JP6738527B2 - Fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a fixing device that fixes an image on a recording medium, and an image forming apparatus that includes the fixing device.

As a fixing device mounted on an image forming apparatus such as an electrophotographic copying machine and a printer, a belt-type fixing device with improved energy saving and first print time has been put into practical use. This belt-type fixing device heats an endless fixing belt with a heating member such as a halogen heater. In recent years, a direct heating type in which a fixing belt having a low heat capacity is directly heated with a heating member (halogen heater) has become popular. doing.

In this direct heating type, it is ideal to heat the fixing belt with a heating width that corresponds one-to-one with the paper width size, but if a general halogen heater is used as the heating member, the paper width size It is the fact that a smaller number of heaters (for example, the central heater and the end heaters) are used for the number of heaters.

When a small number of heaters are used as described above, the frequency of fixing is increased with the heating width of the fixing belt being larger than the width of the sheet. On the other hand, in recent years, since the heat capacity and the thickness of the fixing belt have been further reduced, when such a low heat capacity and thin fixing belt is heated in the non-sheet passing area outside the paper width, the so-called end temperature The rise (excessive temperature rise) becomes severe.

Therefore, conventionally, a movable shield member that shields the radiant heat from the heater is rotationally driven according to the paper size, and a high heat conductive member is attached to the nip portion forming member to suppress the end temperature rise. There is.

If the movable shield member is provided, the size of the device increases and the cost increases. On the other hand, the high thermal conductive member can suppress the temperature rise at the end portion at a relatively low cost, but when continuously passing a sheet of a size smaller than the heating width of the fixing belt (emission length of the central heater) (A6), Even with a high thermal conductivity member that is compatible with the entire width, it has not been possible to effectively suppress the rise in the end temperature. Of course, it is conceivable to suppress the temperature rise of the end portion by increasing the heat capacity and the amount of heat radiation of the high thermal conductive member, but if this is done, fixing failure will occur due to the lowering of the end temperature of the sheet passing area at the time of fixing start-up. The improper fixing is, for example, "cold offset" in which a paper image adheres to the surface of the fixing roller or the fixing belt and is peeled off from the paper.

In order to solve such a problem, conventionally, a fixing device has been proposed in which the nip forming member has a three-layer structure of 1) nip-side high thermal conductive layer, 2) base material layer, and 3) stay-side high thermal conductive layer. (Patent Document 1: JP-A-2015-194661, FIG. 6). In this fixing device, even if the temperature rises in the non-sheet passing area when small size sheets are continuously fed, the heat is moved and diffused in the longitudinal direction by the high thermal conductive layer, which effectively increases the end temperature. Will be suppressed. On the other hand, since the low heat conduction part is formed by the base material layer near the end of the paper passing area, the heat escape to the end is limited, and the end temperature drop at the time of fixing start-up is suppressed.

However, since the device of Patent Document 1 has a three-layer structure for the nip forming member, the number of parts and the number of assembling steps increase, resulting in an increase in cost. Further, due to variations in assembly accuracy among components, variations in heat conduction and accompanying fixing defects (cold offset) may occur.

Therefore, an object of the present invention is to reduce the cost by using a simple structure for the nip forming member, to suppress an increase in the end temperature in the non-paper passing area when the paper is passed while only the first heating member is turned on, and to fix the fixing. This is to suppress the temperature drop at the end portion in the sheet passing area at the time of raising.

In order to solve the above problems, the present invention provides a rotatable endless fixing belt, a first heating member having a first heat generating portion on the widthwise center side of the fixing belt, and a widthwise end portion of the fixing belt. A second heating member having a second heat generating portion on its side, a facing member facing the outer peripheral side of the fixing belt, and a nip provided on the inner peripheral side of the fixing belt and forming a nip facing the facing member. A forming member and a high thermal conductive member having a higher thermal conductivity than the nip forming member, which is arranged on the fixing belt side of the nip forming member, and has one end in the longitudinal direction of the first heat generating portion as a starting point. When the length to the longitudinal outer end of the second heat generating portion located outside the longitudinal one end is L1, and the length to the longitudinal one end of the high thermal conductive member is L2. , L1 and L2 are set to have a ratio of L2/L1=0.88 to 0.96.

According to the present invention, the ratio of the length L1 to the outer end in the longitudinal direction of the second heat generating portion and the length L2 to one end in the longitudinal direction of the high thermal conductivity member is L2/L1=0.88 to 0.96. By setting the temperature in the range, it is possible to suppress an increase in the end temperature and a decrease in the end temperature, so that the cost of the fixing device can be reduced. In addition, since the high-heat conductive member can release heat without excess or deficiency when passing the paper in which only the first heating member is turned on, it is possible to suppress an increase in the end temperature and a decrease in the end temperature at the start-up of fixing. ..

1 is a schematic diagram of an image forming apparatus according to an exemplary embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a fixing device used in the image forming apparatus. FIG. 3 is a perspective view showing a positional relationship in the width direction of a halogen heater, a high thermal conductivity member, and a sheet. FIG. 7 is a schematic view showing the light emission length of a sheet of paper, a halogen heater, and the length (width) of a high thermal conductive member in comparison with the conventional one. (A) is a cross-sectional view of the stay and the nip forming member as seen from the sheet passing direction, (b) is a cross-sectional view of the stay and the nip forming member as seen from the longitudinal direction, and (c) shows a modified example of the high thermal conductive member ( It is a sectional view similar to b). It is an expanded sectional view of a nip forming member. FIG. 6 is a diagram showing a state where the end temperature rises and the end temperature falls for each sheet passing width in the fixing operation using the nip forming member according to the embodiment of the present invention. FIG. 10 is a diagram showing a state where the end temperature rises and the end temperature falls for each sheet passing width in a fixing operation using a conventional nip forming member having a three-layer structure of a high thermal conductivity member. FIG. 11 is a diagram showing a state where the end portion temperature rises and the end portion temperature falls for each sheet passing width in the fixing operation using the conventional nip forming member without the high thermal conductive member. (A)-(d) is a figure which shows the difference in temperature distribution of a fixing belt with the presence or absence of a high thermal conductive member, and the kind of paper width size.

(Image forming device)
Hereinafter, a printer as an image forming apparatus according to an embodiment of the present invention and a fixing device used in the printer will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a color laser printer as an image forming apparatus. At the center of the image forming apparatus 1, four image forming units 4Y, 4M, 4C and 4K are provided. The image forming units 4Y, 4M, 4C and 4K contain developers of different colors of yellow (Y), magenta (M), cyan (C) and black (K) corresponding to the color separation components of the color image. The configuration is the same except that

Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a toner on the surface of the photoconductor 5. And a cleaning device 8 for cleaning the surface of the photoconductor 5. In FIG. 1, reference numerals are given only to the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4K, and the other image forming units 4Y, 4M, and 4C are omitted. To do.

An exposure device 9 that exposes the surface of the photoconductor 5 is disposed below each of the image forming units 4Y, 4M, 4C, and 4K. The exposure device 9 has a light source, a polygon mirror, an f-θ lens, a reflection mirror, etc., and irradiates the surface of each photoconductor 5 with laser light based on image data. The exposure device 9 can also be configured as an LED exposure device.

The transfer device 3 is disposed above the image forming units 4Y, 4M, 4C and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as a primary transfer member, and a secondary transfer roller 36 as a secondary transfer member. The transfer device 3 further 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 over the secondary transfer backup roller 32, the cleaning backup roller 33, and the tension roller 34. Here, the secondary transfer backup roller 32 is rotationally driven, so that the intermediate transfer belt 30 travels (rotates) in the direction indicated by the arrow in the drawing.

Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source is connected to each primary transfer roller 31, and a predetermined direct current voltage (DC) and/or alternating current 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, like the primary transfer roller 31, a power source is also connected to the secondary transfer roller 36 so that a predetermined DC voltage (DC) and/or AC voltage (AC) is applied to the secondary transfer roller 36. It has become.

The belt cleaning device 35 has a cleaning brush and a cleaning blade which are arranged so as to contact the intermediate transfer belt 30. The waste toner transfer hose extending from the belt cleaning device 35 is connected to the inlet of the waste toner container.

A bottle container 2 is provided on the upper part of the printer body, and four toner bottles 2Y, 2M, 2C and 2K containing replenishment toner are detachably mounted in the bottle container 2. A replenishment path is provided between each of the toner bottles 2Y, 2M, 2C, 2K and each of the developing devices 7, and each toner bottle 2Y, 2M, 2C, 2K is connected to each of the developing devices 7 through the replenishment path. Toner is replenished.

On the other hand, in the lower part of the printer body, there are provided a paper feed tray 10 that contains paper P as a recording medium, a paper feed roller 11 that carries out the paper P from the paper feed tray 10, and the like. Here, the recording medium includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, etc. in addition to plain paper. Further, a manual sheet feeding mechanism may be provided on the side surface of the printer body.

Inside the printer body, a conveyance path R is provided for ejecting the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of timing rollers 12 serving as a transport member that transports the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

Further, a fixing device 20 for fixing the unfixed image transferred to the sheet P is disposed downstream of the position of the secondary transfer roller 36 in the sheet conveying direction. Further, a pair of paper ejection rollers 13 for ejecting the paper to the outside of the apparatus is provided on the downstream side of the fixing device 20 in the paper conveyance direction of the conveyance path R. Further, a paper discharge tray 14 for stocking the paper discharged to the outside of the apparatus is provided on the upper surface of the printer body.

(Basic operation of the printer)
Subsequently, a basic operation of the printer according to the present embodiment will be described with reference to FIG. When the image forming operation is started, each photoconductor 5 in each of the image forming units 4Y, 4M, 4C, and 4K is rotationally driven in the clockwise direction in the drawing by the driving device, and the surface of each photoconductor 5 is predetermined by the charging device 6. Is uniformly charged to the polarity.

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 exposed on each photoconductor 5 is monochromatic image information in which a desired full-color image is separated into color information of yellow, magenta, cyan, and black. By supplying toner to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, the electrostatic latent image is visualized as a toner image (visualized). ..

Further, when the image forming operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the figure, and the intermediate transfer belt 30 is circulated in the direction shown 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 in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

Thereafter, when the toner images of the respective colors on the photoconductors 5 reach the primary transfer nip as the photoconductors 5 rotate, the toner images on the photoconductors 5 are formed by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. In this way, a full-color toner image is carried on the surface of the intermediate transfer belt 30.

Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. After that, the surface of each photoconductor 5 is discharged by the discharging device, and the surface potential is initialized.

At the lower part of the printer body, the paper feed roller 11 starts to rotate 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 timing 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.

Then, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 travels around, the transfer electric field formed at the secondary transfer nip causes the intermediate transfer belt 30 to move. Toner images are collectively transferred onto the paper P. Further, at this time, the residual toner on the intermediate transfer belt 30 that could not be completely transferred to the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to and collected in the waste toner container.

After that, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed on the paper P by the fixing device 20. Then, the paper P is discharged to the outside of the apparatus by the paper discharge roller 13 and is stocked on the paper discharge tray 14.

The above description is for the image forming operation when forming a full-color image on a sheet, but a single-color image is formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. It is also possible to form a two-color or three-color image by using two or three image forming units.

(Fixing device)
Next, the configuration of the fixing device 20 used in the printer will be described with reference to FIG. As shown in FIG. 2, the fixing device 20 has a fixing belt 21 as a rotatable fixing rotating body, and a pressure roller 22 as a facing member rotatably provided facing the fixing belt 21.

Further, the fixing device 20 includes a halogen heater 23 (a central heater 23a as a first heating member and an end heater 23b as a second heating member) as a heating member for heating the fixing belt 21 and an inside of the fixing belt 21. The nip forming member 24 is provided, and the stay 25 as a supporting member that supports the nip forming member 24 is provided. Further, the fixing device 20 includes a reflecting member 26 that reflects the light emitted from the halogen heater 23 to the fixing belt 21, a temperature sensor 27 that detects the temperature of the fixing belt 21, and a sheet from the fixing belt 21. It includes a separating member 28 for separating, a pressing member for pressing the pressing roller 22 against the fixing belt 21, and the like.

The fixing belt 21 is composed of an endless belt member (including a film) which is thin and has a low heat capacity and flexibility. Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Alternatively, it is composed of a release layer on the outer peripheral side formed of polytetrafluoroethylene (PTFE) or the like. In addition, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the base material and the release layer.

The pressure roller 22 includes a cored bar 22a, an elastic layer 22b provided on the surface of the cored bar 22a and made of foaming silicone rubber, silicone rubber, fluororubber, or the like, and a PFA provided on the surface of the elastic layer 22b. Alternatively, the release layer 22c is made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by the pressing member and is in contact with the nip forming member 24 via the fixing belt 21.

At a position where the pressure roller 22 and the fixing belt 21 are in pressure contact with each other, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. Further, the pressure roller 22 is configured to be rotationally driven by a drive source such as a motor provided in the printer body.

When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate. When the paper P on which the toner image T is transferred is conveyed from the A1 direction to the nip portion N, the toner image T is fixed on the paper P at the nip portion N, and then the paper P is moved from the nip portion N in the A2 direction. It is supposed to be discharged.

In the present embodiment, the pressure roller 22 is a solid roller, but it may be a hollow roller. In that case, a heating member such as a halogen heater may be provided inside the pressure roller 22. Further, when there is no elastic layer, the heat capacity is reduced and the fixing property is improved, but when the unfixed toner is squeezed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven gloss is present in the solid portion of the image. It can happen.

To prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing the elastic layer having a thickness of 100 μm or more, minute irregularities can be absorbed by elastic deformation of the elastic layer, so that it becomes possible to avoid the occurrence of uneven gloss. Although the elastic layer 22b may be solid rubber, sponge rubber may be used when there is no heating member inside the pressure roller 22.

Sponge rubber is more preferable because the heat insulating property is improved and the heat of the fixing belt 21 is less likely to be taken away to save energy. Further, the fixing rotator and the counter rotator are not limited to being in pressure contact with each other, but may be configured to simply contact with each other without applying pressure.

Both ends of each halogen heater 23 are fixed to the side plates of the fixing device 20. Each halogen heater 23 is configured to generate heat by being output-controlled by a power supply unit provided in the printer main body, and the output control is based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. Done.

By controlling the output of the halogen heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater, or the like may be used as the heating member that heats the fixing belt 21.

The nip forming member 24 is arranged in a longitudinal shape across the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and is fixedly supported by the stay 25. As a result, it is possible to prevent the nip forming member 24 from being bent by the pressure of the pressure roller 22, and to obtain a uniform nip width in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending, but the stay 25 may be made of resin. Is.

Further, the nip forming member 24 is composed of a heat resistant member having a heat resistant temperature of 200° C. or higher. This prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature range, ensures a stable state of the nip portion N, and stabilizes the output image quality. As the base material of the nip forming member 24, a general heat resistant resin can be used as described later with reference to FIGS. 5A and 5B. In this embodiment, as will be described later, LCP having excellent heat resistance and moldability is used as the base material 24a of the nip forming member 24.

The nip forming member 24 has a low friction sheet on its surface. When the fixing belt 21 rotates, the fixing belt 21 slides on the low-friction sheet, whereby the driving torque generated in the fixing belt 21 is reduced, and the load due to the frictional force on the fixing belt 21 is reduced. As a material for the low-friction sheet, for example, Toyoflon (registered trademark) 401 manufactured by Toray Industries, Inc. is preferable.

The reflection member 26 is arranged between the stay 25 and the halogen heater 23. In this embodiment, the reflecting member 26 is fixed to the stay 25. Further, since the reflecting member 26 is directly heated by the halogen heater 23, it is desirable that the reflecting member 26 be formed of a metal material having a high melting point.

By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 to the stay 25 side is reflected to the fixing belt 21. Thereby, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, it is possible to save energy.

Further, without providing the reflecting member 26 as in the present embodiment, the surface of the stay 25 on the side of the halogen heater 23 may be mirror-finished by polishing or painting to form the reflecting surface. Further, the reflectance of the reflecting surface of the reflecting member 26 or the stay 25 is preferably 90% or more.

Since the shape and material of the stay 25 cannot be freely selected in order to secure its strength, it is better to separately provide the reflecting member 26 as in the present embodiment because the self-weight of selecting the shape and material is widened, and the reflecting member 26 is provided. The stay 25 and the stay 25 can be specialized in their respective functions. Further, by providing the reflection member 26 between the halogen heater 23 and the stay 25, the position of the reflection member 26 with respect to the halogen heater 23 becomes closer, so that the fixing belt 21 can be efficiently heated.

Further, in order to further improve the heating efficiency of the fixing belt 21 due to the reflection of light, it is necessary to examine the direction of the reflecting surface of the reflecting member 26 or the stay 25. For example, when the reflecting surface is arranged concentrically around the halogen heater 23, the light is reflected toward the halogen heater 23, and the heating efficiency is reduced accordingly. On the other hand, when a part or all of the reflecting surface is arranged so as to reflect light toward the fixing belt in a direction other than the halogen heater 23, the amount of light reflected in the direction of the halogen heater 23 decreases. The heating efficiency by reflected light can be improved.

Further, the fixing device 20 according to the present embodiment has various structural measures for improving the energy saving property and the first print time. Specifically, the halogen heater 23 can directly heat the fixing belt 21 at a position other than the nip portion N (direct heating method). In the present embodiment, nothing is interposed between the halogen heater 23 and the left side portion of the fixing belt 21 in FIG. 2, and the radiant heat from the halogen heater 23 is directly applied to the fixing belt 21 in that portion.

Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is thin and has a small diameter. Specifically, the thickness of each of the base material, the elastic layer, and the release layer constituting the fixing belt 21 is set in the range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the total thickness is set. It is set to 1 mm or less.

The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, and more preferably 0.16 mm or less. The diameter of the fixing belt 21 is preferably 30 mm or less.

In this embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are equal to each other. However, the configuration is not limited to this. For example, the diameter of the fixing belt 21 may be smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 in the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

(High thermal conductivity member)
In the present embodiment, a high thermal conductive member 24b is attached to the nip portion side of the nip forming member 24 in parallel with the halogen heater 23 (center heater 23a and end heater 23b) as shown in FIG. The emission length of the central heater 23a is set to 217 mm corresponding to the width of the A4 size paper (210 mm).

Further, the light emission length of the end heater 23b is set to 56.5 mm so that the light emission length of the central heater 23a+(2x light emission length of the end heater 23b) corresponds to the paper width (320 mm) of A3 vertical nobi size. It is set (217 mm + 2 x 56.5 mm = 330 mm). The central heater 23a is turned on to correspond to the width of the A4 vertical paper or less, and the central heater 23a and the end heater 23b are turned on to correspond to the A3 vertical and A3 vertical non-wide paper width. There is no standard for "Novi size", and a size that is slightly larger than the standard size of A3 or A4 is generally called "Novi".

The light emission length (217 mm) of the central heater 23a is larger than the width of the A6-size paper (105 mm). Therefore, even if the end heater 23b is turned off and only the central heater 23a is turned on, when the A6 vertical size sheet is continuously fed, the hatched portion 24b1 of the high thermal conductive member 24b in FIG. Is more likely to occur.

This is because the heat of the hatching portion 24b1 moves both inward and outward in the paper width direction, but the amount of heat flowing outward is greater due to the temperature difference between the inside and outside. On the other hand, since the high thermal conductive member 24b is continuous in the longitudinal direction in correspondence with the entire width, if only the central heater 23a is turned on and an A4 vertical size sheet is to be passed, the edge temperature is likely to decrease in the sheet passing area.

There is a trade-off relationship between the "end temperature decrease" and the "end temperature increase". When the thermal conductivity of the high thermal conductive member 24b is increased or the amount of heat transfer is increased, the high thermal conductivity member 24b acts to suppress the end temperature rise, but the end temperature drop is likely to occur conversely. Further, if the thermal conductivity of the high thermal conductive member 24b is lowered or the amount of heat transfer is limited, it is difficult for the end temperature to drop, but the end temperature rise is likely to occur.

In the embodiment of the present invention, when the length of the high thermal conductive member 24b is designed, the fixing start-up operation using only the central heater 23a does not cause the temperature drop at the end portion of the paper passing area and the non-paper passing area. Is designed to have a length that does not cause an edge temperature rise (excessive temperature rise of the fixing belt 21). Specifically, the ratio of L1 and L2 shown in FIG. 4 described later is designed to be L2/L1=0.88 to 0.96.

FIG. 4 shows a comparison between the light emission length of the paper, the halogen heater 23 (the central heater 23a and the end heater 23b), and the length (width) of the high thermal conductive member in the present embodiment and the related art. The high thermal conductive member 24b of the present embodiment is shown on the upper side of FIG. What is shown on the lower side is a conventional high thermal conductive member 24b' for comparison. A heat insulating base material 24a, which will be described later, is disposed on the back side of the high heat conductive member 24b, and the base material 24a and the high heat conductive member 24b constitute a nip forming member 24.

FIG. 4 is a diagram in which the first heating member, the second heating member, the high thermal conductive member, and the central portion of the sheet corresponding to the maximum sheet passing width are aligned. L1 is an outer end in the longitudinal direction of the heat generating portion 23b1 of the end heater 23b, which is located outside the one end in the longitudinal direction of the heat generating portion 23a1 of the central heater 23a serving as the first heating member. Up to. In this embodiment, L1=56.5 mm. L2 is the length from one end in the longitudinal direction of the heat generating portion 23a1 of the central heater 23a to the one end in the longitudinal direction (inside the hole 51) of the heat generating portion 23b1 of the high thermal conductivity member 24b. An effective soaking action cannot be obtained from the hole 51 including the hole 51 to the end portion in the longitudinal direction. In this embodiment, L2=52.0 mm and L2/L1=0.92.

By designing the length of the high thermal conductive member 24b within the range of the ratio (L2/L1=0.88 to 0.96), the edge temperature rise and the edge temperature decrease with respect to an arbitrary amount of paper clearance. Can be suppressed. For example, when the A3 vertical length is 320 mm or when the A3 vertical length is 329 mm, it is possible to suppress the end temperature increase and the end temperature decrease.

The effect of the ratio can be described as follows with reference to FIG. That is, by extending the outer end portion of the high thermal conductive member 24b according to the ratio (L2/L1=0.88 to 0.96), the paper width increase amount of A3→A3 (NOBI: 11.5 mm). 2), the amount of warp (5 mm) of the end heater 23b can be suppressed to be relatively short. As a result, the fixing device 20 can be downsized, and the energy saving can be improved by the end heater 23b which suppresses the amount of warp.

Further, according to the present invention, when the outer end portion of the high thermal conductive member 24b is extended in accordance with the ratio (L2/L1=0.88 to 0.96), the length (width in the sheet passing direction or nip width) and width (the width in the sheet passing direction) and the lateral ( The ratio of the length in the longitudinal direction or the length in the nip axis direction) can be set to be 1:18.8 or more and 1:19.7 or less. Here, the horizontal length of the aspect ratio is the length up to the inside of the hole 51 in FIG.

In order to make the fixing device 20 of the image forming apparatus compatible with A3 standard, it is necessary to lengthen the length of the high thermal conductive member 24b in the axial direction as compared with the conventional device. In this case, the width of the high heat conductive member 24b (width in the sheet passing direction) is usually the same as that of the conventional machine and is not changed in order to reduce the diameter of the fixing belt 21 and save energy.

The aspect ratio (horizontal/vertical) of the high thermal conductive member of the conventional A3 compatible machine was 18.1, but in the present embodiment, the above ratio (L2/L1=0.88 to 0.96) for A3 novi compatibility. However, the aspect ratio can be suppressed to 18.8 or less. Thus, by extending the high thermal conductive member 24b in the nip axis direction with respect to the conventional fixing device, the effect of suppressing the rise in the end temperature of the high thermal conductive member 24b is enhanced with respect to the paper size in which only the central heater 23a is turned on.

Further, in the conventional A3 compatible machine, the length of the high thermal conductive member 24b (the length in the longitudinal direction or the length in the nip axis direction) was 313 mm or more. On the other hand, the present invention extends the lateral length of the high thermal conductive member 24b according to the ratio (L2/L1=0.88 to 0.96), so that the end temperature drop does not occur even though it is an A3 Novi compatible machine. The horizontal length, which is the upper limit, can be set to 325 mm or less.

Outside the range of the ratio (L2/L1=0.88 to 0.96), it becomes difficult to suppress the end temperature increase and the end temperature decrease. That is, when L2/L1<0.88, the length of the high thermal conductive member 24b is insufficient, and the edge temperature rise easily occurs in the non-sheet passing area. Further, when L2/L1>0.96, the length of the high thermal conductive member 24b is too long, and the edge temperature lowers easily in the sheet passing area. Here, since the optimum fixing temperature is generally set to 160 to 180° C., the edge temperature decrease is, for example, less than 160° C., and the edge temperature increase is, for example, 250° C. or more.

In the fixing device 20 of this embodiment, the nip forming member 24 of FIGS. 5A and 5B is configured using the high thermal conductive member 24b designed as described above. In this example, a copper plate having a high thermal conductivity is used for the high thermal conductive member 24b. The high thermal conductive member 24b is formed by bending a copper plate so that the horizontal cross section has a concave cross section.

The formation of the copper plate is not limited to bending and may be welding or the like. Rectangular holes 51 are formed at positions near both ends of the high thermal conductive member 24b. The hole 51 is for positioning and fixing the high thermal conductive member 24b to the base material 24a.

The high thermal conductive member 24b may be a metal thin plate member, or may be a metallic film (uniform temperature layer) coated on the base material 24a of the nip forming member 24. The thickness of the high thermal conductive member 24b is 1 mm or less, preferably 0.4 mm or less. In this way, the high thermal conductive member 24b is made thin to minimize its heat capacity, and the fixing failure due to the temperature drop at the end portion at the time of starting the fixing is suppressed.

When the base material of the fixing belt 21 is a metal such as nickel or SUS, the high thermal conductive member 24b has a copper-based material (for example, thermal conductivity 381 W/m·K) or an aluminum-based material (for example, thermal conductivity 236 W/m). -It is preferable to use a material having a high thermal conductivity such as K). When a resin material such as polyimide (heat conductivity 0.29 W/mK) is used for the fixing belt base material, an iron-based SUS material (for example, heat conductivity 19 W/mK) or the like is used as the high heat conductive member 24b. Metallic materials can also be used. In this embodiment, the high thermal conductive member 24b is made of a copper-based material, and more specifically, the high thermal conductive member 24b is made of a copper-based material having a thermal conductivity of 236 w/(m·k) or more.

The high thermal conductive member 24b is continuous in the longitudinal direction corresponding to the entire width of the fixing belt 21. Here, the length Ls of the high thermal conductive member 24b is not the entire length of the high thermal conductive member 24b but the length inside the hole 51 in the longitudinal direction. Since the effective endothermic effect cannot be obtained from the hole 51 including the hole 51 in the longitudinal direction, it is not included in the length corresponding to the light emission length of the heaters 23a and 23b.

(Nip forming member)
Next, the nip forming member 24 to which the above-described high thermal conductive member 24b is attached will be described with reference to FIGS. 5A and 5B. As shown in FIGS. 5A(a) and 5A(b), the high thermal conductive member 24b is arranged on the lower surface (opposite surface of the nip portion) of the base material 24a of the nip forming member 24.

As can be seen from FIG. 5A, the high thermal conductive member 24b is arranged in non-contact with the stay 25 and the reflecting member 26 (see FIG. 2) arranged inside (upper) the stay 25. Therefore, heat transfer from the high thermal conductivity member 24b to the stay 25 is prevented, and energy saving is not impaired. Similarly, heat transfer from the high thermal conductivity member 24b to the reflecting member 26 can be prevented, and energy saving can be maintained.

The high thermal conductive member 24b is held by a base material 24a made of heat resistant resin. In this embodiment, LCP having excellent heat resistance and moldability is used for the base material 24a. The heat resistant temperature of the LCP is preferably 350° C. or higher in order to withstand the rise in the end temperature when continuously passing a sheet of A6 length. Many of the conventional base materials 24a have a heat resistance of about 250° C., and it is necessary to improve the heat resistance against the rise in the end temperature.

The thermal conductivity of the base material 24a is, for example, 0.54 W/m·K, and this value is extremely smaller than the values of the high thermal conductivity member 24b, the stay 25, and the reflecting member 26. Therefore, a high heat insulating effect is obtained by the base material 24a, and heat transfer from the high thermal conductive member 24b to the base material 24a and the stay 25 is suppressed.

The high thermal conductive member 24b can be made of, for example, copper or aluminum having a high thermal conductivity, and in the illustrated example, it is formed so as to have a concave cross section perpendicular to the longitudinal direction of the high thermal conductive member 24b. The high thermal conductive member 24b suppresses the temperature decrease at the edge of the sheet passing area at the time of fixing start-up, and suppresses the temperature increase at the edge of the non-sheet passing area of the fixing belt 21 that occurs when the small size sheet is passed. it can.

However, if the heat capacity of the high thermal conductive member 24b is too large, the transfer of heat from the fixing belt 21 is increased to prevent the temperature of the fixing belt 21 from rising, resulting in a delay in the start-up time and a delay in the first print time. The lighting rate is increased, and the energy saving is impaired. Therefore, energy saving can be ensured by forming the high heat conductive member 24b as a thin layer member having a low heat capacity.

The bottom wall portion of the concave cross section of the high thermal conductive member 24b serves as a surface facing the nip portion, and the left and right side wall portions 24b2 and 24b3 of the high thermal conductive member 24b sandwich the base material 24a in the sheet feeding direction and have a predetermined height toward the stay 25 side. Standing up. By adjusting the rising height, it is possible to adjust the amount of heat that escapes even in the thickness direction of the high thermal conductive member 24b, and it is possible to further suppress the end temperature rise.

For example, the amount of heat released in the thickness direction of the high thermal conductive member 24b may be partially changed in the longitudinal direction of the high thermal conductive member 24b by partially changing the rising height depending on the position of the high thermal conductive member 24b in the longitudinal direction. It is possible. Therefore, in the longitudinal direction of the nip portion N, it is possible to further finely adjust the suppressing function for increasing the end temperature and the suppressing function for decreasing the end temperature.

In this embodiment, in the case of the “A3 compatible fixing device”, the height Hs of the side wall portions 24b2 and 24b3 of the high thermal conductive member 24b is 1.0 mm to 1 over the entire length in the longitudinal direction of the high thermal conductive member 24b. It is set to 9 mm. Here, the height Hs is the height from the inner surface of the bottom wall of the high thermal conductive member 24b to the upper ends of the side wall portions 24b2, 24b3.

Further, on the inlet side of the nip portion, a plurality of claw portions 24b4 in which the upper end of the side wall portion 24b2 is bent in an L shape are formed at predetermined intervals in the longitudinal direction of the high thermal conductive member 24b. By engaging the claw portion 24b4 with the step portion 24a1 formed on the upper surface of the base material 24a, it is possible to prevent the parts from varying during the assembly of the nip forming member 24 and improve the work efficiency. Further, since the claw portion 24b4 increases the amount of heat released in the thickness direction of the high thermal conductive member 24b together with the side wall portions 24b2 and 24b3, it also has a function of suppressing an end temperature rise.

The cross-sectional shape of the high thermal conductive member 24b does not necessarily have to be concave as described above. As shown in FIG. 5A(c), a flat plate-shaped high thermal conductive member 24b' may be attached to the lower surface of the base material 24a. In this case, since there is no rising portion, it is possible to suppress the amount of heat that escapes in the thickness direction of the high thermal conductive member 24b and suppress the temperature decrease at the end portion.

The base material 24a of the nip forming member 24 may be an inorganic material or an organic material that has a lower thermal conductivity than the high thermal conductivity member 24b, has heat resistance with respect to the operating temperature, and can transmit pressure. Examples of such a material include inorganic materials such as ceramics, glass, and aluminum, rubbers such as silicone rubber and fluororubber, PTFE (tetrafluoroethylene), PFA (tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer), ETFE (ethylene/tetrafluoroethylene copolymer), FEP (tetrafluoroethylene/hexafluoropropylene copolymer) and other fluororesins, PI (polyimide), PAI (polyamide imide), PPS (polyphenylene sulfide), Resins such as PEEK (polyetheretherketone), LCP (liquid crystal plastic, liquid crystal polymer), phenol resin, nylon, aramid, or a combination thereof can be used. In this embodiment, the base material of the nip forming member 24 is formed of liquid crystal polymer (LCP).

The shape of the upper surface (opposite surface of the stay) of the base material 24a made of liquid crystal polymer is formed such that the uneven shape 24a2 is continuous in the longitudinal direction. With such an uneven shape, it is possible to suppress the heat flow to the stay 25 side while enabling the pressure transmission from the stay 25 side to the nip portion. Therefore, the lighting rate of the halogen heater 23 can be reduced, and the thermal efficiency and energy saving can be improved.

(Suppressed state of edge temperature rise and edge temperature decrease)
Next, with reference to FIG. 6A, the suppression state of the end temperature increase and the end temperature decrease according to the embodiment of the present invention will be described. Further, in order to compare the suppression state with a conventional fixing device, FIGS. 6B and 6C show views similar to FIG. 6A for the conventional fixing device. FIG. 6B shows the suppression state of the fixing device using the nip forming member 24 having the three-layer structure disclosed in Patent Document 1 (JP-A-2005-194661, FIG. 6), and FIG. 6C shows the high thermal conductive member. FIG. 7 shows the above-described suppressed state of the fixing device that does not use 24b.

FIG. 6A(b) is a schematic sectional view of the fixing device according to the embodiment of the present invention. A sectional view taken along line AA of FIG. 6B is shown on the upper side of FIG. 6A. The cross section of the figure (a) is a cross section of only one side from the center to the end in the longitudinal direction, and the left end of the figure is the center and the right end is the right end.

The halogen heater 23 is composed of two heaters, a central heater 23a as a first heating member and an end heater 23b as a second heating member. The respective heaters 23a and 23b have different axial positions, and the size of the paper to be passed. The central heater 23a is lit independently, or the central heater 23a and the end heater 23b are lit simultaneously. The above is the same in FIGS. 6B and 6C.

The central heater 23a corresponds to the A4 vertical sheet passing width (210 mm). By turning on the central heater 23a and the end heater 23b, the heat distribution of the entire heater corresponds to the sheet passing width (297 mm and 320 mm) of a large size (A3 length and A3 length nobi).

A central heater 23a, an end heater 23b, and a sheet having a sheet passing width P=A to D are shown on the lower side of FIG. 6A(a). FIG. 6A(c) shows the state where the end temperature rises and the end temperature falls when these sheets are passed. Here, the sheet width is A6 vertical, B is A4 vertical, C is B4 vertical, and D is A3 vertical.

In this embodiment, the nip forming member 24 of FIG. 6A is adopted instead of the three-layer structure nip forming member 24 of FIG. 6B disclosed in Patent Document 1 (JP-A-2005-194661). The nip forming member 24 has a simple structure in which a high thermal conductive member 24b having a length according to the above-described ratio L2/L1 (=0.88 to 0.96) is attached to the lower surface of the base material 24a.

This makes it possible to obtain an edge temperature rise suppression effect equivalent to or higher than that of the three-layer structure with a sheet size of the sheet passing width P=A (A6 length) (δ _A >δ _B ). In addition, since the endothermic masses B and C are not provided in this embodiment, the end temperature drop T _B in FIG. 6B(c) is resolved as shown in FIG. 6A(c).

Further, by eliminating the three-layer structure, the amount of heat absorbed by the high thermal conductive member 24b in the paper passing region is stabilized in the axial direction. As a result, the risk of cold offset due to a local temperature drop is reduced, so that there is a margin in the set temperature, and as a result energy saving and shortening of the warm-up time are achieved.

On the other hand, in the conventional fixing device 20 shown in FIG. 6C that does not have a high thermal conductive member, the edge temperature rises T _A and T _B occur at the sheet passing widths A (A6 length) and B (A4 length). In the fixing device of FIG. 6C, as shown in FIG. 6B, since the nip forming member 24 is composed only of the base material 24a having low heat conductivity, heat is accumulated on the fixing belt 21 in the non-paper passing area during continuous paper passing. This is because.

(Fixing belt temperature distribution)
Finally, it will be described with reference to FIG. 7 how the temperature distribution of the fixing belt 21 changes depending on the presence or absence of the high thermal conductive member 24b and the sheet passing size. As shown in FIG. 7A, when there is no high thermal conductive member 24b, when passing a size smaller than the heat distribution of the heater, for example, at the time of B4 passing in which the central heater 23a and the end heater 23b are simultaneously turned on, The temperature rise in the non-sheet passing area of the fixing belt 21 (the temperature rise at the end portion) becomes large. When the high thermal conductive member 24b is not provided as shown in FIG. 7B, the end temperature rises similarly when, for example, the A6 paper is passed or the postcard is passed while only the central heater 23a is turned on.

However, when the high thermal conductive member 24b that comes into contact with the fixing belt 21 is provided as shown in FIGS. 7C and 7D, the temperature unevenness in the longitudinal direction of the fixing belt 21 is improved by the soaking action of the high thermal conductive member 24b. .. Therefore, as compared with the case of FIGS. 7A and 7B, the edge temperature rise is suppressed during B4 sheet passing and A6 (or postcard) sheet passing.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the above embodiments and various modifications can be made within the scope of the technical idea described in the claims.

1: Image forming device 2: Bottle storage unit 2Y, 2M, 2C, 2K: Toner bottle 3: Transfer device 4Y, 4M, 4C, 4K: Image forming unit 5: Photoconductor 6: Charging device 7: Developing device 8: Cleaning Device 9: Exposure device 10: Paper feed tray 11: Paper feed roller 12: Timing roller 13: Paper discharge roller 14: Paper discharge tray 20: Fixing device 21: Fixing belt 22: Pressure roller 22a: Core bar 22b: Elastic layer 22c: Release layer 23: Halogen heater 23a: Central heater 23b: End heater 24: Nip forming member 24a: Base material 24a1: Step portion 24a2: Concavo-convex shape 24b: High heat conductive member 24b1: Hatch portion 24b2, 24b3: Side wall 24b4 : Claw part 25: Stay 26: Reflecting member 27: Temperature sensor 28: Separation member 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 51: Hole

JP, 2005-194661, A (Drawing 6)

Claims (8)

A rotatable endless fixing belt,
A first heating member having a first heat generating portion on the center side in the width direction of the fixing belt;
A second heating member having a second heat generating portion on the widthwise end side of the fixing belt;
A facing member facing the outer peripheral side of the fixing belt,
A nip forming member that is provided on the inner peripheral side of the fixing belt and that forms a nip facing the facing member;
A high thermal conductive member having a higher thermal conductivity than the nip forming member, which is disposed on the fixing belt side of the nip forming member,
The high thermal conductive member has a bottom wall portion facing the nip, and a concave cross section composed of a side wall portion extending from the bottom wall portion in the thickness direction of the nip forming member, and the side wall portion has a concave cross section. A height of 1.0 mm to 1.9 mm from the inner surface of the bottom wall portion, and an L-shaped claw portion is provided in the longitudinal direction of the high thermal conductive member at the upper end of the side wall portion located on the upstream side in the sheet feeding direction. While forming a plurality at a predetermined interval, the claw portion is engaged with a step portion formed on the upper surface of the nip forming member,
A length from the one end in the longitudinal direction of the first heat generating portion to the outer end in the longitudinal direction of the second heat generating portion, which is located outside the one end in the longitudinal direction, is defined as L1, and A fixing device, wherein a ratio of L1 and L2 is L2/L1=0.88 to 0.96, where L2 is a length to one end in the longitudinal direction. In the fixing device in which the first heating member is lit to correspond to the A4 sheet width and the first heating member and the second heating member are lit to correspond to the A3 non-paper sheet width of 320 mm, the L1=56.5. 2. The fixing device according to claim 1 , wherein the fixing device has a length of L2=52.0 mm. The fixing device according to claim 1 or 2, characterized in that the thermal conductivity of the high thermal conductivity member is 3.81~15.95 (J / K). The stay for fixing said nip forming member on the inside of the fixing belt is disposed, any of claims 1 to 3, characterized in that the upper surface of the stay and the nip forming member abuts on irregularities The fixing device according to item 1. Any one of the fixing device 4 a substrate of the nip forming member from claim 1, characterized in that it has a liquid crystal polymer. Image forming apparatus characterized by mounting the fixing device of any one of claims 1 to 5. A rotatable endless fixing belt,
A first heating member having a first heat generating portion on the center side in the width direction of the fixing belt;
A second heating member having a second heat generating portion on the widthwise end side of the fixing belt;
A facing member facing the outer peripheral side of the fixing belt,
A nip forming member that is provided on the inner peripheral side of the fixing belt and that forms a nip facing the facing member;
A method of designing a fixing device, comprising: a high thermal conductive member having a higher thermal conductivity than the nip forming member, the high thermal conductive member being disposed on the nip side of the nip forming member,
The high thermal conductive member has a bottom wall portion facing the nip, and a concave cross section composed of a side wall portion extending from the bottom wall portion in the thickness direction of the nip forming member, and the side wall portion has a concave cross section. A height of 1.0 mm to 1.9 mm from the inner surface of the bottom wall portion, and an L-shaped claw portion is provided in the longitudinal direction of the high thermal conductive member at the upper end of the side wall portion located on the upstream side in the sheet feeding direction. While forming a plurality at a predetermined interval, the claw portion is engaged with a step portion formed on the upper surface of the nip forming member,
A length from the one end in the longitudinal direction of the first heat generating portion to the outer end in the longitudinal direction of the second heat generating portion, which is located outside the one end in the longitudinal direction, is defined as L1, and A method of designing a fixing device, wherein a ratio of L1 and L2 is L2/L1=0.88 to 0.96, where L2 is a length to one end in the longitudinal direction. In the designing method of the fixing device, the lighting of the first heating member corresponds to the width of A4 paper, and the lighting of the first heating member and the second heating member corresponds to the width of 320 mm of the A3 paper. 8. The fixing device designing method according to claim 7 , wherein the setting is 56.5 mm and the L2 is 52.0 mm.

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