JPS59206853A - Transfer device - Google Patents

Abstract

PURPOSE:To eliminate the defective transfer that arises at the rear end of transfer paper by changing the magnitude of the voltage or current to be impressed on a corona discharging means in such a way that the charge quantity of the corona discharge at the rear end of the transfer paper is made smaller than the charge quantity of the corona discharge at the part except the rear end of the transfer paper. CONSTITUTION:A selector switch SW is kept connected to a terminal A in the stage of starting a copying operation and the high output current from a power source 32 for transfer is impressed on a corona wire 30. On the other hand, the switch SW is connected to a terminal B by the signal from a control circuit 33 at the timing at which transfer paper P detaches from guiding plates 6, 6, and the low output current from a power source 31 for transfer is impressed on the wire 30. More specifically, the current impressed on the wire 30 in accordance with the rear end of the paper P and the part except the rear end thereof is controlled, by which the charge quantity of the corona discharge applied on the rear end of the paper P is made smaller than the charge quantity of the corona discharge applied on the part except the rear end. As a result, the charge quantity applied over the entire surface of the paper p is consequently maintained at the charge quantity enough to obtain satisfactorily stable transfer efficiency and the charge density on the paper P is made uniform over the entire surface of the paper P.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image forming apparatus such as a copying machine and a printer that applies electrophotography, in which an image of a document formed on an image carrier is transferred to a transfer paper. The present invention relates to a transfer device.

BACKGROUND TECHNOLOGY In general, in image forming apparatuses that apply electrophotography, an electrostatic latent image formed on an image bearing member such as a photoreceptor drum is converted into a toner image, and then transferred by a transfer paper guide member such as a timing roller or a guide plate. There is a step of transferring this toner image onto a transfer paper guided and conveyed to a transfer position. For this transfer, a corona discharge transfer device is widely used which applies a charge of opposite polarity to the toner to the back surface of the transfer paper by corona discharge.

By the way, at high temperature and high humidity, the resistance of the transfer paper itself is low F, so the charge applied to the transfer paper moves more easily than at room temperature and humidity, and corona discharge (transfer due to H) occurs. Charge flows through the transfer paper to a conductive member such as a guide plate, and the amount of charge required for transfer is obtained, which is lλ.For this reason,
Transfer efficiency deteriorates and transfer defects occur.

By the way, as shown in Fig. 1, transfer efficiency generally depends on the amount of charge applied to the transfer paper by corona discharge, and is determined by the amount of charge that provides the maximum transfer efficiency (indicated by transfer efficiency l in Fig. 1). I know it exists.

For this reason, in order to prevent transfer defects due to insufficient charge as described above, conventionally, a charge amount greater than the charge amount that provides the maximum transfer efficiency at room temperature and humidity is applied to the transfer paper. The idea was to compensate for the lack of electrical charge and improve transfer efficiency at high temperatures. However, by increasing the amount of charge generated by corona discharge in this way, it is possible to improve transfer efficiency at high temperature and high humidity, but at room temperature and humidity,
Transfer defects started to occur at the trailing edge of the transfer paper.

Specifically, for example, when copying a solid black original, a linear white spot appeared at the trailing edge of the transfer paper.

The inventor of the present invention investigated the cause of this transfer failure and found that it was caused by the following causes.

The cause of this will be explained in detail. First, as shown in FIG.
The distance fdl between the surface of the transfer paper (PI) and the surface of the photoreceptor drum (2) is kept almost constant, and an almost constant air layer is formed between the transfer paper (PI surface) and the surface of the photoreceptor drum (2). It goes without saying that a layer of toner is present in this air layer during transfer.) In other words, the transfer power supply (
Due to the corona discharge of the transfer charger (5) connected to the photoreceptor drum (2), as described above, a charge amount larger than the charge amount that provides the maximum transfer efficiency at room temperature and normal humidity is applied.
) The force that tries to electrostatically attract the surface of the transfer paper (P
Acts on i. However, since the transfer paper (Pi) is held between the timing roller pair (1) and is also sucked by the suction conveyance unit (3), the transfer paper FPI is conveyed under tension and is balanced with the electrostatic adsorption force. A tension force is applied to the transfer paper (Pl. As a result, the distance fd+ is kept approximately constant between the transfer paper fPl and the surface of the photoreceptor drum (2). Therefore, the transfer power supply (4) ), if the output of the transfer paper fPl is constant, the timing roller pair (1)
The amount of charge applied to the transfer paper FPI is maintained at a sufficient amount to obtain good transfer efficiency while passing through the transfer position (1) while being held between the transfer paper The charge densities of are almost the same.

The amount of charge at this time is assumed to be (σ1). (See Figure 1) On the other hand, when the rear end of the transfer paper (I) 1 completely passes through the timing roller pair (1) and leaves the guide plate (6), the tension on the transfer paper fPl disappears and the rear end of the transfer paper (I) The end portion is electrostatically attracted to the surface of the photoreceptor drum (2) as shown in FIG. 2). Figure 2 (bl shows the state in which the rear end of the transfer paper fPl is most strongly attracted to the surface of the photoreceptor drum (2), but as shown in the figure, the distance tdl becomes smaller and the transfer The air layer between the paper fPl and the photosensitive drum (2) decreases. As a result, the amount of charge applied to the transfer paper fPl increases. The amount of charge at this time is defined as (σ2). (See Figure 1) From the above, even if the output of the transfer power source (4) is constant, the amount of charge (σ2
) becomes larger than the amount of charge (σI) applied to the portion other than the trailing edge, and the charge density on the transfer paper fPl becomes non-uniform. Therefore, referring to FIG. 1, the transfer efficiency at the rear end of the transfer paper + Pl is worse than the transfer efficiency at the other parts. For this reason, a phenomenon such as the above-mentioned "white spots" occurred.

Purpose of the Invention The purpose of the present invention is to eliminate the above-mentioned inconvenience, that is, the transfer failure that occurs at the trailing edge of the transfer paper. Another object of the present invention is to provide a transfer device capable of applying a corona discharge type weight such that stable transfer efficiency can be obtained over the entire surface of the transfer paper even under high temperature and high humidity.

Summary The present invention, which achieves the above object, provides a transfer device according to the present invention, which includes a corona discharge means for applying an electric charge to the transfer paper by corona discharge at the transfer position, and a voltage or current for corona discharge to the corona discharge means. 111 electric power supply means for applying the electric power, and the electric power according to 111 so that the amount of corona discharged wax charge at the rear end of the transfer paper is smaller than the amount of corona discharge charge at the portion other than the rear end of the transfer paper. A control means for changing the above-mentioned voltage or current of the supply means is provided to uniformize the amount of charge applied to the transfer paper for transfer.

Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 shows an image forming apparatus to which the present invention is applied, that is, a part of a printer consisting of a known powder image transfer type electrophotographic apparatus,
This is a cross-sectional view of a reader printer capable of positive-positive and negative-positive copying.

In the figure, (15) is a carrier that holds the microfilm flat and has a stand +18) J- that is movable.
The positive image of the microfilm is illuminated by a lamp (7), and at one time the reader passes through a first scanning mirror (8), a swinging mirror (9), a fixed mirror (10), and then a screen (11).
) is projected onto the first line. On the other hand, the printer temporarily retreats to the position indicated by the broken line (9'), and the first scanning mirror (8) and the second scanning mirror (t12) that can move integrally therewith are moved. Once the dashed line (8') and (12
'), and from this position both scanning mirrors (8), (1, 2+ are dashed lines (8"), (+2
”) By integrally serving the position indicated by
The film image projected onto the photosensitive drum (2) l- is scanned in a slit-like manner through a second scanning mirror (I2), a fixed mirror (13), and a slit (14).

On the other hand, as mentioned in -4-, part of the printer consists of a powder image transfer type photocopying device, and a DC scorotron type charger (16) is installed around the photosensitive drum (2).
, the aforementioned slit (14), a developing device (17), a transfer charger (5), a separation charger (19), and a cleaning device are arranged in order along the rotational direction of the photosensitive drum (2).

(21) is a paper feed cassette that stores copy paper of a predetermined size.It is installed from the side of the reader printer body so that it can be set in either horizontal or vertical orientation. (The transfer paper is stored in 21+ (Po), the roller pair (23) is
, transfer position M('I''l) via timing roller pair (1)
supplied to As a sheet feeding means other than the first one, a path from the manual sheet feeding port (25) to the pair of rollers (23) and the pair of timing rollers (1) via the pair of feed rollers is also prepared.

(27) is a fixing device, which discharges the transfer paper after the transfer process to the outside of the fixing machine.

A transfer paper conveyance system including a pair of rollers (1), a pair of timing rollers (1), and the like is driven directly or indirectly together with a photosensitive drum (2) by a main motor (not shown).

The developing device surface is of a type in which a magnet roller (27') and a developing sleeve (28) are rotated together, and a predetermined developing bias is applied to this developing sleeve (28).

The following is the configuration of a reader printer to which the present invention is applied.Next, an embodiment of the present invention in this reader printer will be described based on FIG. In the figure, the transfer charger (5) is shown in Figure 2 (al, (bl)
The configuration is exactly the same as shown in . However, this transfer charger (5) is controlled so that the current applied to the corona wire (30) is switched depending on the rear end and the portion other than the rear end of the transfer paper fPl. , the changeover switch (SW)
It has a control circuit (33) for controlling switching of SW).

The output current of the transfer power source (31) is set smaller than the output current of the transfer power source (32). Moreover, the output current of the transfer power source (32) is stable even under high temperature and high humidity conditions.
It is set to a value that allows a corona discharge charge amount sufficient to obtain good transfer efficiency, that is, a charge amount larger than the charge amount that provides the maximum transfer efficiency at normal temperature and normal humidity, to be applied to the transfer paper fil. Note that the outputs of the transfer power supplies (31) and (32) may be switched and controlled by the changeover switch (SW).

Here, at the start of copying operation, selector switch (SW) is pressed.
is connected to terminal fAI, and corona wire (30)
A high output current from a transfer power source (32) is applied to the transfer power source (32).

On the other hand, at the timing when the transfer paper fPl leaves the guide plates (6), (6), the changeover switch (SW) is connected to the terminal by a signal from the control circuit (33), and the corona wire (30) is connected to the transfer terminal. A low output current of the power supply (31) is applied.

10- That is, the current applied to the corona wire (30) is controlled corresponding to the rear end of the transfer paper tP1 and a portion other than the rear end, and the corona applied to the rear end of the transfer paper (I) is controlled. The amount of discharge charge is smaller than the amount of corona discharge charge applied to the portion other than the rear end portion. As a result, the amount of charge applied to the entire surface of the transfer paper (Pi) is maintained at a sufficient amount of charge to obtain good and stable transfer efficiency, and the charge density on the transfer paper fPl is maintained over the entire surface of the transfer paper fP1. It is evened out.

The present inventor sets the output current of the transfer power source (31) to lOO
~200 μA, and the transfer power source (32
) was set to 400μA and the transferability was investigated. As a result, the transfer failure of the transfer paper fPl was resolved, and the transfer paper fPl
A good transferred image was obtained over the entire surface. It goes without saying that the output current value needs to be set appropriately depending on the image forming apparatus such as a reader printer to be used.

In the above embodiment, two transfer power sources (31) are used.
, (32), but it is also possible to control the amount of corona discharge charge using a transfer power source of variable output voltage or output current type and a control circuit that controls the output voltage or output current. good. Further, it goes without saying that the present invention is widely applicable to image forming apparatuses applying electrophotography.

Effects As is clear from the above explanation, the voltage applied to the corona discharge means is applied so that the amount of corona discharge charge at the rear end of the transfer paper is smaller than the amount of corona discharge charge at the portion other than the rear end of the transfer paper. Or, by changing the magnitude of the current and making the amount of charge on the transfer paper uniform for transfer, it is stable over the entire surface of the transfer paper, not only at normal environmental temperature and humidity, but also at high temperatures. A high transfer efficiency can be obtained, and the conventional problem of poor transfer occurring at the trailing edge of the transfer paper can be completely solved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between transfer efficiency and the amount of charge on transfer paper due to corona discharge, Fig. 2 fat and fbl are cross-sectional views of a conventional transfer device to explain disadvantages in the transfer device, and Fig. 3 4 is a schematic cross-sectional view of an IJ-printer to which the present invention is applied, and FIG. 4 is a cross-sectional view of a transfer device that is an embodiment of the present invention. (1)...Timing roller (2)...Photosensitive drum (5)...Transfer charger (6)...
Guide plate (31>, (32)...transfer power source
(33)...Control circuit fPl...Transfer paper
(SW) ... Changeover switch mountain ... Transfer position Applicant: Minolta Camera Co., Ltd. 13- Fig. 1 Fig. 2 (0) Fig. 2 (b) Sign open ■ 9-206853 (5) ) 2′)□

Claims (1)

[Claims] 1. In a transfer device for transferring an image of a document formed on an image carrier onto a transfer paper guided and conveyed to a transfer position by a transfer paper guide member, electric charge is generated on the transfer paper at the transfer position by corona discharge. a corona discharge means for applying a voltage or current for corona discharge to the corona discharge means; and a power supply means for applying a voltage or current for corona discharge to the corona discharge means; control means for changing the magnitude of the voltage or current of the power supply means so as to make the amount of charge for transfer applied to the transfer paper uniform, A transcription device characterized by: