JP7276700B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to fixing devices and image forming apparatuses.

In recent years, a fixing device used in an electrophotographic image forming apparatus uses a heating element having a resistance heating element on the inner surface of a low heat capacity thin fixing belt for quick start, power saving, cost reduction, and miniaturization. A type that heats by sliding contact is used. Conventionally, in this type of fixing device, a lubricant such as heat-resistant grease is interposed between the fixing belt and the heating member to reduce sliding frictional resistance therebetween.

However, the reduction of frictional resistance by lubricant has the following problems.
1) In the initial state of the fixing device, a large amount of lubricant is interposed between the fixing belt and the heating member. protrude from the end of the belt. As a result, the lubricant becomes insufficient, the frictional resistance between the fixing belt and the heating member increases, and the rotational torque of the pressure roller increases.

2) As the number of sheets passing through the fixing nip increases, part of a large amount of the lubricant interposed between the fixing belt and the heating member seeps out from the end of the fixing belt. Then, the amount of lubricant between the fixing belt and the heating member decreases as the number of passing sheets increases, the frictional resistance between the two increases, and the rotational torque of the pressure roller increases.

3) Lubricants have the property that their viscosity is high at low temperatures and decreases as the temperature rises. For this reason, a large amount of high-viscosity lubricant is interposed between the fixing belt and the heating member in the initial driving state of the fixing device, so that the rotational torque of the pressure roller increases.

The present invention has been made in view of such problems . The purpose is to reduce and extend the life of the rotating member.

In order to solve the above-described problems, the fixing device of the present invention includes a flexible sleeve-shaped rotating member, a heating element sliding on the inner periphery of the rotating member, and the heating element sandwiching the rotating member. A pressurizing member that forms a fixing nip with the rotating member by pressing against the opposing portions, and applies heat of the heating body to the material to be heated by nipping and conveying the material to be heated by the fixing nip. The fixing device is characterized in that an uneven portion is provided on a sliding surface of the heating body with the rotating member.

In the fixing device of the present invention, since the sliding surface of the heating element on which the sleeve-shaped rotating member slides is provided with the uneven portion, the sliding resistance of the rotating member can be reduced and the life can be extended.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 1 is a principle diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 1 is a cross-sectional view of a first fixing device according to an embodiment of the invention; FIG. FIG. 4 is a cross-sectional view of a second fixing device according to an embodiment of the invention; FIG. 5 is a cross-sectional view of a third fixing device according to an embodiment of the invention; 1A and 1B are a plan view, a cross-sectional view, a perspective view, and a perspective view of a fixing device with lubricant applied to uneven portions; FIG. 1A and 1B are a plan view and a cross-sectional view of a fixing device using a planar heating element; FIG. 3D is an enlarged cross-sectional view taken along line IV-IV of FIG. 3A(d), showing an uneven portion of the fixing device; FIG. 10 is a plan view showing another concave-convex portion of the fixing device; FIG. 4 is a perspective view of a fixing device to which an inlet-side rotation guide is added; It is the perspective view which looked at the conventional heater and heater folder from the downward direction. FIG. 2 is a plan view of a conventional heater and a diagram showing temperature distribution of a fixing belt;

Hereinafter, a heating device according to an embodiment of the present invention, and a fixing device and an image forming apparatus (laser printer) using the heating device will be described with reference to the drawings. A laser printer is an example of an image forming apparatus, and the image forming apparatus is not limited to a laser printer. That is, the image forming apparatus can be configured as a copier, a facsimile machine, a printer, a printing machine, or an inkjet recording apparatus, or a multifunction machine combining at least two of these.

The same or corresponding parts in each figure are denoted by the same reference numerals, and redundant description thereof will be appropriately simplified or omitted. Also, the dimensions, materials, shapes, relative positions, and the like in the description of each component are examples, and are not intended to limit the scope of the present invention unless otherwise specified.

In the following embodiments, the "recording medium" is described as "paper", but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper but also OHP sheets, fabrics, metal sheets, plastic films, or prepreg sheets in which carbon fibers are previously impregnated with resin.

The term "recording medium" also includes media to which developer and ink can be applied, recording paper, and recording sheets. In addition to plain paper, "paper" includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

In addition, the term "image formation" used in the following description refers not only to imparting meaningful images, such as characters and figures, to a medium, but also to imparting meaningless images, such as patterns, to a medium. also means

(Configuration of laser printer)
FIG. 1A is a configuration diagram schematically showing the configuration of a color laser printer as an embodiment of an image forming apparatus 100 equipped with a heating device or fixing device 300 of the present invention. FIG. 1B also shows a simplified illustration of the principle of the color laser printer.

The image forming apparatus 100 includes four process units 1K, 1Y, 1M and 1C as image forming means. These process units form images with developers of respective colors of black (K), yellow (Y), magenta (M), and cyan (C) corresponding to color separation components of a color image.

Each of the process units 1K, 1Y, 1M and 1C has the same configuration except that they have toner bottles 6K, 6Y, 6M and 6C containing unused toner of different colors. Therefore, the configuration of one process unit 1K will be described below, and the description of the other process units 1Y, 1M, and 1C will be omitted.

The process unit 1K has an image carrier 2K (for example, a photosensitive drum), a drum cleaning device 3K, and a neutralizer. The process unit 1K further includes a charging device 4K as charging means for uniformly charging the surface of the image carrier, and a developing device as developing means for performing visible image processing on the electrostatic latent image formed on the image carrier. It has 5K and so on. The process unit 1K is detachably attached to the main body of the image forming apparatus 100, and consumable parts can be replaced at the same time.

The exposure device 7 is arranged above each of the process units 1K, 1Y, 1M, and 1C installed in this image forming apparatus 100 . The exposure device 7 is configured to perform write scanning according to image information, that is, to irradiate the image carrier 2K with laser light L from a laser diode reflected by a mirror 7a based on image data.

The transfer device 15 is arranged below each of the process units 1K, 1Y, 1M and 1C in this embodiment. This transfer device 15 corresponds to the transfer means TM of FIG. 1B. The primary transfer rollers 19K, 19Y, 19M and 19C are arranged in contact with the intermediate transfer belt 16 so as to face the respective image carriers 2K, 2Y, 2M and 2C.

The intermediate transfer belt 16 circulates while being stretched over primary transfer rollers 19K, 19Y, 19M, 19C, a driving roller 18, and a driven roller 17. As shown in FIG. The secondary transfer roller 20 is arranged in contact with the intermediate transfer belt 16 so as to face the driving roller 18 . If the image carriers 2K, 2Y, 2M, and 2C are the first image carriers of each color, the intermediate transfer belt 16 is the second image carrier that synthesizes those images.

The belt cleaning device 21 is installed downstream of the secondary transfer roller 20 in the running direction of the intermediate transfer belt 16 . A cleaning backup roller is installed on the opposite side of the intermediate transfer belt 16 to the belt cleaning device 21 .

A sheet feeding device 200 having a tray for stacking sheets P is installed below the image forming apparatus 100 . The paper feeder 200 constitutes a recording medium supply section, and can accommodate a large number of sheets P as a recording medium in a bundle. unitized with.

The paper feeding device 200 is detachable from the main body of the image forming apparatus 100 in order to replenish paper and the like. The paper feeding roller 60 and the roller pair 210 are arranged above the paper feeding device 200 so as to convey the uppermost paper P of the paper feeding device 200 toward the paper feeding path 32 .

A pair of registration rollers 250 as a separating and conveying unit is arranged immediately upstream in the conveying direction of the secondary transfer roller 20 and can temporarily stop the paper P fed from the paper feeding device 200 . Due to this temporary stop, slack is formed on the leading end side of the paper P, and the skew of the paper P is corrected.

A registration sensor 31 is disposed immediately upstream of the registration roller pair 250 in the conveying direction, and the registration sensor 31 detects the passage of the leading edge of the sheet. After the registration sensor 31 detects the passage of the leading edge of the paper, when a predetermined period of time elapses, the paper hits the pair of registration rollers 250 and temporarily stops.

At the downstream end of the paper feeder 200, a transport roller 240 is arranged for upwardly transporting the paper transported from the roller pair 210 to the right side. As shown in FIG. 1A, the transport rollers 240 transport the paper upward toward the pair of registration rollers 250 .

The roller pair 210 is composed of a pair of upper and lower rollers. The roller pair 210 can be of the FRR separation type or the FR separation type.

In the FRR separation method, a separation roller (return roller) to which a constant amount of torque is applied in the direction opposite to the paper feed direction by a drive shaft via a torque limiter is brought into pressure contact with the feed roller to separate the paper at the nip between the rollers. In the FR separation method, a separation roller (friction roller) supported by a fixed shaft via a torque limiter is brought into pressure contact with a feed roller to separate the paper at the nip between the rollers.

In this embodiment, the roller pair 210 is constructed by the FRR separation method. That is, the roller pair 210 consists of an upper feed roller 220 that conveys the paper into the machine and a lower separation roller 230 that is driven by a drive shaft through a torque limiter in the direction opposite to the feed roller 220. consists of

The separating roller 230 is biased toward the feeding roller 220 by biasing means such as a spring. The feeding roller 60 rotates to the left in FIG. 1A by transmitting the driving force of the feeding roller 220 through the clutch means.

The paper P, which has been bumped against the registration roller pair 250 and has slack at the leading end, is transferred to the secondary transfer roller 20 and the drive roller in time with the timing at which the toner image formed on the intermediate transfer belt 16 is appropriately transferred. 18 (transfer nip N in FIG. 1B). Then, the toner image formed on the intermediate transfer belt 16 is electrostatically transferred to the desired transfer position with high precision by the bias applied at the secondary transfer nip. ing.

The post-transfer conveying path 33 is arranged above the secondary transfer nip between the secondary transfer roller 20 and the driving roller 18 . The fixing device 300 is installed near the upper end of the post-transfer conveying path 33 .

The fixing device 300 includes a fixing belt 310 containing a heating device, and a pressure roller 320 as a pressure member that rotates while contacting the fixing belt 310 with a predetermined pressure. The fixing device 300 can have a plurality of configurations as shown in FIGS. 2A to 2C, which will be described later.

The post-fixing transport path 35 is disposed above the fixing device 300 , and branches into a paper discharge path 36 and a reversing transport path 41 at the upper end of the post-fixing transport path 35 . A switching member 42 is arranged at this branched portion, and the switching member 42 swings around a swing shaft 42a. A paper discharge roller pair 37 is arranged near the opening end of the paper discharge path 36 .

The reverse transport path 41 joins the paper feed path 32 at the other end opposite to the branched portion. A reverse conveying roller pair 43 is arranged in the middle of the reverse conveying path 41 . The discharge tray 44 is installed on the upper portion of the image forming apparatus 100 so as to form a concave shape toward the inside of the image forming apparatus 100 .

A powder container 10 (for example, a toner container) is arranged between the transfer device 15 and the paper feeding device 200 . The powder container 10 is detachably attached to the main body of the image forming apparatus 100 .

The image forming apparatus 100 of the present embodiment requires a predetermined distance from the paper feed roller 60 to the secondary transfer roller 20 due to transfer paper transport. Then, the powder container 10 is installed in the dead space generated at this distance to reduce the size of the laser printer as a whole.

The transfer cover 8 is installed above the paper feeding device 200 and in front of the paper feeding device 200 in the pull-out direction. By opening the transfer cover 8, the inside of the image forming apparatus 100 can be inspected. The transfer cover 8 is provided with a manual paper feeding roller 45 for manual paper feeding and a manual paper feeding tray 46 for manual paper feeding.

(laser printer operation)
Next, the basic operation of the laser printer according to this embodiment will be described below with reference to FIG. 1A. First, the operation for single-sided printing will be described.

The paper feed roller 60 is rotated by a paper feed signal from the control section of the image forming apparatus 100, as shown in FIG. 1A. Then, the paper feed roller 60 separates only the uppermost paper sheet from the stack of paper sheets P stacked on the paper feeder 200 and feeds it to the paper feed path 32 .

When the leading edge of the paper P sent out by the paper feed roller 60 and the roller pair 210 reaches the nip of the registration roller pair 250, it becomes slack and waits in that state. Then, the optimum timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the paper P is obtained, and the tip skew of the paper P is corrected.

In the case of manual paper feeding, the stack of paper stacked on the manual feed tray 46 passes through a part of the reverse conveyance path 41 one by one from the uppermost paper by the manual feed roller 45 and is nipped by the registration roller pair 250 . transported to. The subsequent operations are the same as those for paper feeding from the paper feeding device 200 .

Here, as for the image forming operation, one process unit 1K will be described, and the description of the other process units 1Y, 1M, and 1C will be omitted. First, the charging device 4K uniformly charges the surface of the image carrier 2K to a high potential. Then, the exposing device 7 irradiates the surface of the image carrier 2K with the laser light L based on the image data.

On the surface of the image carrier 2K irradiated with the laser beam L, the potential of the irradiated portion is lowered to form an electrostatic latent image. The developing device 5K has a developer carrier that carries a developer containing toner, and the unused black toner supplied from the toner bottle 6K is passed through the developer carrier to form an electrostatic latent image. is transferred to the surface portion of the image carrier 2K.

The image carrier 2K to which the toner has been transferred forms (develops) a black toner image on its surface. Then, the toner image formed on the image carrier 2K is transferred to the intermediate transfer belt 16. FIG.

The drum cleaning device 3K removes residual toner adhering to the surface of the image carrier 2K after the intermediate transfer process. The removed residual toner is transported to and collected by the waste toner conveying means to the waste toner storage section in the process unit 1K. Further, the static elimination device eliminates residual charges on the image carrier 2K from which the residual toner has been removed by the cleaning device 3K.

In the process units 1Y, 1M, and 1C of each color, toner images are similarly formed on the image carriers 2Y, 2M, and 2C, and transferred to the intermediate transfer belt 16 so that the toner images of each color are superimposed.

The intermediate transfer belt 16 onto which the toner images of the respective colors are transferred so as to overlap each other travels to the secondary transfer nip between the secondary transfer roller 20 and the driving roller 18 . On the other hand, the pair of registration rollers 250 sandwiches the sheet of paper that abuts against them and rotates at a predetermined timing. The sheet is conveyed to the secondary transfer nip of the secondary transfer roller 20 . In this manner, the toner image on the intermediate transfer belt 16 is transferred onto the paper P sent out by the registration roller pair 250 .

The paper P onto which the toner image has been transferred is transported to the fixing device 300 through the post-transfer transport path 33 . Then, the sheet P conveyed to the fixing device 300 is sandwiched between the fixing belt 310 and the pressure roller 320, and the unfixed toner image is fixed on the sheet P by applying heat and pressure. The paper P on which the toner image is fixed is sent from the fixing device 300 to the transport path 35 after fixing.

The switching member 42 is in a position where the vicinity of the upper end of the post-fixing transport path 35 is open as indicated by the solid line in FIG. 1A at the timing when the paper P is sent out from the fixing device 300 . Then, the sheet P sent out from the fixing device 300 is sent out to the discharge path 36 via the post-fixing transport path 35 . The paper discharge roller pair 37 pinches the paper P sent to the paper discharge path 36 and discharges it to the paper discharge tray 44 by being rotationally driven, thereby completing single-sided printing.

Next, the case of double-sided printing will be described. As in the case of single-sided printing, the fixing device 300 feeds the paper P to the paper discharge path 36 . When double-sided printing is performed, the pair of paper discharge rollers 37 conveys a portion of the paper P to the outside of the image forming apparatus 100 by rotational driving.

Then, when the trailing edge of the paper P passes through the paper discharge path 36, the switching member 42 swings around the swing shaft 42a as indicated by the dotted line in FIG. do. Almost at the same time as the upper end of the post-fixing transport path 35 is closed, the paper discharge roller pair 37 rotates in a direction opposite to the direction in which the paper P is transported out of the image forming apparatus 100 , and sends the paper P to the reverse transport path 41 . .

The sheet P sent out to the reverse transport path 41 reaches the registration roller pair 250 via the reverse transport roller pair 43 . Then, the registration roller pair 250 finds the optimum timing (synchronization) for transferring the toner image formed on the intermediate transfer belt 16 to the toner image untransferred surface of the paper P, and feeds the paper P to the secondary transfer nip.

Then, the secondary transfer roller 20 and the drive roller 18 transfer the toner image to the toner image untransferred surface (back surface) of the paper P when the paper P passes through the secondary transfer nip. Then, the paper P onto which the toner image has been transferred is transported to the fixing device 300 through the post-transfer transport path 33 .

The fixing device 300 fixes the unfixed toner image on the back surface of the paper P by sandwiching the conveyed paper P between the fixing belt 310 and the pressure roller 320 and applying heat and pressure. In this way, the paper P having the toner images fixed on both sides thereof is fed from the fixing device 300 to the transport path 35 after fixing.

The switching member 42 is in a position where the vicinity of the upper end of the post-fixing transport path 35 is open as indicated by the solid line in FIG. 1A at the timing when the paper P is sent out from the fixing device 300 . Then, the paper P delivered from the fixing device 300 is delivered to the paper discharge path 36 via the fixing transportation path. The paper discharge roller pair 37 pinches the paper P sent to the paper discharge path 36, rotates, and discharges the paper P to the paper discharge tray 44, thereby completing double-sided printing.

After the toner image on the intermediate transfer belt 16 is transferred to the paper P, residual toner remains on the intermediate transfer belt 16 . A belt cleaning device 21 removes this residual toner from the intermediate transfer belt 16 . Further, the toner removed from the intermediate transfer belt 16 is conveyed to the powder container 10 by the waste toner conveying means and collected in the powder container 10 .

(fixing device)
Next, the heating device and the first to third fixing devices 300 according to the embodiment of the invention will be further described below. The heating device of this embodiment is for heating the fixing belt 310 of the fixing device 300 .

The first fixing device, as shown in FIG. 2A, is composed of a thin fixing belt 310 with a low heat capacity and a pressure roller 320 . The fixing belt 310 has, for example, a cylindrical substrate made of polyimide (PI) having an outer diameter of 25 mm and a thickness of 40 to 80 μm.

As the outermost layer of the fixing belt 310, a release layer having a thickness of 5 to 50 μm is formed of a fluorine-based resin such as PFA or PTFE in order to increase durability and ensure release properties. An elastic layer made of rubber or the like having a thickness of 50 to 500 μm may be provided between the substrate and the release layer.

Further, the substrate of the fixing belt 310 is not limited to polyimide, and may be a heat-resistant resin such as PEEK, or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 310 may be coated with polyimide, PTFE, or the like as a sliding layer.

The pressure roller 320 has an outer diameter of 25 mm, for example, and includes a solid iron core 321, an elastic layer 322 formed on the surface of the core 321, and a release layer formed on the outer side of the elastic layer 322. 323. The elastic layer 322 is made of silicone rubber and has a thickness of 3.5 to 4.0 mm, for example.

In order to enhance the releasability of the elastic layer 322, it is desirable to form a release layer 323 of a fluorine resin layer having a thickness of about 20 to 40 μm, for example. A pressure roller 320 is pressed against the fixing belt 310 by an urging means.

A stay 330 and a heater folder 340 are arranged in the axial direction inside the fixing belt 310 . The stay 330 is made of a metal channel material, and both end portions thereof are supported by both side plates of the heating device. The stay 330 reliably receives the pressing force of the pressure roller 320 and stably forms the fixing nip SN.

The heater holder 340 is for holding the heater base material 350 of the heating device and is supported by the stay 330 . By supporting the heater folder 340 with the stay 330, the pressing force of the pressure roller 320 is received by the stay 330, and the fixing nip SN is stably formed.

The shape of the heater holder 340 is such that it supports only two locations near both ends of the substrate 350 in the width direction in order to avoid contact with the high-temperature portion of the substrate 350 . As a result, the amount of heat flowing to heater folder 340 can be further reduced, and fixing belt 310 can be efficiently heated.

However, if it is necessary to suppress the temperature rise on the side of the base material 350 opposite to the sliding surface with the fixing belt 310 , the side opposite to the sliding surface of the base material 350 is intentionally brought into contact with the heater folder 340 . This increases the amount of heat flowing to the heater folder 340 and suppresses temperature rise on the side opposite to the sliding surface of the substrate 350 .

(heating device)
The heating device has a heat-generating member 360 as a heating element composed of a resistance heating element. As shown in FIG. 3A, the heat-generating member 360 is formed on a base material 350 which is an elongated thin metal plate member having uneven portions 351 and which is coated with an insulating material.

Low-cost aluminum, stainless steel, or the like is preferable as the material of the base material 350 . The base material 350 is not limited to being made of metal, and can be made of a heat-resistant resin such as LCP (liquid crystal resin).

The base material 350 made of a metal material or a resin material can be easily molded to form the concave-convex portion 351. As will be described later, friction reduction by the concave-convex portion 351, or in addition to that, the lubricant is stably held in the concave-convex portion 351. It is possible to suppress an increase in rotational torque and wear of the belt 310, thereby extending the life of the belt.

In order to improve the heat uniformity of the heating device and improve the image quality, the substrate 350 may be made of a material with high thermal conductivity, such as copper, graphite, or graphene. The use of these materials with high thermal conductivity makes it possible to uniformize the temperature of the entire heating device and improve the image quality. can be suppressed. In this embodiment, a stainless steel substrate having a short width of 8 mm, a long width of 270 mm, and a thickness of 1.0 mm (more preferably 0.2 to 0.5 mm) is used.

Specifically, the heat-generating member 360 in FIG. 3A is formed in parallel two rows in the longitudinal direction of the base material 350 in a straight line. One ends of the two rows of heat-generating members 360 are connected to power supply electrodes 360c and 360d via power supply lines 369a and 369c with small resistance values formed in the longitudinal direction on one end side of the base material 350, respectively. . The electrodes 360c, 360d are connected to power supply means including an AC power supply.

The other end of the heat-generating member 360 is connected to the other end of the base material 350 by folding it toward the opposite side of the base material 350 in the longitudinal direction via a power supply line 369b having a small resistance value formed in the short direction. It is The heat-generating member 360, the electrodes 360c and 360d, and the power supply lines 369a to 369c are formed with a predetermined line width and thickness by screen printing.

The material of the heat-generating member 360 can be formed by applying a paste prepared by mixing silver (Ag), silver-palladium (AgPd), glass powder, or the like by screen printing or the like, followed by firing. The resistance value of the heat generating member 360 can be, for example, 10Ω at room temperature. The resistance material of the heat generating member 360 may also be silver alloy (AgPt), ruthenium oxide (RuO2), or the like.

A thin overcoat layer or insulating layer 370 covers the surfaces of the heat generating member 360 and the power supply lines 369a to 369c. The insulating layer 370 ensures the slidability of the fixing belt 310 and also ensures insulation between the fixing belt 310, the heat generating member 360, and the power supply lines 369a to 369c.

As the material of the insulating layer 370, heat-resistant glass having a thickness of 75 μm, for example, can be used. The heat-generating member 360 heats the fixing belt 310 in contact with the insulating layer 370 by conducting heat to increase the temperature thereof, and heats and fixes an unfixed image on the paper P conveyed to the fixing nip SN.

(Structure of Concavo-convex Portion of Heater Base Material)
The uneven portion 351 is formed on one side of the heater base material 350, that is, on the surface on the nip entrance side. As shown in FIG. 4A, the uneven portion 351 has fine rib-like convex portions 351a and concave portions 351b arranged regularly in the longitudinal direction of the surface of the base material 350 (horizontal direction in FIG. 4A, perpendicular to the rotation direction of the fixing belt 310). are formed repeatedly at regular intervals. As a result, the contact area between the base material 350 or the heat-generating member 360 and the fixing belt 310 is evenly reduced in the direction orthogonal to the rotation direction, so that the rotational torque of the fixing belt 310 is uniformly decreased in the orthogonal direction, resulting in stable rotation. becomes possible.

The convex portion 351a and the concave portion 351b have a constant length in the transport direction on the paper P nip entrance side. The width or height of the convex portion 351a and the concave portion 351b can be appropriately set to a size that can stably support the fixing belt 310 .

Lubricant G such as heat-resistant grease is accommodated in recess 351b. A part of the lubricant G covers the surfaces of the convex portions 351 a to form a thin lubricant layer with a substantially uniform thickness between the base material 350 and the fixing belt 310 . The lubricant layer further reduces the rotational torque of the fixing belt 310, enabling stable running over time.

The protrusions 351a and the recesses 351b of the uneven portion 351 may be formed parallel to the surface longitudinal direction of the substrate 350 as shown in FIG. 4B. As a result, it is possible to suppress temperature unevenness in the width direction of the fixing belt 310 and the resulting gloss unevenness. Rotational torque of the belt 310 can be further reduced and stabilized.

(Heat generating member using PTC element)
The heat generating member 360 includes a plurality of (six in the illustrated example) PTC elements 361 to 366 as planar heat generating elements formed in a meandering shape with narrow line widths as shown in FIGS. 3B(a) and (b). It can also be configured by connecting in parallel. In this case, if the total resistance value of the heat generating member 360 is 10Ω, the resistance value of each of the PTC elements 361 to 366 is as large as 60Ω.

In order to obtain this large resistance value, the line width of the PTC elements 361 to 366 is made as thin and thin as possible to increase the meandering number. At this time, if there are variations in the line widths and thicknesses of the PTC elements 361 to 366, the amount of heat generated will be uneven.

The PTC element is made of a material having a positive temperature coefficient of resistance (TCR), and is characterized by an increase in resistance (current I decreases and heater output decreases) as temperature T rises. The temperature coefficient of resistance can be, for example, 300 to 1500 PPM (parts per million). The temperature coefficient of resistance can be stored in the memory (non-volatile memory) of the power controller.

The PTC elements 361 - 366 of FIG. 3B are arranged linearly and equally spaced in the longitudinal direction of the substrate 350 . On both sides of the PTC elements 361 to 366 in the short direction, feed lines 360a and 360b having a small resistance are arranged linearly parallel to each other, and both ends of the PTC elements 361 to 366 are connected to the feed lines 360a and 360b. It is A power supply means (power pack) including an AC power supply (100 V AC) is connected to electrodes 360c and 360d formed at one end of each of the power supply lines 360a and 360b.

The substrate 350 is composed of a metal (stainless steel) substrate main body 350a, insulating glass 350b arranged above and below it, and insulating protective layers 350c arranged above and below the insulating glass 350b. The PTC elements 361 to 366 and feeder lines 360a and 360b are covered with an insulating protection layer 350c.

This insulating protective layer 350c can also be made of heat-resistant glass with a thickness of 75 μm, for example. The insulating protective layer 350c insulates and protects the PTC elements 361 to 366 and the power supply lines 360a and 360b, and maintains slidability with the fixing belt 310. FIG.

The PTC elements 361 to 366 can be formed by, for example, applying a paste prepared by mixing silver palladium (AgPd) or glass powder to the base material 350 by screen printing or the like, and then firing the base material 350. can. In this embodiment, the resistance value of each of the PTC elements 361 to 366 is set to 60Ω at room temperature (the total resistance value is 10Ω).

As the material of the PTC elements 361 to 366, in addition to the materials described above, a silver alloy (AgPt) or ruthenium oxide (RuO ₂ ) resistance material may be used. The power supply lines 360a and 360b and the electrodes 360c and 360d can be made of silver (Ag) or silver palladium (AgPd) by screen printing or the like.

The insulating protective layer 350c side of the PTC elements 361 to 366 contacts the fixing belt 310 and heats the fixing belt 310, thereby increasing the temperature of the fixing belt 310 and heating and fixing the unfixed image conveyed to the fixing nip SN.

By using the PTC elements 361 to 366, when the temperature of the PTC elements in the non-paper-passing area rises due to small size paper passing, the amount of heat generated by the PTC elements decreases due to the temperature resistance dependence of the resistance heating element. , the temperature rise can be suppressed. Due to this feature, for example, when printing on paper narrower than the full width of the PTC elements 361 to 366 (for example, within the width of the PTC elements 362 to 365), the PTC elements 361 and 366 outside the width of the paper do not lose heat to the paper. Temperature rises. Then, the resistance values of those PTC elements 361 and 366 increase.

Since the voltage applied to the PTC elements 361 to 366 is constant, the outputs of the PTC elements 361 and 366 outside the width of the paper are relatively lowered, suppressing the edge temperature rise. When the PTC elements 361 to 366 are electrically connected in series, the only way to suppress the temperature rise of the resistance heating elements outside the paper width in continuous printing is to reduce the printing speed. By electrically connecting the PTC elements 361 to 366 in parallel, it is possible to suppress the temperature rise in the non-paper passing portion while maintaining the printing speed.

The ends of the PTC elements 361 to 366 overlap each other in the longitudinal direction as shown in FIG. 3B(a). Thereby, occurrence of temperature unevenness in the longitudinal direction can be suppressed. Such overlap can be achieved by slanting the ends of the PTC elements 361 to 366 as shown in FIG.

The electrodes 360c and 360d may be arranged on both ends of the PTC elements 361 to 368, or may be arranged on one side of the PTC elements 361 to 368 as shown in FIG. 3A(a). By arranging the electrodes 360c and 360d on one side in this way, it is possible to save space in the longitudinal direction.

In FIG. 3B(a), L1: the width of the fixing belt 310, L2: the width of the heating element pattern, and L3: the maximum width of the paper passing have a relationship of L3<L2<L1. Further, the wiring width w2 at the folded portion of the PTC elements 361 and 366 at both ends is formed narrower than the wiring width w1 at the meandering portion for early overheating detection by the temperature sensor.

(Another Embodiment of Fixing Device)
The fixing device 300 is not limited to the first fixing device of FIG. 2A. The second and third fixing devices will be described below with reference to FIGS. 2B to 2C. As shown in FIG. 2B, the second fixing device has a pressure roller 390 on the side opposite to the pressure roller 320, and the fixing belt 310 is sandwiched and heated between the pressure roller 390 and the heating device.

The above-described heating device is arranged inside the fixing belt 310 . An auxiliary stay 331 is attached to one side of the stay 330, and a nip forming member 332 is attached to the other side.

The heating device is held by this auxiliary stay 331 . The nip forming member 332 contacts the pressure roller 320 via the fixing belt 310 to form a fixing nip SN.

The third fixing device, as shown in FIG. 2C, is divided into a heating nip HN and a fixing nip SN. That is, a nip forming member 332 and a stay 333 made of a metal channel member are arranged on the opposite side of the pressure roller 320 from the fixing belt 310 , and the nip forming member 332 and the stay 333 are enclosed. A pressure belt 334 is arranged so as to be rotatable.

Then, the paper P is passed through the fixing nip SN between the pressure belt 334 and the pressure roller 320 to be heated and fixed. Others are the same as the first fixing device in FIG. 2A.

In FIGS. 2A to 2C, when the paper P is passed from the arrow direction toward the fixing nip SN, there is a gap between the fixing belt 310 and the pressure roller 320 (FIG. 2C is between the pressure roller 320 and the pressure belt 334). ), the paper P is heated and the toner image is fixed on the paper P. As shown in FIG. At this time, the fixing belt 310 is heated by heat from the heat generating member 360 while sliding on the insulating layer 370 (or the insulating protective layer 350 c ) of the heat generating member 360 .

The temperature of the heat generating member 360 is detected by a thermistor as temperature detection means, and the power supplied to the heat generating member 360 is controlled by the heating control means according to the detected temperature. The heating control means can be composed of a microcomputer including CPU, ROM, RAM, I/O interface and the like.

When paper is passed, additional electric power is appropriately applied in consideration of the heat removal due to the passage of paper, in addition to the detected temperature. Thereby, the temperature of the fixing belt 310 is controlled to a desired temperature.

(Inlet-side rotation guide for heater base material)
Next, an embodiment in which an entrance-side rotation guide 353 having a curvature portion 352 is provided integrally with the heater base material 350 will be described with reference to FIG. The heater base material of the conventional heating device is generally configured in a flat rectangular shape, and the entrance side and exit side rotation guides for the fixing belt 310 are preferably formed integrally with the heater folder 340 as shown in FIG. It was ordinary (entrance side rotation guide 340a, exit side rotation guide 340b). In this embodiment, an arc-shaped entrance-side rotation guide 353 having a curvature portion 352 is integrally formed on the upstream side of the uneven portion 351 of the heater base material 350 .

By using the aforementioned metal material or heat-resistant resin material for the base material 350, it is possible to easily form a shape having a curvature by press working or the like. By forming the inlet-side rotation guide 353 in an arc shape as shown in FIG. 5, it is possible to ensure heating performance, slidability, and insulation equivalent to those of the heating device having the rotation guides 340a and 340b of FIG. .

In order to mount the heating device on the fixing device 300, the heater folder 340 in FIG. 6 from which the rotation guide 340a is omitted is used as the heater folder. Since there is the curved portion 352 instead of the rotation guide 340a, the rotation stability of the fixing belt 310 is not impaired.

Here, the temperature graph in FIG. 5 shows the distribution of the belt surface temperature after the heating device is heated and controlled to a predetermined target temperature. As in FIG. 7, which will be described later, the belt surface temperature was measured with a thermoviewer in the vicinity of the nip inlet in the belt rotation direction.

Since the conventional entrance-side rotation guide 340a is removed from the heater folder, when the heating device shown in FIG. decline will not occur. Therefore, even if the fixing belt 310 and the exit-side rotation guide 340b come into contact with each other, the temperature at the contact portion does not particularly drop.

Here, when the material of the curvature portion 352 is metal, it has a uniform heating effect in the longitudinal direction of the heating device. Even if the temperature unevenness in the width direction of the fixing belt 310 occurs due to contact with the outlet-side rotation guide 340b or airflow during the rotation of the fixing belt 310 from the fixing nip SN exit to the curvature portion 352, the above-described The uniform heating effect effectively eliminates the temperature unevenness.

In addition, since the substrate 350 and the curvature portion 352 are continuous metal, the heat generated by the heat generating member 360 is efficiently transferred to the curvature portion 352, and the fixing belt 310 contacts the curvature portion 352, thereby fixing the fixing nip SN. The fixing belt 310 is preheated before the entrance, and the fixability of the fixing device 300 can be improved.

Since the base material 350 is made of a metal material, it can be easily formed into a shape with a curvature by press working or the like, and it has a uniform heating effect in the longitudinal direction of the heating device. is as described above.

A convex rib shape may be provided on the upstream side of the curvature portion 352 in the rotation direction of the fixing belt to the extent that temperature unevenness does not occur on the inner peripheral side of the fixing belt 310 . The rib shape can improve the rotation stability of the fixing belt 310 by making it parallel to or perpendicular to the rotation direction of the fixing belt 310 .

The specific shape of the ribs, that is, the width in the longitudinal direction and the contact distance in the rotation direction of the fixing belt 310 are set so as not to generate temperature unevenness of the fixing belt 310 at the inlet of the fixing nip SN. Since the inner peripheral surface of the fixing belt 310 reliably comes into surface contact with the curved portion 352 on the downstream side of the rib, unevenness in temperature of the fixing belt 310 can be smoothed.

The substrate 350 is desirably made of a metal material with good moldability, but it is also possible to use a heat-resistant and insulating resin material. Heat resistance can be ensured by using, for example, polyimide (PI) resin, polyetheretherketone (PEEK) resin, or those reinforced with glass fiber as the resin material.

In addition, the use of a resin material has the advantage of eliminating the need for an insulating layer, which is required in the case of using a metal material, and that it has better moldability than a metal material, resulting in a higher degree of freedom in shape. In this case, if it has a shape like the rotation guide 340a in FIG. 6, it causes partial temperature unevenness in the longitudinal direction.

It is desirable that the width of the curvature portion 352 is equal to or greater than the maximum width of the paper-passing medium on which an image can be formed. Usually, the width of the fixing belt 310 is configured to be equal to or larger than the maximum width of the paper-passing medium on which an image can be formed.

When the curvature portion 352 is provided on the nip inlet side (and) in the inner circumference direction of the fixing belt 310 , the curvature portion 352 guides the inner circumference of the fixing belt 310 . In this case, if the width of the curvature portion 352 is equal to or less than the maximum width of the medium to be fed, the widthwise end portion of the curvature portion 352 comes into contact with the inner circumference of the fixing belt 310 . In this case, the fixing belt 310 is pressed in the contact direction as the passing medium passes, so that the inner periphery of the fixing belt 310 may be scratched at the width-direction end of the curved portion 352 , and the fixing belt 310 may be damaged over time. There is a risk of damage.

A configuration is also conceivable in which flange members that rotatably hold the fixing belt 310 are provided at both ends of the fixing belt 310 in the width direction. There is a risk that the energy saving performance will decrease due to the high temperature of the flange member, and that the flange member will be deformed due to heat. For this reason, it is desirable that the flange member is not brought into contact with the curved portion 352 in the configuration including the flange member.

Although the present invention has been described above based on the embodiments, it is needless to say that the present invention is not limited to the above embodiments and can be variously modified within the scope of the technical idea described in the claims. . For example, in the above-described embodiment, the uneven portion 351 is composed of the rib-shaped convex portion 351a and the concave portion 351b. may In addition to the PTC element, other resistance heating elements such as a ceramic heater can also be used as the resistance heating elements of the above embodiments. Also, the number of PTC elements may be less than six or more than seven. Furthermore, a configuration in which the PTC elements are arranged in a plurality of rows in the lateral direction of the substrate 350 is also possible.

HN: Heating nip N: Transfer nip SN: Fixing nip L: Laser light P: Paper TM: Transfer means G: Lubricant P: Paper
1K, 1Y, 1M, 1C: Process unit 2K, 2Y, 2M, 2C: Image carrier
3K, 3Y, 3M, 3C: Drum cleaning device 4K, 4Y, 4M, 4C: Charging device
5K, 5Y, 5M, 5C: Developing device (image forming unit) 6K, 6Y, 6M, 6C: Toner bottle 7: Exposure device 7a: Mirror 8: Transfer cover 10: Powder container 15: Transfer device 16: Intermediate transfer Belt 17: driven roller 18: drive roller
19K, 19Y, 19M, 19C: primary transfer roller 20: secondary transfer roller 21: belt cleaning device 31: registration sensor 32: paper feed path 33: post-transfer transport path 35: post-fixing transport path 36: paper discharge path 37: Discharge roller pair 41: Reverse transport path 42: Switching member 42a: Swing shaft 43: Reverse transport roller pair 44: Discharge tray 45: Paper feed roller 46: Tray 60: Paper feed roller 100: Image forming apparatus 200: Paper Feeding Device 210: Roller Pair 220: Feeding Roller 230: Separation Roller 240: Conveying Roller 250: Registration Roller Pair 300: Fixing Device 310: Fixing Belt 320: Pressure Roller 321: Iron Core Metal 322: Elastic Layer 323: Release Mold layer 330, 333: stay 331: auxiliary stay 332: nip forming member 334: pressure belt 340: heater folder 340a, 340b: rotation guide 350: heater substrate 350a: substrate main body 350b: insulating glass 350c: insulating protective layer 351: uneven portion 351a: convex portion 351b: concave portion 352: curvature portion 353: entrance side rotation guide 360: heat generating member 360a, 360b: feeder line 360c, 360d: electrode 361 to 366: PTC element 369a to 369c: feeder line 370: Insulating layer 390: pressing roller

JP 2004-184814 A JP 2009-047750 A JP 2017-207535 A JP-A-7-271219 JP-A-8-234602

Claims (7)

A flexible sleeve-shaped rotating member, a heating element sliding on the inner periphery of the rotating member, and a portion facing the heating element with the rotating member sandwiched therebetween are pressed against each other to separate the rotating member and the fixing nip. and a pressure member formed thereon, wherein the heating body is made of metal or heat-resistant resin, and the heating body is made of metal or heat-resistant resin. a resistance heating element formed on a base material made of metal, and an uneven portion is provided upstream of the resistance heating element on the sliding surface of the base material with the rotating member, and the uneven portion of the A fixing device comprising: an arc-shaped rotation guide having a curvature in the rotation direction of the rotating member is formed on the upstream side by an extension of the base material. 2. The fixing device according to claim 1, wherein the uneven portion is arranged on the upstream side of the fixing nip in the rotation direction. 3. The fixing device according to claim 1, wherein the uneven portion has a substantially uniform uneven shape in a direction perpendicular to the rotating direction of the rotating member. 3. The fixing device according to claim 1, wherein the uneven portion has a concave portion and a convex portion extending in a direction parallel to the longitudinal direction of the heating member. 5. The fixing device according to any one of claims 1 to 4, wherein the heating element has a plurality of resistance heating elements arranged at regular intervals in the longitudinal direction of the base material. 6. The fixing device according to any one of claims 1 to 5, wherein a lubricant is held in the uneven portion. An image forming apparatus comprising the fixing device according to any one of claims 1 to 6.

Images