JP2010217201A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and compact image forming apparatus that forms high-quality images on both sides of a transfer material by a one-path system. <P>SOLUTION: The image forming apparatus includes: a photoreceptor on the surface of which a toner image is formed; an intermediate transfer belt which has a function for temporarily holding the toner image transferred from the photoreceptor and a function for conveying transfer material; a conveying means which conveys the transfer material to an intermediate transfer belt; a first transfer means which transfers the toner image formed on the photoreceptor to a first side of the transfer material conveyed by the intermediate transfer belt and the intermediate transfer belt; and a second transfer means which transfers the toner image transferred to the intermediate transfer belt by the first transfer means to a second side of the transfer material conveyed by the conveying means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a double-sided printing function and performing image formation using an electrophotographic system.

  As a method for forming an image on both surfaces of a transfer material, a so-called switchback method and a one-pass method are known. In the switchback method, the transfer material is first passed through the transfer means and the fixing means, an image is formed on one surface of the transfer material, the transfer material is reversed, and then the transfer material and the fixing means are switched back. In this method, double-sided printing is performed by forming an image on the other surface of the transfer material. On the other hand, in the one-pass method, an image is formed on both sides of the transfer material without switching back the transfer material by passing the transfer material on which the image is transferred on both sides by the double-side transfer unit through the fixing unit.

  By adopting the one-pass method, jamming by increasing the cost by providing a complicated mechanism for switchback, extending the image formation time by switchback, and switching back the curled transfer material by heating by the fixing means Etc. can be avoided.

  As an image forming apparatus that uses a one-pass method, for example, in Patent Document 1, there are two intermediate transfer belts, a first intermediate transfer belt and a second intermediate transfer belt, and a transfer material is conveyed by the second intermediate transfer belt. An image forming apparatus is disclosed that transfers a toner image on a first intermediate transfer belt and a toner image on a second intermediate transfer belt to respective surfaces of a transfer material.

  Further, Patent Document 2 discloses an image forming apparatus that transfers a toner image on both surfaces of a transfer material using a pair of photosensitive members for individually forming two toner images having different charging polarities.

  In Patent Document 3, for each color, an intermediate transfer belt for holding a back image and a photoconductor are provided, and transfer is performed using a contact / separation mechanism between the intermediate transfer belt and the photoconductor. An image forming apparatus that forms toner images on both sides of paper is disclosed.

  However, in the image forming apparatus disclosed in Patent Document 1, since the toner image on the back surface is transferred onto the second intermediate transfer belt and then transferred onto the toner image, the toner image on the back surface is transferred. An image defect may be caused by rubbing with the transfer material. Further, since it is necessary to convey the toner image by two intermediate transfer belt lengths before the back surface is transferred, the printing time becomes long.

  In addition, the image forming apparatus disclosed in Patent Document 2 requires a pair of photoconductors and developing units to form toner images with different polarities, which increases the number of parts, resulting in an increase in cost. There is a problem of increasing the size of the apparatus.

  In addition, since the image forming apparatus disclosed in Patent Document 3 is provided with an intermediate transfer belt for each KMCY, a total of four intermediate transfer belts are required. There is a problem of upsizing. In addition, since there are four transfer belts, there is a problem in that color matching cannot be adjusted.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a low-cost and small-sized image forming apparatus that forms high-quality images on both surfaces of a transfer material by a one-pass method.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a photosensitive member that forms a toner image on a surface thereof, a function of temporarily holding the toner image transferred from the photosensitive member, and a function of conveying a transfer material. An intermediate transfer belt; conveying means for conveying the transfer material to the intermediate transfer belt; a first surface of the transfer material on which the toner image formed on the photosensitive member is conveyed by the intermediate transfer belt; A first transfer means for transferring to the intermediate transfer belt; and the toner image transferred to the intermediate transfer belt by the first transfer means is transferred to a second surface of the transfer material conveyed by the conveying means. And a second transfer means.

  According to the present invention, it is possible to provide a low-cost and small-sized image forming apparatus that forms high-quality images on both surfaces of a transfer material by a one-pass method.

1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of a configuration of a fixing device of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention.

  Next, embodiments for carrying out the invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 includes four process cartridges for forming black, yellow, magenta, and cyan (hereinafter referred to as Bk, Y, M, and C) toner images. These use Bk, Y, M, and C toners of different colors as the image forming material, but they have the same configuration except for the toner, and are replaced when the lifetime is reached.

  A process cartridge for forming a Bk toner image includes a drum-shaped photoconductor 11 as an image carrier, a charging device 21, a developing device 31, a drum cleaning device 41, and the like.

  In the photoconductor 11, an aluminum cylinder having a diameter of 25 to 100 [mm] is covered with a surface layer of an organic semiconductor which is a photoconductive substance. An amorphous silicon surface layer may be coated. Further, it may be a belt shape instead of a drum shape.

  The charging device 21 uniformly charges the surface of the photoconductor 11 that rotates clockwise in the drawing by a driving unit (not shown).

  The uniformly charged surface of the photoconductor 11 is exposed and scanned by the laser beam emitted from the exposure apparatus 10 and carries an electrostatic latent image for Bk. The Bk electrostatic latent image is developed into a Bk toner image by the developing device 31 using Bk toner. Here, the toner image is transferred to the back surface of the transfer material, or is primarily transferred onto the intermediate transfer member 5. This position is defined as a first transfer portion.

  The transfer material is conveyed along a conveyance path 9 indicated by a dotted line in FIG. First, the transfer material is conveyed to the intermediate transfer belt by the conveying means. Thereafter, the first transfer unit is conveyed by the intermediate transfer belt, and the toner image on the photoconductor 11 is transferred by the first transfer unit.

  The drum cleaning device 41 removes the toner remaining on the surface of the photoconductor 11 after the transfer process. Further, a static elimination value (not shown) eliminates residual charge of the photoreceptor 11 after cleaning. By this charge removal, the surface of the photoreceptor 11 is initialized and prepared for the next image formation.

  Similarly, in other color, Y, M, and C process cartridges, Y, M, and C toner images are formed on the photoreceptors 12, 13, and 14, respectively, on the back surface of the transfer material or on the intermediate transfer member 5. Transcribed.

  An image data processing apparatus (not shown) generates an exposure scanning control signal based on an image information signal sent from a personal computer or the like and sends it to the exposure apparatus 10. The exposure apparatus 10 serving as a latent image forming unit irradiates each of the photoconductors 11, 12, 13, and 14 in the process cartridge with laser light emitted based on the exposure scanning control signal. Electrostatic latent images for Bk, Y, M, and C are formed on the photoconductors 11, 12, 13, and 14 exposed by this irradiation. The exposure apparatus 10 irradiates the photoconductors 11, 12, 13, and 14 through a plurality of optical lenses and mirrors while scanning laser light emitted from a light source with a polygon mirror that is rotationally driven by a motor. It is. Instead of the exposure apparatus 10 having such a configuration, an exposure unit that irradiates LED light from an LED array may be employed.

  In FIG. 1, an intermediate transfer member 5 is disposed below the process cartridge. The intermediate transfer member 5 is endlessly moved while stretching an intermediate transfer belt 51, which is an endless transfer member. This is arranged in contact with the photoconductors 11, 12, 13, and 14 so as to rotate. The intermediate transfer body 5 includes four transfer rollers 61, 62 and 63 in addition to the intermediate transfer belt. 64, and endlessly moves counterclockwise in FIG.

  The four first transfer rollers 61, 62, 63, 64 sandwich the intermediate transfer belt 51 that moves endlessly between the photoreceptors 11, 12, 13, 14 to form primary transfer nips, respectively. is doing. In these methods, a primary transfer bias having a polarity opposite to that of the toner is applied to the back surface (inner circumferential surface of the loop) of the intermediate transfer belt 11. The application method may be a charger method in which the electrode is discharged.

  The transfer onto the back surface of the transfer material is performed by the four Bk, Y, M, and C toner images individually formed on the four photoconductors 11, 12, 13, and 14 on the back surface of the transfer material by the action of the primary transfer bias. Are transferred in a superimposed manner. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the back surface of the transfer material.

  On the other hand, when transferring to the transfer material surface, first, four Bk, Y, M, and C toner images individually formed on the four photoconductors 11, 12, 13, and 14 are subjected to the primary transfer bias. By the action, primary transfer is performed on the intermediate transfer belt 51 of the intermediate transfer member 5. The intermediate transfer belt 51 has an electric resistance condition suitable for realizing electrostatic transfer with a primary transfer bias. Specifically, a belt layer having a thickness of 50 to 1000 [μm] made of a resin film or rubber is coated with a surface layer made of a material having a low surface energy as needed, and the total volume resistance value is 10 6-14 to the 14th power [Ωcm]. The intermediate transfer belt 51 sequentially passes through the primary transfer nips for Bk, Y, M, and C along with the endless movement thereof. Four Bk, Y, M, and C toner images individually formed on the four photosensitive members 11, 12, 13, and 14 are formed on the intermediate transfer belt 51 of the intermediate transfer member 5 as four-color toner images. .

  Thus, in the embodiment of the present invention, the transfer material conveyed along the conveyance path 9 is transferred at the first transfer portion after being transferred at the second transfer portion. Therefore, here, in double-sided printing, the surface transferred in the first transfer portion is called the back surface, and the surface transferred in the second transfer portion is called the front surface.

  Here, the four first transfer rollers 61, 62, 63, 64 are metal rollers or rollers in which a metal core or a conductive rubber layer or a sponge layer is coated. A primary transfer bias of opposite polarity is applied.

  In FIG. 1, a second transfer roller 7 is disposed below the intermediate transfer member 5. This is arranged in contact with the intermediate transfer member 5 so as to rotate in conjunction with it, and moves endlessly in the clockwise direction in FIG. The second transfer roller 7 sandwiches the intermediate transfer belt 51 to form a secondary transfer nip, and a secondary transfer bias having a polarity opposite to that of the toner is applied to the second transfer roller 7 side. This position is defined as a second transfer portion. Here, the four-color toner image formed on the intermediate transfer belt 51 of the intermediate transfer member 5 is secondarily transferred onto the surface of the transfer material.

  The transfer material on which the toner images are transferred on both sides by the first transfer unit and the second transfer unit is conveyed to the fixing device 81. The fixing device 81 includes two fixing rollers, each of which has a heating unit such as a halogen lamp, and overheats the transfer material sandwiched between the fixing nips from both sides. By this heating, the full color images respectively formed on both surfaces of the transfer material are fixed to the transfer material by softening the toner constituting the image. After the fixing, the transfer material is discharged out of the apparatus through a discharge roller (not shown).

  The surface temperature of the two fixing rollers of the fixing device 81 is detected by the temperature detecting means. Based on the detection result of the surface temperature detected by the temperature detecting means, the power supply to the heat generating means of each fixing roller is turned on / off to maintain the surface temperature of the fixing roller within a certain range (target range). In the case of single-sided printing in which an image is formed only on one side of a transfer material, the image can be fixed with a smaller amount of heat than in double-sided printing. Therefore, energy saving can be achieved by lowering the target surface temperature range during single-sided printing than during double-sided printing. In addition, since a single color image has a smaller amount of toner than a full color image, it is possible to save energy by switching the target range of the surface temperature even during single color printing and full color printing.

  FIG. 2 is a diagram showing an example of the configuration of the fixing device of the image forming apparatus according to the embodiment of the present invention. The pair of upper and lower fixing rollers 200 is formed with a layer (for example, an RTV silicone rubber layer) of a material having a high releasability and a small surface roughness on the cored bar portion, A heater 206 is provided. In this way, a color toner having a low softening temperature to improve color reproducibility by having a surface part having high releasability and comprising a material having a small surface roughness and excellent smoothness. Thus, even when the toner image is formed on the transfer material, a good color toner image can be fixed on both sides of the transfer material without causing toner offset to the fixing roller 200. Note that the surface roughness of the fixing roller 200 is preferably 4 [μm] or less, more preferably about 2 [μm], in terms of Rz of JIS 10-point average.

  Further, around the fixing roller 200, a cleaning member 21, an oil supply member 202, a temperature detecting member 203, a peeling claw 204, an overtemperature preventing member 205, and the like are provided. The upper and lower fixing rollers 200 are composed of the same parts, and the cost can be reduced by sharing various members provided around each roller.

  In FIG. 1, an optical sensor 52 is disposed downstream of the first transfer portion of the intermediate transfer body 5, and the relative positional relationship and density of the four color toner images on the intermediate transfer belt 51 of the intermediate transfer body 5. Is detected. Using the relative positional relationship of the four-color toner images detected by the optical sensor 52, color matching adjustment for adjusting the color shift of each color is performed, and the density of the four-color toner image detected by the optical sensor 52 is determined. Use and adjust the density to adjust the toner adhesion amount of each color.

  As described above, transfer to the back surface of the transfer material is performed directly from the image carrier, and transfer to the front surface is performed by intermediate transfer via the intermediate transfer member, thereby forming a high-quality image on both sides of the transfer material. Can keep. Further, with the above-described configuration, the number of parts can be reduced, so that a small-sized image forming apparatus can be provided at low cost.

  A four-color toner image that is a visible image formed on the intermediate transfer belt 51 of the intermediate transfer member 5 is secondarily transferred onto the surface of the transfer material at the secondary transfer nip. On the intermediate transfer belt 51 of the intermediate transfer member 5 after passing through the secondary transfer nip, residual toner that has not been secondarily transferred adheres to the surface of the transfer material. Since this residual toner comes into contact with the transfer material at the first transfer portion, there is a possibility that the residual toner will become dirty. Therefore, as shown in FIG. 3, cleaning is performed by the intermediate transfer member cleaning device 53 disposed downstream of the second transfer portion. This prevents backside contamination at the first transfer portion. Here, as the intermediate transfer member cleaning device 53, toner recovery means such as a cleaning blade is used. Further, the intermediate transfer body cleaning device 53 may be either a mechanical or electrostatic recovery method.

  In the first transfer portion, when a primary transfer bias having a polarity opposite to that of the toner image is applied to the first transfer roller 61 during duplex printing, the four-color toner image formed on the surface of the transfer material is intermediate between the intermediate transfer member 5. The toner image is reversely transferred to the transfer belt 51, and the transfer material surface toner image is disturbed. Further, the conveyance path 9 downstream from the second transfer portion where the toner image is transferred onto the surface of the transfer material has an unfixed toner image. If the transfer material is conveyed by a conveyance roller or the like, the image is deteriorated. Therefore, as shown in FIG. 3, a pre-fixing roller 82 for fixing the toner image on the surface of the transfer material is provided between the second transfer portion and the first transfer portion of Bk in the transfer material conveyance path 9. Since the pre-fixing roller 82 only needs to be able to fix to the first transfer roller 6 even if the primary transfer bias is applied, the target range of the surface temperature of the fixing roller can be lowered. Instead of the pre-fixing roller 82 having such a configuration, a pre-fixing unit that pre-fixes the toner image on the transfer material surface by applying pressure may be used. By doing so, it is possible to prevent reverse transfer of the toner image on the transfer material surface to the intermediate transfer belt during transfer to the back surface of the transfer material at the first transfer portion.

  In the conveyance path 9 downstream from the second transfer portion where the toner image is transferred onto the transfer material surface, the four-color toner image is not fixed, and if the transfer material is conveyed by a conveyance roller or the like, it leads to image deterioration. Therefore, from the second transfer roller 7 to the pre-fixing roller 82, a conveyance guide plate is provided at a position where the back surface of the transfer material contacts, and the toner image on the surface of the transfer material is conveyed in a non-contact manner, thereby causing image degradation. To prevent.

  At the time of double-sided printing, first, a four-color toner image on the surface of the transfer material is formed on the intermediate transfer belt of the intermediate transfer member 5, and the transfer material is conveyed in accordance with the timing when the leading edge of the toner image reaches the second transfer portion. . Further, it is necessary to form a toner image on the back surface of the transfer material at the timing when the transfer material is conveyed to the first transfer portion of Bk. For this reason, when the image to be formed is long in the sub-scanning direction, the leading edge of the back toner image must be formed while the trailing edge of the front toner image is being formed. Here, the distance from the first transfer roller 61 to the second transfer roller 7 in the movement path of the toner image is L1, and from the second transfer roller 7 to the first transfer roller 61 in the transfer path of the transfer material. Let the distance be L2. At this time, the maximum sheet length L in the sub-scanning direction of an image that can be formed on the transfer material surface during duplex printing is expressed by the following equation.

  L = L1 + L2

  The maximum paper length L in the sub-scanning direction during double-sided printing is stored in the internal memory in advance, and when a double-sided printing instruction is issued from the user, L is compared with the paper length of the paper instructed for printing. If the length of the paper for which printing is instructed is longer, a printing error may be generated. By doing so, it is possible to prevent abnormal images due to overlapping of the toner images on the front and back surfaces.

  Due to the configuration of the apparatus, the maximum sheet length L on which an image can be formed in the second transfer unit is determined. If image formation is performed in the second transfer unit during single-sided printing, the sheet length is restricted. However, there is no restriction on the sheet length in the transfer at the first transfer portion. Therefore, when a single-side printing instruction is issued from the user, L is compared with the sheet length instructed to be printed, and if the printing instruction is larger than L, the first transfer unit forms an image on the surface of the transfer material. By doing so, the restriction on the paper length can be eliminated.

  The fog toner may be transferred onto the intermediate transfer member 5 at the first transfer portion during single-sided printing. In the configuration of the present invention, the toner on the intermediate transfer belt 51 is removed downstream from the second transfer portion in the toner movement path. For this reason, the fog toner on the intermediate transfer belt 51 may be transferred to the back surface of the transfer material (here, the surface printed in the first transfer portion is the front surface) in the second transfer portion. is there. Therefore, when transferring to the surface of the transfer material at the first transfer portion during single-sided printing, a bias having the same polarity as the toner image is applied to the second transfer roller 7 so that defective toner is transferred to the back surface of the transfer material. Prevent transcription. By doing so, it is possible to prevent the back surface of the transfer material from being stained by the residual toner of the intermediate transfer member.

  The fog toner transferred onto the intermediate transfer body 5 at the first transfer portion during single-sided printing is a defective toner and is not necessarily charged to the same polarity. If fog toner has two polarities, it is transferred to the back surface of the transfer material. Therefore, the intermediate transfer member 5 has a link mechanism (not shown) so that the intermediate transfer belt 51 and the second transfer roller 7 can be separated. By doing so, the intermediate transfer belt 51 and the second transfer roller 7 can be separated when transferring to the surface of the transfer material in the first transfer unit during single-sided printing, and transfer is performed in the second transfer unit. You can prevent it from happening. By doing so, it is possible to prevent the back surface of the transfer material from being stained by the residual toner of the intermediate transfer member.

  When the second transfer unit is configured to form an image on the surface of the transfer material during single-sided printing, the transfer material passes through the first transfer unit, so that the maximum sheet length L is restricted. Therefore, as shown in FIG. 4, a path switching device (not shown) that switches the paper discharge path 9 between the second transfer roller 7 and the first transfer roller 61 in the transfer material transport path 9 is provided. This path switching device switches the paper discharge path (dashed line) that has passed through the first transfer section to the paper discharge path (dotted line) that does not pass through the first transfer section. Further, as shown in FIG. 4, a second fixing device 83 is provided between the second transfer roller 7 and the path switching device. Thus, during single-sided printing, transfer material does not pass through the first transfer portion, and single-sided printing is realized with a shorter conveyance path for transferring the surface of the transfer material with the first transfer portion. By doing so, the restriction due to the sheet length can be eliminated.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments thereof, various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the invention as defined in the claims. is there.

  In the image forming apparatus according to the embodiment of the present invention, the toner image transferred by the second transfer unit to the second surface of the transfer material during conveyance by the conveyance unit is transferred to the second surface of the transfer material. You may make it have a fixing means to fix to 2 side.

  Further, in the image forming apparatus according to the embodiment of the present invention, the intermediate transfer belt is in a loop shape, and the size information of the transfer material to be printed from the operator and an instruction to perform double-sided printing or single-sided printing. Receiving means, and the length of the transfer material determined from the size information of the transfer material received by the instruction means is longer than the length of the outer periphery of the intermediate transfer belt. When receiving a printing instruction, the operator may be informed that printing cannot be performed.

  In the image forming apparatus according to the embodiment of the present invention, the length of the transfer material determined from the size of the transfer material that has been instructed by the instruction unit is longer than the length of the outer periphery of the intermediate transfer belt. When a single-side printing instruction is received from the operator by means, the transfer material may be transferred only by the first transfer means.

  The image forming apparatus according to the embodiment of the present invention further includes a conveyance path switching unit that switches a conveyance path along which the transfer material is conveyed by the conveyance unit, and the conveyance unit receives an instruction from the instruction unit. When the length of the transfer material determined from the size of the transfer material is longer than the length of the outer periphery of the intermediate transfer belt, and the instruction means receives a one-side printing instruction from the operator, the conveyance path switching means causes the conveyance. The path may be switched so that the transfer material is not conveyed to the intermediate transfer belt.

DESCRIPTION OF SYMBOLS 10 Exposure apparatus 11 Bk photoconductor 21 Bk charging device 31 Bk developing device 41 Drum cleaning device 5 Intermediate transfer body 51 Intermediate transfer belt 61 Bk first transfer roller 7 Second transfer roller 81 Fixing device 82 Prefixing Roller 83 Second fixing device 9 Transport path

JP 2002-189358 A JP-A-2-259670 Japanese Patent Laid-Open No. 9-211900

Claims (5)

A photoreceptor for forming a toner image on the surface;
An intermediate transfer belt having a function of temporarily holding the toner image transferred from the photoreceptor and a function of conveying a transfer material;
Conveying means for conveying the transfer material to the intermediate transfer belt;
A first surface of the transfer material transported by the intermediate transfer belt and a first transfer means for transferring the toner image formed on the photoreceptor to the intermediate transfer belt;
And a second transfer means for transferring the toner image transferred to the intermediate transfer belt by the first transfer means onto a second surface of the transfer material conveyed by the conveyance means. Image forming apparatus.   And a fixing unit that fixes the toner image transferred by the second transfer unit to the second surface of the transfer material on the second surface of the transfer material during conveyance by the conveyance unit. The image forming apparatus according to claim 1. The intermediate transfer belt has a loop shape,
Having an instruction means for receiving size information of a transfer material to be printed from an operator and an instruction to perform either double-sided printing or single-sided printing;
When the length of the transfer material determined from the size information of the transfer material received by the instruction means is longer than the outer circumference of the intermediate transfer belt, and when the instruction means receives a double-sided printing instruction from the operator The image forming apparatus according to claim 1, wherein the image forming apparatus notifies the operator that printing cannot be performed.   When the length of the transfer material determined from the size of the transfer material received by the instruction means is longer than the outer peripheral length of the intermediate transfer belt, and when the instruction means receives a single-sided printing instruction from the operator, The image forming apparatus according to claim 3, wherein the transfer material is transferred only by the first transfer unit. A conveyance path switching unit that switches a conveyance path along which the transfer material is conveyed by the conveyance unit;
The conveying means has a length of the transfer material determined from the size of the transfer material that is instructed by the instruction means, and is longer than the outer circumference of the intermediate transfer belt, and the instruction means instructs the single-sided printing from the operator. The image forming apparatus according to claim 3, wherein the transfer path is switched by the transfer path switching unit and the transfer material is not transferred to the intermediate transfer belt.

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