JP2010038967A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents a foreign substance mark and a defective image on a recording material and has a compact and low-cost apparatus body. <P>SOLUTION: The image forming apparatus is provided with: an image forming section for forming an unfixed image on the recording material S; a fixing unit 20 for fixing the unfixed image on the recording material S; a transporting roller 231 which is provided downstream of the fixing unit 20 in the transporting direction; a pair of paper discharge rollers 233, 234 which are provided downstream of the transporting roller 231 in the transporting direction; and transporting guides 321, 322 for guiding the transportation of the recording material S. In the image forming apparatus, the transporting roller 231 comes in contact with only a surface on the side that is in contact with a heating member of the recording material S, the transporting velocity Vt of the recording material S in the fixing unit 20, the transporting velocity Vh1 of the recording material S at the transporting roller 231, the transporting velocity Vh2 of the recording material S at the pair of paper discharging rollers 233, 234 are in a relationship of Vt&lt;Vh1&lt;Vh2. In addition, only a leading edge of the recording material S in the transporting direction comes in contact with the transporting guides 321, 322. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a heat fixing system that heats and fixes a toner image formed on a recording material, and an image forming apparatus that includes a conveying unit that conveys the heat-fixed recording material.

  In recent years, image forming apparatuses that employ an electrophotographic method have been improved in image quality, speed, size, and price, and various types of image forming apparatuses that meet these various needs have been put on the market. Has been.

  Among such various types of image forming apparatuses, there are many inline type image forming apparatuses in which a plurality of electrophotographic process units each including a charging device and a developing device are arranged in the apparatus main body for each toner color. Proposed.

  FIG. 8 shows a schematic configuration of a conventional in-line image forming apparatus.

  A conventional image forming apparatus is provided with a recording material conveying belt (ETB) 110 stretched by a driving roller 130, a tension roller 140, and two driven rollers 141 and 142.

  Further, image forming units 70a and 70b provided corresponding to magenta (M), cyan (C), yellow (Y), and black (K) toners on the peripheral surface of the recording material conveyance belt 110 (ETB). , 70c and 70d are arranged in a vertical line.

  The surface of the photosensitive drum 101 in each image forming unit 70 (70a to 70d) is uniformly charged by the charger 200, and the surface is irradiated with the laser light emitted from the exposure optical device 300. A latent image is formed on the surface of the photosensitive drum 101. The latent image is developed by the developing device 400, and the latent image is visualized as a toner image.

  Each color toner image formed on each photoconductive drum 101 is transferred to the recording material S on the conveyance belt 110 by the transfer roller 120 in a transfer portion provided opposite to the photoconductive drum 101, and on the recording material. A color image in which toner images of four colors are superimposed is formed.

  On the other hand, untransferred toner remaining on the photosensitive drum 101 after the transfer of the toner image is scraped off by the cleaner 600 and the surface of the photosensitive drum 101 is cleaned.

  Further, the recording material S is fed from the feeding cassette 170 and then guided to the conveying belt 110 by the pickup roller 180.

  When the toner image is transferred as described above, a bias is applied when the recording material S passes through the nip formed by the suction roller 160 and the driven roller 141, and the recording material S is conveyed to the conveying belt. 110 is electrostatically adsorbed.

  Then, the recording material S adsorbed on the conveyance belt 110 is conveyed upward in FIG. 8 by the conveyance belt 110.

  The recording material S onto which the four color toner images have been transferred in this way is separated by the curvature at the downstream rear end of the conveying belt 110 and conveyed to the fixing device 201.

  The fixing device 201 includes a heating member 2110 having a heating body and a pressure member 2200 that contacts the heating member 2110 and forms a fixing nip portion. The recording material S conveyed to the fixing device 201 is heated and pressurized at the fixing nip portion in the fixing device 201, whereby the toner image on the recording material S is fixed on the recording material S.

  The recording material S immediately after passing through the fixing nip portion is nipped by a pair of conveyance rollers 2310 and 2320 configured as a pair, and is conveyed downstream in the conveyance direction.

  Near the outlet of the fixing device 201, there are provided paper discharge roller pairs 2330 and 2340 for discharging the recording material S conveyed from the conveyance roller pairs 2310 and 2320 to the outside of the apparatus main body and stacking them on the discharge tray 310. Yes.

  By the way, recent color image forming apparatuses are required to have higher-quality images (higher image quality) with higher gloss.

  However, a conveyance roller divided in the longitudinal direction (a direction orthogonal to the recording material conveyance direction) with respect to the image forming surface of the recording material S immediately after the toner image is fixed, and a guide member provided between the rollers. When the sheet-passing rib or the like comes into contact, the image quality of the color image is significantly lowered.

  This is because the surface of the high-temperature toner image that has just been heat-fixed is crushed while being partially cooled, resulting in unevenness in smoothness and the like, and streaky unevenness in the conveying direction of the recording material S.

  As a solution to this problem, a configuration in which two pairs of conveying rollers and a discharge roller pair are wide rollers in the longitudinal direction (substantially the same as the sheet width) so as to be entirely in contact with the longitudinal direction of the recording material S. Is mentioned. According to this configuration, there is no possibility that the toner image immediately after being fixed while the recording material S is conveyed contacts the guide member.

  On the other hand, since the recording material S immediately after passing through the fixing device is nipped and conveyed by the conveyance roller pair, the recording material S is rapidly cooled to cause curling.

However, as a solution to this problem, a configuration has been proposed in which the rollers between the pair of conveying rollers are separated by a predetermined distance (Patent Document 1).
JP 2003-223024 A

  However, in the above conventional example, the conveyance roller pairs 2310 and 2320 are provided so as to come into contact with both surfaces of the recording material S (the surface on the side contacting the heating member of the fixing device and the surface on the side contacting the pressure member). Therefore, the following problems occur.

  For example, when a foreign substance adheres to the surface of the conveying roller 2320 provided on the surface side of the recording material S that is in contact with the pressure member and is transferred to the back surface (second surface) of the recording material S, recording is performed during double-sided printing. In some cases, the back surface (second surface) of the material S may have a foreign matter mark, resulting in an image defect.

  Further, since the paired two transport rollers 2320 and 2310 are arranged on the downstream side in the transport direction of the fixing nip portion, it is necessary to secure a space for the transport rollers 2320 and 2310 configured as a pair. There is a limit to further downsizing and cost reduction.

  Furthermore, if a conveyance roller 2320 that contacts the surface of the recording material S that contacts the pressure member is provided downstream in the conveyance direction of the fixing nip portion, the recording material presence / absence detection means 2100 provided downstream in the conveyance direction of the fixing portion is arranged. Restrictions arise.

  Further, the installation of the conveyance roller 2320 restricts the arrangement of the double-sided reversing unit for conveying the recording material S on which the image is formed on the front surface (first surface) in the double-sided printing mode. A large space is required.

  Further, when the recording material S is deflected downstream from the fixing nip portion in the transport direction, the image forming surface of the recording material S comes into contact with the transport guide member or the like due to the occurrence of the deflection, and as a result, image defects are caused. There is a risk that it will be formed.

  That is, in the conventional image forming apparatus, since two paired conveying rollers are provided as conveying means for conveying the recording material immediately after passing through the fixing nip portion, the arrangement of members near the conveying rollers is limited. As a result, it has been difficult to reduce the size and cost of the apparatus main body.

  Further, as described above, in the conveyance process after passing through the fixing device, the recording material has a foreign object on the recording material because the surface on which the toner image has been fixed contacts the conveyance roller or the conveyance guide member. There was a possibility that a mark and an image defect may occur.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus that can prevent the occurrence of foreign matter marks and image defects on a recording material, and can reduce the size and cost of the apparatus main body.

In order to achieve the above object, the present invention provides:
An image forming unit for forming an unfixed image on a recording material;
A heating member and a pressure member are provided, and the recording material is sandwiched so that the surface of the recording material on which an unfixed image is formed is in contact with the heating member at a nip portion formed by the heating member and the pressure member. A fixing unit for fixing the unfixed image formed on the recording material on the recording material in the image forming unit;
A first recording material conveyance unit provided downstream of the fixing unit in the conveyance direction of the recording material;
A second recording material conveyance unit provided downstream of the first recording material conveyance unit in the conveyance direction of the recording material;
A guide member provided between the first recording material conveyance unit and the second recording material conveyance unit to guide conveyance of the recording material;
In an image forming apparatus comprising:
The first recording material transport unit
In the recording material conveyed from the fixing unit, the recording material has a conveying roller that contacts only the surface on the side in contact with the heating member,
The conveyance speed Vt of the recording material in the fixing unit,
The recording material conveyance speed Vh1 in the first recording material conveyance unit,
Recording material conveyance speed Vh2 in the second recording material conveyance unit,
The relationship is Vt <Vh1 <Vh2,
The recording material that has passed through the first recording material conveying unit is
Only the leading end of the recording material in the conveyance direction contacts the guide member,
Thereafter, when the leading end of the recording material in the conveyance direction reaches the second recording material conveyance unit and is conveyed by the second recording material conveyance unit,
In the recording material, the recording material is conveyed without contacting a surface other than the first recording material conveying unit and the second recording material conveying unit on the side in contact with the heating member.

  According to the present invention, it is possible to provide an image forming apparatus that can prevent the occurrence of foreign matter marks and image defects on the recording material, and that can reduce the size and cost of the apparatus main body.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

[Embodiment]
(Overall configuration of image forming apparatus)
A schematic configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. The image forming apparatus according to the present embodiment is a full-color laser beam printer that employs an electrophotographic system.

  The image forming apparatus 100 includes an image forming unit, a paper feeding / conveying unit, a fixing unit, a paper discharge unit, a double-sided conveying unit, and the like. An image forming unit is disposed at the center of FIG. 1, and a sheet feeding / conveying unit is disposed from the lower right hand to the center of the right hand. The fixing unit and the sheet discharging unit are located above the right hand, and the right hand and the right hand are located above the right hand. A double-sided conveyance unit is arranged downward.

(Image forming part)
The image forming apparatus 100 includes four electrophotographic photosensitive members (hereinafter referred to as “photosensitive drums”) 1 (1a, 1b, 1c, 1d) as four image carriers arranged in parallel in the horizontal direction. I have.

  The photosensitive drum 1 (1a, 1b, 1c, 1d) is rotationally driven clockwise in the figure by a driving means (not shown). The periphery of the photosensitive drum 1 is irradiated with a charging device 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 in order according to the rotation direction, and an optical image based on image information. An exposure device 3 (scanner unit 3) is disposed.

  In the present embodiment, the scanner unit 3 irradiates each photoconductor drum 1 with a laser beam based on image information to form an electrostatic latent image on the surface of the photoconductor drum 1.

  Further, around the photosensitive drum 1, a developing device 4 (4 a, 4 b, 4 c, 4 d) that develops a toner image by attaching toner to the electrostatic latent image on the photosensitive drum 1, and on the photosensitive drum 1 An intermediate transfer unit 5 that primarily transfers the toner image to the intermediate transfer belt 11 is disposed.

  Further, a secondary transfer unit that secondary-transfers the toner image on the intermediate transfer belt 11 to the recording material S from the primary transfer portion where the intermediate transfer unit 5 and the photosensitive drum 1 abut on the downstream side in the conveyance direction of the intermediate transfer belt 11. 24 is arranged.

  Further, around the photosensitive drum 1, a cleaning blade 60 (60a, 60b, 60c, 60d) for removing transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer is disposed.

In the present embodiment, the process cartridge 7 (7a, 7b) in which the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning blade 60 described above can be attached to and detached from the apparatus main body.
7c, 7d) are integrated into a cartridge.

  Further, as shown in FIG. 1, the process cartridge 7 is divided into a photosensitive drum unit 50 including a photosensitive drum 1, a charging device 2 and a cleaning blade 60, and a developing unit 40 including a developing device 4. Hereinafter, the configuration of the process cartridge 7 will be described in detail in order from the photosensitive drum 1.

  In this embodiment, the photosensitive drum 1 (1a, 1b, 1c, 1d) is formed by applying an organic photoconductor layer (OPC photosensitive member) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm.

  Both ends of the photosensitive drum 1 are rotatably supported by a support member, and a driving force from a driving motor (not shown) is transmitted to one end, so that the photosensitive drum 1 is rotated counterclockwise. The

  In the present embodiment, a contact charging type charging device 2 is used as the charging device 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1. More specifically, a charging roller formed in a roller shape was used as the charging member of the charging device 2.

  The surface of the photosensitive drum 1 can be uniformly charged by bringing the charging roller 2 into contact with the surface of the photosensitive drum 1 and applying a predetermined charging bias voltage to the charging roller 2. .

  The apparatus main body is provided with a scanner unit 3 (exposure apparatus) that irradiates the surface of the photosensitive drum 1 with image light.

  In the scanner unit 3, image light corresponding to an image signal is emitted from a laser diode (not shown) as a light source to a polygon mirror 9 that is rotated at high speed by a scanner motor 99.

  The image light reflected by the polygon mirror 9 includes an imaging lens 10 (10a, 10b), a reflection mirror 8 (8a, 8b, 8c, 8d, 8e, 8f, 8g, 8h), and a dustproof glass 30 (30a, 30b, 30c). , 30d) and the like.

  Then, the uniformly charged surface of the photosensitive drum 1 is selectively exposed to form an electrostatic latent image on the photosensitive drum 1.

  Further, a shielding member (not shown) for shielding image light and a slit for securing an optical path is disposed on the dust-proof glass 30 of the scanner unit 3. The shielding member (not shown) is attached so as to be able to rotate and move so that an electrostatic latent image can be formed in conjunction with the operation of mounting the process cartridge 7 on the apparatus main body.

  The developing device 4 (4a, 4b, 4c, 4d) includes a developer storage unit that stores toner (developer) of each color of yellow, magenta, cyan, and black, that is, a toner container (not shown), and a developing unit. It has a frame, that is, a developing container (not shown).

  In each toner container (not shown), a developing roller 41 (41a, 41b, 41c, 41d) is disposed as a developer carrying member that carries and conveys toner facing the photosensitive drum 1.

The toner in the toner container (not shown) is sent to the toner supply roller 43 (43a, 43b, 43c, 43d) by a toner conveyance stirring mechanism (not shown).

  Next, the toner is applied to the outer periphery of the developing roller 41 by the toner supply roller 43 (43a, 43b, 43c, 43d) and the developing blade 44 (44a, 44b, 44c, 44d) pressed against the outer periphery of the developing roller 41. Is done. At this time, the toner is rubbed against the developing blade 44, whereby a charge is imparted to the toner.

  Then, by applying a developing bias to the developing roller 41, toner adheres to the electrostatic latent images formed on the respective photosensitive drums 1, and the electrostatic latent images are developed as toner images.

  The developing device 4 has a suspension structure in which bearing members (not shown) attached to both ends are supported swingably with respect to the photosensitive drum unit 50 by pins around a support shaft (not shown).

  When the process cartridge 7 is a single unit (not attached to the apparatus main body 100), a pressure spring is applied so that the developing roller 41 comes into contact with the photosensitive drum 1 by a rotational moment about a support shaft (not shown) of the developing device 4. The developing device 4 is always urged by (not shown).

  Further, the toner container (not shown) of the developing device 4 has an action for functionally connecting a separation / contact switching means (not shown) of the apparatus main body 100 when the developing roller 41 is separated from the photosensitive drum 1. A separation boss (not shown) as a receiving portion is integrally provided.

  Although not shown, each developing unit 40 is provided with a toner remaining amount detection mechanism. The developing unit 40 senses the transmission time by transmitting LED light into the toner container, and thereby the toner remaining in the developing unit 40 is detected. The amount is detected.

  In the present embodiment, an intermediate transfer belt 11 for transferring a toner image formed on the surface of each photosensitive drum 1 by the above process is provided. The intermediate transfer belt 11 faces all the photosensitive drums 1 (1a, 1b, 1c, 1d), and is arranged so as to be able to circulate so as to contact the surface thereof with a predetermined contact pressure.

The intermediate transfer belt 11 is composed of an endless film-like member having a thickness of about 150 μm and a circumferential length of about 700 mm with a volume resistivity of 10 ¹¹ to 10 ¹⁴ Ω · cm.

  This intermediate transfer belt 11 is supported by rollers 13 and 14 on two axes in the horizontal direction, and circulates so that the toner images formed on the photosensitive drums of the respective colors are transferred to the recording material S via the intermediate transfer belt 11. Moving.

  Primary transfer rollers 12 (12a, 12b, 12c, 12d) are juxtaposed at positions facing the inner side of the intermediate transfer belt 11 and facing the four photosensitive drums 1a, 1b, 1c, 1d. .

  A positive charge is applied from the primary transfer roller 12 to the intermediate transfer belt 11, and a negative toner image on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 11 by an electric field generated by the charge. In this embodiment, the case of using a negative polarity toner is described. However, a positive polarity toner may be used, and in this case, the polarity of the charge applied to the intermediate transfer belt 11 is as described above. And the opposite negative polarity.

Further, a secondary transfer roller 25 is disposed at a position facing the drive roller 13 of the intermediate transfer unit 5. As with the primary transfer roller 12, the recording material S is transferred from the intermediate transfer belt 11.
When the toner image is secondarily transferred, first, positive charge is applied from the secondary transfer roller 25 to the recording material S conveyed to the secondary transfer portion T2.

  Then, the negatively transferred toner image on the intermediate transfer belt 11 that has been primarily transferred is secondarily transferred onto the recording material S that is in contact with the intermediate transfer belt 11 by the electric field formed by this electric charge.

  Further, a cleaning device 15 for removing toner remaining on the intermediate transfer belt 11 after the secondary transfer is disposed at a position facing the tension roller 14 of the intermediate transfer unit 5. The toner removed by the cleaning device 15 passes through a waste toner conveyance path and is collected in a waste toner collection container 26.

(Paper Feeder)
The paper feeding unit feeds and transports the recording material S to the secondary transfer unit T2 that transfers the image on the intermediate transfer belt 11 to the recording material S. A plurality of recording materials S are stored in the paper feeding cassette 17. Has been.

  During image formation, the paper feed roller 18 (half moon roller) feeds the uppermost recording material S of the paper feed cassette 17. The leading edge of the recording material S abuts against the registration roller pair 19 and temporarily stops to form a loop. Then, the rotation of the intermediate transfer belt 11 and the image writing position are synchronized, and the registration roller pair 19 supplies the secondary transfer portion T2. It will be papered.

(Fixing / output section)
The fixing unit 20 (fixing unit) fixes a plurality of color toner images transferred to the recording material S to the recording material S.

  In the fixing unit 20 according to the present embodiment, a heating member that heats the surface of the recording material S on which an unfixed image is formed (unfixed image forming surface) and an unfixed image of the recording material S are formed. And a pressure member that pressurizes the other surface.

  The heating member is a ceramic heater 211 (hereinafter referred to as a heater) that is a ceramic plate-like heating element, a holder member 212 that holds the heater 211, the heater 211, and the endless heat-resistant film 213 that encloses the holder member 212 over the entire circumference. Consists of In this embodiment, the endless heat-resistant film 213 is used, but a configuration using a heating roller may be used instead.

  On the other hand, a pressure roller 22 covered with an elastic layer of silicon rubber on an iron core is used as the pressure member on the opposite side, and the pressure roller 22 is predetermined with respect to the endless heat-resistant film 213. The fixing nip portion is formed by the contact with the pressure.

  The pressure roller 22 is rotationally driven in the fixing nip portion, and the endless heat-resistant film 213 is driven by the pressure roller 22 so that the recording material S can be nipped and conveyed while being pressurized and heated in the fixing nip portion. become. The endless heat-resistant film 213 and the pressure roller 22 forming the fixing nip portion will be hereinafter referred to as “fixing roller pair”.

  With this configuration, an unfixed toner image on the recording material S is heated and pressed in the fixing nip portion, whereby the toner image can be melted and the toner image can be fixed on the recording material S.

  The endless heat-resistant film 213 and the pressure roller 22 are coated with a resin having good releasability such as PFA and PTFE on the outermost layer in order to prevent toner and paper dust from sticking.

  Further, a paper discharge unit is provided on the downstream side of the fixing unit 20 in the conveyance direction, and a single conveyance roller 231 that rotates in contact with the surface of the recording material S that contacts the heating member, and further on the downstream side in the conveyance direction. Disposed paper discharge roller pairs 233 and 234 are provided. In the present embodiment, the conveyance roller 231 is a “first recording material conveyance unit”, and the paper discharge roller pair 233 and 234 is a “second recording material conveyance unit”.

  The conveyance roller 231 and the discharge roller pair 233 and 234 in the present embodiment are wide in which the length in the longitudinal direction (the direction perpendicular to the conveyance direction of the recording material S) is substantially equal to the sheet width of the recording material S. Roller.

  According to the present embodiment, the endless heat resistant film 213, the transport roller 231, and the paper discharge roller 233 are disposed along the transport path of the recording material S on the unfixed image forming surface side of the recording material S. These outermost layers are coated with a resin having good releasability such as PFA and PTFE for preventing toner and paper dust from sticking.

  A paper discharge flag 210 as a recording material detection unit is disposed immediately above the conveyance roller 231. Whether or not the recording material S has been reliably discharged from the fixing roller pair 213 and 22 is determined. It monitors whether there is a paper jam due to wrapping around.

  The paper discharge flag 210 is configured to be swingable, and is biased with a predetermined pressure by a torsion coil spring (not shown) provided at the center of swinging.

(Reversed refeed unit)
An upper side of the fixing unit 20 is provided with a reverse refeeding unit for turning the recording material S upside down and transporting the recording material S to the duplex transport path 27.

  The reversing and re-feeding unit reversely conveys the recording material S at a predetermined timing by a double-sided flapper 32 for selectively conveying the recording material S to the double-sided conveyance path 27 and a control unit A described later. A pair of switchback rollers 251 and 252 are provided for transporting to the front.

  Further, an oblique feed roller unit 28 is provided at a substantially central portion of the double-sided conveyance path 27 formed on the back side of the secondary transfer portion T2.

  By providing the oblique feeding roller unit 28, when the recording material S passes through the double-sided conveyance path 27 from the secondary transfer portion T2, the recording material S in a state skewed with respect to the normal position is sent by one-sided feeding. The material S can be transported while being corrected to a normal position and posture.

  A U-turn path 29 that changes the conveyance direction of the recording material S is provided at the lowest point of the double-sided conveyance path 27, and the recording material S guided to the U-turn path 29 is re-fed to the registration roller pair 19, and then An image is formed on the back surface (second surface) of the recording material S.

(Control part)
The control unit A controls the entire apparatus, and includes, for example, a double-sided printing mode for forming images on both sides of the recording material S and a single-sided printing mode for forming images on one side of the recording material S.

  The control unit A is connected to a host computer (such as a personal computer) (not shown) used by the user, and can select each mode through the screen of the host computer when the user performs printing. When the user selects a desired mode, the control unit A operates the apparatus main body in any mode according to the user's selection.

(Image forming operation)
When forming an image on the recording material S, first, the process cartridges 7a, 7b, 7c, 7d are sequentially driven in accordance with the printing timing, and the photosensitive drums 1a, 1b, 1c, 1d are driven in accordance with the drive. It is rotationally driven in the turning direction.

  Then, the scanner units 3 corresponding to all the process cartridges 7 are driven. By this driving, the charging roller 2 imparts a uniform charge to the circumferential surface of the photosensitive drum 1, and the scanner unit 3 exposes the circumferential surface of the photosensitive drum 1 according to the image signal to perform photosensitive drum 1. An electrostatic latent image is formed on the peripheral surface.

  A developing roller 41 in the developing device 4 forms (develops) a toner image on the circumferential surface of the photosensitive drum 1 by transferring toner to a low potential portion of the electrostatic latent image. The toner images of the respective colors formed on the circumferential surface of the photosensitive drum 1 are primarily transferred onto the intermediate transfer belt 11 in synchronization with the image positions.

  At this time, a full-color toner image is formed on the intermediate transfer belt 11 at the stage where the toner images of all colors are primarily transferred.

  Thereafter, as the intermediate transfer belt 11 rotates, the leading edge of the toner image on the intermediate transfer belt 11 is rotated and conveyed to a point (secondary transfer portion T2) between the intermediate transfer belt 11 and the secondary transfer roller 25. The

  At this timing, the registration roller pair 19 starts rotating so that the printing start position of the recording material S coincides with the leading edge of the toner image on the intermediate transfer belt 11 and feeds the recording material S to the secondary transfer portion T2. .

  The toner image on the intermediate transfer belt 11 is transferred to the recording material S that has been transported to the secondary transfer portion in this manner by an electric field formed between the intermediate transfer belt 11 and the secondary transfer roller 25. Is done.

  Thereafter, the recording material S on which the full-color toner image is transferred is conveyed from the secondary transfer portion T2 to the fixing unit 20. The recording material S is an apparatus in which the unfixed toner image is thermally fixed by the fixing unit 20 and then the unfixed image forming surface is faced down from the discharge portion by the transport roller 231 and the discharge roller pairs 233 and 234. It is discharged out of the main unit.

  When the duplex printing mode is selected, the following operation is performed.

  The recording material S on which the toner image is thermally fixed by the fixing unit 20 passes through the transport roller 231 and is transported to the switchback roller pair 251 and 252 by the double-sided flapper 32 at the double-sided transport position.

  The paper discharge flag 210 detects the timing when the trailing edge of the recording material S has passed through the fixing roller pair and the conveyance roller 231. In response to the detection signal, the double-sided flapper 32 lifts the recording material S by a predetermined angle using a solenoid arm (not shown) to the double-sided conveyance path 27 (single-sided conveyance position).

  While the double-sided flapper 32 is lifted, the switchback roller pair 251 and 252 rotate in the reverse direction, and the recording material S is conveyed to the double-sided conveyance path 27 in a state where the recording material S is reversed.

The recording material S conveyed to the double-sided conveyance path 27 is fed from the skewed state with respect to the regular position by passing through the reverse conveyance path from the secondary transfer portion T2 by the skew feeding roller pair 281 and 282, and is fed to the regular position. It is conveyed while being corrected to the position and posture.

  A U-turn path 29 is provided at the lowest point of the double-sided conveyance path 27 in order to change the conveyance direction of the recording material S, and the recording material S guided to the U-turn path 29 is fed again to the registration roller pair 19.

  Thereafter, in order to form an image on the other surface (back surface, second surface) of the recording material S, an image process similar to that on the front surface (first surface) is repeated.

  The recording material S on which the toner image is fixed by the fixing unit 20 has the image forming surface formed on the second surface through the paper discharge roller pair 233 and 234 in the single-sided conveyance position state where the double-sided flapper 24 is lifted. It is discharged out of the main body in the state.

(Characteristics of fixing / discharge unit)
Hereinafter, with reference to FIG. 2 to FIG. 7, features of the fixing / discharge unit in the present embodiment will be described. 2 to 7 show schematic configurations of the fixing unit and the paper discharge unit in the present embodiment.

  In the present embodiment, the conveyance speeds of the fixing roller pair 213 and 22, the conveyance roller 231 and the paper discharge roller pair 233 and 234 are set as follows. The conveyance speed of the fixing roller pair 213, 22 is Vt, the conveyance speed of the conveyance roller 231 is Vh1, and the conveyance speed of the discharge roller pair 233, 234 is Vh2.

  The relationship among the conveying speed Vt of the fixing roller pair 213 and 22, the conveying speed Vh <b> 1 of the conveying roller 231, and the conveying speed Vh <b> 2 of the paper discharge roller pair 233 and 234 is Vt (100%) <Vh1 (104%) <Vh2 ( Each conveyance speed was set to be 106.5%.

  Further, as shown in FIG. 2, the conveyance direction of the recording material S is guided to the side (unfixed image forming surface side) in contact with the heating member of the recording material S between the fixing roller pair 213, 22 and the conveyance roller 231. A conveyance guide 321 (guide member) is provided. A conveyance guide 322 is provided on the side facing the conveyance guide 321 across the conveyance path of the recording material S.

  In the present embodiment, the conveyance guides 321 and 322 have a shape that does not protrude beyond a virtual line 35 that connects the fixing nip portion formed by the fixing roller pair and the contact surface of the conveyance roller 231 with the recording material S. It is characterized by.

  Further, a conveyance guide 331 for guiding the conveyance direction of the recording material S is provided on the side (unfixed image forming surface side) in contact with the heating member of the recording material S between the conveyance roller 231 and the discharge roller pair 233 and 234. Is provided. A conveyance guide 332 is provided on the side facing the conveyance guide 331 across the conveyance path of the recording material S.

  In the present embodiment, the conveyance guides 331 and 332 have a shape that does not protrude beyond a virtual line 36 that connects the contact portion of the conveyance roller 231 with the recording material S and the contact nip portion of the discharge roller pair 233 and 234. It is characterized by that.

  With this configuration, after the recording material S heated and fixed at the fixing nip portion passes through the fixing nip portion, the leading end of the recording material S first reaches the conveying roller 231 and is further conveyed downstream in the conveying direction. Note that the plurality of conveyance guides in the present embodiment are configured such that only the leading ends in the conveyance direction of the recording material S are in contact with each other.

  Thereafter, as shown in FIG. 4, the paper discharge flag 210 which is a recording material detection means provided above the conveying roller 231 is lifted at the leading end of the recording material S.

  As shown in FIGS. 4 and 5, the tip of the recording material S on the side in contact with the pressure member reaches the lower surface guide portion of the double-sided flapper 32 and the conveyance guide 332 and reaches the paper discharge roller pair 233 and 234.

  After the recording material S starts to be conveyed to the paper discharge roller pair 233, 234, the recording material S is changed from the state of FIG. 6 to the state of FIG. The double side flapper 32 is gradually separated from the lower surface guide portion and the conveyance guide 332.

  That is, in this embodiment, the recording material S is set so that the conveyance speed of the recording material S increases as the recording material S is conveyed downstream in the conveyance direction, and therefore, between the fixing nip portion and the discharge roller pairs 233 and 234. A certain recording material S is stretched downstream in the transport direction.

  With this configuration, when the recording material S is transported, the surface of the recording material S that is in contact with the heating member (unfixed image forming surface) is not rubbed against the transport guide or the like, and there is no slack between the transporting units. The recording material S can be conveyed. The recording material S is discharged to the paper discharge tray 31 by the paper discharge roller pair 233 and 234.

  In the present embodiment, the double-sided flapper 32 and the conveyance path of the recording material S are provided between the conveyance roller 231 and the switchback roller pair 251 and 252 as a conveyance guide on the surface of the recording material S in contact with the heating member. A conveyance guide 342 is provided on the side opposite to that sandwiched therebetween (FIG. 3).

  In the same manner as described above, these shapes are formed so as not to protrude beyond the imaginary line 37 connecting the contact portion of the transport roller 231 with the recording material S and the nip portions of the switchback roller pairs 251 and 252.

  In the present embodiment, the conveying roller disposed on the downstream side of the fixing roller pair 213 and 22 is not a roller pair (two rollers), but only on the heating member contact surface side where an unfixed image of the recording material S is formed. A single conveying roller 231 is arranged.

  With these configurations, during the period from when the recording material S passes through the fixing nip portion to the time when the recording material S is conveyed to the paper discharge roller pair 233 and 234, the surface of the recording material S that contacts the heating member is the conveying roller 231, There is no contact with any structure other than the paper discharge roller pair 233, 234.

  That is, in the present embodiment, the surface of the recording material S on the side in contact with the heating roller 22 in the recording material S is not in contact with a structure other than the first recording material conveyance unit and the second recording material conveyance unit. It is characterized by.

  Therefore, the foreign matter is further transferred to the recording material S in a state where the foreign matter adheres to the conveyance roller and the guide member arranged on the pressure member contact surface side of the recording material S. As a result, the pressure member of the recording material S It is possible to prevent foreign matter marks from being generated on the toner image formed on the contact surface side.

  Further, it is possible to eliminate image defects caused by the toner image being rubbed against the conveyance guide and the like, and the conveyance roller 231 is not formed as a pair of rollers. Can be performed.

Further, a virtual line 35 connecting the fixing nip portion and the contact portion of the transport roller 231 with the recording material S, a contact portion of the paper discharge roller pair 233 and 234 with the recording material S, and the transport roller 231.
The angle B formed by the virtual line 36 connecting the contact portion with the recording material S was 140 °.

  As a result, even when a stiff recording material such as thick paper is used, the recording material S can be transported between the transporting units downstream of the pair of fixing rollers without causing slack, and the toner image can be traced. It is possible to prevent image defects caused by rubbing against a conveyance guide or the like.

On the other hand, at 134.3 °, the recording material S has a strong recording material (basis weight of 150 g / m ² or more). It has been confirmed that the surface rubs against the conveyance guide and starts to cause image defects. Therefore, it is desirable that the angle formed by the virtual line 36 and the virtual line 35 is 135 ° or more.

  Further, the clearance 38 (interval) between the conveyance roller 231 and the recording material conveyance guide 322 facing the recording material S across the conveyance path of the recording material S is set to 2.5 mm or more.

  As a result, even when a recording material with a large curl is used, an image defect occurs due to the toner image being rubbed against a foreign object trace or a conveyance guide between the conveyance units arranged downstream of the fixing roller pair. The recording material S can be transported without doing so.

In the current configuration, when the clearance 38 between the conveyance roller 231 and the recording material conveyance guide 322 facing the conveyance roller 231 across the conveyance path of the recording material S is less than 2.0 mm, the following problems are confirmed. .

For example, in a recording material having a strong stiffness (basis weight of 150 g / m ² or more) or a recording material having a large curl, the side in contact with the pressure member in the recording material S after an image is formed on the second surface particularly during double-sided printing. It has been confirmed that the surface of the surface rubs against the conveyance guide and causes an image defect. Therefore, it is desirable that the clearance 38 between the conveyance roller 231 and the recording material conveyance guide 322 facing the conveyance roller 231 be 2.0 mm or more.

  Further, a paper discharge flag 210 that is a swingable recording material detection unit that detects the presence or absence of the recording material S is provided between the conveying roller 231 and the paper discharge roller pair 233 and 234. Further, the center of swinging of the paper discharge flag 210 is arranged so as to be on the side of the recording material S in contact with the pressure member 22 across the conveyance path of the recording material S.

  As a result, the recording material S is pressed by the urging force of the paper discharge flag 210 from the side where the unfixed image is not formed in the vicinity of the conveyance roller 231.

  With this configuration, even if the recording material S is urged, the recording material S is pressed against the conveyance roller 231, and the side of the recording material S that contacts the heating member (unfixed image forming surface) is rubbed against the conveyance guide or the like. Less likely. Therefore, the recording material S can be stably conveyed without the toner image formed on the recording material S being rubbed by the conveyance guide or the like.

  As described above, according to the present embodiment, it is possible to provide an image forming apparatus that can prevent foreign matter marks and image defects from occurring on the recording material, and that can reduce the size and cost of the apparatus main body. Become.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram of a fixing / discharge unit in the present embodiment. FIG. 2 is a schematic configuration diagram of a fixing / discharge unit in the present embodiment. FIG. 2 is a schematic configuration diagram of a fixing / discharge unit in the present embodiment. FIG. 2 is a schematic configuration diagram of a fixing / discharge unit in the present embodiment. FIG. 2 is a schematic configuration diagram of a fixing / discharge unit in the present embodiment. FIG. 2 is a schematic configuration diagram of a fixing / discharge unit in the present embodiment. 1 is a schematic configuration diagram of a conventional image forming apparatus.

Explanation of symbols

3 Scanner unit 7 Process cartridge 11 Intermediate transfer belt 20 Fixing unit 22 Pressure roller 27 Double-sided conveyance path 32 Double-sided flapper 210 Paper discharge flag 211 Ceramic heater 212 Holder member 213 Endless heat resistant film 231 Transport roller 233 Paper discharge roller 234 Paper discharge roller 251 Switchback roller 252 Switchback roller 321 transport guide 322 transport guide

Claims (4)

An image forming unit for forming an unfixed image on a recording material;
A heating member and a pressure member are provided, and the recording material is sandwiched so that the surface of the recording material on which an unfixed image is formed is in contact with the heating member at a nip portion formed by the heating member and the pressure member. A fixing unit for fixing the unfixed image formed on the recording material on the recording material in the image forming unit;
A first recording material conveyance unit provided downstream of the fixing unit in the conveyance direction of the recording material;
A second recording material conveyance unit provided downstream of the first recording material conveyance unit in the conveyance direction of the recording material;
A guide member provided between the first recording material conveyance unit and the second recording material conveyance unit to guide conveyance of the recording material;
In an image forming apparatus comprising:
The first recording material transport unit
In the recording material conveyed from the fixing unit, the recording material has a conveying roller that contacts only the surface on the side in contact with the heating member,
The conveyance speed Vt of the recording material in the fixing unit,
The recording material conveyance speed Vh1 in the first recording material conveyance unit,
Recording material conveyance speed Vh2 in the second recording material conveyance unit,
The relationship is Vt <Vh1 <Vh2,
The recording material that has passed through the first recording material conveying unit is
Only the leading end of the recording material in the conveyance direction contacts the guide member,
Thereafter, when the leading end of the recording material in the conveyance direction reaches the second recording material conveyance unit and is conveyed by the second recording material conveyance unit,
An image in which the recording material is conveyed without contacting the structure other than the first recording material conveyance unit and the second recording material conveyance unit on the side of the recording material in contact with the heating member. Forming equipment. An imaginary line connecting the nip portion and a contact portion between the recording material in the first recording material conveying portion;
The angle formed by the imaginary line connecting the contact portion with the recording material in the first recording material transport portion and the contact portion with the recording material in the second recording material transport portion is 135 ° or more. Item 2. The image forming apparatus according to Item 1. At a position facing the first recording material conveyance unit across the recording material conveyance path,
3. The image according to claim 1, wherein a guide member for guiding the conveyance of the recording material is provided, and an interval between the first recording material conveyance unit and the guide member is 2.0 mm or more. Forming equipment. Between the fixing unit and the second recording material transport unit,
A swingable recording material detection means for detecting the presence or absence of the recording material is provided,
4. The center of rocking of the recording material detecting means is disposed on the side of the recording material in contact with the pressure member across the recording material conveyance path. The image forming apparatus described in 1.

Images