JP2008009085A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fix a toner image on the front surface and the back surface of paper at a plurality of gloss levels without changing fixing speed and to make the gloss levels uniform between the front surface and the back surface. <P>SOLUTION: The image forming apparatus is equipped with: a transfer part 3 to transfer the toner image to the paper 7 which is being conveyed; a fixing part 4 to fix the toner image on the paper 7; an ejection part 6 to eject the paper; a first conveying part 5 to convey the paper to the ejection part 6 from the transfer part 3 via the fixing part 4; a switchback mechanism to make the paper 7 passing through the fixing part 4 pass through the fixing part 4 again by feeding it backward; and a second conveying part 9 to convey the paper 7 fed backward to the ejection part 6. The image forming apparatus has: a first mode in which the paper 7 passing through the fixing part 4 is ejected without being fed backward; a second mode in which the paper 7 passing through the fixing part 4 is fed backward and guided to the second conveying part 9; and a third mode in which the paper 7 passing through the fixing part 4 is fed backward to pass through the fixing part 4 again, so as to form the image on the back surface of the paper 7 via a third conveying part 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a double-sided electrophotographic color image forming apparatus having a gloss finish level setting function, and in particular, by using double-sided printing means, fixing on the same surface of a recording medium such as paper one or more times to obtain a desired glossiness. The present invention relates to a color image forming apparatus for obtaining a finishing level.

  In general color electrophotographic apparatus, there are cases where a matte finish is required (for example, a monochrome printing contract) or gloss finish (for example, a color photographic image) depending on an object to be printed, and gloss (glossy). ) Control is an essential item. In order to obtain a high gloss, generally, in a color electrophotographic apparatus, there is a method of increasing the amount of heat given to a toner image on a recording medium such as paper by decreasing the fixing speed and lengthening the nip time passing through the fixing nip. Has been taken. In particular, in Patent Document 1, a desired high gloss is obtained by further controlling the fixing speed and the fixing temperature according to the difference in the weighing of the recording medium (glossy paper, plain paper, OHP, etc.).

  In terms of controlling the gloss on both sides of the paper, in Patent Document 2 and Patent Document 3, the improvement of the difference in gloss between the front and back sides during double-sided printing is achieved by controlling the fixing speed and fixing temperature.

  However, in order to make the speed of the sheet passing through the fixing nip variable, it is necessary to control the drive system, and it is also necessary to make the image formation control speed variable depending on the configuration of the device. When only the fixing and drive system are changed, it is necessary to perform multi-speed control of the motor or to change speed by a clutch, and it is necessary to pay attention to motor torque design, vibration, noise and heat generation. Further, in a small machine such as a desktop printer, changing the conveyance speed means changing the image forming speed. In this case, in addition to the above-described shift of the conveyance system, the speed control of the process system and the multi-stage of image formation control are performed. Control is required. Image formation control is sensitive, and in a color machine where stability is required, changing in multiple stages has a high possibility of degrading image quality.

In addition, in the “printing method capable of changing the gloss level of individual elements on a single page” disclosed in Patent Document 4, the paper is passed through a double-sided printing apparatus, resulting in multiple passes through the fixing device. The gloss of the portion of the image on the same surface can be changed depending on the number of passes and the number of times of printing.
Japanese Patent Laying-Open No. 2003-280452 (FIG. 9, paragraph 0057) JP-A-9-34180 (FIG. 1, paragraph 0004) Japanese Patent Laying-Open No. 2003-255755 (FIG. 3, paragraph 0048) JP 2002-304029 A (FIG. 4, paragraph 0024)

  However, in Patent Document 4, although the gloss level can be set for each part in the same plane, it takes a very long time to fix the same plane for each part a plurality of times. Moreover, the use which sets a gloss level for every part in the same surface does not necessarily have high demand.

  Therefore, an object of the present invention is to change the gloss level on one side in a short time in multiple stages. Also, it is necessary to align the gloss levels on the front and back sides when printing on both sides.

  In order to solve the above-described problems, first, an image forming apparatus according to the present invention includes a transfer unit that transfers a toner image onto a sheet being conveyed, a fixing unit that fixes the toner image on the sheet, and a discharge unit that discharges the sheet. A first conveyance unit that conveys the sheet from the transfer unit to the discharge unit via the fixing unit, and a switchback mechanism that reversely conveys the sheet that has passed through the fixing unit and passes the sheet again through the fixing unit. And a second transport unit that transports the sheet toward the discharge unit, bypassing the transfer unit.

  In the present invention, secondly, there is a first mode in which the paper that has passed through the fixing unit is discharged without being reversely fed, and a second mode in which the paper that has passed through the fixing unit is fed back and guided to the second transport unit.

  In the present invention, thirdly, a transfer unit that transfers a toner image onto a sheet being conveyed, a fixing unit that fixes the toner image on the sheet, a discharge unit that discharges the sheet, and a transfer unit that passes through the fixing unit. A first transport unit that transports the paper to the discharge unit, a switchback mechanism that reversely feeds the paper that has passed through the fixing unit and then passes again through the fixing unit, and the back surface of the toner image of the reversely fed paper faces the transfer unit And a third transport unit that transports the

  In the present invention, fourthly, the third transport unit is provided with a back surface auxiliary heating unit that heats the back surface of the toner image of the reversely fed paper.

  According to the present invention, fifthly, there is a third mode in which the sheet that has passed through the fixing unit is reversely fed and again passes through the fixing unit, and an image is formed on the back surface of the toner image on the sheet via the third conveying unit. When the third mode is selected, the temperature of the fixing unit is set lower by a predetermined amount.

  According to the present invention, sixthly, there is a third mode in which the sheet that has passed through the fixing unit is reversely fed and again passes through the fixing unit, and an image is formed on the back surface of the toner image on the sheet via the third conveying unit. When the third mode is selected, the paper pressure of the fixing unit is set lower by a predetermined amount.

  According to the present invention, firstly, since the paper that has passed through the fixing unit is reversely fed and again passes through the fixing unit, high gloss finishing can be performed in a short time.

  According to the present invention, secondly, if the sheet is discharged as it is without running backward through the fixing unit, a constant gloss finish is obtained.

  Third, according to the present invention, double-sided printing is possible.

  According to the present invention, fourthly, the gloss of the front surface and the back surface can be adjusted by adding a heater to the guide plate or by auxiliary heating the back surface of the sheet by using a heat roller.

  According to the present invention, fifth, during double-sided printing, the toner image on the front side of the paper passes through the fixing unit three times, and the toner image on the back side passes through the fixing unit only once. For this reason, in order to preheat the back surface and to prevent excessive gloss of the toner image on the paper surface, the back surface and the back surface of the paper surface can be matched by fixing the back surface at a low temperature.

  According to the present invention, sixth, during double-sided printing, the toner image on the front side of the paper passes through the fixing unit three times, and the toner image on the back side passes through the fixing unit only once. For this reason, in order to preheat the back surface and prevent excessive gloss of the toner image on the paper surface, the front and back gloss can be adjusted by fixing the back surface with a low fixing pressure.

  As described above, as a means for solving the above-described problems, an electrophotographic process station including a developing device based on four colors of CMYK (cyan, magenta, yellow, and black (black)) is used as a basic color reproduction device. Equipped with a double-sided printing device that has a means to switch the transport path that enables shortcuts for the reverse part of the image, and in an electrophotographic apparatus that can set multiple gloss levels, double-sided printing of recording materials such as paper according to the gloss level When passing through the apparatus, the gloss value is changed by printing after returning to the normal conveyance path before the resist without passing through the reverse part of the double-sided printing apparatus.

  The present invention is not limited to a color machine, but can be applied to a monochrome machine, a monochrome machine, and the like.

  By shortcutting the reverse part of the double-sided printing apparatus, productivity can be improved as compared with half-speed control. Although the gloss value is controlled by a known method, finer control is possible by controlling the fixing temperature and the nip amount.

  Furthermore, it has an electrophotographic process station including a developing device based on the color reproduction of four colors of CMYK, and the mounted double-side device has a built-in heater that prevents the temperature of the transfer material from being lowered, and In an electrophotographic apparatus equipped with a double-sided printing device that has means for switching the conveyance path that enables shortcuts to the reverse part of the paper and can change the gloss level, when passing the paper once or more depending on the gloss level While maintaining the paper at a certain temperature with the heater in the duplex printing device, return to the normal conveyance path before resist without passing through the reverse part of the duplex printing device, and change the gloss value by printing and change the entire printing surface. Improved the uniformity of the gloss value.

  According to the present invention, the gloss level on one side can be quickly changed in multiple stages. In addition, the gloss levels on the front and back sides can be made uniform during double-sided printing.

  Embodiments of the present invention will be described below with reference to the drawings. However, even if there are specific descriptions in the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the present embodiment, the present invention is not intended to be limited thereto.

  First Embodiment FIG. 1 is a conceptual diagram of an image forming apparatus according to a first embodiment, and is an apparatus that finishes a toner image on one side with a high gloss.

  The image forming apparatus includes a transfer unit 3 that transfers a toner image to a sheet 7 being conveyed, a fixing unit 4 that fixes the toner image to the sheet 7, a discharge unit 6 that discharges the sheet, and a transfer unit 3 to a fixing unit. 4, a first transport unit 5 that transports the sheet to the discharge unit 6 via 4, a switchback mechanism (not shown) that reversely transports the sheet 7 that has passed through the fixing unit 4, and passes the fixing unit 4 again. A second transport unit 9 that transports the sheet 7 toward the discharge unit 6 before reaching the transfer unit 3.

  The image forming apparatus also includes a first mode in which the paper 7 that has passed through the fixing unit 4 is discharged without being fed back, and a second mode in which the paper 7 that has passed through the fixing unit 4 is fed back to the second transport unit 9. Mode.

  In this embodiment, a four-color rotating developer is used. However, this is merely an example, and a developer for four colors (B, M, C, Y) is fixed at a fixed position around the photoconductor. You may arrange in. Also, four color (B, M, C, Y) image forming means (consisting of a photoconductor, a charging means, a developing means, a transfer means, a cleaning means, a static elimination means, etc.) are arranged in a straight line on the paper on the belt. A tandem type may be used in which toner images of respective colors are sequentially overlapped and fixed as a color image when the four-color superposition is completed. Further, a tandem type may be used in which the toner images of the respective colors are superimposed on the intermediate transfer belt, and after the registration is completed, the image is transferred and fixed on the paper. In other words, the present embodiment does not depend on the method of charging, exposure, development, and transfer in the electrophotographic process.

  Further, the present invention and this embodiment fix a toner image of one or more colors, and naturally include fixing of a black and white image.

  The image forming apparatus according to the first embodiment will be described below with reference to FIG. 1 according to the electrophotographic process.

  The photosensitive drum 2 rotates in the clockwise direction in the figure, passes through a cleaning means (not shown) for cleaning the toner remaining at the end of the previous image formation, and removes the potential remaining at the end of the previous image formation. When passing through a pre-charging means (static elimination means) not passing, passing through a charging means (not shown) for uniformly charging the photosensitive drum 2, and passing through an exposure means (not shown) for exposing an image, an electrostatic latent image is formed.

  When the photosensitive drum 2 comes to the position of the B (black) toner developing device, the electrostatic latent image on the photosensitive drum is developed with B toner.

  The photosensitive drum 2 continues to rotate, and the B toner image is intermediately transferred to the intermediate transfer belt 31.

  Thereafter, when the photosensitive drum 2 further rotates three times, the yellow Y, cyan C, and magenta toner images are superimposed on the intermediate transfer belt, and the intermediate transfer of the color image is completed. Then, a recording medium such as paper 7 is sent out from the paper feed tray, passes through the conveyance roller, proceeds to the transfer unit 3, and a color image image is transferred to the paper at the transfer nip between the intermediate transfer belt 31 and the transfer roller. Then, the sheet enters the fixing unit 4 and the color toner image is fixed.

  When the low gloss finish is acceptable, the sheet 7 is conveyed through the first conveyance unit 5 including the guide roller 71 and passes the heating roller 41 side by the conveyance switching unit 8 so that the toner image on the sheet 7 is fixed. After that, it is immediately discharged to the discharge unit 6.

  On the other hand, when it is desired to achieve a high gloss finish, the sheet 7 that has once passed through the fixing unit 4 is reversely fed by the switchback mechanism (not shown) and then passes through the fixing unit 4 again. The switchback mechanism may be a mechanism for controlling the roller pair of the fixing unit so as to reverse the roller pair when the rear end of the sheet 7 is passing, or a discharge unit (not shown) in front of the discharge unit 6. A mechanism may be provided in which a roller pair is provided, and when the rear end of the sheet 7 passes through the fixing unit 4, the discharge roller pair is controlled to be reversed simultaneously with the roller pair of the fixing unit.

  The reversely fed sheet 7 is reversely fed to the side of the pressure roller 42 by the conveyance path switch 8 and passes through the third conveyance passage 12 including the guide roller 72 and the second conveyance including the guide rollers 73 and 74. After entering the section 9, it is discharged to the discharge section 6. Note that the heater 11 is not driven because the gloss processing on the front side of the sheet 7 has already been completed.

  As described above, the description has been given of performing the two-stage finishing of the low gloss and the high gloss by setting the number of times of the reverse feeding to one, but the multi-stage finishing can be performed by repeating the reverse feeding.

  Here, the number of reverse feeds is determined according to a fixing temperature specified by a CPU (not shown) of the image forming apparatus. By the way, what the user designates is the gloss level (gloss level), not the fixing temperature. That is, assuming that the paper conveyance speed is constant, the glossiness Gij is determined according to the specific fixing temperatures T1, T2, T3,..., Ti and the number of reverse feeds 1, 2, 3,. Here, the glossiness Gij is determined in advance by experiments. In this way, the CPU receives the input of the glossiness designated by the user, searches the corresponding Gij by the look-up table, finds the specific fixing temperature Ti and the number of times of fixing j, and instructs the control means (not shown). Based on an instruction from the control means, the electric power supplied to the heating roller 71 is controlled, and the number of passes through the recording medium reversing means is set in the image forming apparatus. The same applies to the case where the fixing pressure is controlled.

  Second Embodiment FIG. 2 is a conceptual diagram of an image forming apparatus that aligns gloss levels during double-sided printing.

  The image forming apparatus according to the second exemplary embodiment includes a transfer unit 3 that transfers a toner image onto a sheet being conveyed, a fixing unit 4 that fixes the toner image to the sheet, a discharge unit 6 that discharges the sheet, and a fixing unit that fixes the toner image. A first transport unit 5 that transports the sheet to the discharge unit 6 via the unit 4, a switchback mechanism (not shown) that reversely transports the sheet that has passed through the fixing unit 4, and passes the fixing unit 4 again. And a third transport unit 12 that transports the back surface of the toner image of the sheet 7 toward the transfer unit 3. The switchback mechanism may be the same mechanism as in the first embodiment.

  In the figure, the switcher 13 selects either a path for guiding the back surface of the sheet to the transfer section 3 via the third transport section 12 or a path for guiding the back surface of the sheet to the discharge section 6 via the second transport section 9. Used to select. When performing double-sided printing, the switch 13 shifts to the guide roller 132 side and guides the sheet 7 from the guide roller 131 side to the first transport unit 5. The sheet 7 whose front and back are reversed by the switchback in the first transport unit 5 goes to the fixing unit 4 through the transfer unit 3 in order to fix the toner image on the back side. Subsequent gloss finishing is the same as for the surface.

  Further, the third transport unit 9 is provided with a back surface auxiliary heating unit (heater 11) that heats the back side of the toner image of the reversely fed paper. Since the toner image on the back side of the paper passes only once through the fixing unit, a difference occurs in the gloss state between the front side and the back side. In order to increase the gloss on the back surface, the front surface and the back surface gloss are aligned by supplementary heating of the back surface of the paper by, for example, preparing a heater on the guide plate of the third conveyance path or using a heat roller.

  Further, there is a third mode in which the sheet 7 that has passed through the fixing unit 4 is reversely fed to pass through the fixing unit 4 again and an image is formed on the back surface of the toner image on the sheet 7 via the third conveying unit 12. When the third mode is selected, the temperature of the fixing unit is set low by a predetermined amount and / or the paper pressure of the fixing unit is set low by a predetermined amount. When the back surface is finished with a low gloss, the toner image on the paper surface passes through the fixing unit three times. However, since the back toner image passes through the fixing unit only once, the back surface is preheated. In addition, in order to prevent the front surface from becoming excessively glossy, the toner image on the surface of the paper is fixed at a low temperature and / or a low pressure. As a result, the gloss on both sides is adjusted. After fixing the back surface, the sheet 7 is immediately discharged to the discharge unit 6.

  As described above, the description has been made on the assumption that the sheet back surface toner image is fixed only once. However, for high gloss processing, the sheet 7 may be switched back and the back surface may pass through the fixing unit 4 twice. In that case, the front and back gloss may be aligned only by controlling the fixing temperature and / or the fixing pressure without preheating the back surface. When the high gloss process is completed, the sheet 7 is discharged to the discharge unit 6 through the second transport unit 9 illustrated in FIG.

  Embodiment 3 FIG. 3 is a conceptual diagram of a fixing pressure varying unit. A nip pressure adjusting lever 73 for adjusting a fixing pressure is rotatably attached to a rotating shaft of a heating roller 71 that is in pressure contact with the pressure roller 72 to form a fixing nip. One end of the nip pressure adjusting lever 73 is rotatably attached to the support shaft 74. The lower surface of the other end of the nip pressure adjusting lever 73 is connected to the tension spring 76, and further, the lower end of the tip of the other end avoids the tension spring 76 and contacts the cam 75. The spring is fixed to the fixing surface 77. With this configuration, the fixing pressure can be adjusted by adjusting the rotation angle of the cam shaft.

  The present invention can be used in a double-sided electrophotographic color image forming apparatus with a glossiness setting function.

1 is a conceptual diagram of an image forming apparatus according to a first embodiment. Conceptual diagram of an image forming apparatus according to a second embodiment Conceptual diagram of Embodiment 3

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 4 color rotary developing device 2 Photosensitive drum 3 Transfer part 31 Intermediate transfer belt 4 Fixing part 5 1st conveyance part 6 Discharge part 7 Paper 8 Conveyance path switch 9 Second conveyance furnace 10 Reversing part 11 Heater 12 3rd conveyance Part 13 Switch 41 Heating roller 42 Pressure roller 71, 72, 73, 74, 131, 132 Guide roller

Claims (6)

A transfer unit for transferring a toner image to a sheet being conveyed;
A fixing unit for fixing the toner image on the paper;
A discharge unit for discharging the paper;
A first transport unit that transports the sheet from the transfer unit to the discharge unit via the fixing unit;
A switchback mechanism that reversely feeds the paper that has passed through the fixing unit and passes the fixing unit again;
An image forming apparatus comprising: a second transport unit that transports the reversely fed sheet toward the discharge unit, bypassing the transfer unit. A first mode for discharging the paper that has passed through the fixing unit without reverse feeding;
The image forming apparatus according to claim 1, further comprising: a second mode in which the sheet that has passed through the fixing unit is reversely fed and guided to the second transport unit. A transfer unit for transferring a toner image to a sheet being conveyed;
A fixing unit for fixing the toner image on the paper;
A discharge unit for discharging the paper;
A first transport unit that transports the sheet from the transfer unit to the discharge unit via the fixing unit; a switchback mechanism that reversely feeds the sheet that has passed through the fixing unit and passes the sheet again through the fixing unit;
An image forming apparatus comprising: a third transport unit configured to transport a back surface of the toner image of the reversely fed paper toward the transfer unit.   The image forming apparatus according to claim 3, wherein the third transport unit includes a back surface auxiliary heating unit that heats the back surface of the toner image of the paper that has been fed back. The paper that has passed through the fixing unit is reversely fed to pass through the fixing unit again,
A third mode in which an image is formed on the back surface of the toner image of the paper via the third transport unit;
5. The image forming apparatus according to claim 3, wherein when the third mode is selected, the temperature of the fixing unit is set to be lower by a predetermined amount. The paper that has passed through the fixing unit is reversely fed to pass through the fixing unit again,
A third mode in which an image is formed on the back surface of the toner image of the paper via the third transport unit;
5. The image forming apparatus according to claim 3, wherein when the third mode is selected, the paper pressure of the fixing unit is set to be lower by a predetermined amount.

Images