JP2004151301A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize satisfactory both-sided printing as well as simple transfer control, in an image forming apparatus and image forming method for both-sided printing. <P>SOLUTION: Four toner images of respective colors are superposed one on the other on the surface of an intermediate transfer belt 41 and thereby a full-color toner image is formed. As an intermediate transfer belt 41 is rotated, the toner image is conveyed to a secondary transfer position 49 between rollers 45 and 48 and transferred to a recording medium 4. After the transfer, the recording medium 4 is conveyed along a specific conveyance path 5, and the toner image is fixed to the recording medium 4 by a fixing unit 60 in which a fixing temperature is set to 100°C or less. Setting the fixing temperature to 100°C or less restricts a change in the characteristic of the recording medium 4 which results from a fixing process. In addition, conditions under which transfer is performed in transfer (pre-transfer) of a toner image to the surface of the recording medium 4 are the same as those in transfer (post-transfer) of a toner image to the back of it. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method for forming a toner image on both sides of a recording medium such as copy paper, transfer paper, and paper.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in image forming apparatuses such as printers, copiers and facsimile machines, a toner image formed on an image carrier such as a photoconductor or an intermediate transfer medium is transferred to a recording medium, and then the toner image is fixed on the recording medium. The structure which makes it do is adopted. More specifically, a transfer unit such as a conductive elastic transfer roller or a transfer belt is disposed to face the image carrier in order to execute the transfer process. Then, the recording medium is passed to the opposing position, that is, the transfer position, in accordance with the movement timing of the image carrier, and a transfer bias is applied to the transfer means in response to the passage of the recording medium. Thus, the toner image on the image carrier is transferred to the recording medium. The recording medium onto which the toner image has been transferred is conveyed to a fixing unit, and applies pressure and heat to the recording medium to fix and fix the toner image on the recording medium.
[0003]
In an image forming apparatus that performs double-sided printing, after the toner image is transferred and fixed to one surface of the recording medium as described above, the same transfer and fixing process is performed on the other surface of the recording medium. It will be. However, if the transfer and fixing processes are performed on both sides under the same conditions, even if printing on one side (first-stage printing) is performed well, printing on the other side (second-stage printing) may not be performed properly. Was. Therefore, in order to solve this problem, it has been proposed to perform double-sided printing by making the transfer conditions for performing the first-stage printing and the transfer conditions for performing the second-stage printing different (see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-2-27377 (pages 3 to 4, page 6, FIG. 1B)
[0005]
[Problems to be solved by the invention]
However, in the apparatus described in Patent Document 1, it is necessary to change the transfer condition between the first-stage printing and the second-stage printing, and the transfer control becomes complicated. In particular, in an image forming apparatus for forming a color image, four color toner images are superimposed on an image carrier, and the transfer conditions must be strictly controlled in order to transfer the color toner images to a recording medium. . Therefore, in the apparatus described in Patent Document 1, it is necessary to separate the control of the transfer conditions between the first-stage printing and the second-stage printing, and further strictly control the transfer conditions in each printing, which makes transfer control more complicated. It has become something.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus and an image forming method for performing double-sided printing, which enable satisfactory double-sided printing while simplifying transfer control.
[0007]
[Means for Solving the Problems]
An image forming apparatus according to the present invention includes a transfer unit that transfers a toner image formed on an image carrier to a recording medium, and a fixing unit that fixes the toner image transferred to the recording medium by the transfer unit at a predetermined fixing temperature. An image forming apparatus for transferring and fixing a toner image on one surface of a recording medium, and then transferring and fixing the toner image on the other surface of the recording medium. Sets the fixing temperature at least when the toner image is fixed on one surface of the recording medium to 100 ° C. or less, and furthermore, the transfer means determines the conditions for transferring the toner image to one surface of the recording medium and It is characterized in that the conditions for transferring the toner image to the other surface are set to be the same.
[0008]
In the invention having such a configuration, when the toner image transferred to one surface of the recording medium is fixed to the recording medium (first-stage fixing), the fixing temperature is set to 100 ° C. or lower. For this reason, the evaporation of the moisture of the recording medium due to the first-stage fixing is suppressed, and the change in the moisture content of the recording medium is small even after the first-stage fixing, and the fluctuation of the electric resistivity of the recording medium is small. That is, by setting the fixing temperature in the first-stage fixing to 100 ° C. or less, a change in characteristics of the recording medium due to the fixing process is suppressed, and the recording medium is maintained in substantially the same state as before the first-stage fixing even after the first-stage fixing. Can be. Therefore, the transfer conditions for transferring the toner image to the other surface of the recording medium (the latter-stage transfer) are set to be the same as the transfer conditions for the former-stage transfer, so that the toner image can be recorded well on any surface. It can be formed on a medium, and transfer control can be simplified. In particular, when the toner image formed on the image carrier is a color image, it is necessary to strictly control the transfer conditions as described above. Is the same as that of the apparatus described in Japanese Patent Application Laid-Open No. H11-157, which is advantageous in that the control can be simplified more than in the apparatus in which the transfer conditions are changed before and after.
[0009]
In addition, according to the present invention, since a decrease in the amount of water contained in the recording medium can be suppressed as much as possible, it is possible to prevent a problem that the recording medium is wrinkled or curled. Particularly, in an image forming apparatus that performs double-sided printing, it is common to reversely re-feed a recording medium on which pre-printing has been performed to a transfer unit. However, compared to an image forming apparatus that exclusively performs single-sided printing, double-sided printing is performed. Since the wrinkle amount and the curl amount of the recording medium which are allowed in the image forming apparatus described above are small, the present invention is also advantageous in this respect.
[0010]
Further, in the present invention, when performing double-sided printing on each recording medium, the conditions for transferring the toner image to each side are set to be the same, but the transfer conditions are determined according to the surrounding environment of the transfer unit. You may do so. That is, the configuration may be such that the detection unit detects the surrounding environment of the transfer unit, and the transfer condition is determined based on the detection result by the detection unit. When the transfer conditions are set according to the surrounding environment of the transfer unit in this manner, even if the characteristics of the printing medium change due to the surrounding environment such as temperature and humidity, the toner image is always properly transferred to each surface of the printing medium. The transfer can be performed under the conditions, and the toner image can be formed on the recording medium with better image quality.
[0011]
Further, an image forming method according to the present invention is an image forming method for forming a toner image on both sides of a recording medium. In order to achieve the above object, the toner image formed on the image carrier is transferred to a recording medium. A first-stage transfer step of transferring the toner image onto one side of the recording medium at a fixing temperature of 100 ° C. or less, and a first-stage fixing step of fixing the toner image onto one side of the recording medium at a fixing temperature of 100 ° C. or lower; A second-stage transfer step of transferring the toner image formed on the image carrier to the other surface of the recording medium that has undergone the first-stage fixing step under the same conditions; and transferring the toner image transferred to the other surface of the recording medium onto the recording medium. And a post-fixing step of fixing to the other surface.
[0012]
In the invention configured as described above, similarly to the above-described apparatus, the fixing temperature is set to 100 ° C. or less in the pre-fixing step. Even after the process, the change in the moisture content of the recording medium can be reduced, and the change in the electrical resistivity of the recording medium can be suppressed. That is, by setting the fixing temperature in the first-stage fixing step to 100 ° C. or less, a change in characteristics of the recording medium due to the first-stage fixing step can be suppressed, and the recording medium can be maintained in substantially the same state as before the first-stage fixing step. . When the post-transfer process is performed on a recording medium that has undergone such pre-fixing process, the transfer conditions are set to be the same as those for the pre-transfer. Therefore, a toner image can be satisfactorily formed on the recording medium on any surface, and the transfer control can be simplified. In addition, according to the present invention, since a decrease in the amount of water contained in the recording medium can be suppressed as much as possible, it is possible to prevent a problem that the recording medium is wrinkled or curled. Particularly, in the image forming method of performing double-sided printing, similarly to the case of the above-described apparatus, it is particularly important to reduce the amount of wrinkles and curls of the recording medium in order to prevent the occurrence of jams, and the present invention is advantageous in this regard. .
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the printer. This printer forms a full-color image by superimposing four color toner images of yellow (Y), magenta (M), cyan (C), and black (K), or using only black (K) toner. This is an image forming apparatus of a wet development type for forming a monochrome image. In this printer, when a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 responds to the control signal from the main control unit 100 to control each unit of the engine unit 1. And prints out an image corresponding to the image signal on a recording medium 4 such as a transfer sheet, a copy sheet, and a sheet conveyed from a sheet feeding cassette 3 disposed at a lower portion of the apparatus main body 2.
[0014]
In the engine unit 1, yellow (Y), magenta (M), cyan (C), and black (K) process units are arranged along the circumferential direction 47 of the intermediate transfer belt 41 corresponding to the "image carrier" of the present invention. Is provided. Each process unit has the same basic configuration except for the toner color. Therefore, here, the yellow process unit will be described in detail, and the same or corresponding reference numerals will be given to the other toner color process units, and description thereof will be omitted.
[0015]
FIG. 3 is a partially enlarged view of the printer of FIG. In the yellow process unit, the photoconductor 11Y is provided rotatably in the direction of the arrow in FIG. 1 (clockwise direction in the figure). Around the photoreceptor 11Y, a charging unit 12, a developing roller 31, a charge removing unit (not shown), and a cleaning unit 14 are arranged along the rotation direction. In the present embodiment, the charging unit 12 includes a charging roller, and a charging bias is applied from a charging bias generation unit 111 to uniformly charge the outer peripheral surface of the photoconductor 11 to a predetermined surface potential Vd (for example, Vd = DC + 600 V). And has a function as a charging unit.
[0016]
A surface area between the charging unit 12 and the developing roller 31 is an irradiation area of the light beam from the exposure unit 20, and an electrostatic latent image is formed in this irradiation area. That is, the exposure unit 20 exposes the photoconductor 11Y with a light beam according to a control command given from the exposure control unit 112, and forms a yellow electrostatic latent image corresponding to an image signal on the photoconductor 11Y. For example, when a print command signal including an image signal is provided from an external device such as a host computer to the CPU 101 of the main control unit 100 via the interface 102, the CPU 113 responds to a command from the CPU 101 of the main control unit 100 to cause the exposure control unit to execute. A control signal corresponding to the image signal is output to the device 112 at a predetermined timing. Then, in response to a control command from the exposure control unit 112, a light beam is emitted from the exposure unit 20 to the photoconductor 11Y, and a yellow electrostatic latent image corresponding to an image signal is formed on the photoconductor 11Y. When a patch image is formed as necessary, a control signal corresponding to a patch image signal of a predetermined pattern (for example, a solid image, a thin line image, an outline thin line image, or the like) is transmitted from the CPU 113 to the exposure control. The electrostatic latent image corresponding to the pattern is provided on the photoconductor 11Y.
[0017]
The electrostatic latent image thus formed is visualized by the yellow liquid developer 32 supplied from the developing roller 31 of the developing unit 30Y. The developing unit 30Y includes, in addition to the developing roller 31, a tank 33 that stores the liquid developer 32, an application roller 34 that draws up the liquid developer 32 stored in the tank 33 and applies the liquid developer 32 to the developing roller 31. A regulating blade 35 for uniformly regulating the thickness of the developer layer on the application roller 34 and a cleaning blade 36 for removing the liquid developer remaining on the developing roller 31 after supplying the toner to the photoconductor 11Y are provided. . The developing roller 31 rotates at a peripheral speed equal to that of the photoconductor 11Y in a direction (counterclockwise in FIG. 1) that follows the photoconductor 11Y. On the other hand, the application roller 34 rotates at a peripheral speed of about twice the same direction as the developing roller 31 (counterclockwise in the figure).
[0018]
In the present embodiment, the liquid developer 32 includes a yellow toner including a color pigment, a resin that adheres the color pigment, a charge control agent that gives a predetermined charge to the toner, a dispersant that uniformly disperses the color pigment, and the like. And a carrier, and the toner is dispersed in the liquid carrier. Here, in the present embodiment, a non-volatile carrier such as a silicone oil such as polydimethylsiloxane oil is used as the liquid carrier, the toner concentration is 5 to 40% by weight, and a low-concentration developer often used in a wet development method. (The toner concentration is 1 to 2% by weight). Further, the viscosity of the liquid developer 32 is determined depending on the materials constituting the liquid carrier and the toner used, the toner concentration, and the like. In the present embodiment, for example, the viscosity is set to 50 to 6000 mPa · s, which is lower than that of the low-concentration developer. High viscosity.
[0019]
In the developing unit 30 </ b> Y having such a configuration, the liquid developer 32 stored in the tank 33 is pumped up by the application roller 34, and the thickness of the developer layer on the application roller 34 is uniformly regulated by the regulating blade 35. Then, the uniform liquid developer 32 adheres to the surface of the developing roller 31, and is conveyed to the developing position facing the photoconductor 11Y with the rotation of the developing roller 31. The toner is positively charged, for example, by the action of the charge control agent or the like. At the developing position, the toner is moved from the developing roller 31 to the photoconductor 11Y by the developing bias Vb applied from the developing bias generator 114 to the developing roller 31. Then, the electrostatic latent image is visualized. The developing bias Vb is determined by an optimization process using a patch image, and for example, about Vb = DC + 400 V is used.
[0020]
The toner image formed on the photoconductor 11Y as described above is conveyed to a primary transfer position facing the primary transfer roller 53Y as the photoconductor 11Y rotates. The primary transfer roller 53Y is arranged so as to sandwich the intermediate transfer belt 41 with the photoconductor 11Y. The intermediate transfer belt 41 is stretched around a plurality of rollers 43 to 46, and is moved in a direction (counterclockwise in FIG. 1) 47 driven by the photoconductor 11Y by a drive motor (not shown). It runs around at the same peripheral speed. Then, when a primary transfer bias (for example, DC-400V) is applied from the transfer bias generator 115, the yellow toner image on the photoconductor 11Y is primarily transferred to the intermediate transfer belt 41 at the primary transfer position. The residual charge on the photoreceptor 11Y after the primary transfer is removed by a charge removing unit such as an LED, and the residual developer is removed by a cleaning unit 14.
[0021]
The other toner colors are configured similarly to yellow, and a toner image corresponding to an image signal is formed. Then, yellow (Y), magenta (M), cyan (C), and black (K) toner images are superimposed on the surface of the intermediate transfer belt 41 at the positions of the primary transfer rollers 53Y, 53M, 53C, and 53K, respectively. Thus, a full-color toner image is formed. Thus, the four color process units function as “image forming means” for forming a toner image on the intermediate transfer belt 41.
[0022]
The toner image thus formed on the intermediate transfer belt 41 is conveyed to a secondary transfer position 49 sandwiched between the rollers 45 and 48 as the intermediate transfer belt 41 rotates. On the other hand, the recording medium 4 stored in the sheet cassette 3 (FIG. 1) is conveyed to a secondary transfer position 49 by a conveyance unit 70 described later in detail in synchronization with the conveyance of the primary transfer toner image. The roller 48 rotates at a peripheral speed equal to that of the intermediate transfer belt 41 in a direction (clockwise in FIG. 1) driven by the intermediate transfer belt 41, and a secondary transfer bias is applied from the transfer bias generation unit 115. Then, the toner image on the intermediate transfer belt 41 is secondarily transferred to the recording medium 4. As described above, the transfer unit 40 that transfers the toner image by the plurality of rollers is configured, and the rollers 45 and 48 among these rollers transfer the toner image on the intermediate transfer belt 41 to the recording medium 4 by “transfer unit”. The transfer process is executed under transfer conditions corresponding to a transfer environment detected by a sensor described below. In this embodiment, since the roller transfer is employed, the transfer condition can be set by the constant voltage control, and the transfer condition can be set by the constant current control. The transfer may be performed by corona discharge instead of roller transfer. In this case, the transfer condition can be set by controlling the output of corona discharge.
[0023]
The transfer unit 40 is provided with a cleaning unit 51 for removing the residual developer on the intermediate transfer belt 41 after the secondary transfer. Further, a temperature sensor 54 and a humidity sensor 55 are provided to detect the surrounding environment of the secondary transfer position. Output signals from the temperature sensor 54 and the humidity sensor 55 are sent to the CPU 113 so that the transfer environment can be detected.
[0024]
The recording medium 4 on which the toner image has been secondarily transferred as described above is conveyed along a predetermined conveyance path 5 (indicated by a dashed line in FIG. 1), and is fixed by a fixing unit 60 as a “fixing unit” of the present invention. The image is fixed on the recording medium 4 and is discharged to a discharge tray provided on an upper portion of the apparatus main body 2. The fixing unit 60 includes a heating roller 61 having a built-in heating heater 61h, and a pressure roller 62 that contacts the heating roller 61. By controlling the operation of the heater 61h by the heater control unit 116, the fixing temperature in the fixing unit 60 can be adjusted to an arbitrary temperature. In this embodiment, the heater controller 116 adjusts the fixing temperature to 100 ° C. or lower for the reason described later.
[0025]
Further, in the image forming apparatus according to this embodiment, a transport unit 70 for transporting the recording medium 4 along the predetermined transport path 5 is provided. In the transport unit 70, as shown in FIG. 1, a paper feed roller 71 is provided corresponding to the paper feed cassette 3, and the recording medium 4 stored in the paper feed cassette 3 is fed by the paper feed roller 71. The sheets are taken out one by one and conveyed to the feed roller 72. Then, the feed roller 72 conveys the recording medium 4 to the gate roller 73 and temporarily waits at this gate roller position. Then, the gate roller 73 is driven at a timing corresponding to the secondary transfer operation as described above to feed the recording medium 4 to the secondary transfer position 49. On the discharge tray side, there are provided a pre-discharge roller 74, a discharge roller 75, and a reversing roller 76, and the recording medium 4 on which the secondary transfer has been performed passes through the fixing unit 60, the pre-discharge roller 74, and the discharge roller 75. It is transported to the discharge tray side.
[0026]
Here, in order to perform double-sided printing, it is necessary to reverse the recording medium 4 and convey it to the gate roller 73 again, so that the discharge roller 75 can rotate forward and reverse. That is, when the recording medium 4 is directly discharged to the discharge tray, the recording medium 4 is completely conveyed to the discharge tray while continuing the normal rotation. On the other hand, at the time of reverse re-feeding, when the rear end of the recording medium 4 reaches a predetermined position between the pre-discharge roller 74 and the discharge roller 75, the discharge roller 75 rotates in the reverse direction to reverse the recording medium 4. It is sent to the roller 76. Thereby, the recording medium 4 is conveyed to the re-feed intermediate roller 77 along the reversing path 5a. Then, the re-feeding intermediate roller 77 and the pre-re-feed gate roller 78 convey the recording medium 4 to the gate roller 73, and temporarily stand by at the gate roller position. Thus, the recording medium 4 is reversed and re-fed.
[0027]
In FIG. 2, the main control unit 100 includes an image memory 103 for storing an image signal provided from an external device via the interface 102. When the CPU 101 receives a print command signal including an image signal from an external device via the interface 102, the CPU 101 converts the print command signal into job data in a format suitable for an operation instruction of the engine unit 1 and sends the job data to the engine control unit 110. The memory 117 of the engine control unit 110 includes a ROM for storing a control program of the CPU 113 including fixed data set in advance, and a RAM for temporarily storing control data of the engine unit 1 and calculation results by the CPU 113.
[0028]
FIG. 4 is a flowchart showing the duplex printing operation of the printer of FIG. Hereinafter, the double-sided printing operation by the image forming apparatus configured as described above will be described with reference to FIG. In this image forming apparatus, when a print command signal is input from an external device, the main control unit 100 creates job data in a format suitable for an operation instruction of the engine unit 1 based on the print command signal, and sends the job data to the engine control unit 110. Send out. On the other hand, in the engine control unit 110 that receives the job data, the CPU 113 controls each unit of the engine unit 1 according to the control program in the memory 117 to execute double-sided printing.
[0029]
First, in step S1, the CPU 113 of the engine control unit 110 detects the surrounding environment of the secondary transfer position 49, that is, the transfer environment, based on the output signals of the temperature sensor 54 and the humidity sensor 55. This is because the characteristics such as the electrical resistivity of the intermediate transfer belt 41 and the recording medium 4 fluctuate according to the transfer environment. The transfer environment is detected in advance, and the transfer conditions corresponding to the transfer environment are set. (Step S2), the secondary transfer process is always performed under good transfer conditions. In this embodiment, the transfer conditions corresponding to the transfer environment are stored in the memory 117 as a table in advance, and the CPU 113 can obtain the transfer condition corresponding to the transfer environment detected in step S1 from the table. are doing. That is, in this embodiment, the CPU 113 functions as the “transfer condition determining unit” of the present invention. Of course, it is needless to say that the transfer condition may be derived by substituting the output results of the temperature sensor 54 and the humidity sensor 55 into a previously obtained function formula instead of the table.
[0030]
When the transfer conditions are set as described above, a toner image to be printed on the surface (one surface) of the recording medium 4 is formed on the intermediate transfer belt 41 based on the job data (step S3). That is, an electrostatic latent image of each color corresponding to the print command signal is formed on the photoreceptors 11Y, 11M, 11C, and 11K on the recording medium 4. Then, after developing the electrostatic latent images of the respective colors by the corresponding developing units 30Y, 30M, 30C, and 30K to form toner images of the respective colors, these toner images are transferred to the intermediate transfer belt 41 at the respective primary transfer positions. The image is superimposed on the surface by primary transfer, whereby a color toner image is formed on the intermediate transfer belt 41. At the same time, the recording medium 4 is conveyed from the sheet cassette 3 to the gate roller 73 at an appropriate timing, and is kept on standby.
[0031]
In the next step S4, the color toner image on the intermediate transfer belt 41 is secondarily transferred onto the surface of the recording medium 4 while conveying the recording medium 4 from the gate roller 73 to the secondary transfer position 49 (pre-stage transfer step). Then, the recording medium 4 is conveyed to the fixing unit 60 to fix the toner image on the surface of the recording medium 4 (Step S5; pre-fixing step). In this embodiment, the fixing temperature in the fixing unit 60 is adjusted to 100 ° C. or lower, in order to suppress a decrease in the amount of water. That is, it is because the evaporation of the moisture of the recording medium 4 in the pre-fixing step is suppressed, and the fluctuation of the electrical resistivity of the recording medium 4 is reduced even after the pre-fixing step is performed. In other words, in the present embodiment, by setting the fixing temperature in the pre-fixing step to 100 ° C. or less, a change in characteristics of the recording medium 4 due to the fixing process is suppressed, and the recording medium 4 after the fixing process is substantially the same as before the pre-fixing. Are maintained in the same state.
[0032]
The recording medium 4 that has undergone the pre-fixing step is conveyed toward the discharge tray, and it is determined whether or not it is necessary to perform backside printing on the recording medium 4 during the conveyance (step S6). If the job content is single-sided printing, the process directly proceeds to step S7. However, if the job content is double-sided printing, it is determined in step S6 that backside printing needs to be performed. The transmission (step S8) and the series of processes (steps S3 to S5) are executed.
[0033]
When printing on the back side, the recording medium 4 is conveyed to the gate roller 73 along the reversing path 5a as described above, and temporarily stands by at this gate roller position (step S8). By performing reverse re-feeding in this manner, the recording medium 4 can be turned upside down.
[0034]
Then, a toner image to be printed on the back surface (the other surface) of the recording medium 4 is formed on the intermediate transfer belt 41 based on the job data (Step S3). Then, while conveying the recording medium 4 from the gate roller 73 to the secondary transfer position 49 to the secondary transfer position, the color toner image on the intermediate transfer belt 41 is secondarily transferred to the back surface of the recording medium 4 under the same transfer conditions as in the previous transfer step. (Step S4; post-transfer process). Then, the recording medium 4 is conveyed to the fixing unit 60 to fix the toner image on the back surface of the recording medium 4 (Step S5; latter-stage fixing step). The recording medium 4 that has undergone the latter-stage fixing process, that is, the recording medium 4 on which double-side printing has been performed, is conveyed toward the discharge tray. Since the back side printing has been completed at this stage, "NO" is determined in the step S6, and the process directly proceeds to the step S7.
[0035]
In step S7, the recording medium 4 on which an image has been formed is discharged to a discharge tray. Then, while it is determined in step S9 that continuous printing is necessary, steps S1 to S8 are repeated, and the recording medium 4 on which an image is formed is continuously discharged to the discharge tray.
[0036]
As described above, according to this embodiment, the fixing temperature in the first-stage fixing step is set to 100 ° C. or lower, so that the recording medium 4 to be re-fed is substantially in the same state as before the first-stage fixing step. Can be maintained. Since the transfer conditions in the subsequent transfer step are set to be the same as those in the previous transfer step, a toner image can be formed on the recording medium 4 satisfactorily on any surface. In addition, since the transfer conditions are the same for the front and back surfaces of the recording medium 4, the transfer control can be simplified.
[0037]
Further, in this embodiment, the transfer conditions in the first and second transfer steps are shared, but since the common transfer conditions are set in accordance with the transfer environment, the intermediate transfer conditions are set according to the surrounding environment such as temperature and humidity. Even if the characteristics of the belt 41 and the recording medium 4 change, the toner image can always be transferred to the front and back surfaces of the recording medium 4 under appropriate transfer conditions, and the toner image can be transferred onto the recording medium with better image quality. Can be formed.
[0038]
Further, by setting the fixing temperature in the first-stage fixing step to 100 ° C. or less, it is possible to minimize the decrease in the amount of water contained in the recording medium 4, so that it is possible to prevent the recording medium 4 from being wrinkled or curled. Particularly, in an image forming apparatus that performs double-sided printing, a reversing path 5a is provided for reversing and re-feeding the recording medium 4 on which pre-printing has been performed to the secondary transfer position 49, and the pre-fixing process is performed along the reversing path 5a. Since the recording medium 4 that has received the recording medium 4 is forcibly inverted, even if a slight wrinkle or curl occurs, the recording medium 4 may interfere with the reversing path 5a and cause a jam. For this reason, the allowable amount of wrinkles and curls of the recording medium 4 is relatively small in the image forming apparatus for double-sided printing as compared with the image forming apparatus for performing single-sided printing exclusively. However, according to the present embodiment, since the occurrence of wrinkles and curls can be effectively prevented as described above, the degree of freedom in designing the reversing path 5a can be increased, and the occurrence of jams can be reduced. This is very advantageous for a double-sided printing image forming apparatus.
[0039]
The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, the fixing temperature is adjusted to 100 ° C. or less by the heater control unit 116, and the fixing process is performed at the fixing temperature in the first-stage fixing process as well as in the second-stage fixing process. The fixing may be performed at a fixing temperature exceeding ゜ C. That is, in the present invention, it is essential that the fixing temperature is set to 100 ° C. or lower in the first fixing step, but the fixing temperature in the second fixing step is optional.
[0040]
Further, in the above embodiment, the toner image is transferred and fixed on the back surface after the toner image is transferred and fixed on the front surface of the recording medium 4. However, the transfer and fixing in the reverse order are exactly the same. However. In this case, the back surface to be transferred and fixed first corresponds to “one surface of the recording medium” of the present invention, and the front surface corresponds to “the other surface of the recording medium” of the present invention.
[0041]
Further, in the above-described embodiment, the temperature sensor 54 and the humidity sensor 55 are provided as “detecting means” of the present invention, and the surrounding environment (transfer environment) of the secondary transfer position 49 is detected. However, the present invention is not limited to this. For example, only a humidity sensor directly related to the water content may be provided.
[0042]
In the above-described embodiment, the transfer environment is detected (step S1) and the transfer condition is set (step S2) prior to performing the double-sided printing on each recording medium. The present invention is not limited to this, and may be configured to be executed at an appropriate timing, for example, when the operation time, the number of continuous prints, or the like reaches a predetermined value.
[0043]
In the above-described embodiment, the present invention is applied to a so-called tandem type, and a wet type color double-sided printing image forming apparatus.However, the application target of the present invention is not limited to this. The present invention can be applied to all image forming apparatuses that perform double-sided printing. For example, the present invention can be applied to an image forming apparatus that performs monochrome double-sided printing, and can also be applied to an image forming apparatus that performs double-sided printing by a so-called dry developing method. On the other hand, the present invention can be applied to a so-called four-cycle type image forming apparatus that forms a color toner image by switching between a plurality of developing units, and an image using an intermediate transfer drum as the “image carrier” of the present invention. The present invention can be applied to a forming apparatus.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the printer of FIG.
FIG. 3 is a partially enlarged view of the printer of FIG. 1;
FIG. 4 is a flowchart illustrating a duplex printing operation of the printer of FIG. 1;
[Explanation of symbols]
4 recording medium, 32 liquid developer, 40 transfer unit (transfer unit), 41 intermediate transfer belt (image carrier), 45, 48 roller (transfer unit), 54 temperature sensor (detector), 55: humidity sensor (detection means), 60: fixing unit (fixing means), 113: CPU (transfer condition determining means)

Claims (5)

A transfer unit that transfers a toner image formed on an image carrier to a recording medium; and a fixing unit that fixes the toner image transferred to the recording medium by the transfer unit at a predetermined fixing temperature. After transferring and fixing the toner image on one surface of the recording medium, the image forming apparatus transfers and fixes the toner image on the other surface of the recording medium.
The fixing unit sets a fixing temperature for fixing at least the toner image on one surface of the recording medium to 100 ° C. or less, and
The image forming apparatus according to claim 1, wherein the transfer unit sets the same conditions for transferring the toner image to one surface of the recording medium and the conditions for transferring the toner image to the other surface of the recording medium. The image forming apparatus according to claim 1, further comprising an image forming unit that forms a toner image on the image carrier using a liquid developer obtained by dispersing a toner in a liquid carrier. 3. The image forming apparatus according to claim 1, wherein the toner image formed on the image carrier is a color image. Detecting means for detecting a surrounding environment of the transfer means;
The image forming apparatus according to claim 1, further comprising: a transfer condition determining unit that determines the transfer condition based on a detection result by the detecting unit. In an image forming method for forming a toner image on both surfaces of a recording medium,
A pre-transfer step of transferring the toner image formed on the image carrier to one surface of the recording medium,
A first-stage fixing step of fixing the toner image transferred on one surface of the recording medium to one surface of the recording medium at a fixing temperature of 100 ° C. or less;
A second transfer step of transferring the toner image formed on the image carrier to the other surface of the recording medium having undergone the first fix step under the same transfer conditions as the first transfer step;
A post-fixing step of fixing the toner image transferred to the other surface of the recording medium on the other surface of the recording medium.

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