JPH02189565A - Method and device for electrophotographic image formation - Google Patents

Abstract

PURPOSE:To eliminate a potential attenuation part due to a leak of charges and to prevent a black spot from being formed by lowering a surface potential which has a 1st potential to a 2nd potential. CONSTITUTION:The surface potential of the surface of an electro-static latent image carrier 1 which is charged electrostatically to the 1st potential is lowered to the 2nd potential and a negative electrostatic latent image is formed and developed reversely. Either of a corotron charger and a scorotron charger is usable as a 1st charger 2 for the charging to the 1st potential. A scorotron charger is usable as a 2nd charger 3 which supplies charges having the opposite polarity from the 1st potential to lower the surface potential to the 2nd potential, an alternating voltage or a voltage having the opposite polarity from the 1st potential is applied to its charger wire, and a voltage which is nearly equal to the 2nd potential is applied to its grid. Consequently, the partial attenuation of the potential is eliminated and toner which is charged electrostatically to the same polarity with the surface potential never sticks on a background part in spots, so that the potential itself becomes stable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electrophotographic image forming method and an electrophotographic image forming apparatus using a reversal development method.

Conventional technology and its challenges In general, laser beams and LEDs are used as print heads.
In the electrophotographic process using , a latent image is formed as a negative image, so development is done by a reversal development method.

In this electrophotographic process, as shown in FIG. 9, a photoreceptor having a surface potential (Vo) is exposed to light using the print head to form a negative electrostatic latent image, which is then developed. 2 while applying a developing bias of potential (Vb) to the device.
Reversal development is performed using a component developer or other developer, and as a result, toner (T) adheres to the portions from which static electricity has been removed by image exposure, forming an image.

In this electrophotographic process, semiconductor lasers and LEDs have recently been increasingly used as laser beams, and laminated organic photoreceptors that are sensitive to semiconductor lasers and LEDs are mainly used as photoreceptors.

However, depending on the photoreceptor, minute black spots may occur in the background area of the image due to adhesion of excess toner. The reason for this is thought to be that electric field caused by surface charges causes partial charge injection from the conductive substrate portion of the photoreceptor, which causes minute unevenness in the surface potential of the photoreceptor. FIG. 5 schematically shows the surface potential distribution of the photoreceptor. Potential unevenness appears as partial potential attenuation, but the amount of attenuation is not very large, and the potential of the developing bias (V
It is presumed that the attenuation occurs only up to a point higher than b). However, because the change in surface potential is rapid, the edge effect is strong, toner adheres during development, and appears as black spots in the background.

Conventionally, as a countermeasure against this type of phenomenon, the main approach has been to improve the composition of the photoreceptor. For example, there is a technique described in Japanese Patent Application No. 61-263488 filed by the present applicant. However, the actual situation is that improving the composition of the photoreceptor leads to an increase in the cost of the photoreceptor itself, and is not necessarily a complete countermeasure at present.

Therefore, an object of the present invention is to prevent the occurrence of black spots in the background area of an image due to charge leakage in an electrophotographic process using a reversal development method, and to stabilize the surface potential during image exposure so that lines in the image area can be reduced. The aim is to stabilize the thickness and density.

Means and Effects for Solving the Problems In order to solve the above problems, the present invention changes the surface potential of the electrostatic latent image carrier surface charged to the first potential (Vol) to a second potential as shown in FIG. 4a. The potential is lowered to (Vo2), a negative electrostatic latent image is formed, and reversal development is performed. in this case,
The first and second potential difference (Vo 1-Vo2) is the potential (Vo
l) It is preferably approximately equal to or larger than the amount of potential attenuation caused by charge leakage on the surface, so that partial attenuation of the potential is eliminated and the toner charged to the same polarity as the surface potential is removed from the background. There will be no spots attached to the area, and the potential itself will be stabilized.

As the first charger for charging to the first potential, either a corotron tube charger or a scorotron charger can be used. A scorotron charger can be used as a second charger that lowers the surface potential to a second potential by applying a charge with a polarity opposite to that of the first potential. 1
A voltage having a polarity opposite to the potential of is applied, and a voltage approximately equal to the second potential is applied to the grid. When applying an alternating voltage to the charge wire of this second charger, the power supply can be shared with the power supply of the paper separation charger, and when applying a DC voltage, the power supply can be shared with the power supply of the transfer charger. Can be shared. Further, the power source for applying voltage to the grid of the second charger can be shared with the power source for the developing bias. Furthermore, the first and second
When a scorotron charger is used as a charger for both, voltages corresponding to the first potential and the second potential may be applied to both grids.

Example [First Example, see Figures 10 and 3] In Figure 1, the photosensitive drum 0) is a well-known type having a photoconductive layer on its outer peripheral surface, and rotates in the direction of arrow (a). It can be driven, and the next imaging element is arranged around it along the direction of rotation.

Charger (2): This applies a charge of a predetermined potential to the surface of the photoreceptor drum (1), and the power supply (23) is connected to the charge wire (22) (see Figure 2) # Scorotron・Charger (3): Photosensitive drum (1)
This is to stabilize the surface potential of the charge wire (
31) is connected to the power supply (33), and the grid (34)
A 'rjL source (35) is connected to the 'rjL source (35). charge·
A voltage with a polarity opposite to that of the charger (2) is applied from the power source (33) to the wire (31), and the grid (3
4> is supplied with a surface potential (V
A voltage of a potential (Vo2) lower than ol) is applied.

Print head <4): LEDs are arranged in a row, and each LED is turned on and off by an image signal output from a drive circuit (not shown). LE of the part corresponding to the image part
When D is turned on, the surface potential of the photoreceptor drum (1) is lowered at the turned-on portion, forming a negative electrostatic latent image.

Developing device (5): developer conveyance means and development! This is a well-known magnetic brush type device equipped with a developing sleeve (51) that functions as a pole. The developing sleeve (51) has a built-in magnet roller (52) as shown in FIG.
), and is connected to a power source (53) for applying a developing bias. The developer is made of a mixture of a magnetic carrier and an insulating toner, and due to mutual frictional electrification, the toner is charged to the same polarity as the charger (2), and the carrier is charged to the opposite polarity. The developing sleeve (51) is connected to the scorotron from the power source (53).
A developing bias having the same polarity as the voltage applied to the grid (34) of the charger (3) is applied.

Transfer charger (6): applies an electric field to the copy paper passing in close contact with the lower part of the photoreceptor drum ( ), and transfers the toner image formed by the developing device (5) onto the copy paper. It is. A voltage having a polarity opposite to that of the insulating toner is applied to the charge wire from a power source (not shown).

Separation charger (7): A transfer charger (6) is used to separate the copy paper after transfer from the surface of the photoreceptor drum (1).
This eliminates the electric charge applied to the copy paper. An alternating voltage is applied to the charge wire from a power source (not shown).

Cleaning device (8) Clean the photoreceptor drum (
1) Remove the toner remaining on the surface.

Eraser lamp (9): Photoreceptor drum (1) with light irradiation
Erases the charge remaining on the surface of the

On the other hand, copy paper is stored in an automatic paper feed cassette (11), and is fed one by one from the top layer based on the rotation of a paper feed roller (10), and is fed at a predetermined timing by a timing roller (12). is sent to the transcription section in synchronization with After the transfer, the toner image is sent to the fixing device (14) by a conveyor belt (13) equipped with an air suction means (not shown), where the toner image is completely fixed, and then transferred onto the paper output tray (15). It can be drained completely.

Here, specific conditions for each charger, etc. in this example will be shown.

Photoreceptor: Laminated organic photoreceptor system Speed: 85mm/sec Charger (corotron) (2): Power supply (23
) Negative polarity, -5,8kV Scorotron φ charger (3): Power supply (33) Positive polarity, +6. OkV grid (34
): Power source (35) negative polarity, -600V Mesh pitch 0.75mm Distance to photoreceptor 1.0mm Developing bias: Source (53) negative polarity, -450V Transfer charger (6): positive polarity, +6. OkV separate charger (7): ±5.7kV (RMS), 40
0Hz toner: The image forming process under conditions of negative polarity or higher is performed using a scorotron.
The process is similar to the conventional electrophotographic image forming process except that the charger (3>) adjusts (lowers) the initial surface potential.

Therefore, each charge unique to this embodiment ~ (2), (3)
The surface potential formed by this will be explained. When the scorotron charger (3) was turned off and the charging potential due to only the charger (2) was measured, it was -5oov. That is, immediately before being recharged by the scorotron charger (3), the surface potential (Vol) of the photoreceptor is approximately -80
It has become 0■. On the other hand, when the charging potential was measured with both the electrification charger (2) and the scorotron charger (3) operating, it was approximately -600V.

This value is approximately the same as the grid applied voltage (Vg). That is, the surface potential was lowered from about -50 V to about -600 V by Scorotron Charge (3).

In fact, when we conducted an image formation experiment under the above conditions, we were able to obtain a beautiful image with no black spots in the background (white background).

On the other hand, as a comparative experiment (2), when an image was formed using the apparatus of this example without operating the scorotron charger (3), black spots were observed in the background (white background).

Next, we thought that the result of the comparative experiment (2) may be due to the surface potential of the non-image area being 1,800 V, which is higher than the 1,600 V of the example, so we decided to charge it without operating the Scorotron charger (3). The voltage of charger (2) is -5,
Comparative experiment (2) was conducted by lowering the voltage to 5 kV and setting the surface potential to -600 V. As a result, even under these conditions, black spots were observed in the background (white area).

The difference between the comparative experiment ① and this example is presumed to be as follows.

In comparative experiment (■), when a potential of -600V was applied to the photoreceptor, a slight attenuation of the potential occurred as shown in Figure 5, and negatively charged toner adhered to this attenuated portion, leading to black spots. There is.

On the other hand, in this embodiment, immediately after being charged to a potential (Vol) of -800V by the charger (2), a slight attenuation of the potential occurs as shown in FIG. 4a. This is also clear from the results of the comparative experiment (2). Next, in this example, the primary surface potential of -5oov is lowered to around the grid voltage (-600V) by the scorotron charger (3).
As shown in figure b, the surface potential, which has been slightly attenuated, becomes uniform, and as a result, toner fogging on the background area is prevented.Furthermore, the potential is stabilized, so the thickness of the line in the image area The concentration seems to have stabilized.

In order to confirm the above speculation, an experiment was conducted by changing the grid voltage (Vg) of the scorotron charger (3), and the results shown in Table 1 below were obtained.

In Table 1, when the grid voltage (Vg) was set to -750■, some black spots were observed because the grid voltage (Vg) was
When the second potential (Vo2) approaches the first potential (Vol) by the band 1 charger (2) by setting Vg) high, the amount of attenuation is relatively small among the minute potential attenuations. It seems that only the material could be smoothed out evenly, and some black spots appeared.

[Second Embodiment, See Figure 6] In this second embodiment, a scorotron charger (2°) having a grid (24) is used as the first charger in place of the electrification charger (2). A negative voltage is applied to the grid (24) from the power source (25).

In the second embodiment, an image formation experiment was conducted by changing the grid voltage (Vgl) of the first scorotron charger (2゛) and the grid voltage (Vg2) of the second scorotron charger (3). Ta. The results are shown in Table 2 below. Note that other conditions are the same as in the first embodiment.

[Table 2 with blank spaces below] As is clear from Table 2, in this second embodiment, IV
g21 < lVgl I, preferably lvg21
By setting the condition of +100<lVgl, the surface potential can be stabilized and generation of minute black spots in the background area (white background area) can be prevented.

In addition, in this second embodiment, the grid type of the scorotron charger (3)! (negative polarity) and the developing device (
A single power source (36) was used in common with the developing bias 'w power source (negative polarity) of 5). The difference in potential value between the two is the source (3
It is corrected by the voltage dividing resistor in 6). Furthermore, a single electric current m (37) was used as the power source (positive polarity) for the charge wire of the scorotron charger (3) and the power source (positive polarity) for the charge wire of the transfer charger (6).

With the above configuration, the configuration of the power supply section can be simplified, and space and cost reductions can be achieved.

[Third Embodiment, see Figure 7] In this third embodiment, a scorotron charger (
3) Charge wire (31) to power supply (38)
Apply alternating voltage from Specific figures are shown below. Note that the other configurations and conditions are the same as in the first embodiment.

Electrostatic charge-v (2): Power supply (23) negative polarity, -5.8kV Immediate surface potential (Vol) -800V Suflotron charger (3): Electricity m (38) AC±5.5kV (RMS), 400
Hz grid (34): Power supply (35> Negative polarity, -600V Immediate surface potential (Vo2) -600V When image formation was performed under these conditions, minute black spots appeared in the background area (white background area) No occurrence was observed.

[Fourth embodiment, see Figure 8] In the fourth embodiment, an alternating voltage is applied from voltage #1 (39) to the charge wire 31) of the scorotron charger (3) that functions as the second charger. did.

In addition, a Scorotron charger (2) shown in FIG. 6 was used as the first charger.

Specific figures are shown below. Note that other conditions are the same as in the first embodiment.

Scorotron charge y (2'): Power supply (23) negative polarity, -5,8kV Grid voltage Negative polarity, -850V Immediate surface potential (Vol) -850V Scorotron charger (3): Power supply (39) AC± 5.5kV (RMS), 400
) (z grid voltage negative polarity, -600V Immediate surface potential (vo2) -600V When image formation was performed under these conditions, no minute black spots were observed in the background (white background).

In addition, in the fourth embodiment, the charge wire power source (AC) of the scorotron charger (3) and the charge wire type fi (AC) of the separate charger (7) are used.
and are shared by one fi-fi (39). thing.

Accordingly, the configuration of the power supply section can be simplified, and space and cost can be reduced.

[Other Embodiments] The electrophotographic image forming method and apparatus according to the present invention are not limited to the above embodiments, and can be modified in various ways within the scope of the invention.

In particular, the polarities of the chargers and toner may all be reversed, and it goes without saying that the voltage values and the like are merely examples.

As is clear from the above description, according to the present invention, the surface potential having the first potential applied by the first charger is changed from the first potential by the second charger. Since the potential is lowered to a lower second potential, the potential attenuation portion due to charge leakage that existed in the first potential portion is erased, and the occurrence of black spots on the background area due to toner adhesion is eliminated. Since the electrostatic latent image is formed after the prevention is completed and the surface potential is stabilized in the second charger, the line thickness and density of the image area are stabilized. Furthermore, by sharing the power supply of the charger with the power supply of other elements, the t:fi section can be simplified.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing the first embodiment of the present invention, FIGS. 2 and 3 are configuration diagrams including the main power supply circuit, and FIGS. 4a and 4b are diagrams showing the surface potential of the photoreceptor. , FIG. 5 is a diagram showing partial attenuation of the potential. FIG. 6 is a configuration diagram including the main power supply circuit of the second embodiment of the present invention, and FIG. 7 is a configuration diagram of the third embodiment of the present invention.
FIG. 8 is a block diagram including the power supply circuit of the main part of the fourth embodiment of the present invention. FIG. 9 is a diagram showing the surface potential and toner adhesion state during image formation by this type of electrophotographic process. (1)... Photosensitive drum, (2>... Charger, (2')... Scorotron charger, (23
)...DC power supply, (3)...Scorotron charger, (31)...Charge wire, (33)...
・DC power supply, (34)...grid, (35)...
Direct i power supply, (36)...AC power supply, (37)...DC power supply, (3B), (39)...AC power supply, (4)
...Print head, (5)...Developing device, 51
)...Developing sleeve. (6)...Transfer charger, (7)...Separation charger.

Claims (1)

[Claims] 1. A step of charging the surface of the electrostatic latent image carrier to a first potential;
a step of lowering the potential to a second potential lower than the potential of the electrostatic latent image carrier; a step of removing static electricity from the surface potential of the electrostatic latent image carrier having the second potential according to image information to form an electrostatic latent image; 1. An electrophotographic image forming method comprising the steps of: developing the electrostatic latent image using toner charged to the same polarity as the second potential. 2. An electrostatic latent image carrier that rotates in one direction; a first charger that charges the surface of the electrostatic latent image carrier to a first potential; and a first charger that charges the surface of the electrostatic latent image carrier that has the first potential. a second charger that applies a charge of opposite polarity to the first potential to lower the surface potential thereof to a second potential lower than the first potential; and an electrostatic latent image carrier having the second potential. a latent image forming means for forming an electrostatic latent image by eliminating surface potential according to image information; and a developer for developing the electrostatic latent image using toner charged to the same polarity as the first and second potentials. An electrophotographic image forming apparatus comprising: means. 3. The electrophotographic image forming apparatus according to claim 2, wherein the second charger is a scorotron charger, and an alternating voltage is applied to a charge wire of the second charger, and
An electrophotographic image forming apparatus characterized in that a voltage substantially equal to the second potential is applied to the grid. 4. The electrophotographic image forming apparatus according to claim 3, further comprising a power source for applying an alternating voltage to the charge wire of the scorotron charger, and a separation charger for separating the paper from the surface of the electrostatic latent image carrier during toner transfer. An electrophotographic image forming apparatus characterized in that it shares a power source for applying an alternating voltage. 5. The electrophotographic image forming apparatus according to claim 2, wherein the second charger is a scorotron charger, and a voltage having a polarity opposite to the first potential is applied to the charge wire, and a voltage having a polarity opposite to the first potential is applied to the charge wire. An electrophotographic image forming apparatus characterized in that a voltage substantially equal to the second potential is applied. 6. The electrophotographic image forming apparatus according to claim 5, wherein a power source for applying voltage to the charge wire of the scorotron charger and a power source for applying voltage to the transfer charger are shared. Forming device. 7. The electrophotographic image forming apparatus according to claim 2, wherein the second charger is a scorotron charger, and includes a power source for applying voltage to the grid thereof, and a power source for developing bias to be applied to the developing electrode of the developing means. An electrophotographic image forming apparatus characterized by sharing the following. 8. The electrophotographic image forming apparatus according to claim 2, wherein the first and second chargers are both scorotron chargers, and a voltage of a predetermined polarity is applied to the charge wire of the first scorotron charger. A voltage of a first potential with a predetermined polarity is applied to the grid, and a voltage of a second potential is applied to the grid.
An electrophotographic image forming apparatus characterized in that an alternating voltage or a voltage with a polarity opposite to the predetermined polarity is applied to the charge wire of the scorotron charger, and a voltage substantially equal to the second potential is applied to the grid. .