JP5102573B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein.

Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing member such as a fixing roller or a fixing belt and a pressure belt are pressed against each other to form a nip portion, and a toner image is carried on the nip portion. 2. Description of the Related Art A fixing device that conveys a recording medium and fixes a toner image on the recording medium is known (see, for example, Patent Document 1 and Patent Document 2).
Such a fixing device using a pressure belt can secure a sufficient nip width in the conveyance direction at the nip portion, and can reduce the amount of heat taken from the fixing member by setting the heat capacity of the pressure belt small. Therefore, better fixability can be obtained as compared with an apparatus using a pressure roller.

  On the other hand, in Patent Document 1 and the like, a pressure roller that stretches the pressure belt upstream is provided for the purpose of equalizing the pressing force between the fixing member and the pressure belt in the axial direction (width direction). Has been disclosed that comprises a cylindrical outer roll and a crown-shaped inner roll.

  Patent Document 2 discloses a technique for providing a difference in hardness or an outer diameter difference between two rollers forming the nip portion for the purpose of improving the separation of the recording medium sent from the exit of the nip portion. Has been.

JP 2006243321 A JP 2006-98901 A

Although the conventional fixing device using a pressure belt can obtain good fixability, it has more parts than a fixing device using a pressure roller, making the device more complicated and larger. It was.
In order to solve this problem, a method of forming a nip portion (fixing nip portion) by pressing a pressure pad against a heating means via a pressure belt (including a pressure film) can be considered (for example, a special feature). (See Kaih 2007-187889, etc.).

  However, in this case, the running posture of the pressure belt on the outlet side of the nip portion becomes unstable, and the recording medium fed from the outlet of the nip portion is attracted to the fixing member (heating means) and separated from the fixing member. In some cases, such a problem may occur that the separation of the recording medium may be deteriorated. Such a problem occurs particularly when using a recording medium having a small basis weight, a recording medium having a high moisture content after standing for a long time, or a recording medium having an eye direction in a direction crossing the transport direction. It was prominent. In addition, the toner becomes conspicuous even when toner that is easily adsorbed to the fixing member is used.

  The present invention has been made in order to solve the above-described problems, and has a relatively small number of parts, which can obtain good fixing properties without complicating or increasing the size of the apparatus. It is an object of the present invention to provide a fixing device and an image forming apparatus that do not cause poor separation.

According to a first aspect of the present invention, there is provided a fixing device for fixing a toner image onto a recording medium, a heating unit for heating the toner image, and the recording medium being conveyed in pressure contact with the heating unit. Pressurizing means for forming a nip portion, wherein the pressurizing means is in contact with the heating means via the belt member and an endless belt member that travels in a predetermined direction. In accordance with the curvature of the heating means, a pressure pad that is formed in a concave shape toward the heating means, a guide member that holds the posture of the belt member, and the belt member is relaxed on the outlet side of the nip portion. and tensioning means for said belt member is tensioned on the belt member so as not wind around the heating member beyond outlet of the nip portion occurs, the width direction of the belt member in the width direction both end portions move A stopper member which engages with the heating means as well as regulating the those provided with the.

The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the stopper member is provided with a guide portion that maintains a posture of the belt member in a traveling direction at a position excluding the nip portion. It is equipped.

According to a third aspect of the present invention, there is provided a fixing device for fixing a toner image onto a recording medium, the heating means for heating the toner image, and the recording medium being conveyed in pressure contact with the heating means. Pressurizing means for forming a nip portion, and the pressurizing means is in contact with the heating means via the belt member, an endless belt member that travels in a predetermined direction, and the nip portion is In accordance with the curvature of the heating means, a pressure pad formed in a concave shape toward the heating means, a guide member for maintaining the posture of the belt member, and relaxation of the belt member at the outlet side of the nip portion Tension applying means for applying tension to the belt member so that the belt member does not wind around the heating member beyond the outlet of the nip portion, and the pressure pad is provided on the outlet side of the nip portion. And In which Young's modulus of the position corresponding to the inlet side is formed to be lower than the Young's modulus of the position corresponding to the central portion of the nip portion.

The fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the tension applying means is located on the inlet side of the nip portion with respect to the belt member. And / or the guide member is biased so as to apply tension toward the side away from the nip portion.

The fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the tension applying means is an outer peripheral surface of the belt member on the outlet side of the nip portion. However, the belt member is tensioned so as not to overlap with an imaginary line passing through the inlet and the outlet of the nip portion.

  The fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the pressing means is provided between the belt member and the pressing pad. A lubricant holding member that holds the lubricant is provided.

  The fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, wherein the pressure unit supports the pressure pad and the pressure pad. And a biasing member that biases the support member from both ends in the width direction toward the nip portion.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to any one of the first to seventh aspects, wherein the pressure pad is heated when the operation of the apparatus is stopped. It is pressed against the means in a direction inclined toward the upstream side in the conveyance direction of the recording medium.

  A fixing device according to a ninth aspect of the present invention is the fixing device according to any one of the first to eighth aspects, wherein the pressure pad is formed when an infinite flat plate is in pressure contact with the heating means. The nip portion is pressed against the heating means so that the nip width at the nip portion is equal to or less than the nip width of the nip portion.

The fixing device according to a tenth aspect of the present invention is the fixing device according to any one of the first to ninth aspects, wherein the heating means includes an elastic layer and the heating member is interposed via the belt member. A fixing roller that is in pressure contact with the pressure pad; and a heat source that heats the fixing roller.

According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to ninth aspects, the heating means includes a fixing belt stretched around a plurality of roller members, A fixing belt, an elastic member pressed against the pressure pad via the belt member, and a heat source for heating the fixing belt.

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

  In the present invention, the pressure means is mainly composed of a belt member, a pressure pad, and a holding member, and tension is applied to the belt member so that the belt member does not relax on the outlet side of the nip portion. It is possible to provide a fixing device and an image forming apparatus that have a relatively small number of points, can obtain good fixing properties without complicating or increasing the size of the device, and do not cause poor separation of a recording medium. .

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original D to an original reading unit 4. 4 is a document reading unit that reads image information of the document D, 7 is a paper feed unit that accommodates a recording medium P such as cut paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 11Y, 11M, and 11C. , 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each photosensitive drum. A developing unit that develops the electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and a toner image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK Transfer bias roller for transferring superimposed on the recording medium P (1 transfer bias roller), 15 denotes the photosensitive drums 11Y, 11M, 11C, cleaning unit for collecting the untransferred toner on 11BK, a.

  Reference numeral 16 denotes an intermediate transfer belt cleaning unit that cleans the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred and superimposed, and 18 a color toner image on the intermediate transfer belt 17 on the recording medium P. A secondary transfer bias roller 20 for transferring the toner image onto the recording medium P is a fixing device for fixing the toner image (unfixed image) on the recording medium P.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5.

  Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, thereby forming an electrostatic latent image of the cyan component. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .)
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the intermediate transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 at the position of the transfer bias roller 14 (in the primary transfer process). is there.).

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) are run in the clockwise direction in the drawing and are connected to the secondary transfer bias roller 18. Reach the opposite position. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the recording medium P at a position facing the secondary transfer bias roller 18 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and a series of transfer processes in the intermediate transfer belt 17 is completed.

Here, the recording medium P transported between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is transported from the paper supply unit 7 via the registration roller 9 and the like. It is a thing.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P is guided to the registration roller 9 after passing through the conveyance guide. The recording medium P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

Then, the recording medium P on which the full-color image is transferred is guided to the fixing device 20 by the transport belt. In the fixing device 20, the color image (toner) is fixed on the recording medium P at the nip portion between the fixing roller and the pressure belt.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a paper discharge roller, and a series of image forming processes is completed.

Next, the configuration / operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG.
Referring to FIG. 2, the fixing device 20 includes heating units 21 and 25 that heat the toner image T, a pressurizing unit 31 that presses against the heating units 21 and 25 and forms a nip portion where the recording medium P is conveyed, Etc.
The heating means mainly includes a fixing roller 21 that is in pressure contact with the pressure pad 33 via a pressure belt 32 (belt member), and a heater 25 as a heat source that heats the fixing roller 21 by radiant heat.
The pressure unit 31 includes a pressure belt 32 as an endless belt member that travels in the direction of the arrow in FIG. 2, and a pressure pad 33 (pressure) that is in pressure contact with the fixing roller 21 (heating unit) via the pressure belt 32. Members), a support member 34 (support plate) that supports the pressure pad 33, a spring 35 that biases the pressure pad 33 toward the fixing roller 21, and guide members 36A to 36C that hold the posture of the pressure belt 32. A spring 38 as a tension applying means, a lubricant holding member 37 for supplying a lubricant to the inner peripheral surface (sliding surface) of the pressure belt 32, and the like.

  Here, the fixing roller 21 is a thin cylindrical body that is rotationally driven clockwise in FIG. 2 by a drive motor (not shown), and a heater 25 (heat source) is fixed inside the cylindrical body. Yes. The fixing roller 21 is a multilayer structure in which an elastic layer 23 and a release layer 24 (surface coating layer) are sequentially laminated on a cylindrical cored bar 22.

The elastic layer 23 of the fixing roller 21 is made of an elastic material such as fluorine rubber, silicone rubber, or foamable silicone rubber. In particular, when silicone rubber is used as the elastic layer 23, it is preferable to coat a fluorine layer on the elastic layer 23 in order to improve the swelling resistance.
By providing the elastic layer 23 on the cored bar 22 of the fixing roller 21, the separation property of the recording medium P after passing through the nip portion is improved, and the glossiness of the output image when forming a color image is improved. . In order to ensure the above effect, it is preferable to set the thickness of the elastic layer 23 to 0.5 to 3 mm.

  Further, as the release layer 24 of the fixing roller 21, PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like can be used. By providing the release layer 24 on the surface layer of the fixing roller 21, the releasability (peelability) for the toner T (toner image) is secured.

  The heater 25 (heat source) of the fixing roller 21 is a rod-shaped heater having a heating wire inside, and both ends thereof are fixed to the side plate of the fixing device 20. The fixing roller 21 is heated by the heater 25 whose output is controlled by the power supply unit of the apparatus main body 1, and heat is applied to the toner image T on the recording medium P from the surface thereof. The output control of the heater 25 is performed based on the detection result of the roller surface temperature by a thermistor (not shown) that contacts the surface of the fixing roller 21. Further, the temperature of the fixing roller 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 25.

  The pressure belt 32 of the pressure means 31 is obtained by forming a surface layer made of PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin) on a base layer made of polyimide or the like. The pressure belt 32 is held by guide members 36 </ b> A to 36 </ b> C, and travels (rotates) counterclockwise in FIG. 2 as the fixing roller 21 rotates.

  The pressure pad 33 (pressure member) has a rubber layer (elastic layer) made of silicone rubber, fluorine rubber, or the like. The rubber layer of the pressure pad 33 is set to have a layer thickness of 0.5 to 3 mm and a rubber hardness of 5 to 50 Hs. The pressure pad 33 held by the support member 34 (support plate) is urged by the spring 35 and is brought into pressure contact with the fixing roller 21 via the lubricant holding member 37 and the pressure belt 32. In this way, a desired nip portion is formed between the pressure belt 32 and the fixing roller 21. The surface shape of the pressure pad 33 (the surface that forms the nip portion) may be a planar shape or a curved surface shape in accordance with the curvature of the fixing roller 21.

  The lubricant holding member 37 is disposed between the pressure belt 32 and the pressure pad 33. Specifically, the lubricant holding member 37 is supported by the pressure pad 33 in accordance with the shape of the support member 34 (the pressure pad 33 is supported on the surface) having a U-shaped cross section. It is disposed so as to cover the member 34. The lubricant holding member 37 is held by the fixing device 20 so as to be movable in the vertical direction of FIG. 2 together with the pressure pad 33 and the support member 34. Then, the lubricant held by the lubricant holding member 37 is supplied (applied) to the inner peripheral surface (sliding surface) of the pressure belt 32, whereby the friction coefficient of the inner peripheral surface of the pressure belt 32 is increased. Will be reduced. Note that fluorine grease can be used as the lubricant held by the lubricant holding member 37.

  36 A of 1st guide members hold | maintain the attitude | position of the pressure belt 32 from the exit side (it is the left side of FIG. 2) of a nip part to the downstream (it is the downstream of the running direction of the pressure belt 32). The third guide member 36C holds the posture of the pressure belt 32 from the inlet side (the right side in FIG. 2) of the nip portion to the upstream side (the upstream side in the traveling direction of the pressure belt 32). The second guide member 36B maintains the posture of the pressure belt 32 between the first guide member 36A and the third guide member 36C.

Here, the spring 38 is installed in the 2nd guide member 36B and the 3rd guide member 36C among these guide members 36A-36C. The second guide member 36B and the third guide member 36C biased by the springs 38 are tension applying means for applying tension to the pressure belt 32 so that the pressure belt 32 is not loosened on the outlet side of the nip portion. It functions as.
Specifically, by urging the second guide member 36B by the spring 38, the pressure belt 32 is tensioned (pulled) toward the side away from the nip portion (downward in FIG. 2). . Further, by urging the third guide member 36C by the spring 38, the pressure belt 32 is tensioned (pulled) toward the inlet side (the right side in FIG. 2) of the nip portion.

With such a configuration, referring to FIG. 3A, the outer peripheral surface of the pressure belt 32 on the outlet B side of the nip portion does not overlap with the virtual line L passing through the inlet A and the outlet B of the nip portion. Become . This is because tension is applied to the pressure belt 32 (in the direction of the white arrow in FIG. 3A) so that the tension belt 36B, 36C, 38 described above does not loosen the pressure belt 32 on the outlet side of the nip portion. This is because the tension is given.
If the tension urging means 36B, 36C, 38 are not provided, the running posture of the pressure belt 32 on the outlet side of the nip portion becomes unstable. As shown in FIG. 3B, the outer peripheral surface of the pressure belt 32 on the outlet B side of the nip portion overlaps the virtual line L passing through the inlet A and the outlet B of the nip portion . Therefore, the recording medium P delivered from the exit of the nip portion is attracted to the fixing roller 21 and is likely to cause a separation failure that is not separated from the fixing roller 21.
In contrast, in the first embodiment, by providing the tension urging means 36B, 36C, 38, the running posture of the pressure belt 32 on the outlet side of the nip portion is stably sent from the nip portion. Since the recording medium P is guided in the direction of the arrow in FIG. 3A, poor separation is unlikely to occur.

In the pressure pad 33 according to the first embodiment, the Young's modulus at the positions corresponding to the outlet B side and the inlet A side of the nip part is lower than the Young's modulus at the position corresponding to the center part of the nip part. Is formed. That is, the pressure pad 33 is configured to be easily distorted on the outlet B side and the inlet A side of the nip portion. This makes it easier to apply tension to the pressure belt 32 by the tension urging means 36B, 36C, 38 so that the pressure belt 32 does not relax on the outlet side of the nip portion .

Finally, the operation of the fixing device 20 configured as described above will be described.
When the power switch of the apparatus main body 1 is turned on, power is supplied to the heater 25, and the rotation driving of the fixing roller 21 in the direction of the arrow in FIG. 2 is started. The running (rotation) in the direction of the arrow is started.
Thereafter, the recording medium P is fed from the paper supply unit 7, and an unfixed image is carried on the recording medium P at the position of the secondary transfer bias roller 18. The recording medium P carrying the unfixed image T (toner image) is conveyed in the direction of the broken-line arrow (−X direction) in FIG. 2 and reaches the nip portion between the fixing roller 21 and the pressure belt 32 that are in a pressure contact state. Sent in. The toner image T is fixed on the surface of the recording medium P by the heating by the fixing roller 21 and the pressing force of the fixing roller 21 and the pressure belt 32 (pressure pad 33). Thereafter, the recording medium P sent out from the nip portion by the rotating fixing roller 21 and the pressure belt 32 is conveyed in the direction of the broken line arrow (−X direction).
The fixing device 20 according to the first embodiment has a relatively small number of parts, and the pressure belt 32 is disposed without making the fixing device 20 complicated and large, so that a good fixing property can be obtained. . Further, in the first embodiment, since the tension is applied to the pressure belt 32 so that the pressure belt 32 does not relax on the exit side of the nip portion, the separation property of the recording medium P after the fixing process is improved. Can be improved.

  As described above, in the first embodiment, the pressurizing means 31 is mainly composed of the pressurizing belt 32 (belt member), the pressurizing pad 33, and the holding members 36A to 36C, and the outlet B side of the nip portion. Since the tension is applied to the pressure belt 32 so that the pressure belt 32 is not loosened, the number of parts is relatively small, and the fixing device 20 does not become complicated and large, and good fixing performance can be obtained. It is possible to suppress the problem that the separation failure of the recording medium P occurs.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 4 is a configuration diagram illustrating the fixing device according to the second embodiment, and corresponds to FIG. 2 according to the first embodiment. FIG. 5 is a schematic view showing a pressure mechanism installed in the fixing device of FIG. FIG. 6 is a schematic view of the pressure pad 33 and the support member 34 as viewed in the width direction.

  As in the first embodiment, the fixing device 20 according to the second embodiment also includes heating means 21 and 25, a pressing means 31, and the like. The heating means is composed of the fixing roller 21 and the heater 25, and the pressure means 31 is composed of a pressure belt 32, a pressure pad 33, a support member 34, a guide member 36, a spring 38, a lubricant holding member 37, and the like. Has been.

Here, in the second embodiment, unlike the first embodiment, one guide member 36 is integrally installed. The guide member 36 holds the pressure belt 32 in the same manner as the guide members 36A to 36C in the first embodiment.
Also in the second embodiment, the guide member 36 is urged downward by the spring 38 and is tensioned toward the side away from the nip portion with respect to the pressure belt 32 (downward in FIG. 4). Is given.
With such a configuration, also in the second embodiment, the running posture of the pressure belt 32 on the outlet side of the nip portion is stabilized, and the separation failure of the recording medium P sent from the nip portion is less likely to occur.

Here, as shown in FIG. 5, the pressure pad 33 and the support member 34 in the second embodiment are configured so that the support shaft 39a is supported by a pressure lever 39 (biasing member) biased by a spring (not shown). It is urged toward the nip portion around the center of rotation (pressure in the direction of the white arrow in FIG. 5).
More specifically, referring to FIG. 6A, the pressure lever 39 as an urging member urges the support member 34 from both ends in the width direction (the Z direction in FIG. 4) ( It is an urging | biasing of the black arrow direction in FIG. 6 (A).) The support member 34 that supports the pressure pad 33 urges the pressure pad 33 toward the nip from the center in the width direction (the urging in the direction of the white arrow in FIG. 6A). .) With such a configuration, the pressure pad 33 comes into almost uniform pressure contact with the fixing roller 21 (pressure belt 32) in the width direction. Accordingly, as shown in FIG. 6B, the nip width at the nip portion between the fixing roller 21 and the pressure pad 33 (pressure belt 32) is substantially uniform in the width direction, and uneven fixing is produced on the output image. Is less likely to occur.

  In the second embodiment, the nip width of the nip portion formed by pressure contact of the pressure pad 33 is equal to the nip width of the nip portion formed when the infinite flat plate is pressed against the fixing roller 12. It is formed to be as follows. As a result, an output image with good fixability can be formed.

Further, in the second embodiment, as shown in FIG. 5, when the operation of the fixing device 20 is stopped, the pressure pad 33 (support member 34) moves the recording medium P to the fixing roller 21. It is configured to press-contact in a direction inclined by a predetermined angle θ on the upstream side in the transport direction. That is, in the stationary state, the pressure pad 33 is not pressed toward the rotation center of the fixing roller 21 but is pressed in a direction inclined by a predetermined angle θ. As a result, when the recording medium P is fed into the nip portion (when the apparatus is operating), a force in the conveying direction is applied and the pressure contact direction of the pressure pad 33 rotates the fixing roller 21. Head to the center. That is, the pressure contact direction of the pressure pad 33 is directed toward the rotation center of the fixing roller 21 when the apparatus is operated. Therefore, the fixability of the image on the recording medium P passing through the nip portion is efficiently improved.
In the second embodiment, the pressure pad 33 is configured to be inclined at an angle θ with respect to the vertical direction (the direction toward the rotation center of the fixing roller 21) in accordance with the pressure contact direction. However, even if the pressure pad 33 is configured not to be inclined with respect to the vertical direction, the same effect as described above can be obtained if the pressure contact direction is inclined by the angle θ.

  As described above, also in the second embodiment, as in the first embodiment, the pressing means 31 is mainly configured by the pressing belt 32 (belt member), the pressing pad 33, and the holding member 36. Since the tension is applied to the pressure belt 32 so that the pressure belt 32 does not relax on the outlet B side of the nip portion, the number of parts is relatively small, and the fixing device 20 becomes complicated and large. Therefore, it is possible to obtain a good fixing property, and to suppress a problem that a separation failure of the recording medium P occurs.

Embodiment 3 FIG.
7 and 8, the third embodiment of the present invention will be described in detail.
FIG. 7 is a schematic view of the fixing device according to the third embodiment as viewed in the width direction. FIG. 8 is a cross-sectional view showing the guide portion 40 a of the stopper member 40.

The fixing device 20 according to the third embodiment is also composed of heating means 21 and 25, a pressing means 31, and the like as in the second embodiment. The heating means is composed of the fixing roller 21 and the heater 25, and the pressure means 31 is composed of a pressure belt 32, a pressure pad 33, a support member 34, a guide member 36, a spring 38, a lubricant holding member 37, and the like. Has been. The fixing roller 21 is rotatably supported on the side plate 90 of the fixing device 20 via a bearing 91 with reference to FIG.
Also in the third embodiment, the guide member 36 is biased downward by the spring 38, and tension is applied to the pressure belt 32 toward the side away from the nip portion.

  Here, referring to FIG. 7, a stopper member 40 that restricts the movement (belt shift) of the pressure belt 32 in the width direction is installed in the pressure means 31 in the third embodiment. Specifically, the stopper member 40 is positioned on the side plate 90 of the fixing device 20 and is disposed so as to engage with the shaft portion 21a (may be a bearing) of the fixing roller 21. By abutting the stopper member 40 against the fixing roller 21 (shaft portion 21a), the parallelism between the fixing roller 21 and the pressure belt 32 and the distance between the center axes are made constant. Can be stabilized.

Further, the stopper member 40 is provided with a guide portion 40a (rib portion) that holds the posture of the pressure belt 32 in the traveling direction (rotating direction). As shown in FIG. 8, the guide portion 40a is disposed at a position excluding the nip portion. In other words, the guide portion 40a is configured to hold the posture of the pressure belt 32 in the traveling direction in a region other than the nip portion.
With such a configuration, the pressure belt 32 is deformed along the deformation of the pressure pad 33 in the vicinity of the nip portion without being affected by the guide portion 40a. Further, the pressure belt 32 is applied with tension on the outlet side of the nip portion without being influenced by the guide portion 40a and without being relaxed by the downward biasing by the guide member 36. Therefore, a good nip portion is formed, and occurrence of poor separation can be reliably reduced.

  As described above, also in the third embodiment, the pressurizing means 31 is mainly composed of the pressurizing belt 32 (belt member), the pressurizing pad 33, and the holding member 36 as in the above-described embodiments. Since the tension is applied to the pressure belt 32 so that the pressure belt 32 does not relax on the outlet B side of the nip portion, the number of parts is relatively small, and the fixing device 20 becomes complicated and large. Therefore, it is possible to obtain a good fixing property, and to suppress a problem that a separation failure of the recording medium P occurs.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 9 is a configuration diagram illustrating the fixing device according to the fourth embodiment, and corresponds to FIG. 2 according to the first embodiment. The fixing device according to the fourth embodiment is different from that of the first embodiment in which a fixing roller is used as a heating unit in that a fixing belt is used as a heating unit.

As shown in FIG. 9, the fixing device 20 according to the fourth exemplary embodiment conveys the recording medium P in pressure contact with the heating units 25 and 41 to 51 and the heating units 25 and 41 to 51 that heat the toner image T. The pressurizing means 31 and the like for forming the nip portion are configured.
The heating means is an endless fixing belt 41 that travels in the direction of the arrow in FIG. 9, a plurality of roller members 42 to 44 that stretch the fixing belt 41, the fixing belt 41, and the pressure belt 32 via the pressure belt 32. A fixing pad 46 as an elastic member to be pressed, a support plate 47 that supports the fixing pad 46, a spring 51 that biases the fixing pad 46 toward the pressure belt 32, and a tension roller 44 that biases toward the fixing belt 41. The fixing belt 41 is provided inside the spring 50, a pressure contact pad 49 that presses against the tension roller 44 via the fixing belt 41, a heating roller 45 that circumscribes the fixing belt 41, and the heating roller 45 and a plurality of roller members 42 to 44. The heater 25 as a heat source for heating the toner, the low friction member 48 disposed between the fixing pad 46 and the fixing belt 41, and the like. It has been.

  Further, the pressurizing means 31 is configured in the same manner as in the first embodiment. Also in the fourth embodiment, the guide members 36B and 36C are urged by the spring 38, and tension is applied to the pressure belt 32 on the outlet side of the nip portion without causing relaxation.

In the fixing device 20 configured as described above, the heating roller 45 is driven to rotate by a drive motor (not shown), so that the fixing belt 41 travels in the direction of the arrow and the plurality of roller members 42 to 44 rotate in the clockwise direction. Followed rotation. The toner image T on the recording medium P sent to the nip portion is heated by the fixing belt 41 and the pressing force of the fixing belt 41 (fixing pad 46) and the pressure belt 32 (pressure pad 33). Then, it is fixed on the surface of the recording medium P.
In the fourth embodiment, the heater 25 as a heat source is provided in all the four roller members 42 to 45, but the number of roller members in which the heater 25 is provided may be three or less. In addition, a roller member serving as a driving source of the fixing belt 41 may be roller members 42 to 44 other than the heating roller 45.

  As described above, also in the fourth embodiment, the pressurizing means 31 is mainly composed of the pressurizing belt 32 (belt member), the pressurizing pad 33, and the holding member 36 as in the above-described embodiments. Since the tension is applied to the pressure belt 32 so that the pressure belt 32 does not relax on the outlet B side of the nip portion, the number of parts is relatively small, and the fixing device 20 becomes complicated and large. Therefore, it is possible to obtain a good fixing property, and to suppress a problem that a separation failure of the recording medium P occurs.

  In each of the above-described embodiments, the present invention is applied to the fixing device 20 using a heating method using a heater. However, the present invention can also be applied to a fixing device using an electromagnetic induction heating method. . Also in these cases, the same effects as those of the above-described embodiments can be obtained by applying tension to the pressure belt 32 so that the pressure belt 32 does not relax on the exit side of the nip portion.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram illustrating a fixing device installed in the image forming apparatus of FIG. 1. It is an enlarged view which shows the vicinity of a nip part. It is a block diagram which shows the fixing device in Embodiment 2 of this invention. FIG. 5 is a schematic diagram illustrating a pressure mechanism installed in the fixing device of FIG. 4. It is the schematic which looked at the press pad and the supporting member in the width direction. It is the schematic which looked at the fixing device in Embodiment 3 of this invention in the width direction. It is sectional drawing which shows the guide part of a stopper member. It is a block diagram which shows the fixing device in Embodiment 4 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing roller (heating means),
22 cored bar, 23 elastic layer, 24 release layer,
25 Heater (heat source),
31 Pressurizing means,
32 Pressure belt (belt member),
33 Pressure pad,
34 support members,
36, 36A-36C guide members,
37 Lubricant holding member,
38 Spring (tensioning means),
39 Pressure lever (biasing member),
41 Fixing belt (heating means), P recording medium.

Claims (12)

A fixing device for fixing a toner image on a recording medium,
Heating means for heating the toner image;
A pressurizing unit that forms a nip portion in which the recording medium is conveyed in pressure contact with the heating unit;
With
The pressurizing means is
An endless belt member traveling in a predetermined direction;
A pressure pad that presses against the heating means via the belt member and forms the nip portion in a concave shape toward the heating means according to the curvature of the heating means;
A guide member for holding the posture of the belt member;
Tension applying means for applying tension to the belt member so that the belt member is relaxed on the outlet side of the nip portion and the belt member does not wind around the heating member beyond the outlet of the nip portion;
A stopper member that restricts movement of the belt member in the width direction at both ends in the width direction and engages the heating means;
A fixing device comprising: The fixing device according to claim 1, wherein the stopper member includes a guide portion that maintains a posture of the belt member in a traveling direction at a position excluding the nip portion. A fixing device for fixing a toner image on a recording medium,
Heating means for heating the toner image;
A pressurizing unit that forms a nip portion in which the recording medium is conveyed in pressure contact with the heating unit;
With
The pressurizing means is
An endless belt member traveling in a predetermined direction;
A pressure pad that presses against the heating means via the belt member and forms the nip portion in a concave shape toward the heating means according to the curvature of the heating means;
A guide member for holding the posture of the belt member;
Tension applying means for applying tension to the belt member so that the belt member is relaxed on the outlet side of the nip portion and the belt member does not wind around the heating member beyond the outlet of the nip portion;
Comprising
The pressure pad is formed such that Young's modulus at positions corresponding to an outlet side and an inlet side of the nip portion is lower than a Young's modulus at a position corresponding to a central portion of the nip portion. Fixing device. 2. The tension applying unit urges the guide member to apply tension to the belt member toward an inlet side of the nip portion and / or a side away from the nip portion. The fixing device according to claim 3. The tension applying means applies tension to the belt member so that an outer peripheral surface of the belt member on an outlet side of the nip portion does not overlap an imaginary line passing through an inlet and an outlet of the nip portion. The fixing device according to any one of claims 1 to 4.   6. The fixing according to claim 1, wherein the pressure unit includes a lubricant holding member that holds a lubricant between the belt member and the pressure pad. apparatus. The pressurizing means is
A support member that supports the pressure pad and urges the pressure pad toward the nip portion from the center in the width direction;
An urging member for urging the support member from both ends in the width direction toward the nip portion;
The fixing device according to claim 1, further comprising:   8. The pressure pad according to claim 1, wherein when the operation of the apparatus is stopped, the pressure pad is in pressure contact with the heating unit in a direction inclined to the upstream side in the recording medium conveyance direction. Any one of the fixing devices.   The pressure pad is in pressure contact with the heating means such that the nip width in the nip portion is equal to or less than the nip width of the nip portion formed when the infinite flat plate is in pressure contact with the heating means. The fixing device according to claim 1, wherein the fixing device is characterized in that: The heating means includes
A fixing roller having an elastic layer and being in pressure contact with the pressure pad via the belt member;
A heat source for heating the fixing roller;
The fixing device according to claim 1, wherein the fixing device is provided. The heating means includes
A fixing belt stretched around a plurality of roller members;
An elastic member that presses against the pressure pad via the fixing belt and the belt member;
A heat source for heating the fixing belt;
The fixing device according to claim 1, wherein the fixing device is provided. An image forming apparatus comprising the fixing device according to claim 1.

Images