JPS603187B2 - Electrophotographic method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel electrophotographic method and apparatus, and more particularly to an electrophotographic method and apparatus that can satisfactorily reproduce the tonality of an original image.

Conventionally, the Carlson method has been known as a basic electrophotographic method.

In this method, an electrophotographic photoreceptor having a photoconductive layer of amorphous selenium or the like provided on the surface of a conductive substrate is used, and the surface is uniformly charged in a room, and then the original image is exposed. In this way, the surface charge of the photoreceptor in the light irradiation area is discharged to form an electrostatic latent image. It is well known that this static latent image is developed with toner particles and transferred to a transfer material or the like for use. Generally, the brightness reproduction range for originals using the Carlson method is about 0.6 to 0.8, for example, for amorphous documents. The relationship between the latent image potential and the document density when selenium is used is as shown by the solid line in FIG.

As shown in FIG. 2, the actual situation is that the copy density cannot be perfectly reproduced with respect to the original density. As another method of electrophotography, the present applicant has previously developed Hakama Koukai 42
There are methods such as those disclosed in Publication No. 2391 and Samurai Publication No. 43-24748.

The electrophotographic method will be explained in FIG. 3. In each figure in the column indicated by symbol '1', the charge change of the photoreceptor is schematically shown, and in each figure in the column indicated by symbol '21, , the change in the charge density on the surface of the photoreceptor is schematically shown in each figure of the column indicated by the symbol '3}. That is, the photoreceptor 1 basically has a conductive substrate 1, a light guide box layer 12, and a (transparent) insulation sheet 13, and in the first step,
If the photoconductive layer 12 is of N type, primary charging is performed to uniformly charge the surface of the photoreceptor to positive (10), and if it is P type, negative (1). Next, in the 0th step, the original optical image (
In the figure, an original optical image that changes linearly (density) is exposed, and at the same time, primary charging and reverse polarity corona or AC corona discharge are applied to lower the surface potential while changing the charge density according to the original optical image. At the same time as the photoimage exposure, reverse noisy charging or static electricity removal is carried out. In the m-th step, the entire surface of the photoreceptor is exposed uniformly to release the charge near the interface between the photoconductive layer and the insulating layer, which corresponds to the dark part of the original optical image, to reveal a high-contrast surface potential. implement. Then, the electrostatic latent image formed in this manner is subjected to development, transfer and fixing steps to obtain a copy, as in the case of the above-mentioned method. The relationship between the latent image potential and the original density in this case is also as shown by the dashed line in FIG.

Reproduced copies made by electrophotography as described above are
It was sufficiently satisfactory for office purposes and other purposes. However, this method does not faithfully reproduce original documents containing a wide range of grays and shades of the original, and therefore cannot be applied to precision printing or fine art printing that requires faithful reproduction of the original. That is, for conventional xerography, the light gray of the original became lighter on the copy, while the dark gray of the original became darker on the copy.

Also, in the case of color copying, if you want to create subtle color changes,
The color of the copy would be muddy, and there was also the risk that the color would be significantly different from the original. Although these have been improved by improving toner characteristics, the reality is that it is difficult to faithfully reproduce the original. In view of the above points, the present invention proposes an improved electrophotographic method and apparatus that makes it possible to faithfully reproduce the tonality of the original.

That is, the present invention relates to an electrophotographic method and apparatus in which an electrostatic port image is controlled so as to widen the brightness reproduction range. The present invention improves the process shown in the third figure above. Figures 4A and 4B explain the basic steps of the present invention, and each figure in the column indicated by the symbol '1' schematically explains the charge change on the surface of the photoreceptor, and each figure in the column indicated by the symbol '21' Each figure in the indicated column is
This explains the potential change on the surface of the photoreceptor.

Each figure in the column indicated by symbol '31 schematically explains the change in charge density on the surface of the photoreceptor. In the present invention, the first step and the zeroth step are substantially the same as the method shown in the third figure above, which is a premise of improvement.

It should be noted that the number of charges shown in the '1} columns of each figure in FIGS. 4A and 4B is larger than in the previous figures for ease of understanding. In the first step, the surface of the photoreceptor 1, which basically includes a conductive substrate 1, a photoconductive layer 12, and an insulating layer 13, is primarily charged. The charging polarity is set according to the polarity of the light guide layer, and the following explanation will be given using N type. Next, in the 0th step, static electricity is removed by applying a corona of polarity opposite to that of the primary fly or an AC corona voltage to the corona discharger simultaneously with the photoimage exposure. The method of the present invention is characterized in that this static elimination potential is controlled to form a good electrostatic tank image. For this purpose, a grid is provided at the opening of the corona discharger to control the applied voltage. During static elimination in the 0th step, the surface potential Vo after static elimination is controlled to approximately PV or slightly negative. At this time, even though the charges trapped near the interface between the photoconductive layer and the insulating layer are not released in the area where part of the surface charge has been removed, the polarity is opposite to that of the trapped charges on the interface layer. Holes are induced into the conductive layer. Next, the following gradation adjustment process is performed.

In step oa, after static electricity has been removed, the
The figures in the column show changes in surface potential. The solid line curve shows the result after the time elapsed after the static electricity removal was completed. For comparison, the other curves shown in the same figure are shown for the case where the elapsed time is sequentially larger, that is, the dashed line curve is after upper 2, the secondary dashed line curve is after t4, and the broken line curve is after t4. Elapsed time t after the end of static electricity removal. ~Now, 0.1~5. This is the case for $ec. It is understood that the surface potential changes over time after the static electricity removal is completed. In particular, the light image exposure section is
When looking at the intermediate area between the bright area and the dark area (hereinafter referred to as the intermediate area) and the dark area, first, the potential change in the intermediate area is large;
It is small in the light part. However, as time passes, changes in the dark areas become larger and overtake changes in the middle areas.

This phenomenon is similar to the case where uniform exposure is not performed in the m-th step of the third illustrated process described above. That is, FIG. 5 shows the change in the surface potential of the photoreceptor when the photoreceptor is left in the dark after primary charging in the first step and simultaneous discharge with exposure in the second step of the process shown in the third figure.

In the surface potential characteristic curve, E corresponds to the bright portion, E2 corresponds to the intermediate portion, and E3 corresponds to the dark portion. (Also, the dotted lines are shown for reference when uniform exposure is given to each part.) The relationship between the potential changes of each part shown in the characteristic curve shown in the figure is that at ta after static electricity removal is completed. , E, please E3, E2, in comparison, E. <E3<E2, tc, E. <E22
It is E3.

In this manner, the order of the heights of the surface potentials in the bright area, intermediate area, and dark area is reversed with the passage of time. In this way, if the charge is left on the floor after static elimination without uniform exposure, the trapped charges from the middle part to the dark part are mainly released by thermal energy, combine with holes in the conductive substrate, and disappear.

This explains the reversal of rise in surface potential between the intermediate and dark areas. In addition, the potential reversal between the dark area and the intermediate area is caused by the fact that more carriers, which did not contribute to the simultaneous static elimination during exposure, exist in the photoconductive layer as space charges in the intermediate area than in the dark area. This is thought to be because the trapped charges can be effectively released by thermal energy, and potential changes can be caused quickly. Then, in the oa2 step,
While applying blade removal pressure to the corona discharger, the grid potential provided at the entrance of the corona discharger is set to V higher than Vo, and the surface potential of the photoreceptor is controlled to approximately V.

At this time, a part of the surface charge is removed by controlling the potential of the portion of the surface potential exceeding V after the elapse of the elapsed time of step (a) to approximately V.

Next, in the ob-th step, after the end of the oa2 step, and after a certain period of time has elapsed, the trapped charges in the portion near the dark area are released, and the trapped charges are still not released sufficiently in the stage area.

Therefore, a change in surface potential occurs as shown in the figure in column {2) of row b.

Furthermore, in the ob2 step, the grid potential is maintained at the previous control potential V, higher than V2, and corona static elimination is performed.

By this static elimination process, static electricity is removed only from the surface potential portion higher than approximately V2, and a portion of the surface charge at that portion is removed. In the m-th step, the entire surface of the photoreceptor is uniformly exposed for more than about 1 second to release all the trapped charges at the interface that are not restrained by charges on the surface of the insulating layer.

This makes it possible to form a static image on the surface of the photoreceptor having a surface potential that is substantially faithful to the density contrast of the original image. Incidentally, the same static elimination process may be repeated after the above-mentioned steps RO (a), ., and steps OB, , and .

In particular, it is important to repeat the steps oa, , b, , Q, . . . before the potential reversal occurs between the intermediate region and the dark region, where charge release in the darkest region is incomplete. The time it takes for the potential reversal between the intermediate area and the dark area to occur after static elimination is usually 0.
It is about 05-1 sand.

Next, a modification of the basic process of the present invention described above will be explained. In the modified example process, the first step and the 0th step shown in FIG. In the step of leaving the surface of the photoreceptor after the completion of the process, weak uniform flashing is applied, and then the process of the oaZ process is continued. Therefore, this is a modified version of step oa of the above process, and step oa is shown in Figure 6.
It is shown as step a,′. FIG. 6 {21] shows the change in surface potential at the elapsed time t after the completion of turtle removal in the OA2' step.

The solid line curve is for uniform exposure with an illuminance of 1, the dashed line is for an illuminance of 12, the two-dot chain line is for an illuminance of 13, and the dashed line is for an illuminance of 14. This change in surface level due to the increase in illuminance 1 to 14 exhibits almost the same characteristics as in the case of step (21) in step oa of FIG. This deformation process is thought to be based on the same mechanism as explained in the step 0a of FIG.
It is thought that this uniform exposure promotes the release of trapped charges in the fat by thermal energy and effectively contributes to partial release of trapped charges (particularly in the middle part). The uniform exposure amount in this case is not constant depending on the compositional sensitivity of the photoreceptor, but for example, 0.9 ux・sec or less is sufficient, which is much higher than the case of about 101 ux・sec or more normally used in the m-th step. It's small and good. Following the roa,'-th steps in which such a change in surface potential occurs, the oa2'-th step, which is similar to the 0'-th step of the basic process of the present invention, is carried out.

That is, the grid potential is maintained at V,' which is higher than the control potential Vo in step (B), and a corona discharge having an opposite polarity component is performed. Next, a static lightning latent image can be obtained by immediately performing the m-th step of applying strong uniform exposure.

In addition, step Dq ob2 of the basic process of the present invention in FIG. 4B
As shown in step □a of the above deformation process.
' and repeating the oa2' step yields good results.

That is, as the Dq' step, the light illuminance is slightly higher than the uniform exposure in the above-mentioned Ro a,' step (for example, the
Then, in the OQ' step, the grid control voltage V2' is set higher than the previous grit control voltage V,' to produce a similar corona discharge.

After repeating these steps as many times as necessary, the m-th step of applying strong uniform exposure is carried out to obtain a still hazy latent image with well-adjusted gradation.

Further, a further modified process in which the above-mentioned steps RO a,' and OA2' are carried out simultaneously is also effective.

Of course, the same applies to the ob,'-th process and the ob2'-th process. FIG. 7 is a schematic diagram illustrating a concrete example of a copying apparatus implementing the method of the present invention.

The photoreceptor 1 basically includes a conductive substrate 1, a photoconductive layer 12, and a transparent insulating layer 13, and is rotatably drum-shaped.

As the conductive substrate, a metal plate such as aluminum was used, and as the photoconductive layer, cadmium sulfide activated with copper was dispersed in a transparent resin binder, and the photoconductive layer was coated to a thickness of about 50 μm. Moreover, about 25 mm of mylar film is adhered to the surface using an adhesive. The drum-shaped photoreceptor 1 is supported so as to be freely rotatable and rotated in the direction of the arrow. As an electrostatic latent image forming means 2 along one circumference of the drum-shaped photoreceptor, a corona discharger 2 for primary charging, a corona discharger 22 that applies corona discharge containing a reverse gutter component that acts simultaneously with photoimage exposure,
A control grid 23 provided in front of the corona discharger 22
, gradation adjustment corona discharger 24 The corona discharger 24
A control grid 25 provided in front of the corona discharger 24, a full-surface exposure source 26, and a gradation adjusting light source 27 are arranged behind the corona discharger 24 for the modified process of the present invention.

Incidentally, the corona discharge containing a reverse polarity component applied by the corona discharger 22 is a direct current voltage with a polarity opposite to that of the primary charging, or a combination of that direct current voltage and an alternating current voltage, or by applying an alternating current voltage, etc. It is something that is formed. and,
The same can be used in the corona discharger 24 for gradation adjustment. Then, the original optical image to be formed by the static latent image forming means 2 is remounted on the original document table 3.
The original exposure means 4 exposes the photoreceptor.

The original exposure means 4 includes an illumination light source 4 that illuminates the original document table 3, movable mirrors 42 and 43 that move together with the illumination light source and scan the document surface, an optical system lens 44 that forms a light image thereof, and further It has reflective mirrors 45 and 46 that guide the optical image to the photoreceptor surface. On the other hand, a developing means 5 is arranged at a position following the static latent image forming means 2.

Although the figure shows a sleeve type magnetic brush developing device having a sleeve roller 5, it goes without saying that any type of developing device may be used. Paper feeding means 6 for supplying the transfer material P to the surface of the drum-shaped photoreceptor after development is delivered adjacent to the photoreceptor transfer position.

The paper feeding means includes a feed roller 6 that feeds the transfer material P from the cassette, a timing roller 62 that feeds the transfer material to the transfer position in synchronization with the developed image, and the like. Further, the transfer separation means 7 is delivered following the drum-shaped photoreceptor developing means.

That is, the transfer corona discharger 7 is delivered to the transfer position, and the separation roller 72 and other separation mechanisms are delivered to the separation position. The fixing means 8 is delivered to a copy capable of fixing the transferred image on the separated transfer material P. The fixing means 8 includes heating rollers 8, 8
2 and a pressure roller 83. On the other hand, cleaning means 9 is delivered so that the surface of the photoreceptor after transfer can be cleaned and reused. 9 is an elastic cleaning blade.

In the electrostatic latent image forming means 2, in order to form an electrostatic latent image, the corona discharger 2 for primary charging charges the surface of the photoreceptor at approximately +1500°C.
Adjust the discharge level so that it meets V. Next, a corona discharger 22 for simultaneous photostatic charge removal is applied with a control voltage of approximately 1100 volts to a control grid 23 provided in front of the corona discharger 22.
Since V is applied, the surface potential of the photoreceptor also converges to approximately the control voltage value. Next, the gradation adjustment corona discharger 24 that acts on the photoreceptor is the same as the photoimage exposure corona discharger 22.
0 after the end of the action. It is arranged to operate in Sec. A control voltage of about 150 V is applied to a control grid 25 provided in front of this gradation adjusting corona discharger 24. Next, the entire surface exposure source 26 acting on the photoreceptor has a light intensity of 101 y/sec or more.

Further, the light source 27 provided for adjusting the gradation appropriately applies light irradiation to the surface of the photoreceptor at a duration of less than 0.9 seconds, preferably less than 0.9 seconds.

FIG. 8 shows the result of forming an electrostatic port image using such a latent image forming means. That is, the figure shows the original document density as the axis and the latent image potential as the vertical axis, and shows the characteristic of the latent image potential with respect to the original document density. The solid line a shows the case where the above apparatus is operated without turning on the gradation adjusting light source 27. The brightness reproduction range at that time is 1.
The stemness is 0.6 as in the conventional case shown in the first diagram.
It is understood that this is a significant improvement over 0.8.
Furthermore, the latent image potential characteristics shown by the dotted line b in FIG. .

In this case, the control grid 25 is divided so that the process voltage can be applied and released, and a corona discharge is generated through the control grid to which a control voltage of 1,500 V is first applied, and then 1,200 V. Also, in the same figure, the two-dot chain line C
The latent image potential characteristic shown by is obtained when no divided voltage is applied to the control grid 25 as in the above-mentioned solid line a, and when the gradation adjusting light source 27 is turned on, a voltage of 0.11 sec.
This is a case where a uniform exposure of .

It is understood that in this case, the luminance reproduction range further expands and reaches approximately 1.3. As described above in detail in the specific examples, the method of the present invention expands the luminance reproduction range and makes it possible to faithfully and satisfactorily reproduce the original gradation.

Furthermore, the number of repetitions of the exposure and static elimination steps can be controlled in accordance with the gradation of the original image to be reproduced, and the optimum image reproduction can be achieved with the optimum number of steps, which is extremely advantageous. and,
The gradation can be controlled very easily by controlling the intensity of light and controlling the exposure amount of weak uniform exposure, and is very effective in practice. Since the static latent image formed is extremely stable, it is extremely effective for image utilization.

[Brief explanation of the drawing]

FIG. 1 is a document density-latent image potential characteristic diagram based on the follow-up method. FIG. 2 is an original density-copy density characteristic diagram when the latent image is developed. FIG. 3 is an explanatory diagram illustrating the electrophotographic method on which the improvement of the present invention is based. Figures 4A and 4B illustrate the basic process of the present invention, where the 1st column is an explanatory diagram schematically showing the change in charge on the photoreceptor, and the 21st column is an illustration showing the change in potential on the surface of the photoreceptor. An explanatory diagram showing the formula in a simple manner, the 31st column is
FIG. 3 is an explanatory diagram schematically showing changes in charge density on the surface of a photoreceptor.
FIG. 5 is a characteristic diagram of the change in surface potential of the photoreceptor when the m-th step of the process shown in the third diagram is omitted and the photoreceptor is left in fat. Figure 6 shows
FIG. 2 is a schematic diagram illustrating a specific example of a copying apparatus in which a deformation process according to the present invention is carried out in a non-toxic manner. FIG. 8 is a latent image potential characteristic diagram of an electrostatic port image formed by the method of the present invention with respect to document density. In the figure, 1...photoreceptor, 1. ... Conductive substrate, 12 ... Photoconductive layer, 13 ... Insulating layer, 2 ... Electrostatic latent image forming means, 3 ... Document table, 4...Original exposure means, 5...Development means, 6...
Paper feeding means, 7...Transfer/separation means, 8...
...Fixing means, 9...Cleaning means. Tsutomu's drawing of disciples 2 drawing 3rd weight d gathering drawing 3 drawing 7 drawing of disciples〃) Atsuko drawing 8) drawing 8

Claims (1)

[Scope of Claims] 1. Using a photoreceptor whose basic composition is a conductive substrate, a photoconductive layer, and an insulating layer, the surface of the photoreceptor is uniformly charged, and then an original optical image to be reproduced is placed on the surface of the photoreceptor. At the same time as or immediately after the photoimage exposure, static electricity removal is performed to control the potential of the photoreceptor surface to a predetermined potential lower than the uniform charging, and further, following the static electricity removal, the electric potential is lower than the control potential of the previous static electricity removal. The process of eliminating static electricity using a high control potential is carried out one or more times,
An electrophotographic method characterized in that a uniform exposure is then performed to form an electrostatic latent image on the photoreceptor. 2 Using a photoreceptor whose basic structure is a conductive substrate, a photoconductive layer, and an insulating layer, the surface of the photoreceptor is uniformly charged, and then the original optical image to be reproduced is exposed to the surface of the photoreceptor, and the optical image is At the same time as the exposure or immediately after, static elimination is performed to control the potential on the surface of the photoreceptor to a predetermined potential lower than the uniform charging,
Further, following the static elimination, uniform exposure controlled to a predetermined light intensity is performed, and static elimination is performed at least once at a control potential higher than the control potential of the previous static elimination at the same time or immediately thereafter, and then An electrophotographic method characterized by forming an electrostatic latent image on the photoreceptor by uniformly exposing it to light. 3. A photoreceptor whose basic composition is a conductive substrate, a photoconductive layer, and an insulating layer, a corona discharger for primary charging, a photoimage exposure means, and a corona discharge having a polarity component opposite to that of the primary charge simultaneously with or immediately after the photoimage exposure. 1. An electrophotographic apparatus comprising a corona discharger for adjusting gradation, a corona discharger for adjusting gradation, and a full-surface exposure source. 4. An electrophotographic apparatus according to claim 3, wherein the gradation adjustment corona discharger has a control grid to which a control voltage is applied. 5. A photoreceptor basically consisting of a conductive substrate, a photoconductive layer, and an insulating layer, a corona discharger for primary charging, a photoimage exposure means, and a corona discharge of a component with a polarity opposite to that of the primary charging at the same time as or immediately after the photoimage exposure. 1. An electrophotographic apparatus comprising: a corona discharger for adjusting the gradation, a corona discharger for adjusting the gradation, a light source for adjusting the gradation, and a source for full-surface exposure.