Heater, fixing device, and image forming apparatus

A heater is installable in a fixing device having a fixing nip through which a recording medium is conveyed. The heater includes a base including a downstream portion in a recording medium conveyance direction. A heat generator is mounted on the base. A projection is disposed separately from the base and shifted from the heat generator. The projection is disposed opposite the downstream portion of the base. The projection projects toward the fixing nip in a state in which the heater is installed in the fixing device.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-042179, filed on Mar. 8, 2019, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

Exemplary aspects of the present disclosure relate to a heater, a fixing device, and an image forming apparatus.

Discussion of the Background Art

Related-art image forming apparatuses, such as copiers, facsimile machines, printers, and multifunction peripherals (MFP) having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data by electrophotography.

Such image forming apparatuses include a fixing device including a fixing belt serving as a fixing member or a fixing rotator and a heater that heats the fixing belt. The heater heats the fixing belt to a fixing temperature. Thereafter, while a recording medium such as a sheet is conveyed through a fixing nip formed between the fixing belt and a pressure roller, the fixing belt and the pressure roller fix an unfixed toner image on the recording medium under heat and pressure at the fixing nip.

A projection that projects toward the pressure roller is disposed at an exit of the fixing nip or disposed downstream from the fixing nip in a recording medium conveyance direction. The projection improves fixing of the toner image on the recording medium at a position downstream from the fixing nip in the recording medium conveyance direction and facilitates separation of the recording medium from the fixing belt after fixing of the toner image on the recording medium.

SUMMARY

This specification describes below an improved heater installable in a fixing device having a fixing nip through which a recording medium is conveyed. In one embodiment, the heater includes a base including a downstream portion in a recording medium conveyance direction. A heat generator is mounted on the base. A projection is disposed separately from the base and shifted from the heat generator. The projection is disposed opposite the downstream portion of the base. The projection projects toward the fixing nip in a state in which the heater is installed in the fixing device.

This specification further describes an improved fixing device. In one embodiment, the fixing device includes a fixing rotator that is hollow and endless. The fixing rotator rotates. A pressure rotator presses against the fixing rotator to form a fixing nip between the fixing rotator and the pressure rotator, through which a recording medium bearing an image is conveyed. The heater described above contacts an inner circumferential surface of the fixing rotator.

This specification further describes an improved image forming apparatus. In one embodiment, the image forming apparatus includes an image bearer that bears an image and the fixing device described above that fixes the image on a recording medium.

DETAILED DESCRIPTION

Referring to drawings, a description is provided of embodiments of the present disclosure. In the drawings, identical reference numerals are assigned to identical elements and equivalents and redundant descriptions of the identical elements and the equivalents are summarized or omitted properly.

Referring toFIG. 1, a description is provided of a construction of an image forming apparatus1.

FIG. 1illustrates the image forming apparatus1that is a monochrome image forming apparatus and includes a photoconductive drum10serving as an image bearer that bears an image (e.g., a toner image). The photoconductive drum10is a drum-shaped rotator that bears toner as a developer on a surface thereof. The photoconductive drum10rotates in a rotation direction indicated with an arrow inFIG. 1. The photoconductive drum10is surrounded by a charging roller11, a developing device12, a cleaning blade13, and the like. The charging roller11uniformly charges the surface of the photoconductive drum10. The developing device12includes a developing roller19and the like that supply toner onto the surface of the photoconductive drum10, forming a toner image thereon. The cleaning blade13cleans the surface of the photoconductive drum10.

An exposure device is disposed above a process unit. The exposure device emits a laser beam Lb according to image data. The laser beam Lb irradiates the surface of the photoconductive drum10through a mirror14.

A transfer device15including a transfer charger is disposed opposite the photoconductive drum10. The transfer device15transfers the toner image formed on the surface of the photoconductive drum10onto a sheet P.

A sheet feeder4is disposed in a lower portion of the image forming apparatus1. The sheet feeder4includes a sheet feeding tray16(e.g., a paper tray) and a sheet feeding roller17. The sheet feeding tray16loads a plurality of sheets P serving as recording media. The sheet feeding roller17conveys the sheet P from the sheet feeding tray16to a conveyance path5. A registration roller18is disposed downstream from the sheet feeding roller17in a sheet conveyance direction.

A fixing device6includes a fixing belt20heated by a heater described below and a pressure roller21that presses against the fixing belt20.

Referring toFIG. 1, a description is provided of a basic image forming operation performed by the image forming apparatus1having the construction described above.

As the image forming operation starts, the charging roller11charges the surface of the photoconductive drum10. The exposure device emits a laser beam Lb according to image data, decreasing the electric potential of an irradiated portion on the surface of the photoconductive drum10, which is irradiated with the laser beam Lb, and forming an electrostatic latent image on the photoconductive drum10. The developing device12supplies toner to the electrostatic latent image formed on the surface of the photoconductive drum10, visualizing the electrostatic latent image as a visible toner image (e.g., a developed image). The cleaning blade13removes toner and the like failed to be transferred onto the sheet P and therefore remained on the photoconductive drum10therefrom.

On the other hand, as the image forming operation starts, in the lower portion of the image forming apparatus1, the sheet feeding roller17of the sheet feeder4starts being driven and rotated, feeding a sheet P of the plurality of sheets P loaded in the sheet feeding tray16to the conveyance path5.

The registration roller18conveys the sheet P sent to the conveyance path5to a transfer portion where the transfer device15is disposed opposite the photoconductive drum10at a time when the toner image formed on the surface of the photoconductive drum10is disposed opposite the sheet P at the transfer portion. The transfer device15applies a transfer bias that transfers the toner image from the photoconductive drum10onto the sheet P.

The sheet P transferred with the toner image is conveyed to the fixing device6where the fixing belt20that is heated and the pressure roller21fix the toner image on the sheet P under heat and pressure. The sheet P fixed with the toner image is separated from the fixing belt20and conveyed by a conveying roller pair disposed downstream from the fixing device6in the sheet conveyance direction. The sheet P bearing the fixed toner image is ejected onto a sheet ejection tray disposed on an exterior of the image forming apparatus1.

A description is provided of a construction of the fixing device6according to a first embodiment of the present disclosure.

As illustrated inFIG. 2, the fixing device6according to this embodiment includes the fixing belt20, the pressure roller21, a heater22, a heater holder23, a stay24, and thermistors25. The fixing belt20is an endless belt serving as a fixing rotator or a fixing member. The pressure roller21serves as a pressure rotator or a pressure member that contacts an outer circumferential surface of the fixing belt20to form a nip, that is, a fixing nip N, between the fixing belt20and the pressure roller21. The heater22serves as a heater or a heating member that heats the fixing belt20. The heater holder23serves as a holder that holds or supports the heater22. The stay24serves as a support that supports the heater holder23. The thermistors25serve as temperature detectors that detect the temperature of the heater22. A heating controller controls power supplied to the heater22based on the temperature of the heater22, that is detected by the thermistors25, thus adjusting the temperature of the fixing belt20to a desired temperature.

A detailed description is now given of a construction of the fixing belt20.

The fixing belt20includes a tubular base that is made of polyimide (PI) and has an outer diameter of 25 mm and a thickness in a range of from 40 micrometers to 120 micrometers, for example. The fixing belt20further includes a release layer serving as an outermost surface layer. The release layer is made of fluororesin, such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) and polytetrafluoroethylene (PTFE), and has a thickness in a range of from 5 micrometers to 50 micrometers to enhance durability of the fixing belt20and facilitate separation of the sheet P and a foreign substance from the fixing belt20. Optionally, an elastic layer that is made of rubber or the like and has a thickness in a range of from 50 micrometers to 500 micrometers may be interposed between the base and the release layer. The base of the fixing belt20may be made of heat resistant resin such as polyetheretherketone (PEEK) or metal such as nickel (Ni) and SUS stainless steel, instead of polyimide. An inner circumferential surface of the fixing belt20may be coated with polyimide, PTFE, or the like to produce a slide layer.

A detailed description is now given of a construction of the pressure roller21.

The pressure roller21has an outer diameter of 25 mm, for example. The pressure roller21includes a cored bar21a, an elastic layer21b, and a release layer21c. The cored bar21ais solid and made of metal such as iron. The elastic layer21bis disposed on a surface of the cored bar21a. The release layer21ccoats an outer surface of the elastic layer21b. The elastic layer21bis made of silicone rubber and has a thickness of 3.5 mm, for example. In order to facilitate separation of the sheet P and the foreign substance from the pressure roller21, the release layer21cthat is made of fluororesin and has a thickness of about 40 micrometers, for example, is preferably disposed on the outer surface of the elastic layer21b.

A biasing member biases the pressure roller21toward the fixing belt20, pressing the pressure roller21against the heater22via the fixing belt20. Thus, the fixing nip N is formed between the fixing belt20and the pressure roller21. A driver drives and rotates the pressure roller21. As the pressure roller21rotates in a rotation direction indicated with an arrow inFIG. 2, the fixing belt20is driven and rotated by the pressure roller21.

A detailed description is now given of a construction of the heater22.

The heater22is a laminated heater that is elongated in a longitudinal direction thereof throughout an entire length of the fixing belt20in a longitudinal direction, that is, an axial direction, of the fixing belt20. The longitudinal direction of the fixing belt20is perpendicular to a plane of paper inFIG. 2and parallel to the longitudinal direction of the heater22and a longitudinal direction of the heater holder23. The heater22includes a base30that is platy, resistive heat generators31serving as heat generators that are disposed on the base30, and a protective layer32that coats the resistive heat generators31. The protective layer32of the heater22contacts the inner circumferential surface of the fixing belt20. Heat generated by the resistive heat generators31is conducted to the fixing belt20through the protective layer32.

A detailed description is now given of a construction of the heater holder23and the stay24.

The heater holder23and the stay24are disposed inside a loop formed by the fixing belt20. The stay24includes a channel made of metal. Both lateral ends of the stay24in a longitudinal direction thereof are supported by side plates of the fixing device6, respectively. Since the stay24supports the heater holder23and the heater22supported by the heater holder23, in a state in which the pressure roller21is pressed against the fixing belt20, the heater22receives pressure from the pressure roller21precisely to form the fixing nip N stably.

Since the heater holder23is subject to high temperatures by heat from the heater22, the heater holder23is preferably made of a heat resistant material. For example, if the heater holder23is made of heat resistant resin having a decreased thermal conductivity, such as liquid crystal polymer (LCP), the heater holder23suppresses conduction of heat thereto from the heater22, facilitating heating of the fixing belt20. In order to decrease a contact area where the heater holder23contacts the heater22and thereby reduce an amount of heat conducted from the heater22to the heater holder23, the heater holder23includes projections23athat contact the base30of the heater22. According to this embodiment, the projections23aof the heater holder23do not contact a part of a back face of the base30, which is opposite the resistive heat generators31mounted on a front face of the base30, that is, a part of the base30, which is susceptible to temperature increase, thus decreasing the amount of heat conducted to the heater holder23further and heating the fixing belt20effectively.

In the fixing device6according to this embodiment, when printing starts, the driver drives and rotates the pressure roller21and the fixing belt20starts rotation in accordance with rotation of the pressure roller21. Additionally, as power is supplied to the resistive heat generators31of the heater22, the heater22heats the fixing belt20. In a state in which the temperature of the fixing belt20reaches a predetermined target temperature (e.g., a fixing temperature), as a sheet P bearing an unfixed toner image is conveyed in a sheet conveyance direction X through the fixing nip N formed between the fixing belt20and the pressure roller21, the fixing belt20and the pressure roller21fix the unfixed toner image on the sheet P under heat and pressure.

A description is provided of the construction of the heater22in more detail.

As constructions of heaters according to the embodiments of the present disclosure, the following describes a construction of the heater22including the resistive heat generators31connected in series as illustrated inFIGS. 3A, 3B, and 3Cand a construction of each of a heater22A incorporating resistive heat generators35connected in parallel, a heater22B incorporating resistive heat generators35B connected in parallel, and a heater22C incorporating resistive heat generators35C connected in parallel as illustrated inFIGS. 4A, 4B, and 4C, respectively. The positions and the number of the resistive heat generators31,35,35B, and35C described below are examples and modified properly according to the type and the like of sheets P conveyed through the fixing device6.

As illustrated inFIGS. 3A, 3B, and 3C, a surface of the base30, that is, an elongate plate, mounts the resistive heat generators31, feeders33a,33b, and33c, electrodes34aand34b, and the like. The resistive heat generators31are arranged in two lines and extended in the longitudinal direction of the heater22. The feeders33a,33b, and33cserve as conductors. The protective layer32covers the surface of the base30, the resistive heat generators31, and the feeders33a,33b, and33c.

The base30is preferably made of ceramic (e.g., alumina and aluminum nitride), glass, mica, or heat resistant resin (e.g., polyimide), which has an increased heat resistance and an increased insulation. According to the embodiments, the base30is made of an insulating material.

The resistive heat generators31and the feeders33a,33b, and33care made of a conductive material produced by mixing silver (Ag), palladium (Pd), platinum (Pt), ruthenium oxide (RuO2), and the like.

The protective layer32is preferably made of ceramic (e.g., alumina and aluminum nitride), glass, mica, or heat resistant resin (e.g., polyimide), which improves heat resistance and insulation of the protective layer32.

The resistive heat generators31are connected to the electrodes34aand34bthrough the feeders33aand33b, respectively, at one lateral end of each of the resistive heat generators31in a longitudinal direction thereof. A connector and the like contact the electrodes34aand34b, electrically connecting the heater22to an external device. The resistive heat generators31are connected to each other through the feeder33cextending in a short direction of the heater22at another lateral end of each of the resistive heat generators31in the longitudinal direction thereof. The protective layer32covers the base30, the resistive heat generators31, and the feeders33a,33b, and33c. The protective layer32protects the base30, the resistive heat generators31, and the feeders33a,33b, and33cand insulates the heater22from the fixing belt20.

FIG. 3Cis a cross-sectional view of the heater22taken on line A-A inFIG. 3B. As illustrated inFIG. 3C, a projection36is mounted on a surface of a downstream portion30aof the base30in the sheet conveyance direction X, as described below in detail.

Referring toFIGS. 4A, 4B, and 4C, a description is provided of the construction of each of the heaters22A,22B, and22C incorporating the resistive heat generators35,35B, and35C connected in parallel, respectively.

As illustrated inFIG. 4A, the base30mounts the plurality of resistive heat generators35, that is, eight resistive heat generators35according to this embodiment. The resistive heat generators35serving as heat generators are arranged in a longitudinal direction of the heater22A. Feeders33dand33eare disposed at both ends of the base30, respectively, in a short direction thereof. Both lateral ends of each of the resistive heat generators35in a longitudinal direction of the base30are coupled to the feeders33dand33e, respectively. The resistive heat generators35are connected in parallel. The feeders33dand33eare coupled to electrodes34dand34c, respectively, at one lateral end of each of the feeders33dand33ein the longitudinal direction of the heater22A.

According to this embodiment, each of the resistive heat generators35is made of a material having a positive temperature coefficient of resistance (TCR) that is characterized in that, as the temperature of the resistive heat generators35increases, the electric resistance value thereof increases, decreasing the output of the heater22A in portions thereof where the resistive heat generators35are disposed.

Like the resistive heat generators31described above, the resistive heat generators35are made of a conductive material produced by mixing silver (Ag), palladium (Pd), platinum (Pt), ruthenium oxide (RuO2), and the like.

According to the embodiments of the present disclosure, when a small sheet P having a small width in the longitudinal direction of the fixing belt20is conveyed through the fixing device6, the small sheet P does not draw heat from both lateral ends of the fixing belt20in the longitudinal direction thereof and the resistive heat generators35disposed opposite both lateral ends of the fixing belt20, that is, both lateral ends of the heater22A in the longitudinal direction thereof. Accordingly, both lateral ends of the fixing belt20in the longitudinal direction thereof and the resistive heat generators35disposed opposite both lateral ends of the fixing belt20suffer from relatively high temperatures and relatively high resistance values. Since a constant voltage is applied to the resistive heat generators35, an output from the resistive heat generators35disposed opposite both lateral ends of the fixing belt20in the longitudinal direction thereof decreases relatively, decreasing an amount of heat generated by the resistive heat generators35. Thus, the resistive heat generators35suppress an amount of heat generated by the heater22A in a non-conveyance span where the small sheet P is not conveyed, preventing overheating of the fixing belt20in the non-conveyance span.

Conversely, for example, the heater22incorporating the resistive heat generators31connected in series as illustrated inFIGS. 3A, 3B, and 3Cmay prevent overheating of both lateral ends of the fixing belt20in the longitudinal direction thereof by decreasing print speed. However, the heater22A incorporating the resistive heat generators35connected in parallel prevents overheating of the fixing belt20while suppressing decrease in print speed.

As illustrated inFIG. 4B, each of the resistive heat generators35B is inclined into substantially a parallelogram. With the resistive heat generators35that are substantially rectangular as illustrated inFIG. 4A, a heat generation amount of the heater22A at a gap S between adjacent ones of the resistive heat generators35decreases substantially compared to a portion of the heater22A other than the gap S in the longitudinal direction of the heater22A, causing uneven temperature of the fixing belt20. Conversely, according to the embodiment illustrated inFIG. 4B, the adjacent ones of the resistive heat generators35B, each of which is substantially the parallelogram, overlap in a longitudinal direction of the heater22B, suppressing uneven temperature of the fixing belt20.

As illustrated inFIG. 4C, each of the resistive heat generators35C is an elongate linear portion that is bent and turned into a serpentine shape. Since the resistive heat generators35C are elongated, even if the resistive heat generators35C are made of a material that has a low resistance value and is available at reduced costs, the resistive heat generators35C achieve a desired heat generation amount, reducing manufacturing costs of the heater22C.

As illustrated inFIGS. 4A, 4B, and 4C, the projection36is mounted on the surface of the base30of each of the heaters22A,22B, and22C, as described below in detail.

As described above, a heater (e.g., the heater22) incorporating resistive heat generators (e.g., the resistive heat generators31) connected in series or a heater (e.g., the heaters22A,22B, and22C) incorporating resistive heat generators (e.g., the resistive heat generators35,35B, and35C) connected in parallel is employed as a heater according to the embodiments of the present disclosure. The following describes the construction of the heater22depicted inFIGS. 3A, 3B, and 3C, that incorporates the resistive heat generators31connected in series as one example.

As illustrated inFIG. 5, according to the embodiments, a power supply circuit for supplying power to each of the resistive heat generators31is constructed by electrically connecting an alternating current power supply200serving as an external device of the heater22to the electrodes34aand34bof the heater22. The power supply circuit includes a triac210that controls an amount of power supplied to each of the resistive heat generators31. A controller220includes a microcomputer that includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input-output (I/O) interface.

According to the embodiments, the thermistors25serving as temperature detectors are disposed opposite a center span of the heater22in the longitudinal direction thereof, that is, a minimum sheet conveyance span where a minimum size sheet P is conveyed, and one lateral end span of the heater22in the longitudinal direction thereof, respectively. Further, a thermostat27serving as a power interrupter is disposed at one lateral end of the heater22in the longitudinal direction thereof. The thermostat27interrupts supplying power to the resistive heat generators31when a temperature of the resistive heat generators31is a predetermined temperature or higher. The thermistors25and the thermostat27contact the back face of the base30, that is opposite the front face of the base30, that mounts the resistive heat generators31. The thermistors25and the thermostat27detect the temperature of the resistive heat generators31.

The controller220controls the amount of power supplied to each of the resistive heat generators31through the triac210based on temperatures of the resistive heat generators31, that are detected by the thermistors25, respectively. When a sheet P is conveyed to the fixing device6, the controller220determines the amount of power supplied to each of the resistive heat generators31by considering an amount of heat drawn by the sheet P.

A description is provided of a construction of a comparative heater.

The comparative heater includes a base made of a metal plate. The base is bent by hemming to produce a projection disposed at a position on the base, that defines an exit of a fixing nip. Accordingly, the projection is disposed opposite a downstream portion of the fixing nip in a recording medium conveyance direction, improving fixing of a toner image on a recording medium.

Since the projection is produced by processing the base, the projection has a predetermined height or higher due to restriction in processing. Hence, the projection may have a height that is excessively high, increasing a frictional resistance between the base and a fixing rotator (e.g., a fixing belt) that slides over the base and causing the fixing rotator and the like to be damaged easily.

A detailed description is provided of a configuration of the projection36mounted on the surface of the base30of the heater22according to a first embodiment of the present disclosure.

As illustrated inFIGS. 3A, 3B, and 3C, the projection36is mounted on the surface of the base30and is extended in the longitudinal direction of the base30. The projection36is mounted on a portion on the surface of the base30where the resistive heat generators31are not disposed. For example, the projection36is shifted from the resistive heat generators31. Specifically, the projection36is disposed above the resistive heat generators31inFIG. 3Band disposed downstream from the resistive heat generators31in the sheet conveyance direction X. As illustrated inFIG. 3C, the projection36is mounted on the downstream portion30aof the base30. The projection36is disposed separately from the base30. According to this embodiment, the projection36is a part of the protective layer32.

As illustrated inFIG. 2, the projection36projects toward the fixing nip N and the pressure roller21. According to this embodiment, the projection36is disposed opposite a downstream portion of the fixing nip N in the sheet conveyance direction X. As illustrated inFIG. 2, since the projection36is mounted on the surface of the base30, a downstream portion22dof the heater22in the sheet conveyance direction X protrudes beyond a center portion22cof the heater22in the sheet conveyance direction X toward the fixing nip N. The downstream portion22dis disposed downstream from the center portion22cin the sheet conveyance direction X. The center portion22cof the heater22in the sheet conveyance direction X defines a middle region of the heater22when the heater22is divided into three regions in the sheet conveyance direction X. The downstream portion22dof the heater22in the sheet conveyance direction X defines a downstream region of the heater22, that is disposed downstream from the middle region in the sheet conveyance direction X.

The projection36defines a projecting shape that projects toward the pressure roller21and is disposed opposite the downstream portion of the fixing nip N at a part of the heater22. Accordingly, the projection36increases pressure applied to the sheet P at the downstream portion of the fixing nip N during a latter half of fixing, improving fixing performance of fixing the toner image on a surface of the sheet P.

As illustrated inFIG. 2, the protective layer32has a nip forming face that faces the fixing belt20and forms the fixing nip N. The projection36defines a first part of the nip forming face. The projection36preferably protrudes beyond a second part of the nip forming face, that is other than the first part, by a range of from 40 micrometers to 400 micrometers. Since the projection36has a height in the range of from 40 micrometers to 400 micrometers, the projection36sufficiently increases pressure applied to the sheet P at the downstream portion of the fixing nip N during the latter half of fixing, achieving fixing performance of fixing the toner image on the sheet P. If the height of the projection36is excessively high, the fixing belt20may slide over the heater22with an increased frictional resistance. Accordingly, the fixing belt20may suffer from early breakage. Further, the fixing belt20may engage the pressure roller21with a substantial amount, causing early breakage of the pressure roller21. To address this circumstance, the projection36having the height in the range of from 40 micrometers to 400 micrometers prevents early breakage of the fixing belt20and the pressure roller21. In order to prevent early breakage of the fixing belt20and the pressure roller21, the projection36preferably has a height of 300 micrometers or smaller.

Next, a description is provided of a method for manufacturing the heater22.

Paste made of the conductive material described above, of which the resistive heat generators31, the feeders33a,33b, and33c, and the like are made, coats the surface of the base30, that is, a plate, by screen printing. Thereafter, the base30is subject to firing. The processes described above are repeated to produce a multilayer that has a desired thickness. The protective layer32coats the multilayer, producing the heater22. The number of layers of the multilayer increases in a downstream portion of the protective layer32in the sheet conveyance direction X where the projection36is disposed. Thus, the downstream portion of the protective layer32protrudes beyond a portion of the protective layer32, other than the downstream portion, producing the projection36.

For example, as a construction different from the construction of the heater22according to this embodiment, a base made of a metal plate is bent by hemming to produce a projection that is combined or molded with the base. The projection that is molded by bending has a minimum height that is determined based on a plate thickness of the base. Accordingly, it may be difficult to set the height of the projection within the above-described range depending on the plate thickness of the base, causing early breakage of the fixing belt20and the pressure roller21. Conversely, according to this embodiment, the projection36is disposed separately from the base30. For example, the projection36is not molded with the base30. Accordingly, the projection36attains a desired height, preventing early breakage of the fixing belt20and the pressure roller21as described above.

If a part of the base is bent by hemming as described above to produce the projection molded with the base and the resistive heat generators31and the like are produced by screen printing as described above, the thickness and the width of each of the resistive heat generators31may vary depending on lifting of a plate and uneven contact of a spueegee. Accordingly, each of the resistive heat generators31may suffer from variation in the resistance locally and variation in the heat generation amount. Further, each of the resistive heat generators31is subject to disconnection locally at a portion of the resistive heat generator31where the thickness and the width of the resistive heat generator31decrease. Conversely, according to this embodiment, the projection36is disposed separately from the base30. Hence, the projection36is not produced during screen printing, not hindering screen printing. Consequently, the projection36prevents variation in the thickness and the width of each of the resistive heat generators31due to lifting of the plate and uneven contact of the spueegee described above.

A description is provided of constructions of heaters22S,22T,22U,22V,22W,22X,22Y, and22Z according to second to eighth embodiments sequentially, which incorporate projections, respectively, that are different from the projection36of the heater22according to the first embodiment described above.

Hereinafter, the embodiments are described mainly of configurations that are different from those of the first embodiment described above. A description of other configurations that are common to the first embodiment described above is omitted properly.

Referring toFIGS. 6A, 6B, and 6C, a description is provided of the construction of the heater22S according to the second embodiment of the present disclosure.

FIG. 6Cis a cross-sectional view of the heater22S taken on line B-B inFIG. 6B. As illustrated inFIGS. 6A, 6B, and 6C, the heater22S according to the second embodiment includes a projection36S constructed of a feeder361serving as a conductor and a cover portion362incorporated in the protective layer32. The cover portion362covers a surface of the feeder361mounted on the base30. As illustrated inFIG. 6B, according to this embodiment, a single resistive heat generator, that is, the resistive heat generator31, is mounted on the surface of the base30. The feeder361couples the resistive heat generator31to the electrode34b. Thus, a part of the feeder361electrically connected to the electrode34bconstructs a part of the projection36S. A height of the feeder361is greater than a height of the feeder33asuch that the projection36S has a desired height.

As described above, the projection36disposed opposite or mounted on the base30is a part of the protective layer32. The projection36S disposed opposite or mounted on the base30is a part of the feeder361. Thus, a projection (e.g., the projections36and36S) is a part of an element of a heater (e.g., the heaters22and22S) and a part of the element mounted on the base30. Alternatively, a projection may be disposed separately from the element of the heater.

Referring toFIGS. 7A, 7B, and 7C, a description is provided of the construction of the heater22T according to the third embodiment of the present disclosure.

FIG. 7Cis a cross-sectional view of the heater22T taken on line C-C inFIG. 7B. As illustrated inFIGS. 7A, 7B, and 7C, the heater22T according to the third embodiment includes a projection36T disposed separately from the protective layer32. The projection36T is not electrically connected to the electrodes34aand34b.

The projection36T is made of a material that is equivalent to a material of the resistive heat generators31or a material of the feeders33a,33b, and33c, for example. In order to produce the projection36T, the projection36T is made of a pattern material that is equivalent to a pattern material of the resistive heat generators31and the feeders33a,33b, and33cof the heater22T. Thus, the projection36T is produced without preparing a different material. Alternatively, the projection36T may be made of a material different from the material used to produce the heater22T.

If the projection36T is made of the pattern material described above, the paste made of the conductive material repeatedly coats the base30by screen printing as described above into a multilayer. The number of coatings on a mounting portion of the base30, that mounts the projection36T, is greater than the number of coatings on a non-mounting portion of the base30other than the mounting portion. Accordingly, a height of the paste on the mounting portion of the base30is greater than a height of the paste on the non-mounting portion of the base30, producing the projection36T having a desired height.

Since the projection36T according to this embodiment is not electrically connected to the electrodes34aand34b, the fixing belt20is not insulated from the projection36T. Hence, according to this embodiment, as illustrated inFIG. 7C, the protective layer32is not disposed as a surface of the projection36T.

In other words, according to this embodiment, the protective layer32does not construct a part of the projection36T.

Alternatively, the protective layer32may cover the projection36T or the protective layer32may construct a part of the projection36T.

Referring toFIGS. 8A, 8B, and 8C, a description is provided of the construction of the heater22U according to the fourth embodiment of the present disclosure.

FIG. 8Cis a cross-sectional view of the heater22U taken on line D-D inFIG. 8B. As illustrated inFIGS. 8A, 8B, and 8C, the heater22U according to the fourth embodiment includes a projection36U constructed of a protrusion361U and a cover portion362U. The protrusion361U is mounted on the base30and is not connected to the electrodes34aand34b. The cover portion362U is incorporated in the protective layer32and covers a surface of the protrusion361U. The protective layer32constructs a part of a surface of the projection36U, facilitating sliding of the fixing belt20over the heater22U and reducing friction between the fixing belt20and the heater22U.

According to the embodiments described above, the projections36,36S,36T, and36U extend continuously in a longitudinal direction of the heaters22,22S,22T, and22U, respectively. Alternatively, a plurality of projections may be arranged in a longitudinal direction of a heater.

Referring toFIGS. 9A, 9B, 9C, and 9D, a description is provided of the construction of the heater22V according to the fifth embodiment of the present disclosure.

FIG. 9Cis a cross-sectional view of the heater22V taken on line E1-E1inFIG. 9B.FIG. 9Dis a cross-sectional view of the heater22V taken on line E2-E2inFIG. 9B. As illustrated inFIGS. 9A, 9B, 9C, and 9D, the heater22V according to the fifth embodiment includes three projections36V arranged in a longitudinal direction of the heater22V.

In order to reduce friction between the fixing belt20and the heater22V and facilitate smooth rotation of the fixing belt20, a lubricant such as grease is interposed between the fixing belt20and the heater22V. According to this embodiment, a gap S is provided between adjacent ones of the projections36V arranged in the longitudinal direction of the heater22V. The lubricant moves through the gap S upward inFIG. 9Bin a rotation direction of the fixing belt20. Thus, the projections36V do not clog the base30with the lubricant. The projections36V are made of a pattern material that is equivalent to a pattern material of the resistive heat generators31and the like or made of a material that is different from a material of other elements of the heater22V.

According to the embodiments described above, each of the projections36,36S,36T,36U, and36V is disposed opposite or mounted on the downstream portion30aof the base30that is disposed opposite the downstream portion of the fixing nip N in the sheet conveyance direction X. Alternatively, a projection may be disposed downstream from the fixing nip N in the sheet conveyance direction X as illustrated inFIG. 10.FIG. 10is a schematic cross-sectional view of a fixing device6W incorporating a heater22W that includes a projection36W disposed downstream from the fixing nip N in the sheet conveyance direction X. The projection36W projects toward the pressure roller21at a position in a sheet conveyance path, that is disposed downstream from the fixing nip N in the sheet conveyance direction X, improving separation of the sheet P that has passed through the fixing nip N from the fixing belt20.

The above describes examples according to the embodiments of the present disclosure in which the resistive heat generators31are mounted on the front face of the base30, that faces the fixing belt20and the fixing nip N. Alternatively, the embodiments of the present disclosure are applicable to other configurations or constructions. For example,FIG. 11illustrates a fixing device6X incorporating the resistive heat generators31mounted on the back face of the base30, that is opposite the front face of the base30. The following describes projections according to the sixth to eighth embodiments, respectively, that are installed in heaters in which the resistive heat generators31are mounted on the back face of the base30.

Referring toFIGS. 11, 12A, 12B, 12C, and 12D, a description is provided of the construction of the heater22X according to the sixth embodiment of the present disclosure.

FIG. 12Dis a cross-sectional view of the heater22X taken on line F-F inFIG. 12C. As illustrated inFIGS. 11, 12A, 12B, 12C, and 12D, the heater22X according to the sixth embodiment includes a back face protective layer32X that is disposed on a back face30bof the base30and covers the back face30bof the base30and the resistive heat generators31. A front face protective layer37is disposed on a front face30cof the base30.

The back face protective layer32X and the front face protective layer37are preferably made of ceramic (e.g., alumina and aluminum nitride), glass, mica, or heat resistant resin (e.g., polyimide), which improves heat resistance and insulation of the back face protective layer32X and the front face protective layer37. The back face protective layer32X protects and insulates the back face30bof the base30and elements mounted on the back face30bof the base30(e.g., the resistive heat generators31and the feeders33a,33b, and33c). The front face protective layer37protects the front face30cof the base30, over which the fixing belt20slides.

The front face protective layer37includes a projection36X disposed opposite the downstream portion30aof the base30in the sheet conveyance direction X, that is, an upper portion of the base30inFIG. 12D.

Like the embodiments described above with reference toFIG. 2, if the projection36X is disposed opposite the downstream portion of the fixing nip N in the sheet conveyance direction X, the projection36X improves fixing performance of fixing the toner image on the sheet P. Like the embodiment described above with reference toFIG. 10, if the projection36X is disposed downstream from the fixing nip N in the sheet conveyance direction X, the projection36X improves separation of the sheet P from the fixing belt20after fixing.

Referring toFIG. 13, a description is provided of the construction of the heater22Y according to the seventh embodiment of the present disclosure.

As illustrated inFIG. 13, the heater22Y according to the seventh embodiment does not include a protective layer disposed on the front face30cof the base30but does include the back face protective layer32X disposed on the back face30bof the base30and a projection36Y that is disposed separately from the back face protective layer32X. According to this embodiment, the projection36Y is made of a pattern material that is equivalent to a pattern material of the resistive heat generators31, the feeders33a,33b, and33c, and the like or a material that is different from a material of elements of the heater22Y.

Referring toFIG. 14, a description is provided of the construction of the heater22Z according to the eighth embodiment of the present disclosure.

As illustrated inFIG. 14, the heater22Z includes a projection36Z constructed of a protrusion361Z and a cover portion362Z. The protrusion361Z is produced as described above. The cover portion362Z is a part of the front face protective layer37, that covers the protrusion361Z. The cover portion362Z as a part of the front face protective layer37serves as a part of the projection36Z and as a surface of the projection36Z, facilitating sliding of the fixing belt20over the heater22Z and reducing friction between the fixing belt20and the heater22Z.

Next, a description is provided of a positional relation between the projection36having the configuration described above and a sheet in the longitudinal direction of the heater22.

The following describes the positional relation with the construction in which the resistive heat generators31are mounted on the front face30cof the base30as described above with reference toFIGS. 3A, 3B, and 3Cas one example.

As illustrated inFIG. 15, a maximum sheet width W1defines a width in the longitudinal direction of the heater22of a sheet P1having a maximum width of a plurality of widths of sheets P that are conveyed through the fixing device6. A maximum image width W2defines a width in the longitudinal direction of the heater22of a maximum image formed on the sheet P1. According to this embodiment, a length of the projection36in the longitudinal direction of the heater22is not smaller than the maximum image width W2and encompasses the maximum image width W2. According to this embodiment, as illustrated inFIG. 2, the projection36is disposed opposite the downstream portion of the fixing nip N in the sheet conveyance direction X. For example, if the sheets P conveyed through the fixing device6include a postcard, a B5 size sheet in landscape orientation, and an A4 size sheet in landscape orientation, the maximum width of the sheets P is a length of 297 mm of the A4 size sheet in landscape orientation in a longitudinal direction of the A4 size sheet.

According to this embodiment, since the projection36is disposed opposite the downstream portion of the fixing nip N in the sheet conveyance direction X, the projection36increases pressure applied to the sheet P throughout an entire image span on the sheet P at the fixing nip N, improving fixing performance of fixing the toner image on the sheet P throughout the entire image span in the axial direction of the fixing belt20.

Referring toFIG. 16, a description is provided of an embodiment having a positional relation between the projection36W having the configuration described above and a sheet in a longitudinal direction of the heater22W, that is different from the embodiment depicted inFIG. 15.

As illustrated inFIG. 16, a length of the projection36W in the longitudinal direction of the heater22W is not smaller than the maximum sheet width W1and encompasses the maximum sheet width W1. According to this embodiment, as illustrated inFIG. 10, the projection36W is disposed downstream from the fixing nip N in the sheet conveyance direction X.

According to this embodiment, the projection36W improves separation of the sheet P from the fixing belt20after fixing throughout an entire width of the sheet P in a width direction thereof parallel to the axial direction of the fixing belt20.

The above describes the embodiments of the present disclosure. However, the technology of the present disclosure is not limited to the embodiments described above and is modified within the scope of the present disclosure.

The above-described definition that the projection36is disposed separately from the base30denotes that a separate member is attached to the base30by post processing, such as welding, adhesion, and screen printing described above, to produce the projection36. Hence, the above-described definition that the projection36is disposed separately from the base30does not denote that a part of the base30is deformed by bending a metal plate by hemming, for example, to produce the projection36. However, the base30and the projection36may not be made of different materials, respectively.

Alternatively, the image forming apparatus1according to the embodiments of the present disclosure depicted inFIG. 1is not limited to a monochrome image forming apparatus that forms a monochrome toner image. For example, the image forming apparatus1may be a color image forming apparatus that forms a color toner image, a copier, a printer, a facsimile machine, a multifunction peripheral (MFP) having at least two of printing, copying, facsimile, scanning, and plotter functions, or the like.

The recording media include, in addition to plain paper as a sheet P, thick paper, a postcard, an envelope, thin paper, coated paper, art paper, tracing paper, an overhead projector (OHP) transparency, plastic film, prepreg, and copper foil.

The above describes examples according to the embodiments of the present disclosure in which a heater (e.g., the heaters22,22S,22T,22U,22V,22W,22X,22Y, and22Z) is applied to a fixing device (e.g., the fixing devices6,6W, and6X). Alternatively, the heater according to the embodiments of the present disclosure is also applicable to a heater installed in a dryer that dries a drying target. For example, the heater according to the embodiments of the present disclosure is also applicable to a dryer installed in an image forming apparatus employing an inkjet method. The dryer dries ink of an image formed on a surface of a recording medium such as a sheet.

According to the embodiments described above, the base30is made of an insulating material. Alternatively, the base30may be made of a conductive material. For example, as the conductive material, a material having an increased thermal conductivity, such as an iron based material (e.g., SUS stainless steel), aluminum, copper, silver, graphite, and graphene, is preferably used. The material having the increased thermal conductivity evens the temperature of an entirety of the heater by thermal conduction, improving quality of a toner image fixed on a sheet P. However, in this case, an insulating layer is interposed between the base30and the resistive heat generators31and between the base30and the feeders33a,33b, and33c, and the like. As described above, according to the embodiments of the present disclosure, a definition that a heat generator (e.g., the resistive heat generators31,35,35B, and35C) and a projection (e.g., the projections36,36S,36T,36U,36V,36W,36X,36Y, and36Z) are mounted on a base (e.g., the base30) also denotes a configuration in which the heat generator and the projection are mounted on the base via an insulating layer or the like, in addition to a configuration in which the heat generator and the projection are mounted on the base directly.

The above describes examples according to the embodiments of the present disclosure in which the projection is a strip extending in a longitudinal direction of the heater as one example. Alternatively, for example, a plurality of projections, each of which has a decreased length, may be arranged in the longitudinal direction of the heater. The plurality of projections may be mounted on or disposed opposite a downstream portion of the base, that is disposed downstream from the fixing nip N in the sheet conveyance direction X.

A description is provided of advantages of a heater (e.g., the heaters22,22S,22T,22U,22V,22W,22X,22Y, and22Z).

As illustrated inFIG. 2, the heater includes a base (e.g., the base30), a heat generator (e.g., the resistive heat generators31,35,35B, and35C), and a projection (e.g., the projections36,36S,36T,36U,36V,36W,36X,36Y, and36Z). The heat generator is mounted on the base. The projection is disposed separately from the base. The projection is disposed opposite or mounted on the base and disposed at a position different from a position of the heat generator. For example, the projection is shifted from the heat generator. In a state in which the heater is installed in a fixing device (e.g., the fixing devices6,6W, and6X), the projection projects toward a fixing nip (e.g., the fixing nip N) of the fixing device. As illustrated inFIG. 3C, the projection is disposed opposite or mounted on a downstream portion (e.g., the downstream portion30a) of the base in a recording medium conveyance direction (e.g., the sheet conveyance direction X).

Accordingly, the projection has a desired height.

According to the embodiments described above, the fixing belt20serves as a fixing rotator. Alternatively, a fixing film, a fixing sleeve, or the like may be used as a fixing rotator. Further, the pressure roller21serves as a pressure rotator. Alternatively, a pressure belt or the like may be used as a pressure rotator.