JPH0387878A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of lateral streaks and to obtain high transfer efficiency and high picture quality by making an amount of charge the front edge of a transfer material receives different from that the image forming area of the transfer material receives, and causing a properly set current in the image area of the transfer material. CONSTITUTION:In an amount of transfer charge, which is the value at which the transfer material P or a carry sheet 6a receives transfer currents per unit area, T0 is a rise time to when an amount of transfer charge comes to Q0 at which transfer efficiency stabilizes, QTH is an amount of transfer charge at which lateral streaks occur, and TTH is a rise time to when an amount of transfer charge comes to the QTH. Where X is a distance between the front edge of the transfer material and the front edge of a picture formed on the transfer material, the following condition, X>=(T0-TTH)VP.S, is established. Here, the VP.S is a process speed, that is, the rotating speed of a photosensitive drum. Namely, an amount of charge the front edge of the transfer material P receives is made different from that the image forming area of the transfer material P receives, and the properly set current is caused to flow in the image area of the transfer material. Thus, the occurrence of lateral streaks is eliminated, and high transfer efficiency and high picture quality can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming device such as an electrophotographic device or an electrostatic recording device, and particularly relates to an image forming device such as an electrophotographic device or an electrostatic recording device, and in particular, to a device in which a toner image on an image carrier is carried by a transfer material carrying means. The present invention relates to an image forming apparatus capable of electrostatically transferring images onto a transferred transfer material.

[Conventional technology]

In a color electrophotographic copying machine, a transfer material carrying member, usually a carrier sheet such as a high-resistance film, is wrapped around a drum-shaped frame to form a transfer drum, and the transfer material is supplied to the drum.
The end of the transfer material is mechanically fixed and held by a gripper placed on a part of the circumferential surface of the transfer drum. Then, in the process of rotating the transfer drum multiple times, toner images of multiple colors are electrostatically transferred from an image carrier such as a photoreceptor to the surface of a transfer material by multiple transfer. For this purpose, a corona charging device to which a voltage of polarity opposite to that of the toner image on the image carrier is applied is provided on the surface of the carrier sheet opposite to the image carrier, or a conductive roller is provided. , gives the transfer material an electric charge of opposite polarity to that of the toner image.

After that, AC was applied to separate the transfer material from the carrier sheet.
The electrostatic adsorption force (Coulomb force) generated between the transfer material and the carrier sheet is weakened by static eliminating means such as a corona discharger that applies a superimposed voltage and DC voltage, and the separating claw as a separating means is used. It is placed between the transfer material and the carrier sheet to separate the transfer material.

In addition, in a transfer drum equipped with a gripper that grips the transfer material, when the carrier sheet is formed into a drum shape, the gripper part gets in the way, making it impossible to completely clean the carrier sheet, and only the gripper part gets in the way. , the image forming area on the transfer material is narrowed. There is a drawback that so-called image defects occur in the portion where the transfer material is gripped by the gripper.

Therefore, a corona charger is provided on the opposite side of the transfer material holding surface of the carrier sheet, and a conductive roller is provided opposite the transfer material holding surface to electrostatically charge the transfer material against the carrier sheet. A transfer material holding method in which the transfer material is held by suction (JP-A-55
-32079) has been proposed.

In this case, it becomes possible to hold the transfer material on any part of the carrier sheet.

[Problem that the invention is trying to solve]

However, in the above conventional example, when the leading edge of the transfer material on the transfer drum is located in a part other than the frame of the transfer drum, for example, in the sheet part of the transfer drum, when the transfer current is applied, the position corresponding to the leading edge of the transfer material on the image carrier A charge of the same polarity as the transferred charge is placed on the transfer charge, and it becomes a memory. Such a charged memory on an image bearing member due to transfer may not be completely neutralized by ordinary static eliminating means, for example, if the image bearing member is a photoreceptor, an exposure means that exposes the entire surface of the photoreceptor to light. This was particularly noticeable when the charged polarity of the photoreceptor and the polarity of the transferred charge were opposite polarities. As a result, when the next image is formed on the photoreceptor, there is a problem in that the area becomes streaky and the image becomes defective. Particularly, when the length of the transfer material is longer than the circumference of the image carrier, there is a drawback that streaks occur on the transfer material corresponding to the circumference of the image carrier from the leading edge of the transfer material.

[Purpose of the invention]

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an image forming apparatus in which the charging memory of an image carrier is suppressed.

Another object of the present invention is to provide an image forming apparatus that forms good images by suppressing the charging memory.

[Battle bottom of invention]

In order to achieve the above object, the present invention conveys a transfer material and brings it into contact with an image carrier carrying a toner image, and in order to transfer the toner image on the image carrier to the transfer material, In an image forming apparatus, the image forming apparatus includes a movable transfer material carrying means capable of carrying a transfer material, and a transfer means for transferring a toner image on the image carrier to the transfer material, wherein the transfer material supports the transfer material. The amount of charge per unit area received by the leading edge of the transfer material on the upstream side in the direction of movement of the transfer material when carried by the means is different from the amount of charge per unit area received by the image forming area of the transfer material. It is something.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image bearing member, where the photosensitive member is an organic photoconductor of negative polarity.

The drum 1 is rotated at its center and driven to rotate in the direction of the arrow. A primary charger 2, an optical system 3, a developer supply device 4, and a secondary charger 5 are arranged facing the outer peripheral surface of the photosensitive drum 1 in the rotation direction thereof. The secondary charger 5 may be omitted. - The blower 2 applies a negative uniform charge to the photosensitive drum 1, and the optical system 3 applies a color-separated optical image or a light beam corresponding to this to the surface of the photosensitive drum 1 at a predetermined timing, Forms an electrostatic latent image. This optical system 3 uses a laser beam exposure device or the like. Further, the developer supply device 4 is a movable type that moves in a tangential direction facing the surface of the photosensitive drum 1, and has four types of developer: magenta color developer, cyan color developer, yellow color developer, and black color developer. 4 developers 4M, 4C, 4Y that store color developers separately
It also has 4 BK. The developer supplying device causes a selected developer to face the photosensitive drum l in response to irradiation with a light image of a selected color by the optical system 3 or a light beam corresponding thereto, and supplies electrostatically negative toner. The toner image is reversely developed on a portion of the surface of the photosensitive drum 1 that is irradiated with light by the optical system 3.

Furthermore, the photosensitive drum 1 is located in the rotational direction of the photosensitive drum 1.
A transfer drum 6 faces the surface of the transfer drum 6 in contact with or slightly apart from the surface of the transfer drum 6 . The transfer drum 6 has a carrier sheet 6a wound in a cylindrical shape between two cylindrical end frames, and a transfer corona charger 7 is provided on the opposite side of the holding surface of the carrier sheet 6a facing the photosensitive drum l. is installed. The transfer drum 6 is rotatably driven in the direction of the arrow, and on the upstream side of the transfer position, there is an adsorption corona charger 19 on the opposite side of the holding surface, and a conductive roller opposite the holding surface. 2o
are placed respectively. Further, on the downstream side of the transfer position, there is a corona discharger 10 for removing static electricity from the transfer material. 11 are disposed across the carrier sheet 6a, and the transfer material P(
(to be described later) from the carrier sheet 6a. 13 are disposed with the carrier sheet 6a in between, and a separating claw 14 is disposed in the vicinity thereof.

Furthermore, on the downstream side, there is a brush roller 15 for cleaning toner etc. from the holding surface of the carrier sheet, and if necessary, a corona discharger or a brush type remover for removing adhesion forces (residual Coulomb force and van der Waals force). Electric appliances 1
6 is provided.

Further, the transfer material P on which the toner image is formed and separated by the separation claws 14 is supplied to the fixing roller 8 via the conveyor 17, and the image developed with the toner is fixed onto the transfer material.

Furthermore, on the upstream side of the transfer position, there is a corona charger 19 and a conductive roller 2° with the carrier sheet 1-6a in between, and further upstream, the transfer material P is transferred to the registration roller 2.
1 and 21 into the guide 22 and the carrier sheet 6a
A means for supplying a transfer material to the holding surface is provided.

In the figure, the reference numeral 27 is a static eliminator that removes static charges on the surface of the photosensitive drum l, and the reference numeral 28 is a cleaning blade that removes toner. Furthermore, in the vicinity of the separating claw 14, a corona discharger 2 is installed for the purpose of preventing image distortion due to peeling discharge that occurs when the transfer material P is separated from the supporting sheet 6a.
9 and perform AC corona discharge.

In such a configuration, when the surface of the photosensitive drum I is uniformly charged by the primary charger 2 and a color image that has passed through a green filter is first irradiated thereon by the optical system 3, the color image is Of these, a latent image mainly consisting of magenta components is formed there.

In synchronization with this feeding of the latent image, the developer supply device 4 moves in the tangential direction with respect to the photosensitive drum l, so that the developing device 4M containing the magenta developer faces the photosensitive drum l. , a magenta image is developed on the photosensitive drum 1 by electrostatically flying toner onto the latent image.

On the other hand, the transfer material P is introduced into the guide 22 by the action of the registration rollers 21, 21, and is further supplied to the position of the conductive roller 2o along the surface of the carrier sheet 6a. Here, the transfer material P is electrostatically adsorbed and held on the carrier sheet 6a by the corona charger 19, and is sent to the transfer position with respect to the photosensitive drum 1. In this case, the timing of feeding the registration roller 2321 and the timing of latent image formation by the optical system 3 are synchronized, and the toner image on the photosensitive drum 1 and the transfer material P face each other at the transfer position. At the transfer position, the corona charger 7 for transfer works to generate a transfer electric field, and the toner on the photosensitive drum 1 is held on the transfer material P by the charge applied to the carrier sheet.

The toner remaining on the photosensitive drum 1 is neutralized by the static eliminator 27 and then removed by the blade 2B, and the surface of the photosensitive drum 1 is cleaned. On the other hand, the transfer material P attracted to the carrier sheet 6a moves as the transfer drum 6 rotates while carrying the toner image, and passes between the corona dischargers 10.11; is not energized. Further, the pressing rollers 12, 13 are also separated from the carrier sheet 6a, the brush roller 15 and the corona discharger or brush-type static eliminator 16, and the conductor roller 20 are also separated from the carrier sheet 6a, and the Coulomb force without disturbing the toner image on the supported transfer material P.
It passes between the corona charger 19 and the conductive roller 20 and is sent to the transfer position again. Note that the application of voltage to the corona charger 19 and the contact of the conductive roller 20 to the transfer material P in order to attract the transfer material P to the transfer drum 6 are as follows.
Completed before the leading edge of the toner image on the transfer material P reaches the positions of the corona charger 19 and the conductive roller 20,
When passing through this gap, the charge for adsorption is transferred to the transfer material P.
Not granted to Furthermore, before the leading edge of the toner image reaches the transfer position, image formation with the magenta developer has been completed, and the optical system 3 has already irradiated the photosensitive drum 1 with the color image that has passed through the red filter. and
The developer supply device 4 shifts the developer to the developer 4C.
Since the toner is opposed to the photosensitive drum 1, toner is electrostatically ejected to the latent image, and a cyan image is developed on the photosensitive drum 1. Therefore, at the transfer position, the toner image formed by the cyan color developer on the photosensitive drum 1 is transferred superimposed on the toner image formed by the magenta color developer on the transfer material P.

In this way, the optical system sequentially applies a green filter, a red filter, and a blue filter to form color-separated latent images of the same image multiple times on the photosensitive drum 1.
A developer compatible with this, that is, a magenta color developer,
A cyan developer and a yellow developer are supplied from the developer supply device 4 to the photosensitive drum 1, thereby realizing color development as a whole. It goes without saying that the order of supplying the filter and the developer can be appropriately selected as necessary.

After the final toner development, in this embodiment an image using a yellow color developer, is transferred onto the transfer material P, when the transfer material P passes between the corona dischargers 10 and 11, these are energized. 12. When the static electricity is removed, the pressing roller 12.
13 is pressed against the carrier sheet 6a, increasing the curvature at this portion and helping the transfer material P to be peeled off from the carrier sheet 6a. Further, the separating claw 14 comes into contact with or approaches the carrier sheet 6a, separates the leading edge of the transfer material P from the carrier sheet 6a, and supplies the leading end of the transfer material P to the fixing roller 18 via the conveyor 17, thereby producing a toner image on the transfer material P. to become established. During separation, it is preferable to use a corona discharger 29 to prevent image disturbance due to peeling discharge.

In this way, copying of color images can be realized. Note that the optical system 3 does not use a filter, and the developer supply device 4 uses the developing device 4BK for black color developer on the photosensitive drum 1.
When facing each other, a black and white copy is usually achieved.

In this case, since the transfer is performed only once, there are operations of each component that correspond to the final development in color copying.

Furthermore, if necessary, a black image formed by white exposure and a black developer may be superimposed in the final stage of color development.

By the way, FIG. 2 shows the transfer efficiency of the first color (weight of toner on transfer material/weight of toner on photoreceptor before transfer) when the transfer current I of the first color of the transfer corona discharger is changed. , shows an area where horizontal streaks occur on the transfer material with a length corresponding to the circumferential length of the photoreceptor drum from the leading edge of the transfer material. As the transfer efficiency increases and becomes more stable, horizontal streaks occur, and when the current value is set to a value that does not cause horizontal streaks, the transfer efficiency decreases and becomes unstable.

Therefore, it is sufficient to apply a small transfer current at the leading edge of the transfer material (and a transfer current that stabilizes the transfer efficiency in the other image areas on the transfer material).

The value of the transfer current per unit area of the transfer material or carrier sheet, that is, the amount of transfer charge, has a rise characteristic as shown in FIG. The rise time until the transfer charge amount Q0 at which the transfer efficiency becomes stable is defined as To, and the rise time until the transfer charge amount at which horizontal streaks occur becomes Q TH% Q TH is defined as TTH.

If the distance between the leading edge of the transfer material and the leading edge of the image where an image is formed on the transfer material (non-image area) is X, then X〉(To-TT
H) It can be seen that it is sufficient to satisfy vp and s.

However, v p-s is the process speed, that is, the rotational speed of the photosensitive drum.

In other words, a non-image area where a toner image is not formed is provided at the tip of the single copy, and within that area, the amount of charge that stabilizes the transfer efficiency is determined from the amount of charge that does not cause horizontal streaks on the transfer material facing the corona discharger for transfer. Just raise it.

At this time, it goes without saying that no toner image is formed on the area on the photosensitive drum corresponding to the non-image area at the leading edge of the transfer material.

The horizontal streaks described in this embodiment are particularly likely to occur in a high temperature environment. In a high humidity environment, the transfer material has low resistance, so the transfer current and the static elimination current discharged by the static eliminator 11 interfere with each other. The neutralizing current is an AC current or a DC current with a polarity opposite to that of the transfer current. FIG. 4 shows an example of a timing chart of the transfer current and the neutralization current.

When the leading edge of the transfer material is in the transfer area where the photosensitive drum and the transfer corona discharger face each other, the neutralizing current is ON, and when the image area on the transfer material is in the transfer area, it is OFF. . As a result, the transfer current at the leading edge of the transfer material is weakened, and an appropriate setting current is obtained for the transfer current in the image area.

Another embodiment is shown in FIG. Part or all of the shield plate surrounding the wire electrode of the transfer charger is electrically insulated and connected to a constant voltage power source 300. When the leading edge of the transfer material is located in the transfer area, a voltage of opposite polarity to the transfer current is applied to the shield plate, and when the image area on the transfer material is located in the transfer area, the shield plate is set to O potential. As a result, the transfer current at the leading edge of the transfer material is weakened, and an appropriate setting current is obtained for the transfer current in the image area.

Although the above embodiments have been described using a reversal development method, the present invention is also applicable to regular development in which development is performed using toner having a polarity opposite to that of the photoreceptor.

〔Effect of the invention〕

As explained above, according to the present invention, by varying the amount of charge received by the leading edge of the transfer material and the amount of charge received by the image forming area of the transfer material, an appropriate setting current is set in the image area of the transfer material. No horizontal streaks and high transfer efficiency.
This has the effect of providing high image quality.

[Brief explanation of drawings]

FIG. 1 is a graph for explaining the disconnection relationship showing an embodiment of the image forming apparatus of the present invention, FIG. 3 is an explanatory diagram for explaining the rise time of the amount of transfer charge received by the carrier sheet, and FIG. FIG. 5 is a timing chart applicable to the image forming apparatus of the present invention. FIG. 5 is a sectional view showing another embodiment of the present invention. 1......Photosensitive drum 2...
・・・・・・・・・・・・Charger 3・・・・・・・・・
・・・・・・Scanner 4・・・・・・・・・・・・
...Developer 6...Transfer drum 7...Transfer charger 10... ......Outer static eliminator inner static eliminator separation claw 15°

Claims (3)

[Claims] (1) A movable device capable of carrying the transfer material in order to convey the transfer material and bring it into contact with the image carrier carrying the toner image, and to transfer the toner image on the image carrier to the transfer material. In an image forming apparatus comprising a transfer material carrying means and a transfer means for transferring the toner image on the image carrier to the transfer material, when the transfer material is carried by the transfer material carrying means, the transfer If the amount of charge per unit area received by the leading edge of the transfer material on the upstream side in the material movement direction is different from the amount of charge per unit area received by the image forming area of the transfer material, the amount of charge per unit area received by the image forming area of the transfer material is different. An image forming apparatus characterized by: (2) The image forming apparatus according to claim 1, wherein the device includes a charge eliminating means downstream of the transfer means for eliminating charge from the transfer material when the leading edge of the transfer material carried by the transfer material carrying means passes through the transfer area. Forming device. (3) The transfer means is a corona discharger having a wire electrode and a shield member surrounding the wire electrode, and part or all of the shield member is electrically insulated so that the tip of the transfer material passes through the transfer area. The image forming apparatus according to claim 1, wherein a voltage having a polarity opposite to a discharge current of the wire electrode is applied to the shield member.