EP4632494A1

EP4632494A1 - Fixing device and image forming apparatus

Info

Publication number: EP4632494A1
Application number: EP25165903.3A
Authority: EP
Inventors: Seiji Saitoh
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2024-04-09
Filing date: 2025-03-25
Publication date: 2025-10-15
Also published as: JP2025159872A

Abstract

A fixing device (20, 20', 20") includes a fixing member (21, 21'), a heating means (25, 38, 50), a pressure rotator (31), and a nip forming member (26, 26'). The fixing member (21, 21') is rotatable and has an endless shape. The heating means (25, 38, 50) heats the fixing member. The pressure rotator (31) is disposed outside the fixing member to press the fixing member. The nip forming member (26, 26') is disposed inside the fixing member (21, 21') to form a nip between the fixing member and the pressure rotator (31). The nip forming member (26, 26') includes a vapor chamber (28) and a holding member (30). Heat is transferred from an inner circumferential face of the fixing member (21, 21') to the vapor chamber (28). The holding member (30) holds the vapor chamber (28) and includes a plurality of protrusions (30a) in contact with the vapor chamber.

Description

BACKGROUND

Technical Field

Embodiments of the present disclosure generally relate to a fixing device and an image forming apparatus.

Related Art

An image forming apparatus, such as a copier or a printer, includes a fixing device that fixes an image on a recording material. In a case where such a fixing device performs fixing onto a recording material having a width narrower than the heating width of a heating element, it has been known that a rise is made in the temperature of a fixing member in a range out of which the recording material passes (namely, a rise in the temperature of an end).
For example, Japanese Unexamined Patent Application Publication No. 2020-086350 discloses a technique of inhibiting such a rise in the temperature of an end. This literature discloses that a nip forming member disposed inside a fixing member includes a heat pipe to which heat is transferred from the inner circumferential face of the fixing member and a coating layer of a sliding material between the heat pipe and the inner circumferential face of the fixing member. This configuration enables effective inhibition of a rise in the temperature of an end of the fixing member because the heat pipe has high thermal uniformity.
Furthermore, because a hollow heat pipe is disadvantageous in strength, a vapor chamber including a columnar member for reinforcement inside its hollow has been known as an alternative technique to such a heat pipe.
Such a vapor chamber is held in a fixing device by a holding member. Because the vapor chamber has a high thermal conductivity, heat from a fixing member is transferred to the holding member through the vapor chamber. Thus, a deterioration is likely to be made in thermal efficiency.

SUMMARY

An object of the present disclosure is to provide a fixing device that enables inhibition of heat from a fixing member from being transferred to a holding member through a vapor chamber and is high in thermal efficiency.
In order to solve the above-described disadvantage, the present disclosure described herein provides a fixing device that includes a fixing member, a heating means, a pressure rotator, and a nip forming member. The fixing member is rotatable and has an endless shape. The heating means heats the fixing member. The pressure rotator is disposed outside the fixing member to press the fixing member. The nip forming member is disposed inside the fixing member to form a nip between the fixing member and the pressure rotator. The nip forming member includes a vapor chamber and a holding member. Heat is transferred from an inner circumferential face of the fixing member to the vapor chamber. The holding member holds the vapor chamber and includes a plurality of protrusions in contact with the vapor chamber.
The present disclosure described herein also provides an image forming apparatus includes the fixing device.
A fixing device according to an embodiment of the present disclosure enables inhibition of heat from a fixing member from being transferred to a holding member through a vapor chamber, leading to an improvement in thermal efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic view illustrating the entire configuration of an image forming apparatus according to an embodiment of the present disclosure;
FIG. 2 is a cross-sectional view of the configuration of a fixing device according to an embodiment of the present disclosure;
FIG. 3 is a cross-sectional view of the configuration of a fixing belt and a guide member;
FIG. 4 illustrates the configuration of the fixing belt, a pressure roller, a reinforcing member, and a nip forming member;
FIG. 5 is a partial cross-sectional view illustrating an exemplary configuration of the nip forming member;
FIG. 6 is a partial cross-sectional view illustrating an exemplary configuration of a vapor chamber;
FIG. 7 is a partial cross-sectional view illustrating the configuration of a nip forming member according to an embodiment of the present disclosure;
FIG. 8 is a perspective view illustrating a configuration in which a holding member and a vapor chamber are arranged according to an embodiment of the present disclosure;
FIG. 9A is a partial cross-sectional view illustrating a configuration in which protrusions and columnar members are arranged in alignment;
FIG. 9B is a partial cross-sectional view illustrating a configuration in which protrusions and columnar members are arranged out of alignment;
FIG. 10A is a plan view illustrating columnar members that are rectangular in shape and are disposed inside a vapor chamber according to an embodiment of the present disclosure;
FIG. 10B is a plan view illustrating columnar members that are oval or elliptical in shape and are disposed inside a vapor chamber according to an embodiment of the present disclosure;
FIG. 11 is a partial cross-sectional view illustrating the configuration of a holding member according to a modification of the present disclosure;
FIG. 12A is a cross-sectional view of a nip forming member including a holding member having a plurality of protrusions of which the heights gradually decrease along the longitudinal direction of the holding member;
FIG. 12B is a perspective view of the holding member;
FIG. 13A is a cross-sectional view of a nip forming member including a holding member having a plurality of protrusions of which the heights gradually increase along the longitudinal direction of the holding member;
FIG. 13B is a perspective view of the holding member;
FIG. 14A is a cross-sectional view of a nip forming member including a holding member having a plurality of protrusions of which the heights gradually increase along a conveyance direction of the holding member;
FIG. 14B is a perspective view of the holding member;
FIG. 15 is a partial cross-sectional view of the nip forming member of FIG. 14A;
FIG. 16A is a partial cross-sectional view of a nip forming member according to a modification of the present disclosure (version 1);
FIG. 16B is a perspective view of a holding member of FIG. 16A;
FIG. 17 is a partial cross-sectional view of a nip forming member according to a modification of the present disclosure (version 2);
FIG. 18 is a cross-sectional view of the configuration of a fixing device according to a modification of the present disclosure (version 1); and
FIG. 19 is a cross-sectional view of the configuration of a fixing device according to a modification of the present disclosure (version 2).

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. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

DETAILED DESCRIPTION

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.
Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms "a, " "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Embodiments of the present disclosure will be described below with reference to the accompanying drawings. In the drawings for illustrating embodiments of the present disclosure, identical reference numerals are assigned to constituent elements, such as members or constituent components that have identical functions or identical shapes as long as differentiation is possible, and descriptions of such constituent elements may be omitted once the description is provided.
FIG. 1 is a schematic view illustrating the entire configuration of an image forming apparatus according to an embodiment of the present disclosure.
An image forming apparatus 100 illustrated in FIG. 1 includes four image forming units 1Y, 1M, 1C, and 1Bk detachable from the body thereof. The image forming units 1Y, 1M, 1C, and 1Bk are similar in configuration except for containing one-to-one yellow, magenta, cyan, and black developers different in color corresponding to decomposed color components of a color image.
Specifically, the image forming units 1Y, 1M, 1C, and 1Bk each include a photoconductor 2 that is drum-shaped and serves as an image bearer, a charging device 3 that charges the surface of the photoconductor 2, and a developing device 4 that supplies toner as a developer to the surface of the photoconductor 2 to form a toner image. The image forming units 1Y, 1M, 1C, and 1Bk each further include a cleaning device 5 that cleans the surface of the photoconductor 2.
The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoconductor 2 to form an electrostatic latent image, a sheet feeder 7 that supplies a sheet P as a recording material, and a transfer device 8 that transfers the toner image formed on each photoconductor 2 onto the sheet P. The image forming apparatus 100 further includes a fixing device 20 that fixes the toner images transferred to the sheet P and a sheet ejector 10 that ejects the sheet P outward from the image forming apparatus 100.
The transfer device 8 includes an intermediate transfer belt 11 serving as an endless intermediate transfer member stretched by a plurality of rollers and four primary transfer rollers 12 each serving as a primary transfer member that transfers the toner image on the corresponding photoconductor 2 to the intermediate transfer belt 11. The transfer device 8 further includes a secondary transfer roller 13 serving as a secondary transfer member that transfers the toner images transferred on the intermediate transfer belt 11 to a sheet P.
The four primary transfer rollers 12 are in contact with the respective photoconductors 2 through the intermediate transfer belt 11. Thus, the intermediate transfer belt 11 has contact with each photoconductor 2, forming a primary transfer nip therebetween. On the other hand, the secondary transfer roller 13 is in contact with one of the rollers by which the intermediate transfer belt 11 is stretched, through the intermediate transfer belt 11. Thus, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.
The image forming apparatus 100 includes a sheet conveyance path 14 for conveyance of a sheet P fed from the sheet feeder 7. A timing roller pair 15 is provided at a position between the sheet feeder 7 and the secondary transfer nip (secondary transfer roller 13) on the sheet conveyance path 14.
Next, the printing operation of the above-described image forming apparatus will be described with reference to FIG. 1.
In response to an instruction for starting a printing operation, the respective photoconductors 2 in the image forming units 1Y, 1M, 1C, and 1Bk are driven rotationally clockwise in FIG. 1. Then, the charging devices 3 each charge the surface of the corresponding photoconductor 2 uniformly at a high electric potential. Subsequently, the exposure device 6 exposes the surface of each photoconductor 2 based on image information on an original read by an original scanner or print information as a print instruction from a terminal. Thus, due to a drop in the electric potential of the exposed portion of each photoconductor 2, an electrostatic latent image is formed. Then, the developing devices 4 each supply toner to the corresponding electrostatic latent image to form a toner image on the corresponding photoconductor 2.
The toner image formed on each photoconductor 2 reaches the primary transfer nip (the position of the primary transfer roller 12) in accordance with rotation of the corresponding photoconductor 2 and then is transferred to the intermediate transfer belt 11 driven rotationally counterclockwise in FIG. 1 such that the respective toner images on the photoconductors 2 are mutually superimposed in order. Then, the toner images transferred on the intermediate transfer belt 11 are conveyed to the secondary transfer nip (the position of the secondary transfer roller 13) in accordance with rotation of the intermediate transfer belt 11 and then are transferred to a conveyed sheet P at the secondary transfer nip. This sheet P has been supplied from the sheet feeder 7.
The sheet P supplied from the sheet feeder 7 is temporarily kept stopped by the timing roller pair 15 and then is conveyed to the secondary transfer nip at the timing at which the toner images on the intermediate transfer belt 11 reach the secondary transfer nip. Thus, a full-color toner image is borne on the sheet P. After the toner image on each photoconductor 2 is transferred, the toner remaining on each photoconductor 2 is removed by the corresponding cleaning device 5.
The sheet P to which the toner images are transferred is conveyed to the fixing device 20, so that the toner images are fixed to the sheet P by the fixing device 20. After that, the sheet P is ejected outward from the image forming apparatus 100 by the sheet ejector 10, resulting in completion of a series of printing operation.
Next, the configuration and operation of the fixing device 20 installed in the body of the image forming apparatus 100 will be described with FIGS. 2 to 5.
The fixing device 20 serves as a device that conveys a sheet P (sheet on which toner is borne but is not yet fixed) while heating the sheet P. The fixing device 20 includes a fixing belt 21 as a fixing member, a nip forming member 26, a reinforcing member 23, a heater 25 as a heating means (heating source), a reflective plate 27, a pressure roller 31 as a pressure rotator, and a temperature detecting sensor 40 as a temperature detecting means.

Fixing Belt

The fixing belt 21 serves as an endless belt member that has contact with the outer circumference of the pressure roller 31 and rotates in a driven manner in accordance with rotation of the pressure roller 31. The fixing belt 21 is thin with flexibility and rotates (rotates in a driven manner) in the direction of the corresponding arrow in FIG. 2 (counterclockwise). The fixing belt 21 includes a base layer, an elastic layer, and a release layer stacked in order from its inner circumferential face (from its sliding contact face to the nip forming member 26) and has its entire thickness set not more than approximately 1 mm.
The base layer of the fixing belt 21 has a thickness of 30 to 50 µm and is formed of a metallic material, such as nickel or stainless steel, or a resin material, such as polyimide. The elastic layer has a thickness of 100 to 300 µm and is formed of a rubber material, such as silicone rubber, foamed silicone rubber, or fluororubber. Since the elastic layer is provided, no minute asperities are formed on the surface of the fixing belt 21 at a nip. Thus, heat is transferred uniformly to a toner image T on a sheet P, leading to inhibition of occurrence of an image like orange peel.
The release layer of the fixing belt 21 has a thickness of 5 to 50 µm and is formed of a material, such as perfluoroalkoxy alkane (PFA) (i.e., a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene), polytetrafluoroethylene (PTFE), polyimide, polyetherimide, or polyethersulfone (PES). Since the release layer is provided, releasability (detachability) can be ensured to the toner image T.
The nip forming member 26, the heater 25 (heating means), the reinforcing member 23, and the reflective plate 27 are installed inside the fixing belt 21 (on the side of location of the inner circumferential face). The nip forming member 26 inside the fixing belt 21 (on the side of location of the inner circumferential face) is pressed against the pressure roller 31 through the fixing belt 21 such that a nip (fixing nip), through which a sheet P is conveyed while being nipped, is formed.

Guide Member

Referring to FIG. 3, guide members 34 guide one-to-one both ends in the width direction of the inner circumferential face of the fixing belt 21 such that the fixing belt 21 maintains a substantially cylindrical posture. In detail, two guide members 34 are formed of a heat-resistant resin material and are fitted one-to-one to side plates 43 at both ends in the width direction of the fixing device 20.
The guide members 34 each include a guide 34a for holding the fixing belt 21 while keeping the fixing belt 21 having a substantially cylindrical posture and a stopper for regulating movement (skew) in the width direction of the fixing belt 21. Without interrupting the formation of the nip due to the nip forming member 26, the guide members 34 are disposed at both ends in the width direction of the fixing belt 21 and range out of the nip in the circumferential direction of the fixing belt 21.
In the present embodiment, the members in contact with the inner circumferential face of the fixing belt 21 are the guide members 34 in loose contact with both ends in the width direction of the fixing belt 21 and the nip forming member 26. Except for the guide members 34 and the nip forming member 26, no member (no belt guide) for guiding rotation of the fixing belt 21 is provided.

Pressure Roller

As illustrated in FIG. 2, the pressure roller 31 as a pressure rotator includes a cored bar 31a (shaft) and an elastic layer 31b on the cored bar 31a and is driven rotationally in a predetermined direction (clockwise in FIG. 2) due to a driving motor (driving means).
The cored bar 31a of the pressure roller 31 corresponds to a hollow structure formed of a metallic material. The elastic layer 31b of the pressure roller 31 is formed of a material, such as foamed silicone rubber, silicone rubber, or fluororubber. Note that a thin release layer made of PFA or PTFE can be provided as a surface layer to the elastic layer 31b.
The pressure roller 31 is pressed against the fixing belt 21 such that a desired nip is formed between the pressure roller 31 and the fixing belt 21. As illustrated in FIG. 4, the pressure roller 31 is provided with a gear 45 that engages with the driving gear of the driving motor. In addition, the pressure roller 31 has both ends, in its width direction, supported rotatably one-to-one by the side plates 43 of the fixing device 20 through bearings 42. Therefore, the pressure roller 31 is driven rotationally in the direction of the corresponding arrow (clockwise) as illustrated in FIG. 2.
In a case where the elastic layer 31b of the pressure roller 31 is formed of a spongiform material, such as foamed silicone rubber, the pressing force acting on the nip can be reduced, so that the load on the nip forming member 26 can be reduced. Furthermore, the pressure roller 31 has a high thermal insulation and thus heat barely moves from the fixing belt 21 to the pressure roller 31. Thus, an improvement can be made in the efficiency of heating the fixing belt 21.

Nip Forming Member

As illustrated in FIG. 2, the nip forming member 26 is disposed in sliding contact with the inner circumferential face of the fixing belt 21. The nip forming member 26 is pressed against the pressure roller 31 through the fixing belt 21 such that a nip, through which a sheet P is conveyed, is formed.
Referring to FIG. 5, the nip forming member 26 in sliding contact with the inner circumferential face of the fixing belt 21 has a flat counter face (sliding contact face 28a of a vapor chamber 28 described later) to the pressure roller 31. That is, the nip forming member 26 has a sliding contact face 28a (face counter to the pressure roller 31) that is flat in shape. Thus, the shape of the nip is substantially parallel to the image face of a sheet P and thus the adhesiveness between the fixing belt 21 and the sheet P is high, leading to an improvement in fixing. Furthermore, the curvature of the fixing belt 21 increases on the exit side of the nip, so that the sheet P sent out from the nip can be easily separated from the fixing belt 21.
Note that the nip forming member 26 includes a vapor chamber 28 on the side closer to the nip. The vapor chamber 28 will be described in detail later.

Reinforcing Member

As illustrated in FIG. 2, the reinforcing member 23 is installed inside the fixing belt 21 and abuts on the pressure roller 31 through the nip forming member 26 and the fixing belt 21. The reinforcing member 23 enhances the strength of the nip forming member 26 forming the nip and is integrated with the nip forming member 26 by screw fastening.
Referring to FIG. 4, the reinforcing member 23 is wider in width than the nip forming member 26 and has both ends, in its width direction, held movably by the side plates 43 of the fixing device 20. Since the reinforcing member 23 abuts on the pressure roller 31 through the nip forming member 26 and the fixing belt 21, the nip forming member 26 is inhibited from highly deforming at the nip due to the pressing force from the pressure roller 31. In order to fulfill such a function as above, preferably, the reinforcing member 23 is formed of a metallic material high in mechanical strength, such as stainless steel or iron.

Heating Means

The fixing belt 21 is directly heated by radiant heat from the heater 25 (heating means) installed thereinside. The heater 25 as a heating means heats the fixing belt 21 to heat a sheet P. The heater 25 (heating means) heats, as a heating region, the region out of the nip in the circumferential direction of the fixing belt 21.
Specifically, the heater 25 as a heating means is a halogen heater (or carbon heater) and has both ends secured to the side plates 43 of the fixing device 20 (refer to FIG. 4). Then, radiant heat from the heater 25 (heating means) output-controlled by a controller heats mainly a region, which faces the heater 25, in the heating region out of the nip in the fixing belt 21. Furthermore, heat is applied from the surface of the heated fixing belt 21 to the toner image T on the sheet P.
Output control of the heater 25 is performed based on a result of detection of a belt surface temperature from a temperature detecting sensor 40 (temperature detecting means), such as a thermopile or a thermistor, facing the surface of the fixing belt 21. Due to such output control of the heater 25, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

Reflective Plate

As illustrated in FIG. 2, the reflective plate 27 is secured between the reinforcing member 23 and the heater 25. Thus, heat from the heater 25 toward the reinforcing member 23 (infrared rays that heat the reinforcing member 23) is reflected by the reflective plate 27 to heat the fixing belt 21. Therefore, a further improvement can be made in the efficiency of heating the fixing belt 21. The reflective plate 27 can be formed using aluminum or stainless steel. Note that, even in a case where the entirety or part of a counter face of the reinforcing member 23 to the heater 25 is subjected to mirror finishing or is provided with a thermal-insulating member, an effect similar to the above-described effect can be obtained.
As above, according to the fixing device 20 in the present embodiment, the fixing belt 21 is not partially locally heated but is heated over a relatively wide range in its circumferential direction. Thus, even in a case where the fixing device 20 is enhanced in speed, the fixing belt 21 is sufficiently heated, leading to inhibition of occurrence of a defect in fixing. That is, the fixing belt 21 can be efficiently heated with a relatively simple configuration. Thus, reductions can be made in warm-up time and fast print time and additionally a reduction can be made in the size of the fixing device 20.
In particular, according the fixing device 20 in the present embodiment, the fixing belt 21 is directly heated by the heater 25 (heating means). Thus, a further improvement is made in the efficiency of heating the fixing belt 21 and additionally further reductions can be made in the cost and size of the fixing device 20.
Note that, in the present embodiment, the heater 25 (heating means) installed inside the inner circumferential face of the fixing belt 21 includes two heaters, but may include a single heater or three or more heaters. The position of the heater 25 and the shape of the reinforcing member 23 described later in the present embodiment are not limiting. For example, the heater 25 may be disposed upstream of the position in FIG. 2 in the rotational direction of the fixing belt 21 so as to face the fixing belt 21 and then the reinforcing member 23 may have a shape suitable to the disposed heater 25.
The operation in normal mode of the fixing device 20 having such a configuration as above will be briefly described below. When a power switch on the image forming apparatus 100 is turned on, the heater 25 is supplied with power and additionally the pressure roller 31 starts to rotate, as driving, in the direction of the corresponding arrow in FIG. 2. Thus, due to frictional force based on the pressure roller 31 at the nip, the fixing belt 21 rotates in a driven manner in the direction of the corresponding arrow in FIG. 2 (rotates together with the pressure roller 31).
After that, a sheet P is fed from the sheet feeder 7 and then a not yet fixed color image is borne on the sheet P (transferred onto the sheet P) at the position of the secondary transfer roller 13. The sheet P on which a toner image T (not yet fixed image) is borne is conveyed in the direction of an arrow Y10 in FIG. 2 while being guided by a guide plate, and then is sent into the nip between the fixing belt 21 and the pressure roller 31 that are pressed against each other.
Then, due to heat from the fixing belt 21 heated by the heater 25 and pressing force between the nip forming member 26 reinforced by the reinforcing member 23 and the pressure roller 31, the toner image T is fixed to the surface of the sheet P. After that, the sheet P sent out from the nip is conveyed in the direction of an arrow Y11.
Next, a holding member 30 and the vapor chamber 28 included in the nip forming member 26 will be described.
Referring to FIG. 5, the nip forming member 26 in the fixing device 20 in the present embodiment includes the vapor chamber 28 in sliding contact with the inner circumferential face of the fixing belt 21. In detail, the nip forming member 26 includes the holding member 30 (nip forming member body) and the vapor chamber 28.
The holding member 30 is located away from the nip (fixing nip) (inside the fixing belt 21) and holds the vapor chamber 28. The holding member 30 has a certain degree of rigidity and thus does not highly bend even when receiving the pressing force from the pressure roller 31. The holding member 30 holds the vapor chamber 28 and additionally is held by the reinforcing member 23.
Examples of a material for forming the holding member 30 that can be used include resin materials, such as liquid crystal polymers (LCP), polyamide-imides (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), and polyether ether ketone (PEEK).
The vapor chamber 28 serving as a metallic heat dissipation member contains hydraulic liquid, such as water, in a hollow 28b and functions to transfer heat immediately in response to vaporization or condensation of the hydraulic liquid. Referring to FIG. 6, the vapor chamber 28 includes a wick 36 (substantially sponge-like member having a fine pattern inside) almost all over inner wall faces 28c and 28d.
The hydraulic liquid inside the vapor chamber 28 vaporizes due to heat from the heat source and the resultant vapor diffuses inside the vapor chamber 28 to dissipate heat. The vapor having dissipated the heat condenses again as liquid and then the resultant liquid circulates to the heat source again, based on capillary action due to the wick 36. In this manner, the vapor chamber 28 enables high thermal conductivity and thermal uniformity. Note that, since the vapor chamber 28 includes the wick 36 in the hollow 28b, the vapor chamber 28 is different in configuration from a heat pipe as another metallic heat dissipation member.
The vapor chamber 28 has a substantially rectangular frame formed of a material high in thermal conductivity, such as copper, aluminum, silver, or graphite. In the present embodiment, the sliding contact face 28a of the vapor chamber 28 (namely, the face in sliding contact with the inner circumferential face of the fixing belt 21) is flat in shape.
Furthermore, the sliding contact face 28a of the vapor chamber 28 is formed of a low friction material. Specifically, a coating layer 29, which is shaped like a thin film and is made of a low friction material such as a fluoropolymer, is formed on the sliding contact face 28a.
Due to such a configuration, the frictional resistance between the fixing belt 21 and the sliding contact face 28a of the vapor chamber 28 is low, leading to less deterioration of the fixing belt 21 and the sliding contact face 28a in abrasion.
Note that, for achievement of the above-described effect, the sliding contact face 28a is formed of a low friction material, but the other part may be also formed of a low friction material.
As illustrated in FIG. 6, the vapor chamber 28 in the present embodiment further includes a plurality of columnar members 32, between the inner wall face 28c closer to the nip and the inner wall face 28d that is closer to the reinforcing member 23 and faces the inner wall face 28c, in the hollow 28b in which the hydraulic liquid is contained.
That is, the hollow 28b of the vapor chamber 28 is provided not only with a space in which the hydraulic liquid flows but also with a plurality of columnar members 32 without interrupting heat exchange due to a flow of the hydraulic liquid. The columnar members 32 in the present embodiment are identical in material to the frame of the vapor chamber 28 and are integrally formed with the frame of the vapor chamber 28.
Since the columnar members 32 are provided, the vapor chamber 28 is high in mechanical strength and thus deforms hardly even when receiving the pressing force from the pressure roller 31. The nip forming member 26 including the vapor chamber 28 described above enables not only favorable heat exchange but also a stable fixing step over a long period of time with a desired nip shape kept.
Note that, in the present embodiment, the columnar members 32 are each shaped like a quadrangular prism in consideration of the strength of the vapor chamber 28, but the shape of each columnar member 32 is not limited to this shape. For example, the columnar members 32 may be each shaped like a round pillar such that no deterioration is made in the fluidity of the hydraulic liquid in the hollow 28b.
Next, disadvantages of which the present disclosure has been made in consideration and distinctive configurations to solve the disadvantages will be described.
Referring to FIG. 5, the vapor chamber 28 is held by the holding member 30 and has the sliding contact face 28a in sliding contact with the inner circumferential face of the fixing belt 21. The vapor chamber 28 promptly uniforms, in its longitudinal direction, heat from the fixing belt 21, resulting in inhibition of temperature deviation in the longitudinal direction of the fixing belt 21 (a rise in the temperature of an end).
On the other hand, the vapor chamber 28 and the holding member 30 have respective flat contact faces that are mutually in contact all over. Since the contact faces are mutually in contact all over, the heat of the fixing belt 21 is easily released to the holding member 30 through the vapor chamber 28. In particular, immediately after start-up of the fixing device 20, the fixing belt 21 is brought to a high temperature but the holding member 30 remains low in temperature. Thus, the difference in temperature between the fixing belt 21 and the holding member 30 is large, so that heat moves easily. Thus, due to a drop in the temperature of the fixing belt 21, further heating is required, leading to a deterioration in the thermal efficiency of the fixing device 20. In particular, the vapor chamber 28 is high in thermal conductivity and thus causes heat to move promptly. Therefore, some measures are desired.
FIG. 7 is a partial cross-sectional view illustrating the configuration of a nip forming member according to an embodiment of the present disclosure. A holding member 30 includes a plurality of protrusions 30a in contact with a vapor chamber 28. In other words, the holding member 30 has a non-flat face, and the plurality of protrusions 30a has their leading ends in contact with the vapor chamber 28. Thus, the contact area between the holding member 30 and the vapor chamber 28 is smaller than the contact area in FIG. 5.
As a result, the transfer rate of heat from the vapor chamber 28 to the holding member 30 is low, leading to a small drop in the temperature of a fixing belt 21. Therefore, with the vapor chamber 28 effecting thermal uniformity, a fixing device high in thermal efficiency can be achieved.
FIG. 8 is a perspective view illustrating an arrangement configuration of a holding member and a vapor chamber according to an embodiment of the present disclosure. Referring to FIG. 8, a holding member 30 has a flat face, counter to a vapor chamber 28, provided with a plurality of protrusions 30a. On the other hand, the vapor chamber 28 has a hollow 28b provided with a plurality of columnar members 32.
The columnar members 32 of the vapor chamber 28 enhance the strength of the vapor chamber 28 to prevent the vapor chamber 28 from crush-deforming due to pressure at a nip. In the present embodiment, the holding member 30 and the vapor chamber 28 are disposed such that the plurality of protrusions 30a is almost identical to the plurality of columnar members 32 in the longitudinal direction of a fixing belt 21 and in a conveyance direction.
That is, when viewed in the pressing direction of a pressure roller 31, the plurality of protrusions 30a overlap one-to-one with the plurality of columnar members 32.
Therefore, as illustrated in FIG. 9A, force P1 acting on each one of the plurality of columnar members 32 receiving the pressing force W at the nip can be received by the corresponding protrusion 30a. The force P1 acting on each one of the plurality of columnar members 32 and reaction force P2 from the corresponding protrusion 30a are almost aligned, so that the vapor chamber 28 can be prevented from crush-deforming.
In contrast to this case, as illustrated in FIG. 9B, in a case where the plurality of columnar members 32 is not identical in arrangement to the plurality of protrusions 30a, the vapor chamber 28 receives bending stress due to the reaction force P2 from each one of the plurality of protrusions 30a. Thus, depending on the pressing force from the pressure roller 31, crush-deformation may occur.
FIG. 10A is a plan view illustrating the shapes of columnar members disposed inside a vapor chamber according to an embodiment of the present disclosure. FIG. 10B is a plan view illustrating the shapes of columnar members disposed inside a vapor chamber according to another embodiment of the present disclosure. FIG. 10A illustrates columnar members 32 rectangular in shape. FIG. 10B illustrates columnar members 32' oval or elliptical in shape. In either of the cases, the longitudinal direction of the shape of each columnar member is identical to the longitudinal direction of a vapor chamber 28.
A vapor chamber 28 expands thermally due to heating at the time of fixing and has an amount of expansion larger in a longitudinal direction (axial direction) than in a conveyance direction. In this case, similarly, a holding member 30 expands thermally. However, due to difference at least either in material or in temperature, the vapor chamber 28 and the holding member 30 are different in the amount of expansion. Thus, misalignment occurs easily between each columnar member 32 and the corresponding protrusion 30a. In particular, such misalignment is severe in the longitudinal direction in which the vapor chamber 28 has a large amount of thermal expansion.
For solution to this disadvantage, columnar members 32 each having a rectangular, oval, or elliptical cross section are provided. Thus, even in a case where slight misalignment occurs between each columnar member 32 and the corresponding protrusion 30a, an overlap can be ensured between each columnar member 32 and the corresponding protrusion 30a.
Similarly, desirably, the protrusions 30a of the holding member 30 each have a cross section (rectangular, oval, or elliptical cross section) of which the longitudinal direction is identical to the longitudinal direction of the vapor chamber 28.
FIG. 11 is a partial cross-sectional view illustrating the configuration of a holding member according to a modification of the present disclosure. A holding member 30 includes a plurality of protrusions 30a each provided with a thermal-insulating member 33 that serves as a contact part to a vapor chamber 28 and is lower in thermal conductivity than the holding member 30. As the thermal-insulating member 33, a sheet-like member including woven thermal-resistant fibers, a glass wool member, a foamed resin member, or a hollow member can be used. A member including an air layer inside has effective thermal insulation.
Due to such a configuration, a further reduction can be made in the transfer rate of heat from the vapor chamber 28 to the holding member 30, leading to a small drop in the temperature of a fixing belt 21. Therefore, with the vapor chamber 28 effecting thermal uniformity, a fixing device high in thermal efficiency can be achieved.
FIG. 12A is a cross-sectional view of a nip forming member including a holding member having a plurality of protrusions of which the heights gradually decrease along the longitudinal direction of the holding member. FIG. 12B is a perspective view of the holding member.
In this embodiment, a holding member 30 includes protrusions 30a of which the heights gradually decrease from the center toward each end in the longitudinal direction of the holding member 30. Specifically, the heights of the protrusions 30a of the holding member 30 decrease toward each end such that the heights of protrusions 30a1 at the center are highest and the heights of protrusions 30an at both ends are lowest.
A vapor chamber 28 receives, all over its width, a nip pressure from a pressure roller 31 at the time of fixing to deform along the heights of the protrusions 30a1 to 30an. As a result, the center of the vapor chamber 28 is raised, and thus the nip pressure at the center in the longitudinal direction is higher than the nip pressure at the center in a case where the vapor chamber 28 is flat. Thus, an improvement in fixing near the center can be expected. The respective nip pressures at both ends are uniformed, leading to an enhancement in the stability of sheet conveyance.
FIG. 13A is a cross-sectional view of a nip forming member including a holding member having a plurality of protrusions of which the heights gradually increase along the longitudinal direction of the holding member. FIG. 13B is a perspective view of the holding member.
In this embodiment, a holding member 30 includes protrusions 30a of which the heights gradually increase from the center toward each end in the longitudinal direction of the holding member 30. Specifically, the heights of the protrusions 30a of the holding member 30 increase toward each end such that the heights of protrusions 30a1 at the center are lowest and the heights of protrusions 30an at both ends are highest.
A vapor chamber 28 receives, all over its width, a nip pressure from a pressure roller 31 at the time of fixing to deform along the heights of the protrusions 30a1 to 30an. As a result, the center of the vapor chamber 28 is declined, and thus the nip pressure at each end in the longitudinal direction is higher than the nip pressure at each end in a case where the vapor chamber 28 is flat. Thus, an improvement in fixing near each end can be expected. Due to a large tangential force at each end, force to expand a sheet to both ends is large, leading to an enhancement in the effect of preventing a sheet from wrinkling.
FIG. 14A is a cross-sectional view of a nip forming member including a holding member having a plurality of protrusions of which the heights gradually increase along a conveyance direction of the holding member. FIG. 14B is a perspective view of the holding member.
In this embodiment, a holding member 30 includes protrusions 30a of which the heights gradually increase from the center toward each end in the lateral direction of the holding member 30. Specifically, the heights of the protrusions 30a of the holding member 30 increase toward each end such that the height of a protrusion 30a1 near the center is lowest, the height of a protrusion 30a2 is highest on the upstream side (lower side in FIG. 14A) from the protrusion 30a1 in the conveyance direction of the sheet, and the height of a protrusion 30a3 is highest on the downstream side (upper side in FIG. 14A) from the protrusion 30a1 in the conveyance direction of the sheet.
A vapor chamber 28 receives, all over its width, a nip pressure from a pressure roller 31 at the time of fixing to deform along the heights of the protrusions 30a1 and 30a2. As a result, the center of the vapor chamber 28 is declined and thus is shaped like the external form of a pressure roller 31 (refer to FIG. 15). Due to such a configuration, the cross-sectional area in the lateral direction of the vapor chamber 28 is expanded, leading to facilitation of thermal diffusion at either nip end.
The vapor chamber 28 is more stably held by the holding member 30 than a vapor chamber 28 rectangularly cubic in shape is. The pressure distribution in the nip is uniform, leading to an enhancement in the stability of sheet conveyance.
Note that, even in a case where the contact face between the holding member 30 and the vapor chamber 28 is, for example, convex in shape (namely, with no protrusions 30a), such an effect as above can be obtained. However, the transfer amount of heat from the vapor chamber 28 to the holding member 30 increases, leading to a deterioration in thermal efficiency.
FIG. 16A is a partial cross-sectional view of a nip forming member according to a modification of the present disclosure (version 1). FIG. 16B is a perspective view of a holding member.
As illustrated in FIG. 16A, a holding member 30' includes portions (holders 30b), on the upstream and downstream sides in a conveyance direction, holding a vapor chamber 28 with both sides of the vapor chamber 28 interposed between the portions (holders 30b) in the conveyance direction. Thus, the vapor chamber 28 can be securely held against sliding torque due to a fixing belt 21.
As illustrated in FIG. 16B, the holding member 30' may further include portions (holders 30b'), at both ends in its longitudinal direction, for holding the vapor chamber 28 with both sides of the vapor chamber 28 interposed between the portions (holders 30b') in the longitudinal direction. In this case, the holding member 30' can hold the vapor chamber 28 while surrounding all sides of the vapor chamber 28, leading to simplified holding means (e.g., simplified screw fastening) between the holding member 30' and the vapor chamber 28.
In particular, the vapor chamber 28 may be flat in shape as a simple configuration, leading to an improvement in thermal conductivity, an improvement in the productivity of components, and a reduction in manufacturing cost.
FIG. 17 is a partial cross-sectional view of a nip forming member according to a modification of the present disclosure (version 2). As illustrated in FIG. 17, a holding member 30" includes an exit protrusion 30c protruding toward a pressure roller 31, at the exit of a nip on the downstream side in a conveyance direction of a fixing member.
A fixing belt 21 at the exit of the nip is directed to the pressure roller 31 along the exit protrusion 30c, so that a sheet P ejected from the nip is ejected toward the pressure roller 31. Therefore, the sheet P is prevented from winding around the fixing belt 21 after fixing, so that stable separation performance is obtained.

First Modification

FIG. 18 is a cross-sectional view illustrating the configuration of a fixing device according to a modification of the present disclosure (version 1). As illustrated in FIG. 18, a fixing device 20' includes a heating element (resistive heating element) 38 as a heating means that heats a fixing belt 21.
The heating element 38 has a face in sliding contact with the inner circumferential face of the fixing belt 21 and the other face, opposite to the face, in contact with a vapor chamber 28. Then, a nip forming member 26' includes the heating element 38, the vapor chamber 28, and a holding member 30 that holds the heating element 38 and the vapor chamber 28.
The sliding contact face of the heating element 38 to the fixing belt 21 is formed of a low friction material for lower sliding resistance. The holding member 30 includes a plurality of protrusions 30a in contact with the vapor chamber 28.
According to the fixing device 20' having such a configuration, the vapor chamber 28 uniforms the temperature distribution in the width direction of the heating element 38, so that the fixing temperature in the width direction of the fixing belt 21 heated by the heating element 38 is uniformed sufficiently. The transfer rate of heat from the vapor chamber 28 to the holding member 30 is low.
As a result, the heat from the heating element 38 can be efficiently transferred to the fixing belt 21, leading to achievement of a fixing device high in thermal efficiency with the vapor chamber 28 effecting thermal uniformity.

Second Modification

FIG. 19 is a cross-sectional view of the configuration of a fixing device according to a modification of the present disclosure (version 2). As illustrated in FIG. 19, a fixing device 20" includes an electromagnetic induction heating coil 50 as a heating means that heats a fixing belt 21'. Note that the fixing device 20" includes a nip forming member 26 (a vapor chamber 28 and a holding member 30) and a reinforcing member 23 that are identical to the nip forming member 26 (the vapor chamber 28 and the holding member 30) and the reinforcing member 23 in the fixing device 20 in FIG. 7.
The fixing belt 21' includes a heating layer to be heated in an electromagnetic induction manner by the electromagnetic induction heating coil 50, in addition to such a base layer, an elastic layer, and a release layer as described with FIG. 2. The heating layer can be formed, for example, between the elastic layer and the release layer or the base layer can be used as the heating layer. As the material of the heating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, or alloys of any metals of the metals can be used.
On the other hand, the electromagnetic induction heating coil 50 includes an exciting coil, a core, and a coil guide. The exciting coil includes a litz wire made of bundled thin wires extending widthwise to cover part of the fixing belt 21'. The core is a semicylindrical member made of a ferromagnetic material (approximately 1000 to 3000 in relative permeability), such as ferrite, and includes a center core and a side core to form an efficient magnetic flux to the heating layer of the fixing belt 21'. The core is installed facing the exciting coil extending widthwise. The coil guide is made of a resin material high in heat resistance and holds the exciting coil and the core.
The fixing device 20" having such a configuration operates as follows. When the fixing belt 21' rotates in the direction of the corresponding arrow (counterclockwise) in FIG. 19, the fixing belt 21' is heated at a position opposed to the electromagnetic induction heating coil 50. In detail, when a high-frequency alternating current flows through the electromagnetic induction heating coil 50, magnetic lines of force to be bi-directionally alternately switched are formed around the fixing belt 21'. In this case, an eddy current is generated on the surface of the heating layer of the fixing belt 21', and then Joule heat is generated due to the electric resistance of the heating layer. Due to the Joule heat, the heating layer is heated in an electromagnetic induction manner, so that the fixing belt 21' is heated.
Note that, in the example of FIG. 19, the electromagnetic induction heating coil 50 is installed facing the outer circumferential face of the fixing belt 21', but can be installed facing the inner circumferential face of the fixing belt 21'.
Then, according to the fixing device 20" of an electromagnetic induction type having such a configuration, the fixing temperature in the width direction of the fixing belt 21' is sufficiently uniformed by the vapor chamber 28. The holding member 30 includes protrusions 30a in contact with the vapor chamber 28. Thus, the transfer rate of heat from the vapor chamber 28 to the holding member 30 is low.
Some embodiments of the present disclosure have been described in detail above. The above-described embodiments are examples and thus various modifications can be made without departing from the gist of the present disclosure. For example, in the above-described embodiments, the present disclosure has been applied to the fixing devices 20, 20', and 20" each including the pressure roller 31 as a pressure rotator. The present disclosure can be applied to a fixing device including a pressure belt as a pressure rotator. Even with such a configuration, an effect similar to the respective effects in the above-described embodiments can be obtained.
The present disclosure is not limited to the above-described embodiments and it is apparent that above-described embodiments can be modified as appropriate without departing from the technical idea of the present disclosure in addition to what is suggested in the embodiments. The constituent members are each not limited to the number, position, and shape in each embodiment and thus can be each favorably set in number, position, and shape for carrying out the present disclosure.
Furthermore, in the present specification and the drawings, the "width direction" is defined as a direction that is orthogonal to the conveyance direction of a sheet and is identical to a direction along which a fixing belt and a pressure roller each have a rotary shaft.
Aspects of the present disclosure are, for example, as follows.

First Aspect

A fixing device includes: a fixing member that is rotatable and has an endless shape; a heating means to heat the fixing member; a pressure rotator disposed outside the fixing member to press the fixing member; and a nip forming member disposed inside the fixing member to form a nip between the fixing member and the pressure rotator. The nip forming member includes: a vapor chamber to which heat is transferred from an inner circumferential face of the fixing member; and a holding member that holds the vapor chamber. The holding member includes a plurality of protrusions in contact with the vapor chamber.

Second Aspect

In the fixing device according to the first aspect, the vapor chamber includes a hollow and a plurality of columnar members in the hollow. The plurality of protrusions overlap one-to-one with the plurality of columnar members when viewed in a pressing direction of the pressure rotator.

Third Aspect

In the fixing device according to the second aspect, each one of the plurality of protrusions and the plurality of columnar members has a rectangular or elliptical cross section that is longer in an axial direction of the fixing member than in a direction perpendicular to the axial direction.

Fourth Aspect

In the fixing device according to any one of the first to third aspects, each one of the plurality of protrusions of the holding member includes a thermal-insulating member in contact with the vapor chamber, and the thermal-insulating member is lower in thermal conductivity than the holding member.

Fifth Aspect

In the fixing device according to any one of the first to fourth aspects, the plurality of protrusions gradually increase or decrease in height from a center toward each end in a longitudinal direction of the holding member.

Sixth Aspect

In the fixing device according to any one of the first to fourth aspects, the plurality of protrusions gradually increase in height from a center toward each end in a lateral direction of the holding member.

Seventh Aspect

In the fixing device according to any one of the first to sixth aspects, the holding member holds the vapor chamber with both ends of the vapor chamber interposed between upstream and downstream ends of the holding member in a conveyance direction.

Eighth Aspect

In the fixing device according to any one of the first to seventh aspects, the holding member includes an exit protrusion at an exit of the nip on a downstream side in a conveyance direction of the fixing member.

Ninth Aspect

In the fixing device according to any one of the first to eighth aspects, the vapor chamber has a sliding contact face to the fixing member, and the sliding contact face includes a low friction material.

Tenth Aspect

In the fixing device according to any one of the first to ninth aspects, the heating means includes a heater disposed facing the inner circumferential face of the fixing member.

Eleventh Aspect

In the fixing device according to any one of the first to ninth aspects, the heating means includes an electromagnetic induction heating coil disposed facing an outer circumferential face or an inner circumferential face of the fixing member.

Twelfth Aspect

A fixing device includes: a fixing member that is rotatable and has an endless shape; a heating means to heat the fixing member, the heating means including a heating element having a face in sliding contact with an inner circumferential face of the fixing member; a pressure rotator disposed outside the fixing member to press the fixing member; and a nip forming member inside the fixing member to form a nip between the fixing member and the pressure rotator. The nip forming member includes: the heating element; a vapor chamber in contact with another face of the heating element, the other face being opposite to the face; and a holding member that holds the heating element and the vapor chamber. The holding member includes a plurality of protrusions in contact with the vapor chamber.

Thirteenth Aspect

An image forming apparatus includes the fixing device of any one of the first to twelfth aspects.

Claims

A fixing device (20, 20', 20"), comprising:
a fixing member (21, 21') that is rotatable and has an endless shape;

a heating means (25, 38, 50) to heat the fixing member (21, 21');

a pressure rotator (31) disposed outside the fixing member (21, 21') to press the fixing member (21, 21'); and

a nip forming member (26, 26') disposed inside the fixing member (21, 21') to form a nip between the fixing member (21, 21') and the pressure rotator (31),

the nip forming member (26, 26') including:
a vapor chamber (28) to which heat is transferred from an inner circumferential face of the fixing member (21, 21'); and

a holding member (30) that holds the vapor chamber (28),

the holding member including a plurality of protrusions (30a) in contact with the vapor chamber (28).
The fixing device (20, 20', 20") according to claim 1,
wherein the vapor chamber includes:
a hollow (28b); and

a plurality of columnar members (32) in the hollow, and

the plurality of protrusions (30a) overlap one-to-one with the plurality of columnar members (32) when viewed in a pressing direction of the pressure rotator (31).
The fixing device (20, 20', 20") according to claim 2,
wherein each one of the plurality of protrusions (30a) and the plurality of columnar members (32) has a rectangular or elliptical cross section that is longer in an axial direction of the fixing member (21, 21') than in a direction perpendicular to the axial direction.
The fixing device (20, 20', 20") according to any one of claims 1 to 3,
wherein each one of the plurality of protrusions (30a) of the holding member includes a thermal-insulating member (33) in contact with the vapor chamber, and the thermal-insulating member is lower in thermal conductivity than the holding member.
The fixing device (20, 20', 20") according to any one of claims 1 to 4,
wherein the plurality of protrusions (30a) gradually increase or decrease in height from a center toward each end in a longitudinal direction of the holding member.
The fixing device (20, 20', 20") according to any one of claims 1 to 4,
wherein the plurality of protrusions (30a) gradually increase in height from a center toward each end in a lateral direction of the holding member.
The fixing device (20, 20', 20") according to any one of claims 1 to 6,
wherein the holding member (30) holds the vapor chamber with both sides of the vapor chamber interposed between upstream and downstream ends of the holding member in a conveyance direction.
The fixing device (20, 20', 20") according to any one of claims 1 to 7,
wherein the holding member includes an exit protrusion (30c) at an exit of the nip on a downstream side in a conveyance direction of the fixing member (21, 21').
The fixing device (20, 20', 20") according to any one of claims 1 to 8,
wherein the vapor chamber has a sliding contact face to the fixing member (21, 21'), and the sliding contact face includes a low friction material.
The fixing device (20, 20', 20") according to any one of claims 1 to 9,
wherein the heating means (25, 38, 50) includes a heater disposed facing the inner circumferential face of the fixing member (21, 21').
The fixing device (20, 20', 20") according to any one of claims 1 to 9,
wherein the heating means (25, 38, 50) includes an electromagnetic induction heating coil disposed facing an outer circumferential face or the inner circumferential face of the fixing member (21, 21').
An image forming apparatus (100), comprising the fixing device (20, 20', 20") according to any one of claims 1 to 11.