JP2010048961A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the dry state of a recording medium after fixing uniform without enlarging diameters of shafts for rollers in an image forming apparatus for thermally fixing an image formed on the recording medium and then conveying the recording medium after fixing by the rollers. <P>SOLUTION: Five sets of first paper ejecting rollers 44 and pinch rollers 45 are arranged with intervals in the direction of shafts 84, 85 and four sets of second paper ejecting rollers 46 and pinch rollers 47 are arranged with intervals in the direction of the shafts 86, 87. Furthermore, respective nip sections of the second paper ejecting rollers 46 and pinch rollers 47 are arranged in positions not overlapping any nip section of the first paper ejecting rollers 44 and pinch rollers 45 in the conveyance direction of paper 4. Although, in the paper 4 on which the toner is thermally fixed, heat is taken away by the rollers, the paper is cooled, and evaporation of water vapor is suppressed, the dry state of the paper 4 can be made uniform over the entire sheet by the arrangement of the rollers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium, and more particularly, to an image forming apparatus that thermally fixes an image formed on a recording medium and conveys the recording medium after the heat fixing by a roller. .

  2. Description of the Related Art Conventionally, in an image forming apparatus that forms an image by attaching a recording material such as toner to a recording medium such as paper by an electrophotographic method, the image formed on the recording medium is thermally fixed. . When the recording material is toner, the image can be stabilized by melting the toner by this heat fixing and adhering it to the recording medium. In this type of image forming apparatus, the recording medium after the image has been thermally fixed as described above is conveyed by a roller and discharged onto a discharge tray or the like.

  Here, when the fixed sheet is conveyed by a plurality of rollers arranged at intervals in the direction of the rotation axis, the dry state of the sheet differs between where it hits the roller and where it does not hit. That is, since the heat after fixing is taken away by the roller when it hits the roller, the evaporation of water vapor is suppressed, whereas more water vapor evaporates from the place where it did not hit the roller.

In the case of single-sided printing, even if the dry state is uneven as described above, the problem is relatively small to the extent that the paper can be wrinkled. If this occurs, there may be unevenness in the image forming state of the second side. In view of this, it has been proposed to transport the fixed sheet with a roller having the same outer diameter over the entire width of the sheet (see, for example, Patent Document 1).
JP-A-5-40429

  However, when using a roller having the same outer diameter over the entire width of the paper, if the roller is bent, the roller does not uniformly contact the paper, so it is necessary to increase the diameter of the roller shaft. In addition, it becomes difficult to stably convey the paper. Accordingly, the present invention provides an image forming apparatus in which an image formed on a recording medium is thermally fixed, and the recording medium after the heat fixing is conveyed by a roller, after fixing, without increasing the diameter of the roller shaft. The purpose was to make the recording medium dry in a uniform manner.

  The image forming apparatus of the present invention made to achieve the above object includes an image forming unit that forms an image on a recording medium, a fixing unit that thermally fixes an image formed on the recording medium by the image forming unit, and A plurality of first rollers for conveying a recording medium arranged at intervals in the direction of the rotation axis and having an image fixed by the fixing means, and a plurality of arrangements arranged at intervals in the direction of the rotation axis for conveyance to the first roller A second roller for further transporting the recorded medium, and the center position of the nip portion of each second roller in the rotational axis direction is the same as the nip portion of any of the first rollers in the recording medium transport direction. It is characterized by being disposed at a position where it does not overlap.

  In the image forming apparatus of the present invention configured as described above, the recording medium on which the image is formed by the image forming means is sequentially passed through the first roller and the second roller after the image is thermally fixed by the fixing means. Then transported. Here, a plurality of first rollers and second rollers are arranged at intervals in the rotation axis direction, and the center position in the rotation axis direction of the nip portion of each second roller is the nip of any of the first rollers. Both parts are arranged at positions that do not overlap in the recording medium conveyance direction.

  In the present invention, the nip portion of each first roller and the nip portion of each second roller are thus displaced with respect to the width direction of the recording medium (the direction perpendicular to the recording medium conveyance direction). Since it is disposed, the dry state can be made uniform over the entire surface of the recording medium. Further, by using a plurality of rollers arranged at intervals in the rotation axis direction as the first roller and the second roller, each roller can be easily brought into contact with the recording medium. For this reason, the diameter of the shaft of the roller can be reduced, and as a result, the manufacturing cost reduction and size reduction of the image forming apparatus can be favorably promoted. Further, the recording medium can also be stably conveyed.

  Although the present invention is not limited to the following configuration, any combination of the first roller and the second roller does not have the overlapping portion of the nip portion in the recording medium conveyance direction, and Any portion of the recording medium to be conveyed may pass through the nip portion of either the first roller or the second roller. In this case, each part of the recording medium is nipped once by the first roller or the second roller, so that the dried state of the recording medium can be made more uniform.

  Each of the second rollers may have a nip width in the recording medium conveyance direction larger than any of the first rollers. Since the first roller nips the recording medium at an earlier time point than the second roller, the drying of the recording medium is more effectively suppressed, but when the second roller has a larger nip width in this way, Accordingly, the action of cooling the recording medium of the second roller (the action of suppressing drying) becomes stronger. For this reason, the dry state of the recording medium can be made more uniform.

  Each of the second rollers may have a higher thermal conductivity than any of the first rollers. Also in this case, the action of cooling the recording medium by the second roller becomes strong, and the dried state of the recording medium can be made more uniform.

  Furthermore, at least one of the first rollers or the second rollers may correct the curl of the recording medium while conveying the recording medium. In this case, it is possible to satisfactorily correct the curl of the recording medium while the recording medium is warm. Further, such a roller for correcting curl is generally constituted by a combination of a large-diameter roller and a small-diameter roller. However, in the image forming apparatus of the present invention, as described above, the radius of the roller shaft is set. Therefore, the effect of reducing the diameter can be more remarkably exhibited.

  Further, the recording medium may be further provided with a re-conveying unit for conveying the recording medium conveyed by the first roller and the second roller over the entire length in the conveying direction to the image forming unit to form an image. . In this case, since image formation is repeatedly performed on one recording medium, it is possible to satisfactorily form the second image by making the dry state uniform as described above, and making the dry state uniform. The effect appears more remarkably. In addition, after the image on the first surface is formed, the image on the second surface is formed after being transported over the entire length in the transport direction by the first roller and the second roller. The image on the second side can be satisfactorily formed over the entire surface of the recording medium. Note that the first and second surfaces are not necessarily front and back surfaces, and the images of the first and second surfaces may be superimposed on one surface of the recording medium.

  The image forming unit may form an image by electrophotography using a transfer current energized through the recording medium. In the electrophotographic system, the resistance value of the recording medium changes due to drying of the recording medium, and the ease of flow of the transfer current also changes. In the image forming apparatus of the present invention, as described above, the dry state of the recording medium can be made uniform, so that the transfer current can be easily flowed, and the effect becomes more remarkable.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a laser printer 1 as an example of an image forming apparatus to which the present invention is applied. In the following description, the left side in FIG.

(Whole structure of laser printer)
The laser printer 1 is a direct transfer tandem type color laser printer, and includes a substantially box-shaped main body casing 2 as shown in FIG. A paper discharge tray 5 on which paper 4 as a recording medium is stacked is formed. A sheet feeding cassette 7 on which sheets 4 for forming an image are loaded is attached to the lower part of the main casing 2 so as to be able to be pulled out forward. A paper feed roller 9 for transporting the paper 4 is provided at a position above the front end of the paper feed cassette 7, and the paper 4 transported by the paper feed roller 9 is disposed downstream of the paper feed roller 9 in the paper transport direction. A separation roller 10 and a separation pad 11 for separating each sheet are provided.

  When the uppermost sheet 4 of the sheet feeding cassette 7 is pressed toward the sheet feeding roller 9 by a mechanism (not shown) and is sandwiched between the separation roller 10 and the separation pad 11 by the rotation of the sheet feeding roller 9. Separated one by one. Then, the sheet 4 sent out between the separation roller 10 and the separation pad 11 is sent to the registration roller 13 by the pair of transport rollers 12. The registration roller 13 feeds the paper 4 onto the rear belt unit 15 at a predetermined timing.

  The belt unit 15 is attachable to and detachable from the main casing 2 and includes a conveyor belt 18 that is horizontally installed between a pair of belt support rollers 16 and 17 that are spaced apart from each other in the front-rear direction. The conveyor belt 18 is an endless belt made of a resin material such as polycarbonate, and is circulated in the clockwise direction in FIG. 1 when the rear belt support roller 17 is rotationally driven, and is placed on the upper surface thereof. Sheet 4 is conveyed backward. Inside the conveyance belt 18, four transfer rollers 19 arranged to face each photosensitive drum 31 included in an image forming unit 26 described later are arranged in a front-rear direction at regular intervals, and correspond to each photosensitive drum 31. The transfer belt 18 is sandwiched between the transfer roller 19 and the transfer roller 19.

  A scanner unit 20 is provided at an upper portion in the main body casing 2, a process unit 25 as an example of an image forming unit is provided below the scanner unit 20, and the belt unit 15 is disposed below the process unit 25. Has been. The scanner unit 20 irradiates the surface of the corresponding photosensitive drum 31 with laser light L for each color based on predetermined image data at high speed scanning. The configuration of the scanner unit 20 will be described in detail later.

  The process unit 25 includes four image forming units 26 corresponding to each color of black (K), cyan (C), magenta (M), and yellow (Y), and these image forming units 26 are arranged in the front and rear. Is arranged in. In the present embodiment, the image forming units 26 are arranged in the order of black, yellow, magenta, and cyan from the front side of the laser printer 1. Each image forming unit 26 includes a photosensitive drum 31, a scorotron charger 32, a developing cartridge 34, and the like.

  The photoconductor drum 31 includes a grounded metal drum body, and the surface layer thereof is covered with a positively chargeable photoconductive layer made of polycarbonate or the like. The scorotron charger 32 is disposed opposite to the photosensitive drum 31 at a predetermined interval so as not to come into contact with the photosensitive drum 31 in the diagonally upper rear side of the photosensitive drum 31. The scorotron charger 32 uniformly charges the surface of the photosensitive drum 31 to positive polarity by generating corona discharge from a charging wire such as tungsten.

  The developing cartridge 34 has a substantially box shape, and a toner storage chamber 38 is provided at an upper portion thereof, and a developing roller 39 is provided at a lower end thereof. Each toner storage chamber 38 stores positively chargeable nonmagnetic one-component toner of each color of black, cyan, magenta, or yellow as a recording material. This developing cartridge 34 is a well-known cartridge that supplies toner to the photosensitive drum 31 via the developing roller 39 after positively frictionally charging the toner stored in the toner storage chamber 38.

  The surface of the photosensitive drum 31 is first uniformly charged positively by the scorotron charger 32 when rotating. Thereafter, exposure is performed by high-speed scanning of the laser light L from the scanner unit 20, and an electrostatic latent image corresponding to an image to be formed on the paper 4 is formed. Next, the rotation of the developing roller 39 causes the positively charged toner carried on the developing roller 39 to come into contact with the photosensitive drum 31 and be formed on the surface of the photosensitive drum 31. The electric latent image is supplied. As a result, the electrostatic latent image on the photosensitive drum 31 is visualized, and a toner image with toner attached only to the exposed portion is carried on the surface of the photosensitive drum 31.

  Thereafter, the toner image carried on the surface of each photosensitive drum 31 is supplied to the transfer roller 19 by a constant current when the paper 4 conveyed by the conveying belt 18 passes between the photosensitive drum 31 and the transfer roller 19. The images are sequentially transferred onto the paper 4 by a negative transfer bias applied by the control. By transferring the toner image in this way, the sheet 4 on which an image is formed by a so-called electrophotographic method is then conveyed to a fixing device 40 as an example of a fixing unit.

  The fixing device 40 is disposed behind the conveyance belt 18 in the main body casing 2. The fixing device 40 includes a heating roller 41 that is rotationally driven with a heat source such as a halogen lamp, and a pressure roller 42 that is disposed below the heating roller 41 so as to face the heating roller 41 and is driven to rotate. It has. The fixing device 40 heats and fixes the toner image onto the paper 4 by heating the paper 4 carrying the four color toner images while nipping and conveying the paper 4 by the heating roller 41 and the pressure roller 42.

  Then, the sheet 4 on which the toner image has been thermally fixed is nipped by a first paper discharge roller 44 and a pinch roller 45 disposed obliquely above the fixing device 40 and conveyed upward. Subsequently, the sheet 4 is nipped between the second sheet discharge roller 46 and two (exactly two rows as will be described later) pinch rollers 47 and further conveyed while correcting the curl. The paper is nipped between a final paper discharge roller 48 and two pinch rollers 49 provided on the paper, and further curled, and then discharged onto the paper discharge tray 5 described above. The first paper discharge roller 44 and the pinch roller 45 correspond to an example of the first roller, and the second paper discharge roller 46 and the two pinch rollers 47 correspond to an example of the second roller, respectively.

  The scanner unit 20 includes a box-shaped resin housing 50, and, for example, a six-sided polygon mirror 52 driven by a polygon motor 51 is rotatably provided at a substantially central portion inside the housing. The housing 50 is provided with four laser light sources (not shown) near the right side of the polygon mirror 52 as follows.

  The laser light source that emits the laser light Lk corresponding to the black image data is directed to one deflection surface of the polygon mirror 52 that is located slightly downward from the upper position, and the laser light Lk deflected by the polygon mirror 52 is the laser printer. 1 is guided through the first scanning lens 53 (for example, fθ lens). Subsequently, the laser beam Lk is reflected by the reflection mirrors 54 and 55, passes through the second scanning lens 56 (for example, a toric lens), and is irradiated onto the surface of the photosensitive drum 31 disposed at the foremost position.

  The laser light source corresponding to yellow is directed to one deflecting surface (the same deflecting surface as described above) of the polygon mirror 52 located slightly obliquely from the lower position, and the laser light Ly deflected by the deflecting surface is the laser printer 1. Is transmitted through the first scanning lens 53. Subsequently, the laser light Ly is reflected by the reflection mirrors 57, 58 and 59, passes through the second scanning lens 60, and is irradiated onto the surface of the photosensitive drum 31 disposed second from the front.

  The laser light source corresponding to magenta is directed to one deflection surface (a deflection surface adjacent to the deflection surface) of the polygon mirror 52 located slightly obliquely from the upper position, and the laser light Lm deflected by the deflection surface is a laser beam. It is guided to the rear side of the printer 1 and passes through the first scanning lens 61. Subsequently, the laser beam Lm is reflected by the reflection mirrors 62, 63, 64, passes through the second scanning lens 65, and is irradiated onto the surface of the photosensitive drum 31 arranged third from the front.

  The laser light source corresponding to cyan is directed to one deflecting surface (a deflecting surface similar to magenta) of the polygon mirror 52 located slightly obliquely from the lower position, and the laser light Lc deflected by the deflecting surface is a laser printer. 1 is guided to the rear surface side and passes through the first scanning lens 61. Subsequently, the laser beam Lc is reflected by the reflection mirrors 66 and 67, passes through the second scanning lens 68, and is irradiated on the surface of the photosensitive drum 31 disposed at the rearmost position. Note that the scanner unit 20 having such a configuration is known, for example, from Japanese Patent Application Laid-Open No. 2007-253480 and the like.

  The second paper discharge roller 46 is configured to be rotatable in both forward and reverse directions, and is conveyed to the lower surface of the paper feed cassette 7 as indicated by a two-dot chain line in FIG. A re-conveying mechanism 70 as an example of a re-conveying means for conveying the paper 4 to be conveyed to the conveying roller 12 is provided. The re-conveying mechanism 70 is configured to guide the re-conveying path 71 extending in the front-rear direction along the lower surface of the paper feed cassette 7 and the sheet 4 conveyed downward from the second paper discharge roller 46 to the re-conveying path 71. And a chute 72. The re-conveying path 71 is provided with a plurality of re-conveying rollers 73 that convey the paper 4 forward by contacting the paper 4 while rotating, and further, at the front end of the re-conveying mechanism 70. A second chute 74 is provided for guiding the sheet 4 conveyed to the front end of the reconveying path 71 by the reconveying roller 73 to the conveying roller 12.

  For this reason, the sheet 4 on which the image is formed on one side (first side) by the process unit 25 is conveyed until the rear end is nipped between the second paper discharge roller 46 and the two pinch rollers 47, and then the second discharge. By rotating the paper roller 46 in the reverse direction and transporting it to the transport roller 12 by the re-transport mechanism 70, so-called double-sided printing in which an image is formed on the other surface (second surface) of the paper 4 is possible.

(Configuration and effect of paper discharge roller)
Next, the first paper discharge roller 44 and the pinch roller 45 are made of rubber and have substantially the same shape, and rotate around shafts 84 and 85 disposed in the left-right direction. As shown schematically in FIG. 2, the first paper discharge roller 44 and the pinch roller 45 are arranged five by five at intervals in the axis 84 direction of the first paper discharge roller 44. The five first discharge rollers 44 are provided on one shaft 84, but the pinch rollers 45 each have an independent shaft 85, and are individually directed toward the corresponding first discharge rollers 44. It is designed to rotate while being pressed against.

  On the other hand, the second paper discharge roller 46 is made of rubber and has a larger diameter than the first paper discharge roller 44, and rotates around a single shaft 86 disposed in the left-right direction. Four second paper discharge rollers 46 are provided at intervals in the direction of the shaft 86. The pinch roller 47 is made of a resin having a high thermal conductivity or a metal such as aluminum so as to have a diameter smaller than that of each of the above rollers, and rotates around a shaft 87 that protrudes in the left-right direction integrally with each pinch roller 47. The pinch rollers 47 are arranged in two rows of four at a time in the direction of the axis 86 of the second paper discharge roller 46, and rotate in a state of being pressed against the corresponding second paper discharge roller 46 individually. It is supposed to be.

  Further, as shown in FIG. 2, each first paper discharge roller 44 faces each pinch roller 45 and each pair of two pinch rollers 47 faces each second paper discharge roller 46, and each pinch roller 47. Is shorter than the second paper discharge roller 46 in the left-right direction. Further, the nip portions of the second paper discharge roller 46 and the pinch roller 47 of each set are arranged at positions that do not overlap with the nip portion of any of the first paper discharge roller 44 and the pinch roller 45 in the conveyance direction of the paper 4. (See broken line). For this reason, in this Embodiment, the following effects arise.

  That is, the portion of the paper 4 on which the toner is thermally fixed by the fixing device 40 is nipped by the first paper discharge roller 44 and the pinch roller 45 or the second paper discharge roller 46 and the pinch roller 47. The rollers 44 to 47 are cooled by taking heat and the evaporation of water vapor is suppressed. For this reason, the nip portion of the paper 4 has a low dryness after fixing. In the present embodiment, the nip portion of the second paper discharge roller 46 and the pinch roller 47 and the nip portion of the first paper discharge roller 44 and the pinch roller 45 are the width direction (left-right direction) of the paper 4 as described above. Therefore, the dry state can be made uniform over the entire surface of the paper 4.

  In addition, since the first paper discharge roller 44 and the pinch roller 45 nip the paper 4 at an earlier time than the second paper discharge roller 46 and the pinch roller 47, the drying of the paper 4 is more effective. However, the pinch roller 47 is made of a resin having a high thermal conductivity or a metal such as aluminum. In addition, the nip width in the sheet conveyance direction by the set of two pinch rollers 47 and one second discharge roller 46 is larger than the nip width by the set of first discharge rollers 44 and pinch rollers 45. As described above, in this embodiment, the cooling effect of the sheet 4 by the set of the second sheet discharge roller 46 and the pinch roller 47 on the downstream side in the sheet conveyance direction is improved by the difference in the thermal conductivity and the nip width. Therefore, the dry state of the paper 4 can be made more uniform.

  Therefore, in the laser printer 1 of the present embodiment, when double-sided printing is performed by the re-conveying mechanism 70, the dry state and the resistance value are made uniform over the entire width of the paper 4 even when the second side image is formed. be able to. Moreover, the sheet 4 is conveyed until it is nipped by the second paper discharge roller 46 and the pinch roller 47 and then conveyed toward the re-conveying mechanism 70. The resistance value can be made uniform. For this reason, in the laser printer 1, even when the image on the second surface is formed, the ease of transfer current flowing through the transfer roller 19 can be made uniform over the entire surface of the paper 4 to form a good image without unevenness. it can.

  In addition, in the present embodiment, all of the first discharge roller 44, the pinch roller 45, the second discharge roller 46, and the pinch roller 47 are arranged at intervals in the directions of the shafts 84 to 87. It becomes easy to make each roller 44-47 contact the paper 4 uniformly. For this reason, the diameters of the shafts 84 to 87 can be reduced, and as a result, the manufacturing cost reduction and downsizing of the laser printer 1 can be favorably promoted. In particular, the pinch roller 47 needs to be configured to have a small diameter in order to correct the curl of the paper 4, but in the present embodiment, the shaft 87 can have a small diameter as described above. Appears more prominently.

  Furthermore, in the present embodiment, the curl can be corrected well by providing the second paper discharge roller 46 and the pinch roller 47 at positions where the paper 4 is conveyed in a warm state. In this embodiment, when the second paper discharge roller 46 rotates in the reverse direction and the paper 4 is sent to the re-conveying mechanism 70, the second paper discharge roller 46 does not pass between the first paper discharge roller 44 and the pinch roller 45. The evaporation of the toner greatly affects the drying of the paper 4 for about 2 seconds after fixing. For this reason, the influence of the roller that nips the paper 4 after the second paper discharge roller 46 rotates in the reverse direction is reduced. However, when the paper 4 passes through the second paper discharge roller 46 twice, the dry state of the paper 4 may be made more uniform. Needless to say, it may be configured to pass between 44 and the pinch roller 45.

(Another embodiment of the present invention)
In addition, this invention is not limited to the said embodiment at all, It can implement with a various form in the range which does not deviate from the summary of this invention. For example, as shown in FIG. 3, the nip portion of the first paper discharge roller 44 and the pinch roller 45 and the nip portion of the second paper discharge roller 46 and the pinch roller 47 have overlapping portions in the conveyance direction of the paper 4. Instead, any location in the width direction of the paper 4 may pass through any of the nip portions. In this case, each part of the paper 4 is nipped once by the first paper discharge roller 44 and the pinch roller 45 or the second paper discharge roller 46 and the pinch roller 47, so that the dry state of the paper 4 can be made more uniform. it can.

  However, it goes without saying that there may be overlapped portions at the nip portions, or there may be gaps in the width direction at the nip portions as shown in FIG. Even in a portion that is not nipped by any of the first paper discharge roller 44 to the pinch roller 47, the paper 4 is cooled to some extent by the rollers 44 to 47. Can also be formed satisfactorily. Furthermore, as shown in FIG. 4, the set of the first paper discharge roller 44 and the pinch roller 45 may be provided in two or more rows, and conversely, the set of the second paper discharge roller 46 and the pinch roller 47 is divided into two. You may divide and provide in rows or more.

  In each of the above embodiments, a pair of rollers as the first roller and the second roller (a pair of the first paper discharge roller 44 and the pinch roller 45 and a pair of the second paper discharge roller 46 and the pinch roller 47) are used. These are configured by a plurality of rollers arranged at intervals in the rotation axis direction, but one of the rollers forming a pair may be configured by a roller having the same outer diameter over the entire width of the paper 4. In this case, among a pair of rollers, a plurality of rollers arranged at intervals in the rotation axis direction correspond to the first roller and the second roller. In addition, when one of the pair of rollers as described above is a roller extending over the entire width, it is desirable that one of the rollers is a driving side roller. Each pinch roller 47 is not necessarily configured to be shorter than the second paper discharge roller 26 in the left-right direction, and may be configured to be longer. In this case, the width of the nip portion is the width of the second paper discharge roller 46 in the left-right direction (axis 86 direction).

  Further, in each of the above embodiments, the second paper discharge roller 46 is rotated in the reverse direction after the rear end of the paper 4 is nipped by the second paper discharge roller 46 and the pinch roller 47. The second paper discharge roller 46 may be reversely rotated from this state. However, in order to make the image formed on the second side more satisfactory with no unevenness, the nip by the second paper discharge roller 46 and the pinch roller 47 was made at least over the entire length of the image forming range on the second side. Thereafter, it is desirable to reversely rotate the second paper discharge roller 46. In addition to the above-described forms, various known forms can be adopted as the form of the sheet conveyance path for switching the sheet conveyance direction (so-called switchback).

  In addition to the direct tandem color laser printer, the present invention can be applied to various image forming apparatuses such as an intermediate transfer type color laser printer, a four-cycle color laser printer, and a monochrome laser printer. Further, as a developing method, not only a one-component developing method but also a two-component developing method may be used. Further, the re-conveying means is not limited to the one that performs double-sided printing, and may be one that forms images on the same surface of the paper 4 by overlapping a plurality of times, and double-sided printing and image superposition are performed manually. Even in this case, the effect of the present invention is produced.

1 is a longitudinal sectional view illustrating a schematic configuration of a laser printer to which the present invention is applied. It is explanatory drawing which represents typically arrangement | positioning of the discharge roller of the laser printer. It is explanatory drawing which represents typically the modification of arrangement | positioning of the said paper discharge roller. It is explanatory drawing which represents typically the further modification of arrangement | positioning of the said paper discharge roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser printer 4 ... Paper 15 ... Belt unit 20 ... Scanner unit 25 ... Process part 26 ... Image forming unit 31 ... Photosensitive drum 34 ... Developing cartridge 40 ... Fixing device 41 ... Heating roller 42 ... Pressure roller 44 ... 1st Paper discharge rollers 45, 47, 49 ... Pinch roller 46 ... Second paper discharge roller 48 ... Final paper discharge roller 70 ... Re-transport mechanism 84, 85, 86, 87 ... Axis L ... Laser light

Claims (7)

Image forming means for forming an image on a recording medium;
Fixing means for thermally fixing an image formed on a recording medium by the image forming means;
A first roller that conveys a recording medium that is arranged in plural at intervals in the rotation axis direction and on which an image is fixed by the fixing unit;
A second roller that further conveys the recording medium that is arranged in a plurality in a rotational axis direction and is conveyed to the first roller;
With
An image forming apparatus, wherein the center position of the nip portion of each of the second rollers in the rotational axis direction is disposed at a position that does not overlap with the nip portion of any of the first rollers in the recording medium conveyance direction.   Any combination of the first roller and the second roller does not have an overlapping portion of the nip portion in the recording medium conveyance direction, and any portion of the recording medium to be conveyed does not have the first roller. The image forming apparatus according to claim 1, wherein the image forming apparatus passes through a nip portion of one of the second rollers.   3. The image forming apparatus according to claim 1, wherein each of the second rollers has a larger nip width in the recording medium conveyance direction than any of the first rollers.   The image forming apparatus according to claim 1, wherein each of the second rollers has a higher thermal conductivity than any of the first rollers.   5. The image formation according to claim 1, wherein at least one of each of the first rollers or each of the second rollers corrects a curl of the recording medium while conveying the recording medium. apparatus. Re-conveying means for conveying the recording medium conveyed over the entire length in the conveying direction by the first roller and the second roller to the image forming means to form an image;
The image forming apparatus according to claim 1, further comprising:   7. The image forming apparatus according to claim 6, wherein the image forming unit forms an image by electrophotography using a transfer current energized through a recording medium.