EP3699690A1

EP3699690A1 - Heating device, fixing device, and image forming apparatus

Info

Publication number: EP3699690A1
Application number: EP20157559.4A
Authority: EP
Inventors: Hiroshi Yoshinaga
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2019-02-20
Filing date: 2020-02-17
Publication date: 2020-08-26
Also published as: JP2020134717A

Abstract

A heating device (300) includes an endless rotating member (310), a nip formation member (380) disposed inside a loop of the rotating member (310), a heater (361) disposed inside the loop of the rotating member (310) to emit radiant heat, and an opposite member (320) disposed opposite the rotating member (310) to sandwich the rotating member (310) between the nip formation member (380) and the opposite member (320) to form a nip through which a sheet to be heated passes. The heater (361) includes a reflection surface (362) on a surface of the heater (361) to reflect radiant heat, which is not radiated to the nip formation member (380) from the heater (361), toward the nip formation member (380).

Description

BACKGROUND

Technical Field

Embodiments of the present disclosure generally relate to a heating device using a heat source such as a halogen heater, a fixing device, and an image forming apparatus. In particular, the embodiments of the present disclosure relate to a heating device, a fixing device for fixing a toner image on a recording medium with the heating device, and an image forming apparatus for forming an image on a recording medium with the fixing device.

Description of the Related Art

Electrophotographic image forming apparatuses use various types of fixing devices. In one type of fixing devices, a halogen heater heats a thin fixing belt having a low thermal capacity. For example, JP-6164014-B ( JP-2015-69094-A ) discloses such a fixing device. This type of fixing device includes an endless fixing belt, a nip formation member inside a loop of the fixing belt, and a pressure roller outside the fixing belt, and the fixing belt is sandwiched between the nip formation member and the pressure roller.
The halogen heater inside the loop of the fixing belt heats the nip formation member, and the nip formation member heats the fixing belt. The nip formation member is supported by a metal stay having a channel-shaped cross section. A reflection member is disposed inside the stay to prevent overheating of the stay and improve thermal efficiency.
Since the halogen heater radiates heat in all directions in the range of 0 to 360 degrees, in the fixing device disclosed in JP-6164014-B ( JP-2015-69094-A ), the reflection member is indispensable to protect peripheral members that should not be heated, such as stays, from the radiant heat and improve thermal efficiency. However, disposing the reflection member increases the weight and size of the fixing device, and increases the cost because the assembly process of the reflection member is also required. Additionally, a certain distance from the halogen heater to the reflection member causes problems in terms of thermal efficiency and energy saving.

SUMMARY

In view of the foregoing, objects of the present disclosure are to improve the thermal efficiency and energy saving of the fixing device and reduce the weight, the size, and the cost of the fixing device.
It is a general object of the present disclosure to provide an improved and useful heating device in which the above-mentioned disadvantages are eliminated. In order to achieve the above-mentioned object, there is provided a heating device according to claim 1. Advantageous embodiments are defined by the dependent claims.
Advantageously, the heating device includes an endless rotating member, a nip formation member disposed inside a loop of the rotating member, a heater disposed inside the loop of the rotating member to emit radiant heat, and an opposite member disposed opposite the rotating member to sandwich the rotating member between the nip formation member and the opposite member to form a nip through which a sheet to be heated passes. The heater includes a reflection surface on a surface of the heater to reflect radiant heat, which is not radiated to the nip formation member from the heater, toward the nip formation member.
According to the present disclosure, since the reflection surface disposed on the surface of the heater reflects radiant heat to the nip formation member other than radiant heat directly radiated to the nip formation member, a reflector may not be disposed around the heater, which can reduce the weight, the size, and the cost of the heating device. In addition, the radiation area of the radiant heat limited to the nip formation member can improve the thermal efficiency and the energy saving.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram to describe an image forming apparatus according to an embodiment of the present disclosure;
FIG. 2 is a vertical cross-sectional view of a fixing device according to a first embodiment that is used in the image forming apparatus, as viewed from a lateral side of the fixing device;
FIG. 3 is a perspective view of the fixing device with the vertical cross-sectional view of the fixing device in FIG. 2;
FIG. 4 is a vertical cross-sectional view of a fixing device according to a second embodiment that has a reflection surface to limit a radiation area, as viewed from a lateral side of the fixing device;
FIG. 5 is a vertical cross-sectional view of a fixing device according to a third embodiment that has a reflection surface to limit a radiation area, as viewed from a lateral side of the fixing device;
FIG. 6 is a vertical cross-sectional view of a fixing device according to a fourth embodiment that has a reflection surface to limit a radiation area, as viewed from a lateral side of the fixing device;
FIG. 7 is a vertical cross-sectional view of a fixing device according to a fifth embodiment that has a reflection surface to limit a radiation area, as viewed from a lateral side of the fixing device;
FIG. 8A is a diagram illustrating an intensity distribution of radiant heat of a halogen heater; and
FIG. 8B is a diagram illustrating a radiation angle of radiant heat of the halogen heater.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.

DETAILED DESCRIPTION OF EMBODIMENTS

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.
Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable.
Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings illustrating the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below.
With reference to drawings, a description is given of a fixing device according to an embodiment of the present disclosure and an image forming apparatus such as a laser printer using the fixing device. The laser printer is just an example of the image forming apparatus, and thus the image forming apparatus is not limited to the laser printer.
That is, the image forming apparatus can be a copier, a facsimile machine, a printer, a plotter, and a multifunction peripheral having at least two of copying, printing, facsimile transmission, plotting, and scanning capabilities; or an inkjet recording apparatus.
It is to be understood that an identical or similar reference character is given to identical or corresponding parts throughout the drawings, and redundant descriptions are omitted or simplified below. The dimensions, material, shape, and relative position in a description for each constituent component are examples. Unless otherwise specifically described, the scope of the present disclosure is not limited to those.
Although a "recording medium" is described as a "sheet" in the following embodiments, the "recording medium" is not limited to the sheet. Examples of the "recording medium" include not only the sheet but also an overhead projector (OHP) transparency, a fabric, a metallic sheet, a plastic film, and a prepreg sheet including carbon fibers previously impregnated with resin.
Examples of the "recording medium" include all mediums to which developer or ink can adhere, and so-called recording paper and recording sheets. Examples of the "sheet" include thick paper, a postcard, an envelope, thin paper, coated paper (e.g., coat paper and art paper), and tracing paper, in addition to plain paper.
The term "image forming" indicates an action for providing (i.e., printing) not only an image having a meaning, such as texts and figures on a recording medium, but also an image having no meaning, such as patterns on a recording medium.
A configuration of the image forming apparatus according to an embodiment is described below.
FIG. 1 is an explanatory diagram to describe the laser printer as an example of the image forming apparatus 100 including the fixing device 300 according to the embodiment of the present disclosure. The image forming apparatus 100 includes an image bearer 2 such as a photoconductor drum and a photoconductor cleaner 3.
The image forming apparatus 100 further includes a charging device 4 as a charger that uniformly charges the surface of the image bearer, a developing device 5 as a developing unit that renders visible an electrostatic latent image on the image bearer, a transfer device TM disposed under the image bearer 2, a discharger, and the like.
An exposure device 7 is disposed above the image bearer 2. The exposure device 7 performs writing and scanning based on image data, namely, irradiates the image bearer 2 with laser light Lb emitted by a laser diode based on image data and reflected by a mirror 7a.
A sheet feeder 50 including a tray loaded with sheets P is disposed below the image forming apparatus 100. The sheet feeder 50 is configured as a recording-medium supply device and can house a sheaf of many recording media sheets P. The sheet feeder 50 is configured as one unit together with a sheet feeding roller 60 as a conveyor for the sheets P.
Downstream from the sheet feeding roller 60, a registration roller pair 250 as a separation and conveyance means is disposed. The registration roller pair 250 temporarily stops the sheet P fed from the sheet feeder 50. Temporarily stopping the sheet P causes slack on the leading-edge side of the sheet P and corrects a skew of the sheet P.
The registration roller pair 250 sends the sheet P that contacts the registration roller pair 250 and has the slack on the leading-edge side of the sheet P toward a transfer nip of the transfer device TM at a timing to suitably transfer a toner image on the image bearer 2 onto the sheet P. A bias applied at the transfer nip N electrostatically transfers the toner image formed on the image bearer 2 onto the sent sheet P at a desired transfer position.
The fixing device 300 is disposed downstream from the transfer nip N. The fixing device 300 includes a fixing belt 310 as a rotating member that includes a halogen heater 361 as a heater that emits radiant heat, which will be described later, and a pressure roller 320 as an opposite member that rotates while contacting the fixing belt 310 at a predetermined pressure.
Next, operation of the image forming apparatus 100 according to the present embodiment is described below.
The sheet feeding roller 60 rotates in response to a sheet feeding signal from a controller of the image forming apparatus 100. The sheet feeding roller 60 separates the uppermost sheet from a sheaf of sheets P loaded in the sheet feeder 50 and sends the uppermost sheet out to a sheet feeding path.
After the sheet feeding roller 60 sends the sheet P, when the leading edge of the sheet P reaches a nip of the registration roller pair 250, the sheet P forms slack and temporarily stops. The registration roller pair 250 corrects the front-end skew of the sheet P and rotates in synchronization with an optimum timing to transfer a toner image on the image bearer 2 onto the sheet P.
The charging device 4 uniformly charges the surface of the image bearer 2 to high potential. The exposure device 7 irradiates the surface of the image bearer 2 with the laser light Lb based on the image data and reflected by the mirror 7a.
The surface of the image bearer 2 irradiated with the laser light Lb has an electrostatic latent image due to a drop in the potential of the irradiated portion. The developing device 5 includes a developer bearer 5a bearing a developer including toner and transfers unused black toner supplied from the toner bottle to the surface portion of the image bearer 2 having the electrostatic latent image, through the developer bearer.
The image bearer 2 to which the toner has been transferred forms (develops) a black toner image on the surface of the image bearer 2. The transfer device TM transfers the toner image formed on the image bearer 2 onto the sheet P.
A cleaning blade 3a in the photoconductor cleaner 3 removes the residual toner adhering to the surface of the image bearer 2 after a transfer process. The removed residual toner is collected to a waste toner container.
The sheet P as a heated sheet bearing the toner image is conveyed to the fixing device 300. The sheet P conveyed to the fixing device 300 is sandwiched by the fixing belt 310 and the pressure roller 320. Then, heating and pressing fixes the unfixed toner image onto the sheet P. The sheet P fixed the toner image is sent out from the fixing device 300.
Next, a description is given of the fixing device 300 according to the present embodiment of the present disclosure. As illustrated in FIGS. 2 and 3, the fixing device 300 according to a first embodiment includes a thin fixing belt 310 having low thermal capacity and a pressure roller 320.
In order to decrease the thermal capacity of the fixing belt 310, the fixing belt 310 has a total thickness not greater than 1 mm and a loop diameter in a range of from 20 mm to 40 mm. In order to further decrease the thermal capacity, the fixing belt 310 may preferably have a total thickness not greater than 0.2 mm, and more preferably, not greater than 0.16 mm. The loop diameter of the fixing belt 310 is not greater than 30 mm.
The fixing belt 310 may include an inner base layer having a thickness of 20 to 50 µm, an outer release layer having a thickness of 10 to 50 µm, and an intermediate elastic layer having a thickness of 100 to 300 µm. The inner base layer may be made of metal such as nickel or stainless steel (SUS) or resin such as polyimide to reduce the thermal capacity. The inner circumferential surface of the fixing belt 310 may be coated with polyimide or polytetrafluoroethylene (PTFE) as a slide layer.
The outer release layer enhances durability of the fixing belt 310, facilitates separation of the sheet P from the fixing belt 310, and may be made of fluororesin such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like.
The intermediate elastic layer absorbs slight surface asperities of the fixing belt 310 and may be made of rubber such as silicone rubber, silicone rubber foam, or fluororubber. While the fixing belt 310 and the pressure roller 320 press the unfixed toner image against the sheet P to fix the toner image onto the sheet P, the elastic layer having a thickness of about 100 micrometers elastically deforms to absorb slight surface asperities of the fixing belt 310, preventing variation in gloss of the toner image on the sheet P.
The pressure roller 320 having, for example, an outer diameter of 25 mm, includes a solid iron cored bar 321, an elastic layer 322 on the surface of the cored bar 321, and a release layer 323 formed on the outside of the elastic layer 322.
The elastic layer 322 may be made of silicone rubber, solid rubber, or sponge rubber foam and have, for example, a thickness of 3.5 mm. Using the sponge rubber for the elastic layer 322 improves thermal insulation and decreases an amount of heat drawn from the fixing belt 310.
Preferably, the release layer 323 is formed by a fluororesin layer having, for example, a thickness of approximately 40 µm on the surface of the elastic layer 322 to improve releasability. A biasing member presses the pressure roller 320 against the fixing belt 310.
FIGS. 2 and 3 illustrate the pressure roller 320 as a solid roller. Alternatively, the pressure roller 320 may be a hollow roller. In this case, a heater such as a halogen heater may be disposed inside the hollow roller.
A description is given of structures inside a loop of the fixing belt 310.
A stay 330 as a support member and a nip formation member 380 extends axially inside the loop of the fixing belt 310. The stay 330 is formed of a metal channel material having a U-shaped cross section, and both ends in the longitudinal direction are supported by both side plates of the fixing device 300.
The material of the stay 330 is preferably an iron-based metal such as stainless steel (SUS) or Steel Electrolytic Cold Commercial (SECC) that is electrogalvanized sheet steel ensure rigidity. Using such an iron-based material causes the stay 330 to reliably receive the pressing force of the pressure roller 320 acting on the nip formation member 380 and stably form a nip SN.
The nip formation member 380 transfers heat in an axial direction that is the width direction of the fixing belt 310 to uniformize temperature of the fixing belt 310 in the width direction. The nip formation member 380 is made of a thin plate member having high thermal conductivity such as copper (398 W / mK), aluminum (236 W / mK) or silver to smoothly transfer the heat in the width direction. In consideration of cost, processing, and the like, the nip formation member 380 is preferably made of a thin copper plate.
In order to improve the abrasion resistance and the slidability of the nip formation surface, the nip formation surface of the nip formation member 380 may be treated with alumite or coated with fluororesin material. Additionally, a lubricant such as a fluorine-based grease may be applied to the nip formation surface to ensure slidability over time.
In FIGS. 2 and 3, the nip formation surface of the nip formation member 380 is planar. Alternatively, the nip formation surface may define a recess or other shape. A recessed nip formation surface directs a leading edge of the sheet P toward the pressure roller 320 as the sheet P is ejected from the fixing nip SN, facilitating separation of the sheet P from the fixing belt 310 and preventing occurrence of jamming of the sheet P between the fixing belt 310 and the pressure roller 320.
A separator may be disposed downstream from the fixing device 300 in a sheet conveyance direction to separate the sheet P from the fixing belt 310. A pressurization assembly may be disposed to press the pressure roller 320 against the fixing belt 310 and release pressure exerted by the pressure roller 320 to the fixing belt 310.
Specifically, as illustrated in FIGS. 2 and 3, the stay 330 has an upstream side wall 330a, a ceiling wall 330b, and a downstream side wall 330c. The ceiling wall 330b couples the upper end of the upstream side wall 330a and the upper end of the downstream side wall 330c. Both ends of the nip formation member 380 in a short-side direction that is a transverse direction in FIGS. 2 and 3 are fixed and supported on the lower end of the opening formed by the stay 330, that is, the lower end of the upstream side wall 330a and the lower end of the downstream side wall 330c.
Therefore, the stay 330 forms a closed space, that is, the space in which the upper, lower, left and right sides are closed, inside the stay 330. Supporting the nip formation member 380 at two lower ends of the upstream side wall 330a and the downstream side wall 330c of the stay 330 does not increase the thermal capacity of the nip formation member 380. Therefore, the above-described configuration can improve heat transfer efficiency, which can reduce electric power consumption.
The halogen heater 361 as the heater is arranged axially in the closed space inside the stay 330. Both side plates of the fixing device 300 support both ends of the halogen heater 361. The radiant heat emitted by the halogen heater 361 heats the nip formation member 380, and the nip formation member 380 heats the fixing belt 310.
A controller controls the halogen heater 361, for example, based on the surface temperature of the fixing belt 310 that is detected by the temperature sensor disposed opposite the outer circumferential surface of the fixing belt 310 and upstream from the fixing nip in the rotation direction of the fixing belt 310. The controller controls power supplied to the halogen heater 361 so that the temperature of the fixing belt 310 that is referred to as a fixing temperature becomes a desired temperature.
Next, a reflection surface 362 of the halogen heater 361 in the present embodiment is described.
The reflection surface 362 is formed on the upper half of the surface of the halogen heater 361 as illustrated in FIG. 3. This reflection surface 362 is disposed on the surface of a tubular bulb 361a of the halogen heater 361. The bulb 361a is configured by a cylindrical quartz tube that covers the filament 361b of the halogen heater 361.
The halogen heater 361 having the reflection surface 362 in the present embodiment does not need setting the reflector as a separate member as in the prior art and can reduce the size and the cost of the fixing device. Reducing the size of the fixing device 300 decreases the thermal capacity of the fixing device 300 and, therefore, can shorten a warming-up time required for the nip SN to reach the target temperature.
The reflection surface 362 is formed by fixing a heat-resistant reflection material on the upper half of the surface of the bulb 361a. To fix the reflection material, various methods, such as vapor deposition, adhesion, and application, may be adopted. As the reflection material, various kinds of reflection materials having heat resistance, such as ceramics and metals (gold, silver, copper, aluminum), may be used alone or in combination, that is, in the form of mixture. For example, a molybdenum alloy foil or an aluminum foil may be fixed on the upper half of the surface of the bulb 361a.
Use of the halogen heater 361 having the reflection surface 362 increases radiant heat radiated downward in FIGS. 2 and 3, that is, in a direction from the reflection surface 362 to an opening of the stay 330 and limits the heat quantity distribution of the radiant heat in a circumferential direction.
Conventionally, the fixing device includes the reflector as the separate member around the halogen heater 361. To downsize the fixing device, such a configuration needs setting the reflector close to the halogen heater 361. Setting the reflector close to the halogen heater 361 causes disadvantages, that is, the discoloration of the reflector due to high temperature and decrease of the reflectance of the reflector.
In the present embodiment, the heat-resistant reflection surface formed on the bulb 361a of the halogen heater 361 does not discolor even under the high temperature and does not need setting the reflector. Therefore, the present embodiment allows reducing the size of the fixing device without causing the deterioration of energy-saving effect.
Since the reflection surface 362 can limit a radiation area of the radiant heat of the halogen heater 361 to the nip formation member 380, the temperature rise of surrounding members such as the stay 330 can be reduced. The radiation area is an area on a surface to be heated that receives energy of 50% or more, preferably 75% or more, of the largest energy received on the surface to be heated.
The reflection surface 362 is formed on the upper half of the surface of the halogen heater 361, that is, a range of 180° on the upper surface of the halogen heater 361. That is, the reflection surface 362 is formed on the outer peripheral surface of the upper half bulb 361a from the horizontal line passing through the center of the filament 361b of the halogen heater 361. The above-described configuration can narrow the radiation area R1 on the nip formation member 380 formed by the radiant heat with which the halogen heater 361 irradiates the nip formation member 380 down to the inside of the 180° downward radiation angle of the halogen heater 361. The above-described formation range of the reflection surface 362 (a range of 180° on the upper surface of the reflection surface 362) may be changed based on the distance (height) from the nip formation member 380 to the halogen heater 361, the width of the nip formation member 380 in the short-side direction, the width of the nip SN, and the like.
The radiation area R1 is within the width of the nip formation member 380 in the short-side direction, and the upstream end R1a and the downstream end R1b of the radiation area R1 on the nip formation member 380 are located between the upstream side wall 330a and the downstream side wall 330c of the stay 330. Optimizing the distance between the halogen heater 361 and the nip formation member 380 determines the positions of the upstream end R1a and the downstream end R1b of the radiation area R1.
The fixing device 300 is configured as described above. In FIG. 2, when the sheet P is conveyed in a direction indicated by a horizontal arrow and passes through the fixing nip SN, the sheet P is heated between the fixing belt 310 and the pressure roller 320 so that the toner image is fixed to the sheet P.
At this time, the radiant heat from the halogen heater 361 heats the fixing belt 310 through the nip formation member 380. At this time, the reflection surface 362 formed on the bulb 361a of the halogen heater 361 can focus all the radiant heat of the halogen heater 361 on the nip formation member 380 and efficiently heat the nip formation member 380.
A description is provided of the fixing device 300 according to a second embodiment.
FIG. 4 illustrates the fixing device 300 according to the second embodiment. In the second embodiment, a radiation area R2 is formed on the nip formation member 380 by the radiant heat with which the halogen heater 361 irradiates the nip formation member 380. An upstream end R2a of the radiation area R2 in the sheet conveyance direction, which is in an entrance side of the nip SN, is at a corner that is an upstream contact point at which the inner side surface of the upstream side wall 330a of the stay 330 contacts the upper surface of the nip formation member 380.
Additionally, A downstream end R2b of the radiation area R2 in the sheet conveyance direction, which is in an exit side of the nip SN, is at a corner that is a downstream contact point at which the inner side surface of the downstream side wall 330c of the stay 330 contacts the upper surface of the nip formation member 380. Setting the radiation area R2 as described above maximizes an area of a region radiated by the halogen heater 361 on the upper surface of the nip formation member 380 without unnecessarily heating the stay 330. Therefore, the nip formation member 380 can be efficiently heated.
A description is provided of the fixing device 300 according to a third embodiment.
FIG. 5 illustrates the fixing device 300 according to the third embodiment. In the third embodiment, a radiation area R3 is formed on the nip formation member 380 by the radiant heat with which the halogen heater 361 irradiates the nip formation member 380. An upstream end R3a of the radiation area R2 in the sheet conveyance direction, which is in the entrance side of the nip SN, is at an upstream point on the nip formation member 380 corresponding to an entrance of the nip SN, and a downstream end R3b of the radiation area R3 in the sheet conveyance direction, which is the exit side of the nip SN, is at a downstream point on the nip formation member 380 corresponding to an exit of the nip SN.
That is, a width of the radiation area R3 is the same as a width of the nip SN, and the stay 330 is not irradiated with the radiant heat. Setting the radiation area R3 as illustrated in FIG. 5 avoids unnecessarily heating the stay 330. Therefore, the nip SN can be efficiently heated.
In the fixing device 300, the portion to be heated most is the nip SN, and it is more preferable that the nip SN is irradiated with all the radiant heat limited by the radiation area R3 of the halogen heater 361 with the reflection surface. Even with such a configuration, since the nip formation member 380 is made of a material having high heat conductivity such as a metal plate, fixing properties are not affected.
Since the configuration illustrated in FIG. 5 can more efficiently heat the nip SN, the configuration can further improve the energy-saving effect in the fixing device 300. Also, in this case, optimizing the distance between the halogen heater 361 and the nip formation member 380 determines the above-described radiant area R3.
A description is provided of the fixing device 300 according to a fourth embodiment.
FIG. 6 illustrates the fixing device 300 according to the fourth embodiment. In the fourth embodiment, a radiation area R4 is formed on the nip formation member 380 by the radiant heat with which the halogen heater 361 irradiates the nip formation member 380 to improve the fixing properties.
As in FIG. 4, an upstream end R4a of the radiation area R4 in the sheet conveyance direction, which is in the entrance side of the nip SN, is at a corner that is the upstream contact point at which the inner side surface of the upstream side wall 330a of the stay 330 contacts the upper surface of the nip formation member 380. Additionally, as in FIG. 5, a downstream end R4b of the radiation area R4 in the sheet conveyance direction, which is in the exit side of the nip SN, is at a point on the nip formation member 380 corresponding to the exit of the nip SN. That is, in FIG. 6, a direction of the reflection surface 362 of the halogen heater 361 is slightly inclined toward the entrance of the nip SN.
Since it takes time to conduct heat from the nip formation member 380 to the fixing belt 310, preferably, an upstream portion of the nip SN is heated earlier. Therefore, in FIG. 6, the upstream end R4a in the entrance side of the nip SN is set at the inner side of the upstream side wall 330a that is a limit position in the upstream side.
On the other hand, the downstream end R4b in the exit side of the nip is set at the exit of the nip SN. This is because setting the downstream end R4b downstream from the exit of the nip SN does not contribute to heating the nip SN, that is, unnecessarily enlarges heating area and deteriorates the thermal efficiency.
Optimizing the distance between the halogen heater 361 and the nip formation member 380 and optimizing the direction (angle) of the reflection surface 362 of the halogen heater 361 to rotate the reflection surface 362 to upstream side of the nip SN can set the radiation area R4 in FIG. 6. Setting the radiation area R4 as described above can prevent unnecessary heating of the stay 330 and efficiently heat the nip SN.
The direction (angle) of the reflection surface 362 of the halogen heater 361 may be different in the longitudinal direction of the halogen heater 361. For example, the direction of the reflection surface 362 may be inclined toward the entrance side of the nip SN in both end portions of the halogen heater 361 in the longitudinal direction of the halogen heater 361 as illustrated in FIG. 6 and may be directed directly downward in the center portion of the halogen heater 361 in the longitudinal direction as illustrated in FIG. 4 or FIG. 5. The above-described configuration can avoid or prevent decrease of temperature in end portions of the fixing belt 310.
A description is provided of a fixing device 300 according to a fifth embodiment.
As illustrated in FIG. 7, the fixing device 300 according to the fifth embodiment does not include the stay 330. Bent portions 381 and 382 that are bent at right angles to the opposite side with respect to the nip SN at both ends of the nip formation member 380 in the short-side direction that is a transverse direction in FIG. 7 ensures bending stiffness in the longitudinal direction of the nip formation member 380.
In addition, flanges disposed on both sides of the fixing device 300 support both ends in the longitudinal direction of the nip formation member 380. Eliminating the stay 330 can further reduce the size and weight of the fixing device 300.
In FIG. 7, a radiation area R5 formed on the nip formation member 380 by the radiant heat with which the halogen heater 361 irradiates the nip formation member 380 includes the entire upper surface (with a width X) of the nip formation member 380 between the bent portions 381 and 382. Therefore, the nip SN can be efficiently heated.
An intensity distribution of the radiant heat of the halogen heater 361 is described.
FIGS. 8A and 8B illustrate an example of a relationship between the reflection surface 362 of the halogen heater 361 and a radiation angle and a relationship between radiation angles and the radiant heat intensities, that is, an intensity distribution of the radiant heat. FIG. 8B includes a cross-sectional view of the halogen heater 361 with the reflection surface 362. The reflection surface 362 is provided on the upper side of the halogen heater 361, that is, from 90° to 270° in a circumferential direction, and the radiant heat is emitted from the lower side of the halogen heater 361, that is, from 270° to 0° to 90° in the circumferential direction.
As illustrated in FIG. 8A, the intensity distribution of the radiant heat of the halogen heater 361 is set in a lower range, that is, from 300° to 0° to 60° in the circumferential direction, which is narrower than the radiation angle as illustrated in FIG. 8B. Preferably, the narrower range of the intensity distribution than the radiation angle, that is, the radiation range determines a positional relationship between the nip formation member 380 and the halogen heater 361 with the reflection surface 362. For example, the width X of the entire upper surface of the nip formation member 380 illustrated in FIG. 7 may be equal to a width X in which the intensity of the radiant heat is high in FIG. 8A.
As described above, in the embodiments of the present disclosure, since the reflection surface 362 can freely set the radiation area of the halogen heater 361, there is no need to provide a reflection member around the halogen heater 361 as in the related art, which can reduce the size and cost of the fixing device 300.
Including such a fixing device 300 in the image forming apparatus 100 can reduce the size and cost of the image forming apparatus. In addition, forming the reflection surface 362 improves the thermal efficiency, which can shorten a warm-up time and save energy.
The present disclosure has been described above on the basis of the embodiments, but the present disclosure is not limited to the embodiments. Needless to say, various alterations can be made in the scope of the technical idea described in the scope of the claims. For example, although one halogen heater 361 is used in the above-described embodiments, of course, two or three or more halogen heaters may be used.
The plurality of halogen heaters may form a plurality of heating areas each of which corresponds to a sheet size in the longitudinal direction of the heater orthogonal to the sheet conveyance direction. The above-described structure can prevent overheating at both end portions of the fixing device when the fixing device fixes sheets smaller than the heater in the longitudinal direction, reduce thermal damage at the both end portions, avoid unnecessary heating, and improve heat efficiency.
Heating devices according to the embodiments of the present disclosure are applicable to not only the fixing device of the image forming apparatus but also a dryer installed in an inkjet printer.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.

Claims

A heating device (300) comprising:
a rotating member (310) in an endless form;

a nip formation member (380) disposed inside a loop of the rotating member (310);

a heater (361) disposed inside the loop of the rotating member (310) to emit radiant heat,

the heater (361) including a reflection surface (362) on a surface of the heater (361) to reflect radiant heat, which is not radiated to the nip formation member (380) from the heater (361), toward the nip formation member (380); and

an opposite member (320) disposed opposite the rotating member (310) to sandwich the rotating member (310) between the nip formation member (380) and the opposite member (320) to form a nip through which a sheet to be heated passes.
The heating device (300) according to claim 1,
wherein a width of a radiation area on the nip formation member (380) which the heater (361) irradiates with the radiant heat is equal to or less than a width of the nip formation member (380) in a direction in which the sheet to be heated passes through the nip.
The heating device (300) according to claim 1, further comprising a support member (330) disposed inside the loop of the rotating member (310) to support both ends of the nip formation member (380) in a direction in which the sheet to be heated passes through the nip,
wherein a radiation area on the nip formation member (380) which the heater (361) irradiates with the radiant heat is between contact points at which the support member (330) contacts both ends of the nip formation member (380) in the direction in which the sheet to be heated passes through the nip.
The heating device (300) according to claim 3,
wherein the radiation area on the nip formation member (380) which the heater (361) irradiates with the radiant heat is, in the direction in which the sheet to be heated passes through the nip, from an upstream contact point, at which the support member (330) contacts the nip formation member (380), to a point on the nip formation member (380) corresponding to a downstream end of the nip.
The heating device (300) according to claim 1,
wherein a width of a radiation area on the nip formation member (380) which the heater (361) irradiates with the radiant heat is equal to a width of the nip.
A fixing device (300) comprising the heating device (300) according to any one of claims 1 to 5,
wherein the sheet to be heated passes through the nip with a toner image being borne on the sheet.
An image forming apparatus (100) comprising the fixing device (300) according to claim 6.