JP2005241934A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which increases in the temperatures of an image carrier, belt member, and image forming part are securely restrained even in the case where the apparatus is installed in the environment that is the severest to ensure the inside temperature of the apparatus and even in the case of recording in a consecutive recording mode. <P>SOLUTION: The image forming apparatus includes the image carrier for holding a toner image on it, a transfer means for transferring the toner image to a transfer material, a heating means for heating a transfer material, and a cooling means for cooling, on the opposite side, the transfer material heated, the transfer means coming into contact with the transfer material heated by the heating means. In the image forming apparatus, when the transfer material is not present on the opposite side, the cooling means can cool the transfer means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that employs an electrophotographic system.

  In recent years, with the widespread use of electrophotographic color image forming apparatuses, there has been an increasing demand for speeding up color output in addition to the demand for recording quality of color images. Proposed. Among them, there is a color image forming method called a tandem type. In this method, black, cyan, magenta, and yellow toner images are formed on a drum-shaped image carrier, and each color toner image is transferred onto a sheet (transfer material) in a superimposed manner, and finally a color toner image. Is fixed on the sheet.

  As described above, as a method for transferring the image of the image carrier of each color onto the sheet, the sheet is carried and conveyed in a state of being electrostatically adsorbed by a belt called an electrostatic conveyance belt, and then directly transferred onto the sheet. Examples thereof include one that sequentially transfers each color image to a belt called an intermediate transfer belt, and then secondary transfer onto a sheet, and a transfer roller.

  In the tandem color image forming apparatus, more power is required as the number of driving units increases. Also, in a fixing device that heats a sheet and fixes a toner image, the toner is mixed and fixed, so that it requires more power than a monochrome image forming apparatus. For this reason, a lot of heat is generated, and the importance of the cooling means in the machine has been demanded.

  Further, in the case where the double-sided recording is continuously performed, the sheet that has once performed the single-sided recording and has passed through the high-temperature fixing device passes through the image forming unit again with high heat, whereby the image carrier In some cases, the temperature of the image forming unit, transfer means such as a belt, and the like increases.

  For these reasons, the tandem color image forming apparatus has to be designed in consideration of the temperature rise in the apparatus main body, particularly in the image forming section. Specifically, a space is provided between the image carriers or between the fixing device and the image carrier to make it difficult for heat to be transmitted to the image carrier, or a heat insulating material is provided around the heat source such as the fixing device or the power source. In order to prevent heat from being transmitted to the image forming unit.

  In addition, there is an invention in which an air duct is provided between the fixing device and the image forming unit and air is used to make it difficult to transfer heat to the image forming unit by blowing air in the air duct (patent) Reference 1).

  As for the temperature rise during double-sided recording, a sheet is taken out from the machine once in the discharge area after single-sided recording, and the sheet temperature before re-feeding is lowered by blowing air at that position on the sheet image surface. (Patent Document 2).

  Further, with respect to the temperature rise during continuous recording, it is conceivable to reduce the print productivity of double-sided continuous recording from that during single-sided continuous recording to prevent the temperature inside the apparatus from rising. In addition, it was considered that the temperature sensor was installed in the vicinity of the image carrier in the machine, and when the machine temperature exceeded its allowable temperature, control was performed so that double-sided recording was not performed until the temperature fell below the allowable temperature. .

JP 2003-202765 A JP 2003-208043 A

  However, in recent years, tandem color image forming apparatuses have been reduced in size and cost, and a conventional space between image carriers, between a heat source and an image forming unit, or between a heat source and an image forming unit has been developed. It has become difficult to provide a heat insulating material.

  In addition, the color image forming apparatus has been increased in speed, and high productivity has been demanded, and it has become impossible to reduce the throughput of double-sided recording.

  For this reason, the temperature of the image forming unit exceeds the allowable temperature, and there is a risk of causing toner fixation in the toner container and the temperature around the image carrier. In addition, due to the increase in the toner temperature, it may be impossible to stably form an image on the image bearing member or to reliably transfer the toner image formed on the image bearing member to the sheet.

  In addition, the temperature of the transfer means arranged along the image carrier increases, heat is transmitted to the roller that drives the transfer means, and the belt drive roller diameter and belt thickness may change. . Due to this thermal expansion, the belt traveling speed becomes unstable, and a fatal image defect such as color misregistration between colors may occur.

  The present invention has been made in view of the above problems, and the object of the present invention is to provide an image carrier, a transfer device, even when recording is performed in the most severe apparatus installation environment for continuous temperature rise or in continuous recording mode. It is an object of the present invention to provide an image forming apparatus that reliably suppresses the temperature rise of the image forming unit and the image forming unit.

  In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image, a transfer unit that transfers the toner image to a transfer material, and a transfer material. In the image forming apparatus having a heating means for heating and a cooling means for cooling the heated transfer material at the facing portion, wherein the transfer means contacts the transfer material heated by the heating means. When the transfer material is not present, the cooling means can cool the transfer means.

  According to the present invention, it is possible to efficiently cool both the re-fed sheet and the transfer unit with a single cooling unit. Further, during double-sided printing, since the sheet heated by the fixing device can be cooled before being re-fed to the image forming unit, heat transmitted from the sheet to the image forming unit can be minimized.

  Further, when there is no sheet in the refeed path, air passes through the opening hole and is blown to the transfer means, so that the temperature rise of the transfer means can be suppressed. This eliminates changes in the thickness of the transfer means and the diameter of the belt driving roller, thereby reducing the occurrence of image defects such as instability in belt running and color misregistration during continuous printing. In addition, since both the sheet in contact with the image carrier and the transfer unit can be cooled, the temperature of the image carrier can be prevented from increasing, and toner fixation in the toner container and image defects on the image carrier can be reduced.

[Example 1]
Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

[Entire configuration of image forming apparatus]
First, the overall configuration of the image forming apparatus will be described. FIG. 1 is a longitudinal sectional view showing the entire configuration of a full-color laser beam printer as one aspect of an image forming apparatus. In the drawing, the right side is the front (front) side of the printer.

  An image forming apparatus 100 shown in FIG. 1 is a so-called tandem type color image forming apparatus having four photosensitive drums 1a, 1b, 1c, and 1d arranged in parallel in the vertical direction. The photosensitive drum 1 (1a, 1b, 1c, 1d) is driven to rotate counterclockwise in the drawing by a driving means (not shown). A photosensitive device 1 (2a, 2b, 2c, 2d) that uniformly charges the surface of the photosensitive drum 1 in order according to the rotation direction, and a laser beam is irradiated around the photosensitive drum 1 based on image information. A scanner unit 3 (3a, 3b, 3c, 3d) for forming an electrostatic latent image on the body drum 1; and a developing device 4 (4a, 4b, 4c, for developing the toner image by attaching toner to the electrostatic latent image. 4d) An electrostatic transfer unit (hereinafter referred to as belt unit 5) as an example of transfer means for transferring the toner image on the photosensitive drum 1 to the sheet S, and removing the transfer residual toner remaining on the surface of the photosensitive drum 1 after transfer. A cleaning device 6 (6a, 6b, 6c, 6d) and the like are disposed.

  Here, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrally formed into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d). Hereinafter, the photosensitive drum 1 will be described in detail.

  The photoconductor drum 1 is configured by applying an organic photoconductive layer (OPC photoconductor) to an outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. Both ends of the photosensitive drum 1 are rotatably supported by a support member, and a driving force from a driving motor (not shown) is transmitted to one end, so that the photosensitive drum 1 is rotated counterclockwise. The

  As the charging device 2, a contact charging type can be used. The charging member is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1, and the surface of the photosensitive drum 1 is made uniform by applying a charging bias voltage to the roller. In this way, it is charged.

  The scanner unit 3 (3a, 3b, 3c, 3d) is arranged in a substantially horizontal direction with the corresponding photosensitive drum 1, and image light corresponding to an image signal is sent to a scanner motor (not shown) by a laser diode (not shown). Is applied to the polygon mirror 9 (9a, 9b, 9c, 9d) rotated at a high speed. The image light reflected by the polygon mirror 9 selectively exposes the surface of the charged photosensitive drum 1 through the imaging lens 10 (10a, 10b, 10c, 10d) to form an electrostatic latent image. It is composed.

  Each of the developing devices 4 (4a, 4b, 4c, 4d) is composed of a developing unit that stores toner of each color of yellow, magenta, cyan, and black. There is a toner container for storing toner in the developing unit, and the remaining time is detected by sensing the transmission time by transmitting the LED light into the toner container.

In the belt unit 5, an electrostatic conveyance belt 11 that circulates and moves so as to face and contact all the photosensitive drums 1 (1a, 1b, 1c, 1d) is disposed. The electrostatic conveyance belt 11 is composed of a belt member made of polyimide having a circumference of about 700 mm and a thickness of about 150 μm having a volume resistivity of 10 ¹¹ to 10 ¹⁴ Ω · cm. The electrostatic conveyance belt 11 is supported by four rollers, a driving roller 13, driven rollers 14a and 14b, and a tension roller 15 in the vertical direction, and the sheet S is electrostatically adsorbed and carried on the outer peripheral surface on the left side in the figure. Then, the sheet S is circulated so as to contact the photosensitive drum 1.

  The transfer roller 12 (12a, 12b, 12c, 12d) is arranged in parallel at a position in contact with the inside of the electrostatic conveyance belt 11 and facing the four photosensitive drums 1a, 1b, 1c, 1d. A positive charge is applied from the transfer roller 12 to the sheet S via the electrostatic conveyance belt 11, and the sheet S is conveyed from the driven roller 14a side to the driving roller 13 side by the electric field generated by the charge. The negative toner image on the photosensitive drum 1 is transferred to the sheet in contact with the photosensitive drum 1.

  The feeding unit 16 feeds and conveys the sheet S to the image forming unit, and a plurality of sheets S are stored in the feeding cassette 17. At the time of image formation, the sheet S fed by the feeding roller 18 (half-moon roller) and the registration roller pair 19 abuts the leading edge against the registration roller pair 19 and temporarily stops to form a loop. The image writing position is synchronized, and the sheet is fed to the electrostatic conveyance belt 11 by the registration roller pair 19.

  The fixing unit 20 as an example of the heating unit fixes the toner images of a plurality of colors transferred to the sheet S. The fixing unit 20 presses the rotating heating roller 21a and applies heat and pressure to the sheet S in pressure contact therewith. A fixing roller pair 21 including a pressure roller 21b is provided. That is, the sheet S to which the toner image on the photosensitive drum 1 has been transferred is conveyed by the fixing roller pair 21 when passing through the fixing unit 20, and is given heat and pressure by the fixing roller pair 21. As a result, the toner images of a plurality of colors are fixed on the surface of the sheet S. A discharge roller pair 23 is provided downstream of the fixing roller pair 21 and discharges the sheet S to the outside of the apparatus main body. In addition, a discharge sensor (not shown) is disposed between the fixing roller pair 21 and the discharge roller pair 23 to check whether the sheet S has been reliably discharged out of the main body or whether the sheet S has been wound around the fixing roller pair 21. Monitoring.

  Further, this image forming apparatus is configured to be able to perform double-sided recording, and a flapper 24 is swingably supported by the main body downstream of the discharge roller pair 23. At the time of single-sided recording, it is retracted to the position indicated by a two-dot chain line in the figure. When a double-sided recording signal is obtained from the apparatus main body, the position of the front end of the sheet is detected from the signal of the discharge sensor as described above, and the position of the flapper 24 is swung. The swinging operation is performed by a solenoid (not shown). A reversing roller pair 25 is disposed downstream of the flapper 24. The reversing roller pair 25 receives a sheet to be recorded on both sides and then switches back (reverses). The timing of the switch pack is such that the trailing edge position of the sheet S is detected from the signal from the above-described discharge sensor (not shown), and after a predetermined time, the roller rotation is stopped and the sheet pack rotates in the reverse direction.

  A conveying roller pair 26 is arranged on the right side of the reverse roller in the drawing. The conveying roller pair 26 receives the sheet S sent from the reverse roller pair 25 and conveys it to the refeed path 27.

  The refeed path 27 is disposed on the opposite side of the photosensitive drum 1 with respect to the electrostatic conveyance belt 11. In the refeed path 27, a pair of conveying rollers 28 and 29 are arranged up and down to convey the sheet S in the downward direction in the figure. At the lowest point, a U-turn path 30 is provided to change the sheet conveyance direction, and the sheet S guided to the U-turn path 30 is re-fed to the registration roller pair 19.

[Image forming operation]
As an image forming operation, the process cartridge 7 (7a, 7b, 7c, 7d) is sequentially driven in accordance with the recording timing, and the photosensitive drum 1 (1a, 1b, 1c, 1d) is driven in accordance with the drive. It is driven to rotate counterclockwise. Then, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven. By this driving, the charging device 2 applies a uniform charge to the circumferential surface of the photosensitive drum 1, and the scanner unit 3 exposes the circumferential surface of the photosensitive drum 1 in accordance with an image signal to perform the photosensitive drum 1. An electrostatic latent image is formed on the peripheral surface. The developing roller in the developing device 4 transfers (transfers) the toner to the low potential portion of the electrostatic latent image to form (develop) the toner image on the circumferential surface of the photosensitive drum 1.

  At the timing when the leading edge of the toner image on the circumferential surface of the uppermost photosensitive drum is rotated and conveyed to a point facing the electrostatic conveyance belt 11, the recording start position of the sheet S coincides with that point. Then, the registration roller pair 19 starts to rotate and feeds the sheet S to the electrostatic conveyance belt 11.

  The sheet S is pressed against the outer periphery of the electrostatic conveyance belt 11 so as to be sandwiched between the electrostatic adsorption roller 22 and the electrostatic conveyance belt 11, and a voltage is applied between the electrostatic conveyance belt 11 and the electrostatic adsorption roller 22. By doing so, electric charges are induced in the dielectric sheet S and the dielectric layer of the electrostatic transport belt 11 so that the sheet is electrostatically adsorbed on the outer periphery of the electrostatic transport belt 11. As a result, the sheet S is stably adsorbed and carried on the electrostatic conveyance belt 11 and conveyed to the transfer section on the most downstream side.

  While being conveyed in this way, the toner images on the photosensitive drums 1 are sequentially transferred onto the sheets S by an electric field formed between the photosensitive drums 1 and the transfer rollers 12.

  The sheet S to which the toner images of four colors are transferred is separated from the electrostatic conveyance belt 11 by the curvature of the driving roller 13 and is carried into the fixing unit 20. After the toner image is thermally fixed by the fixing unit 20, the sheet S is discharged out of the main body by the discharge roller pair 23 with the image surface facing down from the discharge unit 31.

[Double-sided recording operation]
Next, the double-sided recording operation will be described. When the image forming apparatus 100 receives the duplex recording signal, the discharge sensor detects that the sheet S has passed through the fixing roller pair 21. By the detection signal, the aforementioned flapper 24 is in the state shown in the figure, and the sheet S is guided toward the reversing roller pair 25. The reverse roller 25a rotates in the clockwise direction and conveys the sheet S in the left direction in the figure. The rotation is driven until the sheet S passes through the fixing roller pair 21 and passes through the discharge roller pair 23. After the trailing edge of the sheet S exceeds the above-described discharge sensor (not shown), the reversing roller 25a stops rotating after a predetermined time. Therefore, the flapper 24 swings to the position indicated by a two-dot chain line in the figure, and the reversing roller 25a starts to rotate counterclockwise in the figure. As a result, the sheet S is guided to the refeed path 27.

  The sheet S that has entered the refeed path 27 is sent to the U-turn path 30 by the transport roller pairs 28 and 29 and is transported to the registration roller pair 19. Thereafter, recording is completed by an image forming process similar to that for single-sided recording, and the sheet S is discharged from the discharge unit 31 to the outside of the apparatus main body.

[Jam processing and cartridge replacement]
Next, a configuration relating to jam processing and cartridge replacement of the image forming apparatus 100 will be described with reference to FIGS. FIG. 2 is a cross-sectional view showing a state in which the exterior is opened, and FIG. 3 is an external perspective view showing a state in which the exterior is opened.

  As shown in FIG. 2, the belt unit 5 is fixed to the main body of the image forming apparatus 100 so as to be swingable around a fulcrum 32 provided at the lower part. With this configuration, the belt unit 5 is rotated in the clockwise direction in FIG. The belt unit 5 is covered with a conveyance guide 33 that protects the electrostatic conveyance belt 11 and serves as a guide surface for the sheet S conveyed by the refeed path 27. The detailed shape of the transport guide 33 will be described later.

  The exterior member on the front side of the printer main body is divided into an upper cover 34 and a lower cover 35. Both the upper and lower covers 34 and 35 are provided with conveying ribs on the inner surface and also serve as the sheet guide surface of the refeed path 27. The lower cover 35 is mounted so as to be swingable about a cover fulcrum 36 at the lower end, and is configured to swing clockwise in the figure and open the lower half of the front side of the printer body. .

  As shown in FIG. 3, when the belt unit 5 is opened, it is easy to remove the jammed sheet on the electrostatic conveyance belt 11 and replace the cartridge 7, and there is no obstacle. The replacement of the process cartridge 7 is configured so that the process cartridge 7 can be easily pulled out from the apparatus main body by pulling the process cartridge 7 forward. As described above, when the jammed sheet on the electrostatic conveyance belt 11 is removed and the cartridge is replaced, the operation can be performed with two actions of opening the upper cover 34 and opening the belt unit 5, thereby improving the operability. It is illustrated. Further, in order to remove a jammed sheet in the double-sided path, the user can easily work by opening only the lower cover 35.

[Cooling means]
Next, the cooling means for the sheet S and the electrostatic conveyance belt 11, which is the most characteristic feature of the present invention, will be described with reference to FIG. 1, FIG. 4, and FIG. FIG. 4 is a view for explaining a conveyance guide of the belt unit, and FIG. 5 is an external perspective view for explaining an intake hole.

  As shown in FIG. 1, cooling means including a cooling fan 41, an air duct 42, and an intake hole 43 is disposed on the opposite side of the refeed path 27 from the electrostatic conveyance belt 11. Since the cooling fan 41 is attached to the lower cover 35 and is disposed without protruding from the conveying rib formed on the lower cover 35, there is no problem with respect to the conveyance of the sheet S.

  An air duct 42 is attached to the lower cover 35 below the cooling fan 41. This forms an air intake path of the cooling fan 41, which is formed of resin, and its inner surface is smoothly formed so as not to be a resistance to air flow.

  An intake hole 43 is provided in the lower cover 35 at a position below the air duct 42. As a result, the cooling fan 41 can blow air having the same temperature as the outside air temperature taken in from the intake hole 43 to the refeed path 27. FIG. 5 shows a perspective view of the apparatus main body. A plurality of intake holes 43 are arranged on the front side of the main body. Opening a large number of intake holes 43 in a large area facilitates air intake and increases the cooling efficiency of the cooling means.

  The cooling fan 41 is arranged so as to blow air A toward the re-feeding path 27 and in the direction opposite to the sheet conveying direction in the re-feeding path 27, as indicated by an arrow in the figure. The sheet passing through is configured to be cooled. Here, the sheet conveyance direction in the re-feeding path is vertically downward, and the air A blowing angle by the cooling fan 41 is inclined upward from the horizontal. As shown in FIG. 1, the inclination angle α at this time is such that the angle formed by the transfer material moving direction when cooling the sheet and the air A blowing direction of the cooling fan 41 is not less than 100 degrees and not more than 170 degrees. preferable. In this embodiment, the inclination angle α is set to 140 degrees. This is because it is important to wipe off the wind in the direction opposite to the conveyance direction of the conveyed sheet S.

  Thus, the sheet S heated by the fixing unit 20 can be cooled by the air A. In addition, since the direction of the wind is set in the direction opposite to the conveying direction of the sheet S, the cooling effect more than that in which the air A is applied vertically is obtained on the sheet S. This is because, from the relationship between the relative speed of the sheet S and the wind, the wind speed substantially equal to or higher than the performance (wind speed) of the cooling fan 41 hits the sheet S, so that the cooling efficiency can be dramatically improved. Therefore, there is a possibility that the fan size can be set small, which is effective for cost reduction and space saving.

  Further, since the air A flows while taking the heat of the sheet S from the front end to the rear end of the sheet S, the air A can be efficiently cooled without waste. Furthermore, in this embodiment, since the re-feeding path 27 is a straight path, the sheet S is not unexpectedly curled during cooling, and is an optimal area for cooling.

  The air A blown onto the sheet S moves upward in the drawing and is exhausted through the upper portion of the fixing unit 20 without entering the image forming unit 1 such as the photosensitive drum or the image forming unit such as the scanner unit 3. Conventionally, there has been a case where the exhaust air of the cooling means stays in the machine and promotes the temperature rise in the machine. However, this configuration uses the natural convection in which the heated exhaust air flows from the bottom to the top because the transport direction of the refeed path 27 is vertically downward and the air A is blown upward. Therefore, the air can escape upward without passing through the image forming unit, and the exhaust can be efficiently performed. That is, the countermeasure for raising the temperature inside the machine becomes easy, and the cooling means is the best arrangement.

  As shown in FIG. 4, a conveyance guide 33 is disposed between the electrostatic conveyance belt 11 and the refeed path 27 so as to cover the electrostatic conveyance belt 11. The conveyance guide 33 is made of resin, and six conveyance ribs 44 are integrally formed on the conveyance surface. The transport rib 44 enables the sheet S transported in the refeed path 27 to be transported without receiving excessive sliding resistance from the transport surface. Conveying rubber rollers 28 a and 29 a forming a conveying roller pair 28 and 29 are rotatably attached to the belt unit 5. The conveying roller pairs 28 and 29 are configured to rotate in the clockwise direction in the figure by a driving source (not shown).

  Further, the conveyance guide 33 is provided with a plurality (21 in this embodiment) of opening holes 45 between the conveyance roller pairs 28 and 29 so that the air A generated by the cooling fan 41 described above can be taken in. . The shape of the opening hole 45 is narrowed as it advances downstream in the conveyance direction so that the leading edge of the sheet S conveyed in the refeed path 27 is not caught by the end surface of the opening hole 45.

  Due to the opening hole 45, the air A also enables the electrostatic transport belt 11 to be cooled. In other words, when there is no sheet S in the refeed path 27, that is, when there is no transfer material at the opposite portion of the cooling means, the air A emitted from the cooling fan 41 passes through the opening hole 45 and is the transfer means. Sprayed onto the surface of the electrostatic conveyance belt 11. Even in this case, the direction in which the air A is sprayed onto the electrostatic conveyance belt 11 is the same as the inclination angle α, and is preferably 100 degrees or more and 170 degrees or less.

  Since the air A is blown in the direction opposite to the moving direction of the electrostatic conveyance belt 11, the cooling performance higher than that of the cooling fan 41 can be exhibited as described above. The air A wiped on the electrostatic conveyance belt 11 moves upward in the figure, and is discharged through the vicinity of the fixing unit 20 without entering the image forming unit such as the photosensitive drum 1 or the scanner unit 3.

  With the above configuration, the sheet S can be reliably cooled when the sheet S is in the refeed path 27, and the electrostatic transport belt 11 can be cooled when there is no sheet S. That is, the region of the electrostatic conveyance belt 11 that has been in contact with the sheet S heated by the fixing unit 20 is once cooled by the cooling unit, and then comes into contact with the sheet S heated by the fixing unit 20 again. Therefore, it is possible to realize the cooling of the surface of the electrostatic conveyance belt 11, which has been difficult in the past, without adding a cooling means. That is, both the sheet to be re-fed and the electrostatic conveyance belt can be efficiently cooled with a single cooling means.

Furthermore, since both the sheet S that contacts the image carrier and the electrostatic transport belt 11 can be cooled during image formation, the heat generated by the friction between the image carrier and the cleaning means and the developing means is applied to the sheet S and the electrostatic transport belt 11. Is taken away by heat transfer, and the temperature rise of the image carrier can also be suppressed. As a result, it has become possible to prevent image defects due to a temperature increase of the electrostatic conveyance belt 11 represented by a temperature increase of the image carrier, which has occurred until now, which is typified by a temperature increase of the electrostatic conveyance belt 11 represented by a transfer defect. Further, since the temperature increase of the electrostatic conveyance belt 11 is suppressed, the running performance of the electrostatic conveyance belt 11 is also stabilized.
[Example 2]

  Embodiment 2 of the image forming apparatus according to the present invention will be described. FIG. 6 is a diagram illustrating the image forming apparatus according to the present embodiment, FIG. 7 is a diagram illustrating the cooling unit and the conveyance guide as viewed from the apparatus main body side, and FIG. 8 is an external perspective view illustrating the intake holes. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  An image forming apparatus 150 illustrated in FIG. 6 has a configuration in which the form of the cooling unit is changed from that of the first embodiment. In the present embodiment, the cooling means includes a cooling fan 46, an air duct 47, and an intake hole 48.

  The cooling fan 46 is arranged at the lower part of the lower cover 35 and has a configuration in which outside air is sucked toward the back of the apparatus in FIG. 6 and air B is blown to the refeed path 27 via the air duct 47. . The air duct 47 is made of resin and engages with the cooling fan 46 without a gap, and its inner surface is smoothly formed so as not to resist the flow of air B.

  As shown in FIG. 7, the shape of the air duct 47 is formed to cover the entire width of the sheet S. As a result, the air B is blown with a uniform wind speed over the entire width of the sheet S conveyed in the refeed path 27, and the sheet S can be uniformly cooled over the entire area. Furthermore, by processing the air outlet 47 of the air duct 47 into various shapes, it is possible to finely set the wind direction, distribution, and the like.

  As shown in FIG. 8, an intake hole 48 that allows the cooling fan 46 to communicate with the outside of the apparatus is open on the side surface of the apparatus.

By disposing the cooling fan 46 on the side surface of the main body in this way, it is not necessary to dispose an electrical component on the lower cover 35 that is opened and closed by the user, so that the connection process in the apparatus is simplified. Further, it is not necessary to form an intake hole shape on the exterior surface of the main body, and the product design can be configured without giving visual noise to the user.
[Example 3]

  Embodiment 3 of the image forming apparatus according to the present invention will be described. FIG. 9 is a diagram illustrating the image forming apparatus according to the present embodiment, and FIG. 10 is a diagram illustrating the transport state of the electrostatic transport belt 11 and the sheet. The description is abbreviate | omitted and attached | subjected. This embodiment describes a configuration in which the operation of the cooling unit during double-sided recording is changed, and the temperature distribution (temperature difference) on the belt surface caused by the temperature difference of the electrostatically adsorbed sheet S is minimized. The purpose is to suppress it.

  FIG. 9 shows a state during duplex recording. In the figure, thick lines indicate actual sheets S1 to S3, and a two-dot chain line indicates a belt surface area where the sheet S1 conveyed from the refeed path 27 to the image forming unit is electrostatically adsorbed to the electrostatic conveyance belt 11. 51 is shown. That is, it becomes an area where the sheet S1 having heat is adsorbed and carried.

  In the drawing, the sheet S2 electrostatically attracted to the electrostatic conveyance belt 11 is fed from the main cassette, and the temperature of the sheet S2 is substantially equal to the outside air temperature. On the other hand, the sheets S1 and S3 are re-fed sheets and are heated by the fixing unit 20. In FIG. 9, the sheet S1 is separated from the electrostatic conveyance belt 11, and the sheet S3 is entering the U-turn path 30 from the refeed path 27 by the conveyance roller pair 29.

  Here, in this embodiment, the control means (not shown) that controls the drive source of the conveying roller pair 28 and 29 (the control device of the image forming apparatus main body) is located at the position where the belt surface area 51 is disposed with the opening hole 45. Control is performed so that no sheet exists between the cooling fan 41 and the electrostatic conveyance belt 11 in the refeed path 27 in the conveyed state.

  For example, in the state shown in FIG. 9, the leading end 52 of the belt surface area 51 is behind the trailing end of the sheet S3 in the belt rotation direction, and the timing is set so that the air A is reliably wiped. As shown in FIG. 10, the leading edge of the sheet S <b> 5 to be re-fed next is behind the trailing edge 53 of the belt surface area 51 in the belt rotation direction. Note that the sheet S4 in the drawing is a sheet fed from the main body cassette in the same manner as the sheet S2.

  The control means controls the conveying roller pair 28 in such a conveying sequence, so that the belt surface area 51 on which the heated sheet S1 is adsorbed is surely cooled by the air A. Therefore, the electrostatic conveying belt 11 It is possible to minimize the state where the temperature is not uniform. As a result, the traveling of the electrostatic conveyance belt 11, which has been unstable during conventional double-sided printing, can be stably performed. In addition, since the belt thickness does not change due to the temperature difference, it is possible to reduce image defects such as color shift and image expansion / contraction due to temperature rise.

  In this embodiment, the belt surface is set to be selectively cooled by the conveyance timing (sequence), but a clutch is inserted between the conveyance roller pair 28 in the refeed path 27 and the drive source, Timing may be obtained by temporarily stopping the conveyance by a control means (not shown). That is, when the timing of entering the sheet S5 into the re-feed path 27 is early, the conveying roller pair 28 is stopped and waits until the trailing edge of the belt surface area 51 precedes the leading edge of the sheet S5. Accordingly, the conveyance timing of the sheet S can be reliably controlled, and a state where the sheet S is not in the refeed path 27 can be surely created at the timing when the belt surface is desired to be cooled. As a result, similarly to the above, the heated belt surface can be selectively cooled, and the temperature difference of the belt surface temperature can be minimized.

  Further, an air volume adjusting means for the cooling fan 41 may be provided (a control device of the image forming apparatus main body can be used), and the belt surface may be selectively cooled by switching the cooling fan on and off. Thereby, it becomes possible to cool only the place which wants to cool the belt surface. In addition, the cooling fan 41 may be rotated at full speed when it is desired to cool the belt surface instead of being turned on and off, and in other cases, the air volume may be changed so as to rotate at half speed so as to make the belt surface temperature uniform. . As a result, fine settings can be made by slightly switching the wind speed of the cooling fan 41. According to these configurations, the timing of the belt can be reliably measured and the heated belt surface can be selectively cooled without adding a clutch, as described above. That is, the temperature difference of the belt surface temperature can be minimized without increasing the cost.

  In each of the above embodiments, the transfer unit of the image forming apparatus is an electrostatic conveyance belt that abuts via a sheet, and the toner image is transferred from the photosensitive drum 1 to the sheet that is electrostatically attracted and conveyed. As explained. However, the present invention is not limited to this, and the transfer unit is an intermediate transfer belt in which the transfer unit is in direct contact with the photosensitive drum 1, and the toner images received on the belt in a superimposed manner (primarily transferred) are collectively put on the sheet. Thus, even in a configuration where secondary transfer is performed, the present invention can be suitably applied in the same manner, and the effects of the present invention can be obtained. Similarly, the transfer unit is not limited to a belt shape, and is a transfer roller that conveys a sheet, a transfer drum that carries the sheet, an intermediate transfer drum that carries a toner image, and toner from the intermediate transfer member to the sheet. Even if it is a secondary transfer roller etc. which transfer an image, the effect can be acquired by applying this invention suitably.

  Further, in each of the above-described embodiments, the direction in which the air of the cooling unit is blown is described as being inclined in the direction (upward) opposite to the sheet conveyance direction (downward) in the refeed path 27. However, in the present invention, there are two objects to be cooled, the re-fed sheet and the transfer means, and either of them may be sprayed in the direction opposite to the moving direction of the object to be cooled. Here, in this embodiment, since the sheet conveying direction and the transfer unit moving direction are both vertically downward, there is no difference. However, when these directions differ, it sets to the direction opposite to the moving direction of the object which wants to cool more. For example, when the sheet is at a high temperature and needs to be cooled, the sheet is adjusted in the sheet conveyance direction, and when the transfer unit has a large heat capacity and needs to be cooled, it is adjusted in the belt moving direction. In the case where the transfer means is a belt member, it is a rotating endless belt and moves in all directions within the plane, but here the transfer direction of the transfer means is blown from the cooling means. It is a moving direction of the opposing part which air strikes.

  The present invention can be suitably used for an image forming apparatus capable of duplex recording.

It is a longitudinal cross-sectional view which shows the whole structure of a full color laser beam printer. It is sectional drawing which shows the state which opened the exterior. It is an external appearance perspective view which shows the state which opened the exterior. It is a figure explaining the conveyance guide of a belt unit. It is an external appearance perspective view explaining an intake hole. FIG. 6 is a diagram illustrating an image forming apparatus according to a second embodiment. It is a figure explaining the cooling means and conveyance guide seen from the apparatus main body side. It is an external appearance perspective view explaining an intake hole. FIG. 10 is a diagram illustrating an image forming apparatus according to a third embodiment. FIG. 6 is a diagram illustrating a state of conveyance of an electrostatic conveyance belt and a sheet.

Explanation of symbols

A ... Air S ... Sheet 1 ... Photoconductor drum 2 ... Charging device 3 ... Scanner unit 4 ... Developing device 5 ... Belt unit 6 ... Cleaning device 7 ... Process cartridge 9 ... Polygon mirror
10… Imaging lens
11 ... Electrostatic transfer belt
12… Transfer roller
13… Drive roller
14… driven roller
15… Tension roller
16… Feeding department
17… Feed cassette
18… feed roller
19… Registration roller pair
20… Fixing part
21… Fixing roller pair
21a ... Heating roller
21b… Pressure roller
22… Electrostatic adsorption roller
23… discharge roller pair
24… Flapper
25… Reverse roller pair
25a ... Reverse roller
26… Conveying roller pair
27… Refeeding pass
28, 29… Conveying roller pair
30… U-turn pass
31… discharge section
32… fulcrum
33… Conveyance guide
34… Top cover
35… Bottom cover
36… Cover fulcrum
41… Cooling fan
42… Air duct
43… Intake hole
44… Conveying rib
45… Open hole
46… Cooling fan
47 Air duct
48… intake hole
51… Belt surface area
52… Tip
53… Rear end
100, 150 ... Image forming apparatus

Claims (8)

An image carrier for carrying a toner image, a transfer means for transferring the toner image to a transfer material, a heating means for heating the transfer material, and a cooling means for cooling the heated transfer material at the opposing portion. In the image forming apparatus in which the transfer unit is in contact with the transfer material heated by the heating unit,
The image forming apparatus according to claim 1, wherein when the transfer material is not present at the facing portion, the cooling unit can cool the transfer unit. The image forming apparatus according to claim 1, wherein the transfer unit conveys a transfer material. The image forming apparatus according to claim 1, wherein the transfer unit carries a transfer material. The image forming apparatus according to claim 1, wherein the transfer unit receives a toner image from the image carrier and transfers the toner image to a transfer material. The cooling means cools the transfer material heated by blowing air, and the angle formed by the moving direction of the transfer material when cooling the transfer material and the air blowing direction of the cooling means is 100 degrees or more and 170 degrees or less. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 6. The angle between the moving direction of the transfer means and the air blowing direction of the cooling means is 100 degrees or more and 170 degrees or less at a position where the cooling means blows air onto the transfer means. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the air blown by the cooling unit escapes upward. The region of the transfer unit that is in contact with the transfer material heated by the heating unit is once cooled by the cooling unit, and then controlled so as to come into contact with the transfer material heated by the heating unit again. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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