JP2017173359A - Fixation device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain reduction in cost with a nip formation member simply structured, suppress end temperature from rising upon feeding paper with only a center heat source turned ON and suppress the end temperature from falling upon starting up fixation.SOLUTION: In a fixation device, which includes: a fixation belt 21; a central heater 23a that serves as a first heating member; an end part heater 23b that serves as a second heating member; a nip formation part 24; a pressurizing roller 22 that serves as an opposing member; and a high heat conduction member 24b, with a longer direction one end of a heating part (a first heating part 23a1) of the central heater 23a as an origin, when L1 is defined as a length to a longer direction outer side end part, located on an outer side further than the longer direction one end part, of a heating part (a second heating part) 23b1 of the end part heater 23b, and L2 as a length to a longer direction one end part of the heat conduction member 24b, a ratio between L1 and L2 is configured to fall within the range of L2/L1=0.88 to 0.96.SELECTED DRAWING: Figure 4

Description

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

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

In this direct heating type, it is ideal to heat the fixing belt with a heating width that corresponds to the paper width size on a one-to-one basis. However, when a general halogen heater is used as the heating member, the paper width size is related to cost and other factors. Actually, a smaller number of heaters (for example, a central heater and an end heater) can be used.

In the case where a small number of heaters are used in this way, the frequency of fixing is increased in a state where the fixing belt heating width is larger than the sheet width. On the other hand, since the heat capacity and thinning of the fixing belt have been further advanced in recent years, 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 (overheating) becomes intense.

Therefore, conventionally, a movable shielding member that shields the radiant heat from the heater is driven to rotate according to the paper size, or a high heat conduction member is attached to the nip forming member to suppress the end temperature rise. Yes.

Providing the movable shielding member increases the size of the apparatus and increases the cost. On the other hand, the high thermal conductive member can suppress the rise in the end temperature at a relatively low cost. However, when continuously passing a paper (for example, A6) smaller in size than the fixing belt heating width (central heater light emission length), Even the high thermal conductive member corresponding to the full width cannot effectively suppress the temperature rise at the end. Of course, it is conceivable to suppress an increase in the end temperature by increasing the heat capacity or heat dissipation of the high heat conducting member. However, if this is done, a fixing failure will occur due to a decrease in the end temperature of the paper passing area at the start of fixing. This fixing failure is, for example, “cold offset” in which a paper image adheres to the surface of a fixing roller or a fixing belt and peels off from the paper.

In order to solve such problems, conventionally, a fixing device in which a nip forming member has a three-layer structure of 1) a nip side high thermal conductive layer, 2) a base material layer, and 3) a stay side high thermal conductive layer has been proposed. (Patent Document 1: Japanese Patent Laid-Open No. 2015-194661, FIG. 6). In this fixing device, even if the temperature rises in the non-sheet passing area when small size paper is continuously passed, the heat is moved and diffused in the longitudinal direction by the high heat conductive layer, so that the edge temperature rise is effective. Is suppressed. On the other hand, since the low heat conduction part by the base material layer is formed in the vicinity of the end part of the sheet passing area, the heat escape to the end part is restricted, and the end part temperature drop at the start of fixing is suppressed.

However, since the nip forming member has a three-layer structure in the apparatus of Patent Document 1, the number of parts and the number of assembling steps increase, resulting in an increase in cost. Further, variation in assembly accuracy among components may cause variation in heat conduction and associated fixing failure (cold offset).

Accordingly, an object of the present invention is to reduce the cost by simplifying the structure of the nip forming member, to suppress the rise in the edge temperature in the non-sheet passing region during the sheet passing when only the first heating member is lit, The object is to suppress a decrease in end temperature in the sheet passing area when the sheet is raised.

In order to solve the above-described problems, the present invention provides 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, and an end portion in the width direction of the fixing belt. A second heating member having a second heat generating part on the 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 And a high heat conductive member having a higher thermal conductivity than that of the nip forming member, which is disposed on the fixing belt side of the nip forming member, and starts from one longitudinal end portion of the first heat generating portion. When the length to the outer end in the longitudinal direction of the second heat generating part located outside the one end in the longitudinal direction is L1, and the length to the one end in the longitudinal direction of the high heat conductive member is L2. , The ratio of L1 and L2 is L2 / L1 = A fixing device which is characterized in that the .88～0.96.

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 the one end in the longitudinal direction of the high heat conducting member is L2 / L1 = 0.88-0.96. By setting this range, it is possible to suppress the end temperature rise and the end temperature drop, so that the cost of the fixing device can be reduced. In addition, since the heat can be released without excess or deficiency with the high heat conduction member when the sheet passing through only the first heating member is turned on, an increase in the end temperature can be suppressed, and a decrease in the end temperature at the start of fixing can be suppressed. .

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic diagram illustrating an example of a fixing device used in an image forming apparatus. It is a perspective view which shows the positional relationship of the halogen heater, the high heat conductive member, and the paper width direction. It is the schematic which shows the light emission length of a paper, a halogen heater, and the length (width | variety) of a highly heat-conductive member as compared with the past. (A) is a cross-sectional view of the stay and the nip forming member as viewed from the paper direction, (b) is a cross-sectional view of the stay and the nip forming member as viewed from the longitudinal direction, and (c) is a modification of the high heat conductive member ( It is sectional drawing similar to b). It is an expanded sectional view of a nip forming member. FIG. 10 is a diagram illustrating a state of an end temperature increase and an end temperature decrease for each sheet passing width in a fixing operation using the nip forming member according to the embodiment of the present invention. It is a figure which shows the state of the edge part temperature rise and edge part temperature fall according to the sheet passing width in the fixing operation using the conventional nip forming member which made the high heat conductive member 3 layer structure. It is a figure which shows the state of the edge part temperature rise and edge part temperature fall according to sheet passing width in the fixing operation using the conventional nip forming member without a high heat conductive member. (A)-(d) is a figure which shows the difference in the temperature distribution of the fixing belt by the presence or absence of a high heat conductive member, and the kind of paper width size.

(Image forming device)
A printer as an image forming apparatus according to an embodiment of the present disclosure and a fixing device used in the printer will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a color laser printer as an image forming apparatus. In the center of the image forming apparatus 1, four image forming units 4Y, 4M, 4C, and 4K are provided. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. It is the same structure except having.

Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photosensitive member 5 as a latent image carrier, a charging device 6 that charges the surface of the photosensitive member 5, and a toner on the surface of the photosensitive member 5. And a developing device 7 for cleaning the surface of the photosensitive member 5. 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 4 </ b> K are denoted by reference numerals, and the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C are omitted. To do.

Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. 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. The exposure apparatus 9 can also be configured as an LED exposure apparatus.

A 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 member, four primary transfer rollers 31 as primary transfer members, 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 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 travels (rotates) in the direction indicated by the arrow in the figure.

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

The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed 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 entrance of the waste toner container.

A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K containing replenishing toner are detachably attached to 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 developing device 7 is connected to each of the toner bottles 2Y, 2M, 2C, 2K via the replenishment path. The toner is replenished.

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

In the printer main body, a transport path R is provided for discharging 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 transport members for transporting 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 onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

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

The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run 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 in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated 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. Thereafter, the surface of each photoconductor 5 is neutralized by the static eliminator, and the surface potential is initialized.

In the lower part of the printer main 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 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 charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the transfer electric field formed in the secondary transfer nip causes a transfer on the intermediate transfer belt 30. The toner images are transferred onto the paper P all at once. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container and collected.

Thereafter, 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 out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

(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 includes a fixing belt 21 as a rotatable fixing rotator, and a pressure roller 22 as an opposing member that is rotatably provided to face the fixing belt 21.

Further, the fixing device 20 is arranged inside the fixing belt 21 with a halogen heater 23 (a central heater 23 a as a first heating member and an end heater 23 b as a second heating member) as a heating member for heating the fixing belt 21. A nip forming member 24 provided and a stay 25 as a supporting member for supporting the nip forming member 24 are provided. The fixing device 20 also includes a reflection member 26 that reflects the light emitted from the halogen heater 23 to the fixing belt 21, a temperature sensor 27 as a temperature detection member that detects the temperature of the fixing belt 21, and a sheet from the fixing belt 21. A separation member 28 for separation and a pressure member for pressing the pressure roller 22 to the fixing belt 21 are included.

The fixing belt 21 is composed of an endless belt member (including a film) having a thin wall and having 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). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

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

At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. 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 to 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 may be a hollow roller. In that case, a heating member such as a halogen heater may be disposed inside the pressure roller 22. In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven glossiness is formed on the solid portion of the image. It can happen.

In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided. The elastic layer 22b may be solid rubber, but if there is no heating member inside the pressure roller 22, sponge rubber may be used.

Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is not easily taken away, thereby saving energy. Further, the fixing rotator and the counter rotator are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

Each halogen heater 23 is fixed to the side plate of the fixing device 20 at both ends. Each halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer 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 such output control 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, IH, a resistance heating element, a carbon heater, or the like may be used as a heating member for heating the fixing belt 21.

The nip forming member 24 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and is fixedly supported by a stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained 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 bending prevention function of the nip forming member 24. However, the stay 25 may be made of resin. It is.

The nip forming member 24 is composed of a heat resistant member having a heat resistant temperature of 200 ° C. or higher. This prevents the nip forming member 24 from being deformed by heat in the toner fixing temperature range and ensures a stable state of the nip portion N, thereby stabilizing the output image quality. As the base material of the nip forming member 24, a general heat resistant resin can be used as will be described later with reference to FIGS. 5A and 5B. In this embodiment, as will be described later, an 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 the surface thereof. When the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that 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 of the low friction sheet, for example, Toyoflon (registered trademark) 401 manufactured by Toray Industries, Inc. is preferable.

The reflection member 26 is disposed between the stay 25 and the halogen heater 23. In the present embodiment, the reflecting member 26 is fixed to the stay 25. Moreover, 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 high melting point metal material or the like.

By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21. As a result, 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, energy saving can be achieved.

Further, the reflective surface may be formed by subjecting the surface of the stay 25 on the side of the halogen heater 23 to mirror processing such as polishing or painting without providing the reflective member 26 as in the present embodiment. In addition, the reflectance of the reflecting surface of the reflecting member 26 or the stay 25 is desirably 90% or more.

Since the shape and material of the stay 25 cannot be freely selected in order to ensure the strength thereof, the weight of the selection of the shape and material is increased by providing the reflecting member 26 as in the present embodiment, and the reflecting member 26 is increased. And the stay 25 can be specialized for each function. Further, since the reflecting member 26 is provided between the halogen heater 23 and the stay 25, the position of the reflecting member 26 with respect to the halogen heater 23 is reduced, so that the fixing belt 21 can be efficiently heated.

Further, in order to further improve the heating efficiency of the fixing belt 21 by light reflection, 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 surfaces are arranged concentrically with the halogen heater 23 as the center, the light is reflected toward the halogen heater 23, so that the heating efficiency is reduced accordingly. On the other hand, when a part or all of the reflecting surface is arranged in the direction other than the halogen heater 23 to reflect the light toward the fixing belt, the amount of light reflected toward the halogen heater 23 is reduced. The heating efficiency by reflected light can be improved.

In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further improve energy saving and first print time. Specifically, the fixing belt 21 can be directly heated at a place other than the nip portion N by the halogen heater 23 (direct heating method). In the present embodiment, nothing is interposed between the halogen heater 23 and the left 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 made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall 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 configured to be equal. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at 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 heat conductive member 24b is attached to the nip portion side of the nip forming member 24 in parallel with the halogen heater 23 (central heater 23a and end heater 23b) as shown in FIG. The light emission length of the central heater 23a is set to 217 mm corresponding to the A4 vertical size paper width (210 mm).

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

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

This is because the heat of the hatching portion 24b1 moves in both the inner and outer directions in the paper width direction, but the amount of heat flowing to the outer side is larger due to the temperature difference between the inner and outer sides. On the other hand, since the high heat conductive member 24b is continuous in the longitudinal direction corresponding to the full width, if only the central heater 23a is turned on and an attempt is made to pass the A4 vertical size, the end temperature tends to decrease in the paper passing region.

The suppression of “end temperature drop” and the suppression of “end temperature rise” are in a trade-off relationship. If the thermal conductivity of the high thermal conductive member 24b is increased or the amount of heat transfer is increased, it acts in the direction of suppressing the end temperature rise, but the end temperature drop tends to occur conversely. Further, when the thermal conductivity of the high heat conducting member 24b is lowered or the amount of heat transfer is limited, the end temperature drop is less likely to occur, but the end temperature rise is more likely to occur.

In the embodiment of the present invention, when the length of the high heat conductive member 24b is designed, the fixing start-up operation using only the central heater 23a does not cause a decrease in the edge temperature of the sheet passing area, and the non-sheet passing area. The length is designed so as not to cause an increase in the end temperature (overheating 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 is a comparison of the light emission length of the paper, halogen heater 23 (the central heater 23a and the end heater 23b) and the length (width) of the high thermal conductivity member with the present embodiment. The high heat conductive member 24b of this 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 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 shows the first heating member, the second heating member, the high heat conduction member, and the central portion of the paper corresponding to the maximum paper passing width. L1 is a longitudinal outer end portion of the heat generating portion 23b1 of the end heater 23b, starting from one longitudinal end portion of the heat generating portion 23a1 of the central heater 23a as the first heating member. Is the length. In this embodiment, L1 = 56.5 mm. L2 is the length from the longitudinal end of the heat generating portion 23a1 of the central heater 23a to the longitudinal end of the heat generating portion 23b1 of the high heat conductive member 24b (inside the hole 51). An effective soaking action cannot be obtained from the hole 51 including the hole 51 to the end in the longitudinal direction. In the present 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 = 0.88-0.96), the edge temperature rise / edge temperature drop can be achieved with respect to an arbitrary amount of paper nodding. Can be suppressed. For example, an increase in end temperature and a decrease in end temperature can be suppressed regardless of whether the A3 nobi length is 320 mm or the A3 nobi length is 329 mm.

The effect by the ratio can be said as follows with reference to FIG. That is, by extending the outer end portion of the high heat conductive member 24b in accordance with the ratio (L2 / L1 = 0.88 to 0.96), an increase in the sheet width of A3 → A3 Nobi (Novi: 11.5 mm) ), It is possible to keep the length of the end heater 23b (5 mm) relatively short. As a result, the fixing device 20 can be reduced in size, and the energy saving can be improved by the end heater 23b that suppresses the noisy portion.

Further, according to the present invention, when the outer end portion of the high heat conductive member 24b is extended according to the ratio (L2 / L1 = 0.88 to 0.96), the vertical (width in the sheet passing direction or nip width) and horizontal ( 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 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 Nobi, it is necessary to lengthen the length of the high heat conductive member 24b in the axial direction as compared with the conventional machine. In this case, the width (width in the sheet passing direction) of the high thermal conductive member 24b is normally the same as that of the conventional machine for reducing the diameter of the fixing belt 21 and saving energy, and is not changed.

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 ratio (L2 / L1 = 0.88-0.96) is compatible with A3 nobi. However, the aspect ratio can be suppressed to 18.8 or less. Thus, by extending the high heat conductive member 24b in the nip axis direction with respect to the conventional fixing device, the effect of suppressing the increase in the end temperature of the high heat conductive member 24b is increased with respect to the paper size in which only the central heater 23a is lit.

Further, in the conventional A3-compatible machine, the length (the length in the longitudinal direction or the length in the nip axis direction) of the high heat conductive member 24b is 313 mm or more. In contrast, 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 does not decrease despite being an A3 Novi compatible machine. The upper limit of the horizontal length can be set to 325 mm or less.

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

In the fixing device 20 of the present embodiment, the high thermal conductive member 24b designed as described above is used to configure the nip forming member 24 of FIGS. 5A and 5B. In this example, a high thermal conductivity copper plate is used for the high thermal conductivity member 24b. The high heat conductive member 24b is formed by bending a copper plate so as to have a concave cross section with a cross section perpendicular to the longitudinal direction.

In addition, formation of a copper plate is not restricted to bending formation, Welding etc. may be sufficient. A rectangular hole 51 is formed at a position near both ends of the high heat conductive member 24b. This hole 51 is for positioning and fixing the high heat conductive member 24b to the base material 24a.

The high heat conductive member 24b may be a metal thin plate member, or may be a metallic film (soaking 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 heat conduction member 24b is thinned to minimize its heat capacity, and fixing failure due to a decrease in end temperature at the start of 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 includes 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 (thermal conductivity 0.29 W / m · K) is used for the fixing belt base material, an iron-based SUS material (for example, thermal conductivity 19 W / m · K) or the like is used as the high thermal conductivity member 24b. Metal materials can also be used. In the present embodiment, the high heat conductive member 24b is made of a copper-based material, and more specifically, the high heat conductive member 24b is made of a copper-based material having a thermal conductivity of 236 w / (m · k) or more.

The high heat conductive member 24 b is continuous in the longitudinal direction corresponding to the entire width of the fixing belt 21. Here, the length Ls of the high heat conductive member 24 b is not the entire length of the high heat conductive member 24 b but a length inside the longitudinal direction from the hole 51. Since an effective soaking action 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 heat conductive member 24b is attached will be described with reference to FIGS. 5A and 5B. As shown in FIGS. 5A (a) and 5 (b), the high thermal conductive member 24b is disposed on the lower surface (the nip portion facing surface) of the base material 24a of the nip forming member 24.

As can be seen from FIG. 5A, the high heat conductive member 24 b is disposed in a non-contact manner with the stay 25 and the reflecting member 26 (see FIG. 2) disposed on the inner side (upper side) of the stay 25. Therefore, heat transfer from the high heat conductive member 24b to the stay 25 is prevented, and energy saving is not impaired. Similarly, heat transfer from the high heat conducting member 24b to the reflecting member 26 can be prevented, and energy saving can be maintained.

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

The heat 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 heat conductive 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 heat conductive member 24b to the base material 24a and the stay 25 is suppressed.

The high heat conductive member 24b can be made of, for example, copper or aluminum having a high heat conductivity. In the illustrated example, the high heat conductive member 24b is formed to be concave in a cross section perpendicular to the longitudinal direction of the high heat conductive member 24b. The high heat conductive member 24b suppresses a rise in the end temperature of the non-sheet-passing area of the fixing belt 21 that occurs when the small-size sheet is passed while suppressing a decrease in the end temperature of the sheet-passing area when the fixing is started up. it can.

However, if the heat capacity of the high thermal conductive member 24b is too large, the heat transfer from the fixing belt 21 becomes large and the temperature rise of the fixing belt 21 is hindered, the rise time delay and the first print time delay occur. The lighting rate increases and the energy saving performance is impaired. Therefore, energy saving can be ensured by making the high heat conductive member 24b a thin layer member having a low heat capacity.

The bottom wall portion of the concave cross section of the high heat conductive member 24b is the nip portion facing surface, and the left and right side wall portions 24b2, 24b3 of the high heat conductive member 24b have a predetermined height toward the stay 25 so as to sandwich the base material 24a in the paper direction. I'm standing up. By adjusting the rising height, the amount of heat released even in the thickness direction of the high heat conducting member 24b can be adjusted, and the rise in the end temperature can be further suppressed.

For example, the amount of heat released in the thickness direction of the high heat conduction member 24b can be partially changed in the longitudinal direction of the high heat conduction member 24b by partially changing the rising height depending on the position in the longitudinal direction of the high heat conduction member 24b. Is possible. Therefore, in the longitudinal direction of the nip portion N, it is possible to further finely adjust the suppression function for the end temperature increase and the suppression function for the end temperature decrease.

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

On the nip portion entrance side, 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 heat conductive member 24b. The nail | claw part 24b4 is engaged with the step part 24a1 formed in the upper surface of the base material 24a, and prevents the variation of the components at the time of the assembly of the nip formation member 24, and makes it possible to improve work efficiency. Further, the claw portion 24b4 increases the amount of heat released in the thickness direction of the high heat conductive member 24b together with the side wall portions 24b2 and 24b3, and thus has a function of suppressing an increase in end temperature.

The cross-sectional shape of the high heat conductive member 24b is not necessarily concave as described above. As shown in FIG. 5A (c), a plate-like high heat conduction member 24b 'attached to the lower surface of the substrate 24a may be used. In this case, since there is no rising portion, it is possible to suppress the amount of heat escaping in the thickness direction of the high heat conductive member 24b and to suppress the end portion temperature decrease.

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

The shape of the upper surface (stay facing surface) of the base material 24a made of a liquid crystal polymer is formed into a shape in which the concavo-convex shape 24a2 is continuous in the longitudinal direction. By adopting such an uneven shape, it is possible to suppress the heat flow to the stay 25 side while enabling 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.

(Inhibition state of edge temperature rise and edge temperature drop)
Next, with reference to FIG. 6A, the suppression state of the end temperature rise and the end temperature decrease according to the embodiment of the present invention will be described. Further, in order to compare the restrained state with the conventional fixing device, FIGS. 6B and 6C show a diagram 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 a three-layer structure disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2015-194661, FIG. 6), and FIG. 6C shows a high heat conductive member. This shows the suppression state of the fixing device that does not use 24b.

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

The halogen heater 23 includes two heaters, a central heater 23a as a first heating member and an end heater 23b as a second heating member. The heaters 23a and 23b are different in axial position and have a paper size to be passed. Accordingly, the central heater 23a is turned on alone, or the central heater 23a and the end heater 23b are turned on simultaneously. The same applies to 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 paper passing widths (297 mm and 320 mm) of large sizes (A3 vertical and A3 vertical novi).

6A (a) shows a central heater 23a, an end heater 23b, and sheets having a sheet passing width P = A to D. FIG. 6A (c) shows the state of the edge temperature rise and the edge temperature drop when these sheets are passed. Here, the sheet width is A6 length, B is A4 length, C is B4 length, and D is A3 length.

In the present embodiment, the nip forming member 24 of FIG. 6A is employed instead of the nip forming member 24 having the three-layer structure of FIG. 6B disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2015-194661). The nip forming member 24 has a simple structure in which a high heat conductive member 24b having a length according to the ratio L2 / L1 (= 0.88 to 0.96) is attached to the lower surface of the base material 24a.

As a result, for example, an edge temperature rise suppressing effect equivalent to or more than the three-layer structure can be obtained with a paper size of paper passing width P = A (A6 length) (δ _A > δ _B ). Further, the present embodiment for the endothermic mass B, C is not, the end portion temperature drop T _B in FIG. 6B (c) is eliminated as shown in FIG. 6A (c).

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

On the other hand, in the conventional fixing device 20 without the high heat conductive member shown in FIG. 6C, the edge temperature increases T _A and T _B occur in 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 low thermal conductivity base material 24a, heat accumulation on the fixing belt 21 proceeds in the non-sheet passing region during continuous sheet passing. Because.

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

However, when the high heat conductive member 24b that contacts 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 heat conductive member 24b. . Therefore, compared with the case of FIG. 7 (a), (b), an edge temperature rise is suppressed at the time of B4 paper passing and A6 (or postcard) paper passing.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that 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: Metal core 22b: Elastic layer 22c: Release layer 23: Halogen heater 23a: Central heater 23b: End heater 24: Nip forming member 24a: Base material 24a1: Stepped portion 24a2: Uneven shape 24b: High thermal conductivity member 24b1: Hatched portion 24b2, 24b3: Side wall 24b4 : Claw part 25: Stay 26: Reflective member 27: Temperature sensor 28: Separating member 30: Intermediate transfer belt 31: Primary transfer low LA 32: Secondary transfer backup roller 33: Cleaning backup roller 34: Tension roller 35: Belt cleaning device 36: Secondary transfer roller 51: Hole

Japanese Patent Laying-Open No. 2015-194661 (FIG. 6)

Claims (10)

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 part on the end side in the width direction 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 opposite to the opposing member;
A high thermal conductivity member disposed on the fixing belt side of the nip forming member and having a higher thermal conductivity than the nip forming member;
The length from the one end in the longitudinal direction of the first heat generating portion as a starting point to the outer end in the longitudinal direction of the second heat generating portion located outside the one end in the longitudinal direction is L1, and the high heat conduction member A fixing device in which a ratio of L1 and L2 is set to 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 lighting of the first heating member corresponds to the A4 paper width and the lighting of the first heating member and the second heating member corresponds to the A3 nobi paper width of 320 mm, the L1 = 56.5. 2. The fixing device according to claim 1, wherein L2 is 52.0 mm.   The high heat conductive member has a concave cross section consisting of a bottom wall portion facing the nip portion in a cross section perpendicular to the longitudinal direction, and a side wall portion extending from the bottom wall portion in the thickness direction of the nip forming member, The fixing device according to claim 1, wherein the side wall portion has a height of 1.0 mm to 1.9 mm from an inner surface of the bottom wall portion having the concave cross section.   The fixing device according to claim 3, wherein an upper end of the side wall portion located on the upstream side in the paper feeding direction is extended to an upper surface of the nip forming member.   5. The fixing device according to claim 1, wherein the high thermal conductivity member has a thermal conductivity of 3.81 to 15.95 (J / K). 6.   The stay for fixing the said nip forming member to the inner side of the fixing belt is disposed, and the upper surface of the nip forming member that contacts the stay is formed in a concavo-convex shape. Item 1. The fixing device according to item 1.   7. The fixing device according to claim 1, wherein a base material of the nip forming member is made of a liquid crystal polymer.   An image forming apparatus comprising the fixing device according to claim 1. 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 part on the end side in the width direction 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 opposite to the opposing member;
In a designing method of a fixing device having a high thermal conductive member disposed on the nip portion side of the nip forming member and having a higher thermal conductivity than the nip forming member,
The length from the one end in the longitudinal direction of the first heat generating portion as a starting point to the outer end in the longitudinal direction of the second heat generating portion located outside the one end in the longitudinal direction is L1, and the high heat conduction member A fixing device design method, 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 design method, the lighting of the first heating member corresponds to the A4 paper width, and the lighting of the first heating member and the second heating member corresponds to the A3 nobi paper width of 320 mm. 10. The fixing device design method according to claim 9, wherein the length L5 is 52.0 mm.

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