JP3862436B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer that forms an image on an image carrier by electrophotography and transfers the image onto a transfer material to obtain an image.
[0002]
[Prior art]
FIG. 6 is a schematic configuration diagram of a conventional image forming apparatus. In the figure, 1 is an image carrier (amorphous silicon) that forms an electrostatic latent image, and 2 is a primary charge that charges the surface of the image carrier 1. vessel, 3 denotes a laser beam for forming an electrostatic latent image on the image bearing member 1 is irradiated with the image carrier 1, 4 by applying a voltage between the developing sleeves 4a and the image bearing member 1, electrostatic A developing device that develops an electrostatic latent image to form a toner image on the image carrier 1, 10 is a pre-transfer charger that makes the charge amount of the toner image formed on the image carrier 1 uniform, and 8 is an image carrier 1 is a transfer charger for transferring the toner image formed on 1 to the transfer material 9, and 5 and 6 are separation first and second chargers for separating the transfer material 9 from the image carrier 1, and 7 is a separation first charger. 5, a separation claw 11 for separating the transfer material 9 that could not be separated by the second charger 6, an image without being transferred to the transfer material 9 A cleaning device for removing the toner (transfer residual toner) to the bearing member 1 remaining attached.
[0003]
A semiconductor laser 12 emits a laser beam 3 modulated by an image signal. The laser beam 3 is reflected by a rotary polygon mirror 14 and raster scans the image carrier 1 through an imaging lens 16. Reference numeral 17 denotes a reflecting mirror.
[0004]
In the image forming apparatus having the configuration described above, an image is formed by applying an image forming process such as charging, optical image exposure, and development to a photoconductor, transferring the formed image to a transfer material, and fixing the transfer image. Get.
[0005]
In the image forming apparatus as described above, there is a problem that an ozone product due to corona discharge adheres to the image carrier 1 and an electrostatic latent image flows (blurs) due to moisture in the atmosphere.
[0006]
As a countermeasure, a method of polishing and removing the ozone product is often used by sending a large amount of toner to the cleaning device 11 and using the effect of the toner as an abrasive. This can be achieved by actively performing the development process at a timing not contributing to the transfer process and allowing it to flow into the cleaning device 11 as it is.
[0007]
An image in which a toner image is developed on the image carrier 1 with a certain amount and a constant area on the premise that the toner image is not transferred onto paper is referred to as a “black belt” in the present specification. The operation for forming a black belt mode.
[0008]
[Problems to be solved by the invention]
However, in the above configuration, the transfer material 9 can be reliably separated from the image carrier 1 by the separation claw 7, a good paper conveyance without causing a paper jam is obtained, and no image flow occurs. A large amount of toner at the time of forming the black belt adheres to the separation claw 7 and aggregates, and if the amount exceeds a certain amount, the toner falls on the transfer material (hereinafter referred to as “blurring”), and the image on the transfer material is stained. was there. FIG. 7 shows a schematic diagram of the button dropping.
[0009]
The present invention has been made in view of the above problems, and the object of the present invention is to achieve a satisfactory separation from the image carrier using a separation claw and a good image without blackout using a black belt. It is an object of the present invention to provide an image forming apparatus capable of obtaining a good image while obtaining an image, preventing a dropout at the time of a black belt, and not contaminating an image on a transfer material.
[0010]
[Means for Solving the Problems]
A configuration for achieving the object of the invention according to the present application is formed on an image carrier, a first charger for charging the image carrier, and the image carrier charged by the first charger. A developing means for developing the electrostatic latent image with toner, a separation claw for separating the transfer material that has received the transfer of the toner image from the image carrier, from the image carrier, and more than the developing means. A second charging device disposed downstream of the image carrier in the moving direction and upstream of the separation claw in the moving direction of the image carrier and charged to the same polarity as the toner charged by the first charger. An image forming apparatus comprising: a plurality of charging units including a charging unit; and a cleaning unit that is provided on the downstream side in the moving direction of the image carrier with respect to the separation claw and removes toner on the image carrier. Do not transfer the toner image to the transfer material. When executing the mode in which the toner formed as a proposal is supplied to the cleaning means, at least the second charger among the plurality of charging means is operated, and the charging means having a polarity opposite to that of the charged toner is A control unit that does not operate, and a voltage obtained by superimposing an AC voltage on a DC voltage that is a potential between the potential of the image carrier charged by the first charger and the potential of the electrostatic latent image. And a separation claw voltage applying means to be applied to the device .
[0011]
In the above-described configuration, even in the above mode (black belt mode ), toner hardly adheres to the separation claw, and therefore, dripping from the separation claw to the transfer material is extremely reduced. Therefore, while achieving reliable separation from the image carrier using the separation claw, it is possible to obtain a good image that prevents the dropping of the image and does not stain the image on the transfer material, and further does not cause image flow.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. In the figure, 1 is a photosensitive drum (amorphous silicon) as an image carrier for forming an electrostatic latent image, and 2 is a surface of the photosensitive drum 1. A primary charger for charging.
[0014]
A laser beam 3 irradiates the photosensitive drum 1 according to image information to form an electrostatic latent image on the photosensitive drum 1.
[0015]
A developing device 4 applies a voltage between the developing sleeve 4a and the photosensitive drum 1 to generate an electrostatic latent image to form a toner image on the photosensitive drum 1, and 10 denotes a toner formed on the photosensitive drum 1. A pre-transfer charger that makes the charge amount of the image uniform, 8 is a transfer charger that transfers the toner image formed on the photosensitive drum 1 to the transfer material 9, and 5 and 6 are separations that separate the transfer material 9 from the photosensitive drum 1. First and second chargers.
[0016]
Reference numeral 7 denotes a separation claw for separating the transfer material 9 that could not be separated by the separation first charger 5 and the second charger 6, and 13 is a separation claw voltage application device for applying a voltage to the separation claw 7.
[0017]
Reference numeral 11 denotes a cleaning device that removes toner remaining on the photosensitive drum 1. Reference numeral 12 denotes a semiconductor laser that emits a laser beam 3 modulated by an image signal. The laser beam 3 is reflected by a rotating polygon mirror 14. The photosensitive drum 1 is raster scanned through the lens 16. Reference numeral 17 denotes a reflecting mirror.
[0018]
Next, a part of the operation of the image forming apparatus will be described. The photosensitive drum 1 is uniformly charged to +400 V (Vd) as shown in FIG. 2A by the primary charger 2, and +50 V (Vl) as shown in FIG. Electrostatic latent image is formed.
[0019]
Here, Vd is a potential charged by the primary charger 2, and Vl is a potential attenuated by irradiation with the laser beam 3.
[0020]
Then, by applying a DC voltage Vs to the developing sleeve 4a, the electrostatic latent image is reversed and developed with positively charged toner to form a toner image as shown in FIG.
[0021]
By the way, it is ideal that all the toners are positively charged, but there are actually negatively charged toners. The negatively charged toner is developed to a potential portion of + 400V. Then, the charge amount of the toner is made approximately uniform by the pre-transfer charger 10.
[0022]
Then, a negative charge is applied to the back surface of the transfer material 9 by the transfer charger 8, the back surface potential of the transfer material 9 is set to −450 V as shown in FIG. 2D, and the toner image is transferred to the transfer material 9. The
[0023]
Then, the separation chargers 5 and 6 remove unnecessary -charges applied to the back surface of the transfer material 9, so that the potential of the transfer material 9 becomes about 0 V as shown in FIG. The attracting force between the material 9 and the photosensitive drum 1 is weakened, and the transfer material 9 is favorably separated from the photosensitive drum 1, and a desired image can be obtained on the transfer material 9.
[0024]
As shown in FIG. 3, the separation claw 7 is applied with a DC voltage of 175 V superimposed on a rectangular alternating current having an amplitude of 400 V and a frequency of 2.7 kHz by the separation claw voltage application device 13. This is because the potential of the separation claw 7 is set to a potential between Vd and Vl at the position of the separation claw 7 (an intermediate potential between Vd and Vl), and thereby the negative charge attached to the portion of the potential of Vd. The positively charged toner adhering to the Vl potential portion does not adhere to the separation claw 7 due to the force of the electric field.
[0025]
However, since the electric field force was insufficient by itself, a part of the toner blocked by the separation claw 7 adhered to the separation claw 7 and caused a dropout.
[0026]
Therefore, alternating current is superimposed because the electric field strength needs to be increased without changing the direction of the electric field.
[0027]
By superimposing alternating current, the average electric field when viewed in a macro time is not increased, but a strong electric field is applied in a minute time. For this reason, there is an effect that the toner moves faithfully to the electric field, whereby the toner moves to the photosensitive drum 1 and the amount of toner adhering to the separation claw 7 is drastically reduced. No drop occurred.
[0028]
However, since a large amount of toner is supplied to the separation claw 7 at the time of the black belt, the above-described electric force is not sufficient, and therefore, a dropout occurs.
[0029]
Therefore, in order to further increase the above-described electric force and further increase the adhesion force (reflection force) to the photosensitive drum 1, the amount of charge of the black belt toner is increased to improve the dropout. went.
[0030]
In the image forming apparatus according to the present embodiment, there is a relationship as shown in FIG. 4 regarding the charge amount of the black belt toner and the occurrence state of the blur, and the charge amount of the black belt toner is 7 μC / g or more. I think it should be.
[0031]
At this time, the black belt is A4 and has a printing rate of 6%, once every 200 sheets of a document, 20 mm wide × 300 mm long. In this embodiment, in order to set the charge amount of the toner in the black belt to 7 μC / g or more, either or both of the pre-transfer charger 10 and the separation chargers 5 and 6 having the same polarity as the toner in the charging direction. Is operated by a control means (not shown), and the transfer charger 8 having a reverse charging direction is not operated with respect to the black belt.
[0032]
As a result, the toner charge amount is sufficient with respect to the black belt compared to the conventional case where the pre-transfer charger 10, the transfer charger 8, and the separation chargers 5 and 6 are not operated. No longer occurs. FIG. 8 shows a case where the pre-transfer charger (post) 10, the transfer charger 8, the separation chargers 5 and 6 are all operated as a comparative example, and a black belt toner according to the present embodiment. This shows the amount of charge and the occurrence of dripping.
[0033]
According to this, in order to set the charge amount of the toner in the black belt to 7 μC / g or more, the pre-transfer charger 10 having the same polarity as that of the toner without operating the transfer charger 8 having the opposite polarity to that of the toner. Alternatively, it is necessary to operate either or both of the separation chargers 5 and 6, and at that time, almost no dropout occurs. In particular, both the pre-transfer charger 10 and the separation chargers 5 and 6 are operated. When you let it go, the dropout will be further reduced.
[0034]
Here, the configuration of the separation claw 7 will be described.
[0035]
FIG. 5 shows the separation claw 7 and its vicinity. The separation claw 7 is pressed and brought into contact with the photosensitive drum 1 with an appropriate pressure. The separation claw 7 is provided with a separation claw pressurizing spring 7a, thereby obtaining the above-mentioned appropriate pressure. The separation claw pressurizing spring 7a is made of SUS and is a conductive substance. Further, the separation claw pressurizing spring 7a is provided with a conducting wire 7b, which is connected to a separation claw voltage application device 13 (not shown).
[0036]
The separation claw 7 is made of polyamideimide in the present embodiment. This is not limited to this as long as it is a substance that is not easily destroyed by the collision of the transfer material 9 and does not damage the photosensitive drum 1, and may be polyetherimide or the like.
[0037]
The separation nail 7 was carbon coated. This is for securing the conductivity of the surface of the separation claw 7, and any other material may be coated as long as it is a conductive material. Alternatively, a conductive material may be used for the separation claw itself. In any case, it is sufficient that the conductivity of the surface of the separation claw 7 can be ensured to some extent. The surface resistance of the separation claw 7 used in the present embodiment was 20 kΩ.
[0038]
Further, as an adverse effect of applying a voltage to the separation claw 7, there is a problem that an excessive current flows from the separation claw 7 to the photosensitive drum 1 to damage the photosensitive drum 1 and cause an image defect. This is likely to occur when a voltage is applied to the separation claw 7 when the photosensitive drum 1 is stopped. Therefore, it is necessary to apply a voltage to the separation claw 7 only when the photosensitive drum 1 is rotating. Desirably, the voltage is applied only when the toner comes to the separation claw 7. In particular, it is necessary to apply a voltage when the black belt comes to the separation claw 7.
[0039]
Although the present invention can be applied to any toner, in the present embodiment, a one-component magnetic positive toner is used as the toner.
[0040]
The one-component magnetic toner has excellent points such as no need for agent (carrier) exchange and toner scattering, but has a demerit that the toner is difficult to charge and non-uniform. This is due to the lack of electric power due to the inclusion of magnetism and the absence of carriers.
[0041]
When the charging is non-uniform, particularly when the toner is charged with a reverse polarity or when a portion of the toner is charged with a reverse polarity, the opposite polarities have an adsorbing force, so that the toners are likely to adhere to each other and the toner is likely to aggregate. In particular, positive toner tends to be non-uniform.
[0042]
The reason why the positive toner is likely to be non-uniform is that there are few resins that can be used as the binder. Therefore, for the positive toner, a method of embedding a charge control agent in a binder resin is often used. Since the charge control agent is often not uniformly embedded in the binder, there is a tendency that a negatively charged portion or a positively charged portion is present in one toner. Therefore, there is a tendency that the toner is easily aggregated, and the one-component magnetic positive toner easily adheres to the separation claw 7 due to its high aggregating property and easily aggregates, so that the toner drops easily. Further, since the amount of electric charge is low, the effect of the electric field applied to the separation claw 7 is reduced, and in this respect also, the dropout tends to occur. Also in this respect, the present invention is particularly effective when used for a one-component magnetic positive toner.
[0043]
With the above configuration, the charge amount of the toner at the time of the black belt can be set to a certain amount or more, so that the toner hardly adheres to the separation claw 7 and no dropping occurs and the transfer is performed. A good image could be obtained without staining the image on the material.
[0044]
【The invention's effect】
As described above, according to the present invention, in the black belt mode, among the chargers between the developing means and the separation claws, at least one of the chargers having the same polarity as the toner, for example, a pre-transfer charger, Alternatively, the separation charger is operated, and the charger having the opposite polarity to that of the toner, for example, the transfer charger is not operated, so that the charging amount of the black belt toner becomes sufficient, and the reflection power with the image carrier becomes strong, It becomes difficult for the toner to go to the separation claw, and the effect of the voltage obtained by superimposing the DC voltage on the AC voltage applied to the separation claw is increased, and also in this respect, the toner is less likely to go to the separation claw.
[0045]
For this reason, even when the belt is black, toner hardly adheres to the separation claw, and toner hardly drops from the separation claw onto the transfer material.
[0046]
Therefore, an image forming apparatus capable of obtaining a good image that prevents separation of the image on the transfer material and does not cause image flow while achieving reliable separation from the image carrier using the separation claw. It became possible to provide.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.
2A to 2E are schematic views of the surface of a photosensitive drum and the potential of a transfer material in the embodiment of the present invention.
FIG. 3 is a schematic diagram of the surface of the photosensitive drum and the potential of the separation claw at the separation claw position in the embodiment of the present invention.
FIG. 4 is a diagram illustrating a correlation between a charge amount of black belt toner and a dropout.
FIG. 5 is a schematic view near the separation claw in the embodiment of the present invention.
FIG. 6 is a schematic diagram of a conventional image forming apparatus.
FIG. 7 is a schematic diagram of a dropout.
FIG. 8 shows a case where the precharge toner charger 10, the transfer charger 8, and the separation chargers 5 and 6 are all operated as a comparative example, and the toner charge amount in the black belt according to the embodiment. The chart which shows the occurrence situation of a dripping.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 5,6 ... Separation charger 7 ... Separation claw 8 ... Transfer charger 9 ... Transfer material 10 ... Pre-transfer charger 13 ... Separation claw voltage application device

Claims (7)

An image carrier, a first charger for charging the image carrier, and developing means for developing an electrostatic latent image formed on the image carrier charged by the first charger with toner A separation claw for separating the transfer material that has received the transfer of the toner image from the image carrier from the image carrier, the downstream of the developing unit in the moving direction of the image carrier, and the separation. A plurality of charging means including a second charger disposed upstream of the nail in the moving direction of the image carrier and charged to the same polarity as the toner charged by the first charger; An image forming apparatus having a cleaning unit that is provided downstream of the nail in the moving direction of the image carrier and removes toner on the image carrier.
When executing a mode in which toner formed on the assumption that a toner image is not transferred to the transfer material is supplied to the cleaning unit, at least the second charger among the plurality of charging units is operated. A control unit that does not operate a charging unit having a polarity opposite to that of the charged toner;
A separation nail voltage for applying to the separation nail a voltage obtained by superimposing an AC voltage on a DC voltage that is a potential between the potential of the image carrier charged by the first charger and the potential of the electrostatic latent image. And an applying unit . Wherein, in said mode, the second pre-transfer as charger charger or separation charger image forming apparatus according to claim 1, wherein the operating the. The image forming apparatus according to claim 1 or 2, wherein the development is reversal development. The toner used in the developing means, the image forming apparatus according to any one of claims 1 to 3, characterized in that a one-component magnetic positive toner. The separation pawl, the image forming apparatus according to any one of claims 1, characterized in that the material of the surface of the substrate has conductivity 4. The separation claw voltage applying means, an image forming apparatus according to any one of claims 1 and applying the voltage to the separation claw during the movement of the image bearing member 5. The separation claw voltage applying means according to claim 1, characterized in that a voltage is applied to the separation pawl only when the toner carried on the image carrier comes to a position of the separation claw by the movement of said image bearing member 6. The image forming apparatus according to any one of items 5 to 5 .

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