JP3633160B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus using an intermediate transfer member.
[0002]
[Prior art]
Conventionally, in an electrophotographic image forming apparatus using an intermediate transfer member, an electrostatic transfer device is used for secondary transfer of a toner image formed on the intermediate transfer member by primary transfer onto a recording medium such as paper. A method of performing secondary transfer is widely known. However, due to the unevenness of the surface of the paper, which is the recording medium, the paper and the intermediate transfer member are not maintained in perfect contact with each other at the time of transfer, resulting in a non-uniform gap, disturbing the transfer electric field, and coulomb repulsion between toners. There is a problem that the image quality is deteriorated because the toner repels by force and the transfer efficiency is lowered.
[0003]
In order to solve this problem, Japanese Patent Application Laid-Open No. 51-94939 discloses a multi-color multiple formed on an intermediate transfer member by electrostatically transferring toner images of different colors on the intermediate transfer member in order. A color image forming apparatus is disclosed in which after a toner image is melted, the melted multiple toner image is secondarily transferred to a recording medium and fixed at the same time as the transfer to obtain a color image. In such a simultaneous transfer and fixing method, the transfer of the toner image to the recording medium is performed non-electrostatically, so that the image quality deterioration due to the decrease in the transfer efficiency as described above hardly occurs.
[0004]
Further, JP-A-5-19642 and JP-A-5-249798 disclose that the intermediate transfer member and the recording medium are in close contact so that the toner image is completely transferred from the intermediate transfer member to the recording medium. A technique is disclosed in which the recording medium is peeled off from the intermediate transfer member after heating and pressurization and then cooling until the condensing force between the toners becomes larger than the adhesive force between the toner and the intermediate transfer member. By doing so, the toner transfer efficiency is improved to obtain a high-quality image with good color balance and high gloss.
[0005]
As described above, in order to obtain a high-quality image by an image forming apparatus using the simultaneous transfer fixing method, the intermediate transfer member and the recording medium after the transfer fixing must be cooled while being kept in close contact. However, a force for separating the intermediate transfer member and the recording medium acts.
FIG. 8 is an explanatory diagram showing forces acting on the recording medium after simultaneous transfer and fixing.
[0006]
In the image forming apparatus using the simultaneous transfer and fixing method, the intermediate transfer body 3 and the recording medium 4 are cooled after being heated by the transfer and fixing means. As shown in FIG. Since the rates are different, there is a shift between the two, and a force to peel off acts. Further, in a recording medium such as paper, the paper may curl due to the direction of the fibers. Further, there may be a force that promotes peeling of the recording medium depending on the layout in the image forming apparatus.
[0007]
FIG. 9 is a diagram illustrating a part of an image forming apparatus using the simultaneous transfer fixing method.
In the image forming apparatus shown in FIG. 9, an endless belt-shaped intermediate transfer member 3 that carries a toner image T and rotates in the direction of arrow A, and a recording medium 4 that has been supplied to the secondary transfer position P2 are intermediate transferred. Secondary transfer means comprising a pressure roll 2a and a heat roll 2b for transferring the toner image T onto the recording medium 4 by pressurizing and heating the intermediate transfer body 3 and the recording medium 4 which are superposed on the body 3 and sandwich the toner image T therebetween. 2 and a part of recording medium conveying means such as rollers 22a, 22b, 22c,... For conveying the recording medium 4 before the toner image T is transferred.
[0008]
The recording medium 4 in the tray 23 is supplied to the secondary transfer position P2 by the recording medium conveying means, and is superposed on the intermediate transfer body 3 with the toner image T sandwiched between the pressure roll 2a and the heat roll 2b, and is pressurized and heated. The In the image forming apparatus having the layout as shown in FIG. 9, the pressed and heated recording medium 4 is not maintained in a close contact state until the intermediate transfer body 3, the recording medium 4 and the toner image T are cooled. In addition, the recording medium 4 curls downward due to the gravity of the recording medium 4 itself and often peels off before cooling.
[0009]
As described above, in order to obtain a high-quality image by the simultaneous transfer fixing method, it is necessary that the intermediate transfer member and the recording medium be kept in close contact during a predetermined cooling period after transfer fixing. Despite being important for efficiency and thus image quality, it is difficult to achieve.
In view of the above circumstances, the present invention provides an image forming apparatus capable of obtaining a high-quality image by increasing toner transfer efficiency in an image forming apparatus of a simultaneous transfer fixing method using an intermediate transfer member. Objective.
[0010]
[Means for Solving the Problems]
The image forming apparatus of the present invention that achieves the above object is
A photoconductor on which a toner image is formed, an intermediate transfer member that receives the transfer of the toner image formed on the photoconductor, and a primary transfer that transfers the toner image formed on the photoconductor to the intermediate transfer member The intermediate transfer member and the recording medium supplied to the secondary transfer position are overlapped with the toner image transferred onto the intermediate transfer member at a predetermined secondary transfer position. Secondary transfer means for pressurizing and heating the intermediate transfer body and the recording medium to be sandwiched, and transport means for transporting the recording medium pressurized and heated by the secondary transfer means to a predetermined peeling position together with the intermediate transfer body In an image forming apparatus comprising:
A recording medium adsorbing means for electrostatically adsorbing the recording medium to the intermediate transfer body until the intermediate transfer body and the recording medium are conveyed from the secondary transfer position to the peeling position is provided. And
[0011]
Here, the recording medium adsorbing means may be one that charges the recording medium with a conductive brush and electrostatically adsorbs the recording medium to the intermediate transfer member. Also, the recording medium adsorbing means However, the recording medium may be charged by a corotron and electrostatically adsorbed to the intermediate transfer member.
The secondary transfer means includes a recording medium sandwiching the toner image and a pair of transfer fixing rolls that pressurize and heat the intermediate transfer member, and the recording medium adsorption means charges the recording medium by the transfer fixing roll. The recording medium may be electrostatically attracted to the intermediate transfer member.
[0012]
Further, the recording medium adsorbing means may be one that charges the recording medium with an electric charge having a polarity opposite to the charging polarity of the toner and electrostatically adsorbs the recording medium to the intermediate transfer member.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.
The first embodiment is an example in which the image forming apparatus of the present invention is applied to a digital color printer. Image data from a personal computer (PC) 7 operated by a user is input to an image processing system (IPS) 8 of the image forming apparatus 1. The image data is separated into four colors of yellow, magenta, cyan and black, and then sent to image forming engines 5a, 5b, 5c and 5d corresponding to the four colors of yellow, magenta, cyan and black. Each of the image forming engines 5a, 5b, 5c, 5d has the same type of photosensitive drums 6a, 6b, 6c, 6d, laser driver units 9a, 9b, 9c, 9d, mirrors 10a, 10b, 10c, 10d, and a charger 11a. , 11b, 11c, 11d, developing devices 12a, 12b, 12c, 12d, and cleaners 13a, 13b, 13c, 13d.
[0014]
The first engine 5a for yellow image formation among these four colors will be described in detail below. Around the photosensitive drum 6a rotating in the direction of arrow A, a charging charger 11a for uniformly charging the surface of the photosensitive drum 6a prior to exposure is provided. A developing device 12a is disposed downstream of the charging charger 11a, and a cleaner 13a is disposed further downstream.
[0015]
The above four engines are arranged so as to be in contact with the intermediate transfer body 3 at the respective primary transfer positions P1 of the respective photosensitive drums 6a, 6b, 6c, 6d. Further, transfer corotrons 14a, 14b, 14c, and 14d are provided on the back surface side of the intermediate transfer body 3 at positions where the photosensitive drums 6a, 6b, 6c, and 6d are in contact with the intermediate transfer body 3, respectively.
[0016]
Further, in this image forming apparatus, the intermediate transfer member 3 is stretched and rotated in the direction of arrow B, so that the toner image on the intermediate transfer member 3 is conveyed while being carried together with the intermediate transfer member, Rollers 15a, 15b, 15c, 22a, 22b, 22c, for supplying the recording medium 4 to the secondary transfer position P2 on the intermediate transfer body 3 and transporting it to the recording medium peeling position P3 on the intermediate transfer body 3. A recording medium transport device such as 22d is provided.
[0017]
At the secondary transfer position P2, the toner image on the intermediate transfer body 3 is superimposed on the recording medium 4, and the intermediate transfer body 3 and the recording medium 4 sandwiching the toner image are pressurized and heated to record the recording medium 4. A secondary transfer means 2 including a pair of a pressure roll 2a and a heating roll 2b for transferring the toner image is provided. The heating roll 2b also has a function of stretching the intermediate transfer member 3. On the downstream side of the secondary transfer unit 2, a recording medium adsorption unit 17 that electrostatically adsorbs the recording medium 4 to the intermediate transfer member 3 is provided. Further, a peeling roller 15c having a small radius is provided at the recording medium peeling position P3 on the extended line of the conveyance path of the intermediate transfer body 3, and further, the recording peeled off from the intermediate transfer body 3 is further provided. A discharge roller 24 for discharging the medium 4 to the outside of the apparatus is provided.
[0018]
Next, an image forming operation by the image forming apparatus will be described.
Based on the image data sent from the PC 7, a yellow image is output from the IPS 8 to the laser driver unit 9a of the first engine 5a. Laser light corresponding to the yellow image is emitted from the laser driver unit 9a, and irradiated to the photosensitive drum 6a through the mirror 10a. The surface of the photosensitive drum 6a is uniformly charged by a charging charger 11a in advance, and the uniformly charged surface of the photosensitive drum 6a is exposed to a laser beam to form an electrostatic latent image based on a yellow image. Next, the electrostatic latent image on the photosensitive drum 6a moves to the developing position as the photosensitive drum 6a rotates in the direction of arrow A, and yellow toner is supplied from the developing tank of the yellow developing device 12, and the electrostatic drum image on the photosensitive drum 6a. Thus, a yellow toner image is formed. Next, the yellow toner image moves to the primary transfer position P1 as the photosensitive drum 6 rotates, and is primarily transferred onto the intermediate transfer body 3 by the transfer corotron 14a at the primary transfer position P1. During the primary transfer, a part of the toner remains on the surface of the photosensitive drum 6 without being transferred, but is scraped off by the cleaner 13a.
[0019]
Similarly, a magenta image is formed by the second engine 5b, and the yellow toner image that has been first transferred onto the intermediate transfer member 3 is conveyed in the direction of arrow B together with the intermediate transfer member 3 and is used for the second engine 5b and magenta. The magenta toner image is primarily transferred onto the yellow toner image on the intermediate transfer body 3 in accordance with the timing of reaching the primary transfer position of the magenta where the transfer corotron 14b is provided. Similarly, the third engine 5c performs cyan image formation and primary transfer onto the intermediate transfer member 3, and the fourth engine 5d performs black image formation and primary transfer onto the intermediate transfer member 3, respectively. Four color images are superimposed on the body 3. The toner images superimposed in this way are conveyed to the secondary transfer position P2 as the intermediate transfer member 3 rotates. A secondary transfer means 2 comprising a pressure roll 2a and a heating roll 2b is provided at the secondary transfer position P2, and the toner image on the intermediate transfer body 3 is a recording medium that has been supplied to the secondary transfer position P2. 4 is pressed and heated together with the intermediate transfer body 3 and the recording medium 4 to be secondarily transferred onto the recording medium 4 and fixed, and conveyed to a predetermined peeling position P3.
[0020]
Until the intermediate transfer body 3 and the recording medium 4 are conveyed from the secondary transfer position P2 to the peeling position P3, that is, on the downstream side of the secondary transfer means 2, the recording medium 4 is electrostatically applied to the intermediate transfer body 3. A recording medium adsorbing means 17 to be adsorbed on the recording medium is provided. In the first embodiment, the recording medium adsorbing means 17 uses a conductive brush.
FIG. 2 is a schematic view of a recording medium suction unit using a conductive brush.
[0021]
As shown in FIG. 2, a recording medium adsorbing means 17 comprising a brush charger 19 and a counter electrode roll 20 is disposed downstream of the secondary transfer means 2 comprising a pressure roll 2a and a heating roll 2b. The brush charger 19 is connected to a power source 19a, and the tip of the brush is in sliding contact with the surface of the recording medium 4. The counter electrode roll 20 disposed at a position facing the brush tip is grounded, and the recording medium 4 is slidably contacted with the conductive brush and charged by the voltage applied to the conductive brush, and electrostatically applied to the intermediate transfer body 3. Adsorbed.
[0022]
FIG. 3 is a flowchart of the recording medium suction operation in the first embodiment of the present invention.
The operation from image formation to recording medium discharge will be described with reference to FIGS. First, image data is input from the PC 7 to the image forming apparatus 1 (step S1). The IPS 8 separates the image data into four colors of Sian, Magenta, Yellow, and Black (Step S2). Each engine 5a, 5b, 5c, 5d receives image data corresponding to the engine, and forms a toner image of each color on the photoreceptor (step S3). The toner images formed on the photoreceptors 6a, 6b, 6c, and 6d are primarily transferred onto the intermediate transfer member 3 in order from the first engine 5a (step S4). Next, at the secondary transfer position P2, the toner image superimposed and transferred on the intermediate transfer member 3 is transferred and fixed on the recording medium 4 (step S5). Subsequently, the recording medium 4 is charged by the brush charger 19 of the recording medium adsorbing means 17 and an electrostatic adhesion force is applied (step S6) until the recording medium 4 is conveyed from the secondary transfer position P2 to the peeling position P3. During this time, the recording medium 4 is kept in close contact with the intermediate transfer member 3. In the meantime, the toner is cooled and the condensing force between the toner particles becomes larger than the adhesion force between the toner particles and the intermediate transfer member 3, and then the recording medium 4 is peeled off from the intermediate transfer member 3 and is discharged by the discharge roller 24. It is discharged out of the machine (step S7).
[0023]
FIG. 4 is a schematic diagram illustrating a state where the intermediate transfer member and the recording medium are in close contact with each other by electrostatic adhesion.
As shown in FIG. 4, the intermediate transfer member 3 and the recording medium 4 are kept in close contact with each other by the electrostatic adhesion force that the negative charge on the intermediate transfer member 3 side and the positive charge on the recording medium 4 side attract each other. Is prevented from peeling due to its own weight.
[0024]
FIG. 5 is a graph showing the effect of the recording medium suction means.
The horizontal axis of FIG. 5 shows the voltage applied to the brush charger 19 for recording medium adsorption, and the vertical axis shows the result of visual sensory evaluation of the image quality grade of the image. The relationship between the image quality grade value and the sensory evaluation value is shown at the bottom of FIG.
As shown in FIG. 5, when the applied voltage is low, that is, when the intermediate transfer member and the recording medium are not in close contact, the image quality grade is low. This is presumably because the intermediate transfer member and the recording medium are peeled off before the toner is sufficiently cooled, resulting in an offset phenomenon or a low gloss image. Further, when the applied voltage is not sufficiently high, that is, when the peeling is not performed but the adhesion is insufficient, the image quality grade is not sufficiently improved because the image quality is partially deteriorated. On the other hand, when the applied voltage is sufficiently high, that is, when the degree of adhesion is increased, an image with high gloss and transparency can be obtained, and a sufficiently high image quality grade can be obtained. From the results of FIG. 5, between “I can fully satisfy gloss and transparency” and “I am not satisfied with gloss and transparency, but I do not care”, that is, I am satisfied with the gloss and transparency of image quality grade 4.5 If the required minimum level is set, the corresponding applied voltage is about 750V.
[0025]
Next, a second embodiment of the present invention will be described.
FIG. 6 is a schematic configuration diagram of a recording medium suction unit in the second embodiment of the image forming apparatus of the present invention.
The second embodiment is different from the first embodiment only in that a corotron is used for the recording medium adsorption means 17 ′, and other components are the same as those in the first embodiment.
[0026]
As shown in FIG. 6, in the second embodiment, a recording medium adsorbing means 17 ′ comprising a corotron 21 and a counter electrode roll 20 is provided downstream of the secondary transfer means 2 comprising a pressure roll 2a and a heating roll 2b. Has been deployed. The corotron 21 is connected to a power source 21a, and the counter electrode roll 20 provided at a position facing the corotron 21 is grounded. In this way, by applying a bias voltage between the corotron 21 and the counter electrode roll 20, an electrostatic adhesive force is applied between the intermediate transfer body 3 and the recording medium 4, and the intermediate transfer body 3 The recording medium 4 is conveyed to the peeling position P3 (see FIG. 1) while keeping in close contact with each other. In the meantime, the toner is cooled and the condensing force between the toner particles becomes larger than the adhesion force between the toner particles and the intermediate transfer member 3, and then the recording medium 4 is peeled off from the intermediate transfer member 3 and is discharged by the discharge roller 24. It is discharged outside the machine.
[0027]
The effect of the recording medium adsorbing means 17 ′ is almost the same as in the first embodiment.
Next, a third embodiment of the present invention will be described.
FIG. 7 is a schematic configuration diagram of a recording medium adsorbing unit in the third embodiment of the image forming apparatus of the present invention.
[0028]
In the third embodiment, the secondary transfer unit 25 includes a pair of transfer fixing rolls 25a and 25b, and the recording medium adsorbing unit 17 ″ charges the recording medium 4 with the transfer fixing rolls 25a and 25b. The recording medium 4 is configured to be electrostatically attracted to the intermediate transfer body 3. That is, the secondary transfer means 25 also serves as the recording medium attracting means 17 ″. The other components are the same as those in the first and second embodiments.
[0029]
As shown in FIG. 7, in the third embodiment, one of the pair of transfer fixing rolls 25a and 25b constituting the secondary transfer unit 25 (25a) is a heat roll, and this heat roll is a power source 25c. The other roll (25b) is a pressure roll, and this pressure roll is grounded.
Thus, by applying a bias voltage between the heat roll (25a) and the pressure roll (25b), an electrostatic adhesive force is applied between the intermediate transfer body 3 and the recording medium 4, and the intermediate transfer body. 3 and the recording medium 4 are conveyed to the peeling position P3 (see FIG. 1) while keeping in close contact with each other. In the meantime, the toner is cooled and the condensing force between the toner particles becomes larger than the adhesion force between the toner particles and the intermediate transfer member 3, and then the recording medium 4 is peeled off from the intermediate transfer member 3 and is discharged by the discharge roller 24. It is discharged outside the machine.
[0030]
The effect of the recording medium adsorbing means 17 ″ is almost the same as in the first and second embodiments.
In each of the above embodiments, the recording medium adsorbing unit is configured to electrostatically adsorb the recording medium to the intermediate transfer member by applying a charge having a polarity opposite to the charging polarity of the toner to the recording medium. However, the charge applied to the recording medium is not necessarily limited to the above polarity, and may be a charge having the opposite polarity.
[0031]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, in the simultaneous transfer fixing type image forming apparatus using the intermediate transfer body, the intermediate transfer body, the recording medium, and the recording medium until the toner after the simultaneous transfer fixing is cooled. Since the recording medium is peeled off from the intermediate transfer body after the toner is cooled while being kept in close contact with the electrostatic adhesive force, the toner transfer efficiency is high, the color balance is good, the gloss is high, and the toner High-quality images with excellent transparency can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a first embodiment of an image forming apparatus of the present invention.
FIG. 2 is a schematic diagram of a recording medium suction unit using a conductive brush.
FIG. 3 is a flowchart of a recording medium suction operation according to the first embodiment of the present invention.
FIG. 4 is a schematic diagram illustrating a state where an intermediate transfer member and a recording medium are in close contact with each other by electrostatic adhesion.
FIG. 5 is a graph showing the effect of a recording medium suction unit.
FIG. 6 is a schematic configuration diagram of a recording medium suction unit in the second embodiment of the image forming apparatus of the present invention.
FIG. 7 is a schematic configuration diagram of a recording medium adsorbing unit in a third embodiment of the image forming apparatus of the present invention.
FIG. 8 is an explanatory diagram showing forces acting on a recording medium after simultaneous transfer and fixing.
FIG. 9 is a diagram illustrating a part of an image forming apparatus using a simultaneous transfer fixing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Secondary transfer means 2a Pressure roll 2b Heating roll 3 Intermediate transfer body 4 Recording medium 5a, 5b, 5c, 5d Engine (image forming engine)
6a, 6b, 6c, 6d Photosensitive drum 7 Personal computer (PC)
8 Image processing system (IPS)
9a, 9b, 9c, 9d Laser driver units 10a, 10b, 10c, 10d Mirrors 11a, 11b, 11c, 11d Chargers 12a, 12b, 12c, 12d Developers 13a, 13b, 13c, 13d Cleaners 14a, 14b, 14c, 14d transfer corotron 15a, 15b, 15c, 22a, 22b, 22c, 22d roller 17, 17 ', 17 "recording medium adsorbing means 19 brush charger 19a power supply 20 counter electrode roll 21 corotron 21a power supply 23 tray 24 discharge roller 25 secondary Transfer means 25a, 25b Transfer fixing roll 25c Power supply

Claims (2)

A photoconductor on which a toner image is formed, an intermediate transfer member that receives the transfer of the toner image formed on the photoconductor, and a primary that transfers the toner image formed on the photoconductor to the intermediate transfer member The intermediate transfer body and the recording medium supplied to the secondary transfer position are superimposed with the transfer means and the toner image transferred onto the intermediate transfer body at a predetermined secondary transfer position, A secondary transfer unit that pressurizes and heats the intermediate transfer member and the recording medium sandwiching the toner image; and the recording medium that is pressurized and heated by the secondary transfer unit together with the intermediate transfer member at a predetermined peeling position. In an image forming apparatus provided with a conveying means that conveys up to
Recording medium adsorbing means for electrostatically adsorbing the recording medium to the intermediate transfer body until the intermediate transfer body and the recording medium are conveyed from the secondary transfer position to the peeling position ;
The image forming apparatus, wherein the recording medium adsorbing means charges the recording medium with a conductive brush and electrostatically adsorbs the recording medium to the intermediate transfer member. A photoconductor on which a toner image is formed, an intermediate transfer member that receives the transfer of the toner image formed on the photoconductor, and a primary that transfers the toner image formed on the photoconductor to the intermediate transfer member The intermediate transfer body and the recording medium supplied to the secondary transfer position are superimposed with the transfer means and the toner image transferred onto the intermediate transfer body at a predetermined secondary transfer position, A secondary transfer unit that pressurizes and heats the intermediate transfer member and the recording medium sandwiching the toner image; and the recording medium that is pressurized and heated by the secondary transfer unit together with the intermediate transfer member at a predetermined peeling position. In an image forming apparatus provided with a conveying means that conveys up to
  Recording medium adsorbing means for electrostatically adsorbing the recording medium to the intermediate transfer body until the intermediate transfer body and the recording medium are conveyed from the secondary transfer position to the peeling position;
  The image forming apparatus, wherein the recording medium adsorbing means charges the recording medium by a corotron and electrostatically adsorbs the recording medium to the intermediate transfer member.

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