JP7296037B2 - Fixing device, image forming device - Google Patents

Description

The present invention relates to a fixing device and an image forming apparatus.

In image forming apparatuses such as copiers, printers, facsimiles, or multifunction machines thereof, a fixing method in which a recording medium such as paper on which an unfixed image is formed is formed between a fixing belt and a pressure member of the fixing device. The image is fixed on the surface of the recording medium by conveying it to the nip and applying pressure and heat to the recording medium.

The fixing device is provided inside the fixing belt with a nip forming member that forms a fixing nip by coming into contact with the pressing member via the fixing belt, and a support member that supports the nip forming member.

In this type of fixing device, it is necessary to separate the recording medium that has passed through the fixing nip from the fixing belt and convey it downstream. In order to improve the peelability of the recording medium from the fixing belt, the peelability of the recording medium is improved by increasing the peeling angle, which is the angle between the conveying direction of the recording medium after passing through the fixing nip and the fixing belt. It is already known how to

For example, in the fixing device 100 disclosed in Japanese Patent Application Laid-Open No. 2014-66851, as shown in FIG. forming. The nip plate 103 has a flat plate-like portion 103a, a bent portion 103b extending downward from the rear end of the plate-like portion 103a, and a bottom portion 103c extending rearward from the lower end of the bent portion 103b. The sheet S heated and pressurized at the fixing nip N changes its conveying direction due to the bent portion 103b. That is, the sheet S is separated from the fixing belt 101 at a separation angle α between the conveying direction of the sheet S and the fixing belt 101 .

As in Patent Document 1, by providing a bent portion bent toward the pressure member on the downstream side of the fixing nip, it is possible to provide a large peeling angle of the recording medium from the fixing belt, thereby improving the peelability of the recording medium. can be improved. However, in the configuration disclosed in Patent Document 1, since the portion downstream from the bent portion 103b is not in contact with the pressure member, a nip portion cannot be formed between this portion and the pressure member. There is a problem that the length of the fixing nip in the conveying direction is reduced. Therefore, depending on the configuration of the fixing device, there is a problem that the recording medium cannot be sufficiently heated.

Under these circumstances, an object of the present invention is to sufficiently heat the recording medium and to secure the releasability of the recording medium from the fixing belt after the fixing operation.

In order to solve the above problems, the present invention provides an endless fixing belt, a pressure member that presses the fixing belt, and a pressure member that is provided inside the fixing belt and presses the pressure member through the fixing belt. A fixing device comprising: a nip forming member contacting to form a fixing nip; a heating member for heating the fixing belt; and a supporting member provided inside the fixing belt and supporting the nip forming member. The nip forming member includes a first nip forming portion that abuts against the pressure member via the fixing belt to form a first fixing nip, and a downstream side of the first nip forming portion in the recording medium conveying direction. a second nip forming portion that is provided on the side of the fixing belt and forms a second fixing nip by coming into contact with the pressure member via the fixing belt; Assuming that the downstream portion of the first nip forming portion in the recording medium conveying direction that is directly or indirectly abutted by the support member is the supported portion, the supported portion in the recording medium conveying direction is The inflection portion is provided at a position or downstream thereof, the second nip forming portion is provided downstream of the inflection portion, and the pressing direction of the pressure member with respect to the fixing belt and In the opposite direction, the downstream end portion of the second nip forming portion in the recording medium conveying direction is directed from the upstream side to the downstream side in the recording medium conveying direction in a direction opposite to the pressing direction of the pressure member against the fixing belt. and the inflection portion is provided on the supported portion .

According to the present invention, it is possible to secure the releasability of the recording medium from the fixing belt after the fixing operation, and to sufficiently heat the recording medium.

1 is a schematic configuration diagram of an image forming apparatus; FIG. 2 is a side cross-sectional view of the fixing device; FIG. 2 is a perspective cross-sectional view of the fixing device; FIG. 2 is a front cross-sectional view of the fixing device; FIG. FIG. 4 is a side cross-sectional view of a fixing device different from the present invention; FIG. 5 is a side cross-sectional view of a fixing device according to another embodiment; FIG. 10 is a side cross-sectional view of the fixing device showing elastic deformation of the second nip forming portion according to another embodiment; FIG. 10 illustrates biasing means for biasing the second nip formation; FIG. 10 is a side cross-sectional view of a conventional fixing device;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant description thereof will be appropriately simplified or omitted.

In the center of the color image forming apparatus 1 shown in FIG. 1, an image forming section 2 is arranged in which four process units 9Y, 9M, 9C, and 9Bk are detachably provided. Each of the process units 9Y, 9M, 9C, and 9Bk contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (Bk) corresponding to color separation components of a color image. It has the same configuration except that

Specifically, each process unit 9 includes a photosensitive drum 10, which is a drum-shaped rotating body capable of carrying toner as a developer on its surface, and a charging roller 11 that uniformly charges the surface of the photosensitive drum 10. , a developing device 12 having a developing roller for supplying toner to the surface of the photosensitive drum 10, and the like.

An exposure section 3 is arranged below the process unit 9 . The exposure unit 3 is configured to emit laser light based on image data.

A transfer section 4 is arranged above the image forming section 2 . The transfer unit 4 has an endless intermediate transfer belt 16 stretched around a drive roller 14 and a driven roller 15 so as to be able to circulate, and faces the photosensitive drums 10 of the process units 9 with the intermediate transfer belt 16 interposed therebetween. It is composed of the primary transfer roller 17 and the like arranged at the position. Each primary transfer roller 17 presses the inner circumferential surface of the intermediate transfer belt 16 at its respective position, and a primary transfer nip is formed at a location where the pressed portion of the intermediate transfer belt 16 and each photosensitive drum 10 contact each other. It is

Further, a driving roller 14 of the intermediate transfer belt 16 and a secondary transfer roller 18 are arranged at a position opposed to the driving roller 14 with the intermediate transfer belt 16 interposed therebetween. The secondary transfer roller 18 presses the outer peripheral surface of the intermediate transfer belt 16 , and a secondary transfer nip is formed where the secondary transfer roller 18 and the intermediate transfer belt 16 contact each other.

The paper feed unit 5 is located in the lower part of the image forming apparatus 1, and includes a paper feed cassette 19 containing paper P as a recording medium, paper feed rollers 20 for carrying out the paper P from the paper feed cassette 19, and the like. ing.

The transport path 6 is a transport path for transporting the paper P transported out from the paper feed unit 5. In addition to the pair of registration rollers 21, the transport roller pair extends along the transport path 6 to the paper discharge unit 8 described later. are appropriately placed in the

The fixing device 7 has a fixing belt 22 heated by a heat source, a pressure roller (pressure member) 23 capable of pressing the fixing belt 22, and the like.

The paper discharge section 8 is provided at the most downstream side of the conveying path 6 of the image forming apparatus 1 . The paper discharge section 8 is provided with a pair of paper discharge rollers 24 for discharging the paper P to the outside, and a paper discharge tray 25 for stocking the discharged paper P. As shown in FIG.

Toner bottles 29Y, 29C, 29M, and 29K filled with yellow, cyan, magenta, and black toners are detachably provided on the upper portion of the image forming apparatus 1. As shown in FIG. Each color developing device 12 is replenished with toner of each color from the toner bottles 29Y, C, M, and K through replenishment paths provided between each developing device 12 and the toner bottles 29Y, C, M, and K.

The basic operation of the image forming apparatus 1 will be described below with reference to FIG.

In the image forming apparatus 1, when the image forming operation is started, an electrostatic latent image is formed on the surface of the photosensitive drum 10 of each of the process units 9Y, 9C, 9M and 9Bk. The image information exposed by the exposure unit 3 on each photosensitive drum 10 is monochromatic image information obtained by decomposing a desired full-color image into yellow, cyan, magenta, and black color information. An electrostatic latent image is formed on each photoreceptor drum 10, and toner stored in each developing device 12 is supplied to the photoreceptor drum 10 by a drum-shaped developing roller, whereby the electrostatic latent image is made visible. It is visualized as a toner image (developer image).

In the transfer section 4, the intermediate transfer belt 16 is driven to run in the direction of the arrow A in the figure by the rotational drive of the driving roller 14. As shown in FIG. A constant voltage having a polarity opposite to the charging polarity of the toner or a voltage controlled by a constant current is applied to each primary transfer roller 17 . As a result, a transfer electric field is formed at the primary transfer nip, and the toner images formed on the photoreceptor drums 10 are sequentially superimposed and transferred onto the intermediate transfer belt 16 at the primary transfer nip.

On the other hand, when the image forming operation is started, in the lower part of the image forming apparatus 1 , the sheet P accommodated in the sheet feeding cassette 19 is transferred to the conveying path 6 by rotating the sheet feeding roller 20 of the sheet feeding section 5 . sent out. The paper P sent out to the conveying path 6 is sent to the secondary transfer nip between the secondary transfer roller 18 and the drive roller 14 with the registration rollers 21 measuring the timing. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 16 is applied, and a transfer electric field is formed in the secondary transfer nip. The toner image on the intermediate transfer belt 16 is collectively transferred onto the paper P by the transfer electric field formed in the secondary transfer nip.

The paper P onto which the toner image has been transferred is conveyed to the fixing device 7, where the paper P is heated and pressed by the fixing belt 22 and the pressure roller 23, and the toner image is fixed on the paper P. FIG. Then, the paper P on which the toner image is fixed is separated from the fixing belt 22 , conveyed by the conveying roller pair, and discharged to the paper discharge tray 25 by the paper discharge rollers 24 in the paper discharge section 8 .

The above description is for the image forming operation when forming a full-color image on the paper P, but any one of the four process units 9Y, 9C, 9M, and 9Bk can be used to form a monochrome image, It is also possible to use two or three process units 9 to form a two-color or three-color image.

As shown in FIG. 2, the fixing device 7 includes a fixing belt 22, a pressure roller 23, a halogen heater 31 as a heating member, a nip forming member 32, a stay 33 as a supporting member, a reflecting member 34, and the like. It has As shown in FIG. 3, the halogen heater 31, the nip forming member 32, the stay 33, and the reflecting member 34 are provided inside the fixing belt 22, and and hereinafter also simply referred to as the width direction).

As shown in FIG. 2, the fixing belt 22 is a cylindrical fixing member that fixes the unfixed image T on the paper P, and is arranged on the side of the unfixed image carrying surface of the paper P. As shown in FIG. In this embodiment, the fixing belt 22 is composed of a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide, and PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) or It is composed of an endless belt (including a film) having a release layer on the outer peripheral side made of PTFE (polytetrafluoroethylene) or the like. An elastic layer made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber may be interposed between the substrate and the release layer. If the thickness of the elastic layer is set to about 100 μm, the elastic deformation of the elastic layer when the unfixed image (unfixed toner) is crushed and fixed can absorb minute irregularities on the belt surface, resulting in uneven glossiness. can be avoided. Further, in the present embodiment, a thin belt with a small diameter is used as the fixing belt 22 from the viewpoint of reducing the heat capacity of the fixing belt 22 . Specifically, the thickness of each of the base material and the release layer constituting the fixing belt 22 is set to the ranges of 20 to 50 μm and 10 to 50 μm, and the thickness of the fixing belt 22 as a whole is set to 1 mm or less. are doing. Further, when the fixing belt 22 has an elastic layer, the thickness of the elastic layer is preferably set to 100 to 300 μm. In order to further reduce the heat capacity, the thickness of the fixing belt 22 as a whole is preferably 0.2 mm or less, more preferably 0.16 mm or less. Further, in this embodiment, the diameter of the fixing belt 22 is set to 20 to 40 mm, preferably 30 mm or less.

The pressure roller 23 is a facing member arranged to face the outer peripheral side of the fixing belt 22 . In this embodiment, the pressure roller 23 is composed of a metal core, an elastic layer made of foamed silicone rubber or fluororubber provided on the surface of the metal core, and PFA or PTFE provided on the surface of the elastic layer. A release layer consisting of Further, in this embodiment, the pressure roller 23 is a solid roller, but it may be a hollow roller. In the case of a hollow roller, it is also possible to arrange a heating member such as a halogen heater inside the pressure roller 23 . The elastic layer of the pressure roller 23 may be made of solid rubber, but if a heating member is not arranged inside, it is desirable to use sponge rubber for the elastic layer to improve the heat insulation of the pressure roller 23 . As a result, the heat of the fixing belt 22 is less likely to be lost to the pressure roller 23, and the thermal efficiency of the fixing belt 22 is improved.

Further, the pressure roller 23 is configured to be rotationally driven in the direction indicated by the arrow A in FIG. 2 by a drive source provided in the main body of the image forming apparatus. On the other hand, the fixing belt 22 is driven to rotate in the direction of arrow B in FIG. 2 as the pressure roller 23 is driven to rotate. When the paper P with the unfixed image T transferred is fed between the fixing belt 22 and the pressure roller 23, the paper P is conveyed by the rotating fixing belt 22 and the pressure roller 23 to fixation nips N1 and N2. pass through. At this time, the unfixed image T is fixed on the paper P by applying heat and pressure to the paper P. FIG.

Further, the pressure roller 23 and the fixing belt 22 are configured so as to approach and separate from each other. In the unlikely event that a paper jam occurs in the fixing nips N1 and N2, the pressure roller 23 and the fixing belt 22 are separated from each other to open the fixing nips N1 and N2. It is possible. The pressure roller 23 and the fixing belt 22 may be configured to move one of them toward and away from the other, or may be configured to move both toward and away from each other.

The halogen heater 31 is a heating member that is arranged on the inner peripheral side of the fixing belt 22 and heats the fixing belt 22 from the inner peripheral side with radiant heat by radiating infrared light. A carbon heater, a ceramic heater, or the like can be used as the heating member other than the halogen heater 31 . In the present embodiment, only one halogen heater 31 is arranged inside the fixing belt 22, but a plurality of halogen heaters 31 having different heat generating regions according to the width size of the paper may be used.

The nip forming member 32 sandwiches the fixing belt 22 with the pressure roller 23 to form fixing nips N1 and N2. Specifically, the nip forming member 32 is arranged longitudinally across the width direction on the inner peripheral side of the fixing belt 22 , and is in contact with the inner peripheral surface of the fixing belt 22 . , a bent portion 32b that bends from the upstream end portion of the first nip forming portion 32a in the belt rotation direction to the side opposite to the pressure roller 23 side, and the downstream side of the belt rotating direction of the first nip forming portion 32a, which will be described later. A second nip forming portion 32e and the like are provided. When the pressure roller 23 is pressed toward the nip forming member 32 by a pressure means such as a spring, the pressure roller 23 and the fixing belt 22 come into contact with each other, and fixing nips N1 and N2 are formed therebetween. be.

The nip forming surfaces 32a1 and 32e1 of the first nip forming portion 32a and the second nip forming portion 32e on the side of the fixing belt 22 are in direct contact with the inner peripheral surface of the fixing belt 22, and when the fixing belt 22 rotates. , the fixing belt 22 slides on the nip forming surfaces 32a1 and 32e1. Therefore, in order to improve the wear resistance and slidability of the nip forming surfaces 32a1 and 32e1, the nip forming surfaces 32a1 and 32e1 are preferably anodized or coated with a fluororesin material. Further, in order to ensure slidability over time, the nip forming surfaces 32a1 and 32e1 may be coated with a lubricant such as fluorine-based grease. In this embodiment, the nip forming surface 32a1 has a flat surface shape, but may have a concave shape or other shapes.

Also, the nip forming member 32 is made of a material having a higher thermal conductivity than the stay 33 . For example, the material of the nip forming member 32 is preferably copper (thermal conductivity: 398 W/mk) or aluminum (thermal conductivity: 236 W/mk). Since the nip forming member 32 is made of a material having high thermal conductivity, the radiant heat from the halogen heater 31 is absorbed by the nip forming member 32 and efficiently transmitted to the fixing belt 22 . For example, by setting the thickness of the nip forming member 32 to 1 mm or less, the heat transfer time from the nip forming member 32 to the fixing belt 22 can be shortened. be. Further, when the thickness of the nip forming member 32 is set to be more than 1 mm and 5 mm or less, the heat storage property of the nip forming member 32 can be enhanced.

The stay 33 indirectly contacts the nip forming member 32 from the opposite side (upper side of the figure) of the pressure roller 23 via another member (in this embodiment, the bent portion 34b of the reflecting member 34), It is a supporting member that supports the nip forming member 32 against the pressing force of the pressure roller 23 . Like the nip forming member 32 , the stay 33 is arranged longitudinally in the belt width direction on the inner peripheral side of the fixing belt 22 . In this embodiment, the stay 33 is formed to have a U-shaped cross section, which includes a pair of side wall portions 33a and a bottom wall portion 33b connecting them. The nip forming member 32 is supported by a pair of side wall portions 33a of the stay 33 at both end portions in the belt rotation direction B thereof. In addition, since each side wall portion 33a extends in the pressing direction of the pressure roller 23 (vertical direction in FIG. 2), the rigidity in the pressing direction is increased, and the first Deflection of the nip forming portion 32a is suppressed. Therefore, a nip portion with a uniform width can be obtained over the longitudinal direction. The stay 33 is preferably made of an iron-based metal material such as SUS or SECC in order to ensure its rigidity.

It should be noted that the stay 33 "supports" the nip forming member 32 means a portion of the stay 33 that extends in the pressure direction (vertical direction in the figure) of the pressure roller 23 (side wall portion 33a in this embodiment). ) or to bring the thick portion into contact with the nip forming member 32 from the side opposite to the pressure roller 23 (upper side in the figure). As a result, the bending of the nip forming member 32 due to the pressing force from the pressure roller 23 (especially bending in the longitudinal direction in this embodiment) is suppressed. However, the contact described above is not limited to the case where the stay 33 is in direct contact with the nip forming member 32, but also includes the case of contact via another member as in the present embodiment. "Abutment via another member" means that another member is sandwiched between the stay 33 and the nip forming member 32 in the vertical direction of the drawing, and at least a part thereof corresponds to the stay. 33 contacts another member, and the other member contacts the nip forming member 32 . Further, "extending in the pressurizing direction" means not only the same direction as the pressurizing direction of the pressurizing roller 23, but also extending in a direction having a certain angle from the pressurizing direction of the pressurizing roller 23. It also includes the case where it exists. Even in these cases, the stay 33 can naturally suppress the bending of the nip forming member 32 against the pressure from the pressure roller 23 .

The reflecting member 34 is arranged on the inner peripheral side of the fixing belt 22 so as to face the halogen heater 31, and reflects the radiant heat (infrared light) emitted from the halogen heater 31 to the nip forming member 32 side. . In this embodiment, the reflecting member 34 has a reflecting portion 34a formed with an elliptical cross section and a pair of bent portions 34b that bend away from each other from both ends of the reflecting portion 34a in the belt rotation direction B. are doing. The reflecting member 34 is held by sandwiching each bent portion 34 b between each side wall portion 33 a of the stay 33 and the first nip forming portion 32 a of the nip forming member 32 .

The reflecting portion 34a is arranged such that its elliptical concave curved surface faces toward the nip forming member 32, thereby reflecting the radiant heat from the halogen heater 31 to the nip forming member 32 side. That is, the nip forming member 32 is effectively heated because it is also irradiated with the heat of the infrared light reflected by the reflecting portion 34a in addition to the infrared light directly irradiated from the halogen heater 31 .

In addition, since the reflecting portion 34 a is interposed between the halogen heater 31 and the stay 33 , it also has a function of blocking irradiation of infrared light from the halogen heater 31 to the stay 33 . As a result, wasteful consumption of thermal energy due to heating of the stay 33 is suppressed. Furthermore, in the present embodiment, since an air layer (gap) is interposed between the stay 33 and the reflecting portion 34a, heat transfer to the stay 33 is further suppressed by the heat insulating effect of this air layer.

As described above, in this embodiment, the reflective member 34 is provided so as to cover the halogen heater 31, and the radiant heat and the reflected heat from the halogen heater 31 are provided on the opening side of the reflective member 34, that is, on the nip forming member 32 side. Reflected heat from the member 34 is efficiently collected. Then, the heated nip forming member 32 can efficiently heat the fixing belt 22 at the fixing nips N1 and N2. A stay 33 is provided so as to cover the outer peripheral side of the reflecting member 34 , and the fixing belt 22 is provided on the outer peripheral side of the stay 33 . In other words, the fixing belt 22 faces the halogen heater 31 via the nip forming member 32 in the fixing nip N1 portion in the circumferential direction, and faces the fixing belt 22 via the reflecting member 34 and the stay 33 in the portion other than the fixing nip N1. , facing the halogen heater 31 .

The surface of the reflecting member 34 (reflecting portion 34a) on the halogen heater 31 side is subjected to mirror finishing or surface treatment to increase the reflectance. In this embodiment, the reflectance is measured using a spectrophotometer (UV-visible-infrared spectrophotometer UH4150 manufactured by Hitachi High-Tech Science Co., Ltd.) at an incident angle of 5°. In general, halogen heaters have different color temperatures depending on their uses, and those having a color temperature of about 2500K are used for heating fixing devices. The reflectance of the reflecting member 34 used in the present embodiment is 70% or more with respect to the wavelength of the halogen heater 31 having a high emission intensity, specifically a wavelength of 900 to 1600 nm, more preferably a wavelength of 1000 to 1300 nm. It's good.

Further, the stay 33 may have the function of reflecting the reflecting member 34 and heat insulating. For example, the inner surface of the stay 33 (the surface on the halogen heater 31 side) may be heat-insulated or mirror-finished so that the stay 33 also functions as the reflecting member 34 . In this case, it is possible to omit the reflecting member 34 which is separate from the stay 33 . Moreover, it is desirable that the reflectance of the stay 33 when the stay 33 is mirror-finished is equal to the reflectance of the reflecting member 34 .

The temperature sensor 28 is arranged on the outer peripheral side of the fixing belt 22 and detects the temperature of the fixing belt 22 . In the present embodiment, the temperature sensors 28 are arranged at two locations on the fixing belt 22, namely, the central portion and the one end portion side in the width direction of the belt. The output of the halogen heater 31 is controlled based on the surface temperature of the fixing belt 22 detected by the temperature sensor 28 . As a result, the temperature of the fixing belt 22 is controlled to a desired temperature (fixing temperature). Also, the temperature sensor 28 may be either a contact type or a non-contact type. As the temperature sensor 28, a known temperature sensor such as a thermopile, thermostat, thermistor, NC sensor, etc., can be applied.

As shown in FIG. 4, the fixing belt 22 is rotatably supported by a pair of belt support members 35 inserted at both ends thereof. By inserting the belt support member 35 into the inner circumference of the fixing belt 22 in this manner, the fixing belt 22 is supported in a state in which tension is basically not applied in the circumferential direction when the fixing belt 22 is not rotating, that is, in a so-called free belt system. there is

The pressure roller 23 is urged toward the fixing belt 22 by urging means such as a spring (see arrow H in the figure) at both ends in the longitudinal direction, and is pressed against the fixing belt 22 . As a result, the elastic layer of the pressure roller 23 is crushed and the fixing nip N is formed.

Next, the second nip forming portion 32e provided on the nip forming member 32 will be described in more detail with reference to FIG.

As shown in FIG. 2, the nip forming member 32 has a first nip forming portion 32a on the upstream side (right side in the drawing) in the sheet conveying direction, and a second nip forming portion 32e on the downstream side. While the first nip forming portion 32a has a substantially flat plate shape and is provided parallel to the direction C1 in which the paper P enters the fixing nip N1, the second nip forming portion 32e is arranged in the same direction as the first nip forming portion 32a. and the second nip forming portion 32e, it curves toward the pressure roller 23 from the first nip forming portion 32a. In other words, the second nip forming portion 32e is provided closer to the pressure roller 23 than the first nip forming portion 32a in the direction of contact between the fixing belt 22 and the pressure roller 23 (vertical direction in the figure). In particular, in this embodiment, the inclination is toward the pressure roller 23 (lower side in the drawing) toward the downstream side in the paper conveying direction. Hereinafter, the upstream side and the downstream side in the sheet conveying direction will be simply referred to as the upstream side and the downstream side.

In this embodiment, a supported portion 32c supported by the downstream side wall portion 33a of the stay 33 is provided in the downstream portion of the first nip forming portion 32a. In addition to the supported portion 32c, a supported portion 32z supported by the upstream side wall portion 33a is also provided in the upstream portion of the first nip forming portion 32a.

A bent portion 32f that is bent from the downstream end of the second nip forming portion 32e to the side opposite to the pressure roller 23 is provided at the downstream end of the second nip forming portion 32e. The downstream side of the second nip forming portion 32e including the bent portion 32f is a free end that is not fixed (supported) by the stay 33 or the like.

The paper P conveyed to the fixing device 7 is first conveyed in the direction of the arrow C1 and passes through the first fixing nip N1. That is, the sheet is conveyed in the direction of arrow C1 along the first nip forming portion 32a. After passing through the first fixing nip N1, the sheet P is conveyed to the second fixing nip N2 after changing its conveying direction at the curved portion 32d. That is, the sheet P is conveyed in the direction along the second nip forming portion 32e with the inflection portion 32d as a boundary, and the conveying direction changes to the direction of the arrow C2 toward the pressure roller 23 side.

The paper P is further conveyed and separated from the fixing belt 22 at a separation point D provided at the downstream end of the second nip forming portion 32e. At the separation point D, the paper P is separated from the fixing belt 22 at a separation angle θ formed by the fixing belt 22 and the arrow C<b>2 that is the conveying direction of the paper P to the downstream side.

As described above, in the present embodiment, the nip forming member 32 is provided with the second nip forming portion 32e that is curved toward the pressure roller 23, so that the peeling angle θ can be increased. For example, as a nip forming member different from the present invention, in the case of a nip forming portion 32a' having a substantially flat surface as shown in FIG. Therefore, the peeling angle θ' becomes small.

In contrast, as in the present embodiment, by providing the second nip forming portion 32e curved toward the pressure roller 23 on the downstream side of the nip forming member 32 (especially, the second nip forming portion 32e By providing the downstream end portion closer to the pressure roller 23 than the first nip forming portion 32a), the fixing belt 22 is largely displaced toward the pressure roller 23 side, which is the lower side of the drawing, on the downstream side. , can be brought into contact with the surface of the pressure roller 23 . In other words, the pressure roller 23 is pressed against the fixing belt 22 to form a substantially horizontal fixing nip with the fixing belt 22 (the range of the fixing nip N in FIG. 5). As shown in FIG. 2, even in a region where the outer peripheral surface of the pressure roller 23 is separated from the fixing belt 22 side (for example, a region such as the range X in FIG. It can be displaced to the side and brought into contact with the pressure roller 23 to form the second fixing nip N2. In this way, by deforming the fixing belt 22 toward the pressure roller 23 side by the second nip forming portion 32e, the end point of the second fixing nip N2, that is, the separation point D where the paper P is separated from the fixing belt 22 , the fixing belt 22 can be raised in the conveying direction C<b>2 of the paper P or in the direction away from the surface of the pressure roller 23 . That is, the peeling angle θ of the paper P can be set large, and the peelability of the paper P from the fixing belt 22 can be improved.

In particular, in the present embodiment, by providing a bent portion 32f bent to the side opposite to the pressure roller 23 at the downstream end portion of the second nip forming portion 32e, the extension of the fixing belt 22 on the downstream side of the separation point D Since the direction can be set along the bent portion 32f, the peeling angle θ can be set at a stable angle. In this manner, the separation point D is provided upstream of the downstream end of the nip forming member 32, and the portion downstream of the separation point D, that is, the bent portion 32f of the present embodiment is positioned so that the fixing belt 22 rotates. It can also be provided as a guide portion for guiding. However, a configuration in which the separation point D is provided at the downstream end of the nip forming member 32 without providing the bent portion 32f may be employed.

Further, by forming the second nip forming portion 32e into a curved shape toward the pressure roller 23 side, the second nip forming portion 32e is also formed downstream of the supported portion 32c supported by the stay 33. It can be brought into contact with the pressure roller 23 to form a second fixing nip N2. Therefore, it is possible to form a fixing nip having a sufficient length in the conveying direction, and to improve the fixability of the image on the surface of the paper.

Modifications of the nip forming member will be described below. It should be noted that the description of the configuration common to the above embodiment will be omitted as appropriate.

As shown in FIG. 6, in the present embodiment, a bent portion 32d between the first nip forming portion 32a and the second nip forming portion 32e is provided at the position of the supported portion 32c fixedly supported by the stay 33. As shown in FIG. As a result, the size and shape of the fixing nip in the conveying direction, the peeling angle, etc. can be changed with the inflection portion 32d as a boundary. Particularly in this embodiment, the stay 33 supports the upstream end portion of the second nip forming portion 32e at the downstream end portion of the first nip forming portion 32a in the sheet conveying direction. In this case, the upstream end of the second nip forming portion 32e is a fixed end that is fixedly supported by the stay 33, while the downstream side of the second nip forming portion 32e including the bent portion 32f is the stay 33 It is a free end that is not fixed by such as. As a result, the size and shape of the fixing nip in the conveying direction, the peeling angle, etc. can be changed on the free end side.

Further, the second nip forming portion 32e is made of a highly elastic material, and can be elastically deformed with the supporting portion 32c as a fulcrum. It is desirable that the second nip forming portion 32e be thinner than other portions of the nip forming member 32 so that the second nip forming portion 32e can be easily elastically deformed.

As shown in FIG. 7A, the pressure roller 23 is pressed in the direction of arrow E by a pressure means such as a spring, and the pressure roller 23 is pressed against the fixing belt 22 to form a fixing nip. ing.

In this embodiment, by changing the pressing force of the pressure roller 23 against the fixing belt 22 (nip forming member 32), the second nip forming portion 32e is elastically deformed to change its posture, thereby changing the shape of the fixing nip. can be changed. Specifically, as shown in FIG. 7B, when the pressure roller 23 is pressed against the fixing belt 22 with a greater force, this pressure contact force is applied to the nip forming member 32 via the fixing belt 22. , the second nip forming portion 32e elastically deforms toward the side opposite to the pressure roller 23 with the supporting portion 32c, which is a fixed end, as a fulcrum. As a result, the first nip forming portion 32a and the second nip forming portion 32e shown in FIG. 7B are arranged substantially in a straight line (substantially in the same plane) and extend in a direction horizontal to the conveying direction. One fixing nip N is formed. In this case, the separation angle θ2 is smaller than the separation angle θ1 in FIG. 7(A). Since both ends of the first nip forming portion 32a are fixedly supported by the stays 33, even if the pressing force is changed as described above, the shape of the first nip forming portion 32a hardly changes.

As means for changing the pressing force of the pressure roller 23 against the fixing belt 22 (the nip forming member 32), the pressure roller 23, or the arrangement of the fixing belt 22 and each member in the fixing belt 22 is changed. The pressure roller 23 and the fixing belt 22 may be brought close to each other. , the pressure may be increased. Further, the pressure means for applying pressure to the pressure roller 23 may be configured so that its own pressure is variable. In this embodiment, the pressure roller 23 is pressed toward the fixing belt 22, but the opposite may be true.

Further, as shown in FIG. 8, a biasing spring (biasing means) 37 that biases the second nip forming portion 32e toward the fixing belt side (lower side in the drawing) is provided, and the posture of the biasing spring 37 is changed. The posture of the second nip forming portion 32e may be changed by changing the biasing force of the spring. The biasing spring 37 is connected to the vicinity of the downstream end of the second nip forming portion 32e and biases this portion toward the fixing belt. By changing the biasing force of the biasing spring 37, the size and shape of the fixing nip in the conveying direction, the separation angle, etc. can be changed.

As described above, in the present embodiment, by adjusting the pressing force of the pressure roller 23 against the fixing belt 22 (nip forming member 32), it is possible to change the size and shape of the fixing nip in the conveying direction, the separation angle, and the like. can. Therefore, when the sheet P is difficult to peel off from the fixing belt 22, the attitude is set to have a large peeling angle as shown in FIG. It is possible to change the shape of the fixing nip by changing the posture of the second nip forming portion 32e according to the purpose, such as the posture of forming the fixing nip N having a substantially flat surface as shown in FIG.

The adjustment of the peeling angle and the like by changing the pressure contact force of the pressure roller 23 may be changed according to the type and size of the paper P passed through the fixing device 7, for example. That is, the pressing force of the pressure roller 23 can be set in consideration of the ease of separation of the paper P, the ease of wrinkling, the fixability of the image, and the like, based on the type and size of the paper P.

As in the present embodiment, by providing the bending portion 32d of the first nip forming portion 32a and the second nip forming portion 32e at the position of the supported portion 32c supported by the stay 33, the elastically deformable portion is provided. The second nip forming portion 32e can be elastically deformed in the pressure contact direction (upward direction in FIG. 7) by the pressure roller 23, starting from the position of the inflection portion 32d. Therefore, it becomes easy to adjust the posture of the second nip forming portion 32e, that is, the peeling angle and the shape of the fixing nip, and it becomes easy to change the desired peeling angle and shape of the fixing nip.

As described above, the supported portion 32c may be provided at the inflection portion 32d between the first nip forming portion 32a and the second nip forming portion 32e, or the first nip forming portion 32a on the upstream side of the first nip forming portion 32a. It can also be provided in the middle of the (see Figure 2)

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile machine, or a multi-function machine of these.

Recording media include paper P (plain paper), thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, plastic film, prepreg, copper foil, and the like. included.

REFERENCE SIGNS LIST 1 image forming apparatus 7 fixing device 22 fixing belt 23 pressure roller (pressure member)
31 halogen heater (heating member)
32 nip forming member 32a first nip forming portion 32b bending portion 32c supported portion 32d bending portion 32e second nip forming portion 32f bending portion 33 stay (supporting member)
34 reflecting member 37 biasing spring (biasing means)
D Peeling point N1 First fixing nip N2 Second fixing nip P Paper (recording medium)
θ peel angle

JP 2014-66851 A

Claims (11)

an endless fixing belt;
a pressing member that presses the fixing belt;
a nip forming member that is provided inside the fixing belt and contacts the pressure member via the fixing belt to form a fixing nip;
a heating member for heating the fixing belt;
A fixing device comprising a support member provided inside the fixing belt and supporting the nip forming member,
The nip forming member includes a first nip forming portion that contacts the pressure member via the fixing belt and forms a first fixing nip, and is provided downstream of the first nip forming portion in the recording medium conveying direction. a second nip forming portion that forms a second fixing nip by coming into contact with the pressure member via the fixing belt; and an inflection portion where the extending direction of the nip forming member changes Assuming that the downstream portion of the first nip forming portion in the recording medium conveying direction, which is directly or indirectly abutted by the member, is the supported portion,
In the recording medium transport direction, the inflection portion is provided at the position of the supported portion or downstream thereof, and the second nip forming portion is provided downstream of the inflection portion,
In the direction in which the pressure member presses against the fixing belt and in the opposite direction, the downstream end portion of the second nip forming portion in the recording medium conveying direction extends from the upstream side in the recording medium conveying direction toward the downstream side. extending in a direction opposite to the direction in which the pressure member presses the fixing belt;
The fixing device , wherein the inflection portion is provided on the supported portion . 2. The fixing device according to claim 1 , wherein the downstream end portion of the second nip forming portion in the recording medium conveying direction is not supported by the supporting member. 3. The fixing device according to claim 1, wherein the second nip forming portion is made of an elastic material. The fixing device according to any one of claims 1 to 3 , wherein the second nip forming portion has a smaller thickness than the first nip forming portion. The fixing device according to any one of claims 1 to 4 , further comprising biasing means for biasing the second nip forming portion toward the fixing belt. The fixing according to any one of claims 1 to 5 , wherein the posture of the second nip forming portion with respect to the first nip forming portion is changed by changing the pressing force between the nip forming member and the pressure member. Device. an endless fixing belt;
a pressing member that presses the fixing belt;
a nip forming member that is provided inside the fixing belt and contacts the pressure member via the fixing belt to form a fixing nip;
a heating member for heating the fixing belt;
A fixing device comprising a support member provided inside the fixing belt and supporting the nip forming member,
The nip forming member includes a first nip forming portion that contacts the pressure member via the fixing belt and forms a first fixing nip, and is provided downstream of the first nip forming portion in the recording medium conveying direction. a second nip forming portion that forms a second fixing nip by coming into contact with the pressure member via the fixing belt;
Assuming that the downstream side portion of the first nip forming portion in the recording medium conveying direction, which is directly or indirectly abutted by the supporting member, is the supported portion,
In the recording medium conveying direction, the inflection portion is provided at the position of the supported portion or downstream thereof, and the second nip forming portion is provided downstream of the inflection portion,
The fixing device, wherein the thickness of the second nip forming portion is smaller than that of the first nip forming portion. an endless fixing belt;
a pressing member that presses the fixing belt;
a nip forming member that is provided inside the fixing belt and contacts the pressure member via the fixing belt to form a fixing nip;
a heating member for heating the fixing belt;
A fixing device comprising a support member provided inside the fixing belt and supporting the nip forming member,
The nip forming member includes a first nip forming portion that contacts the pressure member via the fixing belt and forms a first fixing nip, and is provided downstream of the first nip forming portion in the recording medium conveying direction. a second nip forming portion that forms a second fixing nip by coming into contact with the pressure member via the fixing belt;
Assuming that the downstream side portion of the first nip forming portion in the recording medium conveying direction, which is directly or indirectly abutted by the supporting member, is the supported portion,
In the recording medium conveying direction, the inflection portion is provided at the position of the supported portion or downstream thereof, and the second nip forming portion is provided downstream of the inflection portion,
The fixing device further comprises biasing means for biasing the second nip forming portion toward the fixing belt. an endless fixing belt;
a pressing member that presses the fixing belt;
a nip forming member that is provided inside the fixing belt and contacts the pressure member via the fixing belt to form a fixing nip;
a heating member for heating the fixing belt;
A fixing device comprising a support member provided inside the fixing belt and supporting the nip forming member,
The nip forming member includes a first nip forming portion that contacts the pressure member via the fixing belt and forms a first fixing nip, and is provided downstream of the first nip forming portion in the recording medium conveying direction. a second nip forming portion that forms a second fixing nip by coming into contact with the pressure member via the fixing belt;
Assuming that the downstream side portion of the first nip forming portion in the recording medium conveying direction, which is directly or indirectly abutted by the supporting member, is the supported portion,
In the recording medium conveying direction, the inflection portion is provided at the position of the supported portion or downstream thereof, and the second nip forming portion is provided downstream of the inflection portion,
A fixing device, wherein the posture of the second nip forming portion with respect to the first nip forming portion is changed by changing the pressing force between the nip forming member and the pressing member. 10. The fixing device according to claim 6 , wherein the pressing force is changed according to the type of recording medium to be fixed. An image forming apparatus comprising the fixing device according to any one of claims 1 to 10 .

Images