip. Is collectively transferred onto the paper P. Further, the residual toner on the intermediate transfer belt 30 that could not be transferred to the paper P at this time is removed by the belt cleaning device 35, and the removed toner is conveyed to the waste toner container placed in the printer main body. , Will be recovered.

After that, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged to the outside of the device by the paper ejection roller 13 and is stocked on the paper ejection tray 14.
The above description is an image forming operation when forming a full-color image on paper, but a monochromatic image can be formed by using any one of four image forming units 4Y, 4C, 4M, and 4K. It is also possible to form a two-color or three-color image using two or three image-forming sections.

FIG. 2 is a schematic cross-sectional configuration diagram showing an embodiment of the fixing device 20. The fixing device 20 has an endless fixing belt 21 which is a thin and flexible tubular fixing member, and a pressure roller 22 which is a pressure member which abuts from the outer peripheral side of the fixing belt 21. ing. The fixing belt 21 is heated by the radiant heat of the halogen heaters 23A and 23B (hereinafter, also referred to as the first halogen heater 23A and the second halogen heater 23B) as a plurality of fixing heat sources arranged inside (inside the loop). The halogen heater represents a radiant heat source as a fixing heat source which is a main heat source.

Further, inside the fixing belt 21, a nip forming member 24 that forms a fixing nip N with a pressure roller 22 via the fixing belt 21 and a stay member 25 (supporting member) that supports the nip forming member 24 are arranged. Has been done. The nip forming member 24 arranged in the width direction of the fixing belt 21 is fixedly supported by the stay member 25 to prevent the nip forming member 24 from bending due to the pressure from the pressure roller 22. A uniform nip width can be obtained over the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or higher, particularly a heat-resistant resin such as a polyimide (PI) resin or a polyetheretherketone (PEEK) resin, which is reinforced with glass fiber. It is composed of the plastic. As a result, deformation of the nip forming member 24 due to heat is prevented in the toner fixing temperature range, a stable fixing nip state is ensured, and output image quality is stabilized. Further, the stay member 25 and the halogen heaters 23A and 23B are fixedly held at both ends in the longitudinal direction by a side plate of the fixing device 20 or a holder provided separately. End heaters 26a and 26b as end heat sources different from the main heat source (fixing heat source) are integrally attached to both ends of the nip forming member 24 in the longitudinal direction. As the end heater, a contact heat transfer type heat source which is a resistance heating element such as a ceramic sweater is generally used.

A heat transfer assisting member 27, which is also called a heat equalizing member that facilitates heat transfer in the longitudinal direction of the fixing belt, forms each surface of the nip forming member 24 and the end heater 26 facing the inner peripheral surface of the fixing belt 21. It is arranged so as to cover it, preventing heat from staying in the end region of the fixing belt 21 when passing small-sized paper or lighting the end heater 26, and positively in the width direction of the fixing belt 21, that is, Heat is transferred in the longitudinal direction of the heat transfer assisting member 27 to eliminate temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer assisting member 27 is made of a material having high thermal conductivity, such as copper (398 W / mk) or aluminum (236 W / mk), which enables heat transfer in a short time. In the description of FIG. 2, the surface of the heat transfer assisting member 27 facing the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21, and is a nip forming surface, which is formed flat. However, it may have a concave shape or other shape. With the concave nip forming surface, the discharge direction of the paper tip is closer to the pressure roller, the separability is improved, and the occurrence of jam is suppressed.

As is well known, a temperature sensor 29 for detecting the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 21, for example, on the upstream side of the fixing nip in the belt rotation direction, and is downstream of the fixing device 20 in the paper transport direction. On the side, a separating member 41 that separates the paper P from the fixing belt 21 is arranged. Further, a releaseable pressurizing means for pressurizing the pressurizing roller 22 onto the fixing belt 21 is also provided.

In order to reduce the heat capacity, the endless fixing belt 21 which is thin and has a small diameter like a film has a base material on the inner peripheral side made of a metal material such as nickel or SUS or a resin material such as polyimide, and PFA. It is composed of a release layer on the outer peripheral side formed of (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), or the like. An elastic layer made of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the base material and the release layer. If the thickness of the elastic layer is set to about 100 μm, minute irregularities on the belt surface can be absorbed due to the elastic deformation of the elastic layer when the unfixed toner is crushed and fixed, and the occurrence of uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to have a thickness of 1 mm or less and a diameter of 20 to 40 mm as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in the ranges of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, respectively. In order to further reduce the heat capacity, it is desirable that the thickness of the entire fixing belt 21 is 0.2 mm or less, and more preferably 0.16 mm or less, and the diameter is 30 mm. It is desirable to do the following.

The stay member 25 having a T-shaped cross section has an upright portion 25a on the side opposite to the fixing nip N side, and the halogen heaters 23A and 23B as main heat sources are arranged so as to be separated by the upright portion 25a. One of the halogen heaters 23A and 23B has a heat generating portion at the center in the longitudinal direction corresponding to the small size paper, and the other has a heat generating portion at both ends in the longitudinal direction corresponding to the large size paper. The halogen heaters 23A and 23B are configured to generate heat by controlling the output by a power supply unit provided in the printer main body, and the output control is controlled by a temperature sensor 29 provided on the outer periphery of the fixing belt 21 on the surface of the belt. It is performed based on the temperature detection result. By controlling the output of such a heater, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

Further, reflective members 28A and 28B are arranged between the stay member 25 and the halogen heaters 23A and 23B. As a result, the heating efficiency of the halogen heaters 23A and 23B for the fixing belt 21 can be increased, and wasteful energy consumption due to the stay member 25 being heated by the radiant heat from the halogen heaters 23A and 23B can be suppressed. The same effect can be obtained by performing heat insulation or mirror surface treatment on the surface of the stay member 25 instead of providing the reflective members 28A and 28B.

The pressure roller 22 is composed of a core metal, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the core metal, and a release layer made of PFA or PTFE provided on the surface of the elastic layer. It is configured. At a position where the pressure roller 22 is pressed against the fixing belt 21 by a pressure means such as a spring and is in pressure contact with the fixing belt 21, the elastic layer of the pressure roller 22 is crushed to form a fixing nip N having a predetermined width. Ru. The pressurizing roller 22 is rotationally driven by a drive source such as a motor provided in the printer body. When the pressurizing roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 by the fixing nip N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched between the fixing nip N and rotates, and other than the fixing nip N, the fixing belt 21 is guided by the side plate flanges arranged at both ends and travels.

In the present embodiment, the pressure roller 22 is a solid roller, but it may be a hollow roller. In that case, a heat source such as a halogen heater may be arranged inside the pressurizing roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because it has higher heat insulating properties and is less likely to take away heat from the fixing belt 21.

FIG. 3 is a perspective view showing a basic configuration of the nip forming unit. As shown in FIG. 3, the nip forming unit is composed of a nip forming member 24, a stay member 25, a heat transfer assisting member 27, and end heaters 26a and 26b. In the nip forming unit, the surface of the nip forming member 24 opposite to the fixing nip N side is integrated with the plane of the stay member 25 on the fixing nip N side. At this time, a concave-convex shape such as a boss and a pin may be formed on each surface, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. The heat transfer assisting member 27 and the nip forming member 24 may be integrally configured by providing claws or the like to engage with each other, but adhesive or the like may also be used. Recesses 24a and 24b as stepped portions are formed at both ends of the nip forming member 24 in the longitudinal direction, and end heaters 26a and 26b are housed and fixed in these portions. The positional relationship between the end heaters 26a and 26b and the halogen heaters 23A and 23B will be described later.

The surface of the heat transfer assisting member 27 facing the inner peripheral surface of the fixing belt 21 is configured as the belt sliding contact surface 27a, but in terms of mechanical strength, the nip forming surface is substantially the nip forming surface. The surface 24c facing the compression roller 22.

As described above, in the present embodiment, the end heaters 26a and 26b are integrally provided with the nip forming member 24 necessary for forming the fixing nip, so that the end heaters 26a and 26b are provided on the fixing belt 21. It can be placed inside in a small space.

Further, since the surface of the end heaters 26a and 26b facing the inner surface of the fixing belt 21 and the surface of the nip forming member 24 facing the fixing belt 21 are located at the same height (on the same plane), the pressure roller. Sufficient pressure is applied via the heat transfer assisting member 27.

As a result, the fixing belt 21 is in a state of being indirectly in close contact with the end heaters 26a and 26b, so that the belt can run stably. Further, the fixing belt 21 and the end heaters 26a and 26b are in contact with each other with sufficient contact pressure, and good heating is maintained. From these configurations, the reliability of the fixing device 20 is improved.

Further, the heating portion of the fixing belt 21 by the end heaters 26a and 26b is in the nip region. Therefore, the problem of remelting of the unfixed residual toner (quality deterioration) due to heating at a portion different from the fixing nip N as in Patent Document 1 does not occur.

FIG. 4 is a perspective view showing the configurations of the nip forming unit and the halogen heater. As shown in FIG. 4, the stay member 25 is composed of a first member 25A and a second member 25B having a substantially L-shaped cross section, and has a substantially T-shaped cross section. Therefore, the rigidity is high, and it is possible to prevent the nip forming member 24 from bending due to the stress from the pressure roller 22. Further, the stay member 25 (first member 25A and second member 25B) extends linearly in the longitudinal direction of the nip forming member 24 and is fixed to the nip forming member 24. Therefore, a good nip forming surface can be maintained over the entire longitudinal direction of the fixing nip N.

A first halogen heater 23A and a second halogen heater 23B are arranged on both sides of the upright portion 25a in the lateral direction, respectively. That is, the first and second halogen heaters 23A and 23B are mutually shielded by the upright portion 25a. Therefore, unlike the fixing device shown in FIG. 11, the glass tubes of each other are not heated when the heater is turned on, so that the heating efficiency does not decrease. Further, since the first and second halogen heaters 23A and 23B are not surrounded by the stay member 25 (the center of each halogen heater 23 is outside the space surrounded by the stay member 25), the irradiation angles α and β (FIG. FIG. 2) becomes an obtuse angle, and the heating efficiency can be improved.

The cross-sectional shape of the stay member 25 is not limited to the substantially T shape. The first and second halogen heaters 23A and 23B may be arranged so as to sandwich the upright portion 25a and partition the first and second halogen heaters 23A and 23B from each other, and the first member 25A and the second member 25B extend curvedly in the longitudinal direction of the halogen heater. You may. Further, the first member 25A and the second member 25B may be erected in an oblique direction with respect to the nip forming surface of the nip forming member 24.

Next, the arrangement configuration of the heat source that can correspond to the recording material of a special size such as A3 Nobi will be described. FIG. 5 is a schematic view showing the arrangement of the heat generating portions of the halogen heater and the end heater. As shown in FIG. 5, a first halogen heater 23A having a dense light distribution in the central portion in the longitudinal direction and a second halogen heater 23B having a dense light distribution at both ends in the longitudinal direction are arranged. There is. That is, the first halogen heater 23A heats the central range of the fixing belt 21, and the second halogen heater 23B heats the side range of the fixing belt 21.

The heat generating portion 40A of the first halogen heater 23A corresponds to a small-sized recording material such as A4 vertical size, and the heat generating portion 40B of the second halogen heater 23B has an A3 vertical size that cannot be covered by the first halogen heater 23A. Covers the edge range of the maximum standard size recording material that can be used. That is, the heat generating portion 40 including the heat generating portions 40A and 40B of both halogen heaters corresponds to the maximum standard size paper width and does not cover the novi size paper width larger than the maximum standard size.

On the other hand, the end heaters 26a and 26b are located at positions corresponding to both ends in the longitudinal direction of the second halogen heater 23B, and have heat generating portions 42a and 42b for heating both ends of a novi size paper width larger than the maximum standard size. Further, a part of the heat generating portions 42a and 42b of the end heaters 26a and 26b overlap with the heat generating portion 40B of the halogen heater 23B. As a result, the fixing device 20 can handle both ends of a novi size paper width larger than the maximum standard size.

Here, the amount of heat (heating output) actually output by the halogen heater and the end heater will be described. FIG. 6 is a schematic view showing the positional relationship of each heat generating portion of the second halogen heater 23B and the end heater 26b and the state of the heating output of each heater. The upper part of FIG. 6 shows the state of the right end of the heat generating portion of the second halogen heater 23B, and the lower part of FIG. 6 shows the state of the left side of the heat generating portion of the end heater 26b.

In general, the halogen heater has a reduced heating output at the longitudinal end of the heat generating portion (the portion in which the filament is spirally wound). This also depends on the winding density of the filament, and it tends to decrease when the winding density is sparse. As shown in the upper part of FIG. 6, the heat generating portion 40B of the second halogen heater 23B extends from a portion that outputs a predetermined heating output of 100 (%) to a portion where the amount of heat is sagging and the heating output becomes 50%. For example, it can be defined.

Further, as shown in the lower part of FIG. 6, the end heater 26b also has a reduced heating output at the longitudinal end of the heat generating portion 42b (the portion where the heat generating pattern 37 is provided). That is, 100% of the predetermined heating output is not output at the end portion, and the heating output sags.

Therefore, if the heating output drops (sags) at the ends of the second halogen heater 23B and the end heater 26b, good fixing is performed particularly at the ends of the recording material having a size larger than the maximum standard size. There is a risk that it will not be.

Therefore, in the present embodiment, as shown in FIG. 6, the boundary Bh at which the heating output in the heat generating portion 40B of the second halogen heater 23B begins to decrease and the boundary Bc at which the heating output at the heating portion 42b of the end heater 26b begins to decrease. And match. In an actual device, the halogen heater 23B and the end heater 26b are arranged apart from each other in space, so that the boundaries Bh and Bc of the halogen heater 23B and the end heater 26b match each other in the longitudinal direction in the projected state. The same applies to the other end heater 26a.

As a result, in the region where the halogen heater 23B and the heaters 26a and 26b at both ends overlap, the heating output does not decrease, and 100% of the predetermined heating output can be maintained. Therefore, good fixing can be guaranteed even at both ends of a recording material having a size larger than the maximum standard size.

As described above, in the present embodiment, the boundary Bh of the second halogen heater 23B and the boundary Bc of the end heater 26b are matched. However, as described above, since the nip forming unit has the heat transfer assisting member 27 having good thermal conductivity, it is possible to smooth the drop in the heating output to some extent. Therefore, a predetermined allowable range may be provided in the arrangement of the boundary where the heating output of the heaters 26a and 26b at both ends starts to decrease.

Next, how to set the end portion of the heat generating portion near the center of the end heater (boundary Bc at which the heating output starts to decrease) will be described in three patterns using a graph of the heat generating output. The position where the boundary Bc is set has a predetermined allowable range.

(First pattern)
FIG. 7 is a graph showing the heating output of the second halogen heater. The graph depiction shows the output at one end for convenience of explanation. In FIG. 7, the vertical axis represents the output ratio (%) with respect to the predetermined heating output, and the horizontal axis represents the position of the halogen heater 23 in the longitudinal direction. The graph of heating power draws a curve with a convex peak in the longitudinal direction.

In the case of the heating output shown in FIG. 7, the boundary Bc of the end heater 26 (the boundary where the heating output near the center in the longitudinal direction of the heat generating portion 42b begins to decrease) is such that the heating output of the second halogen heater is closer to the end in the longitudinal direction. It is set in the range (the range shown by A in the figure) from the location where the heating output of the peak is 40% to the location near the center in the longitudinal direction where the heating output of the peak is 80%. If the boundary Bc of the end heater 26 is set in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

(Second pattern)
FIG. 8 is a graph showing the heating output states of a halogen heater having a heat generating portion in the central range and a halogen heater having a heating portion in the side region. The heating output of the halogen heater having a heat generating portion in the central range corresponding to the first halogen heater 23A is shown by a broken line graph, and the heating output of the halogen heater having a heating portion in the side portion corresponding to the second halogen heater 23B is shown by a solid line. Indicated by. Multiple halogen heaters that have different light distributions in the longitudinal direction and therefore each have a different heating output pattern can result in different total heating output patterns.

FIG. 9 is a graph showing the heating output of the first and second halogen heaters. As shown in FIG. 9, in the graph of heating output, the output ratio rises to 100% in the vicinity of both ends, and is gentle at almost 100% even in the central region in the longitudinal direction.

Here, the range in which the heating output is approximately 100% is defined as the length (B), and the range in which the output ratio is approximately 100% to 40% is defined as the length (C). At this time, the boundary Bc of the end heater 26 is arranged in a range from the position where the output ratio becomes 40% of the heating output to the length D satisfying (C + B × 1/10) toward the center in the longitudinal direction. .. If the boundary Bc of the end heater 26 is arranged in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

(Third pattern)
FIG. 10 is a graph showing another example of the heating output of the first and second halogen heaters. As shown in FIG. 10, the central region of the graph is gentle, but both ends thereof are higher than the central region. This shape is obtained when the filament of the heat generating portion of the second halogen heater 23B is wound more densely than the filament of the heat generating portion of the first halogen heater 23A.

Here, the range sandwiched between both ends where the heating output is approximately 100% is defined as the length (B'), and the range where the output ratio is approximately 100% to 40% is defined as the length (C). At this time, the boundary Bc of the end heater 26 is within the range from the position where the output ratio is 40% of the heating output to the length D'that satisfies (C + B'× 1/10) toward the center in the longitudinal direction. Be placed. If the boundary Bc of the end heater 26 is arranged in such a range, the heating output at the ends of the end heater 26 and the second halogen heater 23B can be within an allowable range.

Subsequently, an advantageous configuration of the fixing device of the present invention will be described.
Since the heat transfer assisting member 27 is in sliding contact with the inner surface of the fixing belt 21, the friction coefficient becomes large when a metal material such as copper or aluminum is used as it is. If the coefficient of friction is large, the unit torque becomes large, causing problems such as shortening the life of the device.

Therefore, it is desirable that the belt sliding contact surface 27a (see FIG. 3) facing (contacting) the fixing belt 21 of the heat transfer assisting member 27 is smooth and further subjected to low friction treatment. Specifically, the friction between the heat transfer assisting member 27 and the inner surface of the fixing belt 21 is reduced by applying a fluorine-based coating or coating such as PFA or PTFE. It is also desirable to apply a lubricant such as fluorine grease or silicone oil between the heat transfer assisting member 27 and the inner surface of the fixing belt 21, and friction can be further reduced.

Next, a temperature detection unit different from the temperature sensor 29 shown in FIG. 2 that detects the temperature of the fixing belt 21 heated by the end heater 26 will be described. Using a contact type sensor (for example, a thermistor) for temperature detection of the fixing belt 21 has an advantage of low cost and high accuracy. However, there is a possibility that fine sliding contact marks may be generated at the contact position, or minute gloss unevenness may occur in the image at the corresponding position. Therefore, especially in a color image output machine, it is a mainstream not to use a contact sensor within a standard size paper width.

By the way, in the nobi size recording material, the nobi part is the ear part when image is drawn up to just before the edge of the paper of the maximum standard size, a line image called a register mark used for printing alignment, or a small area for color confirmation. It is used as the part where the solid patch of is imaged. And, in the end, it is often cut off. Therefore, even if a contact mark is generated by the contact-type temperature detection unit, it can be said that minute gloss unevenness or the like does not become apparent as an abnormal image.

Therefore, in the present embodiment, as shown in FIG. 11, the temperature detecting portions 45a and 45b (45a are provided at the opposite end portions) for detecting the temperature of the portion heated by the end heaters 26a and 26b of the fixing belt 21. Therefore, the description is omitted) is provided outside the fixing belt 21 and in the longitudinal direction of the fixing belt 21 outside the maximum standard size paper width and inside the novi size paper width larger than the maximum standard size. .. As a result, the temperature can be detected inexpensively and accurately without revealing an abnormal image such as minute uneven gloss. Of course, in order to prevent an abnormal image such as minute gloss unevenness from occurring even in the image range of the nobi portion, a non-contact type temperature detection unit may be used.

Although the configuration for detecting the temperature of the portion heated by the end heaters 26a and 26b of the fixing belt 21 has been described, a sensor for detecting the temperature of a part of the end heater itself is provided, and the end heater is based on the detection result. A method of controlling is also applicable.

Next, a configuration that can be quickly fixed without increasing the load during operation even in a cold state will be described.
As described above, the heat transfer assisting member 27 is in sliding contact with the inner surface of the fixing belt 21. The coefficient of friction can be reduced by applying a lubricant such as fluorine grease or silicone oil between the heat transfer assisting member 27 and the inner surface of the fixing belt 21.

Here, the heat transfer assisting member 27 does not positively absorb the lubricant on the sliding surface. Therefore, it is more effective to use fluorine grease having good retention as a lubricant to suppress an increase in unit torque with time.

However, as a lubricant, fluorine grease in particular has a property that its viscosity changes with temperature. In particular, when the fixing device 20 is started in a cold state, the unit torque becomes large, and the load on the fixing device 20 and the image forming device 1 becomes large.

In order to deal with this problem, the present embodiment proposes a fixing device that operates in the order of heat generation of the end heaters 26a and 26b, rotation of the fixing belt 21, and heat generation of the halogen heater 23 at the start of operation.

That is, when starting the operation of the fixing device 20, the end heaters 26a and 26b are first energized. Next, the detection temperatures of the temperature detection units 45a and 45b are both predetermined temperatures T1 (° C.) (first temperature at which the starting torque of the fixing device 20 becomes a predetermined magnitude; the temperature at which the fixing belt 21 may start rotating). At the above time, the rotation of the fixing belt 21 is started. Alternatively, the rotation of the fixing belt 21 is started when the temperature is determined (estimated) by the thermometer provided inside the image forming apparatus 1. Then, after the fixing belt 21 starts rotating, the halogen heater 23 is energized. These series of operations are due to the following reasons.

The surface of the fixing belt 21 facing the halogen heater 23 is directly heated by the heater, so that the temperature rises. On the other hand, the surface of the fixing belt 21 that does not face the halogen heater 23 is not directly heated by the heater, so that the temperature is lowered. As a result, a temperature difference may occur in the circumferential direction or the longitudinal direction of the fixing belt 21.

Such a temperature difference becomes "temperature spots" in the circumferential direction of the fixing belt 21, and often does not completely disappear even if the fixing belt 21 is idlely rotated for a while. In particular, when starting up a device in a cold state, a large amount of heat is transferred from the fixing belt 21 toward a pressurizing roller having a large heat capacity, so that even if the fixing belt 21 is idle for a long time, temperature spots will occur. It becomes difficult to disappear.

Then, if temperature spots having a large temperature difference occur, the surface of the fixing belt 21 may be distorted due to the difference in the local thermal expansion amount of the fixing belt 21. If the surface of the fixing belt 21 is distorted in this way, a good fixing nip portion is not formed, and an image with deteriorated quality is formed.

Further, if the strain exceeds the yield stress of the fixing belt 21, buckling fracture (kink) may occur in the fixing belt 21. When the fixing belt 21 generates a kink, it develops into an abnormal image and further leads to the destruction of the fixing belt 21. Such a problem is remarkable in a fixing device having improved rising characteristics (heating characteristics) such as the present fixing device.

Therefore, in order to prevent temperature unevenness and buckling fracture (kink), it is necessary to energize the halogen heater 23 after the start of rotation of the fixing belt 21.

As described above, the load on the fixing device 20 and the image forming device 1 can be reduced by starting the operations in the order of energizing the end heaters 26a and 26b, rotating the fixing belt 21, and energizing the halogen heater 23. , Durability can be improved (longer life).

Subsequently, the operation of the fixing device according to the embodiment will be described with reference to a flowchart.
FIG. 12 is a flowchart showing the operation of the fixing device according to the embodiment. Here, the temperature T2 (° C.) is a second temperature (T2> T1) (a temperature at which the fixing device 20 may be started immediately) at which the starting torque of the fixing device 20 becomes sufficiently small.

First, in step S1, the fixing device 20 determines whether the detection temperatures of the temperature detection units 45a and 45b are both higher than the temperature T2 (° C.).

If the detection temperatures of the temperature detection units 45a and 45b are both higher than the temperature T2 (° C.) (YES), the starting torque of the fixing device 20 is sufficiently small. The process proceeds to step S2, and the fixing device 20 starts rotating the fixing belt 21. In this case, the end heaters 26a and 26b do not have to be energized.

On the other hand, if at least one of the detected temperatures of the temperature detection units 45a and 45b in step S1 is the temperature T2 (° C.) or lower (NO), the process proceeds to step S4.

In step S4, the fixing device 20 determines whether the detection temperatures of the temperature detection units 45a and 45b are both higher than the predetermined temperature T1 (° C.) and equal to or lower than the predetermined temperature T2 (° C.).

That is, at the start of the operation of the fixing device 20, the detection temperatures of the temperature detection units 45a and 45b may show different values (different processes) depending on the previous operation content, the leaving time from the previous operation, and the like. If the detection temperatures of the temperature detection units 45a and 45b are both higher than the predetermined temperature T1 (° C.), the starting torque of the fixing device 20 is equal to or less than the predetermined value. From the viewpoint of shortening the first print time, it is desirable to energize the end heaters 26a and 26b and start the rotation of the fixing belt 21 at the same time. Therefore, the process proceeds to step S5, and the end heaters 26a and 26b are energized and the fixing belt 21 is started to rotate.

On the other hand, in step S4, when at least one of the detection temperatures of the temperature detection units 45a and 45b is lower than the predetermined temperature T1 (° C.) (NO), the process proceeds to step S6 to the end heaters 26a and 26b. Start energizing.

Next, the process proceeds from step S6 to step S7, and the fixing device 20 waits until the detection temperatures of the temperature detection units 45a and 45b reach a predetermined temperature T1 (° C.) or higher (in the case of NO).

In step S7, when the detected temperatures are equal to or higher than the predetermined temperature T1 (° C.) (YES), the process proceeds to step S8, and the fixing device 20 starts the rotation of the fixing belt 21.

As described above, when the detection temperature of any of the temperature detection units 45a and 45b is lower than the predetermined temperature T1 (° C.), the end heaters 26a and 26b heat the nip forming unit, and the respective detection temperatures are predetermined. The fixing belt 21 is rotated when the temperature reaches T1 (° C.) or higher. As a result, the difference in starting torque at both ends of the fixing belt 21 can be reduced.

Next, the process proceeds to step S3, and the fixing device 20 energizes the halogen heater 23. Then, the process proceeds to step S9, and the preparation for image formation of the fixing device 20 is completed. Then, the image forming operation by the entire image forming apparatus is started.

FIG. 13 is a graph showing the relationship between the temperature near the fixing nip portion and the unit torque in the fixing device. In FIG. 13, the vertical axis represents the unit torque (Nm), and the horizontal axis represents the temperature (° C.) near the fixing nip portion. The plots marked with ◯ are the unit torques when the linear speed of rotation is 100 (mm / sec), and the plots marked with × are the unit torques when the linear velocity of rotation is 300 (mm / sec).

As can be seen from the graph, even if the temperature near the fixing nip portion is the same, the lower the rotation line speed, the lower the unit torque.

If the temperature is the same, the lower the rotation line speed, the smaller the starting torque, which is advantageous. In order to shorten the first print time, the rotation should be started early, and in the fixing device having a plurality of rotation linear speeds, it is desirable to select a low rotation speed at least until the halogen heater 23 is turned on.

In this case, the timing of switching the low rotation line speed to the high rotation line speed may be synchronized with the timing of turning on the halogen heater 23. Alternatively, if the temperatures in the longitudinal direction and the circumferential direction of the fixing belt 21 fall within the temperature deviation in which the above-mentioned temperature spots and buckling fracture (kink) do not occur, it is not always synchronized with the timing of turning on the halogen heater 23. May be good. Therefore, the timing may be selected from conditions that are advantageous for raising the temperature of the fixing belt 21.

As described above, the fixing device of the present embodiment operates in the order of heat generation of the end heaters 26a and 26b, rotation of the fixing belt 21, and heat generation of the halogen heater 23, so that temperature spots and buckling on the fixing belt 21 occur. It is possible to avoid destruction and reduce the starting torque.

Further, the fixing device of the present embodiment starts the rotation of the fixing belt 21 when the detected temperatures of the temperature detecting units 45a and 45b each detect a temperature of a predetermined temperature (T1). Therefore, the rotation of the fixing belt 21 can be started by using the time when the temperature reaches T1 at which the starting torque is reduced as a trigger.

Furthermore, since the fixing device of the present embodiment has a plurality of rotating linear speeds and operates at a low rotating linear speed at least until the heat generated by the halogen heater 23, it is possible to reduce the starting torque and the first print time at the same time.

(Modification example)
As a modification, instead of the temperature detecting units 45a and 45b, the temperature sensor 29 provided on the outer peripheral side of the fixing belt 21 may detect the temperature of the fixing belt 21. Alternatively, the temperature of the fixing belt 21 may be estimated by a temperature sensor provided inside the image forming apparatus 1. In these cases as well, the flowchart of FIG. 12 can be appropriately read and applied.

The present invention has been described above based on the embodiments. The present invention is not limited to the embodiments, and can be appropriately modified within the scope of the present invention. Further, the image forming apparatus provided with the fixing device of the present invention is not limited to a copying machine or a printer, but may be a facsimile or a multifunction device having a plurality of functions.

1 Image forming device 2 Bottle housing 2C, 2K, 2M, 2Y toner bottle 3 Transfer device 4C, 4K, 4M, 4Y Image forming unit 5 Photoreceptor 6 Charging device 7 Developing device 8 Cleaning device 9 Exposure device 10 Paper feed tray 11 Paper Feed Roller 12 Resist Roller 13 Paper Discharge Roller 14 Paper Discharge Tray 20 Fixing Device 21, 60 Fixing Belt 22 Pressurizing Roller 23A, 23B, 50A, 50B Halogen Heater 24 Nip Forming Member 24a, 24b Recess 24c Surface 25 Stay Member 25A No. 1 member 25B 2nd member 25a Standing part 26a, 26b End heater 27 Thermal transfer assisting member 27a Nip forming surface 28A, 28B, 70 Reflecting member 29 Temperature sensor 30 Intermediate transfer belt 31 Primary transfer roller 32 Secondary transfer backup roller 33 Cleaning Backup roller 34 Tension roller 35 Belt cleaning device 36 Secondary transfer roller 37 Heat generation pattern 41 Separation member 40A, 40B, 42a, 42b Heat generation part 45a, 45b Temperature detection part Bc, Bh Boundary N Fixing nip P Paper α β Irradiation angle

Japanese Unexamined Patent Publication No. 2010-32631 Japanese Unexamined Patent Publication No. 2014-178370

Claims (9)

With a flexible, endless belt,
A pressurizing member provided on the outside of the belt and facing the belt,
A radiant heat source provided inside the belt and
Provided on the inner portion of the belt, the nip forming member for forming a fixing nip between the pressing member and the belt,
A plurality of contact heat transfer type heat sources provided at each end of the nip forming member and heating the longitudinal end of the belt, respectively.
It has a heat transfer assisting member that covers each surface of the nip forming member and the plurality of contact heat transfer type heat sources facing the belt and transfers heat in the longitudinal direction of the belt.
A fixing device in which a lubricant is applied to the inside of the belt, and the fixing device operates in the order of heat generation of the plurality of contact heat transfer type heat sources, rotation of the belt, and heat generation of the radiant heat source. It is equipped with a temperature detection unit that detects the temperature of the belt.
The fixing device according to claim 1, wherein the belt is rotated when the temperature detecting unit detects a predetermined first temperature. Rotating said temperature detecting unit is higher than the first temperature, and, if the start torque detects a sufficiently small second temperature below the temperature, the belt while heating the contact heat transfer-type heat source The fixing device according to claim 2, wherein the fixing device is provided. The fixing device according to claim 3, wherein when the temperature detecting unit detects a temperature higher than the second temperature, the belt is rotated to generate heat of the radiant heat source. A plurality of temperature detectors for detecting the temperature of the belt heated by the plurality of contact heat transfer type heat sources are provided.
The fixing device according to claim 1, wherein the belt is rotated when the plurality of temperature detection units each detect a predetermined first temperature. Wherein the plurality of temperature detection unit is higher than each of the first temperature, and, if the start torque detects a sufficiently small second temperature below the temperature, while heating the plurality of contact heat transfer-type heat source The fixing device according to claim 5, wherein the belt is rotated. The fixing device according to claim 6, wherein when the plurality of temperature detecting units each detect a temperature higher than the second temperature, the belt is rotated to generate heat of the radiant heat source. The fixing device according to any one of claims 1 to 7, wherein the belt has a plurality of rotating linear speeds and operates at a low rotating linear speed at least until heat is generated by the radiant heat source. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 8.

Images